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Design of an Integrated Waste Management Facility for the Dublin Region

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Design of an Integrated Waste Management Facility for the Dublin Region

  1. 1. BSEN40320 – WASTE TO ENERGY PROCESSES AND TECHNOLOGY Integrated WasteManagement Facility for the Greater Dublin Region Martin, L. McKeirnan, D. Kumar-Singh, A. Priyadarshan-Kale, A & Hemant-Karmarkar, M. 11/28/2014 The feasibility of developing an integrated waste management facility to cater for the greater Dublin region was investigated. A suitably-sized site was located with 18km of the city and was designed to include a landfill, incinerator, anaerobic digester and composting facility. The cost of developing the site was estimated to be in the region of €157million however the initial investment is expected to be paid back through the generation of heat and electricity from on-site processes in addition the economies of scale. Overall such a facility is viewed as a worthwhile investment for the sake of upgrading Irelands waste management system to a sustainable entity whilst minimizing the environmental damage associated with waste disposal.
  2. 2. 1 Contents Section 1: Introduction ...........................................................................................................................5 Section 2: Site Selection..........................................................................................................................6 Section 3: Site Layout............................................................................................................................11 ..........................................................................................................................................................13 Section 4: Landfill..................................................................................................................................14 Site Infrastructure.............................................................................................................................14 Landfill Design...................................................................................................................................15 Liner Design.......................................................................................................................................15 Leachate............................................................................................................................................16 Gas ....................................................................................................................................................17 Ground Water and Surface Water....................................................................................................18 Section 5: Incineration..........................................................................................................................20 Incinerator types:..............................................................................................................................21 1. Moving Grate: .......................................................................................................................21 2. Rotary Kiln:............................................................................................................................22 3. Fluidised Bed:........................................................................................................................22 State of the art moving grate incinerator:........................................................................................23 Incinerator Efficiency:.......................................................................................................................25 Section 6: Anaerobic Digestion:............................................................................................................27 Importance of AD:.............................................................................................................................28 Feedstock for AD...............................................................................................................................29 Chemical Reactions in AD .................................................................................................................30 Variable Parameters in AD................................................................................................................31 Temperature .................................................................................................................................31 Redox potential.............................................................................................................................31 C:N ratio ........................................................................................................................................31 pH..................................................................................................................................................32 Inhibitory Substances....................................................................................................................32 Types of AD .......................................................................................................................................32 Single stage and Two-stage digesters...........................................................................................32 High Solid or Dry Anaerobic Digestion and Low solid or Wet Anaerobic Digestion .....................33 Planning and Financial viability.....................................................................................................33 Planning Regulations (SEAI: Application guidelines).........................................................................34
  3. 3. 2 Section 7: Composting ..........................................................................................................................35 Composting in Ireland.......................................................................................................................35 Site layout .........................................................................................................................................36 Windrow (mechanical aeration) .......................................................................................................36 Type of Wastes Used for the Composting process...........................................................................37 Requirements for Composting :........................................................................................................37 Carbon: Nitrogen ratio..................................................................................................................38 Moisture Content..........................................................................................................................38 Oxygen ..........................................................................................................................................38 pH..................................................................................................................................................38 Temperature .................................................................................................................................39 Particle size ...................................................................................................................................39 Conclusion.........................................................................................................................................39 Advantages of composting................................................................................................................40 Section 8: Discussion and Conclusions..................................................................................................41 References: .......................................................................................................................................42 Appendix 1: Incineration efficiency calculations ..............................................................................47 Appendix 2: Methane production rates from landfill equations......................................................48 Appendix 3: Distribution of workload...............................................................................................49
  4. 4. 3 List of figures: Figure 1:Waste Management Hierarchy (EPA, 2004) 5 Figure 2: Dublin Recycling rates 2000-2010 (Dublin Local Authorities, 2012) 6 Figure 3: Potential locations for waste treatment facility (Google Maps, 2014) 7 Figure 4: The composition of Irish MSW 8 Figure 5: Layout of the various waste treatment technologies and the site in Mayne, Co. Meath 13 Figure 6: Liner System Design showing both soil layer and synthetic layer 15 Figure 7 Vertical gas collection system for proposed landfill 17 Figure 8: Methane emissions and uses from 1990-2008. 18 Figure 9: Waste management strategies of different E.U countries. (Eurostat, 2012) 20 Figure 10: Moving Grate Incinerator (igniss.pl, 2014) 21 Figure 11: Rotary Kiln Incinerator (infohouse, 1996) 22 Figure 12: Fluidized bed incinerator (infohouse, 1996) 22 Figure 13: Typical design of a MSW incinerator (Murdoch University, 2014) 23 Figure 14 Figure1. Anaerobic digestion installed capacity in Europe 27 Figure 15: Complete flow Cycle of AD (Photo Courtesy: Pagels Ponderosa; Utah State University): 29 Figure 16 Figure3. Chemical Reactions in Anaerobic Digestion (www.wastewaterhandbook.com,2014) 31 Figure 17: Lemvig biogas plant overview (Source: www.lemvigbiogas.com) 33 Figure 18: Locations of the composting facilities in Ireland (Herity 2013) 35 Figure 19: Diagram of Windrow (Harvest Quest, 2014) 37 Figure 20: Market for Compost in Ireland. McGovern (2012) 40
  5. 5. 4 List of tables: Table 1: Criteria for site selection (Leão et al, 2004) 10 Table 2: Capital costs of the integrated waste facility 12 Table 3: Products from AD 28 Table 4: Constituents of Biogas (Source: SEAI & Teagsac) 28 Table 5: Potential Feedstock for Electricity Production in Ireland ( teagasc 2013) 30 Table 6: Variable Parameters in AD (Zupan & Grilc, 2007) 32 Table 7: Specification for AD plant in Dublin 34
  6. 6. 5 Section 1: Introduction Traditionally in the times of more relaxed environmental laws, landfilling was the preferred option of waste disposal which up until recently appeared to be the most economical means of waste disposal (Daskalopoulos et al, 1998). In Europe, this archaic method of waste disposal is becoming less and less favoured due to EU legislation which insists on countries diverting their waste from landfill and devising more environmentally responsible waste management plans. Ireland’s interpretation of which is expressed in the “Waste Management Act, 1996” and promotes the use of the hierarchy outlined in figure 1.1. Despite the introduction of this act and a rigorous recycling campaign, the majority of the country’s waste still ends up in landfill. As trends of rapid economic growth looks set to continue landfills will reach capacity soon and unless Ireland develops a more sustainable waste management plan there could be a waste crisis on the country’s hands (Davies, 2004). According to Stehlik et al (2009) the development of Waste-To-Energy-Centres (WTEC’s) along with new developments in waste-to-energy processes (WTE), can help rapidly growing countries reach their waste and emissions reduction targets. Ireland’s susceptibility to NIMBYism is hindering our capability to deal with waste adequately (Davies, 2004) and causing the country to fall way behind in meeting emissions reductions in comparison to our European counterparts such as Denmark (Hjelmar, 1997) and Belgium (Van Gervan, 2005). There is ample evidence that the combination of waste sorting and recycling, composting, anaerobic digestion, incineration and finally landfill with biogas recovery is the most efficient way to treat waste with respect to environmental impact and land use reduction (Cherubini et al, 2009; Daskalopoulos et al, 1998; Mendes et al, 2004). The aim of this study is to investigate the feasibility of siting an integrated waste management centre to deal with the municipal solid waste of the greater Dublin area. This centre will incorporate Figure 1:Waste Management Hierarchy (EPA, 2004)
  7. 7. 6  an anaerobic digester and a composting system for the treatment of organic materials,  an incinerator with energy recovery for the treatment of inorganic materials,  a landfill with biogas recovery. Section 2: Site Selection Dublin is the capital city of Ireland with a population of 1.27 million as of 2014. According to the central statistics office this is set to increase to somewhere in between 96,000 and 286,000 by 2021. The city produced almost 1.2 million tonnes of municipal solid waste (MSW) in 2010 with this annual figure expected to rise steadily to 1.4 million tonnes by 2020 (Dublin local Authorities, 2012). According to figure 2 the rigorous recycling campaign implemented by the Dublin councils appears to be successful with targets being exceeded in 2010. However the remaining proportion of waste is still being sent to landfill. Setting aside the emissions from this method of waste disposal for a moment the main issue with this in Dublin’s case is a spatial one. According to Tammemagi (1998) even countries with seemingly endless amounts of space cannot afford to waste land on landfills. In Dublin most of the surrounding area outside the city limits consists of valuable agricultural land. According to DoELG, (1999) the main aim of the 1996 Act is to reduce the amount of waste. The development of an integrated waste facility can significantly reduce the amount of space required to store waste whilst simultaneously using that waste as a resource to generate energy from biogas or refuse derived fuels. When selecting a site there are a vast number of criteria which must be satisfied in order to minimise environmental impact and Figure 2: Dublin Recycling rates 2000-2010 (Dublin Local Authorities, 2012)
  8. 8. 7 human health concerns. Figure 3 shows the final sites considered for the waste management plan. Figure 3: Potential locations for waste treatment facility (Google Maps, 2014) The final three sites considered are roughly 20-30 km form the city centre ranging from 27 hectares to 40 hectares in size. Using the following equations, taken from Kiely (1997) along with population and waste generation estimates from the Dublin local authorities (2012) the optimum sized site was calculated. Assuming a required lifespan of 20 years for a projected population of 1.4 million (CSO,2012) with an average of 3.5 people per household, this gives us a density of 285kg of waste per household per week with an assumed density of 500 kg/m². A) 𝐖𝐚𝐬𝐭𝐞 𝐠𝐞𝐧𝐞𝐫𝐚𝐭𝐞𝐝 = Total population persons per house ∗ household waste per week 10³ = 1,400,000 3.5 ∗ 285 103 = 11,400 𝑡𝑜𝑛𝑛𝑒𝑠 𝑝𝑒𝑟 𝑤𝑒𝑒𝑘 = 592,800 𝑡𝑜𝑛𝑛𝑒𝑠 𝑝𝑒𝑟 𝑦𝑒𝑎𝑟 B) 𝟖𝟓% 𝐕𝐨𝐥𝐮𝐦𝐞 𝐫𝐞𝐝𝐮𝐜𝐭𝐢𝐨𝐧 𝐝𝐮𝐞 𝐭𝐨 𝐢𝐧𝐜𝐢𝐧𝐞𝐫𝐚𝐭𝐢𝐨𝐧, 𝐫𝐞𝐜𝐲𝐜𝐥𝐢𝐧𝐠, 𝐛𝐢𝐨 𝐭𝐫𝐞𝐚𝐭𝐦𝐞𝐧𝐭 = 592,800 ∗ .15 = 88,920 tonnes per year C) 𝐕𝐨𝐥𝐮𝐦𝐞 𝐨𝐟 𝐥𝐚𝐧𝐝𝐟𝐢𝐥𝐥 = 88,920∗103 500kg/m²(density of waste) =177,840m³ per year 𝐇𝐞𝐢𝐠𝐡𝐭 𝐫𝐞𝐬𝐭𝐫𝐢𝐜𝐭𝐢𝐨𝐧 𝐨𝐟 𝟏𝟐. 𝟓𝐦 = 177,840 12.5 = 14227.2𝑚2 = 1.4ℎ𝑎
  9. 9. 8 D) 𝐀𝐫𝐞𝐚 𝐫𝐞𝐪𝐮𝐢𝐫𝐞𝐝 𝐟𝐨𝐫 𝟐𝟎 𝐲𝐞𝐚𝐫𝐬 = 1.4ha ∗ 20(years) ∗ 1.5(extra space for infrastructure) = 42ha Figure 4: The composition of Irish MSW Fig. 4 shows the approximate composition of MSW derived from the Dublin Local Authorities (2012). This is important for determining the size of treatment facilities such as composting, anaerobic digestion and incineration. The projections of these equations suggest that for a 20 year lifespan, the ideal size required would be 42 hectares. At 40hectares, Site A, Mayne is closest to this spatial requirement. Looking at table 1, this site holds a number of advantages over sites B and C located closest to the city centre (18km) but furthest from residential areas (>0.5km). In addition, site A is approximately 2km from the M3 and lies at least 3km from the nearest amenities. Although the population density of this area is low, there are likely to be a number of objections to the development of a waste management centre at this location especially from farmers from the surrounding area, nearby residents, environmental groups and commercial property owners in the area. The Irish public in general has a tendency to object to any kind of new development suggested by the government. Cavazza (2013) suggests that a general lack of public trust in local authorities hinders the development of any kind of new waste technology. It appears that Ireland’s history of cloak and dagger politics is severely impeding the upgrading of its waste management facilities. These concerns could be alleviated by: Glass(9%) Metals(8%) Textiles(2%) Plastic(11%) Organic (21%) Other(17%) Paper(32% MSW Compostion in Ireland
  10. 10. 9  Compensating property owners within a defined radius of the facility with heat and power generated from the on-site facilities.  Carrying out the development with complete transparency, outlining the overall benefits of this facility such as emissions reduction, spatial reduction and jobs.  Encouraging public participation in the planning process. Patel-Tonra (2010), recommend formally inviting any landowners within 1km of the development to an information and Q&A seminar whilst posting newspaper adverts to notify any other interested parties.  Take measures taken to reduce odour, noise and aesthetic pollution such as incorporation of a green buffer region and designated slip road from the motorway for refuse lorries. The biggest drawback of this site is that it borders a tributary to the River Tolka which feeds right into Dublin city (biodiversityireland.ie, 2014) however this issue can be addressed by infrastructural safety measures such as the inclusion of leachate barriers into landfill design. The fine loamy drift soil-type is composed of a 40:40:20 ration of sand, silt and clay (Teagasc, 2014). A higher clay composition would be more ideal to assist in the absorption of odours and leachates thus the landfill design will have to ensure alternative solutions to these issues.
  11. 11. 10 Table 1: Criteria for site selection (Leão et al, 2004) Site A Site B Site C Name of site Mayne Athgoe Slate Quarries (Rathmore ) Size 40 Hectares 32 Hectares 27.9 Hectares Cost (Euro) 1.3 Million 1 Million 485,000 Distance from Dublin 18km 20km 27.3km Distance from Road Network 2 km from M3 2 km from N7 1.5 km from N81 Residential Distance >0.5km <0.4km >0.5km Slope <5° >20° 5°<x>20° Soil Type Fine Loamy Drift with Limestone Fine Loamy Drift with Limestone Fine Loamy over Shale/Slate Current Land Use Agricultural Agricultural Agricultural Distance from Amenities >3km <2km >3km Water bodies Borders tributary to R. Tolka <0.5 km from a drainage ditch <0.5km from a drainage ditch Links to the property http://www.myhome.ie/commercial/brochur e/mayne-clonee-meath-approx-100- acres/2488626 http://www.myhome.ie/commercial/brochur e/athgoe-newcastle-co-dublin-lands-approx- 80-acres-newcastle-dublin-county/2682926 http://www.myhome.ie/commercial/broch ure/farm-c-69-acres-slate-quarries- rathmore-naas-kildare/2913312
  12. 12. 11 Section 3: Site Layout Fig. 5 shows a plan view of the chosen site for the proposed waste to energy centre at Mayne, Co. Meath. An access road of approximately 200m in length will be constructed to connect the WTEC to the Bracetown business park road which is approximately 500m from N3 road. At the site entrance a weigh bridge will be constructed to quantify the amount of waste delivered to the facility. Located immediately after the site entrance are the administration buildings covering an area of 100m². A permanent roadway will be constructed to connect the various waste treatment facilities. To the right of the access road, a sorting centre will be erected. All four municipalities of Dublin are serviced with separate collections of organic waste (brown bins), recyclables (green bins) and unsorted refuse (black bins) meaning the majority of waste is pre-sorted upon arrival. Hence this area need not cover too much area. The anaerobic digester will be located to the north of the site as indicated in fig.5. In accordance with SEAI guidelines (2008) the digester is at least 250m from any residential accommodation in this location taking up approximately 0.5 hectares. The mass burn incinerator will be located to the south of the site to satisfy DEFRA (2010) guidelines of siting the facility at least 500m from residential accommodation and takes up approximately 3ha of site space. This point is the optimum location this site allows with the nearest residences located >600m away to the East of the site. It is proposed to build a CHP plant between these two units. Here electricity and heat can be generated and used for:  supplying electricity and heat for on-site processes  supplying electricity and heat to the nearby industrial estates consisting of Bracetown on the site perimeter and Damastown located 2km to the south east of the site.  Exporting remaining power to the national grid. The landfill will be located in the south east of the site. Even with the mass reduction of wastes exhibited in the treatment processes, the landfill still requires the most substantial space. Fig.5 shows a punnet square of intended development over the 25 year lifespan of the site. This is a worst case scenario as the development would inevitably bring the landfill closer to residential areas. The optimum scenario is that the land indicated by the shaded
  13. 13. 12 area to the south of this site will come available on the market within 5 years of the commencement of waste management activities; and landfill development will be concentrated in this direction, maintaining safe distances from residences. The owner of this property will be more inclined to sell this site considering that its value will depreciate significantly due to the presence of the waste facility in its vicinity. The composting facility, consisting of 3 windrows and a grinding unit will be located to the north of the site taking up 0.2ha for recommended windrow width and separation along with the grinding unit area. This satisfies the minimum distance requirement outlined by Forgie et al, (2004) of 400m away from residential units. Initial use of the compost generated from this facility will be applied as fertilizer to the proposed green buffer zone to facilitate growth. It is proposed that rapid-growing coniferous trees will be planted in the outlined area to obscure the waste treatment facilities on-site from public view. Property/Technology Capital Cost (€) Site 1.3 million Incinerator 150 million Anaerobic Digester 4 million Composting Technology 120,000 Administration buildings 70,000 CHP Plant 350,000 Machinery for site maintenance 400,000 Potential site expansion 750,000 Total building Cost 156,990,000 Table 2: Capital costs of the integrated waste facility
  14. 14. 13 Figure 5: Layout of the various waste treatment technologies and the site in Mayne, Co. Meath Anaerobic Digester Weigh-bridge Access Road Administration Sorting Centre CHP Plant Composting Grinder and Windrows Incinerator Proposed Site Expansion Landfill N3 Dublin City Centre 18km Site Boundary (40ha) Green Buffer Zone Damastown Industrial Estate 2 km
  15. 15. 14 Section 4: Landfill Daire McKiernan Since July 2009, there has been a significant improvement in the operation of MSW landfill sites in Ireland (EPA, 2010). This is due to the regulations which have been enforced and monitored by the EPA. It is imperative that as much biodegradable municipal waste (BMW) as possible is diverted away from the proposed landfill. Article 5 of the Landfill Directive requires that Ireland reduces the amount of BMW being landfilled to 0.427 million by 2016. As landfill has been the cheapest form of waste disposal, it has been the traditional form of waste management. However, in recent years, there has been an increased shift to integrated waste management and the sustainable disposal of our waste. The aim of the EPA, under directives from the European Union, is to reduce the impacts of and reliance on landfill and to promote an integrated management approach to waste disposal (Cummins et al, 2002). The landfill is required to operate in accordance with the Landfill Directive and its main objectives are to prevent or reduce any negative effects on the environment or human health that are associated with the landfilling of waste (EPA, 2010). Under Statutory Instrument No.194 of the Waste Management (Landfill Levy) Regulations 2013, landfill costs are set at €75 per tonne of waste. Site Infrastructure Site facilities such as weighbridge, office and staff buildings and storage facilities for small amounts of oils and chemical wastes have been accounted for in a previous section. A garage or workshop is needed for machinery directly associated with the landfill such as compactors and excavators. The location of this building can be seen in figure 5. A permanent internal road which allows access to the landfill can also be seen. Temporary roads associated with the landfill which lead to the current working cell can be constructed using debris from nearby construction sites. The public’s knowledge of the daily activities which take place in the landfill should be kept to a minimum. This can be carried out by erecting embankments along the perimeter of the site which act as a green buffer zone. Coniferous trees and shrubs should also be added to ensure a permanent green buffer zone for screening of the site and control of air pollution
  16. 16. 15 also. In the initial phases of the landfill, temporary mobile fences may be necessary to screen the cells which are being worked on a daily basis. Landfill Design The primary goal of the landfill design is to reduce as much as possible the negative effects the landfill can have on the environment. This is a containment site, where the leachate and gas are surrounded from the surrounding environment (Kiely, 1997). It is proposed that this landfill occurs in 6 separate phases. Phasing allows the progressive use of the landfill area in terms of filling and restoration being carried out at different locations within the site. This is a ground level landfill and following topsoil removal, waste will be deposited on the surface up to a height of 12.5m. This type of landfill requires the import of daily and intermediate covers which can be constructed using up to 1m of compacted soil to prevent As it is a difficult task to select a location which will have no negative impact or conflicting of interests, the best compromise location has been selected which minimises the impact on the environment and the public also. To ensure minimum pollution and environmental degradation due to the landfill and its operations, a number of landfill designs should be taken into account. These include liner design, leachate and gas management and monitoring of the surrounding ground- and surface water and air quality. Liner Design According to Annex I of the Landfill Directive, protection of soil, groundwater and surface water is to be achieved by the combination of a geological layer and a bottom liner (EPA, 2010). Liners are designed to protect the surrounding water sources by preventing leachate from seeping out of the contained landfill (EPA, 2000). To minimize the impact of leachate, a protective layer called a lining system must be implemented. As this site has a soil composition ratio of 40:40:20, sand, silt and clay (Teagasc, 2014), another protective layer must Figure 6: Liner System Design showing both soil layer and synthetic layer
  17. 17. 16 be added to minimize run off. It is recommended that imported clay of depth 0.5m and compacted in layers of not more than 20cm should be applied. The soil should have a very low hydraulic conductivity of <10-9 m/s. Along with this, a synthetic lining system should be utilized due to the close proximity to the underground tributary to the Tolka River. The various leachate control methods can be seen in fig.6. These are usually made out of polyethylene and up to 2.0mm in thickness (Kiely, 1997). A layer of about 1m of waste should be placed on top of the liner before machinery start to compact the waste. Leachate Leachate is a water-type liquid that is commonly found in landfills that can consist of a number of chemicals. Leachate generally occurs due to rainfall combined with the moisture fraction of the waste. As a result, leachate contains organic material and heavy metals and is toxic to the environment (Kiely, 1997). To collect this leachate, a drainage system must be constructed which consists of a series of wells and pumps. The leachate is then pumped to an onsite storage tank where it is treated in an effluent balance tank which has a series of aerators to agitate the leachate and encourage aerobic conditions. Another method of reducing the potentially toxic composition of leachate is by recirculating through the landfill which dilutes the leachate to acceptable levels. As leachate is produced, it must be collected and removed from the landfill liner. Leachate collection pipes collect this waste which builds up along the landfill liner. These drainage pipes then lead to a leachate collection pond where it can be treated by either biological or physical-chemical methods (EPA, 2000). All active cells should have at least 2 leachate monitoring points with one located at the leachate collection point. Monthly, quarterly and annual monitoring of leachate are requirements as part of the Landfill Directive. Parameters such as leachate level, pH, conductivity, temperature, ammonia, chloride, BOD/COD, total oxidised nitrogen, total phosphate, metals, sulphates and fluoride must be monitored at the aforementioned frequencies (EPA, 2010).
  18. 18. 17 Gas Landfill gas is a product of biochemical reactions which occur within the landfill under anaerobic conditions (Kiely, 1997). The composition of the gas is dependent on a number of conditions such as the type and age of the waste. Landfill gas can have a calorific value of 15 to 21 MJ/m3 with the gas consisting of up to 60% methane and 39% CO2 (EPA, 1997, 2000) and is therefore a possible greenhouse gas and environmental risk. In 2009, it accounted for 71% of all complaints in relation to landfill sites. There are four phases which lead to the production of gas in a landfill: 1. Initial Aerobic Phase – Generally takes days to weeks and O2 is used up as the more easily degradable organic waste is broken down. This results in elevated temperature and CO2 production. 2. First Transition Phase – Lasts from weeks to months as anaerobic and acidic conditions begin to develop due to O2 being completely used up and a drop in pH 6- 4. Hydrogen and CO2 are produced in this stage. 3. Second Transition Phase – This stage takes 3-5 years and involves methanogenic bacteria activity which convert simple acids like acetic and formic acids to methane and methanol. Requires a pH 6-7 to effectively work. 4. Methane Phase – A stable process due to all the organic acids being used up by the methanogenic bacteria. A gas management system must be put in place to reduce impact on air quality, minimise risk of gas migration to other sites, permit effective control of gas emissions and if possible to maximise energy recovery. A landfill gas collection system made up of gas wells, wellheads and collection pipes can be used to actively collect and utilise this resource or to dispose of it through flaring. Fig.7 shows how gas is collected by means of vertical gas collection system. This process can offset some of the costs of control as the gas can be used to make electricity which can Figure 7 Vertical gas collection system for proposed landfill
  19. 19. 18 then be used onsite or sold to local businesses. However, a minimum of 200,000 tonnes of waste is needed to sustain a commercially viable gas electricity scheme (Department of Trade and Industry, 1995). As only 88,920 tonnes/year are expected to go to landfill it will be a number of years before the biogas plant can produce 1MW of electricity. The volume of gas produced from the landfill has been calculated as 435.76L CH4/kg of wet waste (Appendix 2). If the quality of the gas is too low to be collected and used for energy production, it must be disposed of through flaring. At landfill sites across Ireland this is the most common type of disposal of landfill gas with all 31 open landfill sites in 2008 utilising flaring (EPA, 2010). Only 20,000 tonnes of methane produced by landfills in 2008 was utilised through energy recovery with 58,000 tonnes being disposed of through flaring. Figure 8: Methane emissions and uses from 1990-2008. Ground Water and Surface Water The Landfill Directive (EPA, 1999) requires that all ground and surface water be monitored. Monitoring must be carried out to test the quantity and quality of surface and ground water on a period basis. This is done to ensure that any impacts the landfill is having on the environment can be controlled and prevented. Council Directive 80/68/ECC was implemented through the Waste Management Act of 1996 to prevent pollution of ground waters and eliminate the effects of the pollution which has already occurred.
  20. 20. 19 To assess for risks to groundwater, information regarding water table height, location of various groundwater features, ground water quality and groundwater vulnerability should be collected. Surface water management is essential to reduce the amount of leachate produced and minimise the transport of chemicals from the landfill. This can be done by designing a surface water collection system. This collection system allows the collection and transportation of run off to a settlement pond away from the landfill operations. This is done by constructing a series of drainage pipe systems (EPA, 2000).
  21. 21. 20 Section 5: Incineration Luke Martin The incineration of MSW is easily the most controversial waste management process to be incorporated into the proposed waste to energy centre (WTEC) at Mayne. Much to the annoyance of the E.U, Ireland has been slow to adapt their waste management strategy to include modern, environmentally-friendly waste treatment methods (Davies, 2004). Figure 9: Waste management strategies of different E.U countries. (Eurostat, 2012) Fig.9 shows Ireland’s favoured waste disposal methods in relation to the rest of Europe. These figures show the country performs reasonably well in recycling and composting waste with approximately 49% waste diverted by these methods; however a massive percentage of Irelands waste is still being disposed of in landfills. The countries which perform best in minimizing their reliance on landfill, the likes of Denmark, Sweden and the Netherlands, have all invested in the thermal treatment of their waste. Up until 2011, Ireland has resisted the use of incinerators largely due to the factors discussed in section 2 such as “NIMBYism” and lack of trust in planning authorities (Davies, 2004; Cavazza, 2013). The completion of the Indaver WTEC accounts for the 8% of waste which Ireland treats via incineration in figure 1. Contrary to public opinion, the health risks associated with incineration are estimated to be five times lower than those associated with landfill (Moy et al, 2008). In a 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% WasteTreatmentPreferences E.U Country Management of MSW in E.U Countries 2012 Landfilled Recycled/Composted Incinerated
  22. 22. 21 similar study, Cangialosi et al (2008) has claimed that the health impacts which may arise from inhalation, dermal contact or soil and food ingestion of PCDD’s and PCDF’s emitted from incinerators are well below the background levels of these carcinogens. In addition, Sabbas et al (2003) report that incineration can reduce waste to one-tenth its initial volume meaning less space is required for final disposal. This observed 8% towards incineration is a step in the right direction for Irelands waste management plan. Another argument specifically in opposition to incineration is that a move to this technology will discourage the more environmentally-friendly practice of recycling due to the constant demand of feedstock’s for these devices (Snary, 2002). However this argument barely holds water considering 43% of waste in Ireland is going towards landfill despite rigorous recycling campaigns. There is more than enough feedstock composed of non-recyclable material to justify the development of an incinerator. Incinerator types: There are three main types of incinerators classified by the method used to manoeuvre waste through the various heating zones. 1. Moving Grate: This involves a system of moving grates which facilitate the movement of waste through the furnace (Fig.10). The waste goes through three stages of heating. The drying stage at <100°C (A); the pyrolysis stage in which waste is heated in the absence of oxygen at <700°C (B); and the combustion stage at 700-1000°C (C). Flue gas is directed towards a scrubber at 850°C for MSW and 1100°C for hazardous waste to ensure chemical bonds of harmful molecules are broken (DEFRA, 2010). Air is drawn in from below for two functions; to induce combustion and to cool the grates. Grates are arranged at angles to allow waste to proceed through the furnace via gravity. Bottom ash, recovered at the end of the process is roughly 10% the initial volume of the waste. According to Nixon et al (2013) this class of incinerator is the most Figure 10: Moving Grate Incinerator (igniss.pl, 2014)
  23. 23. 22 popular in the U.K as most operators identify moving grate as most reliable technology for heat recovery from waste. 2. Rotary Kiln: This type of incinerator consists of an inclined rotating drum (Fig.11). This is a modular design type consisting of two heating zones; a pyrolysis zone and a combustion zone. The action of rotation on an incline shifts waste slowly through the pyrolysis chamber, where solid waste is volatilized into various gases. The combustion chamber completes the phase change of pyrolysis gases into simpler molecules. This design type is less expensive to build than moving grate and is suited to small scale, specilized treatment plants located in close proximity to the sources of waste (Nixon et al, 2013). 3. Fluidised Bed: This design involves waste being fed through a waste feeder and being immersed in violently moving red-hot sand (fig.12). Waste burns instantaneously on contact with with the sand resulting in a high incineration ratio per unit area. This type of incinerator cannot support the combustion of non- uniform sized material meaning pre- treatment methods such as shredding are required. These systems are easiest Figure 11: Rotary Kiln Incinerator (infohouse, 1996) Figure 12: Fluidized bed incinerator (infohouse, 1996)
  24. 24. 23 to operate with lower start-up and stop times however they require upto 50% higher power demand than moving grate incinerators. According to Nixon et al (2013) the greatest advantage to these systems is that quantities of bottom are significantly reduced. Considering the proposed WTEC is designed to cater for the municipal solid waste from the greater Dublin area, the moving grate incinerator is deemed as the most appropriate technology for this facility. With over 250,000 tonnes of waste expected per year at this facility (Equation 1(B) minus 49% for recycling), efficiency is key. Moving grate incinerators can accept a continuous flow of non-homogenously sized waste without enlisting in the use of pre-treatment methods. This limits the likelihood of malfunctions which, in turn boosts the efficency of collection systems. State of the art moving grate incinerator: Fig.13 shows a schematic of the overall layout of the on-site incinerator including connections to boilers and turbines along with scrubbers to limit the emission of harmful gases and particulates. Figure 13: Typical design of a MSW incinerator (Murdoch University, 2014)
  25. 25. 24 The system begins with the deposition of municipal solid waste into a storage bunker (a). Ideally only unsorted refuse waste will be fed into the storage pit. Waste can be further sorted by a grabber (b), to avoid placing hazardous materials into the hopper(c) or to retrieve non-ferrous metals. The hopper then gradually releases waste into the moving- grate incinerator (d). Waste is shifted through the various heating stages outlined in fig.10 (A, B & C) steadily via the moving grates (e). Temperature must be increased gradually to inhibit the development of cold pockets or gas channelling (DEFRA, 2010). Bottom ash exits the system via the ash chute (f) and is transported via conveyor belt to a slag removal system (g), or a magnet to remove any non-ferrous metal residue (not illustrated in this diagram). Forteza et al (2004) has shown that after a minimum storage time of one month, the leachates within bottom ash stabilize sufficiently to enable environmentally sound usage of these residues in road and pavement construction. Flue gases rise through the combustion chamber (h) at temperatures of 850-1100°C to facilitate the “cracking” of the strong molecular bonds exhibited in furans and dioxins. The breakdown of these bonds leads to the creation of another hazardous compound in Nitrous Oxide. Zandaryaa et al, (2001) recommend the injection of ammonia into the combustion chamber at this stage which acts as a reagent, reducing the harmful NOᵪ into harmless molecular nitrogen and water vapour (process known as selective non-catalytic reduction). At least one auxiliary burner linked to a temperature sensor must be present in this chamber to ensure these temperatures are maintained throughout the entire process followed by rapid quenching of the material (DEFRA, 2010). Failure to do so may allow hazardous compounds to reform (de novo synthesis) in the 400-250°C temperature range. Flue gases continue out of the after-burn chamber to heat the boiler system (i) which generates steam to be exported to an on-site turbine. DEFRA (2010) recommends the use of combination of the following four technologies to maximise energy recovery;  Boiler system to utilize waste heat,  Turbines powered by steam from these boiler to generate electricity,  Combined heat and power (CHP) scheme to utilize exhaust steam,  Internal heat exchangers for flue reheating. Suggestions on where to incorporate such features are discussed in section 3 (site selection). Upon passing the boiler system; flue gases proceed to the economizer (j) where
  26. 26. 25 heat is recycled for on-site usage either for supplementary heat supply to the incinerator itself, or for water and space heating. It is important to locate these heat recovery features at this point in the cycle, straight after combustion because flue gas temperatures are at their highest but also require rapid quenching. After the heat recovery stage, flue gases are now at temperatures of approximately 160°C. It is at this point where the secondary processes associated with gas clean-up begin in order to ensure minimal harmful emissions to the outside environment. Under E.U legislation, all modern incinerators must limit their daily average emissions of HCL and TOC (10mg/m³), HF (1mg/m³), SO₂ (50mg/m³) along with other chemicals such as mercury (DEFRA, 2010). In order to remove these components safely, gases are first treated in a wet scrubber (k) which utilizes reagents which target these specific molecules. These scrubbers also capture fractions of dust simply due to water droplets encapsulating these small particles. Gas is then further treated in a highly efficient filtration device known as an electrostatic precipitator (l). This system utilizes an electro-static charge to which designed to extract the finest portion of particulate matter from the gas. Considering dioxin and furan pollutants are at the centre of most incinerator objections (Davies, 2004), it is necessary to include a further, pre-cautionary filtration system in place to prevent their release. Hence gas passes through a final dioxin filtration system (m) consisting of a catalytic fibre which oxidises dioxins to form CO², HCL and H₂O (Gore Creative Technologies, 2001). The chimney stack (n) should be 70m in height for this plant considering 250,000 tonnes of waste are expected per year (DEFRA (b), 2007). Incinerator Efficiency: According to CEWEP (2012), larger incinerators (intake of 250,000 tpa) in northern Europe tend to have the most favourable R1 value of approximately 0.77. This R1 value is a way of expressing the energy efficiency relative to conventional power plants hence are suitable for heat recovery (European Commission Directive, 2008/98/EC). With heat available in the flue gas in this moving grate incinerator of 8582GJ/day, overall efficiency of this system is estimated at 80% (Kiely, 1997) [Calculations shown in Appendix 1]. Tolis et al, (2010) has calculated payback periods of MSW incinerators to be 26-28 years. Gasification yields greater energy from substrates and has much lower payback periods than mass burn incineration (8-10 years) so one might argue why invest in incineration? According to
  27. 27. 26 Asadullah (2014) these technologies have not yet been successfully up-scaled to deal with the volumes of waste this site will intake nor are the suited to the heterogeneous sizes for MSW. Hence the inferior efficiencies of this incinerator is over written by its versatility in accepting different waste types.
  28. 28. 27 Section 6: Anaerobic Digestion: Anant Kumar Singh Anaerobic digestion is defined as the controlled breakdown of complex organic matter into simpler compounds by anaerobic or facultative bacteria in the absence of oxygen. Anaerobic digestion (AD) is one of the most efficient waste treatment technologies. There is a recent surge in the installation of AD in Europe due to EU attention towards sustainable waste management. The technological advancement in better control and optimization of the anaerobic digestion process is making it financially viable option for waste treatment. More than 80% composting plants in Netherlands and Belgium will have an anaerobic digestion facility installed by 2015 as primary treatment. The economic value associated with syngas makes the AD process more financially feasible than landfill. The proper waste collection and segregation mechanisms are helping the AD to run on specific mixture of waste or residue and improving plant operational condition and reduction of variability. (Baere & Mattheeuws, 2012) Figure 14 Figure1. Anaerobic digestion installed capacity in Europe
  29. 29. 28 Type of product Concentration by mass Uses Biogas 2-4% For power generation or as cooking gas. Fiber 7-25% Nutrient rich can be used as soil conditioner Liquor 75-93% Liquid Fertilizer Table 3: Products from AD Component Concentration (by volume) Methane (CH4) 50-75% Carbon dioxide (CO2) 25-45% Water vapor (H2O) 2-7% Oxygen (O2) <2% Nitrogen (N2) <2% Ammonia (NH3) <1% Hydrogen (H2) <1% Hydrogen sulphide (H2S) 20-20,000ppm Table 4: Constituents of Biogas (Source: SEAI & Teagsac) Importance of AD: ( Baere & Mattheeuws, 2012; Jenkins et al., 2008) 1. It reduces future environmental impacts of waste by degradation into simplest molecules. 2. AD reduces the spread of harmful diseases and weed seeds. 3. Better control of methane emissions than landfill. 4. Waste water treatment and potential application of liquor in the farm as liquid fertilizers. 5. To meet the EU environmental regulation and increase of the renewable energy share. 6. Odour reduction and limited space requirement.
  30. 30. 29 7. Better application of nutrient in the soil and reduction of nitrate run-off into water bodies. Figure 15: Complete flow Cycle of AD (Photo Courtesy: Pagels Ponderosa; Utah State University): Feedstock for AD Waste or agricultural residual having moisture content more than 80% can be used as feedstock for AD. Any type of easily biodegradable waste like grass, MSW, agricultural waste from farm can be used as a feedstock.
  31. 31. 30 Animals Population Wet tonnes available MWh/tonne Potential Electricity MWh Cattle 6.4m 32m 0.04 1,280,000 Pigs 1.4m 2.4m 0.024 57,600 Grass 3.4m hectares 204m 0.250 51m Poultry 13.9m 0.2m 0.180 36,000 Table 5: Potential Feedstock for Electricity Production in Ireland (Teagasc 2013) Chemical Reactions in AD A group of bacterium accomplices the task of anaerobic digestion of organic matter in synergistically. 1. Hydrolysis- The degradation of complex organic matter takes place. Like Carbohydrates, starch, protein, fats into smaller compounds. It is a rate limiting step if cellulose is present in higher amount due to slow degradation of cellulose. Pretreatment of the feedstock is required to improve the hydrolysis. 2. Acidogenesis- These compounds are further broken down into lactic, butyric, propionic, and valeric acid. 3. Acetogenesis- These short chain molecules are further broken down into produce carbon dioxide, Hydrogen and acetic acid by fermentation. This can be rate limiting step if high amount of fat rich substrate is present in the feed. 4. Methanogenesis- This is the last step of biogas production. Different biochemical pathways used by methanogenic bacteria to produce methane, CO2 and other gases. Acetotrophic methanogenesis: It uses acetic acid to produce methane. It is the main producer of methane. 4 CH3COOH 4 CO2 + 4 CH4 Hydrogenotrophic methanogenesis: A small amount of methane is produced by utilizing CO2 and H2. CO2 + 4 H2 CH4 + 2 H2O Methylotrophic methanogenes: It uses methanol to produce methane. 4 CH3OH + 6 H2 3 CH4 + 2 H2O
  32. 32. 31 Figure 16 Figure3. Chemical Reactions in Anaerobic Digestion (www.wastewaterhandbook.com,2014) Variable Parameters in AD Temperature Anaerobic digestion works in a variety of temperatures based on the nature of the bacteria. Generally, physchrophilic bacteria (15-20°C), mesophilic bacteria (25-40°C) and thermophilic bacteria (50-60°C) are the main types of bacteria identified in anaerobic digester. Higher temperature increases the rate of digestion. Mesophilic bacteria are used in AD because it can sustain variation in temperature and require low heat. Redox potential Methanogenic bacteria can work at a redox potential of -300mV to -330mV. Low redox potential is required for the electron transfer in AD. C:N ratio For successful AD operation, the C:N ratio should be from 3:1 to 30:1. But, any further increase in C:N ratio leads to slow growth of bacteria due to absence of nitrogen for the
  33. 33. 32 growth. But, a C:N ratio lowers than 3:1, cause ammonia formation which is toxic to bacteria in high concentration at higher pH. pH The AD works in the pH range of 6.5-7.5. A reduction in the pH below 6.5 due to more acid production has a toxic effect on methnogenic bacteria. The pH reduction below 6.9 is considered as an indication of pH change and proper treatment and buffering system is applied. There are two different buffering systems are applied in the AD to maintain the pH. 1. Carbon dioxide – hydrogen carbonate–carbonate buffering system. 2. Ammonia–ammonium buffering system. Inhibitory Substances Inorganic salts (like sodium, potassium, calcium, Magnesium), heavy metals (lead, cadmium, copper, zinc, nickel and chromium) have inhibitory effect on bacteria in high concentration and simulating effect on low concentrations. Parameter Hydrolysis/ Acidogenesis Methanogenesis Temperature Mesophilic: 25-30°C Mesophilic: 30-40°C Thermophilic: 50-60°C pH value 5.2-6.3 6.7-7.5 C:N:P:S ratio 500:15:5:3 600:15:5:3 Trace elements --- Ni, Co, Mo, Se Table 6: Variable Parameters in AD (Zupan & Grilc, 2007) Types of Anaerobic Digestion Single stage and Two-stage digesters In single phase AD, all the reactions take place in a single compartment. These are simple to design, build, and operate and less capital expensive. These digesters depend on the ability of methanogenic organisms to tolerate a decline in pH by the formation of acidic compounds. More than 80% of the digesters in Europe are based on single stage digesters. The methanogenesis stage is separated from the initial hydrolysis or acidogenesis stage in two stage digesters. The production of biogas is higher and better process control. But, these are capital expensive. (Jenkins et al., 2008; Sinpaisansomboon et al. , 2007; Zupan & Grilc, 2007)
  34. 34. 33 High Solid or Dry Anaerobic Digestion and Low solid or Wet Anaerobic Digestion The solid content is more than 15% of the total feed and rest is water. The substrate and biomass are in presoaked solid form. Due to lesser amount of water, the reactor volume is less and more production of methane. There is reduced inhibitory effect of ammonia in this process. But, the transportation of substrate is energy intensive process. Low solid digesters generally have solid content from 5-15%. These are either batch or continuous based on the plant requirement. (Jenkins et al., 2008; Sinpaisansomboon et al., 2007; Zupan & Grilc, 2007) Planning and Financial viability AD is financially viable and great income source if it is managed properly and constructed on a large scale. As a part of the integrated waste facility, a consistent supply of feedstock is always available. Main revenue sources are biogas sale, heat, liquor production and direct electricity sale. Liquor and fiber is separated in separator and liquor goes to heat exchanger to preheat the cold incoming slurry. Around 20-30% heat generated by the digester is used in the anaerobic digestion process. Figure 17: Lemvig biogas plant overview (Source: www.lemvigbiogas.com)
  35. 35. 34 Specification Proposed plant for Dublin City Lemvig Plant (Case study) Land Area 1 hectare >1 hectares Installed biogas capacity 7100m3 14300m3 Input substrate Around 300t/day≈109500 t/yr 20% industrial waste + 20-30% MSW from home + 50% Slurry Around 615 ton/day (83% manure and 17% organic waste) Conditions Thermophilic Thermophilic Installed Power 1.5MW 3MW Investment 4m (1-2m subsidies from EU) 10.2m (1.2m subsidies from EU & cost included land) Positive factors Free heat to public Cheaper biogas rates and heat- good public perception Operating cost 40,000 40,000-50,000 Payback period 5-6 years 4 years Table 7: Specification for AD plant in Dublin Planning Regulations (SEAI: Application guidelines) 1. All waste storage and treatment must not be within 10m of any watercourse or 250m from any spring well or borehole. 2. Biogas must be burnt in an appliance with a net rated thermal input of less than 3MW. 3. Permitted waste types comprise sludges, plant tissue waste and manure from agriculture, horticulture, forestry and fishing and some wastes from the dairy products industry. 4. A Standard Rules Environmental Permit for off-farm anaerobic digestion is that the distance to any off site building used by the public must be 250m or greater.
  36. 36. 35 Section 7: Composting Aneesh Priyadarshan Kale and Mugdha Hemant Karmarkar Composting is the natural degradation of organic material by micro-organisms and its conversion into a stable earth like material called humus. This process is accomplished in an aerobic environment. This material can be used in soil so as to increase it’s the overall fertility (Curran, 2014). The micro-organisms break down the raw organic matter and get energy which is used up by them for the process of reproduction. (Composting Council of Canada, 2014) The decomposed matter that is left consists of dead and living micro-organisms along with non-degraded organic matter is called as "Compost". Composting in Ireland As seen there are lists of composting facilities in the country. In Ireland, mostly windrows are used for composting technology followed by in-flow and aerated systems. This is because windrows require low maintenance costs, low initial costs (Herity, 2003). Figure 18: Locations of the composting facilities in Ireland (Herity 2013)
  37. 37. 36 Site layout There would be a network of roads connecting the rest of the facility as well as small roads in between the composting unit for movement of machinery and vehicles to carry the compost. There is a grinder located next to the composting unit to reduce waste particles to the required size. For the waste facility windrow composting is been proposed. Windrow (mechanical aeration) Windrows are basically long rows of piles of organic waste. These are turned frequently either manually or mechanically over a period of time so to facilitate movement of air (EPA, 2014). The site is to have a pair of windrows. Preferably the piles are around 1 to 3 meters tall .The width would be around 2-5m. It is kept in such a way that there is enough air flow in it so as to maintain the temperature. There are a number of machines that are used to mix the waste such as front end loaders (EPA, 2014). A series of pipes are to be installed below the composting unit so as to catch the leachate, which can be treated in a small unit next to the composting site. This will help to nullify any soil or ground water pollution from happening. There can also be presence of detachable rooftop, to offer protection from rain and control the temperature. Turning at frequent intervals maintains temperatures. Windrow composting tends to have many benefits over other conventional methods. Since there is frequent turning there is good amount of air exchange that takes place. It also helps to maintain the desired temperature range. Constant and hard-core mixing helps grinding the particles to as small as possible thus increasing microbial activity and at the same time reducing the time.
  38. 38. 37 Figure 19: Diagram of Windrow (Harvest Quest, 2014) Type of Wastes Used for the Composting process Most of the wastes used for the composting process, are biodegradable garden and park wastes, food and kitchen wastes from kitchens, restaurants, fast food joints, caterers, wastes from food processing plants. (Curran 2014) According to ABP 2002 regulations, Category 2 and 3 could be used for composting. Under category 2, manure and gut contents can be used directly in a compost plant. In Category 3, food of animal origin, catering waste is suitable for composting. (Curran 2014) Category 3 before submitting to a compost plant, it should be ssubjected to a treatment (Curran, 2014) It is a highly popular technique as it yields high quality product at the same time it requires less investment as well. The space available in the proposed facility is sufficient enough to have an installation of two windrows. As the final product is of good standard, it can be sold off as high quality compost. Requirements for Composting : The process of composting is carried by diverse population of micro-organisms. To make the process more effective, the system should be managed properly by supplying a sufficient proportion of the parameters required by the micro-organisms (Curran, 2014).
  39. 39. 38 Carbon: Nitrogen ratio Main nutrients required for the composting process is Carbon and Nitrogen. Proper amounts of carbon and nitrogen will help in carrying out the process effectively (Hattemer & Stettler,2000). If the carbon levels are high and decrease in the nitrogen level, the microbial activity will slow down, since, nitrogen is required to break the carbon sources. This will have an adverse effect on the process. If the carbon is less and more amount of nitrogen, excess of carbon will be broken down and nitrogen will be easily lost in the atmospheres in the form of ammonia gas. Thus, the process will be affected in a negative way on the environment resulting in bad composting process. The optimum range of C:N will be 25:1 to 35:1(Earth easy, 2014). When the ratio decreases to 12-20:1, this means that the process is finished (Hattmar & Stettler, 2000). Moisture Content With the help of moisture, the micro-organisms move and transport materials. It is also essential for all the chemical reactions taking place during the process. The optimum moisture content range should be 50-60%. (Curran, 2014). If the moisture content exceeds 60%, the microbes will not thrive. Also, if the content reduces below 15 %, the microbial activity will stop. (Hattemer & Stettler,2000) Oxygen Lack of oxygen can result in anaerobic decomposition which will lead to inefficient compost and undesirable odours. It should be well supplied to the entire pile. The concentration of oxygen required is minimum 5% (Curran, 2014). Despite of the aeration, the amount of air do not reflect the amount of oxygen reaching the microorganism. This is because, most of the micro-organisms require aqueous environment for them to sustain (Hattemer & Stettler, 2000). pH The ideal pH range for the microbial activity is between 6.5 to 8.0 (Hattemer & Stettler, 2000) Acidic pH has a negative effect on the compost. Bacterial growth is significant in such conditions, thus, slowing down the process (Composting Council of Canada, 2014). pH should be considered when some materials are rich in nitrogen. This material will increase
  40. 40. 39 the alkalinity of the compost forming ammonia. This ammonia results in the loss of nitrogen through volatilization. This affects the environment in a negative way (Hattemer & Stettler, 2000). Temperature During the process wherein the micro-organisms break down the materials there is release of heat in the compost. This increases the temperature. It indicates that the process is taking place in a proper manner (Composting Council of Canada, 2014). On the other hand, if the temperature fails to increase, this indicates insufficient amount of nitrogen and moisture content. Temperature is to be maintained around 40-60 degree Celsius (Friesen, 2002). Particle size Different materials used in the compost, have different particle size. The maximum size of the particles should be 12mm.Good particle size leads to good air flow, (Earth Easy, 2014). Conclusions In 1998, the Irish Government policy of waste management aimed to reduce the amount of biodegradable waste dumped in landfills over a period of 15 years. These targets included 50% diversion of the house hold waste to landfills(Citizen Information Board, 2010). Thus a composting unit will not only serve the purpose, but also the compost that is obtained be sold in the Irish market. According to McGovern (2012), the price of compost directly from the site can fetch anywhere between 10-40Euros per m3 of compost. If this is to be further treated and bagged the price of compost is seen to go high as 180 Euros. According to McGovern (2012) the main markets for compost are highlighted in the figure below.
  41. 41. 40 Figure 20: Market for Compost in Ireland. McGovern (2012) Since there is a potential market that is available for the compost, it can serve as a source of revenue for the waste facility. Advantages of composting According to U.S Environmental Protection Agency, (2014) composting has many benefits.  Good quality of compost tends to improve soil quality.  It thus helps reduce dependency of chemical fertilizers on agricultural land by improving crop yield.  Compost has also been known in helping pest and plant diseases.  The compost process tends to absorb odour and treat semi volatile and volatile  The trend of composting tends to move away waste from landfills and incinerators, thus reducing the stress on them as well as bring down the pollution levels associated with them.  The compost obtained when spread on soil tends to arrest soil erosion.  Use of compost means use of less water, fertilizers and pesticides. It is an economic commodity and a low cost option to landfill and other methods.
  42. 42. 41 Section 8: Discussion and Conclusions Overall the task of siting an integrated waste management facility within a reasonable distance of Dublin is feasible. The city provides a more than adequate feedstock to justify the construction of these technologies. Despite exorbitant initial capital costs in the region of 157 million the project is entirely worth undertaking due to the following reasons:  The majority of on-site processes have payback periods within the 25 year lifespan of the site due to power generation (incinerator and AD) as well as commercial ventures (composting, ash for road construction).  These processes reduce the environmental impact of waste disposal considerably by converting waste in controlled environments, capturing harmful emissions before they reach the outside environment thus limiting the emission of GHG’s and other harmful chemicals.  Incineration and AD can generate power, offsetting fossil fuel use by supplying up to 25,000 homes with electricity whilst simultaneously providing the site with power and heat. Nearby industrial estates could avail of this power also.  These processes can enable the recycling of post-treatment residues such as non- ferrous metals from incineration, pathogen-free compost and raw materials which can subjected to the Fischer-Tropsch cycle to make synthetic fuels.  These processes divert a massive amount of waste from landfill; In the case of incineration, 80-90% of the initial volume of the waste can be diverted hence less space is required for the landfill.  Economies of scale; by integrating all these process on one site, many savings can be made from on-site vehicles and by building just one large CHP plant as opposed to a few on a number of sites.  In addition, transport costs and emissions can be reduced by eliminating residue transport to distant sites. Further transport costs can be made by the fact that Ireland would no longer have to export waste to Germany and other countries in Europe to be disposed of appropriately.
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  48. 48. 47 Appendix 1: Incineration efficiency calculations R1 formula for Efficiency of MSW incinerator in relation to conventional power plants (European Commission Directive, 2008/98/EC) : 𝐸𝑛𝑒𝑟𝑔𝑦 𝑒𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦 = 𝐸𝑝 − 𝐸𝑓 + 𝐸𝑖 0.97 ∗ (𝐸𝑤 + 𝐸𝑓) Where : Ep is annual energy produced as heat/electricity Ef is the annual energy input to the system via fuels for production of steam. Ew is annual energy contained in waste by Net calorific value (GJ/year) Ei is annual energy imported excluding Ew and Ef (GJ/reay) 0.97 is a factor accounting for bottom ash+ radiation energy losses Mass/Balance calculations for incineration (Kiely, 1997): Assumptions: MSW: 685,000kg/day of MSW; 374,010 combustible(54.6%); 164,400 non-combustible(24%); 146,590 water(21.4%) Heating Value: 11,780 kJ/kg 5% unburned Carbon in residue with LHV of: 32,564 Total losses of heat (excluding C in residue): 1.66x10⁸kJ/day Boiler efficiency: 85% Calculations: Gross heat input = (685,000kg/day) x (11780kJ/kg)= 8.7x10⁹ kJ/day Heat loss due to unburned C = 164,400kg/0.95 = 173,053 kg/day Unburned C in residue = 173,058kg/day x (0.05) = 8652.65 kg/day Heat Loss in unburned C = (8653kg/day) x (32,564 KJ/kg) = 281,776,292 kJ/day Heat available in flue gas = Gross heat input – (losses due to unburned C + total losses of heat) = (8.7x10⁹ kJ/day – (281,776,292 + 1.66x10⁸) = 8252GJ/day Combustion efficiency = Net available heat/Gross heat input x 100 = 8,252,223,708/8.7x10⁹ x 100 = 94.85% Overall efficiency = (0.9485) x (0.85) = 80%
  49. 49. 48 Appendix 2: Methane production rates from landfill equations Methane production rate of landfill without sulphur but including water is (C70H150O70N) (Adapted from Kiely (1997)). Assumptions CHON is 30% of the wet weight of waste going to landfill. a = 150 (number of atoms in hydrogen molecule) b = 70 (number of atoms in oxygen molecule) c = 1 (number of molecules in nitrogen molecule) d = 4n + a – 2b – 3c 𝑑 = (4 𝑥 70) + 150 − (2𝑥70) − (3𝑥1) = 287 e = 0.96 (fraction of waste converted to biomass) n = 70 (number of atoms in carbon molecule) Solution: 𝑉𝑜𝑙𝑢𝑚𝑒 (𝐿)𝑜𝑓 𝐶𝐻4/𝑘𝑔 𝑤𝑎𝑠𝑡𝑒 = ( 𝑑𝑒 8 ) 𝑉𝑜𝑙𝑢𝑚𝑒 𝑆𝑇𝑃 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒/𝐶𝐻𝑂𝑁 𝑀𝑜𝑙𝑒𝑐𝑢𝑙𝑎𝑟 𝑊𝑒𝑖𝑔ℎ𝑡 = (70𝑥12) + (150𝑥1) + (70𝑥16) + (1𝑥14) = 2124𝑔/𝑚𝑜𝑙𝑒 𝑀𝑜𝑙𝑒𝑠 𝑜𝑓 𝐶𝐻4 𝑝𝑒𝑟 𝑚𝑜𝑙𝑒 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒 = 𝑑𝑒 8 = 287𝑥0.96 8 = 34.5 𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑚𝑒𝑡ℎ𝑎𝑛𝑒 𝑝𝑒𝑟 𝑢𝑛𝑖𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑠𝑡𝑒 ( 𝐿 𝑘𝑔 ) = 34.5𝑥88920 2124/0.3 = 435.76𝐿 𝐶𝐻4/𝑘𝑔 𝑜𝑓 𝑤𝑒𝑡 𝑤𝑎𝑠𝑡𝑒
  50. 50. 49 Appendix 3: Distribution of workload Abstract, table of contents, introduction, site selection, incineration, conclusions and reference list – Luke Martin. Table of figures/tables, Site Layout, Site Map, landfill and proof-reading – Daire McKeirnan. Site Layout and Anaerobic Digestion – Anant Kumar Singh Composting – Aneesh Priyadarshan Kale Composting - Mugdha Hemant Karmarkar

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