The Acidogenic Digestion of the Organic Fraction of Municipal Solid Waste for the Production of Liquid Fuels

Abstract

Several reactors were tested for the anaerobic conversion of the organic fraction of municipal solid waste into volatile fatty acids. The reactors examined included Batch, Semi-Continuous Stirred Tank Reactor and Multistage-Counter Flow Reactor. After reasonable retention times (12 days), Batch systems operating at 15% w/v of dry matter and under pH controlled at 6.5, gave better performances both in terms of total Volatile Fatty Acids (VFA) concentration (23-24 g/l) and conversion yield (215 g VFA/kg volatile solids). However, these conditions of reaction caused a high level of liquefaction of the feedstock which resulted in a difficult down-stream processing. On the contrary, the acidogenesis under uncontrolled pH, allowed the production of leachates directly processable for acids recovery. Based on this reason, the Multistage-Counter Flow Reactor, operating under uncontrolled pH, appeared to be the most promising system. The leachate obtained from such a system was processed to obtain mixtures of C2-C7 methyl esters, potentially usable as octane enhancers. The digested solid was intended to be dried and refined to obtain soil amendment. A process for the treatment of municipal solid waste based on the previous steps and including conventional sorting facilities and units for the incineration of all residual solids, was evaluated to be economically comparable with landfilling. The revenues from the sales of esters and fertilizers were highly sensitive to the yield of the acidogenic step and to the value and the amount of the derived fertilizer. Further research is still in progress to improve the economics of the process. The activities are addressed to study proper procedures for the improvement of the down-stream processing of the mixtures originating from acidogenesis under almost neutral pH.

Design of acidogenic reactors for the anaerobic treatment of the organic fraction of solid food waste

“…It is interesting to compare these results with those reported by D'Addario et al [7]. They obtained 18.5 g TVFA/l and 10.6% of solubilization rate with organic fraction of the municipal solid wastes for the same conditions.…”

“…Acidogenesis was not limited by hydrolysis but the soluble compounds which had been produced were limitant or inhibitor. D'Addario et al [7] had already observed this phenomenon.…”

“…D'Addario et al [7] tested the acidogenic digestion of the organic fraction of municipal solid waste. They obtained at an HRT of 12 days 14.3 g TVFA/l with a completely mixed reactor, 15.6 g TVFA/l with a batch reactor and 18.2 g TVFA/l with a multistage-counter¯ow reactor.…”

“…The VFA would be extracted and converted to products, such as methyl or ethyl esters for commercial purposes, D'Addario et al [7]. The VFA produced could also be the substrate for activities of denitrifying and phosphore removal bacteria.…”

Volatile fatty acids production from food wastes and its application to biological nutrient removal

“…The optimization of fermentation conditions should be carried out for ef®cient biological nutrient removal. The yield of total organic acids were 379±400 g VFA/kg VS 0 , which is signi®cantly higher than 200±250 g VFA/kg VS 0 of the organic fraction of municipal solid waste (OFMSW) by Pavan et al [3] and D'Addario et al [11].…”