Anaerobic co-digestion of press mud with water or sewage at ratios of 1:7.5, 1:10 and 1:12.5 were performed in continuously fed UASB reactors for hydrogen production. At a constant hydraulic retention time of 30 h, the specific hydrogen production rate was 187 mL/g volatile solids (VS) reduced during maximum biohydrogen production of 7960 mL/day at a 1:10 ratio of press mud to sewage. Chemical oxygen demand (COD) and VS reductions of 61% and 59% were noted on peak biohydrogen yield. A pH range of 5-6 was suitable at ambient temperature for entire process; a lower pH was inhibitory. Co-digestion of acidic press mud with sewage controlled pH for fermentation. Hence press mud can be exploited for biohydrogen production. (C) 2010 Elsevier Ltd. All rights reserved.