Strategic Intervention

Wastewater recycling and reuse for sustainable irrigation needs

India has a meagre 4 per cent of the world’s freshwater reserves and houses 18 per cent of the world’s population. Over the years, the demand for water from different consumer segments has been increasing steadily. However, with the fixed supply of water resources, demand will outstrip availability before 2050. Further, per capita availability of water, which is already declining, will plunge from 2,209 cubic metres in 1991 to 1,341 cubic metres by 2025.

To overcome this and ensure sustainable availability of water, measures to improve water use efficiency of different end users is being taken up. In the past few years, the irrigation segment, a major consumer of water with a lion’s share of approximately 88 per cent of freshwater reserves, has been one of the focus areas of the government. At present, there exists a gap of about 15 per cent in the irrigation potential created and utilised. Therefore, the Ministry of Jal Shakti has identified full utilisation of the created facilities as an important strategy to bridge the gap. For this, the government has introduced measures such as improvement in irrigation practices through various flagship schemes such as the Pradhan Mantri Krishi Sinchayee Yojana, the Accelerated Irrigation Benefits Programme, and the Bharat Nirman programme, new irrigation techniques such as drip irrigation and the development of additional irrigation potential.

Apart from these initiatives, another innovative intervention of using recycled wastewater for non-potable purposes is being adopted. To reclaim wastewater, various conventional treatment technologies like activated sludge process (ASP) or sequential batch reactor (SBR) are being deployed. However, at present, acceptance and adoption of recycling and reusing of wastewater is limited. For wider adoption, pilot projects, wastewater reuse policies and regulations, training and innovation, besides the right funding models are the need of the hour.

Recycled wastewater for irrigation

The country needs a continuous supply of irrigation water to ensure abundant crop production. However, several areas are drought-prone and extraction of groundwater is becoming difficult. Several groundwater blocks in the country are already overexploited and rainfall is precarious, resulting in depletion of the groundwater table. In light of these issues, an innovative practice of treating, recycling and reusing wastewater through secondary treatment processes is becoming a viable mode of water conservation.

There exists a huge potential for recycling wastewater. According to the Ministry of Housing and Urban Affairs, about 80 per cent of the water supplied in the country is generated as wastewater. This can be put to use for irrigation purposes apart from other uses in urban areas, for industrial purposes and for households, based on the recycled water quality standards. For instance, to make treated water viable for irrigation purposes, the treated wastewater should be such that the concentration of biochemical oxygen demand (BOD) is 30 mg, aluminium concentration is at 5 mg, arsenic at 0.1 mg, zinc at 2 mg, and phosphorus and nitrogen are completely eliminated besides other chemical composition parameters. This recycled water can then be used both for landscape irrigation (golf courses, horticulture and gardens) and for irrigation of agricultural crops that include food crops, non-food crops and fodder.

Reclamation technologies

For reclaiming wastewater and reusing it, a number of treatment technologies are available. One of the technologies available in the country is ASP, which is a secondary treatment procedure. This conventional wastewater treatment method consists of a primary settling tank, an aeration tank, a secondary settling tank, a sludge return line, and an excess sludge waste line. In this process, sewage and wastewater is treated using bacteria (to degrade biodegradable organics) and air. The method offers efficient removal of excess BOD, chemical oxygen demand and nutrients which then makes the water fit for irrigation.

Another treatment method is SBR, which is a variant of the conventional ASP. It is a batch treatment process that combines primary settling, aeration, secondary settling and decanting of the treated sewage in a series of sequenced reactions in the same basin on a time-deferred cycle. The technology is capable of removing nitrogen and phosphorus concurrently with BOD, and does not require any separate secondary clarifiers, sludge pumping stations, etc.

Apart from this, other wastewater treatment technologies available are the integrated fixed film activated sludge process and tertiary filtration systems. The tertiary filtration process is used to make the water fit for restricted urban use and for potable purposes. This technique deploys sand or carbon filters besides membranes with varying pore diameters for further treatment of water. Finally, disinfectants like chlorine or ultraviolet rays are passed through the water to make it fit for consumption.

That said, to choose from the options available, the focus should be on the required water quality, value, and sustainable design and engineering besides the cost involved in development and operation and maintenance.

Recommendations and conclusion

It has been observed that modern irrigation technologies, particularly sprinkler and drip systems have substantially increased water use efficiency. But given that every drop matter, this is not enough. Transformation in traditional irrigation technologies coupled with wastewater reuse practices is the need of the hour.

Currently, the acceptance and adoption of wastewater reclamation is limited to select cities. A four-point framework involving framing of regulations and legislation that postulates mandatory use of reclaimed water, introduction of technological innovations, and right financial models and incentives, besides creating public awareness and acceptance, is needed.

Due emphasis is required to be laid on efficiency in water use through appropriate demand-side and supply-side management. For ensuring demand-side management, sensitising farmers about the different technologies available for wastewater reuse will help create awareness. For this, the central and state governments must take up pilot wastewater reuse projects in areas where the groundwater table has reduced drastically besides compulsorily reusing treated wastewater at their premises. This will help assess the economic advantage of using recycled water in contrast to other sources. Further, special purpose vehicles must be incorporated for monitoring projects such as wastewater treatment plants and tertiary treatment plants to ensure that adequate water quality is maintained.

Moreover, research and development, training and skill development will play a key role in water use efficiency. Facilitation of behavioural change is another important factor that can be ensured either through introduction of market incentives or through regular campaigns and drives. Lastly, existing wastewater reuse standards followed in the country must be in line with international practices.

Based on a presentation by Dr Uday Kelkar, Director, NJS Consultants, at a recent India Infrastructure conference

 

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