Steps need to be taken to use wastewater for aquaculture and irrigation

Written by A L Ramanathan

Water scarcity may be caused by a variety of factors — temporal or long-term, local or regional, both natural and anthropogenic. The polluted grey and black waters from municipal/industrial effluents, agricultural chemicals and other sources affect all aquatic systems. Almost 50 to 80 per cent of wastewater goes untreated into streams, rivers and groundwater, which hinders our development capabilities and affects our food security. The virus that causes COVID-19 (SARS-CoV-2) has been detected in untreated wastewater, but the Centres for Disease Control and Prevention in the United States (CDC) has said there was no evidence that the novel coronavirus can be contracted by coming into contact with it.

Rivers, water bodies and aquatic life, mountains, forests and wildlife in India symbolise a culture of peace and coexistence with nature. But the projected future scenarios for wastewater are dark — water quality will be deteriorating further by 2030 under all scenarios. Population growth was found to have the highest impact on future water quality deterioration, while climate change had the lowest, although not negligible.

The Ganga is amongst the most polluted rivers in the world with flows obstructed/diverted and fragmented through the construction of dams/barrages, thus losing its self-cleaning capacity. It receives about three billion litres per day of untreated sewage and industrial effluents and enters our rivers. According to the India Meteorology Department (IMD), over the last decade, the monsoon in India has been below normal in six out of 10 years. This complicates matters further.

Water, though annually renewable, is a finite resource. What is needed is equitable and sustainable allocation, balancing the demands of competing stakeholders. The best option in the present-day condition in India is natural pollution control. People-friendly and cost-effective methodologies for mitigation of water pollution need to be developed or refined through continuous research and development. Similarly, technologically simple, cost-effective and energy-efficient sewage treatment plants for community and individual household levels are of urgent necessity.

According to the Niti Aayog, an estimated 600 million people in India face high to extreme water stress. Rivers are stressed and fragmented, and groundwater is overexploited with water levels dipping in several states.

The water quality of rivers has been deteriorating in the last few decades. Various river action plans have been taken up to reduce water pollution in the river, but there has been no visible improvement in the river’s water quality so far. We need to understand the river system, its mechanism, the best location for waste disposal, the amount of waste disposed, the waste assimilative capacity, and the influx of non-point source pollution from urban and agricultural areas, and then to issue advisories to industries and municipal corporations, accordingly. River hydraulics govern the dilution, diffusion, dispersion, reaction and the settling of pollutants.

India has some well-tested ways to use wastewater. The East Kolkata Wetlands, a notified Ramsar Site, are an ideal example of a system of natural bio-treatment of urban wastewater through “Pond System and Plant-Based Waste Management of Sewage Treatment”, and for recycling and utilising the treated wastewater for fish-culture and agriculture. It provides about 13,000 tons of fish per year from its about 300 wastewater fed ponds, 150 tonnes of fresh vegetables per day from the small-scale horticulture plots irrigated with the treated wastewater, and provides water for irrigating paddy cultivation and also serves as a natural sponge for absorbing excess rainfall.

Some 35,000 tonnes of municipally waste and 680 million litres of raw sewage enter the wetland system every day. Still, only 30 per cent of the total wastewater is used for aquaculture or irrigation, while the remaining 70 per cent flows directly to the Bay of Bengal, which pollutes the estuaries region and subsequently reduces aquatic biodiversity and causes large scale death of fish seeds. The problem could be mitigated by taking necessary steps for 100 per cent use of the total wastewater for aquaculture and irrigation. The East Kolkata Wetlands system could be developed as an ideal example of low-cost urban waste management and for recycling of fish culture and organic farming and sanitation technology, especially for developing countries.

Due to the cumulative effects of rapid urbanisation, population growth and climate change, many inland and coastal water bodies around the world are experiencing severe water pollution. So we should look for a green plan for the rejuvenation and preservation of our other great rivers and their sources which are contaminated by wastewater coming from point and non-point sources through ecological friendly ways.

The aquatic systems are facing great ecological crises in recent decades, which have catastrophic consequences for future water resource availability in our country. To help make land-use and climate change adaptation policies more effective at a local scale, we are suggesting the following model for large scale, eco-friendly water management systems for a big country like us, which is a combination of participatory approach and natural remediation and a reusable practical model.

In this model, all city/town/metros drains should have to come to common STPs kept 10 km outside the city. After treatment, they will have to send them to a common drain which is covered with urban forest throughout for over 2-3 km with native plants and shrubs and grasses to control for erosion, enhance bank stability, reduce evapotranspiration and control virus-infected aerosol. This will also reduce the flow rate and help in increasing the residence time of water that allows water to interact with soils and organic matter to naturally remove pollutants and heavy metals.

Then, the water will be free from pollutants (organic and inorganic) when it reaches the main river and will help to rejuvenate the ecosystem fauna and flora, and the river will return slowly to a pristine condition. The main drain will be dredged frequently to get these nutrient-rich sediments by desilting for natural fertilisers, besides being useful for regenerating the enormous volume of wastewater generated by us in a useful manner.

The writer is professor at the School of Environmental Sciences, Jawaharlal Nehru University, New Delhi. Views expressed are his own.

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