Comparative Evaluation of Chemicals and Botanicals based Dehydration of Biogas Slurry

Spent slurry from cattle dung based biogas plant was characterized and dehydrated by coagulation methods. Various chemical and botanical coagulants were tested at their different concentration levels. Alum at 3.6 % (w/v) produced maximum dehydration (40 %) and its dose was further reduced to 2% (w/v) by adding polyelectrolyte dimethylamine ultimately causing 44 % dehydration of fresh biogas slurry. Regarding botanicals, Moringa seed powder showed 30 % dehydration, better results than cactus mucilage (with only 5 % water removal). In case of Moringa, although the water separation was less than alum, the quality of separated water (in terms of EC, pH, N, P, K, TOC) was found better. The Zeta potential values of water separated out by Moringa seed powder and alum were found to be -18.1and -17.3 mV respectively. Our results suggest that although the dehydration capacity of alum was superior than botanicals tested but quality of water removed was better in case of Moringa.