Abstract
The aim of this study was to evaluate the efficiency and optimization of co-digestion using sewage sludge (SS), maize straw (MS) and cow manure (CM) as feeds, and the effects of the mixing ratio and C/N ratio of the substrates were analyzed in detail. Among the three substrates tested, CM/MS exhibited better digestion than CM/SS and SS/MS in terms of all measures, including total daily biogas and net methane volume production, due to the hydrophilic characteristics and high level of biodegradability of CM, as well as its higher C/N ratio. The average biogas production was 613.8 mL/g VS for the co-digestion of CM/MS at a feed concentration of 15 g VS/L and using a 1:1 mixing ratio (C/N ratio of 28.3). The co-digestion of SS/CM/MS performed better than the individual digestion of the components because of the balanced C/N ratios and supply of carbon. The optimum conditions for maximizing methane potential were an SS:CM:MS ratio of 30:35:35 and a bulk VS concentration of 15.0 g VS/L, which led to a maximum methane production of 8047.31 mL (C/N ratio of 12.7). The high-throughput sequencing analysis showed clear differences in microbial communities during the entire co-digestion process.
Highlights
The continuous development of the animal husbandry, wastewater treatment, and agricultural industries in China has resulted in increasing discharges of cow dung, sewage sludge, and maize straw into the environment[1]
hydrophobic acid (HPO-A) (41.2%) and HPI (32.7%) were the predominant fractions of the sewage sludge (SS)-related extracellular polymeric substances (EPS), whereas that of the other three fractions decreased in the trend of transphilic acid (TPI-A) (19.3%) > transphilic neutral (TPI-N) (3.6%) > hydrophobic neutral (HPO-N) (3.3%)
The fractional organics of the supernatant sludge were distributed as HPO-A (37.5%) > HPI (27.3%) > TPI-A (14.9%) > HPO-N (11.8%) > TPI-N (8.5%)
Summary
The continuous development of the animal husbandry, wastewater treatment, and agricultural industries in China has resulted in increasing discharges of cow dung, sewage sludge, and maize straw into the environment[1]. Among all of the disposal processes, anaerobic digestion has attracted much attention in recent years due to its efficient reduction of organic matter and energy extraction (CH4 and H2)[3]. To improve the performance of anaerobic digesters, the co-digestion of different organic wastes, such as activated sludge, kitchen waste, vegetables, livestock, straw and poultry dung, has attracted much attention in recent years[6,7]. Lab-scale anaerobic digesters were operated using different substrates and C/N ratios via the gradual changes in the sewage sludge (SS), cow manure (CM) and maize straw (MS) mixing ratios. The first objective of the present study was to assess the methane production rate and organic removal rate of the co-digesters under different operation parameters. The sequenced genome of the biomass within the reactors was periodically analyzed to identify the variation in microbial communities during the entire co-digestion process
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