Faecal coliform is a challenge in Delhi

Despite treating 72 per cent of its generated sewage estimated at 3,600 million litres per day (MLD), Delhi faces challenges with rising levels of fecal coliform bacteria in the treated effluent from Sewage Treatment Plants (STP). This concerning problem has been highlighted in a recent news article published by the newspaper The Times of India. 

Around 75 per cent of the STPs managed by the Delhi Jal Board (DJB) are failing to effectively treat faecal coliform. The excessive presence of faecal coliform in the treated water has serious implications for human health, particularly as Delhi aims to reuse treated water for various purposes like lake rejuvenation, horticulture and in parks and gardens. To understand the root of the problem, we need to delve into the complex story of how Delhi manages its sewage and septage.

Delhi generates the largest amount of wastewater – around 3,600 MLD of sewage – of which only 71.5 per cent is treated. As much as 55 per cent of the city is covered with a sewerage system supported by 58 pumping stations, 37 STPs across 20 locations. 

Most of these STPs work on activated sludge process technology and a very few on extended aeration, SBR and other technologies. Few of these STPs are designed according to the old discharge norms of CPCB, while 14 STPs comply with the discharge standards set by the Delhi Pollution Control Committee (DPCC). 

Only a few  fully meet the faecal coliform norms set by the Central Pollution Control Board (CPCB). The faecal coliform levels in other STPs were found to be exponentially higher than the desirable limit and maximum permissible limits of 500 MPN / 100 millilitres and 2,500 MPN / 100 ml respectively. 

When it comes to septage management, 68 per cent of the city population is dependent on offsite sanitation systems, according to Census 2011. This figure has reduced to 55 per cent, according to Delhi Master Plan for 2041.

There were around 1,800 unauthorised colonies in the capital region until recent years which lack proper sanitation facilities. These households were dependent on private service providers for emptying these onsite sanitation systems. A shit flow diagram by the Delhi-based think tank Centre for Science and Environment (CSE) stated that the number of these vaccum tankers ranged from 350-400. Out of this, however, only 172 vehicles were authorised by DJB. These vehicles empty the septic tanks, transport the sludge and discharge it at 86 designated SPS / STPs. 

As per the latest figures, around 42.8 million litres of septage was collected in February 2024, which amounted to 1.5 MLD. This is quite low compared to what is generated in the city. First, the number of licensed vendors is grossly inadequate, compared to the total number of vehicles operating in the city. Second, the unauthorised vehicles discharge the sludge in any nearby nallah, open drain or open field to save money on transportation. Third, outlets of the septic tanks are connected with the open drains, which are tapped through interception and diversion and reach the STPs. 

Let’s look at the case of Sangam Vihar. There are 160 tankers working in this area that dispose of faecal sludge in the Dakshinpuri sewage pumping station. The station also receives sewage and septage from RPS colony, Khanpur and Tigri. 

A CSE team discovered during a study that almost all the 60,000 properties in Sangam Vihar had non-sewered sanitation systems of sealed underground septage tanks and generated more than 200 kilolitres a day (KLD) if septage desludging happens every day in Sangam Vihar. 

The non-registered tankers dispose of the septage in the night in the nallas nearby, which also amounts to a considerable quantity. “We have nine tankers of 3,500-9,000 litres capacity and desludge the nearby areas of Batra hospital and dispose it in the SPS,” responded Hiralal (name changed). But a ground inspection showed the reality is different and we found that most of these unauthorised tankers dispose of the septage in the nallas (drains). 

This is only one example. We have 1,800 such colonies generating septage. Besides, urban poor settlements have mushroomed in the Yamuna flood plain area and the sanitation infrastructure inadequacy has become more pronounced. 

In view of the current sewage and septage management practices in the city, we tried to look into the possibilities to address the faecal coliform issue in treated water, so that the water being reuses is free from pathogens. Following are a few suggestions:

Ensuring proper functioning of STPs: Proper functioning of the STPs is a pre-requisite to meet the prescribed effluent discharge standards. Non-working of chlorination units and poor performance of the STPs is due to the absence of regular maintenance and monitoring of STPs. Regular cleaning of tanks, replacement of worn-out equipment and calibration of sensors should be carried out regularly to keep these units functional. Trained operators should be employed to manage and operate the plants effectively.

Upgrading STP technologies: Delhi’s STPs predominantly rely on activated sludge process (ASP), with few facilities utilising extended aeration, sequencing batch reactor or other advanced technologies. ASP relies on microorganisms that “consume” organic matter in sewage, measured by biological oxygen demand (BOD). Lower BOD levels can reduce microbial activity, impacting treatment efficiency. However, BOD might not be the sole factor in this case. ASP has limitations in effectively removing coliform, necessitating the use of high doses of UV or chlorination for coliform removal before applying tertiary treatment. However, high chlorine demand can lead to the formation of carcinogenic compounds, while excessive UV dosage increases capital costs and reduces efficiency. It is crucial to design new treatment plants with better faecal coliform removal efficiency. The existing STPs which lack disinfection units should be equipped with chlorination, ultraviolet or ozonisation units. An assessment of STPs receiving faecal sludge carried out by CSE also confirmed the higher values of faecal coliformsm than the prescribed discharge limit, even though many have a chlorination unit to remove the bacterial load. 

Implementing solid-liquid separation: Unfortunately, the exact amount of septage generated in Delhi remains unknown. This lack of data makes it difficult to accurately assess how much ends up in STPs. STPs, which are mainly designed for regular sewage, struggle to effectively treat septage due to its unique characteristics. Septage has much higher concentrations of organic material and pathogens, compared to typical sewage that can overload the STPs and cause issues like reduced treatment efficiency and possibly higher levels of pollutants like faecal coliform in the treated water. As a precautionary measure, introducing solid-liquid separation at the sewage pumping stations where septage is received, can effectively reduce the presence of faecal coliform in treated water. Studies suggest that most of the pathogens present in septage reside in the separated solids. By removing these solids upfront, solid-liquid separation significantly reduces the overall pathogen burden on an STP. 

Compliance with DPCC standards for upcoming STPs: All upcoming new STP projects and upgradation of STP projects should be designed and constructed to meet all the eight parameters for treated wastewater discharge prescribed by DPCC. 

Strengthening monitoring and reporting: Regular monitoring of faecal coliform levels in treated effluent should be conducted and made publicly available. This transparency will enable public awareness and accountability. Online monitoring systems are crucial for real-time data collection on various water quality parameters, including potential faecal coliform levels. These monitoring systems should be well functioning all the time. Lack of real-time data can hinder early detection of operational issues or inadequate treatment processes within STPs

With a growing population and limited freshwater resources, Delhi is exploring wastewater reuse as a potential solution. However, this ambitious plan hinges on one critical factor: The quality of the treated water. If the treated water isn’t free from harmful pathogens like faecal coliform bacteria, its reuse can pose a serious public health risk.