A key reason for civic authorities' lack of interest in refining sewer water is the high installation, running and maintenance cost of sewage treatment plants. Besides, these require technical manpower and high amounts of energy to operate. As a result, many sewage treatment plants are dysfunctional for long intervals due to power disruptions, technical snags and breakdowns. Moreover, economic returns on investment in wastewater cleaning are usually nil or too little to recover these costs.
Many such failings of conventional sewage treatment techniques have been overcome in a novel, environment-friendly and economically remunerative wastewater purification technology developed by the Water Technology Centre (WTC) of the New Delhi-based Indian Agricultural Research Institute (IARI). Significantly, the new technology uses a plant, Typha latifolia, which grows naturally in wetlands, instead of chemicals, as the cleansing agent to decontaminate dirty water. The technology also does not require much power to operate and it improves the quality of wastewater to levels comparable with Delhi's groundwater. More importantly, it yields handsome economic returns to redeem initial expenses and also make profit in the long-run. The WTC has appropriately termed it the "Cash from Trash" business model of wastewater treatment.
Typha latifolia has some handy special traits for wastewater purification. The most significant of these is its ability to transfer oxygen gathered by its leaves to its roots which, in turn, release it in the water around them. It creates conditions conducive to the emergence and growth of water-cleansing micro-organisms around the roots and in the medium in which these roots grow. These organisms either sequester or remove organic and inorganic pollutants, including heavy metals, present in sewer water, or modify them into relatively less hazardous types. The resultant treated water is, thus, safe for irrigation and several other uses without further purification.
The effectiveness of this pioneering technology has been validated by setting up a sewage treatment unit at the IARI campus, with a capacity to handle 2.2 million litres of sewage every day. Conceptualised and designed by WTC project director Ravinder Kaur, this unit, which costs around Rs 1.2 crore, has the potential to supply adequate treated wastewater to irrigate 132 hectares of farmland. This has reduced the IARI's reliance on dirty water bought from the nearby drain for watering its agricultural fields, thus, saving around Rs 18.5 lakh annually.
This technique is claimed to require just one per cent of the energy normally consumed by conventional wastewater treatment plants. Besides, it does not need skilled people to operate it and produces no sludge, which normally poses disposal problems for conventional sewage recycling ventures. The treatment cost is 50 to 65 per cent lower than that of conventional methods.
A noteworthy feature of the new technology is the production of harvestable vegetative biomass as a by-product, which can be sold to particle board manufacturers at the current price of around Rs 2,000 per tonne. The IARI plant generates dry biomass worth around Rs 18 lakh every year.
Given such valuable aspects of this sewage treatment technology, there is merit in promoting it vigorously. Given the rising scarcity of fresh water and the steady increase in wastewater generation, there is no getting away from the need to recycle dirty water and put it to gainful use. The per capita wastewater generation in class-I and class-II cities, which account for over 70 per cent of the Indian urban population, is around 98 litres per day. This figure is as high as 220 litres a day in the national capital region. The cumulative installed water treatment capacity in these cities, on the other hand, can handle just about 30 per cent of the wastewater generated in these cities. This content needs to be stepped up substantially to reduce these cities' dependence on rapidly depleting groundwater.
surinder.sud@gmail.com