Wastewater must be seen as an environmental pollution issue, one that concerns the water sector needing attention of central, state, and local governments
Photo: Debojyoti Kundu Inadequate water supply and water scarcity in Indian cities have highlighted the importance of reuse and recovery of existing (limited) resources.
Reuse of greywater—which includes all the wastewater without faecal matter generated from domestic streams, such as kitchens, and bathroom—provides an opportunity to reduce this water scarcity by 50 per cent, eventually reducing the water bill and water footprint.
Greywater has a lower contamination making it easier to treat. In India, it is estimated that 31 billion litres of greywater is generated daily.
Black water and grey water are the two broad categories of domestic wastewater. One of the most significant differences between blackwater and greywater lies in the rate of decay of the pollutants in each.
Greywater decomposes faster than blackwater. About 80 per cent of the freshwater used in a household becomes wastewater, of which greywater accounts for 62 per cent. Activities, such as bathing or cleaning dishes, are the main sources for greywater in households.
Reuse of greywater for toilet flushing alone can reduce the freshwater demand by 10-20 per cent. It can help cope with high water consumption patterns and water scarcity worldwide.
In Bengaluru, for instance, only about 40 per cent of the total wastewater generated gets treated, and less than one per cent gets reused, as per a 2018 article by Urban Water Bengaluru.
Instead of releasing wastewater, the greywater generated at the household level can be collected, treated and reused for non-potable purposes like toilet-flushing, car wash and gardening.
A major advantage with greywater is that it is in continuous supply, and can be treated and reused all year long, unlike other conservation methods like rainwater harvesting, that are dependent on a particular factor (monsoon).
Sustainability requires natural resources to be managed through decentralised systems. On-site greywater recycling also reduces the effort and infrastructure in moving this water to a treatment facility.
Most Indian cities do not have a sewerage system; 67 per cent urban households are dependent on on-site sanitation (OSS) systems, especially in small cities.
Such small cities (with a population of less than 0.1 million) generate about 2,900 million litres a day (MLD) of wastewater, making it a major source of water pollution.
Here, septic tank effluent along with the greywater is discarded by the households. Some 94 per cent of this mixed-water (wastewater) is discharged into the environment without any treatment, as per an article by the website Sustainable Sanitation Alliance.
If the wastewater (from the underground drainage systems) and faecal sludge (from septic tanks) is effectively treated, then we would have an immense opportunity to reuse the treated wastewater instead of just discharging it in the open.
Some of the activities where this treated water can be reused in urban, peri-urban and rural areas are irrigation and construction.
In metropolitan cities as well, the wastewater is directly flown into drains or into the waterbodies thereby polluting them. For example, in 600-625 locations in Greater Hyderabad, wastewater is let into stormwater drains (about 1,200 km), leading to contamination and pollution of waterbodies in the city.
As we continue to work towards achieving the Sustainable Development Goals 2030, small towns remain at the heart of the challenge.
Finding appropriate wastewater treatment solutions for these towns, which lie at the nexus of rural and urban dynamics, will be an important step in establishing a water-secure world for all, says a 2022 article by the World Bank group.
The existing situation on-ground—high dependency on OSS systems, high vulnerability from inadequate de-sludging practices, and the differences in the features between underground sewerage and faecal sludge management makes the latter the preferred option for smaller towns, as per a report published by Centre for Policy Research in 2016.
The high levels of water stress in many parts of the country and ever-increasing pressure on freshwater resources are key drivers for utilising greywater. States, including Uttar Pradesh, Madhya Pradesh, Bihar, Jharkhand, Haryana, Karnataka, Gujarat, Maharashtra, Rajasthan, Andhra Pradesh, Telangana, and Odisha face serious problem in providing water to citizens, as per a 2022 paper in International Journal of Applied Environmental Sciences.
By 2030, a minimum 21 cities in India will move towards zero groundwater level, as reported by World Bank on June 9, 2018. Metropolitan cities, like Delhi and Bengaluru, are already facing a water crisis.
A four-member household generates 360 litres of greywater (90 litres per capita per day), and 120 litres of blackwater (30 litres per capita per day).
Usually, greywater and blackwater are not separated, and both flows as wastewater, as per a 2018 article by Urban Water Bengaluru.
National missions, like Swachh Bharat Mission-Urban (sBM-U 2.0) and Atal Mission for Rejuvenation and Urban Transformation (AMRUT 2.0), lay emphasis on the reuse of wastewater and state that cities should meet 20 per cent of their water demand through recycled water, thereby reducing non-revenue water to less than 20 per cent.
Many measures are suggested under the SBM-U 2.0 to tackle the problem of wastewater from small towns, which account for 26 per cent of the urban population of India, as per an article in Sustainable Sanitation Alliance.
A huge population and frequent droughts make greywater reuse systems a must for India. Different treatment systems have been used to reduce contamination in greywater before final disposal/reuse. Currently, over 15 states and Union Territories have framed policies on reuse of treated wastewater, of which few have received approval while the rest are in the draft stage.
In cities like Chennai, which uses 1,200 MLD of water, approximately 600 MLD (50 per cent) is the amount of grey water generated, which gets contaminated after getting mixed with blackwater, as per as per a blog published by the World Bank in 2022.
The Chennai Metro Water Supply and Sewerage Board is pioneering the use of treated wastewater for supply to industries, thereby reducing freshwater demand. In addition, many apartments in Chennai use reclaimed water for toilet flushing and landscaping.
Use of untreated wastewater for irrigation is common in India and leads to public health issues.
The annual health cost per child in an untreated wastewater irrigated environment is around R4,000 per annum, which is 73 per cent higher than that for freshwater-irrigated areas, as per a study published in 2012 in Exposure and Health.
This is reason enough to push for wastewater treatment and reuse. Due to these factors, discussions on reuse of treated wastewater and greywater have gained momentum. However, the priority of separate grey water management and reuse is still a distant dream in India.
Currently, there are three treatment systems used in India to treat wastewater and faecal sludge: sewage treatment plants (STPs), faecal sewage treatment plants (FSTPs) and co-treatment plants (CTP). The by-products (manure, treated wastewater) are then disposed or reused.
Greywater and blackwater management in urban India cannot be separated, since the two gets mixed, and turn into wastewater. A mix of decentralised STPs and FSTPs is required, with other innovative measures and technologies to address wastewater problems.
Many states treat wastewater and septage together. Converting STPs to co-treatment plants has shown a considerable advantage in terms of cost, water quality and reuse of the treated wastewater.
The government is striving to create an enabling environment to encourage reuse of treated wastewater. A strong regulatory structure is essential for a water reuse scheme, as per a 2022 article published by non-profit International Water Association.
Wastewater must be seen as an environmental pollution issue and an issue that concerns the water sector needing attention of Central, state, and local governments.
There are no stringent standards for greywater reuse in the developing countries including India. However, the Central Public Health and Environmental Engineering Organisation, in its manual in 2013, has recommended some guidelines for reuse of treated wastewater for particular usage at individual, institutional and community level.
The Central Ground Water Board also directs that treated wastewater can be used as a source of artificial groundwater recharge once it meets standards and is compatible with existing groundwater. Framework on use of treated greywater for agriculture has been found limited.
Indian state policies prescribe mandatory usage of reused wastewater for industrial zones within a certain distance from a sewage treatment plant (STP). This ranges from 30 km in the case of Karnataka to 50 km in Gujarat, Tamil Nadu and Haryana.
In the revised electricity tariff policy of 2016, there is a provision that requires thermal power plant located within 50 km radius of an STP to mandatorily use treated wastewater produced by the plant.
Innovative thinking and planning about where and how the treated wastewater can be used can lessen demands for freshwater withdrawals, and can result in safe water reuse and environmental sustainability.
In Indian cities, the sewerage facility is quite inadequate to cater to the demand mainly because of the huge volume of wastewater due to the inclusion of greywater with blackwater.
If the greywater is separated from the black water, the gap between the requirement and the availability could be substantially reduced. There is a need to realign the ground realities of OSS systems with their treatment expectations in a scalable, efficient and reliable manner in order to promote usage of treated wastewater.
While centralised wastewater treatment solutions are imperative in large, developed urban centres, they are expensive, energy- and labour-intensive and time-consuming.
In India, cost effective solutions, like decentralised wastewater treatment plants, should be promoted, especially in small cities. The reuse approach should be bottom-up, starting from reuse at source level.
This article was first published in State of India’s Environment 2023 released by Centre for Science and Environment and Down To Earth Magazine on March 23, 2023
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