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Due to extensive industrialization and increase in population density and urbanized societies, the world is faced with problems related to the management of wastewater. On a daily basis, the effluents generated from domestic and industrial activities constitute a main cause of pollution of receiving water bodies, which is a great burden on water quality management. Some of these pollutants are pathogenic microorganisms, phosphorus and nitrogen, hydrocarbons, heavy metals, endocrine disruptors and organic matter. The majority of water related infections, such as cholera, typhoid fever, diarrheoa and others are caused by the presence of pathogenic microorganisms in water. The diseases caused by bacteria, viruses and protozoa are the most common health hazards associated with untreated waters. The main sources of these microbial contaminants in wastewater are human and animal wastes Also, the presence of these phosphorus and nitrogen in excess amounts could lead to the eutrophication of water sources, which may also create environmental conditions that favour the growth of toxin-producing cyanobacteria. Chronic exposure to some of such toxins produced by these organisms can cause a host of other diseases. In addition, the danger of non-biodegradable and recalcitrant pollutants in water is their ability to persist in natural ecosystems for an extended period and have their ability to accumulate in successive levels of the biological food chain. As a result of these negative effects, a number of processes are in place for the treatment of wastewater effluents before discharge into receiving water bodies. This review was therefore aimed at providing an insight into the major pollutants in wastewater effluents and the various treatment processes.
Research Article
Full Length Research Article
1*Akpor, O. B., 2Otohinoyi, D. A., 2Olaolu, T. D. and 3Aderiye, B. I.
1 Microbiology Unit, Department of Biological Sciences, Landmark University, P.M.B. 1001,
Omu Aran, Kwara State, Nigeria
2Biochemistry Unit, Department of Biological Sciences, Landmark University, P.M.B. 1001,
Omu Aran, Kwara State, Nigeria
3Department of Microbiology, Ekiti State University, Ado Ekiti, Ekiti State, Nigeria
Received Article 08th February 2014; Published Article 31st March 2014
Due to extensive industrialization and increase in population density and urbanized societies, the world is faced with problems
related to the management of wastewater. On a daily basis, the effluents generated from domestic and industrial activities
constitute a main cause of pollution of receiving water bodies, which is a great burden on water quality management. Some of
these pollutants are pathogenic microorganisms, phosphorus and nitrogen, hydrocarbons, heavy metals, endocrine disruptors and
organic matter. The majority of water related infections, such as cholera, typhoid fever, diarrheoa and others are caused by the
presence of pathogenic microorganisms in water. The diseases caused by bacteria, viruses and protozoa are the most common
health hazards associated with untreated waters. The main sources of these microbial contaminants in wastewater are human and
animal wastes Also, the presence of these phosphorus and nitrogen in excess amounts could lead to the eutrophication of water
sources, which may also create environmental conditions that favour the growth of toxin-producing cyanobacteria. Chronic
exposure to some of such toxins produced by these organisms can cause a host of other diseases. In addition, the danger of non-
biodegradable and recalcitrant pollutants in water is their ability to persist in natural ecosystems for an extended period and have
their ability to accumulate in successive levels of the biological food chain. As a result of these negative effects, a number of
processes are in place for the treatment of wastewater effluents before discharge into receiving water bodies. This review was
therefore aimed at providing an insight into the major pollutants in wastewater effluents and the various treatment processes.
Key words: Remediation, Pollution, Wastewater
A variety of substances in untreated or improperly
treated wastewater effluents are known to be toxic to
plants and animals, including humans and pose negative
impacts on the environment. The major contaminants in
wastewater effluents are nutrients (nitrogen and
phosphorus), heavy metals, hydrocarbons, organic
matter, microbes and endocrine disruptors are the major
contaminants in wastewater that leads to adverse effects
to both human health and the environment (Davies,
2005). In wastewater, the organic matter and other
forms of contaminants makes it a breeding ground for
most pathogenic organisms, such as bacteria, fungi,
protozoa and viruses. The presence of these organisms
in wastewater is usually accountable for a host of water-
related diseases; hence the need for treatment before
discharging into receiving water bodies (Jegatheesan et
al., 2008). The presence of nitrogenous compounds in
wastewater effluents at concentrations above the
required limit is known to be detrimental to receiving
water bodies.
*Corresponding author: Akpor, O. B.,
Microbiology Unit, Department of Biological Sciences,
Landmark University, P.M.B. 1001, Omu Aran, Kwara State,
Ammonia, which is usually present in wastewater in the
main form of nitrogen, is known to be toxic to aquatic
organisms when in excess concentration. The ingestion
of nitrate containing water could lead to
methemoglobinemia, also called blue babies syndrome
in infants and other susceptible individuals. In addition,
a number of endocrine disruptors, such as 17β-estradiol,
estrone and testosterone have been reported to cause
reproductive organ failure in humans and animals.
Besides, heavy metals, such as zinc and mercury are
reported to lead to protein conformation and causing
cancer (EPA, 2007; Samir and Ibrahim, 2008).In
addition, a variety of pathogenic microorganisms are
known to possess the ability to thrive in wastewater.
When such microbial- polluted wastewater into water
bodies, they pose serious threat to the health of humans
and animals (Surface Water Quality Bureau, 2008).
One of the major contributors to various cases of water
pollution is wastewater effluents. Some of these
problems include metal poisoning, irritations and
pathogenic infections of humans and animals. Another
major problem caused by untreated wastewater effluent
is eutrophication, which excessive nutrient proliferation
could lead to the stimulation of algae growth which can
lead to increased cost in water purification. Other
International Journal of Environmental Research and Earth Science
Vol. 3, No. 3, pp. 050-059, March, 2014
impacts of eutrophication are dissolved oxygen
depletion, physical changes to receiving water bodies,
bioaccumulation and biomagnification of contaminants,
toxic substance release and nutrient enrichment effects
(Akpor and Muchie, 2011). The awareness of most
society towards the prevention of water borne diseases
has brought more attention to the treatment of
wastewater. This is because wastewater treatment is an
important link in the prevention and transmission of
water borne diseases (Davies, 2005). To avoid the
negative impacts of untreated and improperly treated
wastewater effluents, there is the need for effective and
efficient treatment discharge into receiving water
bodies. Wastewater treatment entails the ability to
achieve improvements in the quality of wastewater.
Several methods have been employed in the removal of
pollutants from wastewater. These remediation
processes include physical remediation, chemical
remediation, phytoremediation and microbial
remediation (Rubalcaba, 2007; Prescott, 2011).
Although, these treatment processes play vital roles in
wastewater remediation, they have their flaws, which
necessitate in some cases the application of a
combination of processes for remediation. This study
was therefore aimed at reviewing the major pollutants
in wastewater and their environmental and health
impacts. Also reviewed were the various treatment
processes for the treatment of wastewater.
Impacts of pollutants in wastewater effluents
One of the major threats to aquatic organisms is the
presence of pollutants in wastewater effluents. The
major contaminants in wastewater are nutrients
(nitrogen and phosphorus), hydrocarbons, heavy metals
and microbes.
Effects of nitrogen and phosphorus
The two major eutrophic nutrients in wastewater
effluents are nitrogen and phosphorus. It is indicated
that over 47% and 53% of streams have medium to high
level of phosphorus and nitrogen, respectively
(Watershed Academy Webcast, 2011). In untreated
wastewater, nitrogen is primarily in the form of
ammonia and organic nitrogen, while phosphorus may
exist as soluble orthophosphate ion, organically-bound
phosphate, or other phosphorus/oxygen forms
(Akporand Muchie, 2010). The presence of algal
blooms in water has been indicated to lead to non-linear
decrease in water clarity level. The recognizable effect
of eutrophication is the occurrence of algal blooms,
which in turns leads to the depletion of dissolved
oxygen concentration in receiving water bodies. A low
DO in water bodies is known to the death of aquatic
life, muddy water and drastic reduction of desirable
flora and fauna. In addition, toxic algae, such as
Microsystis, which is known to strongly inhibit large
cladoceransmay also be noticeable in algae blooms
(Jack et al., 2002). Another impact of eutrophication is
an increase in the amount of chlorine required for the
disinfection of water bodies, which could increase the
increasing the risk of cancer (Fisher et al., 2004; Wang
et al., 2007). Also, excessive nutrient proliferation in
wastewater effluents may lead to the stimulation of
harmful microbes like Pfisteria (Hasselgien et al.,
2008). The presence of Pfisteria in a water body is
identified to cause eye and respiratory irritation,
headache, and gastrointestinal complaints (Morris, Jr,
2001; Watershed Academy Webcast, 2011).
Additionally, the presence of remarkably high nitrate
content above a maximum contaminant level of 1o
mg/L in water is known to lead to methemoglobinemia
(blue-baby disease) in infants and other susceptible
individuals. During methemoglobinemia in infants,
nitrate is reduced to nitrite in the digestive system,
which attacks the hemoglobin. Some reports have
suggested that the presence of nitrite could cause
chemical or enzymatic reaction with amine, which to
formsnitrosoamines, which are carinogens (EPA, 2002;
WHO, 2006).
Effects of hydrocarbon
Although petroleum hydrocarbons are toxic to all forms
of life, environmental contamination duetocrude oil is
relatively common because of its widespread use and
associated disposal operations and accidental spills (Lan
et al., 2009; Abha and Singh, 2012).The presence of
hydrocarbon pollutants in wastewater effluents is
known to lead to several health and environmental
impacts, which are of great concern. Although
petroleumis an important energy resources and raw
materials of chemical industry, when in contact with
receiving water bodies could result in serious problems,
such as threat to fishery, marine habitats of wildlife,
human health, and the destruction of ecological balance
which may take years or even decades to recover
(Zhang et al., 2011).
Since petroleum consists of highly toxic chemicals, its
presence in water can cause significant damage to body
organs (liver and kidney) and systems, such as the
nervous, respiratory, circulatory, immune, reproductive,
sensory and endocrine systems (Costello, 1979;
Obidike et al., 2007). Also, a host of other diseases and
disorders could be caused to humans and animals by the
presence hydrocarbons in water. The degeneration and
necrosis of interstitial cell and exudation of the
interstices in the testes of rats have been reported when
exposed to petroleum. It has also been indicated that the
exposure of rats to crude oil could induce reproductive
cytotoxicity that is confined to the differentiating
spermatogonia compartment (Obidike et al., 2007).
Knox and Gilman (1997) have also stated that
petroleum derivatives are associated with associated
childhood cancers. The observation of aspiration
pneumonia in sheep following exposure to gas
condensate has also been indicated in the past (Adler et
al., 1992).
A number of reports of petroleum hydrocarbon
exposure in humans, primates, ruminants, horses,
wildlife and dogs have been reported in literatures
(Bamberger and Oswald, 2010). Although in a report by
Waldner and co-workers (1998), no association
051 International Journal of Environmental Research and Earth Science, Vo. 3, No. 3, pp. 050-059, March, 2014
between the productivity of cattle and exposure to sour
gas pipeline leak was observed, a longer term study by
the same authors in cattle reported an association
between sour-gas flaring and increased risk of still
birth, as well as increase drisk of calf mortality. Studies
on habitat selections have observed that animals, such
as mule deer have a tendency of moving away from
areas of gas development. One such studies, indicated a
drop in deer population dropped by45%within a year
and decrease in their survival rates in area of gas
development (Sawyer et al., 2006).
Effects of Heavy metals
The most anthropogenic sources of heavy metals found
in wastewater are industrial, petroleum contamination
and sewage disposal (Santos et al., 2005). Although,
some heavy metals, such as zinc, copper and iron are
described to be essential in aquatic environment
because of their roles in several biochemical processes,
when present in high concentrations, they become
detrimental (Samir and Ibrahim, 2008). The
incorporation of heavy metals into food chains could
lead to their in aquatic organisms to a level that affects
their physiological state. Because most heavy metals are
known to be toxic and carcinogenic, they represent
serious threat to human health and the fauna and flora
of receiving water bodies. A number of heavy metals,
such as zinc, copper, nickel and arsenic are reportedly
are known for their toxicity, even at very low
concentrations (Dhokpande and Kaware, 2013).
It is indicated that heavy metals have a propensity of
binding with proteins, thereby changing their
conformation and inactivating them, which typically
results to health complications (Prescott, 2011). Some
studies have indicated zinc poisoning to be a cause of
stomach cramps, skin irritations, vomiting, nausea,
anaemia, damaged pancreas, disturbed protein
metabolism, arteriosclerosis, respiratory disorders, and
metal fever (Galadima, 2012). In addition, the presence
of zinc has been shown pose great danger to infants and
unborn, especially when large concentrations of it is
absorbed by their mothers during pregnancy
(Aghahowa, 2012). In addition, the presence of zinc in
wastewater is indicated to cause an increase in water
acidity, which could affect the cultivation and yield of
crops (Oyewale, 2000; Oladele et al., 2012).
Furthermore, apart from been known as one of the
causes of kidney damage, the presence of lead in
humans and animals is revealed to have effects on
haemoglobin synthesis, which could lead to anaemia.
Although some of the effects of lead are reported to be
irreversible, chronic exposure may lead to sustained
decrease in kidney function, which could lead to
possible renal failure. It is hypothesized that one of the
most important factors that influence the aquatic
toxicity of lead is its free ionic concentration and
availability to organisms; hence it is unlikely to affect
aquatic plants at levels that might be found in the
general environment (Baysal et al., 2013). In the case of
mercury, its organic forms are known to be more toxic
to aquatic organisms than the inorganic forms.
Although aquatic plants are affected by mercury in
water at concentrations approaching 1 mg/l for
inorganic mercury, the effect is greater even at much
lower concentrations of organic mercury (Kenawy,
2010). For cadmium, its acute toxicity to aquatic
organisms is variable, even between closely related
species. This variation is said to be related to its free
ionic concentration of the metal. Cadmium is reported
to interact with calcium metabolism in animals. In fish,
cadmium is reported to cause a lack of calcium
(hypocalcaemia). This is probably by the inhibition of
calcium uptake from the water, with the long-time
effects of exposure to cadmium being larval mortality
and temporary reduction in growth (Jarup, 2003).
In addition, although, chromium is necessary for the
metabolism of insulin and essential for animals, at high
concentrations it is known to be toxic to organisms. In
animals, chromium is known to cause skin irritation and
cancer. It is generally indicated that hexavalent
chromium, is more toxic to organisms in the
environment than the trivalent chromium with its ability
to cause irritation and cancer. Chromiumis also
indicated to make fishes to be more susceptible to
infection. A high concentration of chromium is also
known to cause damage in the tissues of several
invertebrates, such as snails and worms (Baysal et al.,
Effects of Microbes
It is indicated that the majority of waterborne
microorganisms that cause human disease are from
fecal wastes that are released by humans or animals that
contain these diseases (Kris, 2007). The most common
health hazards that are associated with the consumption
of untreated drinking and recreational waters are caused
by bacteria, viruses and protozoa. Untreated water is
vehicle for several water-related diseases, such as
typhoid fever, cholera, shigellosis, salmonellosis,
campylobacteriosis, giardiasis, cryptosporosis and
Hepatitis A. The majority of pathogenic
microorganisms have the capacity to cause acute and
chronic diseases with short to long-term effects, such as
degenerative heart diseases and stomach ulcers with
intensity. Viruses are among the most important and
potentially most hazardous pollutants in wastewater.
They are more resistant to treatment, more infectious,
more difficult to detect and require smaller doses to
cause infections (Okoh et al., 2007). For bacteria, they
are the most common microbial pollutants in
wastewater. They cause a wide range of infections, such
as diarrhea, dysentery, skin and tissue infections. The
major pathogenic protozoans associated with
wastewater are Giardia and Cryptosporidium. They are
more prevalent in wastewater than in any other
environmental source (Akpor and Muchie, 2011).
Effects of organic waste and endocrine disruptors
Organic wastes consist of carbon, hydrogen, oxygen,
nitrogen and other elements; and could either be
carbohydrate, protein or fat which are biodegradables.
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The majority of organic materials in wastewater
originate from plants, animals or synthetic sources.
They enter wastewater in through human wastes, paper
products, detergents, cosmetics, foods, and from
agricultural, commercial, and industrial sources. The
presence of organic matter in water lead to imposes an
oxygen demand on the microorganisms that help in the
degradation, hence depleting the level of dissolved
oxygen that is available for other aquatic organisms. A
decrease in dissolved oxygen below a certain point will
have adverse effect on the physiology and metabolism
of aquatic organisms, which lead to their death. The
death of aquatic organisms, such as fish will deplete the
recreational value of such waters due to the release of
odours and the overall degradation of water quality
(Davies, 2005)
Endocrine disruptors are said to be chemicals or natural
by-products in the environment that mimic hormones in
the body. They are also known as exogenous agents that
interfere with the synthesis, secretion, transport,
binding, action, or elimination of natural hormones in
the body that are responsible for the maintenance of
homeostasis, reproduction, development and behavior
(EPA, 2012).They can be divided into two general
classes: endocrine hormones and endocrine mimics,
which include xenobiotics, such as xenoestrogens,
xenoandrogens and phytoestrogens.
The presence of endocrine disruptors in receiving water
bodies is indicated to threaten reproductive success and
long-term survival of sensitive aquatic populations.
Examples of reproductive hormones that are
commonly detected in effluent-affected ecosystems
are 17β-estradiol, estrone, testosterone, and the
synthetic birth control compound, 17α-ethinylestradiol.
There are also a number of other endocrine disrupting
chemicals that share sufficient structural similarity
with the endocrine hormones to interact with animal
endocrine receptors sites and trigger negative effects.
This group, referred to as endocrine mimics generally
exhibit less endocrine reactivity, but are essentially
ubiquitous in wastewater. The endocrine mimics are
often reported at concentrations of 3-5 orders of
magnitude higher than the endocrine hormones
(Bradley and Kolpin, 2013).
Treatment processes for wastewater effluents
The proper treatment of wastewater effluents before
discharging into receiving water bodies is vital to
protect the environment and safeguard public health.
The processes for wastewater treatment are grouped
into the following categories: phytoremediation,
chemical remediation, physical remediation and
microbial remediation processes.
Phytoremediation processes
Phytoremediation is a treatment process that involves
the use of plants. During phytoremediation,
contaminants are either removed or transformed into
harmless and sometimes valuable forms (Leather
international, 2013). The process uses various plants to
degrade, extract, contain, or immobilize contaminants
from soil and water. Although phytoremediation has
received attention over the years and is usually
classified as a clean and cheap method, it has the
following limitations:
For the remediation to take place, the process
involves contact between the root of plant and the
contaminant, hence the plant must be able to extend
its roots to the contaminant or the contaminated
media must be moved into the range of the plant’s
reach (EPA, 2002).
The process is dependent on the growth of a plant;
this makes it to take longer time for remediation to
take place. Because of the length of time that may
be involved, for contaminants that pose acute risks
for human and other ecological receptors, the
process may not be the remediation technique of
choice (EPA, 2002).
Although the process easily be used in places where
the concentration of contaminants at the root zone is
low or at medium level, at high concentrations of
contaminants, there could be inhibition of growth or
death of the plant, hence limiting its effectiveness in
environments where contaminant concentration is
high. (EPA, 2002)
In the application of phytoremediation in the treatment
of wastewater can be classified based on the
contaminant fate and the mechanisms involved
Although a variety of phytoremediation processes
exists, the ones are applicable in wastewater treatment
are phytodegradation, phytoextraction and
phytoimmobilisation (Todd and Josephson, 1996; EPA,
Phytodegradation of wastewater pollutants
Phytodegradation, which is also referred to as phyto
transformation entails the destruction of a contaminant
through uptake by plants as nutrient. In some cases,
certain plants that are used have the ability of taking up
toxic compounds, detoxifying and metabolizing them
as nutrients (Kidney, 1997). A typical application of
phytodegradation in wastewater is the use of microalgae
to reduce the nutrient content in wastewater. Microalgae
have the ability to assimilate nutrients into their cells
(Mamun et al., 2012). The wastewater pollutants that
have reportedly been phytodegraded include chlorinated
solvents, herbicides, and insecticides and inorganic
nutrients. For phytodegradation to occur, the plant used
must have the ability to take up the compound and
metabolise it. In the case of a toxic compound, the
detoxification is a three-phase (bioactivation,
conjugation and compartmentalization) process that is
characterised by the participation of different classes of
enzymes, and by the properties and allocation of their
reaction products (Newman et al., 1998). During
bioactivation, the plant relies on the formation of
reactive groups in the pollutant molecule. The aim of
this phase is for the activation of the compound to the
actual detoxification, which takes place in the next step.
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This phase mainly involves enzymes, such as flavin and
polysubstratemonooxygenase, which exhibit hydrolytic
and redox activity (Zakrzewski, 2000; Walker et al.,
2002). In conjugation, the activated pollutant binds to a
sugar molecules, amino acids or SH-groups of
glutathione to produce less toxic substances that have
polar structures. Depending on whether it is a sugar,
amino acid or glutathione, this reaction is catalysed by
UDP-dependent glucosyl transferase, N-acetyl
transferases and the family of glutathione transferases.
During the last phase, which is known as
compartmentalization, the inactivated pollutant is
removed by conjugation from the cytosol to the vacuole
or apoplast occurs that allows safe deposition of derived
toxins (Spaczyński, 2012).
Phytoextraction of wastewater pollutants
Phytoextraction, which is also referred to as
phytomininginvolves the planting of a crop species that
possess the ability to accumulate contaminants
(hyperaccumulator plants) in the shoots and leaves of
the plants, after which they are harvested and the
pollutant is removed from the site. It is reported that
plants that possess hyper accumulation ability do not
only accumulate high levels of essential micronutrients,
but can also absorb significant amounts of nonessential
metals, such as cadmium (EPA, 2002). For
phytoextraction to occur, the pollutant must be able to
be transported from the root to the shoot of the plant,
through the process of translocation, which is primarily
controlled by two the root pressure and leaf
transpiration. It is only after translocation that the
pollutant can be reabsorbed from the sap into leaf cells.
One of the most efficient metal hyper accumulator is
Thlaspicaerulescens (alpine pennycress). It is indicated
that while most plants show toxicity symptoms at metal
accumulation of about 100 ppm, hyper accumulator
plants, such as T. caerulescens can accumulate up to
26,000 ppm without showing any injury (Brown et al.,
1995). Because hyper accumulator plants have higher
requirement for metals, than non-accumulator species,
they have be shown to colonize metal-rich
environments ((Hajar, 1987; Baker and Proctor,
1990).Phytoextraction is said to be advantageous
because of its environmental friendliness. Just as in all
phytoremediation processes, because it is controlled by
plants, it takes more time to achieve remediation than
other traditional clean-up methods.
Phytoimmobilization of wastewater pollutants
Phytoimmobilization, also known as phytostabilisation
involves the binding of pollutants in water and
rendering them non-bioavailable or immobilized by
removing the means of transport. This can take the
form of binding the pollutant a humic molecule,
physical sequestration of metals as occurs in some
wetlands, or by root accumulation in non-harvestable
plants (EPA, 2002; USDA, 2002). The transport of the
pollutant can be reduced through absorption and
accumulation by the plant roots, adsorption onto roots,
precipitation, complexation, or metal valence reduction
or by binding into humic matter through the process of
humification (EPA, 1997). In some cases,
phytoimmobilisation may occur in water into which
plant roots release plant exudates, like phosphate, so as
to generate insoluble precipitated forms of
contaminants, such as lead phosphate, thus removing
the contaminant from solution without having it taken
up into the plant (Dushenkov et al., 1995).
Chemical remediation processes
Chemical remediation is the use of chemical
compounds in the treatment of pollutants. It include
selectron-beam irradiation, chemical extraction,
radicolloid treatment, sorption to organo-oxide and wet
air oxidation (Hamby, 2000; Rubalcaba, 2007).
Electron-beam irradiation
An electron-beam irradiation operates on the principle
that when water is irradiated with electron beams it has
the ability to produce free radicals (H+ and OH-). The
free radicals can react with organic contaminants, such
as trichloroethylene and carbon tetrachloride, which
could result in the release of harmless chemical entities,
such as CO2, H2O, salts, and other compounds.
(Rosocha, 1994). The use of electron beam technology
has been indicated to be efficient in the removal of up
to 99.99% pollutants in wastewater, when in full-scale
operation (Nyer, 1992). Although it is indicated that the
use of high dose rates of electrons are less efficient than
when low dose rates are used, reports have also shown
that high energy electron-beam irradiation is an
effective and economical means for the removal of
hazardous organic pollutants in water (Hamby, 2000).
Chemical extraction
Chemical extraction, which is also known as solvent
extraction, is the use of chemical compounds for the
removal of pollutants. This technique is mostly
employed in the removal of heavy metals. The
technique involves the use of organic solutions that
contain extractants to transport selected metals from
one aqueous solution to another. When this happens, the
metals are separated, purified and recovered (Zhang,
2010). Most common extractants are organic
compounds with molecular mass 200–450. They are
almost insoluble in water (5–50 ppm) and selectively
extract metals from aqueous solutions. The efficiency of
removal is dependent on the extraction conditions, such
as the type of extractant, anions present in the aqueous
phase, and pH. Chemical extraction is commonly used
in combination with other technologies, such as
solidification/stabilization, precipitation and electro
winning. In water treatment, the process involves the
mixing of wastewater with organic solvent that contains
a reagent. The metal of interest present in the
wastewater reacts with the reagent to form a chemical
compound, which is more soluble in the organic than in
the aqueous solution. As a consequence, the substance
of interest is transferred to the organic solution
(National Technical University of Athens, 2013).
054 International Journal of Environmental Research and Earth Science, Vo. 3, No. 3, pp. 050-059, March, 2014
Radiocolloid treatment
Radiocolloids are known as suspensions of tiny
radioactive particles, which are located in media, such
as water. The inorganic colloids are usually
characterized by concentration, mineralogy, and
radioactivity levels. There are certain radiocollloids,
such as colloids of plutonium and americium whose
presence in wastewater may lead to high level of
radiation, which may be carcinogenic when in contact
with human (Nuttall and Kale, 1994).
One process for the removal of radicolloids in water is
polyelectrolyte capture. A polyelectrolyte capture
process involves the addition of a polyelectrolytic
solution to a medium containing the radiocolloid. The
aim of adding the electrolyte solution is to attach to the
negatively charged radicolloids, since they are
positively charged (Nuttall et al., 1992). The
polyelectrolyte polymer treatment of colloids is
indicated to be successful in laboratory column tests
(Hamby, 2000).
Removal by sorption to organo-oxides
An organo-oxide is a synthetic sorbents that provides an
organic phase with the ability able to bind a non-ionic
organic substance. Organo-oxide synthetic sorbents are
formed when an anionic surfactant adsorbs onto oxides
in an acidic environment. This occurs only when the
oxide is positively charged. The positive charge is only
attained at a pH that is less than the zero point of
charge, i.e. the pH at which solid surface charges from
all sources are zero (Hamby, 2000). According to Park
and Jaffe (1994), the sorption of an anionic surfactant
onto an oxide is inversely proportional to pH. With
respect to the quantity of water treated, organo-oxide
sorbents are said to be less efficient than other
technologies. Despite their inefficiencies, when
compared to other technologies, they have the
advantages of in-situ generation, selective removal of
specific contaminants through the use of a specific
surfactant which can sorb a particular pollutant and the
solute that is removed from the water can be recovered
if so desired (Hamby, 2000).
Wet air oxidation
Wet air oxidation or hydrothermal treatment chemical
treatment process that entails the oxidation of
suspended or dissolved materials in water with
dissolved oxygen at elevated temperatures (Clayton,
2013). The oxidation reaction is said to take place in the
aqueous environment where the water is an integral part
of the reaction. The water provides the medium for the
dissolved oxygen to react with the organic compounds,
which can also react in part with the organic compound.
During wet oxidation, free radicals are formed with
oxygen, which attack the organic compounds and
results in the formation of organic radicals. A number
of catalysts, such as homogeneous Cu2+and Fe3+with
their heterogeneous counterparts, or precious metal
catalysts are known to be effective in wet air oxidation
reaction (Teletzke, 1966). A major characteristic of wet
oxidation is the formation of carboxylic acids, in
addition to carbon dioxide and water. The carboxylic
acid yield is dependent on the design of the wet air
oxidation system (Sadana, 1979).
Physical remediation processes
In modern wastewater treatment systems, physical
remediation techniques are always used in combination
with other treatment processes. Some physical
remediation processes are screening, sedimentation,
comminution, flow equalization and precipitation
(Hamby, 2000).
Screening and Flow Equalization
Screening is the first operation in any wastewater
treatment plant. During screening, large non-
biodegradable and floating solids that frequently enter a
wastewater treatment facility, such as rags, papers,
plastics, tins, containers and wood are removed. The
removal of these materials helps in protecting the
treatment plant and equipment from any possible
damage, unnecessary wear and tear, pipe blockages and
the accumulation of unwanted material, which could
interfere with the required wastewater treatment
processes. Generally, screening is classified as coarse or
fine. The coarse screens are typically used as primary
protection devices and usually have openings of 10mm
or larger. The fine screens are used for the removal of
materials that may cause operational and maintenance
problems in the treatment processes, particularly in
systems that lack primary treatment. The fine screens
have opening sizes of about 3 to 10 mm (GAH Global,
2013; Lenntech, 2013).
In wastewater treatment systems, flow equalization is
the process of controlling hydraulic velocity or flow
rate. In a short term, the process prevents high volumes
of incoming flow (surges) from forcing solids and
organic material out of the treatment process. It also
controls the flow through each stage of the treatment
system; thus allowing adequate time for the physical,
biological and chemical processes to take place
(Norweco, 2013). Typically, flow equalizations are
used for the minimization of the variation of water and
wastewater flow rates and composition. This is because
the existence of wide variations in flow composition
over time could degrade the process performance and
efficiency of a treatment system (Goel, 2013).
Comminution and Sedimentation
A typical comminutor, which serves as both a cutter and
a screen, is essentially aimed for the grinding and
crushing of large solids of wastewater pollutants, such
as organic matter. When in contatct with the
comminutor, these large solids, such as rags and debris
are shred into small particles. Communications do not
remove the particles but only cuts them into smaller
particles when the wastewater passes through (Herbert,
1998). Sedimentation or settling is the separation of
suspended particles that are heavier than water. The
process is based on the gravity force from the
055 International Journal of Environmental Research and Earth Science, Vo. 3, No. 3, pp. 050-059, March, 2014
differences in density between particles and the fluid.
During sedimentation, the settled solids are removed as
sludge while the floating solids are removed as scum.
The efficiency or performance of a sedimentation
process is controlled by the detention time, temperature,
tank design and condition of the equipment (Carlsson,
2001). In wastewater treatment, the most common form
of sedimentation follows the coagulation and
flocculation and precedes filtration. This type of
sedimentation requires chemical addition in the
coagulation or flocculation step thereby removing floc
from the water. The sedimentation at this stage of a
typical wastewater treatment system is said to remove
up to 90% of the suspended particles from the water,
including bacteria (Mountain Empire Community
College, 2013).
Precipitation is the most common method for the
removal of dissolved pollutants from wastewater.
During precipitation, a reagent is added to the mixture
in order to convert the dissolved metals into solid
particle form. The presence of the reagent triggers a
chemical reaction that causes the dissolved pollutants to
form solid particles. The solid particles can then be
removed by filtration. The efficiency of precipitation is
dependent on the nature and concentration of pollutant
to be removed and the kind of reagent used. In some
case precipitation may involve chemical coagulation
process. During chemical coagulation, there is the
destabilization of wastewater particles so that they
aggregate during chemical flocculation. The process
destabilizes these particles by introducing positively
charged coagulants that then reduce the negative
particles’ charge (Edwards, 1995; Thomasnet, 2013).
Microbial remediation processes
Microbial remediation entails the use of microorganism
(bacteria, fungi, protozoa, rotifers and algae) for the
breakdown of organic compounds and or pollutants
(Wilson and Clarke, 1994). The process could be
aspecific or a non-specific one. In a specific process, a
microbe is used to target a single site of a molecule
while in a non-specific process; a chain of microbial
events is involved in the degradation process (Hamby,
2000; Jegatheesan, 2008; Davies, 2005).
All microbial remediation processes are dependent on
environmental conditions, such as pH, molecular
oxygen and nutrient conditions. As an example, the
degradation of petroleum products requires the presence
of oxygen while the degradation of halogenated
compounds requires anaerobic conditions in order to
remove the halogens. In addition, the bioremediation of
a particular waste may require a series of different
environmental conditions for a variety of
microorganisms to cause a chute of reactions (Bellandi,
The primary microorganisms for biodegradation are the
bacteria. They are known to have the ability to degrade
a broad range of wastes. Based on oxygen requirement,
the major groups of bacteria that are utilized in most
treatment plants are the aerobes. These bacteria make
use of the dissolved oxygen in the water. They use the
free oxygen in the water to degrade the pollutants in the
incoming wastewater into energy they can use for
growth and reproduction. Although, oxygen in a
conventional wastewater treatment system is usually
added mechanically to the wastewater through the use
of aerators in the aerated section of the treatment plant,
with a normal influent load of pollutants, the dissolved
oxygen content in the aerated section of most plants is
reported to be 3- 5 mg/l (Cabridenc, 1985;Tong, 2013).
Many species of bacteria are reported to play a part in
the removal of a number of pollutants, such as nitrate
and phosphate, heavy metals and hydrocarbon
pollutants from wastewater treatment systems. Some of
these species Escherichia coli, Acienetobacter,
Aerobacter, Citrobacter, Proteus, Erwinia,
Empedobacter, Achromobacter, Chromobacterium,
Pseudomonas, Acinetobacter, Flavobacterium,
Santhomonas, Streptococcus, Staphylococcus
Micrococcus, Bacillus, Bacterium, Brevibacterium and
Corynebacterium (Cabridenc, 1985; Momba and
Cloete, 1996; Akpor et al., 2013).
Although little is known about fungal adaptations and
processes in degrading anthropogenic substances, they
possess the ability to remediate wastewater. They are
said able to excrete enzymes that breakdown some
exotic compounds, recalcitrant compounds and large
organic molecules that are not readily degraded by most
bacteria. They are also recognized for their superior
aptitudes to produce a large variety of extracellular
proteins, organic acids and other metabolites and for
their capacities to adapt to severe environmental
constraints (Coulibaly, 2003).
Essentially, it is reported that fungi remove metals by
adsorption, chemisorptions (ion exchange),
complexation, coordination, chelation, physical
adsorption and micro precipitation. They are indicated
to have advantages over bacteria in biological
wastewater treatment by also producing valuable
byproducts, such as amylase, chitin, chitosan,
glucosamine, antimicrobials and lactic acids. Also, they
fungi contain a group of extracellular enzymes that
facilitate the biodegradation of recalcitrant compounds,
such as phenolic compounds, dyes, and polyaromatic
hydrocarbons (van-Leeuwen, 2013).
Aspergillu sniger, Aspergillu sflavus, Aspergillu
sversicolor, Aspergillu soryzae, Absidiafusca and
Fusariumverticilliodes, Penicilliumor Cephalosporium
and several other fungi species have been reported in
the removal of eutrophication agents and
bioremediation of metal contaminated waste streams.
There is also a growing interest in the use of fungi for
the removal of nitrogen, phosphorus and metals from
commercial and municipal waste (Price et al., 2001;
Vymazal, 2007; Akpor et al., 2013).
056 International Journal of Environmental Research and Earth Science, Vo. 3, No. 3, pp. 050-059, March, 2014
Protozoa and Rotifers
In wastewater systems, protozoa are associated with the
ingestion of organic matter and other microbes. The
ciliated protozoa are the major groups that are involved
in wastewater treatment because of their ability to grow
on water surfaces, feeding on decayed vegetation and
microbes (Joanne et al., 2011). Protozoa play important
ecological roles in the self-purification and matter
cycling of natural ecosystems. It is generally accepted
that their feeding on bacteria improve the treatment,
thereby resulting in low organic load in treated wastes
(Pauli et al., 2001). They are also reported to possess
the ability to thrive in harsh environment, with
temperature varying between 0°C and 50°C. It is
however argued that their rates of population growth
increase when food is not constrained and temperature
is increased (Mountain Empire Community College,
2012). It is indicated that the excretions by protozoa
contain many mineral nutrients, such as nitrogen and
phosphorus, which help to recycle mineral nutrients in
the activated sludge process. The presence of protozoa
in the aeration tanks of an activated sludge system is
said to be the hallmark of a well operated and efficient
system. The main difficulty in their use in the treatment
of wastewater is their segmentation since the majority
of them are in contact with the sludge (Motta et al.,
2001). A number of protozoa groups (ciliates and
flagellates) have been implicated in the removal and
mineralization of pollutants in wastewater treatment
systems (Akpor et al 2008; Papadimitriou et al., 2010)
The rotifers are microscopic aquatic animals of the
phylum Rotifera, which can be found in many
freshwater environments and in moist soil. They inhabit
the thin films of water that are formed around soil
particles and are known to thrive mostly in still water
environments, such as lake bottoms, as well as flowing
water environments, such as rivers or streams (Orstan,
1999). In wastewater treatment systems, they are
indicated to be beneficial in stabilizing organic wastes,
stimulating microfloral activity, decomposition,
enhancing oxygen penetration and recycling mineral
nutrients. The presence of rotifers in activated sludge
generally means a good, stable sludge with plenty of
oxygen. Although little is known on their role in
nutrient and heavy metal removal in wastewater
treatment systems, it is reported that their principal role
of rotifers in wastewater is the removal of bacteria and
the development of floc. They are also said to
contribute to the removal of effluent turbidity by
removing non-flocculated bacteria (Mountain Empire
Community College, 2013).
Microalgae have been reported to have application in
the removal of nutrients, organic matter, xenobiotic
compounds and metals in wastewater treatment
systems. They are known to assimilate nitrogen in the
form of nitrate, nitrite and ammonium and excess
phosphorus from wastewater. The ability of microalgae
to remove pollutants is dependent on the species that is
used for remediation and the properties of the
wastewater itself. The selection of an appropriate
algal strain for wastewater treatment is therefore
dependent on various factors like the characteristics of
the wastewater, the original habitat of the strain and
the climatic conditions in the treatment plant
(Danilović et al., 2013; Oilgae, 2013). Microalgae are
able to thrive in extreme growth conditions of pH and
salt. They have the ability to remove heavy metals,
produce oxygen with low energy input, fixcarbon
dioxide and produces biomass. They are also reported
to have greater feasibility than other organisms and are
easy to handle. In addition, they low cost and easily
cultured. A limiting factor in the use of microalgae is
that a number of biotic factors, such as the presence of
pathogenic bacteria or predatory zooplankton may have
adverse impact on their. In addition, they can easily be
out-competed by other microorganisms for essential
nutrients. Another major practical limitation in algal
treatment systems is harvesting or separation of algal
biomass from the treated water discharge (Danilović et
al., 2013; Oilgae, 2013).
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hydrocarbons, pathogenic microbes, endocrine
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life and pose as threat to human life. Some of these
problems include eutrophication, metal poisoning,
irritations and several water-related infections. To
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... Plans photodegrades contaminants either by uptake, metabolism or translocation to different plat parts (Ferraji, 2014). Nutrient load reduction in wastewater through microalgae is one of the emerging option (Akpor et al., 2014) as these microalgae can assimilate nutrients in their cells. These microalgae are variedly used to degrade chlorinated solvents, insecticides and pesticides and many other inorganic and organic nutrients (Akpor et al., 2014). ...
... Nutrient load reduction in wastewater through microalgae is one of the emerging option (Akpor et al., 2014) as these microalgae can assimilate nutrients in their cells. These microalgae are variedly used to degrade chlorinated solvents, insecticides and pesticides and many other inorganic and organic nutrients (Akpor et al., 2014). Plants ability to metabolise these nutrients determines the efficacy of the process. ...
... Plants ability to metabolise these nutrients determines the efficacy of the process. When a toxic compound is taken by plants the first stage is activation of compounds by the action of different metabolites like flavin, monooxygenase etc. then its conjugation in plant parts and lastly the plant compartmentalise it in different parts preferably vacuoles or apoplast which ensures safe disposal of these toxic compounds (Akpor et al., 2014). 3. Phytovolatilsation: As the name suggest, phytovolatilsation refers to volatilisation of contaminants via plant parts. ...
Population growth, industrialisation, urbanisation, and climate change have created huge pressure on freshwater resources to fulfil the demand. Approx. 70-80% of the freshwater supply returns as wastewater, which is difficult to tackle and manage. We need to tackle the freshwater demand from different sectors like domestic, industrial, and agriculture. Most important is how to use the wastewater safely in agriculture. Therefore, it is an apt time to refocus on ways to recycle water especially in sectors like agriculture and for ecosystem services. The major concern in using wastewater in agriculture is its quality as the wastewater may carry pathogens, heavy metals, and many other pollutants, which might reach to human beings and animals via food chain. A solution to wastewater reuse is through bioremediation techniques. Bioremediation should be considered as a feasible and futuristic technology for safe use of wastewater in agriculture as it will reduce the burden on centralised water treatment system as well as it being economic and eco-friendly.
... In urban area, the water quality is such a key factor which is hard to identify as its characteristic vary based on numerous factors such as street sweeping, stormwater, wastewater from domestic and small to medium industrial activity [1,2]. These pollutants were pathogenic microorganisms, phosphorus and nitrogen, hydrocarbons, heavy metals, endocrine disruptors, and organic matter [3]. It is becoming the pressure to waterbodies (lake and reservoirs located near the urban area) as they function as the storage in biological treatment to collect the wastewater from the drainage system [4]. ...
... Other organic contaminants like pesticides have significant toxic impacts on living organisms. Since contaminants in water have a bad influence on all organisms and the environment, their elimination is critical (Saxena et al., 2020;Akpor et al., 2014). A summary of the most critical contaminants in wastewater is described below. ...
Freshwater makes up 3% of the world's total water sources. Human and industrial activities generate many pollutants containing heavy metals, dyes, and oils and discharge them into the water sources, which harms human health and the environment. The adsorption process is a suitable and eco-friendly method to eliminate contaminants from water. This method has advantages over conventional procedures. There are many biosorbents and nanoadsorbents for the removal of contaminants from water, including microbial biomass (e.g., algae biomass), agricultural wastes (e.g., activated carbon derived from the leaves and wood of trees), nano-MgO, Fe3O4 nanoparticles, CaO/Fe3O4 nanoparticles as well as a combination of nanoadsorbents and bioadsorbents such as activated carbon/Fe3O4 nanocomposite. The mix of bioadsorbents and nanoadsorbents have shown a high sorption capacity for removing different pollutants from water. This chapter focuses on different types of contaminants like heavy metals, dyes, pesticides, and drugs in wastewater and the advantages and disadvantages of bioadsorbents and nanoadsorbents in removing different contaminants from wastewater. Also, future perspectives for the removal of contaminants by bioadsorbents and nanoadsorbents are presented.
... For instance, humans and plants breath in the air and causes different diseases when metals concentration becomes toxic [58]. Microbial air pollution is another problem related to WW treatment that causes typhoid fever, cholera, diarrhoea, chronic exposure, mental disorder, liver and kidney failure, and various other diseases [58,59]. Microorganisms survive optimally in the presence of air [60] and act as bio-aerosols, transported from various ecosystems (water, soil, water, animals, surface plants, and others) and through sneezing, wind gusts, and coughing. ...
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Water is an essential input for agricultural development and irrigated agriculture. However, groundwater reliance is rising due to lack of canal water and is often inferior quality, costly, scarce, and ultimately expensive for smallholders. Moreover, as hunger rises daily due to population growth, additional irrigation water systems are needed to extend the cropping patterns. Therefore, wastewater (WW) use in agriculture has been increased on a growing scale over the last decades due to its fertilizing capacity and decrease in canal water and freshwater availability. It enhances soil productivity by contributing organic matter contents and preserves water and nutrients for plants. Various traditional treatments such as primary, secondary, and tertiary treatments are being used, but more working is required due to health and environmental issues. Therefore, the end product of tertiary treatments could be mixed with different water sources (for dilution), phytoremediator plants in channels and use of microbes that eat waste food could be adopted because the maximum crop yield is primarily determined by water quality, as well as climatic conditions, water management practices, chemical and physical soil properties. Besides, we can minimize the all-potential risks associated with agricultural activities and production via strengthened strategies, systemic dialogues, and financial frameworks. The present review discusses WW irrigation are that it provides a safer water source to the farmers and has the beneficial elements of providing essential plant nutrients after treatment and environmental sustainability.
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In recent decades, the greatest challenge facing the world has been protecting the environment from various forms of pollution. Water pollution is one of the most crucial environmental problems threatening living organisms’ lives and human health. Mostly anthropogenic, it undoubtedly originates from diverse sources, including agricultural, domestic, and industrial activities. Therefore, adopting sustainable and environmentally friendly practices constitutes an ideal solution for purifying contaminated water to be further used in industrial activities and so on. The valorization of lignocellulosic biomass for the production and conception of value-added products is an attractive and environmentally friendly way of preserving the environment. Lignocellulosic biomass, such as crops, agricultural wastes, forest residues, etc., is a sustainable and plentiful resource that can be valorized and used as robust material for eliminating different pollutants from sewage, including organic pollutants, heavy metals, inorganic compounds, and microorganisms. Indeed, the valorization of biomass wastes is among the most intelligent strategies. It is like killing two birds with one stone: reducing the quantity of biomass waste and benefiting from its physicochemical properties. Feedstocks are rich in cellulose, hemicellulose, and lignin, which have already been proven efficiency in removing persistent pollutants. Moreover, it can undergo physical, chemical, and thermal to prepare cellulose nanocrystals and biochar with high removal ability. The current review discusses the exploitation of lignocellulosic biomass to produce composite materials in the applications of wastewater purification, especially for the removal of different persistent organic and inorganic contaminants. It highlights the recent research studies and the mechanisms involved in eliminating pollutants using lignocellulosic-based materials.
Untreated municipal wastewater has a great impact on the ecosystem due to a large number of nutrients and organic content. As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn are common heavy metal ions present in municipal effluents. In India, more than 38,254 million liters of wastewater are produced in urban areas. The application of effluents and sludges in agricultural practices also increases the deposition of toxic metals in biological systems. With the development of nanoscience and due to the large surface area and relatively minute size, nanoparticles are successfully applied for the remediation of metal ions. Some of the commonly and effectively used nanoparticles for the metal ions removal process are discussed in this chapter.
Environmental economics is a relatively new term for both, economists and environmentalists. However, this space is rapidly evolving and it is trying to make an impact in the field of environmental sustainability. The current paper attempts to assess the monetary cost of a polluted river ecosystem. The case considered in the study is of Kasardi River located in the state of Maharashtra, India which receives partially treated effluent from the adjacent common eftluent preatment plant (CETP). Kasardi being a non-perennial river has its ecosystem and needs conservation by restoring the polluted river stretch and treating the effluent to the prescribed standards before discharge. Due to the non-existence of the market rates for the river ecosystem, surrogates available methods such as avoided cost method (ACM), vatue mransfer Method (VTM), and control cost method (CCM) were employed in ascertaining the economic cost of the polluted ecosystem. Thus derived value is considered as the cost to the environment due to the incurred negative externality. Avoided cost method (ACM) has been used to understand the magnitude of environmental damage caused by the semi-treated effluent discharged into this river using the cost of operation and maintenance of various technologies used in India for industrial wastewater treatment to arrive at a monetary estimate of the damages. Value transfer method (VTM) has also been applied to estimate the economic value by transferring the monetary-based information from past studies adjusted to Indian scenarios to understand the differences in methodologies and magnitude of valuation between the two methods. Further, the cost of delayed action has also been evaluated using control cost method (CCM) and is represented as the river restoration cost. The cost of damages calculated using ACM and VTM is in the range of ~ 210–240 million INR whereas CCM value the damages to be worth ~ 850 million INR. The study demonstrates that timely action can save a lot of resources both in terms of money and the health of the ecosystem.
Significant findings for microbial removal have led to expertise on several kinds of nanomaterials that made new paths for removing various biological contaminants in a variety of water resources in recent years. Furthermore, advancements in multifunctional nanocomposites synthesis pave the enhanced possibility for their use in water treatment system design. The adsorption towards microbial elimination has been reviewed and compared in this review article using four common kinds of nanomaterials: carbon materials, metal oxides, metal/metal oxides, polymeric metal oxide nanocomposites and their most important mechanistic behavior also discussed. We also describe and analyze recent findings on the effects of engineered nanomaterials on microbial communities in natural and artificial environments. Understanding the removal mechanistic strategy is crucial to improving the nanoparticles (NPs) efficiency and increasing their applicability against a variety of bacteria in various environmental conditions. Also, our study focused on their behavioral effects on microbial structure and functionality towards the removal. Future research opportunities connected to the use of nanomaterials in microbial control and inactivation with societal and health implications are also discussed. We also highlight a number of interesting research subjects that might be of futuristic interest to the scientific community.
The practice of wastewater irrigation lessens the pressure on the aquatic environment by minimizing the use of freshwater resources. However, this may lead to significant damage to the human health and environments. Recycled wastewater possesses a substantial amount of nutrients that act as fertilizers for crops and facilitate the metabolic action of microorganisms. The major advantages of wastewater irrigation are increased agricultural production, nutrient recycling, reduced stress on freshwater, economical support and provision of livelihoods for farmers. However, several harmful impacts of wastewater irrigation are also prominent due to inappropriate wastewater management and irrigation practices. These include severe hazards to farmer’s health, contamination of agricultural land and crops with toxic metals, chemical compounds, salts and microbial pathogens. In addition, long-term irrigation using wastewater can significantly affect the groundwater through leakage of salty and toxic metal-rich wastewater making it unfit for human consumption. Wastewater irrigation may also alter the physicochemical properties and microbiota of soil, which in turn can disturb land fertility and crop productivity. Several factors need to be considered while using treated or partially treated wastewater for irrigation such as diversity and type of pollutants, available nutrients, pathogenic microorganisms and soil salinity. In this review paper, we assess the impact of wastewater irrigation on humans as well as on the environment based on available case studies globally, outline current use of wastewater for irrigation of agricultural crops such as cereals, vegetables, fodder crops, including agroforestry and discuss suitable management practices of wastewater reuse for irrigation.Graphic abstract
Municipal wastewater (MWW) effluent discharges can introduce contaminants to receiving waters which may have adverse impacts on local ecosystems and human health. Conservative chemical constituents specific to the MWW effluent stream can be used to quantify and trace wastewater effluent-sourced contaminant inputs. Gadolinium (Gd), a rare earth element used as a contrasting agent in medical magnetic resonance imaging, can be found in urban MWW streams. Dissolved anthropogenic Gd has been shown as an indicator and potential conservative tracer for MWW effluent in receiving waters. Like other known MWW tracers, it can be difficult and expensive to measure. Dissolved rubidium (Rb) to strontium (Sr) ratio enrichment in biological materials such as blood and urine can lead to enriched Rb/Sr values in MWW effluent relative to natural waters. This ratio is relatively easy and inexpensive to measure and represents a promising additional indicator for MWW effluent in receiving waters in urbanized freshwater systems. In July 2015 and 2016 surface water samples were collected from sites in the tidal-fresh Potomac River in the vicinity of the Blue Plains Advanced Wastewater Treatment Plant (BPAWWTP) outfall near Washington, DC USA along with treated MWW effluent samples from the BPAWWTP. Dissolved Rb/Sr ratios were measured in these waters and compared to dissolved Gd concentrations in order to demonstrate the potential for dissolved Rb/Sr ratios as conservative indicators for MWW effluent. Results suggest the dissolved Rb/Sr ratio represents a simple and cost-effective indicator and conservative tracer for MWW effluent that can be used with or in place of other proven tracers to investigate wastewater impacts in highly-urbanized, anthropogenically-impacted freshwater systems like the tidal fresh Potomac River and perhaps in a wider range of geologic settings than previously thought. A case study is presented as an example to demonstrate the potential of using dissolved Rb/Sr ratios to trace MWW-sourced nutrient inputs from a major WWTP like BPAWWTP to the receiving waters of tidal-fresh Potomac River.
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The removal of heavy metal from sludge before disposal or application to farmland is a necessary step to achieve a more safe sludge usage or disposal. Chemical extraction using inorganic acids (nitric, hydrochloric) and organic acids (citric, oxalic) were tested for extraction of chromium, copper, nickel, lead and zinc from contaminated sewage sludge at different pH and reaction time. Results revealed that solubilization of metals using inorganic acids achieved its maximum extraction efficiency (Cr-88%, Cu-82%, Ni-86%, Pb-94%, Zn-89%) at pH value lower than 2 and acid contact times of 1hour. while in case of organic acids oxalic acid does not show good results comparing to citric acid that at pH 2.43 citric acid seemed to be highly effective in extracting Cu (86%), Zn(88%), mostly after 1 day of extraction time, Cr (90%), Ni (96%) at 5 days leaching time, while Pb(85%) removal at the same pH was at a longer leaching time 10 days. At pH 3, citric acid seemed to be also highly effective in extracting Cr (66%), Cu(48%), Pb (66%), Zn(69%) at 1 day, while higher removal was also attained for Ni(68%) at only 4 h leaching time. Finally the extraction efficiencies of citric acid for Cr, Cu, Ni, Pb, Zn, are high enough to reduce the heavy metal content in sludge to levels below the legal standards.
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The reuse of treated effluent (for agriculture and as supplement for drinking water needs) is currently receiving attention as a reliable water source. This paper is aimed at reviewing the environmental and health impacts of untreated or inadequately treated wastewater effluents. The quality of wastewater effluents is responsible for the degradation of the receiving water bodies. This is because untreated or inadequately treated wastewater effluent may lead to eutrophication in receiving water bodies and also create environmental conditions that favour proliferation of waterborne pathogens of toxin-producing cyanobacteria. In extension, recreational water users and anyone else coming into contact with the infected water is at risk. Although various microorganisms play many beneficial roles in wastewater systems, a great number of them are considered to be critical factors in contributing to numerous waterborne outbreaks. Also, wastewater effluents have been shown to contain a variety of anthropogenic compounds, many of which have endocrine-disrupting properties. Since large amounts of wastewater effluents are passed through sewage treatment systems on a daily basis, there is a need to remedy and diminish the overall impacts of these effluents in receiving water bodies. In order to comply with wastewater legislations and guidelines, there is a need for adequate treatment before discharge. This can be achieved through the application of appropriate treatment processes, which will help to minimize the risks to public health and the environment. To achieve unpolluted wastewater discharge into receiving water bodies, careful planning, adequate and suitable treatment, regular monitoring and appropriate legislations are necessary.
The presence of radioactive colloids (radiocolloids) in groundwater has been documented in several studies. There is significant evidence to indicate that these colloids may accelerate the transport of radioactive species in groundwater. Because field experiments are often fraught with uncertainties, colloid migration in groundwater is an area of active research and the role and existence of radiocolloids is being investigated. This paper describes an ongoing study to characterize groundwater colloids, to understand the geochemical factors affecting colloid transport in groundwater, and to develop an in-situ colloid remediation process. The colloids and suspended particulate matter used in this study were collected from a perched aquifer site (located at Los Alamos National Laboratory's Mortandad Canyon in northern New Mexico, USA) that has radiation levels several hundred times the natural background and where previous researchers have measured and reported the presence of radiocolloids containing plutonium and americium. At this site, radionuclides have spread over several kilometers. Inorganic colloids collected from water samples are characterized with respect to concentration, mineralogy, size distribution, electrophoretic mobility (zeta potential), and radioactivity levels. Presented are the methods used to investigate the physiochemical factors affecting colloid transport and the preliminary analytical results. Included below are a description of a colloid transport model and the corresponding computational code, water analyses, characterization of the inorganic colloids, and a conceptual description of a process for in-situ colloid remediation using the phenomenon of polyelectrolyte capture.
Anionic surfactant monomers can be adsorbed onto mineral oxides from the aqueous phase if the pH of the solution is below the oxide's zero point of charge (ZPC). The oxide with anionic surfactant sorbed to it is called organo-oxide, and it acts as a sorbent for nonionic organic pollutants, since these pollutants will partition between water and the organic phase of the sorbent. The advantage of this sorbent is that, unlike activated-carbon, it can be regenerated in-situ. Batch and column experiments were done to demonstrate the use of an organo-oxide for the treatment of water contaminated with a nonionic organic pollutant. The results from column experiments matched well with theoretical predictions based on parameters obtained from batch experiments.
A field pilot study had been constructed in the Liaohe oilfield, China to treat heavy oil wastewater enriched with large amounts of dissolved recalcitrant organic compounds and low nutrient of nitrogen and phosphorus by conventional activated sludge process (CAS) coupled with immobilized biological aerated filter (I-BAF). After biological treatment, the chemical oxygen demand (COD) was removed around 64% when the hydraulic retention time (HRT) was 18 h. The average effluent COD reached approximately 75 mg L−1, which met the national discharge standard. Gas chromatography-mass spectrometry (GC-MS) indicated that the CAS could completely remove phenolic, alkenes, aldehydes and organic acid compounds from the wastewater and the alkane components were removed by the I-BAF. Environment scanning electron microscopy (ESEM) disclosed that bacteria flourished in both reactors during the operating period and most of them resemble rods and filaments. The bacterial community structure analysis based on Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) technology revealed that the predominant bacteria in the CAS reactor belonged to the Pseudomonas, Planococcus groups and the Agrococcus, Acinetobacter groups that were major degraders in the I-BAF reactor. Although some high molecular weight n-alkanes (C15-C23) were found to be refractory in our biotreatment systems, it could be improved by optimizing the process.