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Activated sludge characteristics in a phosphorus depleted environment

1988; Elsevier BV; Volume: 22; Issue: 2 Linguagem: Inglês

10.1016/0043-1354(88)90073-5

1879-2448

Bemt Ericsson, L. Eriksson,

Phosphorus and nutrient management

Abstract New developments of precipitation techniques in Sweden and other countries have been directed towards dual purpose chemical pre-precipitation. This implies not only the removal of phosphorus to avoid eutrophication but also the removal of organics in order to save energy. In this connection the optimization of chemical and biological treatment is particularly interesting. Too low concentrations of BOD and easily assimilated phosphates in the pre-precipitated sewage may have a detrimental effect on the activated sludge process, primarily the sludge characteristics. The experimental studies for optimization of chemical pre-precipitation in Enkoping in 1985 included as an important part the influence of low soluble phosphorus concentrations on the activated sludge process by extreme pre-preciptation in order to attain a lower total phosphorus concentration in the effluent than the standard value 0.5 mg l−1 P. During extreme pre-precipitation conditions the sedimentation characteristics of the activated sludge deteriorated with a very marked increase of sludge volume index and growth of filamentous organisms. Specialized laboratory studies showed that wide variations of pre-precipitation dosages used in the plant trial operation apparently caused shifts in microbial population. This was indicated by variations in the amount of filamentous bacteria. It seems clear that extreme pre-precipitation favours filamentous organisms, probably due to easily assimilated phosphate depletion in this study. Optimized preprecipitation followed by polishing precipitation in a second point is accordingly preferred over just extreme pre-precipitation alone. The findings are also in agreement with other studies, which show that activated sludge properties may be altered by major changes of some operational parameters such as oxygen and substrate concentration, or as in this case, pre-precipitation dosage.