Delhi’s efforts to purify drainwater receives Positive Results

Delhi Jal Board (DJB) along with Irrigation and Flood and Control Department have positioned the city’s first “drain water purification system” in Shahdara, link drain near Akshardham, where the electrocoagulation technique has been used to purify sewage water.

Ankit Srivastava is the Technical Advisor to DJB and and consultant for the ‘city of lakes’ project, under which 200 lakes are to be revived. Ankit Srivastava, last year, along with his team had demonstrated how constructed wetland system can be used to purify sewage water in Rajokri lake. This recent pilot project have helped the team to test the other end of the spectrum whereby, they have successfully come up with a solution to purify and reuse sewage water via a complete technological take. 

The new decentralised sewage treatment plant (D-STP) is set up at Akhshardham. It is an electrocoagulation-based system, that is capable of employing other purifications systems like geo-tubes and further tertiary purification levels. Along with being capable of other purification systems, the plant can recycle drain water and provide three different levels of output water, for which three taps have been installed. “Any STP depends on the design of output level. It can be drinking water level purification, groundwater recharge level purification and for horticulture use,” Srivastava said. Though the plant provides other purification systems, electrocoagulation-based is the primary unit that cleans water upto biochemical oxygen demand (BOD) level 10, further UV and Reverse Osmosis have been used in the next stages to reduce BOD to five and potable water levels.

Explaining the process, he added, “Instead of using chemical coagulants, the electrocoagulation uses metal plates. When direct current is supplied to it, the metal plates turn into ions and help in coagulating the pollutants. The settled solid is then separated. The process can be understood to be similar to the formation of cottage cheese.” 

The plant can easily remove heavy metals, phosphate compounds and problematic pollutants by using electricity-based purification feature.

A DJB official said that the electricity input for the unit is not much and the plant can be run using solar power. He added that the drain water harvesting project can be expanded to recycle and reuse waste water flowing in drains rather than exclusively focusing on rain water. While a natural STP like Rajokri model costs around Rs 1 for purification of 1,000 litres of water, the electrocoagulation will be slightly more expensive. However, the units require less space and are useful for heavily polluted water bodies that cannot be purified using natural STP. “If we remove the land cost required in natural STPs, this technology too can be cost effective. In Mungeshpur drain, we receive 1,200 BOD in effluent coming from factories and this system will be very useful,” the official added.

Ankit Srivastava said, “Both the systems have their own advantages and a combination of the solutions between these two extreme solutions will be used in the 200 selected waterbodies.” 

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