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An Overview on Bioremediation Strategies for Waste Water Treatment and Environmental Sustainability

Saif Ali, Bhavtosh Sharma*, Kanchan Deoli, Deepika Saini, Mamta Bisht

Water Quality Analysis Laboratory, Uttarakhand Science Education & Research Centre (USERC), Dehradun, Uttarakhand, India

Abstract: Water resources are polluted by anthropogenic causes like domestic, agricultural waste and industrial activities. Chemical methods of treating waste water have shown great impact on lives of people as well as other microorganisms. When waste compounds are dumped into water bodies, biological reactions begin that consume oxygen as the organic matter which is broken down by the naturally occurring microorganisms. This review discusses the different methods of waste water treatment using environmental sustainable technique called Bioremediation. A waste management technique called bioremediation uses living organisms to neutralize or eliminate dangerous chemicals from contaminated environments. The environmental science of bioremediation accelerates normal biological processes in order to correct or clean up the contaminated soil and the groundwater also. Presence of heavy metals in water poses a significant ecological threat and one of the most difficult environmental concerns worldwide. An efficient and environmentally favorable approach of bioremediation for treating pollutants has been demonstrated in the paper. In-situ and ex-situ treatments are the two main categories of bioremediation in waste water. Due to its sustainability with the environment and potential cost- effectiveness, microorganism-based bioremediation has a lot of potential for future sustainable development. The mechanisms and types of bioremediation have been summarized and explained herein.

Keywords: bioremediation, wastewater treatment, sustainability, in-situ and ex-situ

Received April 12, 2023; Revised May 07, 2023; Accepted May 18, 2023

Citation: Saif Ali, Bhavtosh Sharma, Kanchan Deoli, Deepika Saini, Mamta Bisht, An Overview on Bioremediation Strategies for Waste Water Treatment and Environmental Sustainability. Applied Ecology and Environmental Sciences, 11 (2). 64-70. January 2023. doi:10.12691/aees-11-2-4

1. Introduction

Hazardous substances have accumulated more in the environment as a result of agricultural techniques, industrial production, and human lifestyle. Health and environmental concerns have significantly increased as a result, and there is an urgent need for eco-friendly solutions to address these problems simultaneously. Bioremediation has become a viable alternative to damaging chemical approaches for sustainable development. Living microbiomes are used in bioremediation to clean the environment and ensure its sustainability. Researchers have created many bioremediation procedures as science and technology have advanced, however due to the nature and type of pollutants, there is no one "silverbullet" that can be used to restore the poisoned environment. The Earth is becoming a giant rubbish dump due to our careless behaviour and ever-increasing population. This condition is getting worse due to resource extraction without consideration [1]. Additionally, it contributes significantly to climate aberrations, environmental degradation, a decline in biodiversity, disease outbreaks, and agricultural problems. To handle this scenario, the current waste management initiatives are becoming insufficient. In addition to decreasing waste output, the current situation necessitates an effective, doable, and environmentally responsible management strategy [2]. To create a clean environment without endangering the ecosystem, bioremediation is a well-known and widely approved solution.

The process of bioremediation either completely removes the pollutants or significantly lowers their concentration. The most significant contributors to this process are plants, fungi, and bacteria, which fall under the categories of phytoremediation, myco-remediation, and remediation. Additionally, myco-remediation and micro-remediation approaches involve a number of other sub-processes to improve the on-site removal of contaminants, including biological stimulation, biological augmentation, biological sparging, etc. [3]. Bio-augmentation involves introducing foreign microorganisms to an ecosystem in order to decompose pollutants, while bio-stimulation processes revitalize the local microorganisms by providing more nutrition and growth factors. On the other hand, bio-sparging uses compressed air to give oxygen and nutrients to a specific zone to promote microbial activity.

Due to globalization and increased industrialization, environmental issues are becoming a bigger challenge for man. Total dissolved solids, biological and chemical oxygen demand, and excessive alkalinity are all characteristics of industrial waste water. Heavy metals and textile industry effluents are present in the waste water. Numerous colours and auxillary chemicals are employed in order to make the highest quality products, which has led to a serious environmental hazard [4]. The treatment of wastewater is one of the most significant biotechnological procedures employed globally and is a major source of concern. In wastewater from both artificial and natural systems, microbial communities from various environments excelled in biodegrading a wide range of chemicals. Microbes can remove a variety of contaminants from various biological wastewater treatment systems [5]. It is quite advantageous to use fungus to remediate wastewater. The use of fungi in wastewater treatment results in the production of fungal biomass for animal feed and human consumption. As well as the conversion of wastewater organics into high-value prospective fungal protein and useful variety biochemicals that are extremely resistant to inhibitory substances. Heavymetals oxidation state can be transformed from one form to another by the action microbes [6].

There are several different bioremediation strategies, and many have proven successful in recovering polluted environments. We can use genetically engineered microorganisms (GEM) strategically to improve bioremediation capacity. This is because it is possible to create a designer biocatalyst that can efficiently break down a variety of pollutants, including resistant substances, by merging novel and efficient metabolic pathways, expanding the range of substrates for existing pathways, and enhancing the stability of catabolic activity [7].

2. Microorganisms for Bioremediation

Water contaminants are broken down, transformed, and absorbed using microorganism-based methods. The findings so far largely support the existence of the proper microbial functional groups in charge of eradicating particular contaminants from wastewater [8]. For in-situ surface water treatment, two microorganism-based techniques are applied effectively. Microbial dosing is used in the first approach, and biofilms are used in the second [9].

2.1. Microbial Dosing

To eliminate contaminants from the water, microbial dosing employs certain and effective microorganisms. Commercial products, like the FLO-1200, could produce amazing results in the reduction of river pollutants when the river is aerated. The potential of microbial degradation for water purification was artificially boosted by the addition of bio-energizer and coupled water mixing [10].

2.2. Biofilm

The bio-film method makes use of a bio-membrane that is attached to the river's natural bed as well as a micro-carrier to transfer the pollutants in the river through adsorption, degradation, and filtration under the influence of dissolved oxygen or artificial aeration. Methods for purifying underground streams include thin layer flow, artificial packing contact oxidation, gravel contact oxidation, and more [10].

3. How Microorganisms Degrade the Pollutants?

Microbes are a key component of bioremediation since they need an energy source from the environment. According to the chemical nature of the contaminants, several types of contaminants are found at polluted sites, and the microorganisms in such sites either breakdown or detoxify the contaminants [11]. A variety of enzymes are secreted by different microorganisms, and these enzymes have the ability to degrade environmentally hazardous chemical substances. Enzymes called oxidoreductases are mostly employed to remove hazardous metals and phenolic compounds from the environment [12]. The soil pollutants are easily accessed by filamentous fungus, which release the enzymes laccase and peroxidase to help detoxify the pollutants [13]. Some soil bacteria have oxygenase enzymes that break down aromatic contaminants in the environment.

The purple nonsulfur bacteria Rhodobactersphaeroides and Rhodobiummarinum are capable of removing heavy metals such as zinc, cadmium, and copper [14]. Pseudomonas putida that has been genetically modified or changed in some other way to have a mechanism for degrading toluene [15]. Microalgae that act as "hyper-accumulators" and "hyper-adsorbents" may be able to detoxify heavy metals from acid mine drainage, such as Spirulina sp., Chlorella, Cladophora, and Phaeodactylumtricornutum [16]. Conjugated consortia of microalgae-bacteria breakdown caffeine and ibuprofen more quickly than single bacterium consortia [17].

4. Techniques for Treating Wastewater

For the treatment of wastewater, a number of conventional physicochemical methods, including coagulation-flocculation, sedimentation, filtrations, and different combinations of these methods, have been used, but they were ineffective [18]. Additionally, there are several potential drawbacks to using these techniques, including the creation of harmful byproducts, the quantity of sludge produced, and the high chemical and energy needs [19].

In biological wastewater treatment methods, bacteria utilize wastewater contaminants as nutrition and break down the organic substrate in the wastewater to produce water and CO₂ and other simpler compounds [20]. In order to protect the wellbeing of living things and the sustainability of the environment, contaminants from different industrial wastewaters are removed using biological wastewater treatment procedures [21]. According on the type of pollutants and their quantities, bioremediation can be carried out in-situ or ex-situ [22].

5. Bioremediation of Heavy Metals

Due to their non-biodegradability and bioaccumulation, heavy metals pose a significant ecological threat and one of the most difficult environmental concerns worldwide [23,24]. Microorganisms possess a variety of anionic structures on their cell surfaces, including hydroxyl, phosphoryl, carboxyl, alcohol, amine, thioether, thiol, ester, sulfonate, and sulfydryl groups. These structures have a negative charge that enables them to bind to metal cations [25]. Surface adsorption is a technique used by microbial cells to absorb heavy metals through biosorption, which is independent of metabolism.

Figure 1. Heavy metals and their degrading microbes [26]

The metabolism-dependent mechanism, which depends on metal infiltration to the centre of the cells and includes sequestration, redox reaction, and species-transformation mechanisms, takes place on the exterior surface of cells by accumulating metals and associating them with extracellular polymers [27].

6. Microbial Degradation of Wastewater in Treatment Plant

Wastewater treatment is categorized as preliminary, main, secondary, or tertiary depending on the degree of pollution reduction [28]. The first stage in wastewater treatment is preliminary treatment, which involves the removal of litter and other hazardous elements to avoid clogging or blocking of treatment plant equipment. The preliminary treatment employs a range of methods to remove particular substances from the wastewater. The methods are screening, shredding, grit removal, pre-aeration, and chemical inclusion [29].

6.1. Preliminary Treatment

Preliminary treatment helps to collect heavy materials from the wastewater flow, such as rags, containers, bricks, and trees, screening must be done using a perforated bar screen [30]. Shredding is done in order to reduce the size the materials in wastewater so that it can fit through the machinery in the treatment facility [29]. Removal of grit can be accomplished through a grit chamber using sludge centrifugal force, aeration, or velocity. In this step, the wastewater and sludge are separated from the solid waste [31]. Pre-aeration step ensures aerobic conditions to be maintained by aerating the effluents. Chemical treatment aids to minimize BOD, odour, and greases, and other things, the effluent stream is treated with chemicals including peroxide, chlorine, acids, mineral salts, bases, and enzymes [32].

6.2. Primary Treatment

The fundamental goal of primary treatment is to physically isolate and reduce organic materials and suspended and floatable solids [33]. Each round of primary treatment can reduce settleable solids by 95%, BOD by 25%–30%, and overall suspended solids by 50%–60%. This method can be carried out in rectangular or circular clearing tanks [29].

6.3. Secondary or Biological Treatment

After primary treatment, the effluent is next sent to secondary treatment where the main objective is to remove biodegradable organic waste. In the secondary treatment, aerobic microorganisms, primarily bacteria, decompose the organic materials in the wastewater to produce inorganic end products like CO₂, NH₃, and H₂O [34]. Effective wastewater treatment demands constant flow of oxygen to the microorganism. Two important types of secondary treatment include fixed-film systems and suspended growth systems [35]. In a fixed film device, microbial biomass or slime added to a medium is used. The bacterium starts destroying and oxidizing the wastewater's biological components as soon as the slime comes into contact with it. The mechanism for suspended growth uses biological growth mixed with wastewater [29]. The waste treatment process is continuously aerated by mechanical stirring [36]. The microbe concentration is kept constant by adding a small quantity of sludge from the prior run.

The sewage effluent is let to stay in an aeration tank for several hours so that the bacteria can break down the organic components into simpler chemicals. Fresh waste can be treated by returning the sludge to the aeration tank, which will promote the development of bacterial microorganisms. To remove microorganisms, the partially filtered water is transferred to a different sedimentation tank. The effluent is often chlorinated to eliminate pathogenic/harmful bacteria in the sedimentation tank before being discharged into collecting water [33].

6.4. Tertiary Treatment

The final stage of sewage treatment, tertiary treatment tends to improve the condition of wastewater before it is discharged into the environment [37]. The BOD is further reduced by this treatment, which also gets rid of colour and other pollutants that secondary treatment techniques weren't capable of completely eradicate. Tertiary treatment methods include carbon adsorption, coagulation and sedimentation, ion exchange, membrane filtering, etc. [38].

7. Bioremediation Types: In-Situ and Ex-Situ Bioremediation

Technologies for treating water can be categorized as physical, chemical, or biological treatment methods. Additionally, they can be categorized as ex-situ or in-situ technologies. Ex-situ remediation procedures include the removal of contaminants from the site, whereas in-situ remediation techniques involve treatment at the site [39,40]. Microbial remediation, aquatic plants, and aquatic animals are usually used in in-situ biological treatments. Ex situ bioremediation methods are often evaluated based on the cost of treatment, the depth of contamination, the type of pollutant, the degree of contamination, the location and geology of the polluted site. Bioremediation techniques should be used as the main strategy in strategies to reduce surface water pollution. High amounts of contaminants have been found in numerous rivers, making water pollution a major issue in developing nations.To overcome this problem, many technologies for pollution management and water treatment can be used [41-51]. Various techniques of in-situ and ex-situ bioremediation have been discussed in Figure 2.

Figure 2. Types of Bioremediation

7.1. Aquatic Plants for Bioremediation

Water contaminants can be reduced or fixed by plants with high toxicity tolerance through adsorption, absorption, accumulation, and breakdown [52,53]. For improving effluent quality, macrophytes like water hyacinth (Eichhorniacrassipes) and water lettuce (Pistia stratiotes) have been employed [54]. Other plants used for wastewater treatment include whorl-leaf watermilfoil (Myriophyllumverticillatum), pondweed (Potamogeton spp.), common reed (Phragmites communis), cattail (Typha latifolia), duckweed (Lemnagibba), and canna (Canna indica) [55]. Aquatic plants can be added to various treatment systems, including built wetlands and floating bed systems, for in-situ surface water cleanup [56] or submerged systems using algae [57].

7.2. Animals for Bioremediation

The removal of organic substance from eutrophic water bodies is significantly influenced by aquatic organisms like clams, snails, and other filter-feeding shellfish [10]. To reduce excessive phytoplankton levels and enhance the quality of water bodies, filter-feeding silver carp (Hypophthalmichthys molitrix) have been introduced as a biological treatment in eutrophic water bodies [58].

Although the final efficacy depends on the conditions of the particular ecosystem, experiments have demonstrated that filter-feeding fish are capable of lowering phytoplankton biomass to a certain extent [59]. Additionally, silver carp are harmed by inorganic or organic contaminants in untreated water and some biotoxins secreted by Microcystis spp., which reduces the effectiveness of this biological treatment. There should be more research done on toxicity and the safety of water quality [60].

7.3. Biostimulation

By introducing certain electron acceptors, donors, or nutrients into the soil or ground water, biostimulation is a way for boosting the activity of inhabitant bacteria. In this process, the microbial community in the intrinsic or natural environment is enhanced, and pollutants are degraded by nutrient accumulation or other limiting conditions [61]. The biostimulation system primarily works to eliminate petroleum pollutants from soil, but it also depends on oxygen availability, pH levels, and soil temperature [62].

7.4. Bioaugmentation

Bioaugmentation is the introduction of endogenous or exogenous microorganisms that can degrade pollutants by increasing their enzymatic activity at the gene level. This technique, primarily applies to oil pollutants, works by increasing the contaminated pollutant's ability to degrade through the employment of a particular strain, consortia, or genetically engineered organism [63]. Genetically modified microorganisms are more effective in breaking down contaminants than naturally occurring bacteria because of their particular DNA modifications and diverse metabolic profiles. Microbes are isolated from the infected spot, differentiated, genetically modified, and then transferred back to the same area [64].

7.5. Bioattenutaion

In a biological process known as bioattenutaion, microorganisms use diverse biological processes to break down pollutants and pollutants in the environment. Microbes use metabolic pathways in order to reduce the volume, toxicity, and mass of contaminants in the atmosphere. Toxicants can also be broken down by diffusion, depression, transformation, solubilization, advection, sorption, volatilization, ion exchange, and other chemical processes. Chemicals can be completely dissolved by microbes in soil and ground water, turning them into harmless gases and water [65].

7.6. Bio-sparging

Bio-sparging is the process of pumping air under pressure to deliver nutrients and oxygen to a specific zone in order to promote local microbial growth and obliterate organic components. In order to increase aerobic breakdown and mineralization, it is frequently employed in conjunction with the bioventing procedure, which includes releasing air into the saturated zone [66].

7.7. Bioventing

By giving existing soil microorganisms air or oxygen, the method known as "bioventing" encourages the in-situ biodegradation of pollutants in soil. Low air flow rates are used in bioventing to deliver just enough oxygen to support microbial activity in the vadose zone. The most typical method of supplying oxygen to soil with residual pollutants is direct air injection. Any substance that can be biodegraded aerobically is suitable for bioventing [67].

7.8. Composting

It is a biological process that involves the aerobic decomposition of complex organic waste from a variety of sources, such as plant and garden waste, food scraps, paper, coffee grounds, etc., into a substance like humus [68].

Figure 3. Different microbial communities in composting [68]

In aerobic composting, waste is broken down while being exposed to air, allowing the decomposing bacteria to break down the waste swiftly and odorlessly [29]. Because of its excellent levels of carbon and nitrogen, the resulting product, also known as manure or compost, is a perfect organic fertilizer for plants [69].

7.9. Biopile

Biopile-mediated bioremediation involves piling toxic soil that has been dug above ground, followed by nutrient enrichment and occasionally aeration to improve bioremediation by essentially boosting microbial activity. Aeration, irrigation, nutrient and effluent collecting systems, and a treatment bed are the elements of this technique. Due to its beneficial qualities, including cost effectiveness, which allows for efficient biodegradation under the condition that nutrient, temperature, and aeration are properly managed, the adoption of this specific ex situ technique is being considered more extensively [70].

7.10. Windrows

As one of the ex situ bioremediation methods, windrows rely on the frequent rotating of the piled polluted soil to increase the activities of the native and/or transitory hydrocarbonoclastic bacteria present in the polluted soil that degrade hydrocarbons. The regular turning of contaminated soil and addition of water promote aeration, uniformize the distribution of pollutants, nutrients, and microbial degradative activities, and speed up the rate of bioremediation, which can be performed by absorption, biotransformation, and mineralization [71].

7.11. Bioreactors

The term "bioreactor" refers to a container in which raw materials undergo a sequence of biological processes to produce a particular product.

The utilization of a bioreactor to clean polluted soil offers significant advantages over conventional ex situ bioremediation procedures, regardless of whether polluted samples are fed into it as dry matter or slurry. One of the main benefits of bioreactor-based bioremediation is the superior control of bioprocess parameters like temperature, pH, agitation and aeration rates, substrate and inoculum concentrations [72].

8. Discussion

The drawbacks of chemical and physical techniques can be overcome by in-situ and ex-situ bioremediation approaches. Another benefit of using bioremediation techniques is that they are inexpensive, have little impact on the environment, and produce no secondary pollutants. To maintain and regulate the hydraulic conditions in open streams, an understanding of in-situ treatment systems is also crucial.

The removal of both conventional (like organics) and nonconventional (like radioactive materials) contaminants from surface waters is accomplished effectively in-situ by aquatic plants. Aquatic animals can improve nutrient regeneration and reduce pollution in aquatic bodies. In-situ therapy techniques that use microorganisms are promising and effective. In addition to rivers and lakes, these techniques need to be tried in other contaminated surface streams, like farm drains. It is important to optimize the bioremediation processes by considering the flow conditions and the availability of nutrients. Ex-situ bioremediation procedures have the significant benefit of not requiring a thorough evaluation of the polluted site prior to remediation; this reduces the length, labour, and cost of the preliminary stage.

9. Conclusion

From the above review, we can consider how important natural resources are to mankind, their contamination led to long-term impacts like pollution, global warming, ozone depletion, and greenhouse gases. Utilizing the bioremediation technique, it is necessary to clean up these natural resources in order to preserve the ecosystem and maintain the environmental sustainability. Research studies should concentrate on understanding the effects of bioremediation on regional ecosystems and biodiversity. It is crucial to incorporate bioremediation techniques into water quality models to ensure successful design and management.

Conflict of Interest

None Declared.

Acknowledgements

One of the authors (BS) is thankful to the Director USERC, Dehradun for necessary support in writing this article.

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