In-situ and ex-situ bioremediation with microbes have been used as a emerging .... Microbial fuel cell that generates electricity while cleaning up nuclear waste.
Ex-situ and In-situ bioremediation strategies with special reference to marine and coastal environments
S.Raja*1 and M.Kalyanasundaram2
*1 Assistant
Professor, PG& Research Department of Zoology, Kongunadu Arts and Science college, Coimbatore-29 2 Associate professor, and Head Dept. of Zoology, Chikkanna Govt. Arts College, Tiruppur-641602.
Introduction The population explosion in the world has resulted in an increase in the area of polluted soil and water.
To meet the demands of the people rapid expansion of industries, food, health care and vehicles is inevitable. Ocean is polluted with oil through land run off, vessels accidents, and Periodic tanker discharges. These oil spills affect plants and wild life including fish, birds and mammals. In-situ and ex-situ bioremediation with microbes have been used as a emerging area in Biotechnology . Bioremediation has several potential advantages over conventional technologies, such as being cost effective, less intrusive to the contaminated site, and more environmental friendly in terms of its end products.
Biological methods are more economical and efficient than chemical and physical.
Definition Bioremediation has been defined as “the act of adding materials to contaminated environments to cause an acceleration of the natural biodegradation processes” (OTA, 1991). The U.S. EPA has defined Bioremediation agents as Microbiological cultures Enzyme additives Nutrient additives that significantly increase the rate of biodegradation to mitigate the effects of the discharge” (Nichols, 2001).
Types of Bioremediation On the basis of removal and transportation of wastes for Treatment
In-situ
Ex-situ
In-situ Bioremediation Approach -I Insert the oxygen and nutrients by circulating aqueous solutions through contaminated water or soil to stimulate naturally occurring bacteria to degrade contaminants. This method will become a safer in degrading harmful compounds.
Approach -II Introduction of certain microorganisms, accelerates the degradation process by enhancing the physicochemical conditions to encourage the growth of microorganisms. Oxygen and nutrients (nitrogen and phosphorus) promote microbial growth.
Ex-situ Bioremediation This process requires excavation of contaminated water to facilitate microbial degradation. Ex-situ is classified as: 1. Solid phase system- Organic wastes • Land farming: Contaminated soil is excavated and spread over a prepared bed and periodically tilled until pollutants are degraded. The aim is to stimulate indigenous biodegradative microorganisms. • Composting: The presence of these organic materials supports the development of a rich microbial population and elevated temperature characteristic of composting. • Biopiles: Biopiles are a hybrid of land farming and composting. Essentially, engineered cells are constructed as aerated composted piles. Engineered cells are constructed as aerated composted piles.
2. Slurry Phase: •
Bioreactors: Three phases e.g., solid, liquid and gas, mixing condition to increase the bioremediation rate.
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Bioventing: Supplying air and nutrients through wells to contaminated soil to stimulate the indigenous bacteria. In this method, low air flow of oxygen provides for the biodegradation of hydrocarbons. • Biosparging: Injection of air under pressure below the water table to increase groundwater oxygen concentrations and enhance the rate of biological degradation of contaminants by naturally occurring bacteria. •
Bioaugmentation: In this known oil-degrading bacteria are added to supplement the existing microbial population into the contaminated sites.
Using microbes More than 200 known species of bacteria, fungi, and yeast which can be used for degradation • To degrade the marine pollution microbes such as Mycobacterium, Pseudomonas, Rhodococcus, Modococci, Streptomyces, Bacilli, Arthrobacter, Burkholderia, Sphingomonas, Aeromonas, Moraxella, Beijerinckia, Flavobacteria, chrobacteria, Nocardia, Corynebacteria, Atinetobacter, and Cyanobacteria etc are used. • Pseudomonas, Alcaligenes, Sphingomonas, Rhodococcus, and Mycobacterium. These microbes have often been reported to degrade pesticides and hydrocarbons, both alkanes and polyaromatic compounds. • Macro nutrient- Carbon: Nitrogen: Phosphorus - 100:10:4. In general, at least 1 ppm of ammonium nitrogen and 0.4 ppm of orthophosphate is required. • Freeze dried bacteria, which can be used for minimum of 2×108 CFU/ml.
• Optimum concentrations of nutrients and oxygen are present and that the pH is between 6 and 9. • Fungi such as the white rot fungus, Phanaerochaete chrysosporium have the ability to degrade an extremely diverse range of persistent or toxic environmental pollutants. Common substrates used are: straw, and saw dust.
Algae
• An alga, Prototheca zopfi which was capable of utilizing crude oil and a mixed hydrocarbon substrate and exhibited extensive degradation of n-alkanes and iso-alkanes as well as aromatic hydrocarbons. • Cyanobacteria, diatoms , green algae, red alga, and brown alga, could oxidize naphthalene. • The macroalgae (e.g. Ulva sp.; Gracilaria sp. and Enteromorpha sp.) in mariculture and Coastal Aquaculture wastewater streams to absorb nutrients and create harvestable material.
Coastal Aquaculture • Biological methods, including Integrated Multi-trophic Aquaculture are now gaining interest for increasing In-situ removal of nitrogen and other nutrients at sea cage sites.
• Several studies on biological nitrogen removal through nitrification, denitrification and anaerobic ammonium oxidation (anammox) have been reported and a number of bacterial groups active in this regard have been described. • The current approach to improving water quality in aquaculture is the application of microbes/enzymes to the ponds known as 'bioremediation'. When macro and micro organisms and/or their products are used as additives to improve water quality, they are referred to as bioremediators or bioremediating agents.
• Biofilters (Ex-situ bioremediation) and also, the macroalgae Gracilaria caudata which was used to remove nutrients from aquaculture effluents .
Organic Detritus • The genus Bacillus like Bacillus subtilis, B. licheniformes, B. cereus, B. coagulans and species Phenibacillus polymyxa are good examples of bacteria suitable for bioremediation of organic detritus, and reduces water turbidity .
Nitrogenous Compounds • Bacteriological nitrification is the most practical method for the removal of ammonia from closed aquaculture systems and it is commonly achieved by setting of sand and gravel bio-filter through which water is allowed to circulate. • The ammonia oxidisers are placed under five genera, Nitrosomonas, Nitrosovibrio, Nitrosococcus, Nitrolobus and Nitrospira, and nitrite oxidisers under three genera, Nitrobacter, Nitrococcus and Nitrospira.
Hydrogen Sulphide (H2S) Under anaerobic conditions, sulphate may be used in place of oxygen in microbial metabolism. This process leads to the production of hydrogen sulphide gas. Photosynthetic bacteria of importance in aquaculture are: Rhodospirillum, Rhodopseudomonas, Chromatium, Thiocystis, Thiospirillum, Thiocapsa, Lamprocystis, Thiodictyon, Thiopedia, Amoebobacter, Chlorobium, Prosthecochloris, Pelodictyon and Clathrochloris.
Environmental factors Weathering processes Weathering processes will affect the ultimate concentrations of petroleum hydrocarbons in the environment in different ways like evaporation may reduce the concentrations.
Temperature The rate of biodegradation generally decreases with decreasing temperature. The optimums temperature in marine environment is15 to 20°C. In temperate regions, seasonal changes in water temperature affect the rate of biodegradation.
Oxygen Aerobic conditions are generally considered necessary for extensive degradation of oil hydrocarbons in the environment. Many studies have shown that oxygen depletion leads to sharply reduced biodegradation activities in marine sediments and in soils.
Other Factors Several variables, including pressure, salinity, and pH may also have important effects on biodegradation rates.
Research prospects Microbes can be develop by recombinant DNA technology Xenobiotics, this is still rarely touched field of research
Microbial fuel cell that generates electricity while cleaning up nuclear waste. Consequently, even though this technology is still in its infancy, this discovery prompts a reexamination of its impact on nuclear energy in the future.
New field of “electromicrobiology” can encompass other microbes with conductive nanowires, such as photosynthetic Cyanobacteria and Thermopilic methanogens
