CITY’S OLDEST STP HAS ZERO IMPACT ON WATER IT TREATS
Study finds Vrishabhavathi plant is working at just two-thirds of its capacity
Stating that currently only a third of Bengaluru's domestic sewage is treated, an assessment of the oldest and second largest sewage treatment plant in the city by scientists from research institute, Ashoka Trust for Research in Ecology and the Environment (ATREE), reveals that it is functioning at only two-thirds of its design capacity and the effluent discharged frequently does not meet effluent discharge standards. The researchers analysed the Vrishabhavathi Valley treatment plant (VVTP).
Only a small fraction of the flow in the Vrishabhavathi stream is currently being treated. "This suggests that paradoxically, the overall wastewater treatment capacity in Bengaluru city is low, notwithstanding evidence of underutilisation of existing wastewater treatment capacity," said Dr Priyanka Jamwal and Dr Sharachchandra Lele, among other researchers from ATREE, Bengaluru, in their findings.
Results also show there was no significant difference in water quality upstream and downstream of VVTP, that is, no net impact of VVTP on water quality of the Vrishabhavathi stream was observed.
An earlier study by ATREE had found heavy metals in water samples from Vrishabhavathi river, which drains 40 per cent of the Bengaluru city area. Once a seasonal river, it currently flows throughout the year, carrying an estimated 600 million litres per day (MLD) of wastewater discharged by the city.
"In addition to industrial pollution, much of the water flowing down the Vrishabhavathi is simply untreated domestic sewage. Today, only a third of Bengaluru's domestic sewage is treated. Overall, wastewater treatment capacity in Bengaluru is much less than the amount of sewage generated and the underground drainage network has not kept pace with the city's growth. To address this, Bengaluru's approach has been to simultaneously extend the underground drainage and build large centralised sewage treatment plants. Simultaneously, the Karnataka State Pollution Control Board (KSPCB) has pushed for apartment-level decentralised STPs through 'zero liquid discharge (ZLD)' laws that require all apartments greater than 50 units to have an in-house STP and to reuse all the treated water they generate," says the paper.
According to the paper, even more than 20 years after the sewage treatment plant was upgraded, only 20 per cent of its intake comes from the underground drainage network. The remaining 80 per cent, said the research team, is picked up from the river, which carries a mix of domestic and industrial wastewater and is much more dilute.
"This also seems to demotivate the Bangalore Water Supply and Sewerage Board (BWSSB) from making the remaining one-third capacity operational," it says.
The findings reveal that most of the wastewater being treated at VVTP consists of water being drawn from the stream, and not from the sewerage network. The presence of industrial effluents may also negatively impact the efficiency of the VVTP plant as 70-80 per cent of the total organic matter in the influent water is non-biodegradable. "Sewage treatment plants are typically designed to treat biodegradable domestic sewage. So, to improve VVTP's efficiency, either taking in stream water needs to be abandoned or treatment technology needs to be changed," it adds.
The paper says that the quality of influent into the treatment plant greatly impacts the treatment efficiency. The effluent from VVTP, observed the researchers, does not meet the discharge standards partly because the inflow quality differs from the treatment plant design specifications and partly due to inadequate training of the operational staff of the operating company, who are unable to adjust operational parameters to fluctuating influent conditions.
ATREE researchers also collaborated with researchers from the Autonomous University of Barcelona and conducted a study on the economic, social, and
institutional factors influencing decentralised urban wastewater reuse. The study found that "at present, no one is complying with, or can comply with the ZLD norm, which requires 100 per cent reuse".
The research team said that even apartments that scrupulously try to follow the rule have surplus treated wastewater that has to be released. "Many other apartment sewage treatment plants don't comply with quality norms. This is due to a combination of factors, which includes apartment financial constraints (decentralised treatment plants place a major burden on small complexes), poor training of sewage treatment plant operators and absence of enforcement on the part of KSPCB," it says.
The scientists have recommended that treatment of massive quantities of domestic sewage being generated will require "exploring different scales and technologies of treatment", even while centralised systems are made more effective and accountable. "Regulators must demand greater compliance from state-owned sewerage boards," they said.
BOTH LOCAL POPULATION AND URBAN CONSUMERS AT RISK
* The team found that the area near Byramangala tank on the Vrishabhavathi river was one of the few periurban areas near Bengaluru, where agriculture is still thriving.
* On one hand, the "nutrient rich" wastewater that the Vrishabhavathi delivers to downstream villages clearly benefits farmers; on the other hand, farmers complain of health problems.
* Irrigation water samples from three villages downstream of Byramangala tank, analysed at ATREE's soil and water quality lab, showed chemical and biological contamination.
* This contamination, particularly heavy metals such as nickel, copper, chromium, lead and manganese, had spread to the soil, the groundwater, and the milk and vegetable samples (like babycorn).
* The analyses suggested that not only the local populations, but urban consumers too are potentially at risk from exposure to heavy metals in their food.
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