The effects of toxic substances on the activated sludge microfauna

The assessment of protozoan populations comprises an important tool in evaluating the efficiency of the activated sludge process for the treatment of wastewater. In this process protozoa play a significant role since they graze on dispersed bacteria, supporting a healthy food web in the activated sludge artificial ecosystem. The objectives of this work were the study of the development of protozoan community during treatment of municipal wastewaters, the investigation of the effects of certain toxic compounds on the relative diversity of microorganisms and their correlation to the effluent quality. Samples were collected from two bench scale units treating simulated municipal wastewaters, including a continuous fed complete mix reactor and a sequential batch reactor (SBR). Certain toxic chemicals were added in the influent to both systems in order to examine their effect to the activated sludge microorganisms. The analysis of the protozoan communities showed that they were affected by the type of operational mode and the presence of toxic compounds in the influent. During the treatment of simulated wastewaters, species that prevailed including Vorticella sp. and Opercularia sp., while a poor development of microorganisms was observed during the operation of the systems fed with toxic wastewaters. Furthermore different species were observed during the addition of toxic compounds. Species such as Tokophrya sp. and Podophrya sp. showed good correlation to the removal efficiency of phenol while Chilodonella sp. and Colpidium sp. showed good correlation to cyanide removal.