Filamentous Bulking and Hindrance of Phosphate Removal Due to Sulfate Reduction in Activated Sludge

Sulfate reduction in the activated sludge cultivated with glucose and peptone in the sequential batch reactor system and the continuous anaerobic-oxic system was examined. In both systems, sulfate reduction occurred. When the sulfate reduction ratio increased, Type 021N or Beggiatoa sp. grew in the sludge and settling characteristics became poor. These results suggested that sulfate reduction was a cause of growth of the filamentous bacteria which could utilize sulfide for the energy source. There was a tendency that the greater the sulfate reduction ratio was, the smaller the phosphate removal ratio was. As a result of batch experiments using the mixed liquor and the wall growing sludge, it was demonstrated that the sulfate reducing bacteria grown in the activated sludge mainly produced acetate from propionate and lactate. About 10⁷~10⁸ MPN of sulfate reducing bacteria grew in 1 g of the activated sludge and about 10⁹ MPN grew in 1 g of the wall growing sludge.