Bengaluru's treated sewage: Boon or bane?

Though it may not be the sole source of heavy metal contamination in vegetables, the water discharged to districts adjacent to Bengaluru must be treated better.
Last Updated : 03 November 2023, 23:46 IST
Last Updated : 03 November 2023, 23:46 IST

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A report by the Environmental Management Policy and Research Institute (EMPRI) on heavy metal contamination among vegetables warned that farmers should not be allowed by law to grow greens and vegetables using drainage and effluent waters.

Since most vegetables and greens come to Bengaluru from neighbouring districts of Kolar, Chikkaballapur and Bengaluru Rural, the attention has turned to the project that pumps secondary-treated sewage water to these districts.

There are two such treated sewage supply projects, from the Koramangala-Challaghatta (KC) Valley and Hebbal-Nagawara Valley. Water goes to Kolar, Chikkaballapura and Bangalore Rural districts. The Minor Irrigation Department looks after the project. The Bangalore Water Supply and Sewerage Board (BWSSB) treats the water, and the Karnataka State Pollution Control Board is supposed to monitor the quality.

Started in 2018, the KC Valley project pumps water to 145 tanks in Kolar and Chikkaballapura. Krishna M, Assistant Executive Engineer associated with the project, says the Minor Irrigation Department takes daily reports from an accredited lab and pumps water only if fit enough. There is no daily checking of treated water for heavy metals.

Venkatesh, a farmer living near Kendatti tank, cites unbearable stench, increased levels of sodium in groundwater, increased mosquitoes, diseases affecting tomato crops, increased use of pesticides and decreased shelflife of crops as some problems. He adds that he cannot grow root vegetables such as potatoes and carrots nowadays.

Many farmers attribute some issues to fake seeds and pesticides various companies sell. Venkataramappa, secretary of the diary producers union in Lakshmisagar, says the borewells are 800-1000 feet deep, and the water table has improved. He says tertiary water treatment will help farmers.

Households in the KC Valley wastewater belt depend on groundwater, which is now recharged through treated water. Shivappa Arivu, a professor at the Government College for Boys, Kolar, says the district, with no water source, suffered from acute drought ten years ago. However, treated water has also brought pollution, allergies and illnesses to people, he adds.

“We need water, but it should be treated well. Wastewater reuse is good, but the government must pay attention to fixing the problems,” he says, seeking tertiary water treatment.

‘All is well’: Study

A writ petition is on regarding the KC Valley project, filed in 2018, seeking to ensure that polluted industrial and chemical effluents and contaminated water are not supplied to tanks of Kolar, Chikballapur and Bengaluru Rural districts.

As per the court directions, a study sponsored by the Minor Irrigation and Groundwater Development Department and conducted by the Centre for Sustainable Technologies, Indian Institute of Science in 2020 evaluated the socio-economic impact of the KC Valley project through a survey.

It found that the heavy metals in KC Valley’s treated water and raw sewage met the Indian drinking water standards. It concluded that there will be no serious threat to human health because of it.

The study highlights the positive impact of the project through increased fruit and vegetable yield, milk production and real estate value. It notes no direct adverse effects of groundwater recharge. 

Yet, it asks for further studies on public health and establishing a proper monitoring system awareness and training programme for farmers about selecting crop patterns, fertiliser use, and irrigation techniques.

Scientists from the Centre for Sustainable Technologies, Indian Institute of Science, declined to comment. A scientist told DH that the treated wastewater is safe and has no heavy metals beyond the limits.

Sewage and heavy metals

Officials feel domestic sewage may not have industrial waste and heavy metals as it is carried through closed conduits of BWSSB. However, the research indicates the contrary. A 2023 study showed high levels of lead, iron, nickel, cadmium, arsenic, chromium, and copper in the wastewater of Delhi, Mumbai, Kolkata, and Chennai.

Many researches done in Kerala, Tamilnadu and Hyderabad show the presence of heavy metals in cosmetics, skin care products and hygiene products, which ultimately join sewage. Lead, mercury and arsenic were shown to exceed the limits.

“Sewage in Bengaluru is not just domestic sewage even if BWSSB carries it,” says Nirmala Gowda, co-founder of Paani.earth, a nongovernment organisation. Textiles and small-scale industries in residential areas release sewage into sewer lines stealthily. Solid waste and microplastics also get mixed up in the sewage, disrupting the biological secondary treatment process, she adds.

A study done using BWSB’s hourly live monitoring data from five STPs of the KC valley project scraped for seven months (January to July, 2023) by Paani.earth shows that the treated water had problems meeting biochemical oxygen demand (BOD) and chemical oxygen demand (COD) standards many a time.

“Nobody is against wastewater reuse. Standard operating procedures should be there to stop the outflow when the parameters are breached. When the project was being done, nobody thought about operational inefficiencies. A small amount of biological pollution can multiply into a larger public health issue. Who is going to monitor this?” asks Nirmala Gowda.

What happens when the parameters go out of limits? A BWSSB official told DH that the agencies contracted with maintaining STPs fix the quality by doing the needful.

Many sources of heavy metals

Sources say the industrial and municipal sewage in all the small towns in all the districts that receive KC Valley water is untreated, which ultimately joins tanks and groundwater. Old leaking borewell metal casings can also lead to contaminated groundwater.

Water from deep groundwater aquifers and alluvial soils may contain heavy metals. A study from Nepal shows elevated concentrations of heavy metals in water drawn from wells ranging from 276 feet to 1,000 feet.

The Minor Irrigation Department has put up boards banning the direct use of water. However, in many areas, farmers use the KC Valley water directly. Untreated wastewater from Belandur and Varthur lakes flowing to Tamilnadu is also used for irrigation, which can lead to contaminated vegetables.

In a visit to a landfill in Mitaganahalli last year, DH observed that the BBMP sends untreated toxic leachate to designated farming plots for fertilising them, which can also cause heavy metal absorption in crops.

Solutions to heavy metal in domestic sewage

1. Reducing the use of personal care products and cleaning products that contain heavy metals.

2. Proper, scientific disposal of pharmaceuticals and over-the-counter medications.

3.Preventing industrial wastewater from being discharged into municipal sewers.

4. Treating domestic sewage before it is discharged into the environment.

5. Not taking wastewater directly for agriculture/ irrigation.

6. Educating people about the sources of heavy metal contamination in domestic sewage and the risks associated with it.

Discussions on for tertiary treatment: Minister

The office of N S Boseraju Minister of Minor Irrigation sent responses to DH's questions related to heavy metal contamination while promising to take up tertiary treatment of sewage water for wastewater reuse projects.

What short-term and long-term action is the Minor Irrigation Department taking to address the problem?

Many studies have been done regarding the quality of secondary-treated water. Even the National Green Tribunal (NGT) has given instructions to monitor the quality of the treated water. We are strictly adhering to those guidelines. The heavy metals are not visible in the household sewage water. No data or study shows that the contamination of vegetables and milk or groundwater occurs because of the treated water. In some cases local body governments (municipalities/ panchayats) are not treating sewage which is entering the tanks directly. Some farmers use the water meant for groundwater recharge directly for agriculture. Contamination of treated water in the tanks should be stopped. I as a minister have written a letter to district in-charge ministers and district commissioners to stop directing untreated sewage water to tanks and to ask local bodies to take the necessary steps to treat it. Studies (socio-economic and scientific) are going on regularly to monitor the impacts of the treated water. A socio-economic survey conducted by ISEC Bengaluru shows economic growth and groundwater levels have risen. We intend to coordinate and collaborate with multiple departments as well as raise public awareness. The government will surely take up tertiary water treatment and ensure that this project continues to benefit future generations.

Is the secondary-treated water across all STPs and all pump houses being monitored and treated for heavy metal contamination? If not what's the plan?

BWSSB does the water treatment and the Minor Irrigation Department does the supply work. BWSSB only uses household sewage water so heavy metal contamination is minimal or zero. IISc research has confirmed the same. After the treatment we will receive it only if the water meets the specified parameters. The Minor Irrigation Department also checks the quality of treated water on a set of parameters. A committee led by IISc scientists assesses water quality regularly as per NGT guidelines. We have directed officials to ensure the water quality meets the necessary standards.

What is stopping the government from going for tertiary treatment? Is it money?

The government of Karnataka is the people’s government and we are doing what the people demand. People are happy with the positive impacts of secondary treatment of water. We are not against tertiary treatment. The decision will be taken at a higher level and discussions are on. Money is not an issue.

Published 03 November 2023, 23:46 IST

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