USE OF PROTOZOA AND METAZOA FOR DECREASING SLUDGE PRODUCTION IN AEROBIC WASTE-WATER TREATMENT

A new approach to decreasing sludge production in aerobic biological w astewater treatment involving use of protozoa and metazoa was tested. The dissolved organics in the two synthetic wastewaters (based on acet ic acid and methanol, respectively) tested were decomposed to >90% and the biomass production was decreased by 60-80%. The total sludge yiel d, expressed as total suspended solids per gram chemical oxygen demand removed, was 0.17 g TSS/g COD in the system fed acetic acid, whereas it was 0.05 g TSS/g COD in the system fed methanol. The explanation fo r this difference was that in the system fed methanol, dispersed bacte ria were obtained that were easily grazed by the protozoa and metazoa in the predator stage. In the system fed acetic acid, the bacteria for med zoogloeal flocs, which protected them from grazing in the predator stage. With both carbon sources a significant release of nitrate (> 7 mg N/l) and of phosphate (> 2.5 mg P/l) was observed in the effluent.