Biomethane production improvement by enzymatic pre-treatments and enhancers of sewage sludge anaerobic digestion

[Display omitted] •Commercial enzymatic addition on anaerobic digestion was studied.•B. licheniformis pre-treatment on anaerobic digestion was studied.•High depuration efficiency was obtained in pre-treated sludge.•Best results were obtained using proteases purified or B. licheniformis in situ.•Both treatments increase the biogas volume in 3.65 and 5.77 times. Enzymatic hydrolysis is recognised as an effective pre-treatment for increasing biodegradability of sludge. In this work, isolated commercial enzymes as well as in-situ enzymes producer bacteria were used respectively as enhancers and pre-treatments of sewage sludge. Biodegradability of sample as well as biomethane potential production were studied. Results showed that depuration efficiencies in terms of CODs (73.5–85.5%) and TVS (28.5–42.7%) were more than twice the control value. In addition, pre-treated samples as well as enhanced samples with enzymes generated more biomethane than control. The optimal ones, were those with the isolated proteases (P) and with bacteria (Bacillus licheniformis) treatment in-situ (F), producing a total volume of 72.4 ± 2.62 ml CH4 and 114 ml ± 0.46 CH4, respectively, increasing the biogas volume in 3.65 and 5.77 times respectively compared with control.