PRESENCE OF PROTOZOA AND METAZOA IN ACTIVATED SLUDGE DURING FAVOURABLE AND UNFAVOURABLE CONDITIONS

Activated sludge, a microbial community, consists of free, flocculated and filamentous bacteria, protozoa, rotifers and a few other higher invertebrates. Protozoa and metazoa are said to be an important factor in shaping the morphological and taxonomical compositions of communities in the activated sludge process. The aim of this study was therefore to determine which protozoa and/or metazoa prevailed during the favourable and unfavourable conditions present. Activated sludge wet mounts and smears were microscopically analysed under 100X magnification using dark field. Each works analysed was classified as a good or poor operating system. The different protozoa and metazoa types were identified and enumerated. The results were graphically represented. It was found that the Amoeba predominates during system start-up and the flagellates along with the Amoeba are present when a toxic overload is experienced. The presence of free-swimming ciliates was indicative of a good operating system. The attached ciliates were found to be good bio-indicators of a toxic upset since ciliates leave their stalks when exposed to this situation. Rotifers were found during favourable conditions and are said to be present in stable activated sludge environments. This study showed that there is a wide range of loadings over which each species may be found but a narrower range over which they may be found in large numbers