CHAPTER-1 1. INTRODUCTION. Environmental pollution is one of the greatest threats to society in the

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1 1 CHAPTER-1 1. INTRODUCTION 1.1 General survey Environmental pollution is one of the greatest threats to society in the future. One of the primary causes of environmental degradation in a country could be attributed to rapid growth of population, which adversely affects the natural resources and environment. Increasing economic development and a rapidly growing population in India has taken the country from 300 million people in 1947 to over one billion people today was putting a strain on the environment, infrastructure, and the country s natural resources. Rapid industrialization further worsens the situation. It was the industrial revolution that gave birth to environmental pollution as we know it today. The emergence of large factories and consumption of immense quantities of coal and other fossil fuels gave rise to unprecedented air pollution and the large volume of industrial chemical discharges added to the growing load of untreated human waste. It was estimated that 10,000 more chemicals are introduced worldwide annually and industrialized countries generate more than 90% of the world s annual total of million tons of toxic and hazardous waste originating from chemical and petrochemical industries. Thousands of hazardous waste sites have been generated worldwide resulting from the accumulation of xenobiotics in soil and water over the years. The future scale has environmental and health problems from industrialization in developing countries which depend greatly on policy actions taken today.

2 2 1.2 Soil contamination Soil contamination is the occurrence of pollutants in soil above a certain level causing deterioration or loss of one or more soil functions (63). Also, soil contamination can be considered as the presence of man-made chemicals or other alteration in the natural soil environment. This type of contamination typically arises from the rupture of underground storage tanks, application of pesticides, and percolation of contaminated surface water to subsurface strata, leaching of wastes from landfills or direct discharge of industrial wastes to the soil. The random dumping of hazardous waste in the industrial area could be the main cause of the soil contamination spreading by rainwater and wind. The most common chemicals involved are petroleum hydrocarbons, solvents, pesticides, lead and other heavy metals. The occurrence of this phenomenon was correlated with the degree of industrialization and intensity of chemical usage. The concern over soil contamination stems primarily from health risks, both of direct contact and from secondary contamination of water supplies (39). Each year around the world thousands of sites complete soil contamination cleanup, some by using microbes that eat up toxic chemicals in soil (Wikipedia), many others by simple excavation and others by more expensive high-tech soil vapor extraction or air stripping method. At the same time, efforts proceed worldwide in creating and identifying new sites of soil contamination, particularly in industrial countries other than the U.S. and in developing countries which lack the money and the technology to adequately protect soil resources.

3 3 1.3 Sediment Contamination Sediment contamination is one of the major environmental issue because of its potential toxic effects on biological resources and often, indirectly on human health. In the aquatic environment particular attention has been devoted to the problem of chemical pollution due to accidental spills, urban and industrial discharges resulting in the introduction of hazardous substances such as hydrocarbons, metals and xenobiotic contaminants (31,277,168). Pollutants from various sources (industrial, mining, municipal sewage, agricultural and other activities) have entered waterways over time. The sediments then become a sink and source of toxic components due to their resuspension and can, thus be one of the largest potential sources of risk to water quality. Sediments are soil particles found at the bottom of lakes, estuaries, rivers and oceans that are of mineral and organic origin. The sediments are comprised of organic matter, iron oxides, carbonates, sulfides and interstitial water. Organic matter was derived from humus, decomposed plant and animal residues and other organic matter, such as algae, worms, amphipods that settle to the bottom of the water body. Other woody or plant material, garbage, dead organisms and other debris can also become components of sediments. Sediments are heterogeneous and can be characterized by grain size distribution and density, water and organic matter contents. Contaminants get to adsorbed on to the smaller soil particles due to higher surface area to volume ratios and higher organic matter contents (232).

4 4 Fine-grained bottom sediments tend to accumulate contaminants due to their sorptive nature, and thus act as important reservoirs for many chemicals. Many contaminants, when released to aquatic systems, degrade, evaporate or flushed out by advective flows. However, depending on the physical properties of the environment and the contaminants, appreciable quantities may be transferred to sediments, resulting in severe and prolonged contamination. Because of slow exchange processes between sediment and water, over time these contaminated sediments can become inadvertent sources of in place chemical to the lake and its aquatic organisms. This bleeding of contaminants from the sediment can lead to detrimental effects on biota and adversely affect water quality. Changes in sediment chemistry, due to seabed disturbances, can result in contaminant remobilization. Subsequently, exposure to a different chemical environment could result in desorption and transformation of contaminants into more bioavailable or toxic chemical forms (240,201). For those chemicals that are persistent in sediments, a frequent regulatory response was to require accelerated clean up of contaminated sites. 1.4 Distribution of contaminants Organic contaminants in soil-sediment systems are mixtures of hundreds of aliphatic, chlorinated, aromatic and other organic compounds, the relative proportions of which vary greatly between sources. Each component differs in its reactivity, solubility, volatility, mineral surface affinity and biodegradability. Furthermore, interactions between components and the mode of introduction of the contaminant into the soil/sediments/sludge, post-depositional, weathering

5 5 and diverse mobility characteristics can drastically alter the composition of the bulk contaminants. Inorganic contaminants also have very complex interactions with both anthropogenic and natural components in the sediments. At elevated concentrations contaminants become a source, which on a cumulative basis may in turn reach humans. Bottom sediments are known to act as a sink for the contaminants introduced into the aquatic system. Since contaminants introduced into the lake waters remain stagnant, as flow rates through lakes are small compared to lake volumes, contaminant residence time was longer, typically years to decades. Virtually all sediments are trapped in the bottom layers of the lake except for contaminants that enter the food chain through bottom feeding fish or become exposed. When water level in the lake drops, bottom sediments become an effective sink for sorbed contaminants. The majority of metal contaminants tend to partition onto the particulate matter such as organic substances, carbonates, clay minerals, oxides and hydroxides of Fe and Mn (36). Research has shown that Fe and Mn oxides/hydroxides along with organic matter are important binding sites for metals in oxic sediment (188,116,241,64) and that the formation of metal sulphides dominates in anoxic sediments (240,58,35). Organic and organometallic contaminants preferentially partition to organic matter in sediment and dissolved organic matter in pore water (76). The composition of pore water was a critical component in organic contaminant partitioning because of the variability in colloidal material, dissolved organic and inorganic chemicals, redox potential, ph and temperature, which may differ significantly from that of the overlying

6 6 water(125). Contaminant concentration in pore water is closely related to the toxicity of sediment. Thus assessment of contaminant concentration in pore water helps to determine the toxicity/bioavailability potential of the sediment (121). Natural and anthropogenic activities have the capacity to remobilize contaminated sediments and release contaminants from sediment and sediment-pore water to the water column. Hydrophobic organic contaminants readily desorbs from sediment, although the rate of desorption tends to decrease with time (42,120,242). 1.5 Contaminant bioavailability and toxicity The use of microorganisms for the remediation of contaminated with hydrophobic organic pollutants like polycyclic aromatic hydrocarbons (PAH s) was often limited by the bioavailability of these compounds. The fate of organic pollutants during bioremediation was influenced by the competing processes of adsorption and biodegradation (78). Whereas the hydrophobic PAH s adsorb tightly to the organic fraction of soil and sediments (107), sorption to the mineral fraction of soil was usually much weaker and was of importance for bioavailability, mainly by intraparticle diffusion (200, 46). The degree of contaminant bioavailability was determined by the reactivity of each contaminant with the biological interface, the presence of other chemicals that may antagonize or stimulate uptake, and external factors such as temperature that affect the rate of biological or chemical reactions (119). Contaminants are available to aquatic organisms via ingestion with food (particulate associated), through membrane- facilitated transport (active) or

7 7 passive diffusion (water dissolved). Bioavailability and bioaccumulation of contaminants in an aquatic environment was mainly dependent on the partitioning behavior or binding strength of the contaminant to sediment (58, 116, and 64). The in situ biodegradation of a contaminant was a function of the catabolic activity of bacteria and bioavailability of the contaminant to bacteria. Chemotaxis, i.e. the movement of bacteria under the influence of a chemical gradient has been postulated to play an important role in enhancing biodegradation as it increases bioavailability of pollutants to bacteria. Some toxic organic compounds are chemo attractant for different bacterial species, which can lead to improved biodegradation of these compounds (24). The role of various surface-active compounds released by hydrocarbon degrading bacteria is to enhance the bioremediation potential by overcoming mass transfer limitation and dissolution rates of these hydrocarbon compounds (Figure 1-1)(82). Some chlorinated hydrocarbons can be employed as terminal electron acceptors for anaerobic microbial respiration, resulting in their reductive dechlorination. This type of metabolism, called dehalorespiration, facilitates the degradation of recalcitrant chlorinated compounds by other microorganisms (124). The application of biosurfactants has been shown potentially to increase the degradation rate of hydrophobic pollutants such as PAHs and PCBs. the bioavailability of these compounds increases as a result of Biological reactions occur in or at the interface of the aqueous phase and surfactants have the ability to desorbs and disperse poorly soluble compounds in small, high-surface-area

8 8 micelles within the water phase. Surfactants can thus improve the accessibility of these substrates to microbial attack (66). Detergents also increase the bioavailability of hydrophobic targeted pollutants to the microbes (114). Figure 1-1 Bioavailability processes in soil and sediment 1.6 Methodologies for soil/sediment /sludge treatment Soil pollution causes significant damage to the environment and human health. Significant progress has been made in regulating soil pollution, with a parallel development of methodologies for soil assessment and remediation. The selection of the most appropriate soil and sediment remediation method depend on site characteristics, concentration, type of pollutants to be removed, and the end use of the contaminated medium. The approach includes isolation, immobilization, toxicity reduction, physical separation and extraction.

9 9 Physical/Chemical Treatment Technologies and Biological Treatment Technologies are the two common methods used for the reclamation of soil/sediment/sludges. Physical/Chemical Treatment may be applicable to a wide variety of materials but can leave hazardous by products or residual sludges. Incineration and other thermal methods were expensive yet very effective in reducing volumes of wastes and completely destroying them. How ever gaseous emissions and ash residues can require further treatment and considered to be expensive. Where as Biological methods allow the discovery and broad flexibile microorganisms in the environment to clean up of chemically contaminated soil/sediment/sludge matrices. Biological treatment is more effective as it can destroy pollutants in eco-friendly manner and cost-effective when compared with other technologies. However it was not generally suitable against some reactive, corrosive, radioactive materials and heavy metals. Yet a potentially greater effectiveness against a broader range of organic compounds was extending in the application of biological methods to more difficult remediation activities Bioremediation technologies Bioremediation of contaminated soil, sediment, sludges, and water involves the use of microorganisms to convert organic contaminants to carbon dioxide and water (a process known as mineralization) or to less harmful compounds. Bioremediation constitutes an attractive alternative to physicochemical methods of remediation. Bioremediation was shown to be a cost-effective and successful method for the remediation of sites contaminated with a wide variety of organic and inorganic compounds). In particular, it can selectively achieve complete

10 10 destruction of organic pollutants without collateral destruction of either the site material or its flora and fauna, and can be used in situ for pollutants that were present at low but environmentally relevant concentrations (213). The contaminant degrading microorganisms were generally bacteria, but can also be fungi (4). For efficient and effective bioremediation, the treatment intersects with various biotechnical, biochemical and genetic engineering areas and also has to apply the interaction between various organic compounds and microorganisms in the environment. The treatment involves biotechnological application of processes that occur in nature which include aerobic and anaerobic processes. In aerobic process, organic components of effluents was oxidized to carbon dioxide or some other metabolic intermediate products in the presence of dissolved oxygen where as in anaerobic metabolism, organic substances were first converted to carboxylic acids and further to carbonic acid, methane and hydrogen in the absence of oxygen. Bioremediation of contaminated soils/sediments depends on two types of biotechnologies based on the nature of microorganisms: a) Activation of the indigenous microflora in the polluted area by addition of nutrients (mainly in the form of mineral fertilizers) and by creating the best conditions for the growth of indigenous micro flora. b) The second type of bioremediation technology is addition of new microorganisms (bacteria and fungi) which are especially capable of producing a wide variety of enzymes that can degrade organic compounds and mineralize them.

11 11 The following are various methods of bioremediation that are used for remediation of contaminated soils/sediments/sludges. i) Bioattenuation or Natural attenuation: This was the method of monitoring the natural progress of degradation to ensure that contaminant concentration decreases with time at relevant sampling points. Bioattenuation was widely used as a cleanup method for underground storage tank sites with petroleum-contaminated soil and groundwater in the United States (184). ii) Bioventing: To stimulate the indigenous bacteria bioventing was the most common in situ treatment and involves supplying air and nutrients through wells to contaminated soil. Bioventing employs low air flow rates and provides only the amount of oxygen necessary for the biodegradation while minimizing volatilization and release of contaminants to the atmosphere. Bioventing works for simple hydrocarbons and can be used where the contamination was deep under the surface. iii) Biosparging Biosparging involves the 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. Biosparging increases the mixing in the saturated zone and thereby increases the contact between soil and groundwater.

12 12 iv) Bioaugmentation Bioaugmentation is a way to enhance the biodegradative capacities of contaminated sites by inoculation of bacteria with the desired catalytic capabilities It is a process where a pool of microorganisms, enzymes or a special degrading agent were added to a volume of contaminated soil or water in order to provide efficient degradation of the contaminations present in the matrix to enhance the biological activity. This is considered to be an effective approach in the case of recalcitrant compounds in the contaminated sites. v) Biostimulation Biostimulation is the process where indigenous microbial populations in the contaminated material were provided by necessary electron acceptors, inorganic nutrients and other supplements to stimulate microbial degradation of the contaminants. vi) Land farming Land farming is a full-scale bioremediation technology that usually incorporates liners and other methods to control leaching of contaminants and requires excavation and placement of contaminated soils. Contaminated media are applied into lined beds and periodically turned over or tilled to aerate. Soil conditions are often controlled to optimize the rate of contaminant degradation vii) Composting Composting is a controlled biological process by which organic contaminants were converted by microorganisms to innocuous, stabilized byproducts. Typically, thermophilic conditions (54 to 65 C) must be maintained to

13 13 compost soil contaminated with hazardous organics. Composting is carried out under controlled conditions in the presence of oxygen resulting in the biological decomposition and stabilization of the biodegradable components. viii) Biopiles Biopile treatment is another full-scale composting technology in which excavated soils are mixed with soil amendments and placed on a treatment area that includes some form of aeration. Biopile composting differs from windrow composting in that the pile was not mixed once constructed. Biopiles are used for the treatment of surface contamination with petroleum hydrocarbons. They are a refined version of land farming that tends to control physical losses of the contaminants by leaching and volatilization. Biopiles provide a favorable environment for indigenous aerobic and anaerobic microorganisms. ix) SEAR - surfactant enhanced aquifer remediation The Surfactant Enhanced Aquifer Remediation process involves the injection of hydrocarbon mitigation agents, especially surfactants into the subsurface to enhance desorption and recovery of bound up otherwise recalcitrant non aqueous phase liquid. This approach provides a cost effective and permanent solution to sites that have been previously unsuccessful in utilizing other remedial approaches. This technology will be successful when utilized as the initial step in a multi faceted remedial approach utilizing SEAR than In-situ Oxidation. x) Phytoremediation Phytoremediation is the method of using plants to clean up potentially damaging spills. Plants work with soil organisms to transform contaminants, such

14 14 as heavy metals and toxic organic compounds, into harmless or valuable forms. This technology typically involves the use of plants to remove, contain, accumulate, or degrade environmental contaminants in soil, groundwater, surface water, sediment, and air. Plants can be used in site remediation, both through the mineralization of toxic organic compounds and through the accumulation and concentration of heavy metals and other inorganic compounds from soil to above ground shoots. The Phytoremediation mechanisms used to treat contaminated soil/sediments/sludges are phytoextraction, rhizodegradation, phytodegradation, phytovolatilization and phytostabilization. Phytoremediation is best used to treat large areas of shallow and moderate level of contamination. It can be applied in conjugation with other treatment methods or used as a final polishing step insitu remediation in the areas of high contamination levels. xi) Bioreactors Bioremediation in reactors involves the processing of contaminated solid material or water through an engineered containment system. A slurry bioreactor may be defined as a containment vessel and apparatus used to create a threephase (solid, liquid, and gas) mixing condition to increase the bioremediation rate of soil bound and water-soluble pollutants as a water slurry of the contaminated soil and biomass (usually indigenous microorganisms) capable of degrading target contaminants Advantages of bioremediation Bioremediation is a natural process and therefore perceived by the public as an acceptable waste treatment process for contaminated soils and sediments.

15 15 Theoretically, bioremediation is useful for the complete destruction of a wide variety of contaminants. Many compounds that are legally considered to be hazardous can be transformed to harmless products. This eliminates the chance of future liability associated with treatment and disposal of contaminated material. Instead of transferring contaminants from one environmental medium to another, for example, from land to water or air, the complete destruction of target pollutants was possible. 1.7 Significance of the work One of the major problems facing the industrialized world today is contamination of soil, groundwater, sediments, surface water and air with hazardous and toxic chemicals. Both organic and inorganic contaminants are important in soil. The most prominent chemical groups of organic contaminants are fuel hydrocarbons, polychlorinated biphenyls (PCB S), chlorinated aromatic compounds, detergents, pesticides. Inorganic species include nitrates, phosphates and heavy metals such as cadmium, chromium etc. Among the sources of these contaminants are agricultural runoffs, acidic precipitates, and industrial waste materials. The production and usage of man-made chemicals in industry has led to the entry of xenobiotics into the environment. As a rule these organic compounds are not found individually but occur in simple or complex mixtures. The mixtures are released into the soils/sediment, surface or ground water, during the release, storage or transport of many chemicals. The number of chemicals found to date was enormous and the types of mixtures are similarly countless. Even at these low

16 16 concentrations, some chemicals are toxic or risk analyses suggest that exposure of large populations to the low concentrations are subjected to biomagnification and may reach levels that have deleterious effect on humans, animals or plants. The persistence of organo-xenobiotics in the environment was a matter of significant public, scientific and regulatory concern because of the potential toxicity, mutagenicity/carcinogenicity and ability to bioconcentrate up the trophic ladder. These concerns continue to drive the need for the development and application of viable and low cost remediation techniques. The remedial technologies involve physical, chemical and biological techniques. Conventional physico-chemical treatment methodologies are drastically losing importance due to their technical complexity and intensive in cost. From techno-economic perspective, bioremediation technologies are preferred if large contaminated areas are involved and biological processes transform them into innocuous end products. The aim of the work was to investigate the feasibility of biosurfactants in bioremediation methodologies for the treatment of various organic and inorganic pollutants in contaminated soils/sediments and sludges. The two major features of high molecular weight hydrocarbons that limit their availability to microorganisms are low solubility and adsorption on soil matrix. Consequently, the use of biosurfactants in contaminated soils was an interesting strategy to enhance contaminant solubility and their removal. Considering the ongoing pollution and toxicity of hazardous organics, developing an effective bioremediation strategy still remains an issue. The two major issues hindering their rapid degradation are: deficiency of nutrients (except

17 17 carbon) and poor availability. Apart from being deficient in nutrients, pollutants like crude oil hydrocarbons, PCB s, PAH s, metallo-organic compounds are highly hydrophobic and require solubilisation by surfactants to increase bioavailability to microbial cells. Surface-active agents (surfactants) play an active role efficiently to increase their bioavailability. Also considering the likely toxicity and environmental pollution posed by the synthetic surfactants, microbially produced biosurfactants represent interesting substitutes from the environment. 1.8 Scope of present work Hyderabad, the capital city of Andhra Pradesh, Southern India has been with the growing industrial activities over the years. Many industrial estates have been developed and these industries are unscrupulously dumping their effluents and wastes into the nearby open areas and lakes thereby depleting the natural flora, fauna and the ecological balance. The pollutantants released into the surrounding environment tend to concentrate in their surrounding soil, water and air environments. The pollutants in soil tend to leach into the ground water there by causing water pollution. These pollutants bioconcentrates up in the tropic ladder and causes various health hazardous to living organisms. The effluents that were released into the near by lakes are causing great concern of the environment. The pollutants in the lake get settled and concentrate on the sediment there by making lakes deadly. In some cases after the partial treatment of effluents, the sludge obtained will be disposed off, is of great concern to the environment. To overcome these problems, remediation of these contaminants is necessary. Considering the advantages of bioremediation over Physio-chemical

18 18 remediation techniques, the biodegradation of a polluted soil, sediment and sludge was taken as a case study. The present work deals with the remediation of the contaminated soil, sediment and sludge collected from various contaminated sites in and around Hyderabad. 1.9 Objectives: To evaluate the potential of different bioremediation approaches such as natural attenuation, biostimulation and bioaugmentation and assessing of the selected contaminant samples. To investigate the possible methods to enhance the rate of biodegradation through application of biosurfactants to soils, sediments and sludge polluted with xenobiotic compounds. To study the production of rhamnolipid biosurfactant by Pseudomonas aeruginosa using fried groundnut oil as an economical carbon substrate and their consequential role in the biodegradation