To recover the biogas from sewage sludge and paper waste (PW), the methanogenic performance of thermophilic anaerobic co-digestion of sewage sludge with PW was assessed by a continuous experiment. The effects on the biogas production and microbial community were investigated by changing the PW ratio from 0 to 66.7%. The optimal performance was obtained at the ratio of sewage sludge: PW = 4:6 (total solids), where the COD removal efficiency and biogas production increased from 58.34±5.90% to 72.92±0.08% and 438±53 to 594±72 mL/g-VSadded, respectively. By investigating the trend of carbohydrate and protein degradation rates, the competition between carbohydrate and protein degradation was quantified. The critical PW addition ratio was about (63.64%), where the protein degradation rate decreased to zero with increasing PW addition. Meanwhile, the microbial analysis showed that cellulolytic bacteria outcompeted proteolytic bacteria and to be the predominant group after PW addition.
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