Sedimentation of Bacillus sphaericus in tap water and sewage water

Formulations of Bacillus sphaericus products: were applied in 1-m columns o f clean water and sewage water in tubes. Samples taken through valves attac hed to the walls of the tubes showed that spores settled as a function of a pplication method, droplet size, particle size, and water characteristics. In a mixture of deionized and tap water, the slowest sedimentation rate was obtained with a primary powder sonicated in water with 0.1% detergent. Thi s product and a commercial fluid product settled faster in sewage water tha n in clean water and after 4 weeks, most spores were found in the sediment. In clean water, most spores remained suspended during the 4 weeks but the density was highest at the bottom. Calculation of total spore numbers in th e columns after 4 weeks indicated that about 90% of spores disappeared in c lean water, and 95-97% disappeared in sewage water. Bioassays showed that t oxicity declined in parallel with the sedimentation, but at a higher rate, indicating a loss of toxicity from the residual spores. (C) 2000 Academic P ress.