Chapter 6 Running Case Assignment Improving Decision Making

Chapter 6 Running Case Assignment: Improving Decision
Making:
Redesigning the Customer Database
Software skills: Database design; querying and reporting
Business skills: Customer profiling
Dirt Bikes U.S.A. sells primarily through its distributors. It
maintains a
small customer database with the following data: customer
name, address
(street, city, state, zip code), telephone number, model
purchased, date of
purchase, and distributor. These data are collected by its
distributors when
they make a sale and are then forwarded to Dirt Bikes. Dirt
Bikes would like
to be able to market more aggressively to its customers.
The Marketing Department would like to be able to send
customers e-
mail notices of special racing events and of sales on parts. It

would also like
to learn more about customers’ interests and tastes: their ages,
years of
schooling, another sport in which they are interested, and
whether they
attend dirt bike racing events. Additionally, Dirt Bikes would
like to know
whether customers own more than one motorcycle. (Some Dirt
Bikes
customers own two or three motorcycles purchased from Dirt
Bikes U.S.A.
or other manufacturer.) If a motorcycle was purchased from Dirt
Bikes, the
company would like to know the date of purchase, model
purchased, and
distributor. If the customer owns a non–Dirt Bikes motorcycle,
the company
would like to know the manufacturer and model of the other
motorcycle (or
motorcycles) and the distributor from whom the customer
purchased that
motorcycle. Dirt Bikes’s customer database was redesigned so
that it can
store and provide the information needed for marketing.

Case Questions:
Develop the following queries and reports that would be of
great interest to
Dirt Bikes’s marketing and sales department.
1- Create a report of customers and motorcycles model grouped
by
manufacturer.
2- Create a query about Dirt Bikes customers who attend racing
events.
3- Create a query of the customers who have more than 12 years
of
education.
Part 1
This is an individual assignment. Read the recent research
article "Biochar Wastewater Treatment 2020." Prepare a 2-3
paragraph response for the following:
What are the main points of the article? How can it connect to
scouring wool washing discussions for the wool industry? How
can this technique be used more broadly in the apparel industry?
Refer to the book Raw Material and Sustainability & Social
Change in Fashion to develop your response. Provide key
citations in APA format.

Part 2
After reading Raw Material Ch. 11- 15 (p. 138- 213), what are
the main points that resonated with you? How does this connect
with broader discussions about sustainable fashion in the book
Sustainability & Social Change in Fashion?
lable at ScienceDirect
Chemosphere 252 (2020) 126539
Contents lists avai
Chemosphere
journal homepage: www.elsevier.com/locate/chemosphere
Review
Biochar technology in wastewater treatment: A critical review
Wei Xiang a, b, Xueyang Zhang a, b, *, Jianjun Chen c, Weixin
Zou d, Feng He e, Xin Hu f,
Daniel C.W. Tsang g, Yong Sik Ok h, Bin Gao b, **
a School of Environmental Engineering, Jiangsu Key Laboratory
of Industrial Pollution Control and Resource Reuse, Xuzhou
University of Technology,
Xuzhou, 221018, China
b Department of Agricultural and Biological Engineering,
University of Florida, Gainesville, FL, 32611, USA
c Mid-Florida Research & Education Center, University of
Florida, Apopka, FL, 32703, USA
d Jiangsu Key Laboratory of Vehicle Emissions Control,
Nanjing, 210093, China
e College of Environment, Zhejiang University of Technology,
Hangzhou, 310014, China

f Center of Material Analysis, Nanjing University, Nanjing,
210093, China
g Department of Civil and Environmental Engineering, The
Hong Kong Polytechnic University, Hong Kong, China
h Korea Biochar Research Centre & Division of Environmental
Science and Ecological Engineering, Korea University, Seoul,
South Korea
h i g h l i g h t s
* Corresponding author. School of Environmental En
Xuzhou, 221018, China.
** Corresponding author.
E-mail addresses: [email protected] (X. Zhang), bg
https://doi.org/10.1016/j.chemosphere.2020.126539
0045-6535/© 2020 Elsevier Ltd. All rights reserved.
g r a p h i c a l a b s t r a c t
� Biochar technologies in various
wastewater treatment are elucidated.
� Feedstock pre-treatment and post-
treatment effect on biochar produc-
tion is reviewed.
� Biochar as an innovative adsorbent to
remove aqueous contaminants is
discussed.
� Future perspectives of biochar tech-
nology in wastewater treatment are
summarized.
a r t i c l e i n f o
Article history:
Received 27 January 2020
Received in revised form

11 March 2020
Accepted 17 March 2020
Available online 18 March 2020
Handling Editor: X. Cao
Keywords:
Engineered biochar
Wastewater treatment
Production technologies
Modification methods
Carbonaceous adsorbents
a b s t r a c t
Biochar is a promising agent for wastewater treatment, soil
remediation, and gas storage and separation.
This review summarizes recent research development on biochar
production and applications with a
focus on the application of biochar technology in wastewater
treatment. Different technologies for
biochar production, with an emphasis on pre-treatment of
feedstock and post treatment, are succinctly
summarized. Biochar has been extensively used as an adsorbent
to remove toxic metals, organic pol-
lutants, and nutrients from wastewater. Compared to pristine
biochar, engineered/designer biochar
generally has larger surface area, stronger adsorption capacity,
or more abundant surface functional
groups (SFG), which represents a new type of carbon material
with great application prospects in various
wastewater treatments. As the first of its kind, this critical
review emphasizes the promising prospects of
biochar technology in the treatment of various wastewater
including industrial wastewater (dye, battery
manufacture, and dairy wastewater), municipal wastewater,
agricultural wastewater, and stormwater.

Future research on engineered/designer biochar production and
its field-scale application is discussed.
Based on the review, it can be concluded that biochar
technology represents a new, cost effective, and
environmentally-friendly solution for the treatment of
wastewater.
© 2020 Elsevier Ltd. All rights reserved.
gineering, Jiangsu Key Laboratory of Industrial Pollution
Control and Resource Reuse, Xuzhou University of Technology,
[email protected] (B. Gao).
mailto:[email protected]
mailto:[email protected]
http://crossmark.crossref.org/dialog/?doi=10.1016/j.chemospher
e.2020.126539&domain=pdf
www.sciencedirect.com/science/journal/00456535
www.elsevier.com/locate/chemosphere
W. Xiang et al. / Chemosphere 252 (2020) 1265392
Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Production technologies . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Pre-treatment technologies . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

2.2. Thermal carbonization technologies . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.3. Post-treatment technologies . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Biochar as an adsorbent for aqueous contaminant removal . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Heavy metal removal . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Organic contaminant removal . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Nitrogen and phosphorus removal . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Biochar technology in wastewater treatment . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Industrial wastewater treatment . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.2. Municipal wastewater treatment . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. Agricultural wastewater treatment . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.4. Stormwater treatment . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

5. Conclusions and future perspectives . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Declaration of competing interest . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Biochar is a porous carbonaceous material produced during the
thermochemical decomposition of biomass feedstock in the
pres-
ence of little or no oxygen. Biomass feedstock can be any
organic
waste materials which include crop and forest residues, wood
chip,
algae, sewage sludge, manures, and organic municipal solid
wastes
(Colantoni et al., 2016; Xiong et al., 2019). Methods for
thermo-
chemical decomposition include pyrolysis, hydrothermal
carbon-
ization, gasification, torrefaction, and microwave heating,
varying
in thermochemical temperature and duration (Mohan et al.,
2014;
Gonz�alez et al., 2017; Fang et al., 2018). Interest in biochar is
largely
based on its two distinct benefits: First, biochar production per
se
can offset greenhouse gas emission because it stores carbon in a

stable form, preventing the release of greenhouse gases into the
atmosphere from biomass degradation (Creamer and Gao, 2016;
Yang et al., 2018a). Second, biochar is an effective, low -cost,
and
environment-friendly adsorbent (Cha et al., 2016; Inyang et al.,
2016), which is related to its relatively large surface area and
abundant surface functional groups (SFG) (Wang et al., 2017a;
Zhang et al., 2017a). Biochar can be used for adsorbing metals/
metalloids and purifying water (Agrafioti et al., 2013; Van Vinh
et al., 2015; Palansooriya et al., 2019), applied to soils for
improving soil fertility and crop productivity (Yoo et al., 2018),
employed for clean energy production to partially replace the
fossil
fuels (Fang et al., 2018; Cao et al., 2019), and utilized as
adsorbent
and catalysts to various pollutants and reduce greenhouse gas
emission (Xiong et al., 2017). As a result, biochar becomes
increasingly important as a solution to some global problems,
such
as climate change, environmental pollution, and soil
degradation
(Creamer and Gao, 2016).
It has been well documented that feedstock, thermochemical
decomposition methods and their temperature and duration can
significantly affect biochar physical and chemical properties
(Yu
et al., 2019). Several previous review articles have discussed
decomposition methods, characterization, and applications of
biochar in removal of different contaminants from aqueous solu-
tions (Mohan et al., 2014; Cha et al., 2016; Tan et al., 2016).
Biochar
properties can also be affected by feedstock pre-treatments and
biochar post-treatments (Wang et al., 2017a; Yang et al., 2019).
As
shown in Fig. 1, pre-treatments vary depending on feedstock

and
the purposes for biochar use, including physical (dry, crush,
sieve,
wash, etc.), chemical (treat with chemicals or functional
materials,
load of precursors and functional agents, etc.), and biological
(bacterial treatment, etc.) methods. Post-treatments mainly rely
on
physical (ball milling, magnetization, etc.) and chemical
(corrosive
treatment, etc.) methods (Zhang and Gao, 2013; Tan et al.,
2016;
Usman et al., 2016). Thus far, only few review articles have
emphasized pre-treatments in relation to feedstock
decomposition
methods and resultant biochar properties as well as post-
treatment
technologies on biochar properties and their effects on
wastewater
treatment.
The overarching objective of this work is to present the first
comprehensive review on the applications of biochar technology
in
wastewater treatment. After summarizing new technologies on
pre-treatment of feedstock, thermal carbonization process, and
post-treatment of biochar (Section 2), this review digests
current
knowledge of biochar as an innovative adsorbent for aqueous
contaminants (Section 3). Most importantly, recent advances of
biochar applications in wastewater treatments, including
industrial
wastewater, municipal wastewater, agricultural wastewater and
stormwater are perspicuously and detailly elucidated (Section
4).
This critical review also discusses the perspectives and future

research directions of the biochar technology in wastewater
treatment (Section 5).
2. Production technologies
2.1. Pre-treatment technologies
Pre-treatment is the first step for biochar production from
different raw materials. In general, these methods can be
classified
physical, chemical, and biological pre-treatment technologies
(Fig. 1).
Physical pre-treatment technology generally includes drying,
crushing, sieving, and washing of biomass feedstock. The
feedstock
riches in lignocellulosic/plant is usually dried to constant
weight at
105 �C or other temperature, ground into smaller particles
using a
hammer mill, and then cut into different pieces (Wang et al.,
2016a;
Essandoh et al., 2017; Zhang et al., 2017a). Occasional ly,
separate
Fig. 1. Biochar production technologies: (a) Biomass. (b) Pre-
treatment technologies. (c) Thermal processes. (d) Post-
treatment technologies.
W. Xiang et al. / Chemosphere 252 (2020) 126539 3
drying step may be needed for some plant feedstock, because
the
plant raw materials vary greatly in moisture contents. Physical
pre-
treatment method for biomass feedstock is related to its own

properties. For example, dewatered sludge is often dried in an
oven
overnight, crushed, sieved, and stored in sealed containers prior
to
use (Agrafioti et al., 2013). Newspapers and cardboard are
commonly shredded and blended into pulp as the feedstock
(Randolph et al., 2017). Paper mill sludge is acid-washed,
rinsed
with deionized distilled water to obtain mineral-free sludge
(Cho
et al., 2017). Algae is alkaline, it is usually rinsed with fresh
water
and then dried, granulated or flaked before pyrolysis (Roberts
and
de Nys, 2016).
Chemical pre-treatment technology often relies on chemical
reactions to change the properties or compositions of feedstock
materials. One type of most commonly used chemical pre-
treatment technique is to treat feedstock biomass materials with
chemicals or functional materials to load chemical precursors or
functional agents into the feedstock. During the treatment, the
biomass feedstock is immersed into a chemical solution or a
colloidal suspension, and then dried prior to biochar production
(Tan et al., 2016). After pretreated with metal ion solutions
such as
FeCl3, AlCl3, and MgCl2, biomass feedstock can be
successfully
converted into biochar-based nanocomposites with metal oxy-
hydroxide (e.g. Fe3O4, AlOOH, and MgO) nanoparticles
stabilized on
carbon surface with the pores of the engineered biochar (Zhang
et al., 2012a, 2013; Zhang and Gao, 2013; Son et al., 2018). On
the
other hand, biomass can be pretreated with engineered nano-
particles and natural colloids including carbon nanotubes, gra-

phene and clay, which also leads to the successful production of
biochar-based nanocomposites (Zhang et al., 2012b; Yao et al.,
2014; Inyang et al., 2015). Corrosive chemicals including acid,
al-
kali, and oxidant have also been applied to pretreat biomass for
the
production of engineered biochar with enlarged surface area,
unique pore structure, enriched SFG, etc. (Zhou et al., 2017a;
Zhao
et al., 2018).
Biological pre-treatment technology is a relatively new concept
that utilizing biological processes to improve biomass feedstock
for
engineered biochar production (Wang et al., 2017a). Bacterial
treatment, particularly anaerobic digestion or biofuel processes,
of
biomass feedstock has been proven to be an effective and
product
‘biologically activated’ biochar with enhanced properties
(Inyang
et al., 2010; Yao et al., 2015). In the literature, several biomass
materials including sugar beet tailings, bagasse, sludge, and
animal
waste were subjected to the anaerobic digestion process first
and
then the residues were converted into biochar through slow py-
rolysis (Inyang et al., 2010; Yao et al., 2011a; Tang et al.,
2019). The
anaerobic digestion pre-treatment would make the obtained bio-
char have a larger specific surface area (SSA) and better
adsorption
performance (Inyang et al., 2010; Yao et al., 2011a). It is
recognized
that utilizing the biological pre-treatment residue materials to
produce biochar can introduce additional benefits such as

reducing
waste disposal costs, and making bioenergy more eco-friendly
(Inyang et al., 2010; Yao et al., 2015). Another biological pre -
treatment method uses biomass enriched with high concentra-
tions of minerals including heavy metals through
bioaccumulation
for biochar production (Yao et al., 2013b; Wang et al., 2017c).
Wang
et al. (2017c) converted a heavy metal hyperaccumulating plant
into biochar and suggested that this technology not only
provides a
safe solution for hyperaccumulator disposal but also produces
value-added biochar nanocomposites.
2.2. Thermal carbonization technologies
Thermal processes for biomass conversion into biochar mainly
Fig. 2. Percent yields of biochar from different feedstock at
different pyrolysis tem-
perature (data are from reference (Yuan et al., 2011; Bian et al.,
2016; Colantoni et al.,
2016; Irfan et al., 2016; Lin et al., 2016; Wang et al., 2016a;
Gonz�alez et al., 2017)).
Fig. 3. Percent of carbon and ash in biochar from different
feedstock at different py-
rolysis temperature (data are from reference (Hossain et al.,
2011; Al-Wabel et al.,
2013; Ma�sek et al., 2013)).
include pyrolysis, microwave-assisted pyrolysis, hydrothermal
carbonization and gasification (Mohan et al., 2014; Wang et al.,

2017a; Fang et al., 2018). Table 1 summaries and compares
these
carbonization technologies.
Pyrolysis is a thermochemical process for decomposing biomass
in an anoxic or hypoxic environment (Cha et al., 2016).
Pyrolysis
processes depend on the operating temperature, heating rate,
and
residence time used, which can affect the compositions and
phys-
icochemical properties of products. The yields of biochar
decrease
with increasing pyrolysis temperature (Fig. 2), whereas ash and
carbon content increase (Fig. 3). It is mainly related to
cellulose,
hemicellulose and lignin decomposition, saline-alkali
separation,
carbonization and other factors in biomass (Hossain et al., 2011;
Al-
Wabel et al., 2013; Ma�sek et al., 2013; Irfan et al., 2016). The
heating
rate determines the pyrolysis speed, and it influences the
charac-
teristics of biochar and the yield of bio-oil and bio-gas (Inyang
et al.,
2010; Cho et al., 2017). Prolonged residence time provides more
complete biomass decomposition while decrease the biochar
pro-
duction yield (Mohamed et al., 2016).
Microwave-assisted pyrolysis (MAP) is considered as a sustain-
able method to produce bio-energy products, including biochar,
bio-oil, and bio-gas (Dai et al., 2017; Mutsengerere et al.,
2019). In
comparison to the conventional methods, MAP technique offers

shorter processing time, lower energy requirement, more
effective
heat transfer, and better selective heating (Zhang et al., 2017b;
Dur�an-Jim�enez et al., 2018). The MAP process is mainly
controlled
by the microwave power, irradiation time, etc. (Lam et al.,
2017;
Dur�an-Jim�enez et al., 2018; Nhuchhen et al., 2018;
Kadlimatti et al.,
2019). The yield of biochar often decreases as the microwave
power
increases, which can be attributed to the high heating rates at
high
microwave power levels (Jimenez et al., 2017; Nhuchhen et al.,
2018). Biochar with high SSA was obtained in a microwave sys-
tem operated at the microwave power of 500 W, irradiation time
of
3 min, and frequency of 2450 ± 25 MHz. (Dur�an-Jim�enez et
al.,
2018). Further microwave treatment, however, resulted in a loss
of SSA, which can be attributed to the degradation of mi cropore
structure of the biochar after the microwave overheating
(Jimenez
et al., 2017).
Hydrothermal carbonization (HTC) is the conversion of wet
feedstock at a temperature range of 120e260 �C into biochar
without pre-drying (Mohan et al., 2014; Cha et al., 2016; Fang
et al.,
2018). The wet biomass is heated and pressurized (2e10 MPa)
for
5e240 min in a confined system (Kambo and Dutta, 2015; Fang
et al., 2018; Zhang et al., 2019a). The biochar produced by HTC
is
Table 1
Summary of common thermal carbonization technologies (Cha

et al., 2016; You et al., 2017; Mutsengerere et al., 2019; Zhang
et al., 2019b).
Thermal carbonization
technologies
Key parameters Temperature/
power range
Residence
time
Desired
product
Advantages
Pyrolysis temperature;
heating rate;
residence time
300e850 �C 1e3 h Biochar Simple, robust, and cost-effective;
applicable to small scale and farm-based
biochar production
Microwave-assisted
pyrolysis
microwave power;
microwave
irradiation time
400e500 W 1e10 min Biochar and
biofuel
volumetric, fast, selective, and efficient heating

Hydrothermal
carbonization
temperature;
residence time;
pressure;
water-to-biomass
ratio
120e260 �C 1e16 h Hydrochar More suitable for feedstock with
high moisture content
Gasification temperature;
particle size;
residence time;
pressure;
gasification agent/
biomass ratio
＞800 �C 10e20 s Syngas Biochar yield of gasification is less
than pyrolysis, but the biochar contains a
high level of alkali salts (Ca, K, Si, Mg, etc.).
usually called hydrochar. Reaction temperature is identified as
the
governing parameter during the HTC (Kambo and Dutta, 2015).
With the increase of temperature, hydrochar contains abundant
acidic functional groups on its surface, which can benefit the
contaminant adsorption capability (Zhou et al., 2017a; Saha et
al.,
2019). Increasing holding temperature and holding time can in-
crease the porous structure of the hydrochar, which increases

the
possibility of the application of hydrochar as an adsorbent
(Shao
et al., 2019).
Gasification is the process converting the biomass to gas fuel
using gasification agents. Gasification temperature is generally
higher than 800 �C (You et al., 2017). The biochar produced
during
gasification usually contains high levels of alkali salts and
alkaline
earth mineral (Kambo and Dutta, 2015; Zhang et al., 2019b),
which
can precipitate many heavy metal contaminants and thus be used
directly as a remediation agent in problem soils (Yang et al.,
2018b;
Yu et al., 2019). Deal et al. (2012) reported that problem soils
amended with gasifier-produced biochar had higher maize
yields,
and the soluble ash content of the biochar had the greatest influ-
ence on soil productivity.
2.3. Post-treatment technologies
Biochar are often post-treated by either physical or chemical
modification methods to increase its SSA, pore volume, surface
chemistry, and functional agents including SFG and composited
nanoparticles (Van Vinh et al., 2015; Tan et al., 2016; Dai et
al.,
2017). In the literature, there are several good reviews that have
provided comprehensive summaries of various post-treatment
technologies for biochar modifications (Tan et al., 2016; Wang
et al., 2017a). This review thus only slightly discusses three
post-
treatment technologies including magnetic, ball milling, and
cor-

rosive (i.e., acid, alkali, or oxidation) treatment (Mohamed et
al.,
2016; Usman et al., 2016; Wang et al., 2017a), which either are
current research hotspots or have not reviewed intensively in
the
literature.
Magnetization is the method that converts biochar into a
magnetic material where magnetic iron oxides including Fe3O4,
g-
Fe2O3, or CoFe2O4 particles are loaded into biochar (Zhang et
al.,
2013; Wang et al., 2015b; Tan et al., 2016; Shengsen Wang et
al.,
2019). Thus, magnetic modified biochar can easily be recovered
from the aqueous solution (Zhang et al., 2013; Mohan et al.,
2014;
Wang et al., 2015b; Son et al., 2018). Magnetic zero-valent iron
biochar derived from peanut hull at 800 �C has a higher
removal
rate for Cr6þ, which is mainly due to its high SSA, pore
volume, and
loaded reductive iron (Liu et al., 2019b). Another method for
pre-
paring magnetic biochar composites is directly chemical co-
precipitate Fe3þ/Fe2þ on biochar surface (Tan et al., 2016).
Mag-
netic switchgrass biochar prepared by the precipitation of iron
oxide using an aqueous Fe3þ/Fe2þ solution has the highest
adsorption capacity for metribuzin (205 mg/g, pH ¼ 2)
(Essandoh
et al., 2017).
Ball milling is a simple and efficient method which uses the
kinetic energy by moving balls to break chemical bonding,
chang-

ing the particle shape and producing nanoscale particles (Lyu et
al.,
2017). After ball milling, the characteristics of biochar were
enhanced including SSA, pore volume, negative zeta potential,
oxygen-containing functional groups, and the adsorption
capacity
(Wang et al., 2017a; Lyu et al., 2018a, 2018b; Xiang et al.,
2020). Ball-
milled bagasse biochar has higher Ni2þ removal efficiency than
pristine biochar, and the adsorption capacity of Ni2þ and
aqueous
methylene both increased (Lyu et al., 2018b). This is mainly
due to
the fact that ball milling can increase the external and internal
surface areas of the biochar and expose its graphitic structure
and
oxygen-containing functional groups (Lyu et al., 2018a).
Nitrogen-
doped biochar has been successfully synthesized by simply ball
milling pristine biochar with ammonium hydroxide, these N
groups
improve the adsorption performances of the biochar on acidic
carbon dioxide and anionic reactive red (Xu et al., 2019). Ball -
milling technology is thus an effective engineering method to
produce novel engineered biochar. The ball-milled biochar
shows
enhanced physicochemical and adsorptive properties, and can be
used in various environmental applications.
Corrosive treatments such as acid, alkali, and oxidation treat-
ments are commonly used chemical modification techniques,
which alter the surface chemistry of the biochar. The corrosive
chemicals, such as HCl, HNO3, KOH, NaOH, KMnO4, and
H2O2 have
been applied to modify biochar for different purposes (Wang et
al.,

2015a, 2017a; Cha et al., 2016; Zheng et al., 2019). The
chemical
modified biochar has higher SSA, more microporous, more
func-
tional groups, and enhanced sorption capacity (Yang et al.,
2019).
Alkali (NaOH)-acid (HNO3) combined modification shows an
obvious increased BET surface area, porosity and oxygen-
containing functional groups of municipal sewage sludge
biochar,
which enhances tetracycline adsorption, up to 286.9 mg/g (Tang
et al., 2018). KMnO4 and KOH treatment increase the SSA of
bio-
char derived from waste peanut shell, resulting in increased
adsorption sites for Ni2þ (An et al., 2019). H2O2 is another
strong
oxidant for modifying biochar (Xue et al., 2012). H2O2-
modified
manure biochar can eliminate heavy metals efficiently, due to
the
increased oxygen and carboxyl group content (Wang and Liu,
2018).
Post-treatment of biochars represent a new area of research. It
modifies existing biochars by increasing biochars’ SSA, pore
vol-
ume, negative zeta potential, oxygen-containing functional
groups,
and the adsorption capacity. Such modified biochars can be
cost-
effective and environmentally-friendly carbon materials with
great application potential in many fields.
3. Biochar as an adsorbent for aqueous contaminant removal
Biochar can be used as an adsorbent to remove different pol -

lutants in water and wastewater. Here, we mainly discuss its use
for
removal of heavy metals, organic contaminants, nitrogen and
phosphorus.
3.1. Heavy metal removal
Heavy metals in wastewater can adversely affect human beings,
animals, and plants. Long term exposure to heavy metals in the
aqueous phase can cause serious health threats even at low con-
centration (Ahmed et al., 2016). Increased evidence suggests
that
biochar obtained from plants and animal residues can
effectively
adsorb heavy metals in water and wastewater (Higashikawa et
al.,
2016; Inyang et al., 2016; Tan et al., 2016; Dai et al., 2017;
Zhou
et al., 2017a). Table 2 summarizes biochar adsorption of heavy
metals in aqueous phase.
Arsenic is an extremely toxic metal and occurs in wastewater as
well as drinking water. The adsorption capacity of As3þ is
enhanced
from 5.7 mg/g to 7.0 mg/g through the surface modification of
bio-
char by Zn(NO3)2 impregnation (Van Vinh et al., 2015).
Biochar
produced from paper mill sludge was applied to adsorb As5þ
and
the maximum adsorptive capacity was 34.1 mg/g (Cho et al.,
2017).
Biochars produced separately from sugarcane straw, rice husk,
sawdust, and chicken manure were mixed with sawdust and used
to remove Cd2þ in water. Results show that increased pyrolysis
temperature from 350 �C to 650 �C triggers the increasing

tread in
percentage removal of Cd2þ (Higashikawa et al., 2016).
Biochars are
also effective in removal of Pb2þ. The removal efficiencies of
Pb2þ by
biochars produced from fresh and dehydrated banana peels are
359 mg/g and 193 mg/g, respectively (Zhou et al., 2017a). Table
2
Table 2
Biochar adsorption of heavy metals in aqueous solutions.
Biochar
feedstock
Pre-treatment Thermal
process
Post treatment Pyrolysis
temperature
(�C)
Biochar
dose (g/
L)
Adsorption
pH
Heavy
metals
Initial
concentration

(mg/L)
Adsorption
capacity
(mg/g)
Removal mechanism Ref.
Bamboo
wood
Oven dried Pyrolysis HNO3þ nZVI
treated
600 2 e Agþ 200 584 Innersphere
complexation and
electrostatic attraction
by outer-layer Fe oxides
under oxic conditions
Wang et al.
(2017b)
Bamboo
wood
Oven dried Pyrolysis H2O2þ nZVI
treated
600 2 e Agþ 200 1217 Innersphere
complexation and
electrostatic attraction
by outer-layer Fe oxides
under oxic conditions
Wang et al.

(2017b)
Pomelo
peel
Dried þ H3PO4
impregnated
Pyrolysis Pristine 250 2 6 Agþ 50 137.4 Chemical adsorption
with oxygenic
functional groups
Zhao et al.,
(2018)
Pine wood Oven dried and
milled
Pyrolysis Ni/Fe-LDH
modified
600 2.5 7.5 As3þ 20 4.38 Electrostatic attraction
and surface
complexation with
hydroxyl groups
Wang et al.
(2016b)
Pine wood Ni/Fe-LDH
modified
Pyrolysis Pristine 600 2.5 7.5 As3þ 20 1.56 Electrostatic
attraction
and surface
complexation with

hydroxyl groups
Wang et al.
(2016b)
Paper mill
sludge
Oven dried and
acid washed
Pyrolysis Pristine 720 1 2.7e10.4 As5þ 26.7 34.1 Chemisorption
or
chemical reaction
process between
available adsorption
sites and adsorbate
Cho et al.,
(2017)
Sewage
sludge
Stirred and
heated
Pyrolysis Pristine 300 4 e As5þ 0.05 e Chemical sorption
Agrafioti
et al.,
(2013)
Sewage
sludge
Stirred and

heated
Pyrolysis Pristine 300 4 e Cr3þ 0.2 e Chemical sorption
Agrafioti
et al.,
(2013)
Rice husk Washed Pyrolysis Polyethylenimine
modified
450e500 1 e Cr6þ 100 435.7 Introduction of amino
group facilitate chemical
reduction of Cr6þ and
increase sorption
capacity
Rajapaksha
et al.,
(2016)
Green
waste
Dried Pyrolysis HCl modified 600 2 3e8 Cd2þ 5.6 6.72
Chemisorption Zhang et al.,
(2018)
Peanut shell Washed, dried
and milled
Pyrolysis Hydrated
manganese oxide
treated
400 0.2 6.5 Cd2þ 10 10 Nonspecific outer-
sphere surface

complexation provided
by oxygen-containing
groups, specific
innersphere
complexation offered by
the impregnated HMO
Wan et al.,
(2018)
Marine
macro-
algal
FeCl3
immersed
Pyrolysis Pristine 500 16.7 e Cu2þ e 69.37 Oxygen-containing
functional groups as
potential adsorption
sites
Son et al.,
(2018)
Banana
peels
Oven dried Pyrolysis Pristine 600 2.5 e Cu2þ 200 75.99
Electrostatic attraction,
partial of physisorption,
ion exchange and
precipitation
Ahmad
et al.,

(2018)
Cauliflower
leaves
Oven dried Pyrolysis Pristine 600 2.5 e Cu2þ 150 53.96
ion exchange and
precipitation
Ahmad
et al.,
(2018)
Pomelo
peel
Dried þ H3PO4
impregnated
Pyrolysis Pristine 250 2 6 Pb2þ 50 88.7 Precipitated by
phosphorous functional
groups
Zhao et al.,
(2018)
Peanut shell Washed, dried
and milled
Pyrolysis Hydrated
manganese oxide
treated
400 0.2 6.5 Pb2þ 20 36 Nonspecific outer-

sphere surface
complexation provided
by oxygen-containing
groups, specific
innersphere
complexation offered by
the impregnated HMO
Wan et al.,
(2018)
Banana
peels
Oven dried Pyrolysis Pristine 600 2.5 e Pb2þ 600 247.1
Table 2 (continued )
Biochar
feedstock
Pre-treatment Thermal
process
Post treatment Pyrolysis
temperature
(�C)
Biochar
dose (g/

L)
Adsorption
pH
Heavy
metals
Initial
concentration
(mg/L)
Adsorption
capacity
(mg/g)
ion exchange and
precipitation
Ahmad
et al.,
(2018)
Cauliflower
leaves
Oven dried Pyrolysis Pristine 600 2.5 e Pb2þ 200 177.8
ion exchange and
precipitation
Ahmad
et al.,

(2018)
Maple
wood
Dried Pyrolysis H2O2 modified 500 5 7 Pb
2þ 50 43.3 Complexation by
oxygen functional
groups
Wang et al.,
(2018)
Pecan
nutshell
Dried and
milled
MAP Pristine e 2 3 Pb2þ 500 80.3 Ion-exchange by
calcium ions on the
material surface
Jimenez
et al.,
(2017)
Banana
peels
Dehydrated
and grinded
HTC Pristine 230 0.25 7 Pb2þ 200 359 Ions exchange and
surface complexation.

Zhou et al.
(2017a)
Banana
peels
H3PO4 soaked HTC Pristine 230 0.25 7 Pb
2þ 200 193 Ions exchange and
surface complexation.
Zhou et al.
(2017a)
Peanut hull Dried HTC Pristine 300 2 e Pb2þ 50 0.88
Complexation with
carboxyl surface
functional groups
Xue et al.,
(2012)
Peanut hull Dried HTC H2O2 modified 300 2 e Pb
2þ 50 22.82 Complexation with
carboxyl surface
functional groups
Xue et al.,
(2012)
also shows biochar adsorption of Cr3þ, Ni2þ and Cu2þ. Biochar
prepared from sewage sludge adsorbed approximately 70% of
Cr3þ

from the aqueous solution (Agrafioti et al., 2013). The
maximum
adsorption capacity of Ni2þ from water by chicken manure
mixed
with sawdust-derived biochars was 11 mg/g at 650 �C
(Higashikawa et al., 2016). Marine macro-algae magnetic
biochars
are rich in oxygen-functional groups, which attributes to their
high
selectivity and adsorption capacity to Cu2þ (69.37 mg/g for
kelp
magnetic biochar and 63.52 mg/g for hijikia magnetic biochar)
(Son
et al., 2018).
3.2. Organic contaminant removal
Organic contaminants are another major type of pollutants in
aquatic environment, which include pesticides, herbicides, and
antibiotics etc.. Table 3 summarizes biochar adsorption of some
organic contaminants in aqueous phase. Organic pollutants are
toxic and can reduce dissolved oxygen in water and cause harm
to
the aquatic ecosystem and human health (Ahmed et al., 2016).
Switchgrass biochar (SGB) and magnetic switchgrass biochar
(MSGB) were employed to remove metribuzin herbicide from
aqueous solutions. The low solution pH value is beneficial to
bio-
char for the metribuzin adsorption compared to the high
solution
pH value. Metribuzin adsorption onto both SGB and MSGB is
un-
affected by temperature increase (Essandoh et al., 2017).
Biochars
can also remove antibiotics, such as sulfonamides and

tetracyclines
(Yao et al., 2012a; Sun et al., 2018). The mechanism underlying
the
removal of sulfonamides and tetracyclines is probably due to
the
electron donor-acceptor interactions and associated with the
attracting groups on surface area rings (Peiris et al., 2017).
Sulfa-
methoxazole (SMX) is one of the typical sulfonamid e
antibiotics
widely used for both human and animals. SMX adsorption onto
the
digested bagasse biochars is mainly controlled by p-p
interaction
and effected by the solution pH value (Yao et al., 2018). Iron
and zinc
doped sawdust biochar shows high simulta neous removal of
tetracycline from aqueous solution. The predominant adsorption
mechanisms include site recognition, bridge enhancement, and
site
competition (Zhou et al., 2017b).
In addition, several studies have also suggested biochar’s ap-
plications for adsorption of organic matter for water treatment,
and
the effectiveness is closely related to the aromaticity index,
polarity
index, SSA, and the quantity of oxygen functional groups
(Mohan
et al., 2014; Cha et al., 2016; Braghiroli et al., 2018).
3.3. Nitrogen and phosphorus removal
Biochar can also absorb nutrients, such as nitrogen and phos-
phorus in aqueous phase (Zhang et al., 2012a, 2014; Yao et al.,
2013b; Zhang and Gao, 2013; Xue et al., 2016). Ammonium, ni -

trate and phosphate are the common forms of reactive nitrogen
and
phosphorus in wastewater, and can lead to eutrophication (Yao
et al., 2012b; Yang et al., 2017; Xu et al., 2018). Table 4 lists
the
adsorptions of nitrogen and phosphorus on various biochars in
aqueous phase. The adsorption capacity of modified biochars
for
nitrogen and phosphorus is significantly higher than pristine
bio-
chars, because the modified biochars have higher SSA, more
reac-
tion activity and SFG.
Post-treatment of biochars have significant effects on ammo-
nium adsorption. Oxidized maple wood biochar has higher
ammonium adsorption capacity than maple wood biochar (Wang
et al., 2016a). Additionally, pyrolysis temperatures affect
ammo-
nium adsorption. Biochars produced from pine sawdust at 300
�C
shows the highest NH4
þ adsorption capacity based on the higher H/
C and O/C ratios and presence of more functional groups on the
surface of it (Yang et al., 2017). This study demonstrates that
chemical bonding and polar interaction between NH4
þ and SFG are
likely mechanisms for enhanced NH4
þ adsorption.
Pre-treatment of feedstock show pronounced effects on
adsorption of phosphorus. The digested sugar beet tailing
biochar

shows the highest phosphate removal ability with a removal rate
around 73% (Yao et al., 2011a). This is probably because the
large
amount of colloidal and nano-sized periclase on its surface,
which
has a strong ability to bind phosphate in aqueous solution. Pre-
treatment can be performed during plant growth. For example,
the biochar derived from tomato plants that enriched with Mg
during their growth, which shows increased adsorption of phos-
phate in aqueous solution, reaching more than 100 mg/g (Yao et
al.,
2013b). Additionally, biochars produced from wood waste pre-
treated with magnesium oxides (Mg-biochar) was used to
recover
ammonium and phosphate (Xu et al., 2018). The struvite
Table 3
Biochar adsorption of organic contaminants in aqueous
solutions.
Biochar
feedstock
Treatment/
Modification
Pyrolysis
temperature
(�C)
Biochar
dose (g/
L)

Organic
contaminants
Initial
concentration
(mg/L)
Adsorption
capacity (mg/
g)
Switchgrass Magnetization 425 1 Metribuzin
herbicide
100 39.6 Electrostatic attraction and hydrogen bonds Essandoh
et al.,
(2017)
Switchgras Pristine 425 1 Metribuzin
herbicide
100 38.2 Electrostatic attraction and hydrogen bonds Essandoh
et al.,
(2017)
Bagasse Anaerobically
digested
600 2 Sulfamethoxazole 10 1.6 p-p EDA interaction Yao et al.,
(2017)
Bagasse Anaerobically
digested

600 2 Sulfapyridine 10 3.2 p-p EDA interaction Yao et al.,
(2017)
Bamboo
sawdust
Graphene
oxide-coated
600 1 Sulfamethazine 10 6.5 p-p EDA interaction, pore-filling,
cation exchange,
hydrogen bonding interaction and electrostatic
interaction
Huang
et al.,
(2017)
Bamboo
sawdust
Pristine 600 1 Sulfamethazine 10 3.1 p-p EDA interaction, pore-
filling, cation exchange,
hydrogen bonding interaction and electrostatic
interaction
Huang
et al.,
(2017)
Sawdust Iron and zinc
doped
600 / Tetracycline 150 86 Site recognition, bridge enhancement,
and site
competition

Zhou et al.
(2017b)
Sawdust Iron and zinc
doped
600 / Tetracycline 100 53.8 Site recognition, bridge
enhancement, and site
competition
Zhou et al.
(2017b)
Peanut
shell
Magnetization 800 2 Trichloroethylene 9.2 4.6 Hydrophobic
partitioning, pore-filling and reductive
degradation.
Liu et al.
(2019b)
Reed Magnetization 600 0.5 Florfenicol 20 5.3 Hydrogen
bonding, pore-filling effect and p-p EDA
interaction
Zhao and
Lang,
(2018)
Reed Pristine 600 0.5 Florfenicol 20 2.6 Pore-filling effect and
p-p EDA interaction Zhao and
Lang,
(2018)

Crab shell calcium-rich
biomass
800 1 Chlortetracycline
hydrochloride
100 70 Cation bridging, electrostatic interaction, hydrogen
bonding and p-p interaction
Xu et al.,
(2020)
Crab shell calcium-rich
biomass
800 1 Chlortetracycline
hydrochloride
2000 1975 Adsorption and flocculation Xu et al.,
(2020)
precipitation on the surface of biochar is the dominant
mechanism
for the removing ammonium and phosphate. Other reports have
also shown modified biochars for removing the nitrate (NO3
�), total
Kjeldahl nitrogen (TKN), total nitrogen (TN), total phosphates
(TP),
and phosphate (PO4
3�) from aqueous solutions (Mohan et al., 2014;
Usman et al., 2016; Sun et al., 2017; Vikrant et al., 2017). A
general

conclusion is that the modifications change biochar surface
chemistry, thus resulting in enhanced nutrients sorption
capacity
compared with pristine biochars.
4. Biochar technology in wastewater treatment
As discussed above, biochars are effective adsorbents for
removal of various contaminants due to its special properties,
such
as large SSA and abundant SFG. Thus, biochars have become
increasingly important as a solution to remediate pollutants in
the
industrial and agricultural sectors for improving environmental
quality (Wang et al., 2017a). Wastewater has been a global
issue,
which is a byproduct of domestic, industrial, commercial or
agri-
cultural activities. Biochars have great potential to be used for
wastewater treatment. This section mainly focuses on discussing
biochar’s applications in treatment of industrial wastewater,
municipal wastewater, agricultural wastewater and stormwater
(Fig. 4).
4.1. Industrial wastewater treatment
The industrial wastewater comes from various sources including
mining, smelting, battery manufacturing, chemical industry,
leather manufacturing, dyes, and others. And the pollutants are
mainly heavy metals and organic pollutants in industrial
wastewater. Biochars have been applied in the treatment of in-
dustrial wastewater.
A biochar mixed with chitosan after cross linking can be casted
into membranes, beads, and solutions. It can be effectively
utilized

as an adsorbent for heavy metals adsorption in industrial waste-
water. The ratio of biochar and chitosan would affect the
adsorption
of copper, lead, arsenic, cadmium and other heavy metals in in-
dustrial wastewater (Hussain et al., 2017). Gliricidia biochar is
a
promising material for crystal violet (CV) removal from an
aqueous
environment in dye-based industries. The CV sorption process
is
governed by the pH value, surface area and pore volume of
biochar
(Wathukarage et al., 2017). Bagasse biochar was used to adsorb
lead
from the battery manufacturi ng industry effluent. The maximum
adsorption capacity can reach 12.7 mg/g and the adsorptive
process
is related to medium pH value, contact time and dosage
(Poonam
and Kumar, 2018). Biochar was also used to recapture nutrients
from ammonium and phosphate-based dairy wastewater. Biochar
can adsorb 20e43% of ammonium and 19e65% of phosphate in
flushed dairy manure within 24 h (Ghezzehei et al., 2014). Thus
far,
most of the experiments on biochar application in removal of
contaminants from industrial wastewater were conducted in lab-
oratory setting, further research and implementation in real -
world
conditions is needed.
4.2. Municipal wastewater treatment
Biochar can be directly used or combined with biofilter and
other technologies for municipal wastewater treatment, which
result in recovery of labile nitrogen and phosphorus (Cole et al.,
2017). Engineered biochar loaded with aluminum oxyhydroxides
(AlOOH) was applied to recycle and reuse phosphorus from

Table 4
Biochar adsorption of nitrogen and phosphorus in aqueous
solutions.
Biochar feedstock Treatment/
Modification
Pyrolysis
temperature
(�C)
Biochar
dose (g/
L)
Nutrient Initial
concentration
(mg/L)
Adsorption
capacity (mg/
g)
Pine sawdust Pristine 300 3 NH4
þ 100 5.38 Chemical bonding and electrostatic
interaction of NH4
þ with the surface functional
groups.

Yang et al.,
(2017)
Wheat straw Pristine 550 3 NH4
þ 100 2.08 Chemical bonding and electrostatic
interaction of NH4
þ with the surface functional
groups.
Yang et al.,
(2017)
Wood waste MgO modified 600 2 NH4
þ 8203 47.5 Struvite precipitation Xu et al.,
(2018)
Sugarcane harvest
residue
MgO particle-
impregnated
550 1.25 NH4
þ 200 22 Struvite crystallization, electrostatic
attraction, and p-p interactions
Li et al.,
(2017)
Wheat straw MgeFe layered
double hydroxides
(LDH)
600 2 NO3

� 45 24.8 Surface adsorption and interlayer anion
exchange
Xue et al.,
(2016)
Peanut shells MgCl2 solution
immersed
600 2 NO3
� 20 94 Surface adsorption Zhang et al.
(2012a)
Hickory wood chips Aluminum salt
treated
600 2.5 Phosphorus 6.4 8.346 Electrostatic attraction Zheng et
al.
(2019a)
Wheat straw Acid wash and
water wash
500e560 12.5 Phosphorus 25 1.06 Adsorption and surface
precipitation Dugdug
et al.,
(2018)
Hardwood Acid wash and
water wash
et al.,
(2018)

Willow wood Acid wash and
water wash
et al.,
(2018)
Wood waste MgO modified 600 2 PO4
3- 318.5 116.4 Struvite precipitation, surface adsorption Xu et
al.,
(2018)
Bamboo MgeAl layered
double hydroxides
(LDH)
600 2 PO4
3- 50 13.11 Interlayer anion exchange and surface
adsorption
Wan et al.,
(2017)
Anaerobically
digested sugar
beet tailings
Pristine 600 2 PO4
3- 61.5 25 Surface adsorption by colloidal and nano-
sized MgO particles
Yao et al.
(2011b)

Cottonwood AlCl3 solution
immersed
600 2 PO4
3- 1600 135 Adsorption by unique nanostructure Zhang and
Gao,
(2013)
Sugar beet tailings MgCl2 solution
immersed
600 2 PO4
3- 1600 835 Surface adsorption Zhang et al.
(2012a)
Tomato leaves Mg enriched 600 2 PO4
3- 588.1 100 Precipitation, surface deposition Yao et al.
(2013a)
Cottonwood HTC þ LDH 180 2 PO43- 2000 386 Surface
adsorption Zhang
et al.,
(2014)
secondary treated wastewater (Zheng et al., 2019a). The
adsorption
mechanism of phosphorus is mainly through electrostatic attrac-
tion. Phosphorus adsorbed on engineered biochar can be utilized
as
a slow-release fertilizer for crop production.
Biochar produced from digested sludge was used as an adsor -

bent for ammonium removal from municipal wastewater.
Biochar
derived at 450 �C has the highest ammonium removal capacity
attribute to its higher surface area and functional group density,
and the process is controlled by chemisorption (Tang et al.,
2019).
Biochar derived from waste sludge was used as catalysts to
ozonate
refinery wastewater and shows high removal rate of the total
organic carbon. Because the biochar contains functional carbon
groups, Si/O structures, and metallic oxides, it can promote
oxida-
tion through the formation of hydroxyl radicals and mineralized
petroleum contaminants (Chen et al., 2019).
Municipal wastewater can be treated with biochar, produced
from municipal biowaste, at the biofiltration stage. Biochar has
a
high porous surface area that allows it to act as a biofilter in
municipal wastewater treatment. The COD, TSS, TKN and TP
of
wastewater reduce 90%, 89%, 64%, and 78%, respectively, after
being
passed through the biochar biofilter (Manyuchi et al., 2018).
Wastewater from residential units not connected to any
municipal
sewage treatment plant was treated with biochar in on-site
sewage
treatment facility (OSSFs) (Blum et al., 2018). The addition of
bio-
char obviously increases the removal rate of some polar and hy-
drophilic compounds. OSSFs thus can be upgraded with low -
cost
biochar adsorbents.
4.3. Agricultural wastewater treatment

Agricultural contamination is becoming increasingly serious
due to the rapid development of agricultural industry, more and
more pesticides or toxic heavy metals are discharged into farm-
lands (Wei et al., 2018). Many researchers have applied biochar
and
its modified forms to treatment of agricultural wastewater
contamination.
Pentachlorophenol and atrazine are two most common pesti -
cides in agriculture. Rice straw biochar and phosphoric acid
modified rice straw biochars show significantly high adsorption
for
imidacloprid and atrazine from agricultural wastewater (Mandal
and Singh, 2017). Soybean and corn straw biochar both show
high atrazine removals and the adsorption capacities are mainly
Fig. 4. Biochar application in wastewater treatment.
due to the pore volume and pH value of biochar (Zhao et al.,
2013;
Liu et al., 2015). Steam-activated biochar can effectively
remove
sulfamethazine and the removal rate is pH value dependent
(Rajapaksha et al., 2015). Zero valent iron magnetic paper mill
sludge biochar (ZVI-MBC) was used for removal of
pentachloro-
phenol (PCP) from the effluent (Devi and Saroha, 2014). The
ZVI-
MBC can simultaneously adsorb and dechlorinate the PCP in the
effluent and achieve the complete removal of PCP. The removal
of
glyphosate, diuron and carbaryl from agricultural wastewater by
biochar have been also investigated. The adsorption capacity of

biochar to pesticides are related to biochar feedstock, functional
materials, and target contaminants (Wei et al., 2018).
The toxic heavy metals in agricultural wastewater is another
pervasive problem. The common concerned toxic metals include
As, Cr, Cu and Pb (Table 2). The adsorption capacity of Cu2þ
and As5þ
in agricultural wastewater by biochar can reach 69.4 mg/g and
34.1 mg/g, respectively; and the adsorption quantity of Cd2þ
and
Pb2þ are ranged from 0.4 mg/g to 12.3 mg/g, and 36 mg/g to 35
mg/
g, respectively (Higashikawa et al., 2016; Cho et al., 2017;
Zhou
et al., 2017a; Son et al., 2018). For the heavy metals in
agricultural
wastewater, the possible adsorption mechanisms usually involve
electrostatic interactions, surface complexation, ion exchange,
intermolecular interaction, cation-p bonding, and p-p
interactions
(Wei et al., 2018).
The adsorption behavior of biochars for various agricultural
contaminants differs widely (Wei et al., 2018). In general, the
adsorption capacities are closely correlated with nano-material
content, SSA, SFG, and porous structures (Cha et al., 2016;
Braghiroli et al., 2018; Son et al., 2018; Wan et al., 2018; Yao
et al.,
2018). In addition, the adsorption mechanism by biochars are
affected by inner-sphere complexes, p-p interaction,
hydrophobic
effect, precipitation, ion exchange, and so on (Yuan et al., 2011;
Cha
et al., 2016; Lef�evre et al., 2018; Wei et al., 2018; Yao et al.,
2018).

4.4. Stormwater treatment
With the development of urbanization, urban stormwater
runoff has been widely concerned due to its influence on water
quality. Stormwater runoff can significantly contribute to the
degradation of natural water quality and requires treatment
before
discharge, which is mainly due to increased concentrations of
metals, organic matter and biological pollutants (Mohanty et al.,
2014; Gray, 2016; Tian et al., 2016; Ulrich et al., 2017; Ashoori
et al., 2019).
Bioretention and biofiltration are commonly used for storm-
water treatments, but the purification of stormwater
contaminants
by these two systems is not ideal (Gray, 2016; Lau et al., 2016;
Ulrich
et al., 2017). Biochar and its modified forms, as the effective
media,
have been applied to stormwater treatment systems (Fig. 5). A
recent study shows that an aluminum-impregnated biochar can
effectively remove As5þ and other runoff pollutants, such as
Pb2þ,
Zn2þ, Cu2þ, and PO4
3�, in a polluted urban water runoff (Liu et al.,
Fig. 5. Biochar application in stormwater treatment: (a)
Potential functions of biochar at different region of
bioinfiltration system (Mohanty et al., 2018). (b) Schematic
diagram of
the enhanced stormwater contaminants removal by biochar-
amended biofilters (Lu and Chen, 2018).

2019a). A biochar-based filtration medium has been effectively
deployed to remove copper and zinc in stormwater runoff, and
the
remove rate reached more than 85% and 95%, respectively. But
the
biochar filtration media need to be carefully tested and designed
to
meet the requirements of stormwater treatment (Gray, 2016).
Biochars have been integrated with biofilters for removing
bisphenol A (BPA) from stormwater. Wood dust biochar shows
a
high adsorption efficiency and increased capacity of BPA
attribute
to its high SSA and pore volume, which also promotes
phragmites
australis growth, increases E. coli, TOC, TSS, nitrogen and
phos-
phorus removal rates (Ashoori et al., 2019). Biochar amendment
has
improved the removal of contaminant in stormwater biofilters,
particularly the toxic trace organic contaminants (TOrCs) that
have
been poorly removed in conventional systems. Biochar-amended
biofilter columns can maintain more than 99% TOrC removal
rate
compared to the unamended biofilter columns. Meanwhile,
biochar-amended biofilter can increase the removal of TOC,
TN, and
TP greater than 60% (Ulrich et al., 2017).
Poultry litter biochars (PLB) pyrolyzed at 500 �C were applied
to
adsorb ammonium in stormwater treatment systems. There is a
significant positive correlation between NH4

þ sorption and biochar
CEC. The ion competition in stormwater adsorption experiments
suggests that NH4
þ adsorption is dominated by cation exchange
(Tian et al., 2016). Zn-activated sewage sludge-based activated
carbon can remove PO4eP and NO3eN effectively from leachate
made from stormwater. And the removal rates of PO4eP and
NO3eN decrease with increasing pH value (Yue et al., 2018).
Biochar
and zero valent iron (ZVI) amending bioretention cells can
increase
the NO3
- removal performance in stormwater system, which pro-
vides an important prospect for increasing nitrate removal effi -
ciency in bioretention systems (Tian et al., 2019).
Biofilters/bioretention system with biochar can also effectively
remove microorganisms from stormwater (Mohanty et al., 2014;
Lau et al., 2016). Biofilters amended with 5% biochar can retain
up
to 3 orders of magnitude more E. coli, and prevent their
mobiliza-
tion during successive intermittent flows. This indicates that
amending biofilters with biochar can improved the removal of
bacteria from stormwater (Mohanty et al., 2014). H2SO4-
modified
wood biochar can be an effective bioretention filter medium for
E. coli removal from stormwater. It improves E. coli retention
and
reduces remobilization. The results indicate that the transport of
E. coli is governed by the morphology structures and hydropho-
bicity of the biochars (Lau et al., 2016).
In general, biochar has been used as filter media in stormwater

treatment. Various removal capacities of contaminants in storm-
water depend on biochar properties, pollutant characteristics,
and
aqueous chemistry (Mohanty et al., 2018). Biochar is more
feasible
and promising than other materials used in stormwater
treatment,
because it is inexpensive and readily available and has many
beneficial functions in stormwater treatment systems.
5. Conclusions and future perspectives
Biochar is an efficient and low-cost adsorbent, which can be
produced from a variety of biomass materials including
agricultural
crop residues, forestry residues, sewage sludge, manures, solid
organic municipal wastes, and thus has been used in wastewater
treatment. This article reviews the current technologies for
biochar
production with an emphasis on feedstock pre-treatment,
thermal
conversion, and post treatment technologies. It summarizes the
biochar application in wastewater treatment including industrial
wastewater, municipal wastewater, agricultural wastewater and
stormwater. Mechanisms underlying the biochar adsorption of
contaminants are discussed.
The main conclusions of this review are as follows: (1) Biochar
properties are related to the type of feedstock, feedstock pre-
treatment technology, thermal process, and post-treatment of
biochars. The modifications of biochars by increasing the SSA,
re-
action activity or by forming functional groups, become increas -
ingly important as a new and exciting area of engineered
biochar
research and its application for improving environmental
quality.

(2) Largely due to the modifications, engineered biochar as an
adsorbent to remove aqueous contaminant, such as heavy
metals,
organic contaminants, nitrogen and phosphorus is controlled by
various mechanisms, mainly including ion exchange,
adsorption,
surface precipitation, surface complexation etc. (3) The
potential of
biochar for removal of pollutants from industrial wastewater,
municipal sewage, agricultural sewage, and stormwater has been
well demonstrated in laboratory. Its application for onsite appli -
cation requires further investigation. Although number of re-
searches have been done on production and application of
biochar
in wastewater treatment, there are still knowledge gaps that
need
to be filled.
Additional studies are still need to: (1) develop the new low -
cost
and high-efficiency modification technology of biochar, (2)
increase
the practical application of biochar in wastewater treatment,
especially in industrial wastewater and municipal wastewater
treatment, and (3) further improve the adsorption capacity of
biochar on heavy metals, organic contaminants, nitrogen and
phosphorus.
Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have

appeared to influence the work reported in this paper.
Acknowledgements
W.X and X.Z. would like to acknowledge the support of the
Natural Science Foundation of the Jiangsu Higher Education In-
stitutions of China (Grant No. 18KJA610003), Key R & D
Projects of
Xuzhou (Grant No. KC18150, KC16SS091), Xuzhou University
of
Technology (Grant No. XKY2018136), and the Project of
Ministry of
Housing and Urban-Rural Development (Grant No. 2013-K4-
27).
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