The effect of antimicrobial chemical, triclosan (TCS) on protozoa present in aerobic and anaerobic bioreactors for wastewater treatment is reported in this study. Bioreactor sludge ciliated protozoa such as Spirostomum, Cyclidium and Colpoda and flagellated protozoa Mastigella were exposed to TCS at 1 mg/L level in batch cultures. The response of TCS on protozoa was followed by microscopic observation of the sludge at specific time intervals. Among the protozoa in aerobic sludge, Colpoda exhibited strong sensitivity to triclosan and the cells distorted and burst in 20 minutes period. Mastigella and Spirostomum were resistant to triclosan for first two days, but afterwards the mobility was found declined and subsequently mortality increased to 100% in four and five days respectively. Anaerobic sludge ciliate, Cyclidium exhibited morphological distortion and motility decline after 1 hour exposure to triclosan. The sludge flocs were affected and pelagic cell count declined by the presence of triclosan at the tested level.
Keywords: antimicrobial compounds, grazing fauna, triclosan, wastewater treatment