Sustainable and novel closed loop approach to convert black and grey water from multi-storey residential buildings into reusable water and biogas

Domestic blackwater treatment is one of the challenging issues in developing countries. The present study focused on the management of liquid and solid waste generated from human activities using eco-friendly technologies powered by renewable solar energy. This treatment was performed close to the source of waste generation to overcome issues of transportation. The reduction in required water demand for human activities (mainly in water stressed regions of the world) by the recirculation of greywater and reuse of blackwater upon treatment is discussed in this study. The proposed system was designed for a community of 100 families with 3 people (2 adults and 1 children) per family. On average, the total discharge from the considered population was 3,900 litres of wastewater and 160kg of faeces per day. The treatment of wastewater was performed using a multi-effect distillation (MED) system powered by solar evacuated tube collector field with an area of 205 m2. When the MED operated for 5 hours/day with an average solar irradiation of 864.45 W/m2 in the month of April, it was found to deliver a recovery rate of 49.25% at the test location of Chennai, India. When operating the MED unit for 300 days in a year, around 13.22 tons of distillate yield was produced. The semi-solid waste separated from the wastewater was supplied to a biogas digester for production of biogas and organic fertilizer. The methane output from the system was found to be around 1875.37 kg along with 55.27 tons of organic fertilizer per annum. The performance analysis of the proposed system was carried out by simulating the developed mathematical model using Matlab R2020a.