Food waste (FW) single-substrate anaerobic digestion usually suffers from rapid acidification and inhibition of oil and salt. To overcome these problems and improve the process efficiency, supplementing other substrates has been used in FW anaerobic digestion. This study investigated the biogas production potential through co-digestion of FW with kitchen waste (KW) or garden waste (GW) in different ratios under thermophilic conditions. The results showed that the optimal ratios were FW:KW=60:40 and FW:GW=80:20 which biogas production improved 73.33% and 68.45% compared with single FW digestion, respectively. The organic matter removal rate of co-digestion was 84.46% for FW+KW group (RFK) and 65.64% for FW+GW group (RFG). Co-digestion increased the abundance of the dominant hydrolytic bacteria Defluviitoga and Hydrogenispora and hydrogenotrophic methanogen Methanoculleus. Furthermore, glycoside hydrolases (GHs), vital carbohydrate-active enzymes (CAZymes), were improved by co-digestion. Co-digestion could also effectively promote the function of cellulase and hemicellulose. This strategy for utilizing different organic wastes together as co-substrate provides a new avenue for bioenergy production.

In order to improve the efficiency of anaerobic digestion of long sludge retention time (SRT) sludge and seek a suitable disposal method for the massive plants harvested from constructed wetlands, we prepared Calamus-derived biochar (Calamus-BC) and added it to thermophilic anaerobic digestion (TAD) system of long SRT sludge. Moreover, the effect of Calamus-BC supplemental level (0, 5, 10, 15, 20 g/L) on TAD was explored through a series of batch experiments. Results showed that Calamus-BC addition can increase the conductivity and pH in TAD of long-SRT sludge obviously, thereby promoting methane production, reducing total VFAs accumulation and shortening the lag phases. When the Calamus-BC dosage was 15 g/L, the cumulative CH4 yield reached the highest 246.73 mL/g VS, which was 43.4% higher than the control group. Furthermore, it proved the modified Gompertz model was suitable for the actual evolution of CH4 production in TAD of long-SRT sludge. This study provided an alternative for efficient biomass stabilization and bioenergy recovery from long-SRT sludge and supplied a feasible resourceful approach for massive Calamus from constructed wetlands in water rehabilitation engineering.

In order to evaluate comprehensively the impact of calcium peroxide (CP) on anaerobic digestion (AD) of primary sludge (P-sludge) and secondary sludge (S-sludge) of anaerobic/anoxic/aerobic process, a series of batch experiments were conducted in the lab scale. Results showed that CP pretreatment could kill Fecal Coliform completely in 72.0 h and promote the solubilization of S-sludge more significantly than P-sludge. Compared with the control, the maximum CH4 production potential and the maximum specific CH4 production rate of P-sludge AD only increased by 11.2 % and 6.10 %, respectively, but those of S-sludge AD increased by 40.7 % and 58.4 % after the same pretreatment, indicating that CP pretreatment was more conducive to methane production of Ssludge. Moreover, the increase of alkalinity and initial acetate concentration of S-sludge was greater than that of P-sludge after pretreatment according to the process analysis of hydrolysis. Notably, CP pretreatment reduced the PO43-P concentration and chromaticity in the AD supernatant of both sludges, which was beneficial to the subsequent treatment of biogas slurry. In addition, CP pretreatment increased the content of total nutrient and decreased the content of harmful heavy metals in both biogas residues. Conclusively, compared with P-sludge, CP pretreatment is more suitable for S-sludge AD. This work firstly provides a comprehensive evaluation of CP pretreatment to waste sludge produced in anaerobic/anoxic/aerobic process of wastewater treatment plant (WWTP), which is of great significance in enriching the pretreatment technology of waste sludge and promoting the application of CP pretreatment in WWTP.