Algal-based wastewater treatment: Evaluation of nitrogenous byproducts in chlorinated effluent

Water reuse is gaining traction as a means of balancing the water portfolio in the face of rapidly growing demand for potable water in water-stressed regions. While current guidelines for restricted reuse require final disinfection of the reclaimed water and residual free chlorine, the common practice of disinfection by chlorine can potentially form carcinogenic byproducts depending on certain precursors and the disinfectant demand. This study evaluated the formation of nitrogenous byproducts of chlorination in an algal-based wastewater treatment system (AWTS) capable of yielding discharge-ready effluent with non-detectable levels of pathogenic bacteria. Impacts of chlorination of the AWTS effluent were evaluated here in terms of selected nitrosamines to determine if a comprehensive DBP assessment would be justifiable. Optimal chlorine demand of the AWTS effluent to satisfy the reuse guidelines was found as 13.0 mg Cl-2/L at pH of 6. Under this condition, none of the seven nitrosamines analyzed in this study were >50 ng/L. This finding is corroborated through non-targeted screening by liquid chromatography/high resolution mass spectrometry of the unchlorinated AWTS effluent revealing negligible levels of amines, which have been reported as key precursors of nitrosamines. Results of this study indicate that the AWTS holds promise in delivering safe reuse-quality effluent, warranting further comprehensive assessments.