Anaerobic digestion of dewatered primary sludge (DPMS) from the Nagaon paper mill Morigaon Assam
The solid dewatered primary sludge (DPMS) from the chemical pulping is the largest by-product of the pulp and paper industry and is often dumped on disposal sites, generating leachates and causing soil pollution. Since the energetic use of DPMS has also not yet been done satisfactorily, the anaerobic digestion-aspect has to be looked at closely. Here a biochemical methane potential (BMP) study, followed by a batch experiment to determinate the energetic potential and the process stability under optimized conditions, in order to, eventually, discover an alternative treatment of DPMS to the poisonous disposal on agriculture land in Morigaon was carried out. The BMP-experiments were executed with DPMS and digester sludge (DS) as inoculum in North-Guwahati, Assam. The initial laboratory BMP-experiments were performed with duplicated glass batch reactors for different F/M-ratios of 0.5,1.0,1.5 and 2.0 as well as with two control bottles, only filled with DS. The highest gas production amount of 1,970 mL as well as the highest TVS-reduction of 38.4 % was observed over a period of 30 days for a F/M-ratio of 1.5. The later value was then also used in the subsequent batch reactor experiments. Here the maximum gas production rate increased up to 1,930 ml/d on the initial days and reached a constant methane gas generation level until day 60. SCOD- and VFA- concentration increases also initially, but decreased after day 10 and continued to do so until day 60. At the very end, the cumulative methane gas production (with the optimal F/M-ratio) of the batch experiment was fitted successfully by a three parameter Gompertz kinetics model.