1. BIODEGRADATION OF SYNTHETIC PRODUCTSSadiq

2. BIODEGRADATION Biodegradation (i.e. biotic degradation) is a chemical degradation ofmaterials (i.e. polymers) provoked by the action of microorganisms such asbacteria, fungi and algae. Biodegradation is expected to be the major mechanism of loss for mostchemicals released into the environment. This process refers to the degradation and assimilation of polymers by livingmicroorganisms to produce degradation products. Biodegradable materials degrade into biomass, carbon dioxide and methane.In the case of synthetic polymers, microbial utilization of its carbon backboneas a carbon source is required. Natural polymers (i.e., proteins, polysaccharides, nucleic acids) are degradedin biological systems by oxidation and hydrolysis. 3. MICROORGANISMS IN BIODEGRADATIONBACTERIA Bacteria important in the biodegradation process include, inter alia, Bacillus (capable ofproducing thick-walled endospores that are resistant to heat, radiation and chemicaldisinfection) Pseudomonas, Klebsiella, Actinomycetes, Nocardia, Streptomyces, Thermoactinomycetes,Micromonospora, Mycobacterium, Rhodococcus, Flavobacterium, Comamonas, Escherichia,Azotobacter and Alcaligenes(some of them can accumulate polymer up to 90% of their drymass).FUNGI Fungi active in the biodegradation process are Sporotrichum, Talaromyces, Phanerochaete,Ganoderma, Thermoascus, Thielavia, Paecilomyces, Thermomyces, Geotrichum,Cladosporium, Phlebia, Trametes, Candida, Penicillium, Chaetomium, andAerobasidium . 4. TYPES OF BIODEGRADATIONThe biodegradation process can be divided into Aerobic degradation Anaerobic degradationAerobic biodegradation:Polymer + O2 -> CO2 + H2O + biomass + residue(s)Anaerobic biodegradation:Polymer -> CO2 + CH4 + H2O + biomass+ residue(s)If oxygen is present, aerobic biodegradation occurs and carbon dioxide is produced.If there is no oxygen, an anaerobic degradation occurs and methane is produced instead ofcarbon dioxide .The chemical structure (responsible for functional group stability, reactivity, hydrophylicityand swelling behavior) is the most important factor affecting the biodegradability of polymericmaterials. Other important factors are inter alia, physical and physico-mechanical properties,e.g., molecular weight, porosity, elasticity and morphology 5. PolymerOligomers,dimers,monomersMicrobial biomassCh4, H2s,H2o,Co2Microbialbiomass Co2,H2oDEPOLYMERASESAerobic Anaerobic 6. BIODEGRADATION OF SYNTHETIC PRODUCTSSYNTHETIC COMPOUNDS(XENOBIOTICS) Nitro aromatic compounds (NACs), polycyclic aromatics and other hydrocarbons (PAHs)that are constituents of crude oil, and halogenated organic compounds together constitutea large and diverse group of chemicals that are responsible for causing widespreadenvironmental pollution. Xenobiotics are manmade compounds, frequently halogenated hydrocarbons, that arenotoriously difficult for microbes to breakdown in the environment. Biodegradation ofsynthetic materials is complicated. Anaerobic bacteria able to degrade xenobiotics are present in various anaerobic habitats,inter alia sediments, water laden soils, reticuloruminal contents, gastrointestinal contents,sludge digesters, feedlot wastes, groundwater, and landfill sites. D. oleovorans, G. metallireducens, D. acetonicum, Acidovorax, Bordetella, Pseudomonas,Sphingomonas, Variovorax, Veillonella alkalescens, Desulfovibrio spp., Desulfuromonasmichiganensis, and Desulfitobacterium halogenans are the major groups of anaerobicmicroorganisms involved in biodegradation of xenobiotic compounds. 7. BIODEGRADATION OF AROMATIC COMPOUNDS Aromatic compounds are ubiquitous in nature. Most are not of biosynthetic origin but are derived from the pyrolysis of organic compounds. Benzene ring is the most widely distributed unit of chemical structure in nature. Benzene,ethyl benzene, toluene, styrene, and the xylenes are among the 50 largest-volume industrialchemicals produced, with production figures of the order of millions of tons per year. Thesementioned compounds are widely used as fuels and industrial solvents. Provide the starting materials for the production of pharmaceuticals, polymers,agrochemicals, and more . Aromatic compounds can be degraded under nitrate-reducing, iron-reducing, sulfate-reducing,and methanogenic conditions. Aerobic degradation of aromatic compounds involves their oxidation by molecular oxygen. Microorganisms use oxygen (during aerobic respiration) to hydroxylate the benzene ring,finally the aromatic double bonds are cleaved to degrade the aromatic compounds. Pseudomonas, Ralstonia, Burkholderia, Sphingomonas, Flavo- bacterium , Bacillus andmarine sulfate reducing bacteria (that use sulfate as the electron acceptor)..are some of theexamples of microbes degrading aromatic compounds. 8. BIODEGRADATION OF PLASTICS There are different mechanisms for the degradation of plastics: thermal, chemical, photo andbiodegradation. Polyethylene is a synthetic polymer having high hydrophobic level and high molecular weight. Polyurethanes (PU) represent the most common class of polymers which is used in themedical, automotive and industrial fields. polymers are consumed by various microorganisms as carbon and energy sources and variousenzymes like polyhydroxyalkanoates (PHA) depolymerases secreted by them help in thedegradation of plastics. Some of those bacteria that can degrade polyester in vitro and which utilize the PUR as solecarbon source have been identified from the genera Pseudomonas, Comamonas, and Bacillus. Emericella, Trichoderma, Aspergillus, Fusarium, Gliocladium and Penicillium. Geomycespannorum was found to be the predominant plastic degrading fungi. 9. PVA BIODEGRADATION Poly(vinyl)alcohol is a vinyl polymer in which the main chains are joined by only carbon-carbonlinks. first report of degradation by Fusarium lini . Scientists have isolated the Pseudomonas bacteria from soil bacterium growing on PVA asthe source of carbon. Pseudomonas is the main PVA degrader. This bacterium produces and secretes an enzyme that degrades PVA. Polivinyl alcohol dehydrogenase (PVADH) from Pseudomonas ssp.POLY CAPROLACTONE PCL is a synthetic linear polyester with almost 50% crystallinity. It is biologically degradable , the environmental degradation of PCL is affected by theactions of bacteria that are widely distributed in the ecosystem. some filamentous fungi and yeasts also can hydrolyze PCL to water-soluble products. Pullularia pullulans can efficiently degrade a lower molecular weight PCL film PCL degrading microorganisms that produce different types of PCL hydrolases and lipasesof R. delemar and Rhizopus arrhizus. Ester-linkages of PCL are easy to hydrolyze by microbial enzyme degradation. 10. POLY L-LACTIDE (PLA) PLA is a biocompatible thermoplastic with a melting temperature of 175C. It is synthesized by the polymerization of L-lactic acid. PLA can be hydrolyzed by the lipase from R. delemar and the proteinase K fromTritirachium album and also by the polyester polyurethane depolymerase fromComamonas acidovorans. PLA is more resistant to microbial attack in the environment than other microbial andsynthetic polyesters.POLYESTERS Monomers are bonded by ester linkages. Enzymes that degrade this polymer are ubiquitous in living organisms (e.g.,Thermomonosfora Fusca and Streptomyces albus). The most important factors affecting biodegradability are molecular mass and crystallinity 11. POLYETHYLENE (PE) Polyethylene is widely used for various one-trip applications like food packaging, retailindustry uses and agricultural uses. PE is the most problematic plastic that is resistant to microbial attack. Polyethylene is a synthetic polymer with CH2-CH2 repeating units in the polymer backbone. This polymer is resistant to biodegradation, which results from highly stable C-C and C-Hcovalent bonds and high molecular weight. The mechanism of biodegradability of polyethylene includes alteration by adding a carbonylgroup (C=O) in the polymer backbone. The altered polyethylene molecule undergoes biotic oxidation.carbonyl groups(In PE)mono oxygenase enzymealcoholalcohol dehydrogenasealdehydealdehyde dehydrogenaseFatty acidUndergo biodegradation 12. NYLON Nylons are produced in large quantities as fibers and plastics all over the world. Nylon is one of the most important synthetic polymers. The very poor biodegradability of nylon due to its strong intermolecular cohesive force causedby hydrogen bonds between molecular chains. Nylon is a synthetic polyamide with repeating amide groups (-CONH-) in its backbone. Bacterium Geobacillus thermocatenulatusis used to biodegrade nylon 12 and nylon 66. Bacterial degradation of nylon 12 is associated with the enzymatic hydrolysis of amine bonds. Some forms of nylons have been shown to biodegrade by fungi and bacteria. 13. MECHANISM OF ENZYMATIC BIODEGRADATIONMicroorganismsSecretion of extracellular enzymesAdherence of enzymes to the plastic surfaceCleavage of polymer chainsErosion of plastic surface i.e BiodegradationEnd products like CO2, H2O and CH4 are produced 14. MECHANISM OF ENZYMATIC BIODEGRADATION The most attractive plastic waste treatment method is enzymatic degradation. Polyethylene degradation through microbial enzymes comprises two steps. Firstly enzyme adheres to the polyethylene substrate and then catalyzes a hydrolic cleavage. Intracellular and extracellular depolymerases in fungi and bacteria degrade the polyethylene. Complex polymers disintegrate into short chains of oligomers, dimers, and monomers whichcan pass through the bacterial membranes and act as a source of carbon and energy. Thisprocess is referred as depolymerisation. And mineralization is the degradation process inwhich the end products are carbon dioxide (CO2), water (H2O) or methane (CH4) areproduced . Temperature, pressure and moisture are the physical parameters which mechanically damagethe polymers due to which the biological forces like enzymes and other metabolites producedby microbes induce the process. 15. ENZYMES VARIES WITH PLASTICSEnzymes are very specific in their action on substrates, so the different enzymes help in thedegradation.Laccase produced by the actinomycete R.ruber, involved in biodegradation of polyethylene. Laccasesare mostly present in lignin- biodegrading fungi, where they catalyze the oxidation ofaromatic compounds. Laccase activity is known to act on non-aromatic substratesPapain and urease are the two proteolytic enzymes were found to degrade medical polyester polyurethane.Polymer degraded by papain was due to the hydrolysis of urethane and urea linkagesproducing free amine and hydroxyl groups.Some strains which are capable of degrading the polyethylene are Brevibacillus spp., Bacillusspp., where proteases are responsible for degradation .The enzymes responsible for biodegradation by Pseudomonas spp. are serine hydrolases,esterases and lipases 16. SIGNIFICANCE OF ENZYME BIODEGRADATIONBiodegradation process is very eco-friendly. The growth of the microbes responsible forbiodegradation must be optimized by controlling the temperature, humidity, incubation time andthe substrate like polyethylene, polyurethane which are consumed as a carbon and energysource. This helps in the production of large amount of enzyme. These microbial enzymes inducethe rate of biodegradation of plastics very effectively without causing any harm to theenvironment 17. BIOPLASTICS Bioplastics are biodegradable plastics. It means these types of plastics are either producedfrom fossil materials or can be synthesized from biomass or renewable resources. Plastics can be biodegradable by improving the hydrophilic level, or polymer chain length canbe reduced by oxidation which is to be accessible by microbial growth. Some polymers are being used for the manufacture of biodegradable plastics likepolyhydroxybutyrate (PHB) and copolymers containing other hydoxyalkanotes. Thesepolymers are consumed by various microorganisms as carbon and energy sources and variousenzymes like polyhydroxyalkanoates (PHA) depolymerases secreted by them help in thedegradation of these types of plastics . The major advan- tages of biodegradable plastics are that they can be com- posted withorganic wastes and returned to enrich the soil. Their use will not only reduce injuries to wild animals caused by dumping of conventionalplastics, but will also lessen the labor cost for the removal of plastic wastes in the environment They could be recycled to useful monomers and oligomers by microbial and enzymatictreatment.