Droughts, explosive population growth and the continuing view that water is an infinite resource are reasons for water shortages in many areas of the world. Reusing wastewater as part of sustainable water management allows water to remain as an alternative water source for human activities reducing the demand on groundwater. Initially, wastewater reuse was focused for irrigation and non-potable purposes, but with more innovative advancements in technology, wastewater reuse domain has significantly expanded. Typical wastewater treatment processes are fit for non-potable water reuse that does not necessitate the wastewater to be treated to drinkable standards.
Treatment of raw water from rivers, lakes and wells must meet drinkable standards. To achieve this, intensive energy is required and this is yet another issue when it comes to energy supply in rural areas. Access to modern energy is an economic and social priority for the rural population owing to its direct environmental and economic benefits.
Jacqueline Stagner and David Ting at the University of Windsor in Canada in collaboration with Akhilesh Soni at Indian Institute of Technology presented a design of a self-sustainable stand-alone water treatment system. The application of the innovative system which is “taking wastewater reuse into another level” was driven by renewable energy sources and was designed for an off-grid community. Their design philosophy was the use of solar energy as a primary source and wind power as a secondary source in powering the purification system. Their research work is published in Sustainable Energy Technologies and Assessments.
The water purification process presented by the authors implemented two models of renewable energy, wind and solar. Wind power was applied to drive a vacuum pump, which reduced the air pressure inside the system. They optimized the number of processing stages to be four. This was based on the fact that increasing the number of stages would not be economically viable. The vapor pressure was maintained in the successive stages of the still at 31, 27, 20, and 18 kPa.
The researchers used constricting nozzles to connect the household drain with the recirculating loop and still. Solar power was used to heat the water in the chambers of the still. This solar energy was transferred to the system from the bottom chamber through a heat exchanger, and from the top of the chamber through heating the water directly.
The authors observed that the fresh water production capacity of the proposed solar-collector four-stage solar still, operating for 6 hours a day and a constant flux of 850W/m2, was 17.4kg/m2/day. This value was higher than for conventional solar stills. They found that the annual cost of the system was about Rs7450, and per unit water cost in the range of 0.5-1.2Rs/kg for the wind speed ranging from 1-5m/s. In the absence of wind, a hand-driven wheel could be used to drive the reciprocating pump to propel the water from ground to roof level.
Considering wind speeds of approximately 1-5 m/s, the proposed multistage solar desalination system can meet the fresh water needs for urban as well as rural communities by distilling 25-45kg/day. This wastewater reuse innovation will advance the application of recycled water as a reliable alternative water source.
Akhilesh Soni, Jacqueline A. Stagner, and David S.-K. Ting. Adaptable wind/solar powered hybrid system for household wastewater treatment. Sustainable Energy Technologies and Assessments. Available online 8 March 2017Go To Sustainable Energy Technologies and Assessments