Effects of disintegration on anaerobic degradation of sewage excess sludge in downflow stationary fixed film digesters

Abstract

The effects of mechanical disintegration on anaerobic digestibility of sewage excess sludge in downflow stationary fixed film (DSFF) digesters were investigated on laboratory scale. Mechanical pretreatment using a high pressure homogenizer led to significantly enhanced concentrations of soluble proteins and carbohydrates in the feed sludge. Using DSFF digesters with two different tubular plastic media as support material it was shown that a stable digestion process could be achieved at hydraulic retention times (HRT) down to 5 days. Compared to conventional digesters at 10 d and 15 d HRT respectively, the degradation of volatile solids was enhanced up to 25%, also resulting in a higher specific biogas production. Further investigations on degradation of soluble proteins and carbohydrates showed that a slowly degradable fraction of carbohydrates was released via disintegration. Using the distribution of chain length and the concentrations of volatile fatty acids as process parameters, the dependability on the HRT and the degree of disintegration (the release of soluble COD) predominated the effects of specific surface area of the support media.

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 .…”

Heavy metal uptake by wheat from a sewage sludge-amended calcareous soil

“…This can result in beneficial effects on soil fertility and plant nutrition (Casado-Vela et al 2007; Gascó and Lobo 2007). Moreover the organic matter added by sludge can improve many physical properties of agricultural soils such as water holding capacity, aeration and porosity (Engelhart et al 2000). However, if the quality of the sludge is not controlled, its application can also result in excessive concentrations of trace metals such as Pb, Cd, Zn, Cu and Ni in soils (Adamu et al 1989;Al-Najar et al 2005;Keller et al 2001).…”

Heavy metals in sewage sludge amended soils determined by sequential extractions as a function of incubation time of soils

“…It provides organic matter (OM) to soil and this addition may represent a good alternative to prevent degradation of soils (Roldan et al, 1996) and to improve many physical properties of agricultural soils such as water holding capacity, aeration, porosity and cation exchange capacity (Engelhart et al, 2000). Moreover, the application of this residue offers the possibility of recycling plant nutrients with the beneficial effects on soil fertility and plant nutrition (Casado-Vela et al 2007;Gascó and Lobo, 2007).…”