Deactivation of internal recirculation in a full-scale Biological Nutrient Removal (BNR) Wastewater Treatment Plant (WWTP) reveals outstanding microeukaryotic bioindicators

Abstract

The bioindicator potential of the microeukaryotic community in a full-scale A2O wastewater treatment process was assessed after deactivating the internal recirculation in one of the two parallel treatment lines of the plant. The deactivation of the internal recirculation in one of the lines (NIR-line), led to a strong decrease in nitrogen removal efficiency (53 \% ammonia-uptake in the NIR-line versus 97 \% in the unaltered line or IR-line), as well as to a lower organic matter removal (95 \% BOD5 removal versus 97 \% in the IR-line). The microeukaryote community structure changed greatly confirming trends observed in experimental studies and showed a decrease in abundance and richness in the NIR-line. However, this line showed a significant higher abundance of certain ciliate species, such as Epistylis camprubii and Vorticellides infusionum, which are common species in conventional activated sludge. Conversely, the IR-line showed useful indicators of internal recirculation, associated with much higher ammonium and BOD5 removal. These results show that identification to ciliate species level provides a more reliable bioindication in nutrient removal systems, supporting the importance of research on biological parameters, mainly protists, as simple and useful tools for plant operators to manage nutrient removal processes. These observations extend the current boundaries of bioindication.