Abstract
Three semicontinuous continuous stirred-tank reactors (CSTR) operating at mesophilic conditions (35°C) were used to investigate the effect of hydraulic retention time (HRT) on anaerobic digestion of wheat straw. The results showed that the average biogas production with HRT of 20, 40, and 60 days was 46.8, 79.9, and 89.1 mL/g total solid as well as 55.2, 94.3, and 105.2 mL/g volatile solids, respectively. The methane content with HRT of 20 days, from 14.2% to 28.5%, was the lowest among the three reactors. The pH values with HRT of 40 and 60 days were in the acceptable range compared to that with HRT of 20 days. The propionate was dominant in the reactor with HRT of 20 days, inhibiting the activities of methanogens and causing the lower methane content in biogas. The degradation of cellulose, hemicellulose, and crystalline cellulose based on XRD was also strongly influenced by HRTs.
Highlights
The estimated annual production of wheat straw is 681.92 million tons of dry biomass, produced as a by-product of wheat cultivation throughout the world [1]
The main objective of this research was to identify the effect of hydraulic retention time (HRT) on anaerobic digestion of wheat straw in the semicontinuous continuous stirred-tank reactors (CSTR)
The effects of HRT on anaerobic digestion of wheat straw in CSTR were conducted after all digesters reached steady-state
Summary
The estimated annual production of wheat straw is 681.92 million tons of dry biomass, produced as a by-product of wheat cultivation throughout the world [1]. In China, the utilization of wheat straw for renewable energy is increasing gradually due to the greenhouse gas reduction and renewable energy demand [3]. The conversion of wheat straw to renewable energy could be achieved in many ways. Biogas production through anaerobic digestion is considered ideal due to the economic benefit and energy efficiency [4, 5]. Anaerobic digestion is a complex biochemical process, whereby microbes decompose organic matter and produce biogas. A number of parameters could influence the performance and biogas production for semicontinuous or continuous anaerobic digestion [1], including substrate characteristics, organic loading rate (OLR), hydraulic retention time (HRT), temperature, and pH. Literature is still lacking in the effects of HRT on anaerobic digestion of wheat straw, the typical lignocellulosic wastes
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