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This study investigated methane production, long-chain fatty acids (LCFAs) profile, and predominant microorganisms in anaerobic digestion (AD) of lipid-rich swine slaughterhouse waste (SSW). The maximum methane yield was 999.2 mL/g VS. LCFAs, as inhibitory hydrolysis products, accumulated first to 1165 mg/L on day 3, and then decreased sharply to 125.7 mg/L on day 9, and finally were degraded to 20 mg/L on day 27. Linoleic acid (C18:2), oleic acid (C18:1) and palmitic acid (C16:0) were the dominant LCFAs. The easy conversion of C18:1 to C16:0 compared with difficult degradation of C16:0 resulted in an increase of C16:0 on day 4–6. Predominant microorganisms were Clostridium, Syntrophomonas and Methanospirillum. This study proved the high methane potential of lipid-rich SSW and gained insights into the degradation process by analysis of intermediates of LCFAs and predominant microorganisms. The results can provide valuable guidance for efficient utilization of this waste to produce methane in future.

The purpose of this study was to evaluate biomethane production in anaerobic digestion of swine slaughterhouse waste (SSW) and the effect of lipase pretreatment on biomethane yield. Lipase extracted from porcine pancreas was employed to hydrolyze SSW at 37 °C for 24 h. Three different lipase concentrations of 0.04, 0.2, and 0.4% (w/v) were adopted. Anaerobic digestion was carried out in batch style for 50 days. The results showed that the highest experimental biomethane yield (EMY) of 851.6 mL/g of VSadded was achieved when the lipase concentration of 0.2% (w/v) was used, which was significantly higher (18.4%; α < 0.05) than that of the untreated group. Furthermore, the highest biodegradability (Bd) of 72.7% was also achieved at 0.2% (w/v) lipase-pretreated group. Results proved that the conversion of SSW to biomethane was improved through pretreatment of lipase hydrolysis and offered a promising method for disposal of SSW.

China produces large amount of cotton stalk (CS) residues as agricultural biomass, which are incinerated on-site, causing air pollution. The high organic content of CS could be utilized for biogas production, but the direct digestion without pretreatment always leads to a low methane yield and biodegradability, due to the complicated structure of lignocellulose. In order to search best fitting pretreatment methods in effective anaerobic digestion (AD) of CS, effects of various pretreatments including KOH, NaOH, Ca(OH)2, alkali hydrogen peroxide (AHP), H2SO4, H3PO4 and steam explosion (SE) were studied. It was seen that all treatments resulted in varying methane yields. Among all the pretreatments, acid pretreatment is not suitable for AD of CS. The results showed that the highest cumulative methane yield (CMY) of 192.4 mL·gVS−1 was obtained after 3% AHP pretreatment of CS, and the methane yield improved by 254.3% than the untreated CS. Therefore, AHP treatment was proven to be an efficient pretreatment technique. XRD and FTIR analyses had shown that pretreated CS had favorable structural changes. This research is beneficial in developing environment friendly and cost-effective pretreatment technologies to utilize CS for methane production in future application.