Feasibility of anaerobic co-digestion of pig waste and paper sludge

Pig waste (PW) and paper sludge (PS) possess complementary properties that can be combined for successful anaerobic digestion. Biochemical methane potential (BMP) tests revealed that a PW:PS 3:1 (v/v) ratio had the highest normalized CH4–COD removal (54%), while PS had the lowest value (11%) and PW had 44%. Batch BMP tests revealed a significant decrease in lag times for methane production in the order of PW:PS 1:3 (14 days) < PW:PS 1:1 (17 days) < PW:PS 3:1 (20 days) < PW (23 days). Hydrolysis constants (khyd) were higher for all PW:PS combinations than for either of the individual waste streams: 0.004 d−1 (PS) < 0.02 d−1 (PW) < 0.024 d−1 (PW:PS 3:1) < 0.03 d−1 (PW:PS 1:1) < 0.05 d−1 (PW:PS 1:3). Semi-continuous reactors performing co-digestion of PW and PS at a 2:1 ratio showed 1.5 times higher methane production than baseline PW-only reactors, confirming the BMP results.