Education

BIOREMEDIATION: ROLE IN SUSTAINABLE AQUACULTURE

  • Shashank Singh 1*, Adita Sharma 2*, Debasmita Jana 3*, Tanushri Ghorai 2*, Iffat Jahan 4* and Vipin Kumar Misra 5*
    1. Acharya Narendra Deva University of Agriculture & Technology, Kumarganj, Ayodhya, U.P.
    2. College of Fisheries, Dr. Rajendra Prasad Central Agriculture University, Dholi, Muzaffarpur, Bihar
    3. Neotia University, Department of Fishery, West Bengal
    4. ICAR- Central Institute of Fisheries Education, Mumbai, Maharashtra
    5. Krishi Vigyan Kendra, West Kameng, Dirang, Arunachal Pradesh
    * Corresponding E-mail: ssaqua7@gmail.com

Abstract

The expansion of aquaculture industry is a good sign to fulfill the increasing demand of fish. This development also leads to degradation of the environment due to the excess use of feed and fertilizers in the aquaculture systems. An ecofriendly technique has been identified and defined as Bioremediation to overcome this vital problem. Bioremediation is the natural or managed biological degradation of environmental pollution. It is an integral part of environmental biotechnology and can be used to immobilize the contaminants by using micro or macro organisms that targets particular pollutants. This article will help to understand the benefits of bioremediation for sustainable aquaculture production.

Introduction

Aquaculture is world’s fastest growing food production sector and plays a vital role in human nutrition. Mostly it is an eco-friendly practice but intensification and use of excess fertilizers and feed at some places made it unsuitable and need proper management. As a result, aquaculture in freshwater and brackish water bodies is creating a lot of pollution in the environment. Bioremediation process can minimize the organic load and pollutants from the system. This process can be used to stabilize, extract or reduce the toxicity of contaminated soil and groundwater. It is a technology that will have huge implications for a country with very little water, a rapidly expanding population, extensive mineral resources compounded by water treatment and management challenges. In this process, a special mechanism is use to reduce or eliminate the toxic pollutants from the polluted system. It can be defined as biological mechanism to destroy, transform or immobilize environmental contaminants to protect potential sensitive receptors. The organisms may be naturally occurring or laboratory cultivated.Biodegradation of a compound is often a result of the actions of multiple organisms and the microorganisms are used to perform the function of bioremediation are known as bioremediators. They offer a natural, ecofriendly and economical solution to the problems associated with incineration and chemical treatment. The bioremediation promote the growth and health of bacteria in order to increase the degradation of unwanted contaminants. There are mainly two types of environmental conditions prevail for the treatment of the environment which includes aerobic (where oxygen is added in any form) and anaerobic (where nitrate, iron, or other electron acceptor is added). While sometimes the combination of these two is use.There are two types of biological technologies available for bioremediation:

I. In situ Bioremediation
II. Ex situ Bioremediation

In situ Bioremediation (ISB) is a technology that are used “in place” without removal of the contaminated matrix. Both intrinsic and engineered bioremediation technologies can be used in In situ bioremediation. The bioventing and biosparging is most important type of In situ Bioremediation. Bioventing is the pumping air into the soil and involves supplying air and nutrients through wells to contaminated soil to stimulate the indigenous bacteria. This form of bioremediation requires good nutrient and environmental conditions for biodegradation. Biosparging is injecting air under pressure below the water table to increase groundwater oxygen concentrations. In this method, the rate of biological degradation of contaminants by naturally occurring bacteria is increase which enhances the mixing in the saturated zone and thereby increases the contact between soil and groundwater. There are several factors which one should consider in any in situ process:

a) Geochemistry – the interaction of any treatments with the soil mineralogy
b) Hydrogeology – how does the subsurface water move
c) Biodegradability – rate, extent and pathways of degradation
d) Redox condition – is this an oxidizing or reduced environment

Advantages of In situ Bioremediation

In situ Bioremediation have following advantages:
1. Generally the most desirable options due to lower cost and less disturbance
2. Provide the treatment in place avoiding excavation and transport of contaminants
Ex situ Bioremediation (ESB) is a process where contaminated water or soil is removed from the environment by biological organisms. In such type of bioremediation, bioreactors and added nutrients can be used to speed up the breakdown of environmental pollutant. This type of bioremediation includes:

1. Land farming: It is a simple technique in which contaminated soil is excavated and spread over a prepared bed and done at regular interval until pollutants are degraded.
2. Composting: It is a technique that combines contaminated soil with non-hazardous organic amendants such as manure or agricultural wastes and presence of organic materials support the development of a rich microbial population and elevated temperature.
3. Biopiles: It is used for treatment of surface contamination with petroleum hydrocarbon and they are a refined version of land farming that tends to control physical losses of the contaminants by leaching and volatilization.
4. Bioreactor: Bioreactors are engineered containers that give contaminated material (slurry or aqueous mixture) and biomass of an artificial environment. Bioreactors have the advantage of allowing complete control over pH, temperature and oxygen levels.

Factors of Bioremediation

There are several factors essential for control and optimization of bioremediation processes, these factors include:

1. The existence of a microbial population capable of degrading the pollutants
2. The availability of contaminants to the microbial population
3. The environmental factors (type of soil, temperature, pH, the presence of oxygen and nutrients)
4. Microbial growth and activity are readily affected by pH, temperature and moisture.
5. Microorganisms have been also isolated in extreme conditions; most of them grow optimally over a narrow range, so that it is important to achieve optimal conditions.

Process of Bioremediation

(a) Bioaugmentation
The addition of microorganisms to the reaction chamber whether in situ or above ground is called Bioaugmentation. There are few considerations before addition of microorganism, includes: ability to survive, ability to function and assurances that they are non-pathogenic to higher life forms.
(b) Phytoremediation
Phytoremediation remove contaminants from soil and water using plants and the term “phytoremediation” is coined in 1991. There are five types of phytoremediation techniques classified based on the contaminant fate:

(1) Phytoextraction is the process used by the plants to accumulate contaminants into the roots and above ground shoots or leaves. This technique saves cost of remediation by accumulating low levels of contaminants from a widespread area.
(2) Phytotransformation is the process which refers to the uptake of organic contaminants from soil sediments and subsequently, their transformation to more stable, less toxic or less mobile form. For example, metal chromium transform from hexavalent chromium (toxic) to trivalent chromium (less mobile and non carcinogenic form).
(3) Phytostabilization is a technique in which plants reduce the mobility and migration of contaminated soil. The leachable constituents are adsorbed and bound into the plant structure so that they can form a stable mass of plant which will check re- entry of contaminants into the environment.
(4) Rhizodegradation is the process to breakdown of the contaminants through the activity existing in the rhizosphere. This activity is performed by the proteins and enzymes produced by the plants or by organisms like bacteria, yeast, and fungi present in the soil.
(5) Rhizofiltration is a water remediation technique which facilitates the uptake of contaminants by plant roots. This process is used to reduce the contamination in natural wetlands and estuarine areas.

Microbial Bioremediation of Various Pollutants

Bioremediation is a natural process that uses microorganisms to transform harmful substances into non-toxic CO2 and H2O. This technique is different from remedies where contaminated soil or water is removed for chemical treatment or decontamination, incineration in a landfill. Microorganisms play a significant role in the mineralization of pollutants either by natural selection or through recombinant DNA technology. Microbes such as algae, fungi and bacteria play an important role by giving us a helping hand in bioremediation of the xenobiotic compounds. The purified degrading enzymes- Azoreductases, Nitrilase and Oragnophosphate hydrolases could be efficiently utilized in industry for the treatment of effluents. Several man-made non-biodegradable chemicals are widely used to increase the agricultural output which includes morpholine, methyl parathion, organophosphorous compounds and benzimidazoles. These pesticides and insecticides also contribute to enhance the pollution load in the environment. Different, pure isolates of Pseudomonas sp. have been well characterized for complete and partial mineralization of pesticides and fungicides. Pseudomonas sp. has also been used for oil hydration by means of both aromatic and aliphatic hydrocarbon degradation

Essential factors for Microbial Bioremediation

Factor Factor Desired Conditions
Microbial population Suitable kinds of organisms that can biodegrade all of the contaminates
Oxygen Enough to support aerobic biodegradation (about 2% oxygen in the gas phase or 0.4mg/liter in the soil water)
Water Soil moisture should be from 50-70% of the water holding capacity of the soil
Nutrients Nitrogen, phosphorus, sulfur, and other nutrients to support good microbial growth
Temperature Appropriate temperature for microbial growth (0-40o C)
pH Best range is from 6.5 to 7.5

Steps in bioremediation:

Advantages of Bioremediation

1. Highly specific
2. Less expensive than excavation or incineration processes
3. If mineralization occurs get complete degradation and clean up
4. Does not transfer contaminants from one environment to another
5. Uses a natural process
6. Good public acceptance
7. Process is simple
8. If using ISB treat the groundwater and soil at the same time

Disadvantages to Bioremediation

1. Not instantaneous
2. Often need to develop a system
3. Always need to test and optimize conditions empirically – not with computer models
4. May have inhibitors present
5. Compounds may not be in a biodegradable form – polymers, plastics
6. Compounds may be recalcitrant – higher congeners of PCBs

Bioremediation and its role in Aquaculture:

The large amounts of organic wastes are produced by intensive farming of shrimp and fish and accumulate in the pond bottom which cannot be utilized by phytoplankton. Oxidation of these organic wastes deplete the level of dissolved oxygen in pond's soils which encourage the formation of toxic metabolites such as hydrogen sulfide, ammonia and nitrite and enhance the mortality rates in aquaculture farming. To get rid of this undesirable condition and to improve water quality the probiotics and enzymes are applied to achieve sustainability. Probiotics helps in manipulation of microorganisms in ponds to enhance mineralization of organic matter. In addition, the use of probiotics can increase the population of food organisms; control pathogenic microorganisms; improve the nutrition level of aquaculture animals and immunity of cultured animals to pathogenic microorganisms and provide essential nutrients to enhance the nutrition of the cultured animals. There are various probiotic bacteria have their different role:

Probiotics Role
Bacillus sp. Mineralization and Breakage of proteins
Nitrosomonas sp. Oxidation of ammonia
Nitrobacter sp. Oxidation of nitrites
Aerobacter sp. Reduction of organic matter
Cellulomonas sp. Breakage of plant material

Conclusion

Bioremediation is a choice that offers the possibility to pulverize or render innocuous different contaminants using natural biological activity. It utilizes moderately low-cost, low-technology techniques, which generally have a high public acceptance and can frequently be completed nearby. This multidisciplinary and successful application requires deep understanding of all the relevant scientific fields and attenuation processes. Bioremedial approach will help to clean the environment by enhancing decomposition of the undesirable organic substances. This scientific and ecofriendly technology can minimize the toxic gases like ammonia, nitrite, hydrogen sulfide, methane etc. and improve the aquatic environment which will help to maintain a healthy aquatic environment for aquaculture purpose and assure for producing less expensive animal protein.

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