Session- Plastics:  Challenges and Solutions




MSW Composting: Comminution of Non-Degradables Into Humus-Plastic Aggregatess




Woods End Research Laboratory, USA


Municipal Solid Waste (MSW) has for decades been processed into compost. Community collection of residential trash followed by discrete steps of pre-sorting and tumbling or batch processing and windrowing are the characteristics of the industry.  European studies in the 80's showed high levels of contamination may result when metals, PCB's and PAH's inadvertently enter the fine compost fraction from non-segregated sources and subsequent physical comminution and particle size reduction in pre-grinding and processing/turning steps. The results of these studies provided new impetus towards source separation and nongrinding of initial MSW wastes. Our present study is conducted intensively for two MSW streams from New York City and subsequently compared with 4 other MSW compost streams from other cities in North America. The results indicate that despite non-grinding prior to batch composting and careful post-compost screening steps to remove plastic or non-degradable fractions called "overs", a net increase in non-degradable fines resulted. These non-degradable fines are not be measured by the classifcal procedure to determine inert content. Chemical and refined separation techiques including optical miscroscopy, FTIR, SEM and chemical screening are employed and indicate that MSW compost fines are comprised largely of an aggregate of PVC, PET, Polyester, polystyrene and other non-degradbale fractions of fibers of 100-200 micron dimension interspersed with humus. High chemical residue content of phthalate esters confirms plastic donors with are refractory to composting. The study suggests that correct characterization and use of MSW compost products needs to be examined more carefully before expansion of the industry.


Biopolymers in Biological Solid Waste Treatment


LUC DE BAERE  and  Richard Tillinger




The purpose of most of the biopolymers is that the products containing the biopolymers can ultimately be disposed of together with other postconsumer waste in biological solid waste treatment systems. It is in combination with the treatment of municipal solid waste that biopolymers can attain their greatest environmental and economic benefit. Non-degradable plastics are an important and ever increasing component of the municipal solid waste. They offer specific opportunities as far as the calorific value is concerned in order to produce high-quality RDF. On the other hand, non-degradable plastics present various challenges when it comes down to biological treatment systems. They require specific handling such as debagging and cause certain processing as well as compost quality problems. Biopolymers could solve many of these problems, especially for the treatment of yard waste, biowaste or the wet fraction coming from source separate collection. Two cases of operating plants, one aerobic and one anaerobic plant, will be examined with regard to treatment problems due to the presence of non-degradable plastics, the impact of the introduction of biodegradable bags, and the potential savings if all of the plastics present in the incoming wastestream were made up of polymers.


Movement of Foreign Matter in Municipal Solid Waste Compost Amended Soil


PAGE, NATASHA T. (1) and Leonard, Jerry J.(1)


(1) University of Alberta, Canada


Composting MSW and sewage treatment biosolids has become an increasingly popular alternative to landfilling the waste. The final product is utilized as a soil amendment in agricultural, horticultural, and reclamation industries, if the compost meets standards limiting contaminants.  Little data exists on the amount of plastic, glass, and metal particles present in non-source separated MSW compost and their fate when used to amend agricultural soils. Two compost samples from the same batch of MSW were analyzed in this study.  One came directly from the curing pile, while the other was subjected to a final screening with a 3/4 trommel screener. Size and type of FM content were measured in the compost samples to determine their mass fractions. Plastics were broken up into different categories based on physical size and shape.  The size ranges include 0.5 < 2mm, 2 < 12.5 mm, 12.5 < 25 mm, and >25mm.  The plastic was further divided into fibres, films, chips, and blocks.  A rainfall simulator was utilized to assess how intense rainfall influenced FM particle movement on and through the soil profile. Compost was added at 50T/ha to 42L of gray luvisolic soil in 0.95 x 0.5m trays at 5 degrees and 12 degrees slopes, and subjected to 65mm/h rainfall.  FM was filtered from the runoff and measured at 20min intervals for 80min.  The most abundant FM was plastic, with trace amounts of glass and metal.  The highest number of fibres came from paper products.



Testing the Biodegradability of Polymeric Materials


GEORGE M. SAVAGE and Luis F. Diaz


CalRecovery, Inc., Concord, CA


The introduction of new biodegradable polymeric materials into manufactured products raises the question of the fate of these materials when they enter the post-consumer waste stream. In particular, their performance when subjected to biological processing is of utmost importance to the operators of solid waste processing facilities. Some key considerations are the rate of biodegradability and the operating conditions required for processing waste containing biodegradable polymers. Methods of measuring biodegradability are presented along with the results of degradability testing. The relation of methods of measurement of biodegradability to actual conditions experienced during biological processing (including backyard composting) is also described.