Protozoans are valuable indicators of the wastewater biological treatment process and are used in a variety of water resource recovery facilities (WRRF). The aim of this study was to determine the applicability of the Sludge Biotic Index (SBI) as an indicator of activated sludge purification efficiency during different influent loadings: municipal wastewater (M) and municipal wastewater combined with industrial wastewater from a sugar refinery (M + S). Despite the higher organic load during the M + S period, purification efficiency was higher for BOD5 , compared with the M period. SBI values were high during both periods, indicating stable sludge, excellent biological activity, and good to very good performance. According to the share of indicator taxa, better conditions of activated sludge were found during the M + S period. Protozoan abundance differed between the two study periods, as well as purification efficiency for some parameters. Certain taxa showed a significant correlation with purification efficiency for specific parameters. Although SBI is a useful tool for estimating activated sludge health, it should be used in combination with additional indicator metrics and/or a species-specific approach. PRACTITIONER POINTS: Activated sludge can have high purification efficiency during the co-treatment of industrial and municipal wastewater. The Sludge Biotic Index is applicable as an indicator of activated sludge condition during the treatment of municipal and sugar refinery wastewaters. A combination of indicators and a species-specific approach can give better estimation of the health of activated sludge.
Keywords: bioindicators; ciliates; microfauna; purification efficiency; wastewater.
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