Screening pretreatment methods to enhance thermophilic anaerobic digestion of pulp and paper mill wastewater treatment secondary sludge.

Highlights: [•] Anaerobic digestion of pulp and paper mill secondary sludge was studied. [•] Effect of 12 pretreatments (single or combinations) on methane yield was studied. [•] Pretreatment methods used were hydrothermal, enzymatic, ultrasound and chemical. [•] Hydrothermal pretreatment alone and in combinations increased methane yields. [•] Hydrothermal pretreatment alone and in combinations fastened methane production. [Copyright &y& Elsevier]