Green technology-for-bioremediation-of-the-eutrophication-phenomenon-in-aquatic-ecosystems-a-review

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African Journal of Aquatic Science
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Green technology for bioremediation of
the eutrophication phenomenon in aquatic
ecosystems: a review
Mostafa El-Sheekh, Mohamed M Abdel-Daim, Mohamed Okba, Samiha
Gharib, Asgad Soliman & Hala El-Kassas
To cite this article: Mostafa El-Sheekh, Mohamed M Abdel-Daim, Mohamed Okba, Samiha
Gharib, Asgad Soliman & Hala El-Kassas (2021) Green technology for bioremediation of the
eutrophication phenomenon in aquatic ecosystems: a review, African Journal of Aquatic Science,
46:3, 274-292, DOI: 10.2989/16085914.2020.1860892
To link to this article: https://doi.org/10.2989/16085914.2020.1860892
Published online: 01 Mar 2021.
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African Journal of Aquatic Science 2021, 46(3): 274–292
Printed in South Africa — All rights reserved
Copyright © NISC (Pty) Ltd
AFRICAN JOURNAL OF
AQUATIC SCIENCE
ISSN 1608-5914 EISSN 1727-9364
https://doi.org/10.2989/16085914.2020.1860892
African Journal of Aquatic Science is co-published by NISC (Pty) Ltd and Informa UK Limited (trading as Taylor & Francis Group)
Eutrophication is the process by which a body of water is
enriched with dissolved nutrients (such as phosphates) that
stimulate the growth of aquatic plant life, typically resulting
in dissolved oxygen depletion. It occurs in lakes, streams,
rivers, and coastal waters. This phenomenon causes
enormous disruptions to aquatic ecosystems. It occurs
at the point when a waterway moves toward becoming
improved in key limiting nutrients, particularly phosphates
(Figure 1), and stimulating symptomatic changes, including
the expanded production of algae and/or higher plants
(Kelly et al. 2009). In their work on eutrophication, Zhang et
al. (2020) stated that ‘It is the main cause of impairment of
numerous freshwater and coastal marine environments in
the world’. It is characterised by the depletion of fish species
and excessive, inordinate ‘plant and algal’ development
because of the surge of at least one determinant required
for photosynthesis like daylight, CO2, and nutrient
supplements (Arpa Umbria 2009; Zhang et al. 2020).
Causes of eutrophication
Human activities have accelerated the amount and degree
of eutrophication through two sources: non-point and point
eutrophication.
The introduction of non-point sources of nutrients, such as
nitrogen and phosphorus, into aquatic ecosystems, leads to
drastic outcomes for the environment, and most importantly
for water used in aquaculture and for drinking (Chislock et
al. 2013). The increase in these two nutrient supplements
prompts an unstable ascent in the development of green
growth, called algal blossoms. Nitrogen reaches oceanic
biological systems by means of direct uptake, fixation by
living biota and water effluents. Eutrophication additionally
incorporates the expansion of the organic compounds in the
sedimentary material, as stated by Meis and Spears (2009).
Non-point sources of eutrophication are overflow from
agribusinesses/water systems, spillover from the field, urban
spillover flood from mines, climatic influence over water
bodies, and other land exercises creating pollution (Ansari
et al. 2014). Significant ecological gains following reductions
in major point sources such as wastewater and industrial
effluents (metropolitan and mechanical), rich in bioavailable
phosphorus (P) discharges, have been reported (Withers
et al. 2014). Similarly, this has been shown for other point
sources such as wastewater effluent spillover and leachate
from waste transfer framework, overflow and invasion from
animal feedlots, spillover from mines, and tourist modern
destinations. Flood of both storm and sanitary sewers,
Review Article
Green technology for bioremediation of the eutrophication phenomenon in
aquatic ecosystems: a review
Mostafa El-Sheekh1
* , Mohamed M Abdel-Daim2,3
, Mohamed Okba4
, Samiha Gharib4
, Asgad Soliman4
and
Hala El-Kassas4
1
Botany Department, Tanta University, Tanta, Egypt
2
Department of Zoology, King Saud University, Riyadh, Saudi Arabia
3
Pharmacology Department, Suez Canal University, Ismailia, Egypt
4
National Institute of Oceanography and Fisheries, Alexandria, Egypt
*Correspondence: mostafaelsheikh@science.tanta.edu.eg
Eutrophication is a serious phenomenon that leads to vigorous algal blooms that alters the structure of ecosystems.
It is caused by non-point sources of nutrients; as nitrogen and phosphorus, and point sources as wastewater effluent.
Distinctive algae groups are responsible for this phenomenon, such as diatoms, blue-green algae, green algae, and
dinoflagellates. Numerous solutions have been considered to control eutrophication and harmful algal blooms such
as the biological removal of nitrogen and phosphorus. Advanced treatments (i.e. green technology) depend upon
the remediation of wastewater before discharge, such as the removal of phosphorus using agricultural waste-based
biosorbents (AWBs) from water and wastewater, and phosphorus sorption performance by both unmodified and
modified AWBs. Phyto-remediation includes many procedures that encompass the cost-effective and environmentally
friendly methods used to remove or reduce excess natural/inorganic contaminants in groundwater, surface water, and
soil. Due to the rapid growth of duckweeds and their ability to rapidly remove minerals as phosphates and nitrogen from
the water, duckweed may be the most promising plant for controlling eutrophication and, therefore, harmful algal blooms.
Keywords: algae, blooms, eutrophication, macrophytes, phytoremediation, red tide, toxins, water quality
Definition of eutrophication
Published online 01 Mar 2021

African Journal of Aquatic Science 2021, 46(3): 274–292 275
discharges from sewage treatment or industrial plants and
fish farms are examples of point sources (Arefin and Mallik
2017).
Types of eutrophication
Natural eutrophication
Over hundreds of years, the continuous build-up of inorganic
and organic materials started to fill numerous lake basins.
Inorganic materials are mainly nitrogen and phosphorus.
The main source of nitrogen pollutants is runoff from
agricultural land, whereas most phosphorus pollution comes
from households and industry, including phosphorus-based
detergents. Nitrogenous fertilizers have largely been linked
to concerns over the relationship between water quality
and eutrophication. Organic matter may originate from
many different sources. Historically, the largest sources
were discharges of raw sewage. Other sources of organic
loads include wastewater treatment plants, industrial
facilities, agricultural runoff, stormwater, combined sewer
overflows, urban runoff, and runoff from natural systems
such as forests (Lowe 2005). As the lakes turn out to be
more eutrophic, they can support more living creatures,
including harmful algae, accordingly with higher nutrient
supplements. In the meantime, their littoral range rises due
to sedimentary build-up, which not only disturbs the water
characteristics, but also helps colonise terrestrial vegetation
in the expanding shallows. The time of these processes
depends upon both the qualities of the pond (dissolved
oxygen with a maximum value of 18 mg l−1
and minimum
value of 6 mg l−1
, pH ranging between 7.5 and 8.5, the
carbonate hardness should be approximately 125 ppm, the
maximum ammonia level should be 0.5 ppm, the maximum
nitrites level should be 0.25 ppm, Nitrate levels should be
approximately 20–60 ppm, phosphorus not more than 30
mg m3
) as well as the climate conditions (Ansari et al. 2011;
Chislock et al. 2013; Zhu et al. 2020). Nutrient enrichment
or natural eutrophication occurs through the addition of
sediment, rainfall, the decay of resident animals and plants,
and their excreta.
Cultural eutrophication
The modification of nutrient addition to water bodies by
humans’ activity can drastically raise eutrophication,
resulting in major environmental changes that would last
for decades. Khan and Mohammad (2014) stated that
the ‘Cultural eutrophication is primarily associated with
phosphorus, which is found in fertilizers and partially treated
sewage’. Phosphorus has been observed to be a strong
stimulator of algal growth. Soil erosion is a primary source
of man-caused sedimentary eutrophication created by the
evacuation of trees and vegetation. The health of aquatic
creatures is straightforwardly tied to humans’ activity
that happens through the entirety of water bodies, which
requires successful land administration with the ecological
arrangement (Ansari et al. 2011; Ansari et al. 2014).
Cultural eutrophication is creating dense phytoplankton
blooms that reduce water quality and light penetration,
Figure 1: Eutrophication process. Adapted from Arpa Umbria (2009)

El-Sheekh, Abdel-Daim, Okba, Gharib, Soliman and El-Kassas
276
causing die-offs of various kinds of life. Furthermore, higher
degrees of photosynthesis resulting from the eutrophication
process can exhaust dissolved inorganic carbon and
raise pH to harmful levels. As the algal blooms die, the
decomposition process exhausts the dissolved oxygen
resulting in hypoxic conditions (Marsden and Bressington
2009). Therefore, the examples of cultural eutrophication
are the human-generated fertilization of water bodies,
treated sewage and runoff from farms and urban areas,
raw sewage, and sewage dumping.
Eutrophication impacts
The allelopathic and antagonistic influences of the
biophysical conditions of the eutrophic region make serious
dangers to human beings and the ecosystem (Smith et al.
1999; Sala and Mujeriego 2001; El-Sheekh et al. 2010;
Ansari et al. 2014). Such influences lead to the modification
of the nutrient cycles of watersheds of agro-conditions.
Nitrogen and phosphorus blooms are identified with
the stream, subsurface stream, profound drainage,
notwithstanding the reaping of plants and creature items as
well as the loss of volatile gases (Sala and Mujeriego 2001;
Kormondy 2003).
The economic and social impacts of harmful micro-algae
are especially apparent when algae affect marine food
resources, e.g., aquacultures (Smith et al. 1999; El-Sheekh
et al. 2010; Sanseverino et al. 2016).
Eutrophication can lead to an increase in harmful algae
blooms (HABs), i.e., a natural phenomenon caused by a
mass proliferation of phytoplankton (cyanobacteria, diatoms,
and dinoflagellates) in water bodies (Figure 2) (Wetzel
2001). HABs spoil water quality by producing odours or thick
scums, toxic or inedible phytoplankton species, taste, scent,
and water treatment issues, loss of attractive fish species,
decreased biodiversity, changes in species composition and
predominance, and the discoloration of the water, which can
be aesthetically unpleasant.
Algae associated with eutrophication
As indicated by the definition of eutrophication, distinctive
algae groups are reported to be available in the water
bodies (Paerl ‎2008). These groups include cyanobacteria,
Furcellaria, Phycodrys, ‘Green tides’, chlorophytes,
cryptophytes, diatoms, and dinoflagellates. Algae
proliferate when different collaborating natural substance,
and physical components act synergistically to make
Figure 2: Direct and indirect impacts of algae bloom. Adapted from Sanseverino et al. (2016)

an ideal development condition (Gladyshev and Gubelit
2019). HABs cause different levels of eutrophication.
Cyanobacterial toxins and their effects are discussed in
detail due to their genuine effects on aquaculture life forms
and human life (Paerl 2008).
Blue-green algae (Cyanobacteria) and their impacts on
aquatic ecosystems
Toxic metabolites from these prokaryotic photosynthetic
cyanobacteria (Microcystis, Nodularia, Cylindrospermopsis,
Anabaena, Planktothrix, Aphanizomenon, Gloeotrichia,
Lyngbya) include compounds that show hepatotoxicity and
neurotoxicity. From the cyanobacterial hepatotoxins, the
microcystin LR (MC-LR) and nodularin represent a serious
threat to drinking water and recreational lakes worldwide.
These toxins possess strong hepatotoxic activity, which
poses a major risk to animals and humans, causing illness
and death. In recent years the cyanobacterial neurotoxin
anatoxin-a is becoming a serious problem in freshwater
bodies triggered by eutrophication and climate change.
Anatoxin-a is suspected to have a distinct toxic mechanism
affecting on the physiological and nervous systems
in exposed organisms (Ha and Pflugmacher 2013).
Therefore, recreational exposure to toxic Cyano-HABs
can cause serious problems (Pilotto et al. 1997). The
classification of cyanobacterial strains and their harmful
effect are illustrated in Table 1.
Financial and sociocultural influences of cyano-HABS
Cyano-HABs can have huge financial impact because of
their negative influence on the human wellbeing and their
adverse effects on aquaculture, recreation, and tourism.
Poisons and taste-and-scent mixes (geosmin and MIB)
result in elevated treatment costs for drinking water
facilities, and algae mats can hinder lakes’ efficiencies.
Furthermore, the major causes of economic losses for
catfish aquaculture are off-flavour substances. Moreover,
the closure of recreational water bodies to secure human
wellbeing can inflict income losses for nearby communities
(Jewett et al. 2007).
Other freshwater HABs
Another non-cyanobacterial freshwater HABs lead to serious
harm due to the generation of excessive algal biomass or the
synthesis of compounds that are poisonous to aquatic biota,
fish, and human beings. In general, unlike Cyano-HABs, they
have had indirect impacts on human health in the United
States and other nations (Landsberg 2002; Fire et al. 2020).
These include some members of dinoflagellates and both
haptophytes, green algae, and euglenophytes, as well as
raphidophytes, diatoms, and cryptophytes.
In the Great Lakes, nuisance caused by macro- and
microalgae species of the green algae (Chlorophyta) have
been recorded. For example, Cladophora, has recently
been reported to cause serious impacts (Landsberg
2002). Cladophora sp. ‘foul-smelling nuisance’ blooms
accumulated on seashores can shut water pipes, and potent
pathogenic microorganisms such as E. coli are reported as
well. This results in negative economic impact due to the
reduced beach use. Experimental studies revealed that the
resurgence of green seaweeds in the Great Lakes might
be related to the introduction of the zebra mussel, which
resulted in excess water clarity (Lowe and Pillsbury 1995).
Red tide
Red tides are not just a major nuisance for beachgoers; they
are also lethal to marine creatures like fish, flying creatures,
and manatees. Furthermore, they can seriously affect
human wellbeing. A red tide occurs when the population of
certain kinds of algae known as dinoflagellates explodes,
creating what is called ‘harmful algal blooms’ HABs. When
these microalgae reproduce excessively and bunch in
one zone of the ocean, they can change the colour of the
water, as stated by the Centers for Disease Control and
Prevention. A shade of red is always seen, which may range
from pink or orange to brown or yellow (Anderson 2004).
There are three fundamental sorts of algae related to
red tides, Karenia brevia, Alexandrium fundyense, and
Alexandrium catenella (Smetacek and Zingone 2013).
Various variables can make an algal bloom increase such
as lower salinities, high nutrients content in the water, and
hotter than-common surface water temperatures. The
algae connected to red tides contain a toxin that influences
the nervous and digestive systems of creatures. The
common toxins produced by Cyano-HABs are microcystin,
nodularin, cylindrospermopsin, anatoxin-a, lyngbyatoxins,
and saxitoxins. Red tides are usually accomplished by
the die-off of fish, birds, and other living creatures that
feed on fish. Significantly bigger creatures that feed upon
any of these marine lives might be killed if they consume
enough of the poison. Red tides happen around the world,
and a few reports demonstrate that their recurrence is on
Aplysiatoxins Lyngbya, Schizothrix, Oscillatoria Dermatotoxic Kato and Scheuer (1974)
Lyngbyatoxin-a Lyngbya Dermatotoxic Fujiki et al. (1981)
Microcystins Microcystis, Oscillatoria, Nostoc, Anabaena,
Anabaenopsis, Phormidium
Hepatotoxic Carmichael (1992)
Nodularin Nodularia, Nostoc Hepatotoxic Carmichael (1992)
Cylindrospermopsin Cylindrospermopsis, Anabaena, Aphanizomenon,
Raphidiopsis, Oscillatoria, Lyngbya, Umezakia
Hepatotoxic Ohtani et al. (1992)
Humpage and Falconer (2003)
Anatoxin-a Anabaena, Oscillatoria, Aphanizomenon Neurotoxic Rapala et al. (1993)
Anatoxin-a(s) Anabaena Neurotoxic Mahmood and Carmichael (1986)
Saxitoxins Anabaena, Aphanizomenon, Lyngbya,
Cylindrospermosis
Neurotoxic Sivonen and Jones (1999)
Table 1: Cyanotoxins, toxin producing cyanobacterial strains and the toxicity effects

278
the ascent, as indicated by Chislock et al. (2013). Recently,
Genitsaris et al. (2019) found that the main forming red
tide in Thessaloniki Bay, Eastern Mediterranean, was the
phytoplankton blooms dominated by mucilage-producing
diatoms that alternated with red tide events formed by the
dinoflagellates Noctiluca scintillans and Spatulodinium
pseudonoctiluca.
Water managers routinely use a variety of frameworks
to constrain the effects of social eutrophication, including
(1) preoccupation of abundant nutrient supplements
(2) changing nutrient supplement proportions, (3) physical
blending, (4) shading water bodies with murky liners or
water-based stains, and (5) use of proficient algaecides
and herbicides (Downing et al. 2001; Huisman et al.
2004). However, these systems have turned out to be
inadequate, particularly for huge, complex biological
communities. Water quality can often be enhanced by
diminishing the nitrogen and/or phosphorus contributions
to oceanic frameworks, and there are a few surely
understood examples where the control of nutrients has
significantly enhanced water purification (Abou-Shanab
et al. 2014). Dorgham (2011) reviewed the problem of
eutrophication in all Egyptian water bodies. He discussed
the main reasons for the eutrophication of the coastal
area of Egypt on the Mediterranean Sea, which extends
1 200 km. He also reviewed the main reasons for the
eutrophication in the coastal strip between Alexandria
and Mersa Matruh. This area hosts a huge number of
touristic villages, which are usually crowded by visitors
during summer. Other activities, such as fishing, industry,
tourism, trading and agriculture, oil and gas production,
and transportation, also affect the pollution status of
the water and hence affect the eutrophication. The five
lagoons connected to the Mediterranean Sea also receive
huge amounts of agricultural, industrial, and municipal
wastes, which are discharged from surrounding cities and
cultivated lands. Dorgham (2011) concluded that the level
of eutrophication along the Egyptian coast varied according
to the volume and contents of discharged wastes.
Green technology applications
Key strategies to control eutrophication
The different green technological techniques treating the
causative reasons of eutrophication i.e. nutrients (nitrogen
& phosphorus) are discussed. Different techniques have
to be considered to attain this goal, including; reducing the
imported nutrients, industrial pollution control, agricultural
pollution control, manure, and the pesticides utilised in-store
zones incrementing the potential dangers of eutrophication.
In this way, the reasonable utilisation of compost can
diminish the loss of nutrient supplements. Incredible
endeavours ought to be made to create eco-agribusiness,
and new farming innovations ought to be received as to
control supplement sources (Jiang and Pei 2007).
Domestic pollution control
Natural measures
Some investigations have demonstrated that the presence
of submerged vegetation can adequately block the
twist of green growth and control further eutrophication
advancement. In addition, it can enhance the living
conditions for different living creatures, increment natural
assorted variety, and keep up the biological parity of water
bodies (Yuan et al. 2008).
Designing measures
At present, the building measures incorporate silt digging,
profound air circulation, and water preoccupation.
Water preoccupation is a technique used to weaken the
eutrophicated lakes so as to lessen the poisons’ fixations
(Chen et al. 2004).
Development of a stable ecosystem
Ecological Scheduling of Reservoir; it is important to
ponder the effect of hydrological, meteorological, and other
different procedures on green growth and other amphibian
life in spatio-fleeting variation. As indicated by various
hydrological and natural attributes, the biological activity of
supplies ought to be done along with flood control, control
age, the executives of the downstream channel, and
ecological assurance to control the green growth sprout
(Cai and Hu 2006).
Water quality monitoring
Continuous environmental monitoring should be carried
out to enhance and understand the state of water quality
after storage in reservoirs and rivers. It is, therefore
extremely important to establish a network of environmental
monitoring in the main flow of rivers and reservoirs,
to monitor timely the water quality. As a result of the
environmental monitoring process, accurate information and
a scientific basis are provided to prevent the proliferation
of aquatic organisms so that the local authority establishes
practical management policies and control strategies
(Fraser et al. 2006).
The strategy used to maintain water quality and control
degradation in open storage reservoirs uses ventilation to
provide oxygen (Asano et al. 2007) and to stop plankton
growth. In addition, copper sulfate and certain algal species
can be used for such purpose. Asano et al. (2007) also
recommended not using chlorine to prevent plankton growth
in open reservoirs because it is found to increase odours.
In the case of closed tanks, the basic strategy is to
provide recycling of the storage contents and the additional
chlorine dose to keep the residual at a sufficiently high
level through using air pumps to aerate the stored water.
Generally, for the closed storage tanks that have a small
scale, the entry and exit pipes must be in such a way as
to ensure that the water is recycled without an additional
device (Singleton and Little 2006). The addition of chlorine
is usually used in land-based irrigation and some industrial
reuse applications (Robertson et al. 2003).
The gathering, treatment, and release or reuse of
wastewater close to the site where the wastewater
has been collected are called an on-location treatment
framework. Septic tanks profluent containing critical
fixations of the nutrient supplements and pathogens have
routinely been released to sand or soil for further treatment
via different processes in the drain field. This system has
advantages and disadvantages (Yadav 2018).

Biological nitrogen removal
Nitrification and denitrification are the two main biological
processes carried out by bacteria related to the nitrogen
cycle. In the nitrification process, bacteria firstly oxidise
ammonium to nitrite and then oxidise it to nitrate similar
to what occurs in some genera of algae (Schmidt et al.
2003; Winkler and Straka 2019). Without oxygen and in
the presence of organic electron donors, denitrification
takes place as an anoxic process by some bacteria such as
chemo-organotrophic, litho-autotrophic, and phototrophic
bacteria (Lopez-Ponnada et al. 2017). This process is
started in an alkaline medium (Metcalf and Eddy 2003).
Arun et al. (2019) evaluated a novel nitrogen-removal
method using a mixed consortium of microalgae, and
enriched ammonia-oxidizing bacteria. They also used
methanol with a denitrifier in a photo-sequencing batch
reactor for treating ammonium rich wastewater. The
high activities of ammonia monooxygenase and nitrite
reductase enzymes revealed the strong role of ammonia-
oxidizing bacteria and methanol with the denitrifiers for
achieving shortcut nitrogen removal from the wastewater.
Recently, El-Sheekh et al. (2020) used the microbial cell
immobilization technique for wastewater treatment, which
increased the quality of treated industrial wastewater and
reduced or eliminated total nitrogen by 90%.
Anaerobic/anoxic/oxic process
This system is dependant on the nitrogen evacuation and
the anaerobic/oxic process, which is a blend of the changed
Ludzack-Ettinger (MLE) methodology or Phoredox process
for phosphorus expulsion. When the systems are joined to
make this technique, the adequacy of nitrogen evacuation
is like the MLE method, yet the expulsion of phosphorus is
not as effective, owing to the reusing of nitrate. Regardless
of how much of the expulsion of nitrate is achieved by
recycling the nitrate to the anoxic zone, total clearing is
improbable, and some nitrate is reused to the anaerobic
zone (Mowlaei et al. 2005).
Conventional biological nitrogen removal method
Biological perspectives are the best effective, economical,
and practical method to remove nitrogen compounds from
discharging waters (Zhu et al. 2008).
Anaerobic ammonium oxidation (Anammox)
Anaerobic ammonium oxidation by anammox bacteria
is latterly known as a process that converts ammonium
nitrogen to nitrogen gas by using nitrite as the electron
acceptor. The anammox is the process of ammonia
oxidation and is named after Arnold Mulder (Kuenen 2008).
This process (Figure 3) seems to be more favourable than
nitrification-denitrification due to its efficiency, cheap, and
eco-friendly nature. The anammox process is performed
by litho-autotrophic bacteria from phylum Planctomycetes.
Strous and Jetten (2004) stated that the three processes,
including denitrification, nitrification, and anammox, were
applied to exclude nitrogen from different wastewaters.
For the first time, in 1995 denitrification by anaerobic
ammonia oxidation bacteria occurred at a pilot factory in
the Netherlands in which wastewater discharged from a
yeast factory was treated (Mulder et al. 1995). Van de
Graaf et al. (1995) designed a tracer study using 15NH4
−
and 14NO2
−
as tracers in a fluidised bed reactor (FBR)
to evidence the usage of nitrite as the electron acceptor.
The authors found that the final product was nitrogen gas
(14-15N2). So that two nitrogen atoms came from 15NH4
and 14NO2
−
, and anammox bacteria used nitrite as an
electron acceptor, not nitrate.
Since the disclosure of anammox microorganisms,
numerous scientists have contemplated the procedure and
the bacterial species engaged with anammox. Presently,
cell components, physiology, and response component of
anammox microbes are notable. Up until this point, five
anammox genera and eleven anammox species have
been disconnected and distinguished in the bacterial order
Brocadiales of the phylum Planctomycetes (Kartal et al.
2012).
The anammox species are not present in an unadulterated
culture, and accordingly, they have been given Candidatus
(Ca.) status and cannot be developed as an unadulterated
animal category. These species thrived well from frameworks
of wastewater treatment, marine, and crisp water situations.
Ca. Brocadia caroliniensis (the 10th anammox microscopic
organisms) was isolated from slimes of nitrification-
denitrification frameworks that treated fluid swine compost,
and these anammox microbes were preserved in the
Agricultural Research Service Culture Collection (NRRL) at
Peoria, Illinois, USA, with promotion number NRRL B-50286
(Magrí et al. 2012). As of late, another marine anammox
bacterium (the 11th anammox species), incidentally named
‘Ca. Scalindua profunda’ has been distinguished (Van de
Vossenberg et al. 2013). This anammox process is more
interesting for the following points:
1) Saving power up to 60% because it is an anaerobic
process and no aeration cost is needed.
2) Reducing the agents used as the organic carbon
source is unnecessary.
3) Reducing both sludge production and sludge treatment
cost.
4) Space reduced up to 50%.
5) CO2 will be reduced to ˃ 90%, and so, it is considered
eco-friendly.
Anammox microorganisms are chemoautotrophic
microscopic organisms that can use CO2 as an inorganic
carbon source to oxidise ammonium to nitrogen gas.
In this way, an overabundance of inorganic carbon is
required to develop anammox microscopic organisms
and protect the anammox movement (Kimura et al. 2011).
Liao et al. (2008) examined the impact of bicarbonate on
the anammox procedure in the sequencing group reactor
(SBR). They watched an expansion in anammox action as
the impact of bicarbonate focus expanded from 1.0 to 1.5
g l−1. In any case, anammox movement is repressed at a
higher bicarbonate fixation level (2.0 g l−1), because of the
increment of free smelling salts (FA) focus (Liao et al. 2008).
Egli et al. (2001) found that the optimum growth temperature
for the anammox bacteria has fluctuated between 30 and 40
°C, and the growth pH was between 6 and 9 (Awata et al.
2013). Generally, nitrite is not present in real wastewater.
The limitation of the direct reaction of the anammox process
can be affected by the absence of nitrite in wastewater (Jin
et al. 2012).

280
Biological phosphorus removal
Many applications are available for controlling PO4
3–
pollution (Zou, and Wang 2016; Stokholm-Bjerregaard
et al. 2017; Nielsen et al. 2019; El-Sheekh et al.
2020). Biological and chemical precipitations are the
most commonly applied methods. Phosphorous in
the wastewater can be subsequently removed as it is
combined into the cell biomass and wasted in sludge.
Nielsen et al. (2019) studied the microbiology of enhanced
biological phosphorus removal (EBPR) and argued that
the genus Tetrasphaera could be as important as Ca. The
EBPR process was first described by James Barnard in
the 1970s (Barnard 1976). EBPR requires anaerobic and
aerobic/anoxic conditions, and this process does not work
under tropical conditions, mainly because it was believed
that the Glycogen Accumulating Organisms (GAOs) would
outcompete Polyphosphate Accumulating Organisms
(PAOs). During the anaerobic stage, PAOs incorporate
fermentation products as intracellular storage products,
delivering phosphorous from the stored Poly-Phosphates
(PP) and the fermented products. EBPR is affected by
many environmental factors such as ‘temperature, pH,
sludge retention time, excessive aeration and nitrate, as
well as nitrite and carbon source’ (Oehmen et al. 2007).
Constructed wetlands for phosphorous and nitrogen
removal and assimilation
The erection of wetland frameworks is utilised to treat
septic release by utilizing a blend of soil, microorganisms,
and plants to treat the wastewater. There are two principal
kinds of wetland frameworks (White et al. 2011). Firstly,
the Free Surface Flow Wetlands that have uncovered
surfaces, where the water and squanders are exposed to
the environment. A Free-Surface Flow Wetland looks and
acts like a characteristic region (Figure 4). Plants in the
wetland are picked for their filtration abilities. In addition,
there is a dirt layer at the base of the wetland that treats
the wastewater as a dirt ingestion framework.
Secondly, the Subsurface Flow Wetland, where the
water level is kept below the surface and is exposed to the
climate. The wetlands lessen the scent of water and the
reproduction of flies. The Subsurface Flow Wetlands are
developed to clear up wastewater (Villaseñor et al. 2013;
Vymazal 2020).
Figure 3: Microstructure of anammox granules by scanning electron microscopy and the tertiary structure model proposed for anammox
granules. (a) the external surface; (b) the internal surface; (c) the cross section surface; (d) the fracture surface; (e) the magnifying view of
external surface; (f) the magnifying view of internal surface; (g) the magnifying view of the cross section surface; (h) the magnifying view of
the fracture surface; (i) Anammox bacteria floc aggregate formation: (1) interactions between individual anammox bacterial cells; (2) grouping
of anammox bacteria encapsulated by thin extracellular polymeric substance (EPS) layers; and (3) cementing of the groups together with
other bacteria and polymers to form compact aggregates. Adapted from Lin and Wang (2017) with permission

There are different methods for phosphorous and
nitrogen removal by macrophytes. Benthic algae and
submerged plants have a role similar to some products
for phosphorous inactivation (Meis and Spears 2009). The
output is resulting from phosphorous consumed by plants in
designed wetlands and plants in floating wetlands. One part
of such result is represented as auto-purification capacity,
however, the role of submerged plants and free-floating
vegetation is neglected since it is difficult to control this type
of vegetation and predict their effects dependably. Besides
water treatment, the designed wetland will remediate and
precipitate sediment as well (El-Sheekh et al. 2017a).
Macrophytes consume phosphorous from lake water,
considering the high value of pH. Finally, nutrient removal
can be realised by increasing the number of wetlands. The
aesthetic value of the wetlands may increase additional
advantages (Chimney and Pietro 2006).
Advanced treatment systems
Advanced treatment systems differ from traditional systems
in many ways; however, the main difference is that they
remediate wastewater before discharge (Lin et al. 2016).
Also, advanced treatment systems have advantages
over traditional systems such as the potential to remove
significantly more bacteria and organic material than a
conventional septic system, take up less room in the yard,
and reduce nutrient output.
Risk management frameworks consolidate cautiously
structured remediation steps and make conditions to
encourage a reliably high level of remedy. Generally,
propelled treatment frameworks control the stream by
utilising siphons and clocks to abstain from over-burdening
the treatment and last transfer segments amid times of
high water utilization, which could happen amid a morning
session of action (Jardine et al. 2003).
Risk management frameworks might likewise contribute
to the decrease in the pathogens as well as the nutrient
supplements in the profluent, relying upon the arrangement
and plan of the framework. Frameworks working for
nitrogen decrease largely distribute the profluent once
again into the septic tank where crude and treated
emanating wastes are blended, making conditions that
encourage the nitrogen expulsion by valuable microbes
(Lin et al. 2016).
Advanced remediation systems are planned as
a legitimate arrangement of treatment segments to
accomplish certain dimensions of treatment, determined
by nearby state or provincial overseeing offices. Since not
all advances can accomplish compelling supplements’
removal and additionally pathogen decrease, advances
are initially picked depending on the required dimension of
treatment (El-Sheekh et al. 2016; Zhang et al. 2020).
Remediation frameworks achieve the best outcomes
while producing waste effluents with certain substance
and microbiological qualities. For example, in small
communities with existing homes and fizzled septic
frameworks, the propelled treatment frameworks with the
littlest impressions are most ideally utilised as substitution
frameworks. Propelled treatment frameworks ordinarily
require semi-yearly or yearly support so as to work
legitimately and ought to be cultivated by a prepared and
qualified specialist co-op (Kartal et al. 2012).
Phosphorus removal and recovery using agricultural
waste-based biosorbents (AWBs) from water and
wastewater: a green technology
Agricultural waste-based biosorbents (AWBs) such as
sugarcane bagasse, coir pith, eggshell, and wood have
been successfully used for bioremediation of phosphorus-
polluted wastewaters (Paredes-López and Alpuche-
Solís 1991; Strauss 1997). Not long ago, different
treatment advances became accessible for controlling
PO4
3–
contamination (Benyoucef and Amrani 2011).
Understanding distinctive types of P in fluid arrangements
empowers a proper determination of treatment advances.
Figure 4: Schematic layout of a constructed wetland with horizontal subsurface flow, 1: inflow distribution zone filled with large stones;
2: impermeable layer; 3: filtration material; 4: vegetation; 5: water level in the bed; 6: outflow collection zone; 7: drainage pipe; 8: outflow
structure with water level adjustment. Used from Vymazal. (2010) with permission

282
However, in common water bodies, P can exist in various
structures as detailed by Jyothi et al. (2012).
AWBs have many advantages: this technique can keep
surface water from eutrophication, attributable to the
creation of cleaner effluents, a decrease of P contamination
brought about by mining exercises. In addition, the reuse of
the farming squanders to control PO4
3–
contamination gives
a feasible choice to decrease squanders with minimal effort
and environmental friendly way (Ismail 2012; Eljamal et al.
2013). This likewise fits well with one of the 12 standards
of Green Technology, for example, the ‘utilization of
sustainable assets’ (Srivastava and Goyal 2010) where the
expense of water treatment will be diminished (Liu et al.
2012; Peng et al. 2012). Therefore, this treatment ought to
be considered as a promising green innovation.
Factors influencing phosphorus biosorption
Different factors have been reported to affect phosphorus
removal by AWBs, including pH, temperature, initial
phosphorus concentration, AWBs Dosage (Zhang et al.
2011; Ismail 2012), interfering anions, and contact time
(Eljamal et al. 2013)
Applications of AWBs as a green technology for the
remediation of eutrophication
Phosphorus adsorption performance by unmodified AWBs
Natural AWBs and their reported adsorption capacities for
PO4
3–
are sugarcane bagasse, coir pith, eggshell, wood,
Orange peel, soybean milk residues, etc. (Paredes-López
and Alpuche-Solís 1991; El-Sheekh et al. 2009).
Phosphorus adsorption performance by modified AWBs
The vast majority of unmodified AWBs are wasteful in
disinfecting P from water and wastewater. The reason
should be the absence of anion restricting locales on the
AWBs surface. Therefore, to enhance the partiality of
AWBs towards P, AWBs should be cationised (Mallampati
and Valiyaveettil 2013). This should be possible by means
of metal stacking, hybridizing with synthetic inorganic
compounds, and joining with ammonium-type synthetic
compounds (Han et al. 2005). Among these techniques,
metal stacking has all the earmarks of being straightforward
and successful. It was found that metal oxides (for example,
Fe, Al, and Mn) with some minimal effort materials,
assumed imperative jobs in their PO4
3–
maintenance ability
(Liu et al. 2012).
Phosphorus removal innovative technologies and their
applications
The economical wastewater treatment advancements include:
1) Incorporated (multi-stage) developed wetlands and
phosphorus evacuation channel frameworks.
2) Phosphorus expulsion and sequestration channels for
the point contamination sources.
3) Straightforward ‘torpedo’ channel frameworks
for farming tile deplete and urban tempest water
surges (for catching and treating phosphorus
and solids contamination starting from non-point,
diffuse contamination sources). These treatment
advancements are productive for phosphorus
bioremediation along with the decrease of other
different contaminations, including various metals
and minerals. In addition, the phosphorus held by the
filtration material can be reused by synthetic manure,
to upgrade soils utilised for horticulture and the ranger
service (Drizo 2011).
The other two technologies are designated for
phosphorus removal from point pollution sources and for
phosphorus removal from agricultural effluents (USDA
NRCS 2008), as well as urban drain outflows (Drizo et
al. 2011). Thus, not only should we continue research,
development, and implementation of phosphorus removal
technologies, but also we have to discover the ways of
phosphorus reuse (Le Corre et al. 2009).
Phyto-remediation
Phyto-remediation includes many procedures that utilise
plants to evacuate natural/inorganic contaminants in
groundwater, surface water, and soil. Plants can be used
for this procedure, which involves enhanced rhizosphere
biodegradation, water-fuelled control, phyto-debasement,
and phyto-volatilisation in defiled regions and wastewater.
It utilises a collection of plant frameworks to help in site
remediation (Sengupta and Dalwani 2008). There are six
basic types of phyto-remediation techniques (Miller 1996):
1) Phyto-sequestration or phyto-stabilisation: using
plants to reduce the mobility and migration potential of
contaminants in soil.
2) Rhizo-degradation: a water remediation technique
involving the uptake of contaminants by plant roots.
It involves the stimulation of rhizosphere bacteria by
exudates from plants to enhance the biodegradation of
soil contaminants.
3) Phyto-hydraulic degradation: the use of deep-rooted
plants to degrade groundwater contaminants that come
into contact with their roots.
4) Phyto-extraction or phyto-accumulation: plants take up
or hyperaccumulate contaminants through their roots
and store them in the tissues of their stems or leaves.
5) Phyto-volatilisation: plants take up volatile compounds
through their roots, and transpire the same
compounds, or their metabolites, through the leaves,
thereby releasing them into the atmosphere.
6) Phyto-degradation: applicable to both soil and water,
involving the degradation of contaminants through
plant metabolism. Contaminants are taken up into
the plant tissues where they are metabolised, or
biotransformed.
Why the use of phyto-remediation?
Phyto-remediation is vastly known by the general
population as the ‘green solution’ to our ecological issues
in contrast to other therapeutic strategies (Sengupta and
Dalwani 2008). An advantage of using plants is that they
control 80% of the vitality in many biological communities
and need not compete for other nutritional sources because
(1) the photosystem is ready to make nicotinamide adenine
dinucleotide phosphate (NADPH); (2) CO2 is diminished
and this results in huge green biomass; and, (3) poisonous
metal particles are diminished.

Plants are able to facilitate remediation processes at a
large scale through their broad root frameworks, through
which they:
• acquire 16 metals for typical development;
• bioaccumulate toxic metals;
• debase dangerous natural, synthetic compounds; and,
• aid bacterial remediation strategies through
phyto-remediation.
Phyto-remediation does not have a damaging effect on
soil health and structure. In fact, plant growth is going to
improve the general state of the soil, despite the level of
contaminants in the soil. Phyto-remediation can also be
utilised in situ to remediate shallow soil and groundwater,
as well as surface water.
In any application, phyto-remediation is low-cost, however
the true expense of its routine use remain unknown.
Aquatic plants
The ability of Eichhornia crassipes (water hyacinth) for
phyto-remediation of various toxic substances has been
established (Xia and Ma 2006; Mishra et al. 2007; Mishra
and Tripathi 2009). It represents its ability to remove
approximately 60–80% nitrogen (Fox et al. 2008) and
approximately 69% potassium from water (Zhou et al. 2007).
Duckweeds
Duckweeds (Figure 5) expel supplements from their
condition. Therefore, it is collected to clear nitrogen
and phosphorus. Nevertheless, the use of duckweed in
recuperation and evacuation of the nutrient supplements
was seen to be constrained by numerous elements (Cheng
et al. 2002). Plants with solid resilience for poisons can
relieve or fix water toxins through adsorption, assimilation,
amassing and debasement (Gagnon et al. 2012).
Duckweed was used to remove supplements in eutrophic
water as a result of its ability to function in overabundant
supplement conditions and to its brisk improvement
(Li et al. 2009) with the goal that these supplements
can be removed by collecting the duckweeds (Li et al.
2007) while eutrophic water can be re-established by
combining diverse innovations. Lemna minor is sensible
for the phyto-remediation of eutrophic waters (Ansari
and Khan 2008). Various numerical models have been
made for duckweed frameworks to portray its applications
(Frédéric et al. 2006) with diverse duckweed development
parameters (Lasfar et al. 2007).
The financial value of duckweeds
The economic values and the utilizations of duckweeds
have been outlined via Landesman et al. (2010) as follows:
1) It can substitute soybean dinner for various animals.
2) It has a protein similar to higher plants’ proteins.
3) Dried duckweed can give beta-carotene in
domesticated animals abstained from food, thus
reducing expenses.
4) Dried duckweed can be utilised in biofuel generation.
Macrophytes
Macrophytes, for example water hyacinth (Eichhornia
crassipes) and water lettuce (Pistia stratiotes), have been
utilised for updating emanating quality (Zimmels et al.
2008). Whorl-leaf watermilfoil (Myriophyllu mverticillatum),
pondweed (Potamogeton sp.), regular reed (Phragmites
communis), cattail (Typha latifolia), duckweed (Lemna
gibba), and Canna indica are likewise utilised for
wastewater treatment purposes (Allam et al. 2016).
By and large, aquatic plants (Figure 6) can be
considered for in-situ surface water remediation in various
treatment frameworks, for example, inbuilt wetlands and
gliding bed frameworks (Ruan et al. 2006) or submerged
frameworks utilizing green growth (Kalin et al. 2005).
These kinds of remediation strategies work either with
aquatic plants incorporating toxins clearly into their tissues
or by extending the bacterial biodiversity in the rhizosphere
leading to an increased need for the assortment of
compound and biochemical reactions that can upgrade
cleaning (Hadad et al. 2006).
The role of higher plants in the green remediation of
the eutrophication phenomenon in aquatic water bodies
is as follows: Aquatic higher plants in eutrophicated water
bodies can expel N by direct uptake and by being a carbon
source as well as a surface substrate for microorganisms
and green growth, which additionally use N as a supple-
ment and can change N into vaporous state that is released
to the atmosphere (Babourina and Rengel 2010). Rooted
submerged higher plants transport oxygen to immersed
soils, which increments microbial nitrification, subsequently
giving NO3 to the water section.
There are factors affecting N evacuation productivity
by sea-growing plants that incorporate N. Such factors
are light, temperature, pH, season, plant collecting, and
accessibility of different nutrient supplements. These
components contrast for various plant species. There are
sure hindrances of utilizing the planted drifting bed in lake
reclamation. The issue confronting plant-based frameworks
is being touchy to supplement accessibility, contaminations
stack, and occasional changes because of the difference
Figure 5: Duckweeds; Spirodela polyrhiza (large), Wolffia arrhiza
(small) and Lemna minor (intermediate). Credit: Christian Fischer,
CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0),
via Wikimedia Commons (https://commons.wikimedia.org/wiki/
File:Wolffia-Spirodela.jpg)

284
in normal metabolic exercises (Yudianto and Yuebo 2011).
Hence, some treatment frameworks were imagined to
recreate the characteristic oceanic plants and to conquer
the inconveniences of the living plants. Water Mats, for
example, are a kind of counterfeit ocean growth with a high
surface zone that is intended to support colonization and
development of anaerobic microscopic organisms, oxygen-
consuming microorganisms, green growth, zooplankton,
and other sea-going creatures (Jiao et al. 2011). Further,
evacuation of toxins by microbes in the framework
can be upgraded by techniques such as immobilised
microorganisms (Sun et al. 2009) as well as by using
biofilm bearer (Li et al. 2010). Expanding the plant inclusion
plays an essential role in improving expulsion productivity
too (Zhao et al. 2012; Zhu et al. 2020). Additionally, the
decision of fitting plant species appeared mostly to
enhance toxin expulsion, and this appears a vital road to
investigate for advancing treatment framework proficiency
(Gagnon et al. 2012).
Overcoming the disadvantages of the living plants
Aqua mats, for example, are a kind of fake kelp with a high
surface zone that is intended to empower colonization
and development of various oceanic life forms (Xiao et
al. 2010). Further, evacuation of poisons by microscopic
organisms in the framework can be improved by
strategies such as immobilised microbes (Sun et al.
2009) and additionally by using biofilm bearer (Li et al.
2010). Increasing plant inclusion plays an imperative role
in improving expulsion productivity as well (Zhao et al.
2012). The decision of choosing the suitable plant species
appears to enhance toxin expulsion, and this appears
as a critical road to investigate for advancing treatment
framework productivity (Gagnon et al. 2012). Nevertheless,
plant-based frameworks are viewed as a minimal effort,
sunlight-/vitality based, eco-accommodating innovation
for in-situ decontamination of water, and control water
eutrophication. Therefore, more examinations ought to be
considered for enhancing these frameworks relying upon
the stream conditions and supplement accessibility (Saeed
and Sun 2012).
Simultaneous microalgae biomass production and
wastewater treatment
Microalgae compete with higher plants as amazing
supplement evacuation forms. They manifest the N and
P at approximately 10% and 1%, respectively, on a dry
weight premise. Likewise, microalgae societies can lessen
lingering groupings of these supplements to vanishingly
low dimensions and take into consideration a huge
changeability in N: P proportions, from approximately 3
to 30 N for every P, on a load premise, contingent upon
constraining supplement. At last, microalgae communities
have been proposed for a few years as a strategy for the
uptake of CO2 and generation of biofuels, thus a way for
ozone-depleting substance relief (Benemann et al. 1978;
El-Sheekh et al. 2020).
The coordination of the evacuation of the green growth
biomass in an eutrophic water body gives prompt natural
enhancement by tending to both the reason for the green
growth sprout and its consequences. Green growth
collection will likewise constrain the development of the
heterotrophic microscopic organisms that are the immediate
reason for hypoxia (Kuo 2010). Ordinary green growth
reaping strategies incorporate trawling with tiny fishnets and
voyaging screens. Gröndahl (2009) reported a pilot-scale
experiment to collect cyanobacteria in the Baltic Sea.
Microalgae lakes have been used for a very long
while for the treatment of metropolitan wastes and other
Figure 6: Examples of the types of plants identified in the different stages of eutrophication in short-retention-time Rivers. (a) Tall submerged
plants: Callitriche stagnalis and Fontonalis antipyretica (b) Floating plants: Nymphoides peltata (c) Emergent plants (mixed with tall
submerged plants): Sparganium emersum (d) Filamentous algae (Hilton et al. 2006, with permission)

wastewaters, with the microalgae giving oxygen to the
bacterial decay of the natural squanders. High-rate lakes,
with channels and mechanical blend, were presented 50
years prior (Abdel-Raouf et al. 2012). However, high
rate lakes display higher algal cell densities, leading to
green growth expulsion, thus pointing to the necessity
for wide-scale applications. Oar wheel-blending gives a
controllable and adaptable blending routine than siphons
and permits dealing with the lake culture to advance algal
cells that will, in general, flocculate and settle (Benemann
et al. 1980). Nonetheless, it has not been conceivable to
exhibit such a ‘bioflocculation’ form with the unwavering
high quality required for algal reaping in metropolitan
wastewater treatment.
Hence, in the ebb and flow plans, high-rate lakes
are trailed by huge settling or ‘development’ lakes, and
frequently the effluents from the lakes are utilised in
the water system, groundwater revives, or comparative
applications. Microalgae wastewater treatment forms are
dependent on high rate lake innovation, and ease algal
reaping remains an research and development challenge.
One process that achieves this objective is the Partitioned
Aquaculture System (PAS) (Brune et al. 2001).
The expulsion of leftover supplements from wastewaters,
supposed ‘tertiary treatment,’ explicitly N and P, has
additionally been concentrated with an assortment of
procedures, from connecting algal communities to control
algal culture in cooling repositories (Kotasthane 2017).
Integrated green algal technology for eutrophic
wastewater bioremediation and biofuel production
The main calculated improvement of this thought was
achieved by Oswald and Golueke (1960). It was based on
the green growth development, where the biomass was
gathered by an essential flocculation-settling step, and the
concentrated green growth mass anaerobically was handled
to make biogas (methane and CO2). The biogas would be
used to deliver control and the piped gas CO2, nearby the
supplements in the gushing, is used to grow increasingly
the algal development. The make-up water and nutrients’
enhancements (e.g. C, N and P) would be given from
wastewaters. Moreover, by removing nitrogen and carbon
from water, microalgae can help decline eutrophication in the
maritime condition (El-Sheekh et al. 2019).
A starter building cost investigation proposed control
age costs like those foreseen for atomic vitality. A more
point-by-point contemplating level of the layout of this
thought was achieved by Benemann et al. (1978), who
expressed that with ideal suspicions (minimal effort of
collection, high productivities), such systems could convey
biogas seriously with anticipated oil-based good expenses.
As a major aspect of this exertion, a few rather increasingly
point-by-point building plans and cost investigation
brainstorming were completed amid the 1980s (Benemann
et al. 1982), again with numerous positive presumptions,
specifically high productivities. Right now, algae have
additionally gotten a colossal measure of consideration
as an option for biofuel feedstock because of their high
photosynthetic and development rate than any of the other
earthbound plants. Algae collected in wastewater can likewise
be utilised for the generation of high-vitality fuel fills and mixes,
for example, acetone, butanol, and ethanol (ABE).
A few algae, for example, Botryococcus braunni,
Chaetoceros calcitrans, a few types of Chlorella,
Isochrysis galbana, Nannochloropsis, Schizochytrium
limacinum, Scenedesmus sp. have been examined as a
potential wellspring of biofuel (Singh and Gu 2010).
Algae can flourish in nitrogen-and phosphorus-rich
conditions found basically in many wastewaters (Pittman et
al. 2011). Algae might be bridled to evacuate, as well as
assimilate these essential supplements to return them to
the earthbound condition as rural manure. This could give a
high incentive result of green growth that is principally being
developed for biofuel (Figure 7).
Immobilised microalgae
Many microalgae have the tendency to attach to a natural
or artificial surface and grow on it. The living algal cells
are usually immobilised by natural or synthetic means. It
is prevented from moving independently from its original
location to all parts of an aqueous phase of a system, and
this process is reversible (Tampion and Tampion 1987).
In this technique, the immobilised microalgae biomass,
biological or inert, may assist the required biotechnological
benefits such as the removal of pollutants. The immobilised
microalgae are efficient in removing nitrogen, phosphorus,
and toxic metals from wastewater. Algae have additionally
been broadly examined and utilised effectively to treat an
assortment of business and modern wastewater sources
(El-Sheekh et al. 2017b). Dosnon-Olette et al. (2010)
utilised immobilised biomass of different Scenedesmus sp.
to phyto-remediate the farming fungicides dimethomorph,
pyrimethanil and herbicides. Numerous metals can be
bioremediated and biosorbed from squanders utilizing
green growth; for example, Chlorella sp. (Markou and
Georgakakis 2011; El-Sheekh et al. 2017b).
Algal–bacterial symbiosis
Wastewaters rich in nutrient supplements, when released in
regular surface waters, may result in blossoms of poisonous
green growth and cyanobacteria (Srivastava et al. 2015).
Heterotrophic microscopic organisms require carbon and
different supplements for development and are generally
utilised for the treatment of wastewater. Normally, algal–
bacterial frameworks have been widely utilised in the
treatment of supplement rich wastewaters since the 1950s.
One of the most punctual portrayals of algal–bacterial
connections in wastewater treatment was introduced
by Oswald and Gotaas (1957). Early photosynthesis
based frameworks were neither circulated air-through nor
blended. Along these lines, the treatment effectiveness
accomplished with these frameworks was of a small amount
of what could be accomplished with lakes or frameworks,
thus was developed later (Hoffmann 1998). Ramanan et
al. (2016) suggested that algal–bacterial advantageous
interaction results in sewage treatment with the trade of O2,
CO2, and NH4+ ions (Figure 8). The modes of interactions
between algae and bacteria, and their inter-relation with
the environment are represented in Figure 8. Carbon and
macro-and micronutrients seem to play a central role in
the mechanism. The mechanism involves the exchange of

286
vitamins, nitrogen, carbon, and phytohormones between
algae and bacteria (Ramanan et al. 2016). Amin et al. (2015)
proved that both algae and bacteria altered their metabolism
to suit each other’s needs, and this interaction is potentially
very prevalent in the marine ecosystem. They concluded
that Indole Acetic Acid (IAA) was transferred to algae in
exchange for organosulfur compounds by Sulfitobacter.
The algal-bacterial symbiosis is of great importance to the
environmental green technology. Praveen and Loh (2015)
stated that algae produce photosynthetic oxygen that could
be used for algae–bacteria-based wastewater treatment.
Algae and bacteria combination/symbiosis proved to be
important in bioremediation of toxic chemicals and metals
(El-Sheekh et al. 2020). Figure 8 shows that parasitic
bacteria are known to help in the revival of HAB infested
freshwater and marine environments (Ramanan et al. 2016).
Nanomaterial-based innovation
Nanomaterial-based innovation is one of the quickest
developing and intriguing fields concerning the 21st
Century (Fryxell and Cao 2007). Nanomaterials are
regularly characterised as a material or a structure at a
size of less than 100 nanometres. Nanomaterials are
Figure 7: Schematics of an integrated algal culture system for bioremediation and biofuel production, Sivakumar et al. (2012) with
permission
Figure 8: The algal–bacterial association in aquatic ecosystem and some proven mechanisms, adapted from Ramanan et al. (2016) with
permission

delegated zero-dimensional (for example, quantum
specks), one-dimensional (e.g. nano-wires and nano-films),
two-dimensional (e.g. nano-bars and nano-cylinders),
and three-dimensional, (e.g. nanocubes). Nanomaterial
indicates exceptional wonders, for example, volumetric
impact, quantum-estimate impact, and naturally visible
quantum passage and dielectric restriction impacts
(El-Sheekh and El-Kassas 2016; El-Sheekh et al. 2019).
To maintain support for any society is to ensure the
wellbeing of human life and sustain nature’s resources
for the present and future. These nanomaterial impacts
offer upgraded basic, attractive, electrical, and optical
properties, adding to the extraordinary potential to trade
existing materials for society welfare (Roco et al. 2011).
The implementation of the green process requires an
assessment of the ecological weight in polluted zones
by using resource data, compound substance use, and
imperativeness use to determine the ideal degree from
every zone and the treatment procedures required for
remediation (Pokhodenko and Pavlishchuk 2002).
Nanomaterials are assuming a vital role in the green
process by building material substitution, vitality utilisation
decrease, source sparing and maintainable advancement,
and by diminishing squanders and the utilization of
non-inexhaustible common assets, as well as tidying up
existing contamination (Masciangioli and Zhang 2003).
On the other hand, green nanotechnology has been
proposed as the enhancement of clean advancements, to
confine potential normal and human prosperity threats related
to the make and use of nanomaterials, and to supplant
existing materials with nanomaterials that are increasingly
economical. Nanomaterials can be manufactured with explicit
properties that can identify specific contamination inside a
blend. The small size of nanomaterials, together with their
high surface-to-volume proportion, can prompt an extremely
delicate location. These properties are accurate checking
gadgets for exact and delicate contamination. Nanomaterials
can likewise be built to effectively cooperate with a toxin and
deteriorate it to less-lethal intermediates (El-Sheekh and
El-Kassas 2014, 2016).
Phosphorus is one essential non-point source of eutrophi-
cation. Lignocellulose-based anion evacuation media (LAM)
have been created in a relationship with iron nano-covering
innovation as a method for phosphorus adsorption from
tainted water. The press-covered lignocelluloses pellets have
been demonstrated as a proficient adsorbent for phosphorus
expulsion from contaminated water (Kim et al. 2006).
Shockingly, naturally orchestrated nanoparticles were
used for the bioremediation of eutrophic wastewater.
Wang et al. (2014) used the leaf concentrates of green
tea and Eucalyptus autonomously to synthesise iron
nanoparticles (Fe-NPs) and used it for the ejection of
nitrate from wastewater. This application demonstrated the
high ejection efficiency of the green orchestrated Fe-NPs
and that it showed steady results, thus, offering a potential
management option for nitrate remediation.
Economic importance of harmful algal blooms
Harmful algal blooms (HABs) represent a natural
phenomenon occurring by a massive growth of
phytoplankton, such as cyanobacteria, dinoflagellates, and
diatoms in waterbodies. The blooms affect the environment,
human health, and aquatic life due to the production of
different toxins in both marine and freshwater ecosystems
(El-Sheekh et al. 2019). Many bloom episodes (HABs) have
significant impacts on socio-economic systems. Some of
the economic importance of (HABs) is the fish mortality and
the illnesses caused by the consumption of contaminated
seafood. According to the technical report of Sanseverino et
al. (2016), the economic loss of the HABs are categorised
into 1) human health impacts; 2) fishery impacts; 3) tourism
and recreation impacts; 4) monitoring and management
costs. Figure 2 summarises the economic importance of
algal bloom and its relations to climate and environmental
factors. The released toxins during (HABs) affect the humans
through consumption of contaminated seafood, inhalation via
aerosols or wind-dispersed particles of dried algal material,
ingestion of water or scum, and direct contact with skin or
conjunctiva. The toxins cause amnesic shellfish poisoning,
paralytic shellfish poisoning, diarrhetic shellfish poisoning,
neurotoxic shellfish poisoning, and ciguatera fish poisoning.
Harmful algal blooms (HABs) also affect fish production.
The released toxins from algae during (HABs) may find its
route to the fishes. In addition, algae proliferation may cause
oxygen depletion in water bodies leading to fish mortality.
The mortality of fishes may increase the prices of fishes,
and this represents an economic impact of HABs in the
commercial fisheries field. For example, Pretty et al. (2003)
recorded a loss of approximately £29 000 to £118 000
annually in the United Kingdom, due to HABs in freshwater.
The changes in the waterbodies environment induced by
algae bloom affect the tourism and recreation economy.
These changes include the discoloration of the water, the
accumulation of dead fish on beaches, and the smell coming
from algae decomposition. The study by Dodds et al. (2009)
recorded an economic loss in the tourism/recreation sector
due to eutrophication of freshwater estimated at $1.16 billion
annual value loss in the United States of America. The
economic effects of HABs on monitoring and management
programs include costs for water sampling to assess the
presence of toxins and the test on shellfish products in
order to prohibit their placing on the market in case of
contamination. In addition, the expenses for water treatment
required to remove toxins from the public water supply,
costs of actions to remove odour compounds associated
with blooms, or to identify the factors causing blooms and
expenses of actions to destroy HABs during the blooming
process (Anderson 2009).
Conclusion
Eutrophication is becoming a severe problem worldwide,
resulting from the great amount of anthropogenic
nutrients entering the aquatic habitats through numerous
land runoffs distributed mainly along the rivers and sea
regions and coasts. These nutrients and other pollutants
cause abnormally intensive phytoplankton blooms, which
lead to the deterioration of the waters and consequently
affect the biota and human health. In addition, alterations
in the dynamics of the plankton community, species
composition, and dominance occur as a result of

288
eutrophication. Therefore, it is suggested to solve the
problem of eutrophication in the aquatic habitats through
green technology, depending upon remediating wastewater
before discharge by the removal of phosphorus using
agricultural by-products from water and wastewater. The
green technology phyto-remediation is a cost-effective and
environmentally friendly method used to remove excess
contaminants in groundwater, surface water and soil.
ORCIDs
Mostafa El-Sheekh: https://orcid.org/0000-0002-2298-6312
Mohamed M Abdel-Daim: https://orcid.org/0000-0002-4341-2713
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Manuscript received: 14 May 2020, revised: 2 December 2020, accepted: 4 December 2020
Associate Editors: J Taylor and N Rivers-Moore

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