Influence of the degree of waste pre-treatment on carbon emissions' production and nature.

Abstract

This study was carried out to gain knowledge of the degradation processes in an anaerobic environment of pre-treated waste for different degrees of pre-treatment and the evolution of waste pre-treatment by forced aeration. Pre-sorted MSW (MSW) was pretreated by composting for 16 weeks in a laboratory scale using forced aeration. Oxygen concentrations were maintained at 15-18% of oxygen in air for the first 8 weeks and 10-15 % for the later 8 weeks. The ambient temperature was kept constantly between of 20-35 QC. Representative samples of waste from the reactor were collected every fortnight wherein analysis and full characterisation on the solid matter (C/N ratio, TS and VS, R17, Biogas) and on the eluate (BOO, COD, TOC, TKN, Conductivity, pH, NOx and NH3)) were conducted. The process showed a sharp increase in temperature in the first 6 weeks, ranging from 30- 70 QC indicating a period of high biological activity, a decrease from day 30 to day 50 from 70 to 30 QC and a consistent decrease throughout the later days of the process from 35-25 QC. The sharp increase in temperature signifies a period of maximum biological activity, where readily biodegradable material decomposes as well as some of the resistant materials pointing out the success and efficiency of the forced aeration process. For the first 25 days in an anaerobic environment, waste pre-treated for four weeks was the most active, indicated by a large volume of gas produced. For the MSW pre-treated for 8, 10, 12 and 16 the volume of gas produced remained basically similar throughout the length of the experiments. CH4 production in an anaerobic reactor shows an increasing trend for all degrees of stabilisation up to 6 weeks, after that the gas production and quality deceases and is comparable to the remaining degrees of treatment. A gradual decrease in concentration of key parameters (organics) analogous to the European limit in Europa (1998), were observed after 5 weeks pre-treatment. The study highlighted that the highest efficiency of pre-treatment is achieved in 6 to 8 weeks and, therefore it is not recommended to prolong the treatment any further.