10 thermal technology

International Conference on Solid Waste 2011
Moving Towards Sustainable Resource Management
Thermal Technology

Proceedings of the International Conference on Solid Waste 2011- Moving Towards Sustainable Resource Management,
Hong Kong SAR, P.R. China, 2 – 6 May 2011
309
STATUS AND PERSPECTIVES OF WASTE INCINERATION IN CHINA
M. Nelles 1*, T. Dorn 1, K. Wu 2, J. Cai 2
1 University of Rostock, Rostock, Germany
2 University of Hefei, Hefei, China
* Corresponding author. Tel: +49 381 498 34 00, Fax: +49 381 498 34 02,
E-mail:michael.nelles@uni-rostock.de
ABSTRACT Municipal waste incineration in China is currently playing a minor role in the whole waste
disposal segment. Primarily, this is caused by the very high specific treatment costs due to costly machinery
investments. On the other hand the large amount of biodegradable fractions in the waste and resulting high
water content does not promote incineration either. Today more than 60 Waste Incineration Plants (WIP)
are in operation in china. Due to the low heating value of the municipal solid waste in China, incineration
either requires co-firing of other combustibles or an elaborate pre-drying mechanism. Usually, coal-firing is
applied to support a complete combustion. All WIPs do meet with operational problems and offer sample
possibilities for optimization and efficiency enhancements. Current plans show that approximately 400 new
incineration plants are envisaged over the next ten years. This will also require adaptation of technology and
suitable pre-treatment of the biodegradable fractions.
Keywords: Waste incineration, Organic waste, China, Germany
Introduction
Global warming, acid rain, depletion of the ozone layer, ocean pollution, and other forms of environmental
pollution are influencing human life on a global scale. Along with greater affluence, mass production and
consumption since the opening up policy 30 years ago have brought this problem to China. Now, 16 of the
world’s 20 most polluted cities are located in China. Pollution came to China; today, Chinese pollution
affects the world. According to World Bank and other publications, China is spending 3 to 10 % of its GDP
on dealing with environmental pollution. In 2004, China overtook the US to become the world’s largest
generator of waste [1]. This was largely a result of a more affluent population, predominantly located in
China’s first and second tier cities, copying a newly attainable Western lifestyle. Today, approximately 660
cities in China generate in excess of 225 million tons of MSW per year.
The present paper provides an overview of the state of MSW management in China with the focus on waste
incineration. The current waste management process in China is focussed on land-filling and includes waste
collection, transfer and separation, as well as recycling and final disposal. Key characteristics of China's
municipal waste composition and generation are identified, leading to propositions on enhancing the current
situation of MSW incineration in China. Based on the own case study “Waste Incineration in China” in 2009,
additional analysis 2010 in China and the long term experience in Germany, some proposals for a
sustainable role of the thermal waste treatment in the circular economy of China are made in the
conclusions.
Generation, Composition and Disposal of MSW in China
Economic and social progress, leading to new consumption highs, have also brought growth and increasing
diversity – of waste. The total volume of municipal waste collected in 1981 amounted to 26.1 mill. Tonnes.
By 2002, more than 20 years later, that figure had quadrupled to 110 mill. Tonnes. That is an annual growth
of 8.2 %, compared to an annual population growth of around 4.4 %. In 2002 the statistical parameters of
the waste collection database were changed, so historical comparisons cannot be accurately made, however
they show a 4.6 % growth in municipal waste from 2003 (148 mill. tonnes) to 2005 (155 mill. tonnes) and a
decrease in real terms by 2007 (148 mill. tonnes), showing that the propagation of “3R” has made a
noticeable entry. From 2003 to 2006 the number of waste treatment and disposal facilities also shrunk (by
27 %) to 419 facilities. Total capacity however, rose by 17.5 % to 258,000 tonnes a day, indicating that
more modern and efficient disposal units were put into operation [2]. Research in that field showed, that the
current statistics only cover the large municipalities whereas the rural backcountry is not accounted for.
United Nations and World Bank estimate the rural waste generation to 0.8 to 1 kg/person and day, adding
some 360 kg to each head of the rural population. Considering that still 52 % of Chinas populace lives on

the countryside, this adds to another pile of 65 million tons per year. Thus the total waste volume that should
be dealt with in a sanitary way is more than 225 million tonnes per year.
Waste composition studies have shown, that the organic fraction of municipal solid waste (OFMSW) is
above 60 % after sorting of recyclables (plastics, wood, glass and paperetc.) The results are serious
environmental burdens caused by landfill gas and leachate emissions. As an example, results of waste
sorting studies of the Tongji University for Shanghai and own investigations for Hefei are shown in figure 1.
Figure 1. Residual waste composition in Shanghai [3] & Hefei
The relevant government authorities have acknowledged that the environmental protection and a modern
waste management system hold key roles in sustainable and responsible development. To drive this on,
China is actively pursuing an exchange of experience and know-how with the developed world. Against this
background China made in the last years great efforts to establish the waste incineration. A number of
incineration facilities were build and operating experience gained.
Case Study
Incineration of (Organic) Waste in China
The University of Rostock investigated the status of waste incineration in China. In the following, the main
results of 2009 and 2010 are represented [4, 5]. Though waste incineration does not yet play a major role in
China’s disposal strategy, currently 16 % of MSW is combusted while more than 80 % still goes into
landfills. The limitation of land resources, water table contamination, fire- and explosion hazards as well as
residential unrest due to foul odors lead to a growing number of WIPs. The combustion of MSW through
incineration plants offers several advantages over landfilling: volume is drastically reduced to 10 to 30 % of
initial values; the material is rendered inert; and, provided high-calorific material is burnt, the resultant
energy can be recovered and transformed into heat and electricity. The major drawbacks are the high
investment costs for the incineration plant; the need for trained manpower; and the need to treat flue gas,
bunker leakage water and ash, as these contain highly toxic elements.
Within the framework of a study of Chinese WIPs, 30 plants were shortlisted for visits in April and May of
2009. Telephone calls and direct contact to operators during the annual convention of the WIP Association
in Shenzhen showed that many of the plants do not allow visitors. As a result, only 15 of the 77 plants
currently in operation (19.5 %) could be visited (Table 1). Many of the plants that do not allow visitors and
thus could not be viewed belong to operators who have reference plants which they proudly display.
Operators are quite selective about whom to show which plant, because most of the plants are run with a
much higher coal co-firing content than officially admitted.
China currently has 77 waste incineration plants (WIPs) in operation, using three main technologies. Most
large cities use the stoker grate technology, which was imported at the end of the 1980’s. As an innovative
response to implementation problems (further described below) China adapted fluidized bed furnaces to
310 Proceedings of the International Conference on Solid Waste 2011- Moving Towards Sustainable Resource Management,

implement waste-co-firing. Stoker grate hold an approx. 60 % market share and fluidized bed furnaces
hold an approx. 33 % market share, with rotary kiln technology accounting for the final 7 %. Where
implemented, rotary kilns tend to have a capacity under 100 t/d and are used in hazardous waste
applications (e.g. Hangzhou DADI). Stoker grate WIPs typically have a daily capacity of 1,000 to 1,500
t/d, each line having a maximum throughput of 500 t/d. Fluidized bed furnaces have a smaller capacity
ranging between 100 to 500 t/d. Interestingly the larger stoker grate plants do not generate more electric
power. Indeed, early plants faced a series of operational troubles, which in turn led to a series of
adaptations.
311
Table 1. Waste incineration plants for MSW in China 2009/2010 [4]
Discussions with plant operators gave valuable insight into operational methodology as well as problems
and solutions. Most of the plants were designed for a calorific value of 5 to 7 MJ/kg. In actual practice only
a value of < 5 MJ/kg is achieved due to the high water and organic content. Research showed even today,
due to the high content of wet organic fractions, the average lower heating value of Chinese MSW ranges
from 3 to 5 MJ/kg, as opposed to the 6 to 7 MJ/kg typically required to obtain a smooth combustion process.
MSW bunkers are therefore crucial to pre-dry waste. Within 5 to 7 days, up to 20 % of water content is lost
to leakage, which puts an enormous strain on the water treatment facility, where installed. Other
developments to combat the challenges presented by the high water content of the MSW are an extension in
length of the stoker grates, to allow for further drying and combustion time. Last but not least, insulation
walls have been reinforced to keep losses at a minimum. Despite these measures, most of the waste’s heat
value is used to evaporate the MSW’s high water content, rather than superheating the turbine’s steam
circles. Given that water reduction during firing accounts for 80 % of weight and volume loss, it is not
surprising that fluidized bed technology came into favour. By co-feeding MSW into the coal-fired
combustion process, power generation units can claim ‘renewable energy status’ and receive the subsidized
energy price of 0.55 RMB/kWh, as opposed to the standard 0.33 RMB/kWh paid to wholly coal-fired power
stations. District heating is unknown, as heating is not common in southern China (south of the Yangtze
River) and tariff and supply regulations are missing.
All plants cover their costs through tipping fees and co-generation fees. With regards to problems
mentioned during WIP operation, these were corrosion within the flue gas system (40 % of plants),
treatment of leakage water of the bunker (20 % of plants), internal energy consumption (electric efficiency:
20 % of plants), service and maintenance (13 % of plants) and problems caused by the high water/organic
content (grate furnaces).
Bottom ash and slag residues from incineration are used as road and construction materials. Typically slag is
first sifted for any remaining metals and then sold on to construction companies. Fly ash from the exhaust
gas stream is considered to be hazardous waste, which the Chinese State Environmental Protection Agency
guidelines require to be stabilized (through cement) and disposed of in secure landfill sites. This rule is
however still in the implementation stage, which means that plants are not yet all in compliance. In terms of

air pollution and residues, most Chinese WIPs use air pollution control systems (APC) comprising of an
active carbon adsorption system, dry or semi-dry scrubbers, and textile filters [4]. These should be sufficient
to properly treat exhaust gases, however due to the corrosive and abrasive materials, they require frequent
servicing and maintenance. As maintenance is generally neglected, many plants operate without the
required filtering equipment, or with only limited (and insufficient) results.
One of the major problems of all WIPs is the large amount of biodegradable fractions in the waste and
resulting high water content does not promote incineration either two solution options are here possible:
Either the separate collection of the biodegradable waste and utilization in compost and/or biogas plants, as
is done successfully for example in Germany. Or the mixed wet residual waste is treated by pre-drying and
mechanical conditioning, which allows an optimized thermal utilization. Foreign entrants promoting
pre-drying technology in combination with existing coal-fired power stations, using the hot flue gases to
reduce the water content, achieve an RDF quality near to lignite characteristics. Such RDF can then be used
to substitute costly primary fossil fuel. Technologies are available, however prior to being transferred to and
implemented in China, they need to be carefully evaluated to match local conditions, which may greatly
differ from the parameters at the technology’s inception in Europe or America.
Conclusions
The study outcome showed that the China is making great efforts to establish incineration plants for the
MSW treatment, while still at the beginning stage. There were few technical and organizational problems to
resolve and to realize an ecological useful operation of WIPs in China. To mentioned are here among others
the urgently required improvement of the flue gas cleaning systems and the disposal of the solid incineration
residues. The main problem is, that the most WIPs combust waste with high organic and water content,
which is ecologically and energetically unrewarding.
References
[1] World Bank (WB). 2005. Waste management in China: issues and recommendations.
http://siteresources.worldbank.org/INTEAPREGTOPURBDEV/Resources/China-Waste-Manageme
nt1.pdf
[2] Figures from the China Statistical Yearbook 2010, http://www.stats.gov.cn
[3] Sorting results of Prof. Chen (10/2003-9/2004), Tongji University, Shanghai
[4] Dorn, T.; Nelles, M.; Flamme, S.: State and development of the waste incineration in China, in
Bilitewski, B.; Faulstich, M.; Urban, A. (eds.): Proceedings 15. Conference Thermal Waste
Treatment, march, 9.-10. 2010 in Dresden/Germany, ISBN 978-3-934253-57-5, pp. 13-33, in
German.
[5] Dorn, T.; Flamme, S.; Nelles, M.: Conditions to a successful Technology Transfer explained on
samples of Waste Disposal Sector, in Nelles, M., Cai, J, Wu, K. (Eds.): Proceedings ICET 2010, 3.
International Conference on Environmental Technology & Knowledge Transfer 13.-14 May 2010
Hefei, Anhui, P.R. China, pp. 27- 37, ISBN 978-3-86009-066-4.

AN EXPERIENCE SHARING FROM JAPAN – ADVANCED WASTE-TO-ENERGY
313
TECHNOLOGY FOR CLEAN ENVIRONMENT
H. Fukai *, T. Aoki, A. Okamoto
JFE Engineering Corporation, Yokohama, Japan
* Corresponding author: E-mail: fukai-hajime@jfe-eng.co.jp, Tel: +81-45-505-7821
ABSTRACT Waste management is one of the important roles for the society to maintain our living
environment clean and healthy. In Japan, Thermal Treatment has been the major technology for hygienic
MSW (Municipal Solid Waste) treatment for log period. In this paper, how the thermal treatment
developed to Waste-to-Energy is described. The current overall situation of MSW management is
presented as well. Several major thermal treatment processes are introduced with technical
countermeasures against environmental impact.
Keywords: Waste-to-energy, Solid waste, Gasification, Hong Kong, Japan
Introduction
Japan has a history of treating wastes thermally for more than a century, with learning experience of not
only the technical aspects but also management approaches. This does not mean only thermal treatment is
adopted in Japan as MSW solution, but other activities like recycling or reducing waste are also developed.
Now thermal treatment developed Waste-to-Energy as a power source in Japan and sharing the above
experience serve as a good reference in locating the most suitable solution for the MSW management.
History of Thermal Treatment of MSW in Japan
Back in 1880s, before thermal treatment is adopted, epidemics such as cholera and typhus became
widespread in Tokyo. Direct dumping of waste caused lots of flies with germs. To improve the situation, the
government enacted "Waste material cleaning act" in 1890.
This act set important concepts. One is local government responsibility of city cleansing including waste
collection and disposal. The other is that the wastes shall be incinerated to a maximum extent.
These still remain in the current law in Japan and now each local government owns and operates their own
thermal treatment plant, and the number of plants in operation is more than 1,300 plants.
Facts & Figures of Waste Management
Figure 1 illustrates the trend of total MSW generation and daily amount per person. MSW generation
increased drastically during 1985 to 1990, when “bubble economy”, and started to reduce from 2000, when
“3R”(Reduce, Reuse and Recycle) policy was announced by Japanese government. As a result, Figure2
shows that landfill remaining lifetime is increasing, although landfill remaining capacity is decreasing.
However, 3R is not only a reason to extend landfill lifetime, but the development of thermal treatment is
still working as a very important roles.
Thermal processes applied in Japan
The most widely adopted technology as Waste-to-Energy is “Stoker” type furnace in Japan, and now 75
percent out of 1,300 thermal treatments have Stoker type technology. And “Gasification” technologies are
emerging in rather smaller capacity of Waste-to-Energy plants.
Stoker Type
Stoker type is highly matured technology for thermal treatment of wastes with more than 40 years operation
history in Japan, and because of well-proven records, stoker type is now suitable for rather large capacity of
Waste-to-Energy facility, i.e. 500 ton per day in a single furnace or more.Recently, ash melting furnaces are
incorporated with this type of furnaces, e.g. stoker or fluidized bed, to extend capability of recycling ash.
Ash changes into molten slag in the ash melting furnaces by heat from electricity of fossil fuel. Molten slag
is recycled as a material for road construction.

1,500
1,400
1,300
1,200
1,100
1,000
900
60,000
55,000
50,000
45,000
40,000
35,000
30,000
Annual MSW Generation ( ,000tons/year)
Per Capita Disposal Rate of MSW (g/day/person)
Figure 1. Trends of total MSW generation and Per Capita Disposal Rate of MSW
㻝㻝㻚㻣
㻝㻞㻚㻤㻝㻞㻚㻥㻝㻞㻚㻤㻝㻟㻚㻞
㻝㻟㻚㻤㻝㻠㻝㻠
㻝㻠㻚㻤
㻝㻡㻚㻢㻝㻡㻚㻣
Figure 2. Trends of remaining capacity and life of landfills for MSW
㻝㻤
㻞㻝
㻝㻠
㻣
㻟㻜㻜㻌
㻞㻜㻜㻌
㻝㻜㻜㻌
Gasification Type
Even “Gasification” is a conventional technology, its application for MSW was not so common and is now
emerging in Japan. Lots of Japan-origin gasification technologies for MSW are proposed.While the
technical characteristics are different in each type, the main objective of developing the gasification process
is to reduce the mass volume of residues, i.e. gasification furnace does not discharge ash, but can produce
molten slag that can be recycled. On the other hand, conventional Stoker needs ash melting furnace to
produce recyclable slag. In fact, industrial standards for the slag utilization for road construction are
established and slag from the MSW gasification facility has been already used in a market.
Pollution Control Technology
During operation of Waste-to-Energy, emission control is very important and its major effluents are flue gas,
ash and wastewater. Their countermeasure technologies have been highly developed to meet with each local
or international regulation to protect environment. In this paper, dioxins emission is referred, as it is the
latest item of emission and frequently discussed.
800
25,000
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007
Per Capita Disposal Rate of MSW
(g/day/person)
MSW Generation ( ,000t/year)
Fiscal Year
Source : Ministry of Environment (Japan)
㻝㻣㻞㻝㻣㻤㻝㻣㻞㻝㻢㻡㻝㻢㻜㻝㻡㻟㻝㻠㻡㻝㻟㻤㻝㻟㻟㻝㻟㻜㻝㻞㻞㻝㻞㻞
㻜
㻜㻌
㻝㻥㻥㻣㻝㻥㻥㻤㻝㻥㻥㻥㻞㻜㻜㻜㻞㻜㻜㻝㻞㻜㻜㻞㻞㻜㻜㻟㻞㻜㻜㻠㻞㻜㻜㻡㻞㻜㻜㻢㻞㻜㻜㻣㻞㻜㻜㻤
㻾㼑㼙㼍㼕㼚㼕㼚㼓㻌㼅㼑㼍㼞㼟
㻾㼑㼙㼍㼕㼚㼕㼚㼓㻌㻯㼍㼜㼍㼏㼕㼠㼥
㻔㼙㼕㼘㼘㼕㼛㼚㻌㼙㻟㻕
㻲㼕㼟㼏㼍㼘㻌㼅㼑㼍㼞
㻾㼑㼟㼕㼐㼡㼍㼘㻌㼂㼛㼘㼡㼙㼑㻾㼑㼙㼍㼕㼚㼕㼚㼓㻌㼅㼑㼍㼞㼟

Dioxins
Dioxins emission from MSW thermal treatment has been a major issue that people concerns. Figure 4
describes the typical methods for suppressing the formation and removal of dioxins in recent
Waste-to-Energy plant. Dioxins are generated in the furnace where waste is burning, so the first and most
important countermeasure to reduce dioxins is controlling stable combustion in the furnace, especially
keeping 3T’s are most important. Second countermeasure is quick quenching of flue gas after the furnace as
Dioxins
Recycling
9.78
315
Table 1. Features of Stoker and Gasification Furnaces
Stoker
High Temperature Gasification
& Direct Melting Furnace
- Wide range of Capacity
- Well Proven with 40 years operations
- Less energy consumption
- Discharge Ash to final disposal
- Very wide range of accepting waste
- New proven technologies
- Need supplementary agent; cokes and lime
- Less discharge without Ash
Total waste
generation
48. 11
Group
Collection
2.9 3
Planned
Treatment
45. 18
(100%)
Reclamation
w/treatment
4.5 1
(10.0%)
Final
Disposal
5.5 3
(12.3%)
Treatment
Residue
9.2 2
(20.4%)#2
Final Disposal
w/treatment
4.7 1
(10.4%)#3
Direct
Recycling
2.3 4
(5.2%)
Intermediate
Treatment
41. 97
(93.0%)#1
Direct Final
Disposal
1.2 0
(2.9%)
Reduction
w/treatment
32. 76
(72.6%)
Domestic
Self-disposal
0.0 5
by local
community
Unit: million tons
by local
government
Figure 3. MSW treatment flow of fiscal year 2008 in Japan
can be generated around 300 degree C as well. To secure dioxins emission, further treatment for flue gas can
be applied with activated carbon injection before dust collection or SCR (catalyst) after dust
collection.These recent development of the preventive technologies has made it possible to reduce the
amount of dioxins to the level of public acceptance even in densely populated urban areas in Japan. And the
emission level of dioxins measured at stack is far less than 0.1 ng-TEQ/m3N, which is the common emission
standard in most of countries.

Figure 4. Dioxin countermeasures in Waste-to-Energy
Conclusions
Even 3R activities have been more and more active in Japan, there still be amount of MSW that should be
sent to Waste-to-Energy facility for thermal treatment. The effect of the facility is obvious; generating
power from waste, reducing amount of waste for final disposal and extend lifetime of landfill consequently.
As such, Japan is always developing technology like gasification, or making effort to minimize
environmental impact from these facilities. Based on these experiences for long time period, we are sure to
contribute developing countries environmental circumstances with these technologies.
References
[1] Annual Report on the Environment. 2004. the Sound Material-Cycle Society and the Biodiversity in
Japan 2010, Ministry of the Environment (2010)
[2] Waste Report 2010, Clean Association of Tokyo 23 (2010)
[3] Encyclopedia of waste treatment, N. Kojima et.al, Maruzen (2003)

317
REVIEW OF MSW THERMAL TREATMENT TECNOLOGIES
K.C.K. Lai 1, I.M.C. Lo 2*, T.T.Z. Liu 3
1 Environmental Protection Department, The Government of the Hong Kong SAR, China
2 The Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong, China
3 Harbin Institute of Technology, Shenzhen Graduate School. Xili, Shenzhen, China 518055.
* Corresponding author: E-mail: cemclo@ust.hk, Tel: +852-2358 7157
ABSTRACT Thermal technologies currently available for MSW treatment include incineration,
gasification and pyrolysis technologies. Plasma gasification and pyrolysis technologies for mixed MSW
treatment are still limited in small-scale. In addition, rotary kiln incineration systems are mainly used for
sludge, industrial or hazardous waste treatment and their applications for mixed MSW are rare because of
operation and maintenance issues/limitation. Among the moving grate incineration, fluidized bed
incineration and gasification technologies, moving grate incineration is the most favorable technology to be
adopted for a large-scale mixed MSW treatment since it is the only thermal technology which has been
adopted for treating over 3,000 tonnes per day of mixed MSW. It has the longest track record of operation
and shows the highest capability to tolerate fluctuation of MSW characteristics with robust nature when
handling mixed MSW, whereas the other two are less robust and usually require pretreatment of MSW.
Keywords: MSW, Incineration, Gasification, Pyrolysis
Introduction
Review of the municipal solid waste (MSW) management practices worldwide indicates that thermal
treatment technology is playing an important role in MSW treatment. In some regions/ countries such as
Germany (data provided by Eurostat), Japan (Ministry of the Environment), Netherlands (Eurostat),
Singapore (Ministry of the environment and water of Singapore) and Taiwan (Department of Waste
Management & Recycling Fund Management Board), thermal treatment technology is the core part of their
MSW treatment systems. In pursuance of Directive 1999/31/EC on landfill of waste, European Union (EU)
members tend to treat or reduce the MSW by alternative solutions (i.e., thermal treatment technology,
recycling or composting) so as to reduce the organic waste delivered to landfills. Hence, the amount of
MSW being treated by thermal technology in EU 27 countries, on average, increased from 14% in 1995 to
20% in 2007 (Eurostat). In the of view of significant role of thermal treatment technology for MSW
treatment, this paper reviews the latest development as well as pros and cons of different types of thermal
treatment technologies including incineration, gasification and pyrolysis.
Review of MSW Thermal Treatment Technologies
Moving grate Incineration Technology
Moving grate incineration involves the combustion of mixed MSW on a moving grate consisting of a
layered burning on the grate transporting MSW through the furnace (Niessen, 2002), as shown in Fig. 1a
(EC, 2006). The waste is first dried on the grate and then burnt at high temperature (850 to 950 oC) with a
supply of air. Because of the application of the grate system, moving grate incineration technology does not
need prior MSW sorting or shredding and it can also accommodate large variations in MSW composition
and calorific value. In addition, moving grate incineration is a very robust and forgiving technology in terms
of waste inputs. Recent review of the information obtained from the associated main suppliers including
Hitachi Zosen (Hitachi), JFE Engineering Corporation (JFE), Kawasaki, Mitsubishi Heavy Industries Ltd.
(Mitsubishi) and Takuma Co. Ltd (Takuma) indicates that over 93% of their MSW thermal treatment plants
installed worldwide adopts moving grate incineration systems. Similar phenomenon is also reported by
other main suppliers in Europe. It was also reported that at least 106 moving grate incineration plants were
built worldwide for MSW treatment since 2003.Moving grate incineration system has a long track record of
operation for mixed MSW treatment and has over 100 years operation experience. It is currently the main
thermal treatment facility being adopted for mixed MSW treatment. In comparison with other thermal
treatment technologies, the unit capacity and plant capacity of the moving grate incineration system is the
highest, which range from 10 to 920 tpd and 20 to 4,300 tpd, respectively. Nowadays, moving grate
incineration system is the only system which has been thoroughly proven to be capable of treating over

3,000 tpd of mixed MSW without requiring any pretreatment or preprocessing steps. One of the largest
moving grate incineration plants was installed by Mitsubishi in 2000 in Singapore and its total capacity is
4,300 tpd composed of six lines of furnaces.
Figure 1. Schematic diagram of (a) moving grate, (b) fluidized bed, and (c) rotary kiln incineration systems
(EC, 2006)
Fluidized Bed Incineration Technology
Fluidized-bed incineration system (Fig. 1b) is an alternative design to conventional combustion system in
which the moving grate is replaced by a bed of granular materials fed by an air distribution system.
Bubbling and circulating bed types are the main types of fluidized beds used in the incineration system. The
incineration process is controlled by varying the waste feed rate and the air flow to the furnace. If the
process is shut down for short duration, the temperature of sand bed is typically be maintained at 450-550oC
for quick recovery back to 850-950oC (Niessen, 2002). In comparison to moving grate incineration system,
the fluidized-bed incineration system generally offers more intense mixing, longer residence time and better
residue burnout and is generally used for treatment of wastes with relatively homogeneous composition and
small size. Its application for waste combustion began in early 1960s. Since then, more than 100 commercial
plants have been installed in the U.S. and there are over 300 plants worldwide. Its application is mainly to
municipal sewage sludge, industrial and hazardous wastes such as plastics, waste oil, paper, paper pulp,
waste tire, etc. It is recently reported that about 75% (weight) of the wastes currently being treated by JFE
and Mitsubishi fluidized-bed incineration systems are either sewage sludge or industrial/hazardous wastes;
while mixed MSW only occupies 25%. Moreover, as recently reported by Hitachi, JFE, Kawasaki, Seghers,
Mitsubishi and Takuma which had installed over 850 MSW incineration plants worldwide, only about 2%
of their MSW incineration plants adopt fluidized-bed incineration systems. Thus, it is generally recognized
not a common technology for mixed MSW treatment probably due to its poor performance on treating
highly heterogeneous MSW. In fact, pre-treatment of MSW into homogenous feedstock is a pre-requisite
prior to feeding of MSW in a fluidized bed incinerator.
Operation problems typical to fluidized bed incinerators include: (1) methods of charging waste to the
furnace to ensure good distribution; (2) bed agglomeration; (3) deposit formation and (4) bed erosion. The
fluidized bed incineration plants currently in operation have the much lower unit capacity (10-80 tpd) and
plant capacity (10-200 tpd) than the moving grate incineration plants. As reported by Hitachi, two fluidized
bed incineration plants with a total capacity of 30x2 tpd and 50x2 tpd were installed in Japan in 1999. For
JFE, the plant capacity of their fluidized bed incineration plants for mixed MSW treatment was reportedly
ranging from 26x1 tpd and 82.5x2 tpd. Although a fluidized bed incineration plant with a total capacity of
514x3 tpd was installed in Allington Quarry, UK in November 2006, material recovery facility are required
to remove the recyclables from the mixed MSW and homogenize the MSW size.
Rotary Kiln Incineration Technology
Rotary kiln system was originally designed for processing basic building materials (e.g. cement). Because
of its unique capability to achieve a more complete combustion, it has been further developed to apply for

industrial and hazardous wastes incineration (Niessen, 2002), but its application for MSW is rather limited.
Generally, a rotary kiln incineration system has 2 chambers: a primary and secondary chamber (Fig. 1c).
The primary chamber is an inclined refractory lined cylindrical tube for conversion of solid fraction to gases,
through volatilization, destructive distillation and partial combustion reactions. The secondary chamber is to
complete gas phase combustion reactions. A rotary kiln incineration system normally does not require prior
sorting or shredding, and can accommodate large variations in waste characteristics. It provides good and
uniform interaction of waste and combustion areas as well as is easily controlled the residence time of waste
in combustion chamber, generally resulting in a more complete combustion than other incineration systems.
The downside of a rotary kiln incineration system includes the relatively high capital cost and land
requirement in comparison with other incineration technologies. High heat loss from the kiln shell also leads
to its low energy efficiency. Another disadvantage is that the inherent construction of a kiln emphasizes the
suspension of particulate in the gas stream and tends to limit mixing of pyrolyzed waste combustible matter
with combustion air, resulting in high particulate and hydrocarbon concentrations in the flue gas. The
following technical problems may also appear when treating MSW:
Erosion of the refractory materials - MSW is quite abrasive and may lead to significant erosion of the
refractory lining materials throughout the operation;
Plastics deposition - At the colder feed end of the rotary kiln furnace, plastics can melt, but not combust
leading to a layer of plastic coating onto the internal refractory lining surface;
Clinkering - Clinkering is the formation of solid aggregates through fusion of the MSW ash that adhere onto
the refractory-lined surface. It can block the air ports which further reduces air cooling effect, thereby
leading to a higher temperature and further clinkering; and
Kiln length - If the kiln is too long, the end of the kiln could get lower temperature because of an insufficient
heat released from the combusted waste, thereby resulting that any slag will solidify and form aggregates in
this area.
Nowadays, most of the rotary kiln incineration systems installed are used for sludge, industrial or hazardous
waste treatment and their applications for MSW treatment are rare. For instance, none of the 50 rotary kiln
incineration systems installed by JFE, Kawasaki, Mitsubishi and Takuma are for MSW treatment.
According to our research, Hitachi and B&W Volund are the only suppliers currently reporting that their
rotary kiln incineration systems have been used for MSW treatment, but their systems are actually not a pure
rotary kiln and usually combined with moving grate incineration unit to avoid formation of clinker.
Gasification Technology
Gasification is a process that converts carbonaceous materials into gaseous mixtures by reacting raw
materials at a high temperature with a limited amount of oxygen and/or steam. The resulting gas mixture
consisting of various energy-rich gas products, such as CO, H2 and CH4, is called syngas. For MSW
treatment, development of gasification technologies has been via air, oxygen or steam gasification. The
operating temperatures for air, oxygen and steam gasification generally range from 700 to 1,400 oC. The
main systems available for waste gasification include updraft, downdraft, fluidized-bed, entrained flow and
rotary kiln gasification systems. The characteristics of the gasification systems, waste composition and
operational conditions can result in tars and hydrocarbon gases, which are the undesired products from
incomplete gasification. Utilization of syngas is often by direct combustion in a boiler or furnace. The heat
energy is used either for process heat or to produce steam for electricity generation.
The major waste types currently being treated by the gasification technologies include municipal wastes (i.e.
mixed MSW, refuse-derived fuel (RDF), and sewage sludge), industrial and hazardous wastes, and
agricultural wastes. The current gasification plants in operation have a much lower unit and plant capacity
than the moving grate incineration plants for mixed MSW treatment in which their unit capacity and plant
capacity generally range from 20 to 150 tpd and 30 to 405 tpd, respectively. One of the advantages of the
gasification technology over the incineration technologies is that it generally generates less volume of the
flue gas and less amount of gas pollutants, thereby resulting in requiring less expensive gas cleaning
equipment for off-gas treatment. However, pretreatment of MSW to produce fine granules is normally
required since gasifier is less robust for mixed MSW treatment. The track record and operating experience
319

of the gasification technology for MSW treatment is also very limited especially for large-scale treatment.
Up to 2008, there were only approximately 90 gasification plants installed worldwide for MSW and RDF
treatment (Archer et al., 2008), which are small number in comparison to 900+ moving grate incineration
plants installed. All the recently installed gasification plants by Hitachi, JFE and Nippon Steel are limited to
the plant capacity ranging from 19x2 to 135x2 tpd.
Plasma Gasification Technology
Plasma gasification is an advanced waste treatment technology. It involves transformation of carbon-based
materials of the waste under oxygen-starved environment using an external high heat source (i.e. plasma).
The temperature of plasma gasification can be as high as 2,700-4,400ºC or even up to 10,000oC (McKenna,
2009). At such high temperatures, any metals will melt and any inorganic materials such as soil and gravel
will be transformed into a vitrified glass. There is no ash remaining to go back to landfills. Any organic
matter present will form the syngas, which can be used for subsequent heat energy or electricity generation.
The gas composition coming out of a plasma gasification system is lower in trace contaminants than with
any kind of thermal treatment system. There are usually no tars or furans in the syngas. Since plasma
gasification of MSW requires significant amounts of energy for creating ultra high temperature condition
within the furnace, the energy being recovered from the MSW is usually low. A review of the latest
development of the plasma gasification indicates that this technology is mainly adopted for some specific
uses, such as treating industrial and hazardous wastes, and even low-level radioactive wastes because of the
high temperature condition created by the plasma. Phoenix Solutions Corporation (Phoenix), PyroGenesis
Inc. (PyroGenesis), and Westinghouse Plasma Corporation (Westinghouse), the key
manufacturers/suppliers of the plasma gasification systems for waste treatment, reported that the main
waste types currently being treated by the plasma gasification systems mainly include sewage sludge, auto
shredder residues (ASR), MSW ash, PCBs-contaminated wastes, dioxin-contaminated soils, medical wastes,
etc. Its application for municipal waste treatment is rare and mainly limited to RDF treatment.
PyroGenesis had recently reported that they had installed a pilot plant at PyroGensis’ facilities in January
2002, which was capable of treating between 0.5 and 2.5 tpd of mixed MSW, hazardous flammable waste
and ASR. Pheonix reported that 2 plasma gasification plants were installed in Panama (200 tpd) in 2008 and
in Poland in 2006 (300 tpd) for MSW treatment, but their systems require mechanical and biological
pre-treatment of mixed MSW to produce RDF. As informed by Westinghouse, the demonstration plant with
a plant capacity of 85 tpd of mixed MSW installed at Ottawa, Canada in 2007 is the only plasma gasification
plant for MSW (alone) treatment, but it adopts a combination of gasification process followed by plasma
gasification of the products of incomplete treatment. Other Westinghouse’s plasma gasification plants are
installed for the treatment of industrial/ hazardous wastes or mixture of MSW and industrial wastes.
Pyrolysis Technology
Pyrolysis is theoretically a zero-air indirect-heat process in which organic waste is decomposed to produce
oil, carbonaceous char and combustible gases. Since no air is required, there would be less volume of flue
gas generated for treatment in comparison to incineration and gasification process. Unlike incineration and
gasification systems which are self-sustaining and use air or oxygen for waste combustion, an external
source of heat is required to drive the pyrolysis reactions. Also, relatively low temperatures, in the range of
400 to 800oC, are required for pyrolysis. Examples of pyrolysis systems generally for waste treatment
include fluidized-bed, fixed-bed, rotary kiln and entrained flow systems. Pyrolysis offers the benefit of
using the generated oil, which could be used directly in fuel applications. The solid char may be used as a
solid fuel, carbon black or upgraded to activated carbon. The combustible gas produced may contain
sufficient energy to supply the energy requirements of the waste pyrolysis systems themselves. Generally,
most of the waste pyrolysis systems are still at pilot-scales in which sewage sludge and hazardous waste are
the main feedstocks. It is less robust than moving grate incineration technology so that its application for
mixed MSW treatment is limited and not suitable for large scale uses. If applied, preprocessing of mixed
MSW into RDF is usually required. A review of the latest development of the pyrolysis technology indicates
that there is still very little track record of the pyrolysis plant for MSW treatment. Up to 2008, there were
approximately 30 pyrolysis plants for MSW or RDF treatment worldwide (Archer et al., 2008). According
to the information provided by Hitachi which is one of the key pyrolysis suppliers, the typical unit capacity

and plant capacity of a pyrolysis plant for MSW treatment usually fall within 60 to 80 tpd and 130 to 160 tpd,
respectively.
Conclusions
Review of various types of thermal technologies for MSW treatment indicates that moving grate
incineration system is the most favorable technology for large-scale treatment of mixed MSW since it has
been fully proven for the large-scale application without requiring preprocessing of MSW and has the
longest track record of operation. It also shows the highest capability to tolerate fluctuation of MSW
characteristics with robust nature. For the other incineration technologies, gasification and pyrolysis
technologies, they are either limited in small-scale, limited for industrial/hazardous waste treatment,
requiring preprocessing of mixed MSW before feeding, which make them not suitable for large-scale mixed
MSW treatment.
References
[1] W. R. Niessen. 2002. Combustion and Incineration Processes – Third Edition, Revised and Expanded,
321
Marcel Dekker, Inc., New York.
[2] EC 2006. Integrated Pollution Prevention and Control - Reference Document on the Best Available
Techniques for Waste Incineration, European Commission.
[3] Y. Nie. 2008. Development and prospects of municipal solid waste (MSW) Incineration in China.
Frontiers of Environmental Science and Engineering in China 2: 1-7.
[4] E. Archer. K. Whiting. J. Schwager. 2008. Briefing Document on the Pyrolysis and Gasification of
MSW, Juniper Consultancy Services Limited, Gloucestershire, England.
[5] P. McKenna. 2009. Into thin air. New Scientists 25: 33-36.

HYDROTHERMAL TREATMENT OF INCINERATION FLY ASH: THE EFFECT OF
IRON OXIDES
D.Z. Chen *, Y.Y. Hu, P.F. Zhang
Thermal & Environmental Engineering Institute, Tongji University, Shanghai, China
*Corresponding auther.Tel:+86 15800446445, E-mail:chendezhen@tongji.edu.cn
ABSTRACT The effect of iron oxides on decomposition of PCDD/Fs contained in incineration fly ash
during hydrothermal process was investigated. Experimental results indicated that iron oxides formed from
mixture of ferrous sulphate and ferric sulphate in the hydrothermal reactor enhanced PCDD/Fs
decomposition, especially for the decomposition of 2378-TCDD and 2378-TCDF at the reaction
temperature of 290ºC. The decomposition rate of PCDD/Fs was increased to 89.6% by I-TEQ when iron
was added as mixture of ferrous and ferric sulphates at 3% (wt/wt); while without active spike of iron salts,
the decomposition rate of PCDD/Fs was only 46.17% by I-TEQ. When iron oxides were formed from
mixture of ferric and ferrous sulphates, cooling procedure after hydrothermal process becomes more
flexible, and longer reaction time was helpful to increase decomposition rates.
Keywords: Incineration fly ash, Iron oxides, Hydrothermal process, PCDD/Fs, Decomposition rate
Introduction
The cheap iron oxides (FexOy) have been reported to have a positive effect on catalytic oxidation of gaseous
dioxins (PCDD/Fs) at temperatures below 200ºC, in the presence of ozone[1]. It is reasonable to believe
iron oxides might also have catalytic effect on decomposition of PCDD/Fs contained in municipal solid
waste (MSW) incineration fly ash during hydrothermal process.
Hydrothermal process for incineration fly ash provides a relatively milder condition compared to
high-temperature refractory conditions and it is less energy consuming due to its moderate operating
temperatures[2]. Elimination of the PCDD/Fs in fly ash under hydrothermal condition has been explored by
Yamaguchi et al. [3] and they showed that PCDD/Fs would decompose when the hydrothermal reactions
took place under 573K for 20 minutes in 1N NaOH solution containing 10% (vol/vol) methanol, and that
toxicity of PCDD/Fs in the treated fly ash decreased to 0.03 ng-TEQ/g. Although good results were obtained
in their work, the reagent, methanol that they used was poisonous and the caustic alkaline conditions would
not be acceptable in practice under high pressure.
Under hydrothermal conditions iron added in form of Fe(II) would generate FeOOH or FeO oxides that bind
to heavy metals [4]; and these newly formed iron oxides could act as potential catalysts for PCDD/Fs
decomposition also. The objective of this study is to prove this effect.
Materials and Methods
Materials
MSWI fly ash was sampled from a full-scale operating incinerator in southeast of China, which adopts
spray-dry flue gas scrubbing system followed by a bag filter. The total PCDD/Fs concentration of raw fly
ash was 11463.3ng/kg and its toxicity was 628.8ng-TEQ/kg. Its original iron content was 1.42%, so it was
pre-treated to remove soluble iron content. Ferrous sulphate and a mixture of ferrous and ferric sulphate
were introduced during hydrothermal process. Both ferrous sulphate and ferric sulphate used here were of
analytical purity.
Experimental Methods
The autoclave used for the hydrothermal process is reported in Xie et al.[2]. For each experimental batch,
pre-treated fly ash and twice-deionised water were mixed, ferrous and ferric salts were dissolved into the
suspension according to special dosages as given in Table 1. Afterwards the suspension was pumped into
the autoclave to be heated to 563K (with corresponding pressure of 7.44MPa) and kept mixing at that
temperature for 0.5 to 3 hours, in this process new iron oxides were formed. After hydrothermal treatment,

the samples were sent to an authorized dioxin laboratory for analysis of PCDD/Fs concentrations with help
of HRGC-HRMS method.
Table 1. List of experimental scenarios with different Fe(III)/Fe(II) addition ratio (wt % of fly ash)
Scenario 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Fe (II) (wt%) 1.0 4.0 0.33 0.33 0.33 0.33 0.33 6.0 5.0 0.66 1.33 0 0 0
Fe (III) (wt%) 2.0 0 0.67 0.67 0.67 0.67 0.67 0 0 1.34 2.66 0 0 0
Reaction time 1h 0.5h 1 h 2h 3h 1h 2h
Ending
procedure Cooling slowly Cooling
quickly Cooling slowly Cooling
quickly
Results and Discussion
Effect of Cooling Procedure
The influence of cooling procedure after hydrothermal thermal treatment is shown in Table 2. For Scenarios
(12), (13) and (14) there was no addition of Fe. For Scenario (4) and (5) the same iron was added except for
the difference in cooling procedures adopted after hydrothermal treatment. It can be seen that fast cooling
after hydrothermal treatment is preferable if no iron is added. When iron was added as a mixture of Fe (II)
and Fe (III), cooling slowly was better for reducing the toxicity of the final PCDD/Fs. Usually the fast
cooling cannot be ensured in practice, so addition of iron is preferable.
323
Table 2. Concentration of PCDD/PCDFs after hydrothermal thermal treatment (I-TEQ ng/g)
PCDD/Fs Scenario
(12) (13) (14) (4) (5)
2378TCDD 0.115968 0.152708 0.119956 0.038292 0.035450
2378TCDF 0.007716 0.009067 0.006463 0.004531 0.003408
Total I-TEQ 0.300384 0.237185 0.195197 0.103560 0.143741
Influence of Iron Dosage
The changes in the decomposition rates of PCDD/Fs with Fe dosage, when .the reaction time was 1h and
slow cooling was adopted for the ending procedure is shown in Fig. 1. The decomposition rate was defined
as the ratio of the reduced concentration of the 17 toxic isomers’ to their original concentrations; or the ratio
of the reduced I-TEQ value to its original I-TEQ value. When no iron was added, (Scenario (12))
decomposition rates were 80.0% for the 17 toxic isomers and I-TEQ was reduced by 46.17%. While for
this treated fly ash the total concentration of PCDD/Fs including all non-toxic isomers was 47.54ng/g.
In Fig. 1. it is shown that when ferric/ferrous sulphate was added, decomposition rate of total 17 toxic
isomers (marked as C in Fig.1) increased in general compared to Scenario (12), and decomposition rate in
I-TEQ value increased dramatically with its maximum reaching 89.59% at 3%wt (Scenario (1)). Fe addition
did not only improve the decomposition rates of the 17 toxic isomers but also enhanced the destruction of
the total PCDD/Fs by reducing their concentration from 47.54 ng/g for Scenario (12) to less than 20 ng/g. As
Fe addition rose to 4wt% through mixture of ferrous and ferric salts (Scenario (11)) the decomposition rates
decreased and concentration of PCDDs/Fs increased (Fig. 1). But as Fe was added in the form of Fe (II) at
4wt% (Scenario (2)) the decomposition rates were higher again, showing different iron oxides act
differently. From the data in Fig.1 it can be seen that the best results for I-TEQ value reduction are at iron
supplementation at 3%wt as a mixture of Fe (II) and Fe (III).
Influence of Iron Addition on 2378-TCDD Concentration
Concentration of 2378-TCDD is most important for reducing PCDD/Fs toxicity in fly ash. Some scenarios
are compared in Table 3 for their 2378-TCDD and 2378-TCDF concentrations. It can be seen that iron
added as mixture of Fe (II) and Fe (III) results in much lower 2378-TCDD and 2378-TCDF concentrations,

showing that iron oxides formed from mixture of Fe (II) and Fe (III) is more effective for reducing the most
toxic 2378-TCDD; therefore iron oxides formed from mixture of Fe (II) and Fe (III) are preferable.
Figure 1. Decomposition rates of PCDD/Fs vs. Fe dosage (Fe(2.3): iron added as a mixture of Fe(II) and
Fe(III) salts; Fe(2): iron added in form of Fe(II))
Table 3. Comparison of 2378-TCDD concentration after treatment with different Fe addition mode
PCDD/F
content
Scenario (ng/g)
(12) (2) (9) (8) (4) (10) (1) (11)
2378TCDD 0.115968 0.05598 0.049 0.0866 0.03829 0.02749 0.02125 0.009775
2378TCDF 0.07716 0.01535 0.049 0.036 0.04531 0.03454 0.02097 0.02878
total I-TEQ 0.30038 0.096 0.143 0.121 0.10356 0.10702 0.05811 0.10426
Influence of Reaction Time
Table 4 shows 2378-TCDD/F data of some scenarios with different reaction times but the same iron
concentration. It can be seen that longer reaction time is more favorable when a mixture of Fe (II) and Fe (III)
was added.
Table 4. Comparison of dioxin concentrations after undergone different treatment time
PCDD/F content
(ng/g)
Scenario /time (h)
(3) /0.5 (4) /1 (6) /2 (7) /3
2378TCDD 0.085317 0.03829 0.089675 0.026513
2378TCDF 0.14433 0.04531 0.03832 0.03223
Total I-TEQ 0.2388 0.10356 0.1537 0.0903
Conclusion
Iron oxides formed from hydrothermal process were investigated to check for their effects on decomposing
of PCDD/Fs in MSWI fly ash. Experimental results show that iron oxides formed from a mixture of ferric
and ferrous salts were more effective to enhance dioxins’ decomposition than iron oxides formed from
ferrous salt alone, especially to reduce concentrations of 2378-TCDD/F. The best result was obtained for
scenario with iron addition of 3%wt, and longer reaction time is preferable.
Acknowledgements
The work is financed by China National Hi-Tech Project (Grant No.2008A A06Z340) and NSFC project
(Grant No. 50708068).

References
[1] C.W. Hou, H.C. Shu, C.H. Pao, F.H. Jyh, B.C. Moo. 2008. Catalytic oxidation of gaseous PCDD/Fs
325
with ozone over iron oxide catalysts. Chemosphere, 44: 388–397.
[2] J.L. Xie, Y.Y. Hu, D.Z. Chen, B. Zhou. 2010. Hydrothermal treatment of MSWI fly ash for
simultaneous dioxins decomposition and heavy metal stabilization. Front. Environ. Sci. Engin. China
3: 108-115.
[3] H. Yamaguchi, E. Shibuya, Y. Kanamaru, K. Uyama, M. Nishioka, N. Yamasaki. 1996.
Hydrothermal decomposition of PCDDs/Fs in MSWI fly ash. Chemosphere, 32: 203-208.
[4] Y.Y. Hu, D.Z. Chen, T.H. Christensen. 2007. Chemical stabilization of incineration fly ash with
FeSO4 under hydrothermal conditions. Environmental Pollution Control, 4-8 (in Chinese).

THERMAL TREATMENT FOR BIOSOLIDS – ANOTHER BREAKTHROUGH?
K.R. Tsang 1*, F. Sapienza 2
1 CDM, Raleigh, North Carolina, USA
2 CDM, Cambridge, Massachusetts, USA
* Corresponding author. Tel: +1 9197875620, Fax: +1 9197815730, E-mail: tsangkr@cdm.com
ABSTRACT In the U.S. there have been considerable interests in recent years on alternative thermal
treatment processes. Conventional thermal treatment processes include thermal combustion, wet air
oxidation, and thermal pre-treatment. A number of alternative thermal processes have emerged in recent
years. These processes include thermal hydrolysis (Cambi, Biothelys), modified wet air oxidation processes
for sludge conditioning and to produce carbon source for wastewater treatment (Athos, Minerals), sludge
conditioning processes such as SlurryCarb and ThermoFuel, as well as various gasification processes. Most
of these processes are not new and had been tried in the past, some with limited success, and others with
failures. Other processes, such as gasification, thermal hydrolysis, and the SlurryCarb process have attracted
a lot of attention in the past few years. A review of these processes indicates that thermal processing may
offer some needed alternatives for residuals management.
Keywords: Sludge, Biosolids, Thermal treatment
Introduction
Sludge management continues to post a significant challenge as environmental agencies around the world
tackle water quality issues by imposing higher wastewater treatment standards. The traditional practice of
reusing treated sludge (biosolids) through land application has frequently been challenged by the public and
environmental interest groups. The concerns about the negative impacts of sludge reuse on land have
driven a number of European countries towards thermal treatment. In the U.S., beneficial use of biosolids
has long been advocated. Despite major public education and information efforts by municipalities and
professional organizations in the U.S., land application of biosolids continues to meet resistance. While
research results continue to show that biosolids reuse on land is safe and beneficial, emerging pathogens and
contaminants such as pharmaceutical products continue to raise concerns. As these concerns will not be
easily addressed, biosolids reuse on land will continue to face challenges. Most European countries have
already moved away from biosolids land application in favour of thermal treatment. Instead of utilizing the
nutrient contents of sludge, interest is shifted toward the beneficial use of the fuel content.
Thermal treatment of sludge is not new. Conventional thermal treatment processes include thermal
oxidation (incineration) and wet air oxidation, which have been practiced for some time. Although
incineration is a well-established and widely practiced technology, it has not been favourably viewed by the
public in the past. Ash disposal is also of concern. In addition, a large amount of flue gas is required to be
treated before discharging to the atmosphere. In comparison, for gasification utilizing pure oxygen, the
amount of flue gas released per kilogram (kg) of dried sludge processed can be reduced by more than 10
times (Werther, 1999). This may have significant cost impacts as air quality requirements will continue to
demand higher levels of flue gas treatment. The recent ongoing effort by the U.S. Environmental Protection
Agency (EPA) to reclassify municipal sludge as solid waste provided additional fuel for sludge incineration
opponents. However, recently a more favourable perception of incineration has been noted when it is
combined with energy recovery.
Thermal Treatment Processes
Thermal processing of biosolids (other than incineration) appears to be gaining favour in the last couple of
years as the concerns on land application remains and the promise of energy recovery by these processes
make them compatible with the popular theme of sustainability, energy efficiency, and carbon reduction.
Thermal processes can be grouped into several categories as follow:
Low temperature thermal treatment
Thermal conditioning
Wet oxidation
Pyrolysis/gasification

327
Combustion/incineration
Vitrification/melting
Low Temperature Thermal Treatment
These processes involve heating the sludge to below 100oC, primarily for disinfection purposes such as the
Bio Pasteur process. Low temperature treatment has also been proposed as a process to solubilise COD,
resulting in less sludge yield.
Thermal Conditioning
Thermal conditioning processes include thermal hydrolysis such as Cambi, Biothelys, and Exelys processes
which treat the sludge at around 150-175oC, at pressure of 6-15 bars. These processes aim to condition the
sludge for enhanced anaerobic digestion, including higher organic loading, increased volatile solids
reduction and gas yield, as well as improved dewaterability post digestion. Thermal hydrolysis has gained
popularity in the past decades, with over 20 plants operating primarily in Europe, and a number being
planned over the world.
Besides thermal hydrolysis, other hydrothermal processes also aim at changing the characteristics of sludge
using elevated temperature and pressure. Examples of these processes are SlurryCarb and Thermofuel.
SlurryCarb is a carbonization process operating at around 230oC and 27 bar pressure. The first commercial
facility in the U.S. is currently going through final start-up. This process renders the sludge rheology such
that dewaterability of the treated sludge is markedly improved. After dewatering and thermal drying, a
product with calorific value matching coal can be obtained. A rich side-stream produced requires separate
treatment. The process is claimed to be more energy efficient than conventional thermal drying (Enertech,
2008). The Rialto, California facility receives dewatered primary and waste activated sludge for treatment.
ThermoFuel operates at 276oC and 82 bar pressure, and only targets waste activated sludge. Both processes
produce a dried fuel for use.
Wet Oxidation
Wet oxidation has been used to treat sludge and other organic wastes. It is a thermal process which takes
place in an aqueous phase at temperature of 150-330oC and pressure of 10-220 bar using pure oxygen or air.
High pressure is used to maintain sludge in liquid phase. Organic matter is converted to carbon dioxide,
water, and nitrogen in the process. Most of the processes involve oxidation at subcritical condition (below
374oC and at pressure of 100 bar). These include the Zimpro and Athos processes. For sludge treatment, the
Zimpro process operates around 220oC and 35 bar pressure whereas Athos operates at 235oC and 44 bar
pressure. VerTech is a deep well technology proposed to achieve the high pressure through a below ground
reactor. While wet oxidation under sub-critical condition can convert the sludge successfully, the resultant
side stream and emissions are laden with offensive odour and high organic loads. Wet oxidation can also
take place under supercritical conditions (above 374oC, and 220 bar pressure). Under these conditions all
organics will be converted to minerals, water, and carbon dioxide.
Pyrolysis/Gasification
Pyrolysis is a thermal decomposition of organic substances in the absence of oxygen at temperatures
ranging from 300 to 900oC. A series of complex chemical reactions lead to the breakdown of organics and
separation into individual gases. The products are pyrolysis gas, char, and oil. The gas, char, and oil can all
be burned as fuel. Pyrobuster, one of the technologies marketed by Eisenmann, has two operating facilities
in Europe. The Italian facility has been operating since 2006. The technology employs two rotary reactor
chambers with pyrolysis taking place in the first chamber, and the combustion of the pyrolysis product in the
second chamber.
Gasification is the thermal conversion of carbonaceous solids to combustible gas and ash in a net reducing
environment [1] Oxygen is added in a controlled manner at sub-stoichiometric level. Organic compounds
are turned into gaseous compounds (syngas) that can be combusted for energy. Gasification has recently
been touted as a promising process to manage sludge. The basic principles of biomass gasification have
been understood for centuries. Gasification of sludge has the potential benefits of incineration, including

complete sterilization of sludge and reduction of the mass to the minimum amount of ash for disposal.
Technical challenges of sludge gasification include the varying feed sludge characteristics, relatively high
tar content in the syngas, and potential emission of heavy metals and other compounds.
Combustion/Incineration
Sludge incineration has been practiced for many years and is an established technology. While a number of
technologies can be applied, predominant technologies are multiple hearth furnaces and fluidized bed
furnaces, with the fluidized bed technology regarded as “state-of-the-art”. Sludge incineration requires
excess air which results in costly flue gas cleaning systems as nitrogen, chlorine, sulphur, mercury, dioxin,
and furans, etc. are released as gaseous pollutants during sludge combustion. Recent emphasize in the U.S
have been on energy recovery systems for sludge incinerators.
Vitrification/Smelting
While a number of incineration plants have been operating successfully, ash disposal remains a challenge.
Sewage sludge has a relatively high ash contents. In addition, ash contains most of the contaminants not
removed or stabilized during the combustion process. When incineration occur above the melting point of
the ash (1250-1300oC), in addition to achieving complete thermal destruction of the organic substances in
the sludge, a molten ash having a density two to three times that of incinerated sludge ash is formed. The
molten ash has glasslike characteristics, bounds heavy metals and other contaminants remaining, and is
suitable to be used in construction. A number of smelting plants were constructed in Japan. In the U.S., a
plant was constructed in Illinois employing the Minergy technology. Unfortunately, this facility is no longer
operating due to persistent operating issues.
Comparisons of Processes
Given the mixed history of success for various thermal processes, it is important to consider a number of
factors when making technology assessments. Basic questions related to the nature of the process from the
technical, environmental, and economic perspectives will need to be asked and answered. A comparison
of these thermal processes is made by considering the following factors:
New or re-emerged technology
Net energy producer or consumer
Side-stream production and characteristics
Operational challenges
Odor, emissions, and other environmental impacts
A summary of this comparison is presented in Table 1.

329
Table 1. Comparison of Thermal Processes
Processes Status Energy Side Streams and operation
challenges Other Impacts
Thermal
Hydrolysis
Proven Enhances energy
production in
anaerobic
digestion system.
Nutrient rich sidestream from
dewatering downstream of
digestion must be dealt with.
Odour potential from
pressure relief valves
and other areas
remain.
Wet
Oxidation
Emerging Producer For operation in super critical
conditions, a number of operating
challenges remains, including
handling of liquid oxygen, and
preventing the coating of pipe
interior surface.
Commercialization of
the first U.S
installation continues
to be a challenge.
Pyrolysis/
Gasification
Emerging Neutral Facilities usually coupled with a
dryer to produce the feed. Syngas
cleaning and slagging are
challenges.
First sludge gasifier in
the U.S. is still going
through startup and
continued process
modifications.
Incineration Proven Energy producer
if dewatered cake
26-28%
Fluidized bed technology is well
established.
More stringent air
emission requirements
in future.
Smelting Proven Energy consumer While a number of plants have
been operating in Japan, a recent
full-scale plant in the U.S. has
failed.
Operating costs
reportedly to be high.
Conclusions
A number of thermal processes have re-emerged as potential candidates to provide an alternative biosolids
management strategy to municipalities. While some of these processes promise benefits including
renewable energy, reduced carbon footprint, and sustainable management strategy, realization of these
benefits are site and process specific. Thermal hydrolysis coupled with anaerobic digestion appears to be
gaining popularity. Pyrolysis and gasification are also making progress although more operating experience
must be gained from these facilities to ascertain operating cost and issues.
References
1 B. McAuley, J. Kunkel, S.E.Manahan. 2001. A new process for the drying and gasification of sewage
sludge. Water Engineering and Management, 18-23.
2 Enertech presentation, 2008.
3 J. Werther, T. Ogada. 1999. Sewage sludge combustion. Progress in Energy and Combustion Science,
25: 55-116.

PRODUCTION AND PROPERTIES OF GLASS-CERAMICS FROM SEWAGE SLUDGE
RESIDUE BY MICROWAVE MELTING METHOD
Y. Tian 1,2*, D. Chen 1, D. Wu 1, W. Zuo 1
1 School of Municipal and Environmental Engineering, Harbin Institute of Technology, Harbin 150090,
China
2 State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology
(SKLUWRE, HIT), Harbin 150090 ,China
* Corresponding author Tel: +86 451 8608 3077/+86 138 0458 9869, Fax: +86 451 8628 3077, E-mail:
hittianyu@163.com
ABSTRACT This paper described an advisable method to produce glass-ceramics using sewage sludge
residue by the microwave melting method. In a microwave oven, the sewage sludge residue was prepared by
pyrolyzing sewage sludge in an inert atmosphere, and then mixed with CaO 10.47wt% and SiO2 10.48wt%
to achieve the powder. The quenched glass was obtained by melting the powder in a corundum crucible at
about 900ɗ for 10min by the microwave radiation. The two-layer structure was used to improve the
microwave absorbing capabilities of the glass powder in the experiment of the microwave melting. The
nucleation and crystallization experiments, which were 820ɗ for 1h and 900ɗ, 950ɗ炻1000ɗ, 1050ɗ
for 2h respectively, were carried out on the basis of differential thermal analysis (DTA). X-ray diffraction
(XRD) analysis of the produced glass-ceramics revealed that the main crystalline phase was anorthite. The
prepared glass-ceramics were characterized by physical, mechanical and chemical measurements. From the
result of the toxicity characteristic leaching procedure (TCLP) it was found that the glass-ceramics prepared
from sewage sludge residue had a strong fixing capacity for the heavy metals such as lead (Pb), zinc (Zn),
cadmium (Cd) etc.. All results showed that the glass-ceramics prepared from sewage sludge residue by
microwave melting method could be widely used in some applications, especially as the construction
material. At the same time, it showed that the microwave sintering was found to be economically charming
owing to reduction in melting time and energy consume based on fast heating and volumetric heating of
samples.
Keywords: Glass-ceramics, Sewage sludge residue, Microwave melting, Heavy metal, TCLP
Introduction
A large amount of sludge is produced in a sewage treatment plant per day. At present, methods used for the
treatment of sewage sludge are landfill and incineration, none of which are of no defects[1]. Meanwhile,
people have paid considerable attention to the pyrolysis of sewage sludge[1-4]. However, pyrolysis gives
rise to the same collateral products (sewage sludge residue) as the incineration. Plenty of municipal waste
incineration fly ash is currently used in road [1], in cement-based products [1] and as an aggregate in
concrete [1]. Moreover, sewage sludge residue, which was obtained by microwave pyrolysis, contains a
great amount of SiO2, Al2O3 and CaO, which are the key glass network formers, hence it could be taken as
a raw material source of the glass-ceramic production.
Recently, a number of reports have been published on glass-ceramics using fly ash from municipal solid
wastes(MSW) incineration plants by the electric furnace[1-3]. Compared with conventional sintering, the
most fascinating effects during microwave heating are the higher density and the shorter time [4]. The
microwave sintering of calcium phosphate ceramics is found to be economically exciting because of
substantial reduction in processing time and energy expenditure due to volumetric heating of samples [4].
Therefore, it is possible to produce glass ceramics from sewage sludge residue by the microwave sintering.
The aim of this paper is to produce the glass by microwave melting technology and establish a better
understanding of the viability of utilizing the sewage sludge residue to fabricate the glass ceramics for the
construction usage. The produced glass-ceramics were characterized by toxicity characteristic leaching
procedure (TCLP) for leachability test and X-ray diffractometry (XRD) for crystal structure determination.
Moreover, other properties, such as water absorption rate, volumetric density and hardness were also
examined.

An aerobically digested sewage sludge obtained from the wastewater treatment plants in Harbin was used.
The solid residue was produced by pyrolyzing sewage sludge in a microwave oven. The chemical
composition of the residue was determined by X-ray fluorescence spectrometry (Axios PW4400,
PANalytical), as shown in Table 1. CaO was added in sewage sludge residue to lower the melting
temperature. SiO2 was intercalated in sewage sludge residue to form the target crystalline phase.
The mixture which contained sewage sludge residue 79.05wt%, CaO 10.47wt% and SiO2 10.48wt%, was
pressed under uniaxial pressure (1.5MPa) to form cylinders (Φ10×5mm cylinder).The formed body was
melted in a corundum crucible by the microwave sintering. In order to improve the microwave absorbing
capabilities of the sample, the double-layer structure composed of wave-absorbing powder and
wave-transparent powder was used in the experiment of the microwave melting. The powder of
wave-absorbing layer had a composition of 90wt% of active carbon and 10wt% of Al2O3, the ratio of the
wave-transparent powder mixed with active carbon and Al2O3 was 5:5. The formed body was subsequently
sintered and heat treated at certain temperatures, then cooled to room temperature.
0 2 4 6 8 10 12
1000
900
800
700
600
500
400
300
7HPSHUDWXUH˄ ć˅
7LPH˄ PLQ˅
1210
801
852
690
600 700 800 900 1000 1100 1200 1300
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
˄ ć˅
7HPSHUDWXUH˄ ć˅
331
Table 1. The main chemical composition of sewage sludge ash by microwave pyrolysis
Composition SiO2 Al2O3 CaO MgO P2O5 Fe2O3 K2O Na2O TiO2 ZnO others
(%) 47.616 18.343 7.908 2.504 7.158 8.292 2.740 1.333 0.814 0.165 0.421
Powder X-ray diffraction (XRD) patterns for main crystalline phases in glass-ceramics were recorded on a
P|max-γβ X-ray diffractometer with 50mA and 40kV CuKα radiation (Japan). The leached properties of Zn,
Pb and Cd from the glass ceramics were evaluated according to the China Leachability Toxicity Standard
method (GB/T 15555.1-15555.11). The concentrations of heavy metals in the leaching solution were
determined by a PerkinElmer Optima 5300DV Inductively Coupled Plasma-Atomic Emission spectrometer
(ICP-AES, Waltham, MA). Physical properties such as density and water adsorption were measured
according to the Archimedes principle using water as a medium.
Thermal properties such as the transition temperature and crystallization temperature were analyzed by
differential thermal analysis (DTA, TGA/SDTA85IE) and the results are shown in Fig.2. An endothermic
peak with a onset of 690Ԩ was the glass transition temperature. And two exothermic crystallization peaks
occurred at 801Ԩ and 852Ԩ. The melting endothermic peak was at about 1210Ԩ, and heat treatment
experiments proved that the produced sample had molten completely at 1210Ԩ. Therefore, the nucleation
temperature selected for heat treatment in this study was 820Ԩ for 1 h. The crystallization temperature was
900Ԩ, 950Ԩ, 1000Ԩ and 1050Ԩfor 2 h.
Figure 1.The temperature and DTA curve of the quenched glass by microwave melting.
The X-ray diffraction patterns of the glass and the glass ceramics are given in Fig.2. For the glass sample, no
significant crystalline phases could be detected by XRD, as it was expected. As shown in Fig.2, the

glass-ceramic after heat treatment had the crystalline phases. However, there were no apparent crystalline
phases at 900Ԩ for 2h owing to the lower temperature. From 950Ԩ to 1050Ԩ for 2h, it was found that the
major phase of the glass-ceramics was anorthite. It was obviously beneficial for the application of the
residue as the raw material.
The toxicity characteristic leaching procedure (TCLP) results of the sewage sludge residue and
glass-ceramics are shown in Table 2. The solid residue generated in the process of the microwave pyrolysis
had a relatively low concentration of the heavy metals. Table 2 depicts that the concentrations of heavy
metals leached from the sample were far lower than the limits specified in the Chinese standards. The results
established that glass-ceramics had a high immobilization capacity for heavy metals such as Cu, Pb, Zn, Cd,
Cr and As. Physical and mechanical properties of the produced glass-ceramics are summarized in Table 3.
In this study, a dense material can be obtained in a much shorter time by the microwave sintering. Fig.1
depicts that the quenched glass was sintered in the microwave furnace for 3min from room temperature to
900Ԩ and then 10min soaking time at about 900Ԩ. If using the traditional sintering, it needed about 45min
at the maximum rate of 20Ԩ/min to 900Ԩ. Furthermore, the heat power of a muffle furnace is 6000W and
the microwave power is 2000W. Results showed that the microwave heating was more economic than the
traditional sintering at the heating time and the power. It indicates that the whole process is economical.

anorthite

ćKćK
ćKćK
ćKćK
20 40 60 80 100
3600
3000
2400
1800
1200
600
0
Figure 2. X-ray diffractograms of glass-ceramics after the heat treatment.
Table 2. Results from TCLP leaching test of the selected samples. ND: not detectable
Table 3. Properties of the selected glass-ceramics
as-quenched glass
Intensity (cps)
2theta (deg.)
ćKćK

Conclusions
Glass-ceramics were produced using sewage sludge residue, CaO and SiO2. The parameters for producing
the glass-ceramics were melting at 900Ԩ for 15min by the microwave radiation, nucleating at 820Ԩ for 1h,
and crystallizing at 1000Ԩ for 2h. Under these conditions, the sintered glass-ceramics showed good
mechanical properties and bending strength. The leaching of heavy metals from glass-ceramics was far
lower than the specified limits in the Chinese standards. Meanwhile, microwave sintering was charming
owing to reduction in sintering time and energy consume due to fast heating of samples.
Acknowledgements
This study was supported by the National High-tech RD Program (863 Program) of China (No.
2009AA064704).
References
[1] J. Werther, T. Ogada. 1999. Sewage sludge combustion. Prog Energy Combust Sci. 25: 55-116.
[2] J.A. Menéndez, M. Inguanzo, J.J. Pis. 2002. Microwave-induced pyrolysis of sewage sludge. Water
333
Res. 36: 3261-3264.
[3] M. Inguanzo, A. Domínguez, J.A. Menéndez, C.G. Blanco, J.J. Pis. 2002. On the pyrolysis of sewage
sludge: the influence of pyrolysis conditions on solid, liquid and gas fractions. Journal of Analytical
and Applied Pyrolysis. 63: 209-222.
[4] A.Domínguez, J.A. Menéndez, M. Inguanzo, J.J. Pis. 2005. Investigations into the characteristics of
oils produced from microwave pyrolysis of sewage sludge. Fuel Processing Technology .86:
1007-1020.
[5] M.M.C. Alkemade, M.M.Th. Eymael, E. Mulder, W. de Wijs. 1994. Environmental aspects of
construction with waste materials, Elsevier Science, B.V., Amsterdam. p. 863.
[6] P. Filipponi, A. Polettini, R. Pomi, P. Sirini. 2003. Waste Manage. 23:145.
[7] J. Pera, L. Coutaz, J. Ambroise, M. Chababet. 1997. Cem. Concr. Res. 27:1.
[8] J. Yang, B. Xiao, A.R. Boccaccini. 2009. Preparation of low melting temperature glass-ceramics from
municipal waste incineration fly ash, Fuel. 88: 1275-1280.
[9] R.C.C. Monteiro, S.J.G. Alendouro, F.M.L. Figueiredo, M.C. Ferro, M.H.V. Fernandes. 2006.
Development and properties of a glass made from MSWI bottom ash, Journal of Non-Crystalline
Solids. 352:130-135
[10] G. Qian, Y. Song, C. Zhang, Y. Xia, H. Zhang, P. Chui. 2006. Diopside-based glass-ceramics from
MSW fly ash and bottom ash. Waste Manage. 26: 1462-1467.
[11] S. Mahajan, O.P. Thakur, D.K. Bhattacharya, K.Sreenivas. 2008. A comparative study of
Ba0.95Ca0.05Zr0.25Ti0.75O3 relaxor ceramics prepared by conventional and microwave sintering
techniques, Materials Chemistry and Physics. 112: 858-862.
[12] A. Chanda, S. Dasgupta, S. Bose, A. Bandyopadhyay. 2009. Microwave sintering of calcium
phosphate ceramics, Materials Science and Engineering C 29:1144-1149.

PHASE TRANSFORMATION OF METALS IN REUSING THE INCINERATION ASH OF
CHEMICALLY ENHANCED PRIMARY TREATMENT SLUDGE AS CERAMIC RAW
MATERIALS
K. Shih
Department of Civil Engineering, The University of Hong Kong, Hong Kong, HKSAR, China
Tel: +852 28591973, Fax: +852 25595337, E-mail: kshih@hku.hk
ABSTRACT This study provided the possible solid state reactions when reusing the sludge incineration
ash generated from the chemically enhanced primary treatment (CEPT) as the ceramic raw materials. Nickel
and copper oxides were used to simulate the hazardous metal phases in the raw materials, and the ash iron
content was found to act as a beneficial role to incorporate the hazardous metals into the metal ferrite phases
(NiFe2O4 and CuFe2O4). Experimental results of sintering the NiO+Fe2O3 and CuO+Fe2O3 systems
further confirmed the potential of high metal incorporation efficiencies by having iron-containing precursor
in the ceramic sintering process. Both ferrite phases were examined by a prolonged leaching experiment
modified from the widely used Toxicity Characteristic Leaching Procedure (TCLP) to evaluate their long
term metal leachability. The leaching results indicate that both NiFe2O4 and CuFe2O4 products were
superior to their original oxide forms (NiO and CuO) for the immobilization of hazardous metals.
Keywords: Sludge, Incineration ash, Spinel, Ceramic
Introduction
Wastewater sludge ash may contain hazardous metals, such as Cd, Cr, Pb, Ni, Cu, Zn, Mn [1, 2]. Its disposal
into landfill is not environmentally sustainable because of the additional consumption of non-renewable
resources, including material, space and energy. To be more sustainably transforming waste to resource,
opportunities of reusing or recycling incineration ash need to be sought to promote the “cradle-to-cradle”
design in the waste management plan. Merino et al. [3] studied the ceramic characteristics of using sludge
ash alone or mixing with additives (kaolin, montmorillonite, illitic clay, powdered flat glass). Studies of
mixing incinerated sewage sludge ash into clay-based building products have concluded no adverse effect
on final fired body or ceramic texture [4, 5]. Results obtained by Li et al. [6] showed that when mixed with
ashes and/or clay minerals, finely ground glass may act as a flux reducing the leaching by inertization of
hazardous constituents. Shih et al. successfully stabilized nickel into its mineral phases by sintering nickel
oxide with alumina (Al2O3), hematite (Fe2O3), and kaolinite (Al2Si2(OH)4) as the ceramic raw materials
[7-9]. They pointed out that leachability of nickel dropped dramatically in its alumina and ferrite spinel
phases when compared to that of nickel oxide. Copper has also been investigated through the incorporation
experiment, and the result demonstrates a great reduction of leachability of copper when it was incorporated
into CuAl2O4 spinel structure [10].
In Hong Kong, the majority of municipal wastewater sludge is generated from the chemically enhanced
primary treatment (CEPT). And the major metals within the bottom ash of incinerating CEPT sludge are Fe,
Si, Ca and Al. In this paper, we will discuss the possible solid state reaction when reusing such sludge
incineration ash for the ceramic raw materials. Nickel and copper oxides were used to simulate the existence
of potential hazardous metals in the ceramic raw materials for the purpose of exploring the product safety
during the beneficial use of incineration ash. The effect of incorporating nickel and copper into crystal
structures was observed under a 3 h sintering scheme with temperatures ranging from 650 °C to 950 °C. A
modified toxicity characteristic leaching procedure (TCLP) was carried out to evaluate the nickel and
copper leachabilities of NiO, CuO and their corresponding product phases.
Fe2O3 was used to simulate the major components of ferrite bottom ash through incinerating CEPT sludge.
NiO and CuO were used to simulate the phases of potential hazardous metals in the ash. The Fe2O3 and NiO
(or CuO) were mixed to a total dry weight of 60 g at the Ni/Fe (or Cu/Fe) molar ratio of 1:2, together with
500 mL of deionized water for ball milling of 18 h. the slurry samples were then dried at 95 °C for 3 d and
homogenized again by mortar and pestle. After that, the powder samples were pressed into 20 mm diameter
under 640 MPa pressure. The pelletized samples were then heat treated at a rate of 10 °C/min in a top hat

furnace (Nabertherm) and sintered at temperature range from 650 °C to 950 °C for 3 h. The fired samples
were air-quenched and ground into powders for XRD analysis and leaching test.
The X-ray powder diffraction data were collected using D8 Advanced Diffractometer (Bruker AXS)
operating at 40 kV and 40 mA with Cu Kα radiation. Phase identification was conducted using the Bruker
software Diffrac-plus EVA supported by the Powder Diffraction File database of the International Centre
for Diffraction Data (ICDD). The modified toxicity characteristic leaching procedure (US EPA SW-846
Method 1311) was used to evaluate the leachability of the product phase. The pH 2.9 acetic acid solution
was prepared as the leaching agent from 5.7 mL glacial acetic acid and dilution with MilliQ water to a
volume of 1 L. Each leaching vial was filled with 10 mL of leaching agent. The vials were rotated
end-over-end at 60 rpm for agitation periods of 0.75-22 or 26 days. At the end of each agitation period, the
leachates were filtered with 0.2 μm syringe filters, and the concentrations of Ni (or Cu) were derived from
ICP-AES (Perkin-Elmer Optima 3300 DV).
Formation of NiFe2O4
In 2010, Raghavan [11] organized the phase diagrams in the Fe-Ni-O system, and the reaction between NiO
and Fe2O3 was indicated as follows:
NiO + Fe2O3 (hematite) → NiFe2O4 (trevorite) (1)
Fig. 1(a) suggests that there are three phases present in the samples sintered at the temperature range 750 to
950 °C, i.e., NiFe2O4 (PDF # 54-0964), NiO (PDF # 73-1519 ), and Fe2O3 (PDF # 86-0550). Though it is
difficulty to identify NiO phase from qualitative analysis since all the reflections of NiO overlay those of
NiFe2O4, we can estimate the existence of NiO due to the remaining of Fe2O3. From the computed phase
diagram of Fe2O3- NiO [12], the formation temperature of NiFe2O4 should be lower than 600 °C. However,
NiFe2O4 was found only at temperature at 750 °C or higher in the 3 h sintering (Fig.1(a)). Such result
indicates that the diffusion between Fe2O3 and NiO should be an important factor needed to be considered.
The solid state reaction is not only determined by thermodynamic constraints but also by the diffusion
process. As the heating temperature increased, the peak intensity of the (220) plane of NiFe2O4 increased
(Fig. 1b). On the contrary, the peak intensity of the (104) plane of Fe2O3 phase decreased with the
increasing temperature. Since no amorphization has been reported in the phase diagram, the above result
indicates that the formation of NiFe2O4 spinel phase increases with the increasing sintering temperature.
Figure 1. (a). XRD results of sintering Fe2O3 and NiO mixtures at different temperatures for 3 h, (b) selected
335
peaks between 29° and 35°to represents NiFe2O4 (S), Fe2O3 (H), and NiO (N)

Formation of CuFe2O4
When sintering the mixture of CuO and Fe2O3, the potential reaction can be provided as follows:
CuO + Fe2O3 (hematite) → CuFe2O4 (2)
CuFe2O4 has two crystallographic structures: cubic phase with a lattice parameter of 8.38 Å, and tetragonal
phase with lattice parameters of a=8.126 Å and c= 8.709 Å. The tetragonal-to- cubic transition temperature
can be influenced by the atomic iron-to-copper ratio as well as by the oxygen deficiency in copper ferrite
[13].
Fig. 2(a) shows the XRD patterns of samples sintered at different temperatures (650, 750, 850, 950 °C) for 3
h. At 650 °C, only the reflections of CuO and Fe2O3 phases were observed, and no signal attributable to
CuFe2O4 compound (cubic or tetragonal) was observed. Such result indicates that there was no reaction
between CuO and Fe2O3 at such temperature within the sintering scheme. However, Lu et al. [14] reported a
different result, i.e. tetragonal CuFe2O4 was formed when sintering at 600 °C for 1 hour. The difference may
arise from the different types of raw materials. Lu et al. used the sludge as the reactants, and some
components in the sludge may further initiate the catalytic reaction between Fe2O3 and CuO. When the
treatment temperature was increased to 750 °C, tetragonal CuFe2O4 (PDF #72-1174) was detected, together
with the CuO (PDF # 45-0937) and Fe2O3 (PDF # 86-0550) phases. When the temperature was increased to
950 °C, the tetragonal CuFe2O4 (PDF # 72-1174) was the only observable copper ferrite phase.
As illustration Fig. 2(b), the increase of sintering temperature up to 950 °C was followed by a significant
increase in the intensity of the selected X-ray diffraction peak of CuFe2O4 phase. In contrast, the intensities
of the selected X-ray patterns of both CuO and Fe2O3 phase decreased with the increasing temperature.
Such results can be concluded that the formation of CuFe2O4 is strongly affected by the sintering
temperature can be effectively enhanced by increasing the sintering temperature to 950 °C.
Figure 2. (a). XRD results of sintering the Fe2O3 and CuO mixture at different temperatures for 3 h; (b) The
selected diffraction peaks between 32.5° and 39.5° to represent CuFe2O4 (Ct), Fe2O3 (H), and CuO (C)
Leaching Behavior of NiFe2O4, CuFe2O4, NiO and CuO
Fig. 3 shows that the concentrations of nickel and copper leached from NiO and CuO were much higher
than those from NiFe2O4 and CuFe2O4. Within the first few days, the increase of nickel and copper
concentrations in leachates were much greater than those for the remainder of the experiment. The metal
leaching behavior is generally associated with the proton-cation exchange mechanism as described in Eqs.
(3), (4), (5) and (6). Therefore, the much less Ni or Cu leachability has indicated the relatively superior
resistance in the acidic attack, such as in the cases of NiFe2O4 and CuFe2O4.
NiO(s)+2H(+ aq)
→ Ni(aq)
2++H2O (3)

+ → Cu(aq)
337
CuO(s)+2H(aq)
2++H2O (4)
NiFe2O4(s)+8H(aq)
+ → Ni(aq)
2++2Fe(aq)
3++4H2O (5)
CuFe2O4(s)+8H(aq)
+ → Cu(aq)
2++2Fe(aq)
3++4H2O (6)
Figure 3. Nickel and copper concentrations in the leachates of NiO, CuO, NiFe2O4 and CuFe2O4. Each
leaching vial was filled with 10 mL extraction fluid and 0.5 g powder and then tumbled end-over-end at 60
rmp
Conclusions
The results indicate that the incorporation of nickel and copper ions into NiFe2O4 and CuFe2O4 phases is an
environment-friendly strategy to reduce their environmental hazard. This study also suggests a reliable
mechanism of further immobilizing hazardous metals during the beneficial use of the waste incineration
ash of CEPT sludge as a part of the ceramic raw material.
References
[1] C. Wang, X. Hu, M.L. Chen, Y.H. Wu. 2005. Total concentrations and fractions of Cd, Cr, Pb, Cu, Ni
and Zn in sewage sludge from municipal and industrial wastewater treatment plants. J. Hazard. Mater.
119: 245–249
[2] D. Marani, C.M. Bragulia, G. Mininni, F. Maccioni. 2003. Behavior of Cd, Cr, Mn, Ni, Pb, and Zn in
sewage sludge incineration by fluidized bed furnace. Waste Manage. 23: 117–124.
[3] I. Merino, L.F. Arevalo and F. Romero. 2007. Preparation and characterization of ceramic products
by thermal treatment of sewage sludge ashes mixed with different additives. Waste Manage. 27:
1829–1844.
[4] M. Anderson. 2002. Encouraging prospects for recycling incinerated sewage sludge ash (ISSA) into
clay-based building products. J. Chem. Technol. Biotechnol. 77:352-360.
[5] M. Anderson and R.G. Skerratt. 2003. Variability study of incinerated sewage sludge ash in relation
to future use in ceramic brick manufacture. Br. Ceram. Trans. 102: 109-113.
[6] C.T. Li, Y.J. Huang, K.L. Huang and W.J. Lee. 2003. Characterization of Slags and Ingots from the
vitrication of municipal solid waste incineration ashes. Industrial Engineering Chemistry Research.
42: 2306-2313.
[7] K. Shih, T. White and J.O. Leckie. 2006. Nickel stabilization efficiency of aluminate and ferrite
spinels and their leaching behavior. Environ. Sci. Technol. 40:5520–5526.
[8] K. Shih and J.O. Leckie. 2007. Nickel aluminate spinel formation during sintering of simulated

Ni-laden sludge and kaolinite. J. Eur. Ceram. Soc. 27:91–99.
[9] K. Shih, T. White and J.O. Leckie. 2006. Spinel formation for stabilizing simulated nickelladen
sludge with aluminum-rich ceramic precursors. Environ. Sci. Technol. 40:5077–5083.
[10] Y.Y. Tang, K.M. Shih and K. Chan. 2010. Copper aluminate spinel in the stabilization and
detoxification of simulated copper-laden sludge. Chemosphere. 80: 375-380.
[11] V. Raghavan. 2010. Fe-Ni-O. Journal of Phase Equilibria and Diffusion. 31: 369-371.
[12] M.A. Rhamdhani, P.C. Hayes, and E. Jak. 2008. Subsolidus phase equilibria of the Fe-Ni-O system.
Metall. Mater. Trans. B. 39B: 690–701.
[13] S.C. Schaefer, G.L. Hundley, F.E. Block, R.A. McCune and R.V. Mrazek. 1970. Phase equilibria and
X-ray diffraction investigation of the system Cu-Fe-O. Metall. Trans. A 1: 2557-2563.
[14] H.C. Lu, J.E. Chang, P.H. Shih and L.C. Chiang. 2008. Stabilization of copper sludge by
high-temperature CuFe2O4 synthesis process. J. Hazard. Mater. 150: 504-509.

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