Environmental Science Water Research & Technology PAPER Cite this: DOI: 10.1039/c9ew01106d Received 13th December 2019, Accepted 24th February 2020 DOI: 10.1039/c9ew01106d rsc.li/es-water Field testing of an onsite sanitation system on apartment building blackwater using biological treatment and electrochemical disinfection† Siva Kumar Varigala, ab Meghan Hegarty-Craver, c Srinivas Krishnaswamy, a Prakash Madhavan, d Milan Basil, d Praveen Rosario, d Antony Raj, d Viswa Barani, e Clement A. Cid, * f Sonia Grego cg and Michael Luettgen h The Closed Loop Advanced Sanitation System (CLASS) was designed to treat, disinfect, and recycle toilet blackwater from existing flush toilets in a multi-story apartment building. Two systems were tested at two unique sites in Coimbatore, India for a combined 7500+ treatment hours resulting in more than 180 000 L of treated water. The CLASS prototypes used a combination of biological pretreatment and electrochemical oxidation processes to produce treated water that nearly met the stringent requirements outlined in the standard ISO 30500. The nutrient and organic loading from the toilet blackwater was predominantly reduced by over 85–95% and 80–87%, respectively, through biological processes that were achieved using either a sequencing batch reactor (SBR, site A) or an anaerobic–aerobic biodigester (EcoSan, site B). Complete disinfection of E. coli with nil CFU per ml was achieved using electrochemical processes that also served to remove the remaining organic and nutrient loading to over 90–96%. The treated water was reused for flushing by the residents of the apartment building for 89 days. 1. Introduction Minimizing the use of water or producing high quality water is of particular interest in water stressed areas of the world such as India 1 that has been recently facing life-threatening water shortages in its cities. 2 To an increasing extent, wastewater is being seen as a resource that has potential for reuse after appropriate treatment. For instance, as illustrated by Sushmitha et al., diverse greywater treatment and recycling technologies like membrane bioreactors, rotating biological contactors, and constructed wetlands are being implemented in increasing numbers across India. 3 Therefore, treatment and recycling of remaining household wastewater (i.e., blackwater) presents an excellent opportunity to completely recycle wastewater generated at the household scale and alleviate the need for sewer connection. 4,5 The challenges with onsite treatment of excreta are multiple: the treatment technology must be reliable, easy to use, low-cost, and, more importantly, used by the intended people. Although the biological treatment processes like the complete mix activated sludge process and sequencing batch reactor process are proven effective for significant removal of organic and nutrient loading from wastewater, 6 they do not ensure complete removal of pathogens. Further, if this treated wastewater is to be reused, several site-specific regulations for disinfection are enforced. 6 Schmalz et al. acknowledged that electrochemical oxidation could be a promising alternative to membrane filtration, ozonation, UV irradiation and chlorination for the disinfection of biologically treated effluents. 7 Also, the study proposed that the combination of biological and electrochemical treatment Environ. Sci.: Water Res. Technol. This journal is © The Royal Society of Chemistry 2020 a Dept. Chem. Engineering, BITS Pilani, Goa, 403726 India b ITC-Kohler Co., Pune, Maharashtra, 411013 India c RTI International, Research Triangle Park, NC 27709, USA d RTI Global India Pvt Ltd, New Delhi, 110037 India e PSG Institute of Medical Sciences and Research, Coimbatore, 641 004 India f California Institute of Technology, Pasadena, CA 91125, USA. E-mail: ccid@caltech.edu g Center for WaSH-AID, Duke University, Durham, NC 27708, USA h Kohler Co., Kohler, WI 53044, USA † Electronic supplementary information (ESI) available. See DOI: 10.1039/ c9ew01106d Water impact Pollution from untreated sewage is a significant problem in India and many developing countries. Safe reuse of treated blackwater for toilet flushing can reduce this pollution while mitigating pressure on scarce water resources. This article describes a lengthy field-testing campaign to characterize an onsite blackwater treatment and recycling technology for residential buildings in two sites in India. Open Access Article. Published on 16 March 2020. Downloaded on 4/17/2020 8:49:05 AM. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. View Article Online View Journal