Biodegradation Bioremediation.pdf

BIOLOGICAL TREATMENT OF WASTES AND POLLUTANTS  Wastes and Pollutants What is waste?? A heterogeneous mass generated by human and animal activities fit for discarding Pollutant is a waste material that pollutes air, water or soil. Exist in solid, liqu...

BIOLOGICAL TREATMENT OF WASTES AND POLLUTANTS  Wastes and Pollutants What is waste?? A heterogeneous mass generated by human and animal activities fit for discarding Pollutant is a waste material that pollutes air, water or soil. Exist in solid, liquid and gaseous forms Human activities agricultural, industrial, municipal, commercial, mining, residential and transportation- Solid waste Wastes have physical, chemical and biological constituents which cause toxicity in flora and fauna. Severity of a pollutant depend on its; Chemical nature Concentration Persistence Damage done to environment can be long term or short term.  NON-BIODEGRADABLE COMPOUNDS Compounds that cannot be digested via biological means. Some scientists believe that “nothing is non-biodegradable” Even if so, some compounds take too long to be degraded in the environment and by the time, damage done to environment may be severe. Xenobiotic compounds are also falls under non-biodegradable compounds.  XENOBIOTIC COMPOUNDS A foreign chemical found within an organism, but is not normally naturally produced by or expected to be present within that particular organism. Example: Antibiotics within human body Chemical compounds which are present in much higher concentrations than usual within an organism also falls under this class. Term often used in context of pollutants. Dioxins and polychlorinated biphenyls. (xenobiotic to whole biota, not existed before human synthesis) Alkyl Benzene Sulfonates  RECALCITRANT COMPOUNDS Xenobiotic compounds that are completely resistant to biodegradation. Simple structural changes can lead these to be biodegradable. A xenobiotic may become recalcitrant due to followings; They may not be recognized by the existing bio-degradative enzymes They may be highly stable, i.e., chemically and biologically inert due to the presence of substitution groups like halogens, nitro-, sulfonate, amino-, methoxy- and carbamyl groups Insolubility in water or absorbance to external matrices like soil highly toxic or give rise to toxic products due to microbial activity large molecular size prevents entry into microbial cells Inability of the compounds to induce the synthesis of degrading enzymes Lack of the permease needed for their transport into the microbial cells. Process Options for Organic Waste Process Options Biological Direct Land Landfill Incineration Processing Disposal Anaerobic Specialised Composting Digestion Methods Marketable Products  Biological Treatment Composting – Aerobic degradation – Natural or forced Aeration Mechanical Biological Treatment – Pre-treatment which recovers maximum value from waste with the residue being used either as a fuel, a compost or going to landfill Methanisation or Anaerobic Digestion – Anaerobic Fermentation  Composting & Classification Definition:- “Composting is the biological decomposition of the organic constituents of wastes under controlled conditions to a state sufficiently stable for nuisance-free storage and utilization.” Performed either by households or in large centralised units Compost systems can be classified on three general bases: 1. Oxygen usage (aerobic & anaerobic) 2. Temperature (Mesophilic 15-40OC & Thermophilic 45-65 OC) 3. Technological approach (static pile or windrow, and mechanical or "enclosed" composting)  Compost Mechanism of Composting Composting is a biochemical process in which aerobic and anaerobic microorganism decomposes organic matter into valuable manure called as compost. Release heat (Thermophilic state, which helps to destroy pathogens) Organic matter Organic matter compost Temp 55-60o c (Mesophilic state ,Temp. 25- 30o c, promote mesophilic microbes for rapid decomposition ) Phases of Composting Initial decomposition is carried out by mesophilic microorganisms, which rapidly break down the soluble, readily degradable compounds. As the temperature rises above about 40°C, the mesophilic are replaced by thermophilic, At temperatures of 55°C and above, many microorganisms that are human or plant pathogens are destroyed. During the thermophilic phase, high temperatures accelerate the breakdown of proteins, fats, and complex carboydrates like cellulose and hemicellulose, the major structural molecules in plants. temperature gradually decreases and mesophilic microorganisms once again take over for the final phase of "curing" or maturation of the remaining organic matter.  Phase of Composting Microorganisms + OM -------> H2O + CO2 + Heat + Humus 3 phases under optimal conditions (1) Mesophilic - lasts couple of days (~40oC) (2) Thermophilic can last a few dys to several mts ( 55oC–65oC) (3) Several-month cooling and maturation phase  Biological Processing Options Turned Windrow Static Aerated Pile In-Vessel  End Uses of Compost Soil Improvement - soil structure, condition and fertility Growing media - component of mixes used to grow crops in containers Mulches - suppress weed growth, conserves water and also to maintain soil temperatures. Mulching also protects plants from frost. Restoration - used for soil “forming” and soil improvement Landfill Applications - improvement of landfill covers – soil formation Anaerobic Digestion (AD)  Mechanical Biological Treatment (MBT) MECHANICAL SECTION aims – reducing waste size (shredding) – separating recyclables – separating dry/wet fractions (sieving) BIOLOGICAL SECTION aims – stabilising of the waste organic matter (bio-stabilisation) – drying of the waste (bio-drying) The biological element of an MBT process can take place prior to or after mechanical sorting of the waste  OBJECTIVES OF MECHANICAL-BIOLOGICAL WASTE TREATMENT Reduce the volume of the waste to be dumped and thus preserve the required landfill volume. Reduce the biological activity of the organic fraction in the household waste such that as little landfill gas as possible can escape in an uncontrolled manner on the dumpsite. Minimize the harmful substances which may enter the groundwater together with the leachate. Mechanical Biological Treatment (MBT)  Key categories of biological treatment Options Biological Treatment I Aerobic – Bio-drying / Bio-stabilisation: partial composting of the (usually) whole waste. II Aerobic – In-Vessel Composting: may be used to either bio- stabilise the waste or process a segregated organic rich fraction. III Anaerobic Digestion: used to process a segregated organic rich fraction. Waste water treatment  WASTE WATER Any water that has been adversely affected in quality by anthropogenic influence. Or addition of substances or energy forms that directly or indirectly alter the nature of the water body in such a manner that negatively affects its legitimate uses Origin ; Domestic, industrial, commercial or agricultural activities or surface runoffs, storm runoffs etc. Pollutants; Suspended solids, BD & NBD organic matter, nutrients, pathogens, metals, inorganic dissolved solids.  ADVERSE EFFECTS OF POLLUTED WATER When effluent discharged into a river body such as lake, river or sea a number of process occur like physical, chemical and biological characteristics of water change which cause loss of organism. The extent of damage depend upon type of pollutant present in effluent. Non bio-degradable pollutant like mercury are most deadly as they accumulate in aquatic organism which lead to Biomagnifications. When polluted water is discharged in to the environment; Drinking water may taste bad Eutrophication of water bodies Floating oil blankets Odor problems, aesthetic concerns Decrease of aquatic life forms etc.  WASTE WATER TREATMENT  removal or modification of pollutants for safe discharge of water into the environment.  uses microbes to decompose organic matter in sewage.  Wastewater treatment systems are designed to digest much of the organic matter before the wastewater is released.  Treatment of wastewater are generally divided into three groups- 1. Primary /Physical/Mechanical Treatment 2. Secondary Treatment or Biological Treatment 3. Tertiary Treatment or Advance Biological or Chemical Treatment  Wastewater treatment Processes Wastewater treatment methods Primary/Physical/ Tertiary/Chemical Secondary/Biological Mechanical Aerobic Anaerobic Precipitation Adsorption Disinfection Screening Mixing Flocculation Flotation Filtration Sedimentation Gas Transfer 1. Primary treatment Physically removes large solids using grates, screens, and settling tanks. Large pieces of debris are removed by screening, and suspended particles are removed from the water through settling processes. This is most commonly done with an automated mechanically raked bar screen in modern plants serving large populations, while in smaller or less modern plants, a manually cleaned screen may be used. The raking action of a mechanical bar screen is typically paced according to the accumulation on the bar screens and/or flow rate. The solids are collected and later disposed in a landfill, or incinerated.  Typical materials that are removed during primary treatment include  fats, oils, and greases  sand, gravels and rocks  larger settleable solids including human waste  floating materials  Screening : to remove large objects, that could plug lines or block tank inlets  Grit chambers: slows down the flow to allow grit to fall out (horizontal, aerated and vortex).  Sedimentation tank (settling tank or clarifiers) : Settle-able solids settle out & are pumped away, while oils float to the top & are skimmed off as scum.  The organic matter which settle down is called primary sludge which is then passed for aeration in aeration tanks.  30-40% BOD removal- treatment efficiency.  Sedimentation is enhanced by the addition of alum at the treatment plant which produces a sticky flocculant precipitate. BAR SCREEN & SEDIMENTATION TANK  AERATION TANKS  The effluents from primary treatment are then carried to aeration tanks.  Continuously aerated for the growth of aerobic m.os. Flocculation occurs.  These m.os degrade the organic matter present in the effluents. 2. Secondary treatment Elimination of organic and inorganic contaminants, through the effect of microbiological activity upon wastewater material.  4 methods include :- 1) Activated sludge 2) Trickling filters 3) Oxidation ponds or lagoons 4) Biological contractor system/ Rotating disc The most widely used and effective methods of secondary treatment involve activated sludge treatment (AST).  1) ACTIVATED SLUDGE SYSTEM Aerobic sewage treatment in which flocculated biological growth is circulated & is in contact with organic waste in presence of oxygen is called activated process sludge ACTIVATED SLUDGE ORGANISM  Particles of the flock inactivated sludge consist of mixed species of micro organisms, act in antagonism & synergism.  Bacterial population, free swimming ciliates & flagellates, protozoans, rotifiers & nematodes increases  They embed themselves in a mass of polysaccharide gum called zoogleal film.  Zoogloea ramigera  Oxidize sewage rapidly ; active in floc formation  Other m.os in zooglea are Escherichia, sps of Pseudomonas, Alkaligens, Bacillus, Sphaerotilus, Achromobacter, Flavobacterium, Nitrosomonas, Beggiatoa, Thiothrix, Nocardia, Mycobacterium, Geotrichum, Nitrobacter, several protozoans etc.  BOD reduction – 80-95%  End result is mineralization of C,N & P  Most of settled sludge moved to anaerobic sludge digestor.  2. TRICKLING FILTERS  Sewage is sprayed or drained over a rock bed or molten plastic.  Rocks large- air penetrates  Small- increased surface area for microbial activity  No filtration action  Slimy gelatinuous film of aerobes (zoogleal slime, a biofilm) grow on bed  Envelop- Exopolysacc.- gum  3. BIOLOGICAL CONTRACTOR SYSTEM/ ROTATING  A biofilm – based design. DISC  Series of disc of several diameters are mounted on a shaft.  Disc rotates slowly ; their lower part (40%) submerged in waste water.  Aeration provided.  Rotation causes accumulated biofilm to slough off when thick ❖ Biofilters hosts : Nematodes, insect larvae,  Equivalent to floc microfungi, algae, small worms and freshwater leech. accumulation.  4. OXIDATION PONDS OR LAGOONS  Sewage pond is deep-entirely anaerobic.  2 stages: Sludge settles out Effluent pumped to an adjoining pond or system of shallow ponds enough to aerated by wave action Algal growth is encouraged ; since difficult to manage aerobic condition.  Bacterial action – decomposing organic matter & generate CO2  Algae use CO2- photosynthesis- produce O2-inturn encourage aerobial activity in the sewage.  Considerable amount of organic matter in the algal form accumulates; not a problem ; since pond is nutrient-rich.  BENEFICIAL BACTERIA 1) Biofilm forming bacteria Are present in the trickling filter phase of the secondary treatment process, considered to be beneficial in the removal of organic materials. Pseudomonas, Zooglea, Chromobacter, and Flavobacterium, namely a few of whom are aerobic heterotrophic organisms. Such bacteria are exposed to oxygen during the treatment to break down the organic molecules. 3. Tertiary treatment (Chemical treatment) Provides a final treatment stage to raise the effluent quality before it is discharged to the receiving environment (sea, river, lake, ground, etc.). More than one tertiary treatment process may be used at any treatment plant. Removal of further nutrients and pathogens, using methods such as filtration, passage through wetlands, or disinfection by treatment with chlorine, ozone or ultraviolet light. If disinfection is practiced, it is always the final process. It is also called "effluent polishing." Removes disease-causing organisms from wastewater  CHLORINATION  Chlorine is used in 2 forms – Cl2 gas form or hypochlorite tablets  Cl react with water to form HOCl, which rapidly dissociate to form hypochlorite ion.  Cl is effective against enteric bacteria.  Most common  Advantages: low cost & effective  Disadvantages: chlorine residue could be harmful to environment.  Dechlorination done.  OZONATION  Disinfection achieved by formation of free radicals as oxidizing agents.  More effective against viruses & bacteria than chlorination.  Advantages:  safer than chlorination  fewer disinfection by-product  Disadvantage:  high cost  low solubility of ozone in water  UV RADIATION  Damage the genetic structure of bacteria, viruses and other pathogens.  Advantages: no chemicals are used More rapid water taste more natural No by-products formed  Disadvantages:  high maintenance of the UV- lamp  MEMBRANE FILTRATION  Membrane technologies disinfect treated wastewater by physically filtering out micro organisms.  Does not require addition of reactive chemicals  No toxic by-products are produced. ❖ Membrane technologies include: ❖ reverse osmosis,ultrafiltration, microfiltration, nanofiltration.