Innovative restoration for eutrophic drinking water sources:
approaches, application and evaluation
Chen Lan *
School of Management Science and Engineering, Guizhou University of
Finance and Economics, Guiyang 550025, China;
*Correspondence: lanchen@mail.gufe.edu.cn (C.L.)
Abstract: Drinking water sources have higher water quality
requirements because of their special uses. Many drinking water sources
in the world have been polluted or are being polluted for a long time,
resulting in eutrophication. We define the approaches that have been
developed in the last 10 years and achieved good effect as innovative
restoration approaches. In this paper, the traditional, and frequently
used restoration approaches in recent 30 years were briefly reviewed,
and the innovative technologies and methods were summarized and
evaluated in detail. In light of the impact of COVID-19, we have also
put forward rational suggestions on water quality restoration of
transboundary rivers to provide scientific reference for global public
health safety and protection.
Keywords: eutrophication, drinking water sources, COVID-19,
transboundary water, public health
1. Introduction
Drinking water sources refers to the water area and the related land
area with a certain water supply scale, including rivers, lakes and
reservoirs, which can provide water for urban residents and public
services. Surface water and groundwater are usually regarded as the raw
water supply sources for drinking water (Katsanou & Karapanagioti
2017). According to the different geographical and hydrological
conditions, different countries or regions will decide to obtain water
resources from different raw water supply sources (Stuyfzand & Raat
2010; Gaget et al. 2017; Gao et al. 2018; Bexfieldet al. 2019; Carrard et al. 2019; Li et al. 2019).
Considering development difficulty, technical difficulty and investment
cost, the surface water sources, include rivers, lakes and reservoirs,
which can be found in many places of the earth, was chosen for
development and utilization of water resources in lots of regions (Tanget al. 2014; Skariyachan et al. 2015; Duan et al.2017; Li et al. 2018). However, many of these water sources
around the world are eutrophic due to ongoing damage or serious
pollution in the past (Mehner et al. 2008; Conley et al.2009). Eutrophication will lead to significant deterioration of water
quality, and the content of toxic gas of hydrogen sulfide and harmful
heavy metals exceeds the standard (Chen et al. 2015; Huseret al. 2016; Sinha et al. 2017; Sojka et al. 2018).
Moreover, a large number of reducing compounds appears due to the water
hypoxia caused by eutrophication, with the combined effects of hydrogen
sulfide, will cause color, smell and taste problems in water quality,
which increasing the cost of water treatment (Bierlein et al.2017; Geerdink et al. 2017; Vinçon-Leite & Casenave 2019). The
removal of reducing compounds will also increase the dosage of oxidants
in drinking water treatment equipment, such as liquid chlorine.
Excessive oxidant consumption can form disinfection by-products, causing
secondary pollution and affecting human health (Zhai et al.2017). The restoration of eutrophic drinking water sources is urgent
extremely. So far, a variety of restoration approaches targeting
drinking water sources were developed, presenting varying implement
difficulty and restoration effectiveness (Erftemeijer & Lewis III 2006;
Vickie & John 2006; Bormans et al. 2016; Sillanpaa et al.2018; Preece et al. 2019; Parde et al. 2021). In terms of
time, comparing to the approaches that have been existed for more than
half a century approximately, some approaches are relatively new and
have only been developed and applied in recent decades.
The aims and significance of this review were as follows: (1) to
distinguish old approaches from new approaches better and lay a good
foundation for the improvement or optimization of approaches
subsequently; (2) to understand the dynamics information of lake
restoration; (3) to minimize the time spent researching lake restoration
techniques or methods; and (4) to avoid repetitive work and improve the
significance and value of research. This paper made a brief review of
the traditional and frequently used restoration approaches, summarizing
the innovative technologies and methods of drinking water source
restoration in detail, and giving a more focused evaluation on the
innovative restoration.
2. Materials and Methods
Based on the investigation of the published literatures in the past, we
obtain the information about this study to analyze and comb the research
content of innovation restoration comprehensively. The research in this
paper was carried out based on Web of Science and Google Scholar. All
databases included in these two retrieval platforms are searched. We
conducted a comprehensive literatures search on these two platforms and
found almost all literatures about the restoration approaches of
eutrophic drinking water sources. Of course, the literatures we search
and filter must be published in English. These related papers are
classified as the screening papers of this study. All relevant
literatures were screened and selected by the authors independently to
assess their relevance to the purpose of the review. A large number of
articles found in the search progress were filtered to exclude the
literatures which were not suitable for the purpose of the review. Among
the selected qualified papers, we summarized the traditional and
innovative restoration techniques or methods. We defined innovative
restoration approaches as those which do not belong to traditional
restoration approaches, and have appeared in the recent 10 years.
3. Results and Discussion
3.1 Traditional approaches with high application frequency
Traditional approaches are a kind of pollution control techniques or
methods for direct treatment of sediment pollution sources. A large
number of studies have shown that after controlling the input of
exogenous phosphorus effectively, the release of endogenous phosphorus
can still maintain the eutrophication state of water body for a long
time, and even directly lead to sudden water quality deterioration
events such as blue algae outbreak (Heisler et al. 2008; Watsonet al. 2016). When the exogenous input was gradually controlled,
the release of endogenous phosphorus accelerated the eutrophication
process of the lake (Wang et al. 2019; Zhan et al. 2019).
How to effectively control endogenous pollution of sediment is the key
to eutrophication management. According to the different principles,
traditional restoration can be divided into physical restoration,
biological restoration and physicochemical restoration. Among the three
categories, the most frequently used technologies include sediment
removal, reoxygenation, hypolimnetic withdrawal, phytoremediation and in
situ passivation.
3.1.1 Physical restoration
Sediment removal mainly uses engineering measures to eliminate sediment
pollution. This method can directly remove the polluted sediment out of
the system. The typical engineering technology adopted is environmental
dredging. Environmental dredging is the interdisciplinary engineering
technology of dredging engineering and environmental engineering which
originating from Japan and western (Pequegnat 1975; Terashima et
al. 1991). In 1969, the first lake dredging project aimed at improving
the water environment was carried out in lake Suwa in Japan (K et
al. 1995). So far, many lakes or reservoirs in the world have been
carried out the dredging restoration (Erftemeijer & Lewis III 2006;
Patmont & Palermo 2007; Bridges et al. 2010; Fox & Trefry 2018;
Chen et al. 2020a).
Reoxygenation technology began with the reoxygenation system developed
by Mercier et al. in 1949 (Mercier & Perret 1949). Its principle is to
complete the water reoxygenation of lake by pumping the hypoxic water
from the lake bottom to the lake surface. In 1973, Fast et al. used the
side flow pump to pump the hypoxic water in deep water to the oxygen
output pipe on the shore for reoxygenation, which was one of the
earliest reported application cases of hypolimnetic oxygenation
engineering in the world (Fast et al. 1975). In the following
years, experts continued to study the technology of hypolimnion
reoxygenation and optimize the reoxygenation method (Speece et
al. 1971; Whipple et al. 1975). Up to now, reoxygenation has
been successfully used to restore water environment in many lakes in the
world (Vickie & John 2006; Choi & Ahn 2014; Lan et al. 2017;
Preece et al. 2019; Lan et al. 2021).
Hypolimnetic withdrawal is a technique for extracting rich nutrients and
reducing substances from the water body in lower lake during the
stratified period of eutrophic lakes to reduce the load inside the lake
(Bormans et al. 2016). It has been more than 60 years since the
method was first used (Dunalska et al. 2007). Hypolimnetic
withdrawal could be useful in improving water quality (Nürnberg 1987,
2007; Dunalska et al. 2014). Moreover, it is most useful for
stratified lakes with high nutrient content in the hypolimnion (Nürnberg
2019).
3.1.2 Biological restoration
Phytoremediation method is to use large submerged plants to degrade
sediment pollutants and eliminate or reduce the toxicity of pollutants
(Melzer 1999; Park et al. 2016). Transplanting submerged plants
can absorb nitrogen and phosphorus from sediment into the plants and
reduce the release flux of phosphorus at sediment-water interface. In
recent decades, there have been many cases of using phytoremediation to
restore water environment of lakes (Knopik & Newman 2018; Wang et
al. 2020c; Li et al. 2021).
3.1.3 Physicochemical restoration
The principle of in situ passivation technology is to use chemical
reagents and physical covering to fix the pollutants in the sediment in
situ. The pollutants in the sediment will be adsorbed, passivated or
even prevented from being released into the overlying water. This
physicochemical technology has been applied to endogenous remediation of
sediment abroad since 1970s (Cooke & Kennedy 1978). In situ passivation
has been successfully applied in many lakes abroad, and has attracted
more and more attention now (Rydin & Welch 1998; Malecki‐Brown et
al. 2009; Yang et al. 2020b).
3.2 Innovative restoration techniques or methods
The approaches that have been developed in the last 10 years, and
achieved good effect are defined as innovative restoration approaches. A
summary of studies involving the innovative restoration for eutrophic
water is present in Table 1.
3.2.1 Comprehensive approach
This comprehensive approach is achieved by a combination of biological,
chemical and technical methods(Grochowska 2020). The approach is
performed in five main steps based on the current status of the lake:
(1) Firstly, the introduced water is purified by hydrophilic plants
(Glyceria maxima, Phalaris arundinacea and Phragmites australis )
and sorption material (expanded clay) for deeply treatment. (2) The
second step, as the most important step, is that according to the
current load of the lake, the polluted water flowing into the lake must
be piped into the bottom to ensure that there is no external negative
interference to maintain good water quality; (3) Then, in the phosphorus
inactivation method, mainly iron and aluminum coagulants are used to
permanently lock phosphorus in the sediment; (4) After a long period of
passivation, anti-cyanobacterial preparation will be introduced into the
bottom zone. Following the previous step; (5) microbiological probiotic
preparation will be added to the same zone to enhance the effect. The
earliest successful case of this approach appeared in Poland (Lake
Miłkowskie) in 2018 (Grochowska 2020). In this case, the restoration
reduced the excess nutrients in the lake and controlled the growth of
phytoplankton.
3.2.2 Combined biomanipulation (CB)
The concept of traditional biomanipulation was first proposed in 1975
(Shapiro 1975). Biomanipulation refers to the management of aquatic
communities that control natural populations of organisms for the
purpose of improving water quality (Kasprzak et al. 2002; Mehneret al. 2002; Jeppesen et al. 2007). CB accomplished by
combining 4 methods, including creating submerged plant, fish,
macrobenthos, and zooplankton communities. Prior to this combined
approach, most of the biomanipulations (such as fish biomanipulation,
zooplankton biomanipulation, planting of submerged macrophytes,
constructing ecological floating beds and effective microorganisms) were
often applied independently to the specific water bodies in which they
were good at purifying (Zeng et al. 2017; Liu et al. 2018;
Bi et al. 2019). In the case of lakes with complex pollution
situation, an independent method or a combination of fewer methods is
often difficult to achieve the expected restoration goals. In this
context, a combination of four biomanipulations were proposed. In 2018,
CB was carried out in lake Dongpo in China. The results show that the
implementation effect is good. The transparency of water has been
improved, while the contents of total phosphorus, total nitrogen and
chlorophyll-a have been reduced.
3.2.3 Ecohydrological restoration approach
The urban rivers, artificial lakes and watercourses, which often been
regarded and used as landscape, are a kind of small ecosystems. They are
usually formed naturally or constructed artificially, which can give
people a sense of beauty. This type of water body is mainly shallow
water systems (there are also exist deep water systems in the karst
areas (Lan et al. 2021)). The ecohydrological restoration
approach improves inflowing water by constructing hybrid systems and
sequential sedimentation-biofiltration systems (SSBS). Simultaneously, a
variety of biological methods including the development of
landform-adjusted shoreline vegetation, the construction of floating
islands and the regulation of the biological structure of the eco-system
were used to improve water quality and maintain the effectiveness
(Jurczak et al. 2019a). The results showed that most of the water
quality indexes were improved. The nutrient concentration was still
lower than before. Moreover, the control of microcystins and
chlorophyll-a was also improved.
3.2.4 Geoengineering approach
Oxygen nanobubbles is a kind of water quality restoration approach with
high stability and mass transfer efficiency. The principle is that the
porous natural mineral zeolite is used to prepare oxygen-carrying
materials, which adsorb oxygen based on the huge specific surface area
and rich internal pore cavity of the oxygen-carrying materials, and
transport the zeolite to the sediment surface by natural sedimentation
to achieve efficient oxygen-increasing of sediment-water interface. This
method has been widely used in groundwater remediation, surface water
remediation and refractory wastewater treatment (Khuntia et al.2012; Li et al. 2014; Temesgen et al. 2017). It has been
applied to long-term anaerobic remediation of lake sediment-water
interface in recent years (Shi et al. 2018; Zhang et al.2018; Yu et al. 2019; Wang et al. 2020a; Zhang et
al. 2020).
3.2.5 Green energy artificial floating island (GAFI)
Artificial floating island (AFI) are variations of wetlands, aquatic or
terrestrial plants, growing in a hydroponic manner with buoyant frames
floating on the surface of water bodies (Chang et al. 2017).
AFI are divided into three categories, including traditional plant
floating island technology, complex floating island technology and
moveable floating island-wetland technology. The three artificial
floating island technologies are gradually upgraded and perfected in
terms of technical complexity and application scope. Traditional plant
floating island technology consists of polymer material carrier and
aquatic plants. Based on the former, complex floating island technology
replaces polymer material carrier with more advanced fixed biofilms or
biocords. Moveable floating island-wetland technology makes AFI movable
and adding wetland to improve water quality (Chang et al. 2017).
GAFI was combined the advantageous components for AFI with an aerator
device powered by a solar system. In 2012, this technology was
implemented in the lake Lize, China, for the first time and achieved
good restoration effect (Lu et al. 2015). Compared with the
traditional artificial floating island technology, it can quickly
improve the water quality in a short period of time and reduce the
nitrogen content of the water body. Subsequently, some cases about the
application of this technology were published (Chang et al.2014a; Chang et al. 2014b; Chang et al. 2014c; Chenet al. 2014; Yeh et al. 2015).
3.2.6 Improved effective microorganism (IEM)
Microbial biotechnology is the most recent approach to waste water
treatment (Mielczarek et al. 2013). Effective microorganism (EM)
method is one of the restoration methods proposed in recent years. It
was primarily proposed by Dr. Teruo Higa in Japan (Higa & Parr 1994).
The microorganisms of EM aiming at the inhibition of harmful bacteria
through competitive exclusion (Dondajewska et al. 2019b). In
recent decades, many cases of EM implementation have been reported
(Szymanski & Patterson 2003; Zakaria et al. 2010; Shalaby 2011;
Sitarek et al. 2017). In 2015, an method was named as IEM was
developed to restore water quality in a wetland in Republic of Korea
(Park et al. 2016). The principle of the improved method is to
mix 450 g loess, 25 mL of EM solution, 25 g EM bokashi mixture to
produce EM soil balls in weight of 500 g. After soil balls producing,
they were incubated for 6 days for microbial growth. In order to
improving the hardness of the soil balls carrier, calcium oxide, silicon
dioxide and citrate buffer (for pH controlling) were added in a certain
proportion to the soil ball-making process. The result of the case
showed that the modified soil balls effectively improved the water
quality of the ponds, the lakes, and the streams.
3.2.7 Sustainable approach
Sustainable approach is a restoration approach based on the concept of
nature-based. The implementation effect of traditional restoration
methods is temporary or expensive. This approach is a new method to
restore the polluted water quality of lake by using the internal
restoration mechanism of the ecosystem itself. The application of this
approach can gradually restore or reconstruct the ecosystem without
intense and expensive human intervention. The sustainable approach was
implemented in lake Uzarzewskie, Poland in 2008. In this case, a
combination of physical, chemical and biological methods was used to
improve the water quality.
The physical method mainly uses hypolimnion aeration, the chemical
method mainly uses compounds with phosphorus prediction, and the
biological method mainly uses biomanipulation which based on fry
stocking. In addition, the water with high nitrate concentration is
introduced to the bottom of the anoxic lake. After 10 years of
continuous monitoring, the results showed that the total biomass
decreased, as well as chlorophyll-a. The water transparency increased
significantly to an average of 2 m. Cyanobacteria were replaced bydiatoms , dinoflagellates and chrysophytes .
3.2.8 Large-scale constructed wetland (LCW)
Constructed wetland (CW) is a comprehensive ecosystem constructed and
controlled by man-made operation. It uses the triple synergy of physics
and biology to purify the polluted water body. CW has been widely used
to treat various types of wastewater for a long time, such as textile
waste, dairy waste, industrial waste, piggery waste, tannery waste,
petrochemical waste, municipal waste, etc (Calheiros et al. 2007;
Saeed et al. 2019; Parde et al. 2021). It was also
reported that CW are used in flood control, habitat for wildlife and
recreational space (Brouwer & Bateman 2005; Janssen et al. 2005;
Davis et al. 2008). Some studies in recent years have shown that
LCW can also be used to improve lake water quality of eutrophication
(Dunne et al. 2012; Dunne et al. 2013; Martín et
al. 2013). However, judging from the results of our investigation,
there are not many published cases. In 2003, the earliest case of LCW
used to treat the water quality of eutrophic lake appeared in the lake
Apopka, USA (Dunne et al. 2012). Waterflows passed through the
marsh flow-way by gravity in this system of the case, entered each of
the four independently operated cells via gated culverts, and was
purified finally.
3.3 Evaluation of the innovative restoration techniques
In this section, we first classify the above eight innovative
technologies into combined implementation type and independent
implementation type according to the principles. The classification
standard here is mainly based on whether the principle of this approach
involves three or more of the physical, chemical, biological,
physicochemical, biochemical, eco-hydrological, etc. The principle
covered one or at most two categories that we define them as independent
implementation type, otherwise as combined implementation type. Then,
every innovation approach in each category is evaluated in Table 2.
3.3.1 Combined implementation type
Comprehensive approach, ecohydrological restoration approach, CB and
sustainable approach are defined as combined implementation type. In the
application process of comprehensive approach and sustainable approach,
a special kind of technical method is applied, that is, water body is
introduced to the bottom of lake through artificial pipelines. The
purpose of the same step in the two approaches is similar. The water
brought to the bottom of the lake has been purified by plants and
reduced nutrients within the comprehensive approach. It contains a lot
of oxygen and comes from the sewage treatment plant. The water do not
directly discharged to the water surface, which is conducive to control
the growth of blue algae and the oxygen supplement in bottom water body.
The oxygen-rich water replenishment to the hypolimnion, the oxygen
concentration in the lower layer of the lake increases (wind aeration is
also for this purpose), which inhibits the release of ammonium nitrogen
in the sediments and increases the content of nitrate in the sediments.
At the same time, the content of ammonium nitrogen in water was reduced
by nitrification. Within the sustainable approach, the spring water with
high concentration of nitrate was introduced to the bottom of the
hypoxic lake. Its purpose is also to increase the content of nitrate and
the redox potential at the sediment-water interface, promote
denitrification, and generate molecular nitrogen to be discharged out of
the system. Mineralizing bacteria was used mainly because of the higher
oxygen content in sediment in the coastal zone of the Miłkowskie Lake,
to accelerate the process of mineralization accumulated at the bottom of
organic matter. This method is mainly applicable to lakes with high
oxygen content in sediment. The removal of phosphorus in these two
approaches is precipitation or passivation, which is the conventional
phosphorus removal method. The two approaches are suitable for lakes
with high level of eutrophication, or the lake need to gradual
reconstruct the structure and functioning of the ecosystem without
taking too deeply intervening actions (Dondajewska et al. 2019a;
Grochowska 2020).
Planting aquatic plants has been used to improve water quality within CB
and ecohydrological restoration approach, is the traditional method of
biological manipulation.
Considering different water quality with water environment conditions
comprehensively, to further select other collocation methods. CB is
mainly suitable for the shallow lakes which has a high concentration of
nutrients even after serious reductions in the load of nutrients, and
high concentrations of algae, in particular cyanophytes. The approach
has a higher efficiency and a significant effect on water quality that
is difficult to treat, involving many principles. Thus, the ecological
risk of this approach is very low. It is very friendly to the large
lakes of drinking water sources. Ecohydrological restoration approach is
mainly applicable to shallow rivers and lakes. The sedimentation system
and filtration system in this method are used in conjunction with
plant-based biological manipulation. The approach is suitable for urban
eutrophication cascade reservoir and small urban water ecosystem. Based
on the characteristics of small cascade reservoirs, this technique is
very suitable for step-by-step restoration. Some of the urban’s rivers
with the characteristic of narrow and long, which serve as drinking
water sources, also meet the requirements of step-by-step restoration.
River landscape is an important urban infrastructure, which not only
plays a role in flood control, drainage, shipping, but also undertakes
urban tourism, leisure, beautification and other functions. Therefore,
planting plants can also beautify the three-dimensional landscape of the
city to a certain extent. Aquatic plants provide fish not only with food
but also with a habitat to live. At the same time, it can also play a
role in purifying water quality through ecological circulation. Planting
aquatic plants with different morphological characteristics and
flowering period in water meets the requirements of human for water
landscape culture.
3.3.2 Independent implementation type
Geoengineering approach, IEM, GAFI and LCW are defined as independent
implementation type.
Oxygen nanobubbles is a new method to restore eutrophic lakes by
increasing oxygen and reducing the content of phosphorus and other
nutrients in water. The most important advantage of oxygen nanobubbles
method is that it can directly oxygenate the sediment water interface.
The traditional oxygenation principle mainly includes two categories
which is breaking the thermocline, mixing the upper and lower water
bodies, and injecting air or oxygen into the hypolimnetic water bodies
of the lake. The former carries out oxygen mass transfer through the
exchange of oxygen-enriched water on the water surface and anoxic water
on the bottom of the lake, having a lower reoxygenation efficiency.
Injecting air or oxygen into the hypolimnion is an improved
reoxygenation method based on the former. The efficiency has been
greatly improved. Although the traditional reoxygenation methods having
high efficiency, no matter what kind of traditional reoxygenation
principle is selected, large engineering equipment or cost will be used,
which is very difficult for institutions with limited funds or
inconvenient field operation. Compared with other oxygenation methods,
oxygen nanobubbles method only needs to put the configured
oxygen-carrying materials into the water body directly from the water
surface, and sinking by gravity to the sediment-water interface. This
method not only greatly speeds up the contact time between oxygen and
sediment water interface, but also is very cheap from the perspective of
cost. Effective microorganism is a new compound microbial agent, which
does not contain harmful substances and does not pollute the
environment, and can be used to degrade nitrogen and phosphorus in
water. In many cases with mass flow and high flow rate (especially in
some rivers and streams), the structure of the soil balls was not stable
enough to be dispersed. By proportionally adding calcium oxide and
silicon dioxide during the producing process increased hardness of the
soil balls for four times. This is more conducive to the stable
existence of soil balls after being put into the water body. At the same
time, the flourishing eukaryotic and prokaryotic microbial communities
within the soil balls also enhance the structural stability of the soil
balls. IEM is more suitable for small and middle size water bodies.
GAFI is a method to improve the purification speed of traditional AFI by
adding a solar-powered aeration device while retaining the advantages of
traditional AFI. As AFI technology, GAFI can also provide water
purification, create living spaces for organisms, improve landscape and
protect the shore with wave elimination effects. Therefore, we believe
that GAFI can be tried to apply in lakes with large fluctuation of water
level and lakes where it is difficult to restore the shore aquatic
plants due to waves, or closed waters with landscape requirements. This
method is very suitable for water restoration with landscape occasions.
The purification efficiency of the method is very high. Aeration and
planting can increase the beautification degree of water landscape to a
certain extent. In order to restore the lost nature, the unit price of
this method is very high. An important part of the expensive unit price
is that the labor costs account for a large proportion. As long as the
carrier materials were processed, its price increasing a lot
accordingly. But the market in each country is different, resulting in
the unit price in different countries varying greatly. As similar as
GAFI, there are still many projects using CW at present. LCW has the
characteristics of large buffer capacity, good treatment effect and
simple process, and can also be used to improve the water quality of
watershed. In a few reports, this method has been used to improve the
water quality of eutrophic lakes with good effect. In particular, it
gives full play to the productive potential of resources, prevents the
re-pollution of the environment, obtains the best benefits of water
restoration, and has higher environmental benefits, economic benefits
and social benefits.
3.3.3 Comprehensive suggestions
Due to the lack of relevant information in the published literatures, we
cannot make a very accurate comparison of these eight approaches.
However, we made subjective evaluations of these technologies based on
our experience and some published data. We believe that CB,
ecohydrological restoration, geoengineering approach, IEM and the
sustainable are economic relatively. If the restoration involves
landscape water, GAFI or ecohydrological restoration approach can be
used. When the area of the target water body is relatively large that we
think it is more appropriate to choose CB or LCW. If the water body
entering the lake needs further purification and has high requirements
for nitrogen removal, comprehensive approach or sustainable approach can
be selected. If you want to have simple equipment or tools or steps in
the field that you can use the geoengineering approach or IEM method. Of
course, the above suggestions are made without considering the cost of
investment. Thus, the high and low costs mentioned in this article are
relative comparisons among these eight technologies (e.g., the
investment of these technologies are obviously cheaper compared to
dredging). The specific approach selection should be considered
comprehensively according to the cost requirements, hydrological
conditions and site conditions.
3.4 Influence of COVID-19
3.4.1 Fecal-oral transmission
Since the COVID-19 pandemic began in 2019, it has spread to more than
200 countries, infected about 370 million people and killed more than 5
million people. In addition to conventional respiratory droplet
transmission, the COVID-19 virus has now been confirmed to be
transmitted by aerosol and fecal-oral route (Anderson et al.2020; Hindson 2020; Vardoulakis et al. 2022). The COVID-19
pandemic poses a significant threat and disruption to the global public
health system.
Fecal-oral transmission refers to a way which the virus is excreted via
defecating from a patient and then eaten by people who are vulnerable to
infection through other means, leading to the spread of the disease.
SARS-CoV-2 (the virus name) in COVID-19 is more infectious than SARS-CoV
(the virus name) in SARS. The main performance is that it has more
lasting survival activity in the external environment. Stool which is
defecating into drains through toilets requires strict disinfection
procedures to prevent it from entering to the water supply.
3.4.2 Transboundary rivers
River water is an important vector of virus transmission. Moreover,
transboundary rivers pose a greater risk of transmission of the virus
than rivers within borders, because its geographical location involving
more countries. For example, In the Belt and Road Initiative, the
districts that the overland Silk Road Economic Belt passing through,
almost all belongs to China’s international river areas. The water
resources of transboundary rivers are the basis for the survival of
neighboring countries and downstream countries. In order to prevent the
spread of the virus among the neighboring countries through the flow of
water in transboundary rivers, the protection of water sources in
transboundary rivers is essential.
3.4.3 Suggestions fort transboundary water restoration
Water is key for pandemic suppression and prevention (Cooper 2020).
Since the outbreak of COVID-19 in 2019, there have been few report about
improving the water quality of transboundary rivers (Chakrabortyet al. 2021a; Chakraborty et al. 2021b). The water quality
restoration approaches of transboundary rivers during COVID-19
outbreaks, which were reported as bioremediation. This is closely
related to the hydrological characteristics and pollution of rivers. In
previous chapters, we have also outlined some rules and requirements for
the use of biological manipulation. As the lake Vembanad in India, many
of the world’s long and narrow transboundary rivers also have such
conditions. At present, we believe that when choosing restoration
approaches for water quality of transboundary rivers, biological
approaches can be chosen as far as possible, so that bacteria and
viruses can be filtered more efficiently. Of course, more time and cases
are needed to support this view. With the help of remote sensing images,
some researchers have found that after the outbreak of the epidemic, the
water quality of the severely polluted transboundary rivers have been
improved due to the long-term industrial shutdown and the reduction of
human activities (Yunus et al. 2020). This indicates that
transboundary rivers have a certain self-purification ability during the
lockdown, and also providing some new research clues for the water
quality restoration of transboundary rivers in the future. Of course,
the best approach for restoring is prevention in advance. Protection of
transboundary rivers also needs to be strengthened. Countries
(especially the neighboring upstream and downstream countries) that
transboundary rivers pass through should cooperate with each other to
build cooperation and coordination mechanism and long-term management
mechanism for water resources protection of transboundary rivers. In
general, it is also necessary to strengthen water monitoring and
establish water environment monitoring and early warning mechanism and
emergency mechanism for transboundary rivers.
4. Conclusions
Water playing an important role in people’s life, is the most important
and indispensable material resources for human survival and development.
The review of drinking water source restoration approaches (especially
innovative approaches) can strengthen the understanding of restoration
principles and theories by researchers from a macro perspective, and
save studying time greatly. The eight innovative approaches discussed in
this paper are defined as combined implementation type and independent
implementation type. They all have high efficiency for restoration, but
with various investment cost and implementation difficulty. Therefore,
we should choose the approach according to the suitable conditions of
approaches and project budget. Meanwhile, we should choose the approach
according to the suitable conditions of approaches and project budget.
Meanwhile, the outbreak and epidemic of COVID-19 pose a serious
challenge to the protection of drinking water sources around the world.
However, there are still few literatures on the association between
SARS-CoV-2 and restoration approaches, and further research in this
direction can be strengthened in the future.