Bacillus thuringiensis fermentation of primary and mixed sludge:: Rheology and process performance

Bench scale fermentation of primary, mixed, and secondary (raw and hydrolyzed) sludge and starch industry wastewater was carried out using Bacillus thuringiensis (Bt) var. kurstaki HD-1 to test their feasibility as potential growth substrates on the basis of rheology and process performance in comparison to soyameal (semisynthetic) commercial medium. All fermented media exhibited pseudoplastic pattern, followed power law for viscosity with greater shear thinning for primary sludge (raw and hydrolyzed). Improved rheology correlated well with the fermented broth morphology. The total cell and viable spore counts, oxygen consumption, maximum specific growth rate (mu(max)), and entomotoxicity were, respectively, 2, 4, 1.5-2, and 3 folds lower in primary sludge in contrast to mixed sludge, rendering primary sludge unsuitable as raw material for Bt fermentation and eventual formulation. Further, the rheology studies of secondary sludge and starch industry wastewater proved them to be good Bt fermentation alternatives.