Reuse of Treated Domestic Sewage for Irrigation Purposes Using the Algal-based Treatment System

The increase in freshwater scarcity in developing countries drives to use of poor-quality water for agricultural purposes. The usage of treated sewage for irrigation is increasing worldwide as an alternative resource. But the presence of heavy metals, especially chromium (Cr), resulted in phytotoxicity, low yield and accumulation in the food chain. It leads to detrimental effects on humans and animals. So, efficient eco-friendly remediation techniques are essential to address the current problem. The present investigation aims to treat domestic sewage using biological reactors, then biosorption of total Cr using acclimatized algal species. The efficiency of sewage treatment was observed in terms of chemical & biochemical oxygen demand, total Kjeldahl nitrogen, and ammonia by 92.40 ± 2.21%, 94.70 ± 2.24%, 56.40 ± 17.03% and 80.80 ± 7.80% respectively. Total-Cr presence was 64.20 ± 16.75 mg/L in raw sewage and 55.70 ± 6.70 mg/L in final treated sewage water without algal pond treatment. The algae were acclimatized in metal stress conditions to produce the extracellular polymer for Cr biosorption. After the biosorption in the algal pond, the water contains only 4.41 ± 1.16 mg/L of total Cr with a removal efficiency of 92.00 ± 2.01% in 50 days of monitoring. The Cr-removed treated sewage (CRTS) was reused to cultivate Amaranthus sp. and compared with chromium-containing treated sewage and tap water irrigated plants. The CRTS irrigated plants showed better growth, development and higher protein, carbohydrate and lipid content than others. The algal cell wall offered many functional groups that could bind with Cr ions were confirmed using Fourier transform infrared spectroscopy analysis and proton nuclear magnetic resonance spectroscopy.