Emerging contaminants in conventional and advanced biological nutrient removal based wastewater treatment plants in India- insights into the removal processes

Emerging contaminants (ECs) in the environment are a cause of concern due to their potential toxic effects. The study investigates the fate of 20 ECs covering a wide range of physical-chemical properties in ten full-scale municipal wastewater treatment plants (WWTPs). The plants were based on conventional technologies such as waste stabilization pond, upflow sludge blanket reactor, activated sludge process, and biological nutrient removal-based technologies such as anoxic-aerobic process, anaerobic-anoxic-aerobic process, biodenipho process, sequencing batch reactor, and densadeg-biofor process. Covering all the wastewater and sludge treatment lines, the mass balance approach was followed to investigate the fate of ECs at each treatment stage. The amount of ECs entering and leaving the WWTPs ranged from 0.82 to 11.94 kg/day and 0.027 to 0.70 kg/day, respectively. Antibiotics showed limited removal and were detected in the 0.006 to 0.18 kg/day range. The ECs were mainly detected in the aqueous phase in all the treatment steps. However, the contribution from the particulate and sludge phase cannot be neglected. The sorption of ECs on sludge depended on the sludge's characteristics. It was found to be the highest in the primary sludge. The measured sorption coefficient indicated that both hydrophobic and electrostatic interactions of ECs with the sludge are insufficient in explaining the sorption behaviour of a contaminant. The mass balance studies show biodegradation as the major removal pathway in all the WWTPs. The study provides the environmental mass load of ECs from Indian WWTPs. It will help understand the removal mechanisms of ECs in different types of wastewater treatment techniques.