A critical review of conventional and emerging wastewater treatment technologies

Water stress is a major concern in today's world as many cities worldwide face fast depleting potable water supply. The prevailing water emergency warrants a conscious effort to reuse mitigated wastewater such that the use of residual natural reserves is limited to drinking purposes only. To accomplish adequate wastewater remediation, the greatest challenge, apart from policy and implementation fronts, lies in maximizing the overall efficiency of wastewater treatment (WWT) systems. In light of this, the current review makes a unique effort to help navigate the challenge by summarizing the present scenario of WWT technologies, focusing on the progress so far and the prospects in the next 30 years or so. The study comprehensively reviews various wastewater technologies and aims to help countries, like India, deal with the obstacles encountered while selecting and engineering suitable systems. It compares them based on their advantages and disadvantages, including budget allocation and timeframe for installing and commission of the treatment plants. Depending upon the wastewater characteristics and the expected end-use of treated wastewater, a comprehensive survey of prevalent aerobic, anaerobic, and biological treatment techniques has been done. Emerging WWT technologies, such as advanced oxidation processes, membrane filtration techniques, microbial electrolysis cell technologies, and in situ methods, which are currently in the development and deployment stages, have also been discussed. The study outlines the scope, limitations, and advancements of existing and prospective wastewater remediation approaches and suggests their decentralized implementation at the community scale as stop-gap solutions to poor wastewater management.