Impact of different particle size distributions on anaerobic digestion of the organic fraction of municipal solid waste

Abstract

Particle size may significantly affect the speed and stability of anaerobic digestion, and matching the choice of particle size reduction equipment to digester type can thus determine the success or failure of the process. In the current research the organic fraction of municipal solid waste was processed using a combination of a shear shredder, rotary cutter and wet macerator to produce streams with different particle size distributions. The pre-processed waste was used in trials in semi-continuous 'wet' and 'dry' digesters at organic loading rate (OLR) up to 6 kg volatile solids (VS) m -3 day -1 .The results indicated that while difference in the particle size distribution did not change the specific biogas yield, the digester performance was affected. In the 'dry' digesters the finer particle size led to acidification and ultimately to process failure at the highest 1 * Corresponding author: Tel.: +44 (0)2380 592188; fax: +44 (0)2380 677519; E-mail address: Y.Zhang@soton.ac.uk (Yue Zhang) 2 OLR. In 'wet' digestion a fine particle size led to severe foaming and the process could not be operated above 5 kg VS m -3 day -1 . Although the trial was not designed as a direct comparison between 'wet' and 'dry' digestion, the specific biogas yield of the 'dry' digesters was 90% of that produced by 'wet' digesters fed on the same waste at the same OLR.

Anaerobic Digestion of Municipal Biowaste for the Production of Renewable Energy: Effect of Particle Size

“…Nevertheless, for all of the samples, the uniformity coefficient, Cu, was greater than 3 (Table 4), which indicates the variability of particle sizes. This result agrees with the investigations performed by Zhang and Banks (2013), who assert that during the grinding processes, different particle sizes are achieved; these can influence certain phases of the AD process, particularly hydrolysis, when the greatest enzymatic activity during the anaerobic process occurs. Figure 3 shows that the lag phase for the latter was approximately 2.5 d (60 hours), which indicates that although the substrate predominantly contains particulate organic material, its size not only allowed adaptability of the biomass but also the microbial communities rapidly transformed the MBW (Mata et al, 2000).…”

“…Moreover, the sizes of the smallest particles can lead to shorter retention times, which entails lower operational costs. Although In the literature there are different recommended particle size ranges (0.1-30 mm), it is recommendable to evaluate this aspect for each particular case (Zhang and Banks, 2013). Banks et al (2010), in a large scale study, found that with particle sizes between 10 and 30 mm, the optimum methane production was achieved without reaching the point at which particle sizes can cause excessive production of volatile fatty acids (VFAs).…”

A comprehensive review on operating parameters and different pretreatment methodologies for anaerobic digestion of municipal solid waste

“…Davidson et al found small variations in both methane yields per g VS (gram volatile solids) and content of methane in biogas after pretreatment [75] 7 Organic fraction of municipal solid waste No significant enhancement is found with mechanical pretreatment methods [76] 8 Organic fraction of municipal solid waste Shredder with magnetic separation method yielded a higher (5.6-13.8% as compared to the other methods) methane production [77] 9 Food waste The screw press pretreatment method also result in a loss of biodegradable materials and nutrients, even though it enhances the biogas production in general [78] 10 Food waste Size reduction through a beads mill resulted in a 40% higher COD solubilization, which led to a 28% higher biogas production yield [79] 11 Organic waste As the methanogens are sensitive to acidic intermediates, excessive size reduction may result in a decreased AD process performance [80] 12 Municipal solid waste Electroporation pretreatment of OFMSW resulted in 20-40% higher biogas production [81] 13 Sludge Liquefaction resulted in 15-26% higher biogas production [64] 14 Organic fraction of municipal solid waste Sonication resulted in 16% higher cumulative biogas production as compared to untreated substrates [82] 15 Organic solid waste Size reduction up to 0.35 mm resulted in a 20% increase, and no significant difference was observed with further size reduction [83][84][85][86] 16 Sewage sludge Achieved a 25% increased VS reduction with HPH method [84] 17 Waste activated sludge Studied sonication of waste activated sludge (WAS) and obtained only a negligible increase in both VS destruction and mesophilic methane production [83][84][85][86][87] 30-60% are obtained for highly particulate organic matter as manures. The pH in the reactor plays an important role in the biogas composition especially in the equilibrium of the CO 2 .…”

Effect of substrate pretreatment on particle size distribution in a full-scale research biogas plant

“…In order to generate the best possible biogas yield and to avoid problems with the process technology, substrate pretreatment is applied at many BGP. Pretreatment of materials with a high fiber content results in a smaller particle size and therefore increases the substrate surface to provide more access for microbial degradation, hence the rate and degree of degradation increases after size reduction (Palmowski and Müller, 2003;Zhang and Banks, 2013). The literature provides many examples about the positive effect of pre-treatment on biogas production.…”