Microeukaryotic communities diversity with a special emphasis on protozoa taxa in an integrated wastewater treatment system

Abstract This study developed an integrated wastewater treatment system that combines an upflow anaerobic sludge blanket (UASB), downflow hanging non-woven fabric (DHNW), and anaerobic baffled reactor (ABR) to explore the effect of treatment stages on the diversity of microeukaryotic communities. This study aimed to bridge the knowledge gap regarding the influence of integrated system stages on microeukaryotic community diversity. Through 18S rRNA amplicon sequencing, we identified unique microeukaryotic communities across different stages, with the aerobic phase hosting 35.77% of unique amplicon sequence variants (ASVs). The results of principal component analysis (PCA) and non-multidimensional scale analysis (nMDS) demonstrated the significant influence of wastewater treatment on both environmental factors and the microeukaryotic communities. Ciliophora was notably abundant in the effluent (42.09%) and sludge (17.11%). The aerobic stage was dominated by Ochrophyta, a diverse group of algae instrumental in nutrient removal, such as nitrogen and phosphorus, through biological processes. A redundancy analysis (RDA) revealed a positive correlation between chemical and biochemical oxygen demand and Cryptomycotina, highlighting its potential as a bioindicator for treatment efficacy. The detection of protozoan species, such as Acanthamoeba castellanii and Vermamoeba vermiformis , in the outlet stage poses health risks, whereas Cryptosporidium sp. was found in both the inlet and aerobic stages but not in the outlet. Our study reveals the complex nature of microeukaryotic diversity in the wastewater treatment system and its implications for treatment performance and public health.