https://doi.org/10.37955/cs.v5i4.205
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eISSN: 2600-5743
Systematization of the impact of
wastewater on society and the
application of biochar as an
alternative to the current crisis.
Sistemtización de la afectación en la sociedad de
las aguas residuales y la aplicación de biocarbón
como alternativa a la crisis actual
Juan Carlos González Delgado
Mater in Territorial Planning and Environmental Management. Universidad Nacional de Tumbes,
Tumbes, Peru. juancarlosgondel@gmail.com. https://orcid.org/0000-0001-6282-1478
Alfredo Xavier González Delgado
Civil Engineering. University of Guayaquil, Guayaquil, Ecuador.
fitogonzal@gmail.com. https://orcid.org/0000-0001-7045-9253
Feliciano Javier González Delgado
Mater in Territorial Planning and Environmental Management. Universidad Nacional de Tumbes,
Tumbes, Peru. feliciano@knights.ucf.edu. https://orcid.org/0000-0001-6282-1478
Gerardo Juan Francisco Cruz Cerro
D. in Environmental Sciences, Universidad Nacional de Tumbes, Tumbes, Peru.
gcruz@untumbes.edu.pe. https://orcid.org/0000-0001-6096-0183
Abstract
Biochar is an effective agent for wastewater treatment, soil
remediation and gas retention. This review article reports research on
biochar production, technology and application in wastewater
treatment. There are different types of biochar production
technologies, which emphasize pre-treatment and post-treatment of
the feedstock. Biochar is used as an adsorbent for the removal of heavy
metals, organic pollutants, nitrogen and phosphorus found in
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wastewater. When a biochar is modified in its original particles, it can
achieve a better adsorption capacity, since its surface area increases
and its pore structure is improved. In the first instance, this review
article focuses on the evaluation of biochar as a technology for the
treatment of industrial, municipal and agricultural wastewater. Future
challenges in the search for technologies to design an engineered,
modified biochar and its application in the removal of pathogens from
wastewater would be under discussion. Based on this review article, it
can be concluded that biochar represents a new sustainable
technology, and that it provides an economical solution for wastewater
treatment.
Resumen
El biocarbón es un agente efectivo para el tratamiento de aguas
residuales, remediación de los suelos y para la retención de gases. Este
artículo de revisión, relata investigaciones sobre la producción del
biocarbón, su tecnología y aplicación en el tratamiento de aguas
residuales. Existen diferentes tipos de tecnologías para la producción
del biocarbón, las cuales ponen un énfasis en el pre-tratamiento y pos-
tratamiento de la materia prima. El biocarbón es usado como
adsorbente para la remoción de metales pesados, contaminantes
orgánicos, nitrógeno y fosforo que se encuentra en el agua residual.
Cuando un biocarbón es modificado en sus partículas originales, este
puede lograr una mejor capacidad de adsorción, dado que su área
superficial aumenta y la estructura de sus poros se mejora. En primera
instancia, este artículo de revisión se enfoca en la evaluación del
biocarbón como una tecnología para poder realizar el tratamiento de
las aguas residuales industriales, municipales, de agricultura. Retos
futuros en la búsqueda de tecnologías para poder diseñar un biocarbón
ingenieril, modificado, y su aplicación en la remoción de patógenos del
agua residual estaría en discusión. Basado en este artículo de revisión,
se puede concluir que el biocarbón representa una nueva tecnología
sostenible, y que aporta como una solución económica para el
tratamiento de aguas residuales.
Palabras clave/ Keywords
Wastewater, Production technologies, Organic pollutants, Organic
pollutants
Aguas residuales, Tecnologías de producción, Contaminantes
orgánicos
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Introduction
Due to advances in science and technology, there are many chemicals
that are used to improve the quality of human life as well as certain
consumer products (Wong, Ngadi et al. 2018). However, the abuse
and lack of control of chemical and domestic wastes before being
discharged into the receiving water body cause negative effects on
terrestrial and marine life (Sabeen, Noor et al. 2018). Wastewater
contains different types of pollutants such as heavy metals, organic
toxic compounds, inorganic substances, pathogenic microorganisms
including bacteria, fungi, protozoa, rotifers, algae and viruses (Essa
and El-Gayar, 2018). Residual biomass is a solid waste that are
regularly dumped or fall into decomposition in the open air without
prior treatment causing negative environmental impact (Tomczyk,
Sokołowska et al. 2020). There are conventional anaerobic methods
for wastewater treatment which occupy little space, are economical,
but present limitations in the final effluent results (Gallego-Schmid
and Tarpani 2019). On the other hand, there are sophisticated aerobic
methods for wastewater treatment, where good results are obtained,
but at a high operating cost that end up making a project more
expensive (Yenkie, Burnham et al. 2019). Therefore, it is important to
use sustainable, economical treatment systems such as the adsorption
method through biochar (Blanco-Canqui-2019).
Biochar is a high-carbon and porous product, which is obtained from
waste biomass and decomposed by pyrolysis technique (Deng, Zhang
et al. 2017). There are a number of feedstock in the form of wastes
such as plant residues, futas, sludge, manures, which are used as
biomass (Chen, Xie et al. 2018; Chen, Zhang et al. 2017). Adsorption
is one of the most widely used technologies for wastewater purification
in the removal of organic molecules and heavy metals on an industrial
scale (de Caprariis, De Filippis et al. 2017, Huang, Song et al. 2019).
The current objective of the present review is to present the current
state of the art related to wastewater treatment using biochar for the
treatment of heavy metals and organic pollutants in wastewater.
Materials and Methods
This is a qualitative-documentary research article. The methodology
developed begins with the collection of information on biochar and its
main properties. Then, emphasis is placed on production technologies.
Likewise, it is considered important to know the effects of heavy metals
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and organic pollutants on the environment. With this previous
information, we proceed to the analysis of biochar as an adsorbent
medium for aqueous pollutants as well as in wastewater treatment.
Biochar is a porous carbon material, which is produced during the
thermochemical decomposition of biomass feedstock without the
presence of oxygen. The biomass feedstock can be any organic waste,
which includes crop and forestry residues, including wood chips, algae,
sewage sludge, compost, and municipal solid waste (Colantoni, Evic et
al. 2016, Xiong, Iris et al. 2019). Among the methods for
thermochemical decomposition are pyrolysis, hydrothermal
carbonization, gasification, torrefaction, microwave heating, which
vary in temperature and thermochemical duration (Fang, Zhan et al.
2018). The interest in biochar is transcendental, since it does not lead
to two major benefits: First, biochar production is considered to
effectively utilize the feedstock of a biomass and thus avoid the
emission of greenhouse gases that may deteriorate the environment
(Yang, Igalavithana et al. 2018). Secondly, biochar is an effective,
economical, and environmentally friendly adsorbent (Cha, Park et al.
2016), in which its extensive surface area is highlighted (Wang, Gao et
al. 2017). Biochar can be useful for the adsorption of heavy metals to
obtain purified water (Palansooriya, Yang et al. 2020), and it can also
be used to improve soil fertility and thus crop yield (Yoo, Beiyuan et al.
2018).
Feedstock, thermochemical decomposition methods, temperature and
duration can affect the physical and chemical properties of biochar
(Moreira, Noya et al. 2017). The pre-treatment of feedstock as well as
the final treatment of biochar are considered as important factors that
can affect its properties (Tan, Liu et al. 2016, Yang, Wan et al. 2019).
Pretreatment varies depending on the feedstock and the intended use
of the biochar, including physical (drying, washing, screening),
chemical (the use of chemical agents) and biological (bacterial
treatment among others) methods. Post-treatment basically lies in the
physical (magnetization) and chemical (corrosion treatment, among
others) methods (Usman, Ahmad et al. 2016).
Pretreatment is the first step in the production of biochar, where there
are technologies for physical, chemical and biological areas. Within the
physical method, there is drying, screening, flattening, washing of the
raw material. The lignocellulose plant is usually dried to maintain a
constant weight at a temperature of 105C, it can also be ground and
then cut into pieces (Essandoh, Wolgemuth et al. 2017). Occasionally,
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drying needs to be considered for certain plants that are used as raw
material, because plant materials vary substantially in their moisture
content. Chemical pretreatment is actually based on chemical
reactions in order to change the properties or compositions of the
feedstock materials. One of the known methods is when the feedstock
is immersed in a chemical agent or colloidal suspension, and then
dried prior to biochar production (Cha, Park et al. 2016). After
pretreatment with metal ions in solutions such as FeCl3, AlCl3, MgCl2,
the biomass feedstock can be converted into nanocomposite-based
biochar where nanoparticles is placed on the surface of biochar(Son,
Poo et al. 2018). On the other hand, biomass can also be treated with
nanoparticles or natural colloids including carbon nanotubes,
graphene and clay, which leads to successful production of
nanocomposite-based biochar (Li, Huang et al. 2019). The technology
for biological pretreatment is relatively a new concept, which uses
biological processes in order to upgrade biomass feedstock to produce
biochar (Wang, Gao et al. 2017). Some biomass materials such as
sugar beet, bagasse, sludge and animal excrement are first exposed to
an anaerobic digestion process, and then the waste generated can be
converted into biochar through slow pyrolysis (Wang, Ok et al. 2020).
This pre-treatment step with anaerobic digestion leads to the
production of biochar with large surface area and better adsorption
degree (Wang, Guo et al. 2020). There is also another biological
pretreatment, where a large amount of heavy metals are concentrated
in the biomass in order to produce biochar (Yang, Wan et al. 2019).
Thermal processes used to convert biomass to biochar include
pyrolysis, microwave-assisted pyrolysis, hydrothermal carbonization
and gasification (Wang, Xu et al. 2018).
Pyrolysis is a thermochemical process to decompose biomass in an
anoxic or hypoxic environment (Cha, Park et al. 2016). Pyrolysis
processes are going to depend on temperature, heating rate, and time,
these parameters can affect the physicochemical composition of the
product properties. The biochar yield decreases with increasing
pyrolysis temperature. When the heating rate in turn determines the
speed of pyrolysis and its influence on biochar (Cho, Kwon et al. 2017).
The time factor causes the biomass to complete its decomposition,
while decreasing the yield of biochar production (Mohamed, Kim et al.
2016).
Microwave-assisted pyrolysis is a method to produce bioenergy
products including biochar, bio-oil and biogas (Mutsengerere,
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Chihobo et al. 2019). This method offers shorter processing times,
requires less energy, is more effective in heat transfer (Duran-Jimenez,
Monti et al. 2017).
Hydrothermal carbonization is a method to convert the wet feedstock
into a biochar at a temperature of 120-160C. The wet biomass is
heated and pressurized in the range of 2-10MPa for 5-240 minutes in
a confined system (Zhang, Zhu et al. 2019). This method produces
what is known as a hydrocarbon. As the temperature increases, the
hydrocarbon contains some functional acidic groups on its surface,
which can benefit the adsorption capacity of contaminants (Saha, Saba
et al. 2019).
Gasification is a process that converts biomass into gas fuel through
the use of gaseous agents. The gasification temperature is usually
above 800 C (You, Ok et al. 2017). Biochar obtained from gasification
usually contains high levels of alkaline salts and minerals, which can
precipitate heavy metals and thus act as a possible solution in soil
remediation (Zhang, Zhu et al. 2019). Post-treatment of biochar is
normally used in order to increase surface area, pore volume and
compounds such as nanoparticles (Tan, Liu et al. 2016). Among the
biochar post-treatment methods, there are magnetic procedure,
corrosion and milling (Usman, Ahmad et al. 2016, Wang, Gao et al.
2017).
The magnetic method converts biochar into a material where magnetic
iron oxide including Fe3O4, Fe2O3, or CoFe2O4 particles are charged
inside the biochar (Wang, Zhao et al. 2019). The magnetic biochar
modified by being easily coated by aqueous solutions (Son, Poo et al.
2018).
Ball milling is another method that is simple and efficient, which uses
kinetic energy to move the balls to break the chemical bond, thereby
changing the shape of the particles as nanoparticles are produced (Lyu,
Gao et al. 2017). Once the process of this method is completed, an
improved biochar is obtained in aspects such as surface area, pore
volume, and adsorption capacity (Xiang, Zhang et al. 2020). Bagasse-
based and ball-milled biochar has good ability to remove and adsorb
Ni2+ (Lyu, Gao et al. 2018). This method improves the physical,
chemical and adsorption properties of biochar, which allows it to be
used in different environments.
Corrosive treatment method such as acid, alkali, oxide are frequently
used to modify the surface chemical conditions of biochar. Chemical
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corrosion such as HCI, HNO3, KOH, NaOH, KMnO4, and H2O2 have
been applied for different purposes (Zheng, Yang et al. 2019). Biochar
when chemically modified achieves more micropores, extensive
surface area, as well as better adsorption capacity.
Environmental deterioration is one of the major issues in the world
where there is a great concern about pollution arising from heavy
metals known as inorganic pollutants and also pesticides, antibiotics
which are one of the organic pollutants that reach the receiving body
known as water (Wang and Wang 2019); these pollutants are causing
eutrophication, global warming, and soil deterioration (Zhang, Zhou
et al. 2018). They are also resistant to biodegradation and thus can
reach the food chain by bioaccumulation (Raza, Hussain et al. 2017,
Shakoor, Bibi et al. 2018). Heavy metals have ions that happen to be
toxic and carcinogenic, which affects the human body (Wong, Ngadi et
al. 2018). Anthropogenic activities such as the use of pesticides,
industrial manufacturing, mining works, originate organic pollution
that mix in water with heavy metals and cause soil weathering that
eventually leads to deterioration in water quality (Shakoor, Nawaz et
al. 2017).There are other sources that generate organic pollutants such
as leachate from municipal solid waste (Shehzad, Bashir et al. 2016).
In order to remove heavy metals from water, various methods such as
ion exchange, electrolysis, chemical precipitation have been evaluated
(Rajapaksha, Alam et al. 2018, Yuan, Cheng et al. 2019). However,
adsorption technique is an effective and economical method for the
removal of heavy metals from water (Shakoor, Niazi et al. 2016).
Adsorbents are accessible materials in the environment, this is why
biochar is considered as a good alternative for toxic removal from
water (Moreira, Noya et al. 2017, Wu, Huang et al. 2017).
Soil and water protection and treatment has been considered as one of
the biggest challenges for mankind (Mostafazadeh, Zolfaghari et al.
2016). Heavy metals are categorized according to their toxicity and
chemical behavior in water systems (Shakoor, Niazi et al. 2015, Liu, Xu
et al. 2017) . Heavy metals that a high toxic degree such as Cd, Ni, Cr,
Hg, Cu, Mn, Pb, Zn, are found in wastes coming from wastewater,
mining activities, smelting operations, battery manufacturing, dyes,
pigments, electrical appliances (Godlewska, Schmidt et al. 2017). In
order to minimize water concentrations of toxic heavy metals,
wastewater from domestic discharges, industrial and agricultural
activities must be remediated before being deposited on the land
surface or in the receiving water body (Shakoor, Niazi et al. 2019). The
technique using microbial biomass to treat heavy metals, is expensive,
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consumes considerable energy and produces a toxic sludge. In
addition, the results obtained in its treatment are not effective (Kang,
Oh et al. 2015). Thus, the adsorption method with biochar is
considered an effective, economical and versatile technique for the
removal of heavy metals (Godlewska, Schmidt et al. 2017).
Biochar obtained from plants and animal waste can perfectly adsorb
heavy metals from wastewater (Dai, Fan et al. 2017, Zhou, Chen et al.
2017). Arsenic is a toxic metal that appears in wastewater as well as
natural water. The adsorption capacity of As3+, improves from 5.7
ug/g up to 7.0 ug/g through the impregnation of Zn(NO3)2 on the
biochar surface (Moreira, Noya et al. 2017). When biochar from
sugarcane, rice husk, chicken manure is mixed with sawdust, effective
results in the removal of Cd2+ from water are obtained. The increase
in the pyrolysis process temperature from 350 C to 650C, in turn
determines an increase in Cd2+ removal capacity (Higashikawa, Conz
et al. 2016). Biochar having fresh and dehydrated banana feedstock,
manages to have Pb2+ removal of 359mg/g and 193mg/g respectively.
(Zhou, Chen et al. 2017). Biochar with chicken manure feedstock and
mixed with sawdust at a temperature of 650 C, achieves adsorption
capacity of 11 mg/g Ni2 + (Higashikawa, Conz et al. 2016). Biochar
with seaweed feedstock has plenty of oxygen and is effective for Cu2+
adsorption (Son, Poo et al. 2018).
Organic pollution includes pesticides, herbicides, antibiotics, among
others. These pollutants are toxic and reduce dissolved oxygen in
water, which causes harm to the aquatic ecosystem as well as human
health (Ahmed, Zhou et al. 2016).
Biochar that is made from grass is found to be useful for adsorption of
herbicides in aqueous solutions. In order to obtain better results, it is
considered that the pH of being low in the solution (Essandoh,
Wolgemuth et al. 2017). Iron, zinc impregnated on a sawdust biochar
shows high removal of tetracycline from aqueous solution (Zhou, Chen
et al. 2017).
Biochar can also adsorb nutrients such as nitrogen and phosphorus in
aqueous phase (Xue, Gao et al. 2016). Ammonium, nitrate and
phosphate are the most common forms of nitrogen and phosphorus
reaction in wastewater, leading to eutrophication (Xu, Lin et al. 2018).
The use of pine sawdust as feedstock to make biochar at a temperature
of 300 C shows a high adsorption capacity of NH4+(Yang, Lou et al.
2018). Additionally, biochar produced from wood waste pre-treated
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with magnesium oxide is effective for the removal (Xu, Lin et al. 2018)
of ammonium and phosphate.
Biochar is an important solution to remediate pollution in the
industrial and agricultural sectors (Wang, Gao etal. 2017). Wastewater
is a global problem, involving domestic, industrial, commercial and
agriculture sectors, where biochar shows great prowess for wastewater
treatment.
Industrial water comes from different sources such as mining,
smelting, battery, chemical industry, leather manufacturing, among
others. Industrial wastewater is dominated by heavy metals and
organic pollutants. Biochar mixed with chitosan can be fused in
membranes, which is an effective adsorbent of heavy metals in
industrial water. The rate of biochar and chitosan could affect the
adsorption of copper, cadmium, arsenic and other heavy metals that
are in industrial water (Hussain, Maitra et al. 2017). Biochar made
from bagasse proves to be a good adsorbent of lead that is held as an
effluent in battery manufacturing. The maximum adsorption capacity
obtained is 12.7 mg/g, and the adsorption process is directly related to
an average pH value, contact time and dosage (Bharti and Kumar
2018).
Biochar can be combined with filters or other technologies for
municipal wastewater treatment. The combination of aluminum and
oxyhydroxides with biochar can be applied to recycle and reuse
phosphorus from secondary wastewater treatment (Zheng, Wang et al.
2019). The adsorption mechanism of phosphorus is through
electrostatic attraction. The treated sludge can produce a biochar as an
adsorbent for the ammonium that is present in municipal wastewater.
A temperature of 450 C is the optimum to be able to reach its
maximum ammonium removal capacity, this process is controlled
through chemical adsorption (Tang, Alam et al. 2019). The wastewater
coming from waste, can be treated with biochar, which with its high
pore surface area helps the respective filtration (Chen, Yan et al. 2019).
The development of agriculture has increased, and thus controls on
heavy metals and pesticides must be very robust (Wei, Li et al. 2018).
Biochar made with a raw rice base is effective for adsorption of
atrazine, which is categorized as one of the common pollutants in
agriculture (Mandal, Singh et al. 2017). The adsorption capacity of
biochar on pesticides is going to depend on the feedstock, functional
materials, and contaminants (Wei, Li et al. 2018). The most common
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heavy metals found in agriculture are As, Cu, Cr and Pb. The
adsorption capacity of Cu2+ and As5+ from wastewater in agriculture
is 69.4 mg/g and 34.1 mg/g respectively. The adsorption amount on
Cd2+ and Pb2+ is in the range of 0.4 mg/g to 12.3 mg/g, and 36 mg/g
to 35 mg/g respectively (Higashikawa, Conz et al. 2016, Cho, Kwon et
al. 2017, Zhou, Chen et al. 2017, Son, Poo et al. 2018). In adsorption
mechanism frames electrostatic interactions, ion exchange,
intermolecular interrelationship (Wei, Li et al. 2018). Adsorption
behavior differs widely for various pollutants in agriculture (Wei, Li et
al. 2018). Adsorption capacity is closely related to nano material
content, surface area, pore structure (.
Results
Biochar is a low-cost adsorbent, which can be produced from a variety
of materials including forest residues, treated sludge, municipal
organic waste, crop residues, manures, which have been used for
wastewater treatment. This article reviews the technologies used to
produce biochar and emphasizes technologies for feedstock
pretreatment, thermal conversion, and post-treatment. It also
summarizes that biochar can be applied for the treatment of municipal
wastewater, agricultural wastewater, and industrial wastewater.
Although some research has been conducted on the application of
biochar for wastewater treatment, there are still some gaps in the field.
Research is needed on: (1) developing technologies for biochar to treat
pathogens found in domestic wastewater. (2) increasing the practice
of municipal and industrial wastewater treatment. (3) to improve the
adsorption capacity of heavy metals, organic pollutants, nitrogen and
phosphorus. (4) to analyze which would be the best raw material to
produce a biochar that can remove pathogens from wastewater. (5) to
investigate the method of impregnation of nanoparticles in order to
establish which would be the optimal compound for the treatment of
pathogens.
Conclusions
Among the main conclusions of this review article are: (1) Biochar
properties are related to the type of feedstock, technology for feedstock
pretreatment, thermal process, and biochar post-treatment. The
modification of the biochar in its surface area, the formation of
functional groups, reaction activities, are activities that turn out to be
important in order to create a well-designed biochar, known as an
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engineered carbon. (2) As adjustments are made to biochar
manufacturing, a well-engineered carbon is created that removes
aqueous pollutants such as heavy metals, organics, nitrogen and
phosphorus. (3) Biochar has a potential ability to remove pollutants
from industrial, municipal and agricultural wastewater that has been
demonstrated at the laboratory level, however, the application of
biochar requires further research in the future.
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