Risk assessment of a municipal extended aeration activated sludge treatment plant using physico-chemical and in vitro bioassay analyses

The present study involves physico-chemical profiling and toxicity assessment of wastewater and sludge samples collected from subsequent treatment stages of extended aeration activated sludge (EAAS) process based municipal wastewater treatment plant (WWTP). Wastewater samples were collected from inlet, aeration tank, final settling tank and outlet, while sludge samples were collected from sludge bed. All the samples were tested for their physico-chemical properties using titrimetry, multi elemental analysis and Gas chromatography and Mass spectrometry (GC-MS) (in scan and SIM (selective ion monitoring) modes). Toxicity testing was done using in vitro bioassays viz., 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay for cytotoxicity, 7-ethoxyresorufin-O-deethylase (EROD) assay for dioxin-like behaviour and alkaline comet assay for genotoxicity, on human hepato-carcinoma HepG2 cell line. Post-treatment liquid samples showed 12 fold chemical oxygen demand (COD) reduction and met discharge standards for most of the tested parameters. However, detection of organic contaminants such as phenols, phthalates and polycyclic aromatic hydrocarbons (PAHs) and a correlated low toxicity reduction in liquid and sludge samples after treatment revealed the need for up-gradation of the existing testing and treatment technologies. (C) 2022 The Author(s). Published by Elsevier B.V.

Automated summary

The present study conducted physico-chemical profiling and toxicity assessment of wastewater and sludge samples from a municipal wastewater treatment plant. The results showed that the post-treatment liquid samples met discharge standards but still contained organic contaminants, suggesting the need for improvement in testing and treatment technologies.