Bioremediation Chapter Notes | Biotechnology for Class 12 - NEET PDF Download

Introduction

• Human activities at domestic, agricultural, and industrial levels introduce numerous pollutants into air, water, and soil, creating alarming environmental issues globally.
• Untreated chemical toxicants, excess fertilizers, and pesticides from agriculture often drain into water bodies, threatening ecosystems, flora, fauna, and human health.
• Elimination of these pollutants from ecosystems is highly desirable to mitigate environmental damage.
• Microorganisms have been identified that can modify and degrade synthetic agrochemicals, aiding in pollutant removal.
• Bioremediation is the process of using living organisms (bios) to remediate or address damage caused by chemical toxicants, focusing on waste and pollutant management through conventional and biological methods involving microorganisms and plants.

Ananda Mohan Chakrabarty

• Ananda Mohan Chakrabarty (4 April 1938 – 10 July 2020) was an Indian American microbiologist renowned for developing genetically engineered organisms via plasmid transfer.
• In 1965, he earned his Ph.D. from the University of Calcutta and moved to the University of Illinois, USA, for further studies.
• His research focused on environmental microbiology, aiming to develop microbes for biodegradation.
• In 1971, he created a genetically engineered Pseudomonas strain capable of using oil as a nutrient, termed “multi-plasmid hydrocarbon-degrading Pseudomonas,” which could digest most hydrocarbons in oil spills.
• He was the first to receive a patent for a recombinant microbe, a significant milestone as patenting living organisms was not permitted at the time.
• His efforts led to the 1980 Supreme Court case “Diamond v. Chakrabarty,” which established the legality of patenting microbes and higher organisms.
• His research group later pioneered work on cupredoxin (proteins) from Pseudomonas and its role in cancer biology.
• Chakrabarty served as an expert on legal issues related to patents and intellectual property rights.
• In 2007, the Indian government awarded him the Padma Shri for his contributions.

Waste Water Treatment

• Wastewater from homes, communities, or industries is collectively called sewage, which is challenging to treat due to antiseptics, chemicals, and high oxygen demand.
• Various industries (e.g., dairy, tannery, cannery, distillery, oil refinery, textile, coal and coke, synthetic rubber, steel) produce characteristic sewage, some of which are readily treatable, while others resist biological treatment.
• An average individual in India produces approximately 0.8 kg of waste per day.

Composition of Sewage

• Sewage comprises human excreta, wash waters, industrial waste, agricultural wastes, and livestock wastes (e.g., from poultry, cattle, horses).
• Municipal sewage is approximately 99% water and 1% inorganic and organic matter in suspended and soluble forms.
• Suspended matter includes lignocellulose, cellulose, proteins, fats, and inorganic particulate matter.
• Soluble matter includes sugars, fatty acids, alcohols, amino acids, and inorganic ions.
• The organic content of sewage is measured by biochemical oxygen demand (BOD), which indicates the oxygen required to stabilize decomposable organic and oxidizable inorganic matter through aerobic biological action.
• BOD reduction is a key metric for evaluating the efficiency of mechanical, chemical, and biological sewage treatment.
• Untreated sewage contains high levels of suspended solids (100–750 mg/L), total nitrogen (20–80 mg/L), total phosphorus (5–20 mg/L), chlorides (230–2700 mg/L), grease and oil (50–100 mg/L), BOD (100–300 mg/L), chemical oxygen demand (COD) (600–900 mg/L), pH (5–7.5), and total coliform (10⁷–10⁵).
• Treated sewage significantly reduces these levels: suspended solids (up to 35 mg/L), total nitrogen (up to 15 mg/L), total phosphorus (up to 5 mg/L), chlorides (<250 mg/L), grease and oil (<10 mg/L), BOD (up to 25 mg/L), COD (75–100 mg/L), pH (6.5–8.5), and total coliform (not detectable).
• Sewage contains diverse microorganisms, including bacteria, fungi, protozoa, algae, nematodes, amoebae, and viruses, with microbial populations ranging from a few lakhs to several millions per milliliter.
• Common bacteria in sewage include coliforms, streptococci, clostridia, micrococci, Proteus, Pseudomonas, and lactobacilli, primarily from intestinal and soil sources.
• Pathogenic organisms in domestic wastewater include bacteria (e.g., Escherichia coli causing gastroenteritis, Salmonella typhi causing typhoid, Vibrio cholerae causing cholera, Shigella sp. causing shigellosis), viruses (e.g., adenovirus causing respiratory diseases, enteroviruses and rotavirus causing gastroenteritis, hepatitis A virus causing infectious hepatitis), protozoa (e.g., Entamoeba histolytica causing amoebic dysentery, Giardia lamblia causing giardiasis, Balantidium coli causing balantidiasis), and helminths (e.g., Ascaris lumbricoides causing ascariasis, Schistosoma sp. causing schistosomiasis, Fasciola hepatica causing fascioliasis, Taenia saginata causing taeniasis).

Biochemical Oxygen Demand (BOD)

• BOD measures the amount of dissolved oxygen required by microorganisms to oxidize organic matter in sewage.
• Higher BOD indicates more oxidizable organic matter, classifying sewage as “strong,” while lower BOD indicates “weak” sewage.
• Strong sewage rapidly depletes dissolved oxygen in water bodies, leading to the death of aquatic fauna like fish, increased organic matter decomposition, and water becoming unsuitable for recreation or drinking.
• BOD is measured by diluting a sewage sample with oxygen-saturated water, incubating it at 20°C for five days alongside a control (diluted water), and measuring residual oxygen in both.
• The difference in oxygen levels reflects the sewage’s oxygen consumption capacity, expressed in parts per million (ppm).
• For high organic load samples, sewage is diluted with double-distilled water, aerated for one hour, and pH adjusted to 7.0 using a buffer.
• BOD is calculated as: BOD (O₂ mg/L) = (D₁ – D₂) × 100 / % dilution or (D₁ – D₂) × Dilution factor, where D₁ is dissolved oxygen before incubation and D₂ is after incubation.
• Dilution factors vary based on sample volume and dilution water added (e.g., 1000 mL sample with no dilution water = factor 1; 50 mL sample with 950 mL dilution water = factor 20).

Waste Water Disposal Plant

• Sewage treatment is essential before disposal to prevent water bodies from becoming disease vectors, depleting oxygen, initiating foul-smelling anaerobic processes, harming aquatic life, and rendering water unfit for drinking or recreation.
• Treatment aims to kill pathogens, prevent anoxia, raise pH to alkaline levels, increase photosynthetic rates, and reduce organic content.
• Wastewater is routed to sewage disposal plants for primary (physical/mechanical), secondary (biological), and tertiary (advanced) treatments before discharge into water bodies.

Primary or Physical Treatment

• Primary treatment involves physical or mechanical methods like screening, grit chambers, and sedimentation to remove coarse solid materials.
• Screening removes bulky foreign matter such as bottles, paper, and wooden boxes.
• Sewage passes through grit chambers with graded opening filters to remove finer particles.
• In sedimentation tanks, sewage is held for 2–10 hours, allowing coarse solids to concentrate as primary sludge, which is collected for further processing.
• Primary treatment achieves 30–40% BOD removal, after which sludge and liquid effluent are processed separately in secondary treatment.

Secondary or Biological Treatment

• Secondary treatment removes suspended organic material remaining after primary treatment through microbiological degradation (hydrolysis, oxidation, reduction).
• Decomposition and stabilization can occur aerobically or anaerobically, depending on waste characteristics and engineering choices.
• Aerobic methods include the activated sludge process, trickling filters, and oxidation ponds, while anaerobic methods involve anaerobic sludge digestion.
• During aerobic treatment, complex organic matter is mineralized into oxidized inorganic materials like sulfates, phosphates, nitrates, CO₂, and H₂O.

Activated Sludge Process

• The activated sludge process involves an aeration tank and a settling tank, where compressed air maintains aerobic conditions.
• Aerobic microbes break down organic carbon, nitrogen, and phosphorus into minerals.
• Sludge settling in the second tank, called activated sludge, contains a high density of bacteria adapted to the system’s environment.
• Part of the activated sludge is piped to a sludge digester, while the rest is recycled to the aeration tank to activate incoming effluent.
• Oxygen is pumped into the sewage tank, and aerobic microorganisms oxidize organic matter to CO₂ and H₂O.
• About 90% of organic matter is digested, but the effluent still contains nitrates and phosphates, which can cause eutrophication, requiring tertiary treatment.

Trickling Filter

• In the trickling filter process, sewage post-primary treatment is sprayed via rotating sprinkler arms onto a filter bed of crushed stones, gravel, clinker, and slag.
• Spraying saturates the effluent with oxygen, and the bed’s surface and stones are coated with a microbial film (bacteria, fungi, protozoa, algae).
• As effluent seeps through, aerobic microbes degrade organic matter.
• Treated effluent is collected at the tank bottom, passed to a sedimentation tank, and subjected to tertiary treatment.
• Primary and secondary treatments together reduce BOD by up to 90%, total nitrogen by 50%, total phosphorus by 30%, and suspended matter by 90%.

Eutrophication

• Excessive nutrients (nitrogen and phosphorus) from sewage or agricultural runoff promote the growth of photosynthetic microorganisms, particularly algae and phytoplankton, causing algal blooms.
• This phenomenon, called eutrophication, can occur naturally or anthropogenically due to human activities like discharging nitrate- or phosphate-containing wastes, detergents, fertilizers, or sewage into water bodies.
• Algal blooms block light, causing submerged plants to die, and release toxins harmful to aquatic flora.
• Nutrient exhaustion and toxins stunt algal growth, leading to decomposition by heterotrophic microbes, depleting dissolved oxygen and killing aquatic fauna like fish.
• Natural eutrophication results from nitrogen- and phosphorus-rich streams merging into lakes, causing organic debris and silt accumulation, making lakes shallower and warmer.
• Warm-water organisms outcompete cooler-environment species, and marshy and floating plants overgrow, potentially converting the lake into land over time.
• Anthropogenic eutrophication is faster than the slow natural process.

Sewage Oxidation Ponds or Lagoons

• Oxidation ponds, up to 5 feet deep, are used in rural areas with ample land to treat sewage effluent via wind action and algal photosynthesis.
• Oxygenation occurs naturally through wind and algal activity or mechanically via aeration.
• Efficient lagoons reduce BOD by 75–95% or more, with oxygen from air and algae meeting the effluent’s BOD, supporting aerobic microbial growth and organic matter digestion.
• Oxidation ponds are increasingly used in arid areas to conserve groundwater for domestic, industrial, irrigation, and recreational purposes.

Anaerobic Sludge Digestion

• Anaerobic treatment uses anaerobic microorganisms to process waste in the absence of oxygen, digesting complex organic material for growth and reproduction.
• Primary treatment sludge is digested anaerobically in a specialized tank, where microbes degrade organic matter into soluble substances and gases like methane (60–70%), CO₂ (20–30%), H₂S, and small amounts of H₂ and N₂.
• The gas mixture can power sewage plants or be used as fuel.
• Anaerobic digestion takes 30–40 days for completion.
• Remaining sludge is dewatered via air-drying on sand filter beds, vacuum filtration, centrifugation, or wet air oxidation before final disposal.
• Dewatered sludge is pulverized, incinerated, or sold as fertilizer (e.g., Milorganite), containing nitrogen, phosphorus, and potassium essential for plant growth, with heating killing pathogens.

Tertiary or Advanced Treatment

• Tertiary treatment removes non-biodegradable organic pollutants and mineral nutrients (nitrogen and phosphorus) from secondary-treated effluent to prevent eutrophication.
• Non-biodegradable organic pollutants are removed using activated carbon filters.
• Phosphorus salts are precipitated by liming, forming insoluble calcium phosphate (Ca₃(PO₄)₂), which settles and is removed.
• Nitrogen, mainly as ammonia, is removed by volatilization through vigorous aeration at high pH and elevated temperatures in a metal tower with plastic baffle plates, where air removes ammonia gas.
• Carbon absorption (carbon polishing) removes dissolved organic compounds by passing effluent through a tower packed with carbon particles, to which organic matter adheres.
• The final step involves chlorination using sodium or calcium hypochlorite (NaOCl or CaOCl₂) or chlorine to disinfect the effluent, producing clean water unsuitable for drinking.

Solid Waste Management

• Solid wastes are non-liquid materials from households, streets, industrial, commercial, and agricultural activities.
• Major sources include residential areas, industries, commercial establishments, institutions, construction and demolition sites, municipal services, manufacturing processes, and agriculture.
• Residential wastes include food waste, paper, cardboard, plastics, glass, leather, yard waste, wood, metals, ashes, and special wastes (e.g., bulky items, electronics, batteries, oil, tires, hazardous waste).
• Industrial wastes include housekeeping waste, packaging, food waste, construction and demolition materials, hazardous waste, ashes, and special waste.
• Commercial wastes include paper, cardboard, plastics, wood, food waste, glass, metals, special waste, and hazardous waste.
• Institutional wastes are similar to commercial wastes.
• Construction and demolition wastes include wood, steel, concrete, and dirt.
• Municipal service wastes include street sweepings, landscape and tree trimmings, and sludge from water and wastewater treatment plants.
• Manufacturing process wastes include industrial process wastes, scrap materials, off-specification products, slag, and tailings.
• Agricultural wastes include spoiled food wastes, agricultural waste, and hazardous wastes like pesticides.

Risks of Solid Waste

• Solid waste provides breeding sites for mosquitoes and flies, vectors for diseases like dengue and yellow fever (Aedes mosquitoes), malaria (Anopheles mosquitoes), and microfilariasis (Culex mosquitoes).
• Burning solid wastes produces carcinogens and toxins.
• Poor collection and disposal management leads to leachate pollution of surface and groundwater, especially if toxic substances are disposed near drinking water sources.
• Unhygienic and polluted environments from solid waste affect human health.
• Examples include the plague outbreak in Surat, Gujarat, linked to mishandled solid waste disposal, and dengue fever in Delhi associated with stagnant water in open sewage and drains.

Solid Waste Management Strategies

• Solid waste management involves collecting, treating, and disposing of discarded or no-longer-useful solid material, critical for urban area management to prevent unsanitary conditions, environmental pollution, and vector-borne diseases.
• It encompasses controlling generation, collection, storage, transfer, transport, processing, and disposal in alignment with public health, economics, engineering, conservation, aesthetics, and environmental considerations.
• Effective management involves identifying waste types, sources, potential health hazards, volume, and safe collection, transportation, and disposal methods.
• Two primary approaches are dumping and recycling the waste.

Sorting and Management of Solid Waste

• Sorting waste at the generation point into categories maximizes recycling efficiency.
• Organic waste (e.g., fruit and vegetable waste, animal dung, fallen leaves) can be composted to produce soil conditioners and fertilizers.
• Home-level composting uses suitable containers, with contents usable as fertilizer after weeks.
• Vegetable waste and dried weeds can be chopped, compressed into bricks, and sun-dried for use as cooking fuel, replacing charcoal or wood.
• Glass and plastic waste can be reused in industries to produce new items.
• Construction debris can be reused as filling material under floors during new construction or building projects.
• Used tires can be recycled at specialized units or buried to prevent water collection and mosquito breeding, with burning avoided due to toxic fume emissions.

Solid Waste Management at Community Level

• Household items like plastics, bones, metals, used batteries, and broken glass, which cannot be degraded at home, require community-level facilities for processing.
• Community refuse pits, located away from water sources to prevent leaching, are fenced to keep animals out and used for non-home-degradable waste.
• Trained personnel, aware of safety precautions, collect waste at community sites for transfer to designated city disposal sites as needed.

Managing Special Solid Wastes

Medical Solid Waste

• Healthcare solid waste from medical facilities and homes contains infectious pathogens, with increased volumes during pandemics (e.g., masks, gloves, PPE kits, syringes, needles).
• High-risk medical waste must be segregated per guidelines and incinerated.
• Handlers must wear masks and gloves, and in the absence of incinerators (e.g., at home), waste should be treated with strong disinfectants.
• Sharp needles and glassware must be disinfected, and needles destroyed to prevent reuse.

Slaughterhouse Wast

• Slaughterhouse waste includes decaying animal carcasses, blood, fecal matter, hair, and bones, handled by trained staff at designated sites complying with health standards.
• Regular inspections by authorities ensure proper disposal.

Industrial Solid Waste

​​​​

Disposal of Toxic Chemicals

Composting, Vermiculture and Methane Production

• Composting is a powerful biological, chemical, and physical process where organisms degrade waste under suitable conditions, producing CO₂, water, heat, and humus.
• It is a key environmental tool for degrading toxic and persistent compounds in water and soil, recycling complex molecules.

Mechanism and Procedure of Composting

• Degradable waste is sorted, ground, mixed with water and sewage sludge containing organisms, and maintained at optimal conditions (e.g., 45–65% moisture) for microbial activity.
• Composting can be aerobic or anaerobic, with aerobic processes requiring sufficient oxygen in the compost heap or pit.
• Compost pit design ensures maximum degradation efficiency.
• Composting proceeds through three phases: mesophilic (moderate-temperature, lasting days), thermophilic (high-temperature, lasting days to months), and a cooling and maturation phase (several months).
• Temperature changes reflect dominant microbial communities: mesophilic microbes rapidly break down soluble compounds, producing heat; thermophilic microbes dominate above 40°C, accelerating degradation of proteins, fats, and complex carbohydrates like cellulose and hemicellulose.
• At 55°C and above, pathogens are destroyed, but decomposition slows, requiring aeration to maintain temperatures below 65°C.
• The final curing phase involves mesophilic microbes maturing remaining organic matter.

Organisms Involved in Composting Process

• Diverse microorganisms (unicellular and multicellular) contribute at different composting stages, with changing microenvironments favoring specific organisms.
• Bacteria constitute 80–90% of microorganisms in compost, with Thermus bacteria active at high temperatures.
• Actinomycetes, filamentous bacteria, degrade lignin, cellulose, chitin, and proteins, breaking down woody stems, bark, newspapers, and cardboard.
• Fungi, including molds and yeasts, decompose complex polymer waste and are active throughout temperature phases, primarily in the compost’s outer layer.
• Protozoans, single-celled organisms in water droplets, act as secondary consumers, feeding on organic material, bacteria, and fungi.
• Compost contains insects, mites, sow bugs, ants, earthworms, and other worms, with worms indicating nutrient-rich, fertile soil.
• Vermiculture and methane emission are integral to composting, enhancing soil fertility by recycling human-generated waste.

Management and Disposal of Biomedical Waste

• Biomedical waste is generated during diagnosis, treatment, immunization, research, biological production, testing, or health camps for humans or animals.
• The Biomedical Waste Management Rules (BMWM), 2016, categorize biomedical waste into four color-coded groups: yellow, red, white, and blue.
• Yellow category includes anatomical waste (human tissues, body parts, fetuses, animal carcasses), soiled waste (items contaminated with body fluids, blood, swabs), discarded/expired medicines (antibiotics, cytotoxic drugs, ampoules, vials), chemical waste (disinfectants, insecticides, solvents, reagents, heavy metals), contaminated beddings, and microbiology/biotechnology/clinical lab waste (blood bags, specimens, cultures, toxins, culture devices).
• Red category includes contaminated plastic waste (intravenous tubes, bottles, catheters, syringes without needles, cut fixed-needle syringes, urine bags, vaccutainers, gloves).
• White category includes sharps (used, discarded, or contaminated metal sharps, needles, syringes with fixed needles, needle-tip cutter needles, blades, scalpels, puncture-causing objects).
• Blue category includes metallic body implants and broken, discarded, or contaminated glass (medicine vials, ampoules).
• WHO classifies biomedical waste into four risk groups: Risk Group 1 (low/no risk, unlikely to cause disease), Risk Group 2 (moderate individual risk, low community risk, treatable pathogens), Risk Group 3 (high individual risk, low community risk, non-spreading pathogens, treatable), and Risk Group 4 (high individual and community risk, transmissible pathogens, limited treatment).
• Biomedical waste from healthcare facilities, labs, research centers, veterinary institutes, mortuaries, and blood banks is highly infectious, requiring segregation at the point of generation.
• Containers, bins, bags, and sharp boxes must be available, with trained staff segregating waste and clear instructions/posters near disposal points.
• WHO recommends segregation schemes: infectious waste (yellow, biohazard symbol, leak-proof plastic bags, collected when three-quarters full or daily), sharp waste (yellow, marked “SHARPS,” puncture-proof containers, collected when three-quarters full), pathological waste (yellow, biohazard symbol, leak-proof bags, collected when three-quarters full or daily), chemical/pharmaceutical waste (brown, hazard symbol, plastic/rigid containers, on demand), radioactive waste (radiation symbol, lead box, on demand), and general healthcare waste (black, plastic bags, collected when three-quarters full or daily).
• The Mayapuri Radiological Accident (April 2010, Delhi) involved a cobalt-60 gamma unit sold to a scrap dealer, dismantled, and cut into pieces, hospitalizing eight people, with one death.
• Radioactive waste disposal follows the Atomic Energy (Safe Disposal of Radioactive Wastes) Rules, 1987, mandated by the Atomic Energy Regulatory Board (AERB).

Bioremediation of Pesticides

• Pesticides are diverse chemicals used to protect crops or stored grains from pests like insects, rodents, weeds, bacteria, larvae, and fungi, categorized as organochlorine, organophosphorus, organometallic, synthetic pyrethroids, carbamates, and inorganic pesticides.
• Organochlorine pesticides (e.g., DDT, lindane, endosulfan, aldrin, dialdrin, atrazine) are lipid-soluble, disrupt the nervous system, are toxic, and highly persistent.
• Organophosphate pesticides (e.g., parathion, malathion, dimecron, diazinon) contain phosphate groups, inhibit cholinesterase, are highly toxic, and less persistent.
• Carbamate pesticides (e.g., carbaryl, carbofuran, IPC) are carbamic acid derivatives, inhibit cholinesterase, are highly toxic, and less persistent.
• Synthetic pyrethroids (e.g., cypermethrin, deltamethrin) are pyrethrum plant analogs, disrupt the nervous system, and degrade in sunlight or soil within days.
• Organometallic pesticides (e.g., methylmercury) are absorbed through skin, gastrointestinal tract, or respiration, are toxic, and highly persistent.
• Inorganic pesticides (e.g., arsenic, mercury, cadmium, sulfur) coagulate proteins, affect the central nervous system and enzyme function, and are highly persistent.
• Pesticides were key to the Green Revolution in the late 1960s, enabling food self-sufficiency in India.
• DDT, the first synthesized pesticide (organochlorine), was initially effective against malaria-carrying Anopheles mosquitoes but later became ineffective due to resistance and harmed non-target species.
• Due to their hydrophobic and lipid-soluble nature, organochlorines are non-biodegradable and persist in the environment.
• Organophosphates are acutely toxic, inhibiting cholinesterase and causing acetylcholine accumulation, with residual forms potentially more harmful than the original.
• Carbamates and pyrethroids are easily hydrolyzed and degraded, while organochlorines and organometallics persist and accumulate in non-target organisms, including humans, via biomagnification.
• Biomagnification involves pesticides or their metabolites entering plants and accumulating through trophic levels, reaching significant levels in soil, water, and organism tissues.
• Removing long-lasting toxic compounds from soil and water is critical for ecosystem health and non-target organisms, including humans.

Bioremediation of Pesticides Using Microorganisms

• Bioremediation removes or alters the toxic nature of pesticides to minimize adverse environmental and health impacts, using microorganisms to degrade or transform them into non-toxic substances.
• Numerous microorganisms (bacteria, fungi, algae, microbial strains) with wide-spectrum metabolism can utilize chemicals for energy or possess enzymes to degrade pesticides.
• Key enzymes include cytochrome P450 (oxidative breakdown of pesticides/xenobiotics), esterases (hydrolytic breakdown of organophosphates/carbamates), oxidases (redox reactions), peroxidases (oxidative degradation of organometallics), and transferases (glutathione transfer and oxidative degradation of electrophilic pesticides).
• Degradation involves complex enzymatic reactions like oxidation, reduction, hydrolysis, group transfer, and conjugation with sugars or amino acids, making pesticides less toxic and water-soluble.
• Ananda Mohan Chakrabarty created a “superbug” (Pseudomonas putida) by inserting hydrocarbon-degrading genes from four Pseudomonas strains (degrading camphor, naphthalene, octane, xylene) using rDNA technology, recognized with a U.S. patent.
• In situ bioremediation cleans up petroleum spills or restores degraded ecosystems (e.g., from mining or toxic accumulation).
• Intrinsic in situ bioremediation relies on naturally present microorganisms, is cost-effective, minimally disruptive, and involves low public exposure but is slow and often incomplete.
• Engineered in situ bioremediation promotes microbial growth by circulating oxygen, nitrogen, and growth-promoting substances through injection and extraction wells, with oxygen acting as an electron acceptor.
• Ex situ bioremediation involves excavating contaminated soil for treatment, used for heavily contaminated sites.
• Slurry bioreactors agitate contaminated soil with water and nutrients to enhance microbial degradation under optimal conditions, with mobile bioreactors enabling treatment near contaminated sites.
• Land farming applies nutrients and moisture to a land bed to facilitate microbial bioremediation.
• Composting mixes contaminated soil with organic agricultural wastes (e.g., straw, corncobs) to supply air and water, though excavation and transport pose exposure risks.
• Biopiles involve excavating contaminated soil and mixing it with leachate materials to degrade and drain toxic substances.
• Oilzapper, developed by TERI with the Department of Biotechnology, India, uses a consortium of five non-pathogenic bacterial strains to biodegrade aliphatic, aromatic, and asphalting oil fractions.
• Oilzapper is immobilized on powdered corncob for application in oil-contaminated environments and has cleaned over 750,000 metric tons of oil sludge and contaminated soil in India and Middle Eastern countries.
• TERI and ONGC formed ONGC TERI Biotech Limited (OTBL) to implement Oilzapper, using fermentation facilities of various capacities (15,000 to 10 liters).

Phytoremediation

• Plants play a significant role in uptaking or remediating toxic substances in soil or water, with microorganisms in the rhizosphere aiding the process.
• Plants like Brassica napus and Helianthus annus accumulate mercury and lead from contaminated soil.
• Rhizosphere microorganisms facilitate phytoremediation through biochemical processes like chelation, methylation, pH alteration, redox reactions, and changing toxicant bioavailability.
• Some plants accumulate heavy metal-containing compounds, reducing their toxicity.
• Nitrogen-fixing bacteria (diazotrophs) convert atmospheric nitrogen into ammonia and urea, which plants uptake, enhancing soil fertility.
• Diazotrophs produce plant hormones (e.g., indole acetic acid, gibberellins) and remediate heavy metals like lead, zinc, and nickel, supporting crop growth.
• Examples include Azotobacter chroococcum (maize, mustard; reduces soil pH, produces hormones, remediates lead/zinc), Rhizobium leguminosarum (maize; reduces soil pH, produces hormones, remediates lead/zinc), and Rhizobium sp. (pea, lentil; produces siderophores, hormones, remediates nickel/zinc).
• Aquatic plants like Hydrilla verticillata and Nymphaea alba reduce chromium in polluted water, aiding phytoremediation.