Effluent quality and reuse potential of urban wastewater treated with aerobic-anoxic system: A practical illustration for environmental contamination and human health risk assessment

The agricultural sector requires a large volume of water (similar to 70 % of global water), which makes this sector difficult to produce enough food for the rapidly growing population demand with the existing scarce available freshwater source. As a viable alternative water source, urban wastewater reuse is a potential candidate. However, wastewater reuse and disposal before treatment pose a significant threat to human health and ecological systems. This study was aimed to treat urban wastewater using aerobic-anoxic system and then effluent evaluated to grow different vegetables. Wastewater samples collected (Arba Minch town) at nine sites during different seasons were used to characterized water quality (physicochemical and biological) parameters and feed aerobic-anoxic reactors. Health risk as a result of vegetable ingestion was investigated using HRI, THQ, and HI. Statistically significant (p < 0.05) seasonal variation results were observed for temperature, NH4-N, NO2-N, and sodium adsorption ratio. The performance of aerobic-anoxic treatment for COD, BOD5, TSS, NH4-N, TN, and TP was 91-94, 92-95, >96, 92, 88, and 58 %, respectively. The order of heavy metals concentration in raw wastewater was Fe > Pb > Zn > Mn > Cu > Cd, which is lower than corresponding heavy metals in vegetables having the order Fe > Mn > Zn > Pb > Cu > Cd. The phytotoxicity effect was significantly higher for cabbage followed by lettuce and tomato. The HRI, THQ, and HI values for Cd and Pb >1.0 (exceeded WHO and FAO limits) for vegetables irrigated with wastewater, which could result in health risk in adults and children. Overall, results confirmed that wastewater after aerobic-anoxic treatment is a sustainable approach to maintain safe environmental and human health.

Automated summary

The agricultural sector requires a large volume of water, which is difficult to produce food for the growing population. Urban wastewater reuse is a potential alternative water source. The study shows that wastewater treated with aerobic-anoxic system can maintain safe environmental and human health.