The use of protozoa to indicate changes in the performance of activated sludge plants

A quantitative and qualitative survey of the microfauna at two activated sludge plants in the Leeds area, was carried out on a weekly basis. The frequency of occurrence and order of importance of the different species observed is described. The specific distribution of the protozoal population was found to be dependent upon prevailing environmental factors and plant operating conditions. As these also control the quality of the final effluent, it was possible to correlate plant performance and operating conditions with the distribution of species within the activated sludge reactor. A method for predicting effluent quality and operating conditions from the structure of the protozoal community was derived based on multiple regression analysis. The number of protozoa required for a successful prediction was minimized from 31 to 20 without a significant loss of accuracy using stepwise regression techniques.