India's BARC develops small solar RO and UF units
Domestic and community-level reverse-osmosis (RO) desalination units have been developed for producing safe drinking water by Saly T Panicker at the Desalination Division of India's Bhabha Atomic Research Centre.
According to Dr PK Tewari, president of the Indian Desalination Association, solar desalination is an attractive alternative for remote and rural areas where grid electricity is not available. Thousands of villages in India are reported to be unable to connect to the power grid, due to their remoteness.
In the smaller RO unit, the feed water is passed through the membrane with the help of a direct current (DC) pump connected to the photovoltaic (PV) panels without any batteries. The unit can be operated for 9-10 hours on a sunny day, which can cater for the drinking and cooking requirements of 3-4 families at an average rate of 5 L per person per day.
The domestic solar RO unit (10 L/h capacity) contains a cartridge prefilter and a spiral-wound RO membrane element. The UF unit (50-100 L/h) consists of candle and capillary type filters.
Water conservation becomes an issue, when the natural recharge rate of the source is slow as in the case of groundwater. For this reason, a significant fraction of the concentrate stream (which otherwise is rejected) is recycled back, so that fresh feed as well as discharge volumes can be minimized.
The community-level solar RO plant consists of RO modules, prefilters, chemical-dosing system, pumps and UV for disinfection on the desalination side and PV panels, inverter, charge regulator and battery storage on the power side. It produces 250 L/h drinking-quality water from brackish water of 2,000-2,500 ppm TDS.
In the case of low salinity (1000 ppm) brackish water, the concentrate also can be used for non-potable purposes depending on product recovery. This prevents wastage of water through reject disposal.