Plastic waste management

PLASTIC WASTE MANAGEMENT

PLASTIC WASTE MANAGEMENTVISHNU RAJ R14CE63R09

Plastics Plastics are synthetic polymers derived from petro-fossil feedstock and made-up of long chain hydrocarbons with additives

Two types of plastics Thermoplastics(Recyclable)-become soft when heated, can be moulded or shaped with pressure when in plastic stateThermosets (Non Recyclable)-Once set cannot be remoulded /softened by applying heat.

Types of Plastics

Environmental Issues

Plastic waste disposal on land makes it infertileBurning generates toxic emissions -CO, HCl, Dioxin, FuransLeaching out of toxic chemicals added as additivesLittering Affects waste processing facilities like compostingIn efficient usage of crude oil resources

Plastic Waste Management

Recycling of plastics

Primary Recycling: involves processing of a waste into a product with characteristics similar to those of original product.Secondary (Mechanical)Recycling: processing of waste plastics into products that have characteristics dissimilar from those of original plastic productsTertiary(Chemical) Recycling: extraction of chemicals from plastic wastesQuaternary Recycling: recovery of energy from wastes

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Sorting Of Plastic WastesDensity sortingHydrocyclones- uses centrifugal force, enhance material wettability.Heavy medium separation -using tetrabromoethaneTriboelectric separation- sorts materials on the basis of a surface charge transfer phenomenonSpeed accelerators Paint Removal Grinding & Solvent stripping

Mechanical RecyclingCan only be performed on single-polymer plastic

Steps involvedCrushing/ShreddingContaminant separation: FloatationMillingWashing and DryingAgglutinationExtrusion

Mechanical recycling steps as described by Aznar et al. (2006).

Existing recycling processes & IssuesSelection of waste: Toxic wastes are separatedSegregation of plastics waste: Segregation shall be done in accordance with IS 14535Processing (extrusion process) Washing generates waste water having high pollution load & needs treatment before proper disposal

Exposure of workers in reprocessing plant to toxic dyes and additives

CONVERTING WASTE INTO A RESOURCEquality concerns when converting waste plastics into fuelresources areSmooth feeding to conversion equipmentEffective conversion into fuel productsWell-controlled combustion and clean flue gas in fuel user facilities

plastics & fuel they produce

SOLID FUEL PRODUCTIONTwo types of solid fuelrefuse derived fuel (RDF)refuse-derived paper and plastic densified fuel (RPF) Thermoplastics act as a binder for the other components Contamination of plastics with other plastics containing halogens (Cl, Br, F), N, S and other hazardous substances may cause air and soil pollution

Production method

Involves two steps- pretreatment and pellet productionTwo types of commercial production systemslarge-scale model(3 ton/hour)with pretreatment for the separation of undesirable contaminationsmall-scale model (150 kg/hour) without pretreatment equipmentHeating valuesRDF: 4000 5000 kcal/kgRPF: 6000 8000 kcal/kg

Schematic diagram of pretreatment process

Schematic diagram of a pelletizing process

Liquid Fuel Production

Based on the pyrolysis of the plastics and the condensation of the resulting hydrocarbonsThermoplastics (PE, PP, and PS)are used for conversion.Decomposition occur at 450 to 550 C.The products generated from include gasoline, diesel, benzene, naphtha, and fuel oil The by-products from the process - sludge and gas are reused.

PVC plastics waste is not used as the chlorine can be converted into HCl as a by-product

Schematic diagram of a liquid fuel production plant (UNEP, 2009)

Gaseous Fuel ProductionWaste plastics undergo thermal decomposition in a tank reactor for an extended time at a reaction temperatureOccurs at higher temperatures 800 -1000 CTwo types of gaseous fuel are produced: Gaseous hydrocarbon & SyngasCalorific value of syngas ranges between the calorific value of biogas and LNG/LPG.

Gasification process for converting plastic wastes to chemicals (PCD, 2011)

ObservationsImpact, Los Angels Abrasion & Crushing Value increased with the increase in the percentage of plastics.Better skid resistance Unevenness index values were low (3000 mm/km) indicating good surface evenness.Better resistance towards water stagnation i

Co-processing of Plastic waste in Cement Kiln

Plastic waste is used as an alternative fuel in cement Kilns Primary fuel and raw material are substituted by waste

Pre-processing of plastic waste

Plastic waste is sun dried and subjected to shredding before feeding into cement kilns

PVC containing plastic waste is not used as it impair the cement quality

Plasma PyrolysisDisintegration of organic compounds into gases and non leachable solid residues in an oxygen-starved environmentUses ions and excited molecules with high energy radiation to decompose chemicalsHigh temperature decomposes waste material into simple molecules

Efficient way of treating chlorinated plastics Dioxins and furans emissions are below the prescribed limits ie, the range of 0.005-0.009 ng/m3Ideal for decentralized disposal of plastic waste Reduction in volume of organic matter > 99%Segregation of the waste is not necessary

DEGRADABLE PLASTICS TypesPoly-Lactic Acid (PLA) produced in a two-step fermentation and chemical polymerization processPolyhydroxyalkanoate (PHA) synthesized by bacteria as intracellular carbon and energy storage compoundsPoly olefins modified by adding transition metals/compounds Oxo-biodegradable plastics

Moisture and heat attack PLA polymer chains, splitting them apart through hydrolysis, to lactic acid monomers which are consumed by microbesPHA plastics are attacked by microorganisms that secrete PHA depolymerizer, and most products take three to nine months to degradePolyolefins are decomposed by UV or heat-initiated oxidation

Plastic degradation processes

Photo degradation: Degradation caused through the action of sunlight on the polymerBiodegradation :Degradation that occurs through the action of microorganisms such as bacteria, yeast, fungi, and algae etc.Biodeterioration: Degradation that occurs through the action of microorganisms such as beetles, slugs, etc.Autooxidation :Degradation caused by chemical reactions with oxygen.Hydrolysis: Degradation that occurs when water cleaves the backbone of a polymer, resulting in a decrease in molecular weight and a loss of physical propertiesSolubilization: Dissolution of polymers that occurs when a water-soluble link is included in the polymer

Compatibility of Degradable Plastics with Current SWM PracticesComposting Require specific levels of moisture and oxygen & inadequate temperatures may not initiate the key hydrolysis reaction for PLAs Recycling The increase in input heterogeneity will reduce the quality of the recovered plasticWaste-to-Energy Incineration Less CO2 emissionsLandfilling Decay and release of more methane , production of higher strength leachate & sequestration of carbon,

DrawbacksHigher costsDifficulty in recycling concerns regarding potential later degradation of the end productsRequirement of specific levels of moisture and oxygen for initial reactions to occur

References

Recycling and recovery routes of plastic solid waste (PSW): A review, S.M. Al- Salem , P.Lettieri, J. BaeyensEnvironmental evaluation of plastic waste management scenarios: L. Rigamontia, M.Grossoa, J. Mllerb, V. Martinez Sanchezb,S. Magnania, T.H. ChristensenA Review of Plastic Waste Management Strategies:Javeriya Siddiqui and Govind Pandey, International Research Journal of Environment SciencesDevelopment of process for disposal of plastic waste using plasma pyrolysis technology and option for energy recovery: M. Puncochara, B. Rujb, P. K. ChatterjeeDegradable Plastics and Solid Waste Management Systems: David J. Tonjes ,Krista L. Greene

IS 14534 1998 -GUIDELINES FOR RECYCLING OF PLASTICSPreliminary Study On The Conversion Of Different Waste Plastics Into Fuel Oil : Yasabie Abatneh, Omprakash SahuBiodegradability of Plastics : Yutaka Tokiwa,Buenaventurada P. Calabia,Charles U. UgwuandSeiichi AibaRecycling of plastic: accounting of greenhouse gases and global warming contributions : Thomas Astrup, Thilde Fruergaard, Thomas H. Christensen