The term “Environment” is defined as our surroundings which includes the abiotic component (the non living) and biotic component (the living) around us. The abiotic environment includes water, air and soil while the biotic environment consists of all living organisms – plants, animals and microorganisms. Environmental pollution broadly refers to the presence of undesirable substances in the environment which are harmful to man and other organisms. In the past decade or two, there has been a significant increase in the levels of environmental pollution mostly due to direct or indirect human activities. The major sources of environmental pollution are –Industries, Agricultural sources (mainly rural area), anthropogenic sources (man related activities mainly in urban areas), biogenic sources etc. The pollutants are chemical, biological and physical in nature. The Chemical pollutants include- gaseous pollutants (hazardous gases like sulfur dioxide, nitrogen oxide), toxic metals, pesticides, herbicides toxins and carcinogens
Etc. The physical pollutants are- heat, sound, radiation, and radioactive substances. The pathogenic organisms and some poisonous and dangerous biological products are the biological pollutants.
Controlling the environmental pollution and the conservation of environment and biodiversity and controlling environmental pollution are the major focus areas of all the countries around the world. In this context the importance and impact of biotechnological approaches and the implications of biotechnology has to be thoroughly evaluated. There have been serious concerns regarding the use of biotechnology products and the impact assessment of these products due to their interaction with the environmental factors.
A lobby of the environmentalists have expressed alarm on the release of genetically engineered organisms in the atmosphere and have stressed on thorough investigation and proper risk assessment of theses organisms before releasing them in to the environment. The effect of the effluents from biotechnological companies is also a cause of concern for everyone. The need of the hour is to have a proper debate on the safety of the use of the biotechnological products.
The efforts are not only on to use biotechnology to protect the environment from pollutionbut also to use it to conserve the natural resources. As we all know that microorganisms are known natural scavengers so the microbial preparations (both natural as well as genetically engineered) can be used to clean up the environmental hazards.
Development of alternate cleaner technologies using biotechnology
Biotechnology is being used to provide alternative cleaner technologies which will help to further reduce the hazardous environmental implications of the traditional technologies. E.g. some Fermentation technologies have some serious environmental implications. Various biotechnological processes have been devised in which all nutrients introduced for fermentation are retained in the final product, which ensures high conversion efficiency and low environmental impact.
In paper industry, the pulp bleaching technologies are being replaced by more environmentally friendly technologies involving biotechnology. The pulp processing helps to remove the lignin without damaging valuable cellulosic fibres but the available techniques suffer from the disadvantages of high costs, high energy use and corrosion. A lignin degrading and modifying enzyme (LDM) was isolated from Phanerochaete chrysosporum and was used, which on one hand, helped to reduce the energy costs and corrosion and on the other hand increased the life of the system. This approach helped in reducing the environmental hazards associated with bleach plant effluents.
In Plastic industry, the conventional technologies use oil based raw materials to extract ethylene and propylene which are converted to alkene oxides and then polymerized to form plastics such as polypropylene and polyethylene. There is always the risk of these raw materials escaping into the atmosphere thereby causing pollution. Using biotechnology, more safer raw materials like sugars (glucose) are being used which are enzymatically or through the direct use of microbes converted into alkene oxides.e.g. Methylococcus capsulatus has been used for converting alkene into alkene oxides.
Integration of biological steps in pulping process leading to lignin degradation
Bioremediation is defined as ‘the process of using microorganisms to remove the environmental pollutants where microbes serve as scavengers. The removal of organic wastes by microbes leads to environmental cleanup. The other names/terms used for bioremediation are biotreatment, bioreclamation, and biorestoration. The term “Xenobiotics” (xenos means foreign) refers to the unnatural, foreign and synthetic chemicals such as pesticides, herbicides, refrigerants, solvents and other organic compounds. The microbial degradation of xenobiotics also helps in reducing the environmental pollution.
Pseudomonas which is a soil microorganism effectively degrades xenobiotics. Different strains of Pseudomonas that are capable of detoxifying more than 100 organic compounds (e.g. phenols, biphenyls, organophosphates, naphthalene etc.) have been identified. Some other microbial strains are also known to have the capacity to degrade xenobiotics such as Mycobacterium, Alcaligenes, Norcardia etc.
Factors affecting biodegradation
The factors that affect the biodegradation are: the chemical nature of xenobiotics, the concentration and supply of nutrients and O2, temperature, pH, redox potential and the capability of the individual microorganism. The chemical nature of xenobiotics is very important because it was found out that the presence of halogens e.g. in aromatic compounds inhibits biodegradation. The water soluble compounds are more easily degradable whereas the presence of cyclic ring structure and the length chains or branches decrease the efficiency of biodegradation. The aliphatic compounds are more easily degraded than the aromatic ones.
It is a process by which the microbial activity can be enhanced by increased supply of nutrients or by addition of certain stimulating agents like electron acceptors, surfactants etc.
It is possible to increase biodegradation through manipulation of genes i.e. using genetically engineered microorganisms and by using a range of microorganisms in biodegradation reaction.
Depending on the method followed to clean up the environment, the bioremediation is carried out in two ways:
A) In situ bioremediation - In situ bioremediation involves a direct approach for the microbial degradation of xenobiotics at the site of pollution which could be soil, water etc. The adequate amount of essential nutrients is supplied at the site which promotes the microbial growth at the site itself. The in situ bioremediation is generally used for clean up of oil spillages, beaches etc. There are two types of in situ bioremediation-
1) Intrinsic bioremediation- The microorganisms which are used for biodegradation are tested for the natural capability to bring about biodegradation. So the inherent metabolic ability of the microorganisms to degrade certain pollutants is the intrinsic bioremediation. The ability of surface bacteria to degrade a given mixture of pollutants in ground water is dependent on the type and concentration of compounds, electron acceptor and the duration of bacteria exposed to contamination. Therefore, the ability of indigenous bacteria degrading contaminants can be determined I laboratory by using the techniques of plate count and microcosm studies. The conditions of site that favour intrinsic bioremediation are ground water flow throughout the year carbonate minerals to buffer acidity produced during biodegradation, supply of electron acceptors and nutrients for microbial growth and absence of toxic compounds.
2) Engineered in situ bioremediation- When the bioremediation process is engineered to increase the metabolic degradation efficiency (of pollutants) it is called engineered in situ bioremediation. This is done by supplying sufficient amount of nutrients and oxygen supply, adding electron acceptors and maintaining optimal temperature and pH. This is done to overcome the slow and limited bioremediation capability of microorganisms.
Advantages of in situ bioremediation
a) The method ensures minimal exposure to public or site personnels.
b) There is limited or minimal disruption to the site of bioremediation.
c) Due to these factors it is cost effective.
d) The simultaneous treatment of contaminated soil and water is possible.
Disadvantages of in situ bioremediation
a) The sites are directly exposed to environmental factors like temperature, oxygen supply etc.
b) The seasonal variation of microbial activity exists.
c) Problematic application of treatment additives like nutrients, surfactants, oxygen etc.
d) It is a very tedious and time consuming process.
B) Ex-situ bioremediation - In this the waste and the toxic material is collected from the polluted sites and the selected range of microorganisms carry out the bioremediation at designed place. This process is an improved method over the in situ bioremediation method. On the basis of phases of contaminated materials under treatment ex-situ bioremediation is classified into two : a) Solid phase system and (b) Slurry phase systems.
A) Solid phase treatment- This system includes land treatment and soil piles comprising of organic wastes like leaves, animal manures, agricultural wastes, domestic and industrial wastes, sewage sludge, and municipal solid wastes. The traditional clean-up practice involves the informal processing of the organic materials and production of composts which may be used as soil amendment. Composting is a self heating, substrate-dense, managed microbial system which is used to treat large amount of contaminated solid material. Composting can be done in open system i.e. land treatment and/or in closed treatment system. The hazardous compounds reported to disappear through composting includes aliphatic and aromatic hydrocarbons and certain halogenated compounds. The possible routes leading to the disappearance of hazardous compounds include volatilization, assimilation, adsorption, polymerization and leaching.
B) Slurry phase treatment- This is a triphasic treatment system involving three major components- water, suspended particulate matter and air. Here water serves as suspending medium where nutrients, trace elements, pH adjustment chemicals and desorbed contaminants are dissolved. Suspended particulate matter includes a biologically inert substratum consisting of contaminants and biomass attached to soil matrix or free in suspending medium. The contaminated solid materials, microorganisms and water formulated into slurry are brought within a bioreactor i.e. fermenter. Biologically there are three types of slurry-phase bioreactors: aerated lagoons, low shear airlift reactor, and fluidized-bed soil reactor. The first two types are in use of full scale bioremediation, while the third one is in developmental stage.
Advantages of ex-situ bioremediation
a) As the time required is short, it is a more efficient process.
b) It can be controlled in a much better way.
c) The process can be improved by enrichment with desired and more efficient microorganisms.
Disadvantages of ex-situ bioremediation
a) The sites of pollution remain highly disturbed.
b) Once the process is complete, the degraded waste disposal becomes a major problem.
c) It is a costly process.
Several types of reactions occur during the bioremediation/microbial degradation
a) Aerobic bioremediation- When the biodegradation requires oxygen O2 for the oxidation of organic compounds, it is called aerobic bioremediation. Enzymes like monooxygenases and dioxygenases are involved and act on aliphatic and aromatic compounds.
b) Anaerobic bioremediation-This does not require oxygen O2. the degradation process is slow but more cost effective since continuous supply of oxygen is not required.
c) Sequential bioremediation- Some of the xenobiotic degradation requires both aerobic as well as anaerobic processes which very effectively reduces the toxicity e.g. tetrachloromethane and tetrachloroethane undergo sequential degradation.
Use of genetic engineering and genetic manipulations for more efficient bioremediation
In recent years, efforts have been made to create genetically engineered microorganisms (GEMs) to enhance bioremediation. This is done to overcome some of the limitations and problems in bioremediation. These problems are:
a) Sometimes the growth of microorganisms gets inhibited or reduced by the xenobiotics.
b) No single naturally occurring microorganisms has the capability of degrading all the xenobiotics present in the environmental pollution.
c) The microbial degradation is a very slow process.
d) Sometimes certain xenobiotics get adsorbed on to the particulate matter of soil and thus become unavailable for microbial degradation.
As the majority of genes responsible for the synthesis of enzymes with biodegradation capability are located on the plasmids, the genetic manipulations of plasmids can lead to the creation of new strains of bacteria with different degradative pathways. In 1970s, Chakrabarty and his team of co-workers reported the development of a new strain of bacterium Pseudomonas by manipulations of plasmid transfer which they named as “superbug”. This superbug had the capability of degrading a number of hydrocarbons of petroleum simultaneouslysuch as camphor, octane, xylene, naphthalene etc. In 1980, United States granted the patent to this superbug making it the first genetically engineered microorganism to be patented.
In certain cases, the process of plasmid transfer was used. E.g. The bacterium containing CAM (camphor degrading ) plasmid was conjugated with another bacterium with OCT (octane degrading) plasmid. Due to non-compatibility, these plasmids cannot coexist in the same bacterium. However, due to the presence of homologous regions of DNA, recombination occurs between these two plasmids which results in a single CAM-OCT plasmid giving the bacterium the capacity to degrade both camphor as well as octane.
A new strain of Pseudomonas sp. (strain ATCC 1915) has been developed for the degradation of vanillate (which is a waste product from paper industry) and sodium dodecyl sulfate (SDS, a compound used in detergents).
Biotechnological method to reduce atmospheric carbon dioxide (CO2)
Carbon dioxide is the gas that is the main cause of green house effect and rise in the atmospheric temperature. During the past 100-150 years, the level of CO2 has increased about 25% with an increase in the atmospheric temperature by about 0.5% which is a clear indication that CO2 is closely linked with global warming. There is a steady increase in the CO2 content due to continuous addition of CO2 from various sources particularly from industrial processes. It is very clear that the reduction in atmospheric CO2 concentration assumes significance. Biotechnological methods have been used to reduce the atmospheric CO2 content at two levels:
a) Photosynthesis- Plants utilize CO2 during the photosynthesis which reduces the CO2 content in the atmosphere. The equation for photosynthesis is:
6CO2 + 6H2O---------->C 6 H12 O6 + 6O2
The fast growing plants utilize the CO2 more efficiently for photosynthesis. The techniques of micropropagation and synthetic seeds should be used to increase the propagation of such fast growing plants.
Further, the CO2 utilization can be increased by enhancing the rate of photosynthesis. The enzyme ribulose biphosphate carboxylase (RUBP-case) is closely linked with CO2 fixation. The attempts are being made to genetically manipulate this enzyme so that the photosynthetic efficiency is increased.
Some microalgae like Chlorella pyrenodiosa, Spirulina maxima are known to be more efficient than higher plants in utilizing atmospheric CO2 for photosynthesis and generate more O2 than the amount of CO2 consumed.
The growing of these microalgae near the industries and power plants (where the CO2 emission in to atmosphere is very high) will help in the reduction of polluting effects of CO2. Using genetic engineering, attempts are going on to develop new strains of these microalgae that can tolerate high concentrations of CO2. A limited success has already been reported in the mutants of Anacystis nidulans and Oocystis sp.
b) Biological Calcification- Certain deep sea organisms like corals, green and red algae store CO2 through a process of biological calcification. As the CaCO3 gets precipitated, more and more atmospheric CO2 can be utilized for its formation. The process of calcification is as follows:
H2O + CO2---------->H2CO3
H 2CO3 + Ca 2+----------------> CaCO3 + CO2 + H2O
Treatment of sewage using microorganisms
The sewage is defined as the waste water resulting from the various human activities, agriculture and industries and mainly contains organic and inorganic compounds, toxic substances, heavy metals and pathogenic organisms. The sewage is treated to get rid of these undesirable substances by subjecting the organic matter to biodegradation by microorganisms. The biodegradation involves the degradation of organic matter to smaller molecules (CO2, NH3, PO4 etc.) and requires constant supply of oxygen. The process of supplying oxygen is expensive, tedious, and requires a lot of expertise and manpower. These problems are overcome by growing microalgae in the ponds and tanks where sewage treatment is carried out. The algae release the O2 while carrying out the photosynthesis which ensures a continuous supply of oxygen for biodegradation.
The algae are also capable of adsorbing certain heavy toxic metals due to the negative charges on the algal cell surface which can take up the positively charged metals. The algal treatment of sewage also supports fish growth as algae is a good source of food for fishes. The algae used for sewage treatment are Chlorella, Euglene, Chlamydomnas, Scenedesmus, Ulothrix, Thribonima etc.