Decentralized STPs in the Delhi Capital Region

Guest blog by Kelly D. Alley and Nutan Maurya

The territory under the jurisdiction of the New Delhi Municipal Council, or Lutyen’s Delhi, is lush with beautiful gardens. The New Delhi Municipal Council maintains around 8,000 parks and uses about 80 million gallons of water a day for grass, plants, shrubbery and trees. The Delhi Jal Board estimates that the total water treated at its sewage treatment plants is about 455 million gallons a day (mgd) of which they provide 142 mgd for horticulture and irrigation in the Delhi metropolitan region. With groundwater levels depleting to over 300 feet in some sections of Delhi, there has been increasing focus on curtailing use of groundwater for horticulture and other non-essential services. In this context, the National Green Tribunal has directed all urban municipalities to use treated wastewater for horticulture.   

In March 2016, the New Delhi Municipal Council took the decision to promote decentralized sewage treatment plants to help deal with the wastewater load in the city and promote recycling of treated water for functions such as horticulture and irrigation. This would help cut the dependency on groundwater and begin a separation of fresh and contaminated water. Fresh water sources from the upper catchments of the Ganga and Yamuna rivers could be better protected from pollution if wastewater were diverted away from in stream flows and used. Decentralized wastewater treatment systems are also promoted through AMRUT, or the Smart Cities program in the Ministry of Housing and Urban Development, so at least in central policy there is an option to move forward with this new idea.

The NDMC has just developed seven functioning sewage plants and has plans to create over 10 more within its jurisdiction. The NDMC will use this new water source to meet horticulture needs in the capital region and at the same time save groundwater and begin the process of removing wastewater flows from river flows. This blog post will introduce the seven sewage treatment plants that have been completed so far and explain the local water economics and the new PPP framework they are using. This is a cost effective way to wean the city off its dependency on groundwater as long as the treatment plants can be operated and maintained according to the standards of treatment laid out in the contracts. Another question is: what else can be done with these treatment plants to help promote the reuse of treated water for non-essential services?

First we need to explain the context of water usage and pricing. The New Delhi Municipal Council region consumes around 125 million liters per day (mld) of potable water, 120 mld of which it buys from the Delhi Jal Board for around Rs 15 a kiloliter. Bore wells and rain water harvesting make up the rest of the need and the estimated cost to procure groundwater is around Rs 10 a kiloliter. The NDMC then distributes the 125 mld of water purchased from the Delhi Jal Board through its pipe grids and by water tankers to non-piped areas. It is sold according to a rate scheme that gives the first 20 kiloliters of water at a nominal rate per connection per month with scaled rates based on increasing consumption after that. About ten percent of the NDMC’s water budget is being used for maintenance of the city gardens and for other beautification structures such as fountains and lakes. This amount has been sourced through groundwater and with “unfiltered water” provided by the Central Public Works Department. The latter is procured from the Okhla sewage treatment plant.

At present there are 2 private companies working with the NDMC to construct and maintain these new decentralized Sewage Treatment Plants (STPs). Ecosystem Resource Management Pvt Ltd has built 5 plants (four operating and one under construction) on the Soil Biotechnology model invented by Professor Shankar’s team at IIT-Bombay. Over twenty years, MSc and PhD students were involved in developing the soil biotechnology approach and it is now a patented method for wastewater treatment. The plants can be built quickly and operated with low skilled labor. They require very little power and take up much less land than conventional plants. The land requirement is 500 m2 for a 500 kld plant. The other company working with the NDMC is SS Engineering Corporation. They have built two plants on the MBR or Membrane Bioreactor model and a third is currently under construction. This method also requires very little land but consumes more power through its activated sludge process. The sludge generated from this process must be collected every day and distributed for horticulture and irrigation. The capacities of these plants run from 100 to 500 kiloliters per day. So far both these technologies have been constructed in gardens around the NDMC area. The NDMC plans to install smaller units in schools and housing colonies. These smaller projects will be undertaken by NEERI—the National Environmental Engineering Research Institute—using their own patented phytorid technology.

In following, we will describe eight plants, six that are functioning and two that are under construction.

Nehru Park SBT This is a 500 kld plant based on the Soil Biotechnology (SBT) method. This method was developed by Professor Shankar and his team at IIT-Bombay and the design was obtained from Vision Earth Care in Mumbai (web: http://www.visionearthcare.com/). This plant provides 500 kiloliters of treated water per day to the NDMC and the NDMC uses all of it for the sprawling Nehru Park.

The wastewater is drawn from an underground nala nearby and pumped to the STP. The nala carries about four times the wastewater that is taken for this decentralized treatment plant. The rest of the wastewater flows to the large centralized sewage treatment plant at Ohkla where it is treated using the activated sludge process. All of the STPs described in this article draw their wastewater from a nearby drain or nala, and therefore avoid the need to build long pipelines from many point sources of wastewater.  The longest pipeline among these plants is around 750 meters. So a significant savings occurs in the collection and transport of the wastewater to the plant.

Lodhi Garden This SBT plant treats 500 kiloliters per day. It was inaugurated on September 14, 2017. It will be connected to the garden’s underground water grid and will relieve the need to pump up groundwater. Tankers from the NDMC will also take the water and distribute it to gardens nearby.

Gol Market/ CPWD Housing Complex This plant is the only one of the six that is adjacent to a housing complex. The smell is much less than a conventional sewage plant because the sewage is sprinkled across the gravel rather than swished around in a large open air tank. The wind occasionally blows some smell toward the complex. Various measures to combat mosquito breeding have been undertaken and have to be closely attended to. The tank was painted to improve the ambience of the area. Generally, these SBT tanks are not unsightly and they give off a clean, paved look when viewed from the top level of the unit. The flowers and trees in and around the units also give it a rather pleasant appearance.

Rose Garden This SBT plant is located at one corner of the beautiful BRICS Rose Garden adjacent to Shantipath where embassies and high commissions reside. It treats 100 kiloliters per day of wastewater that is drawn from the nearby sewer line. After treatment through the soil biotechnology process, this treated water feeds the two rose gardens on either side of Shantipath and waters the bushes and flowers running along Shantipath near the Japanese High Commission. The other gardens along Shantipath are watered by the unfiltered source provided through the CPWD pipes. But they could eventually consume this treated water if an additional STP is constructed in the area. The railway museum has also expressed interest in using the treated water for their gardens.

Motibagh garden The plant at Motibagh uses the MBR or membrane bioreactor process. Raw wastewater is pumped into the green tanks and they are filled to the top. The wastewater is then churned and bubbled in these tanks so that it is aerated. The resident bacteria eat the sludge and bacteria in the water. Then the water passes through a membrane that filters it further. The treated water is provided to tankers that line up on the side street. The treated water is taken to the city parks and to garden areas not serviced by underground water pipes.

Satya Sadan The second MBR plant is located at Satya Sadan, at the edge of a very quiet neighborhood near the Safdarjung airport. The plant treats 500 kiloliters per day by feeding wastewater into open tanks that stand about 5 feet tall. The wastewater is aerated and then passed through a membrane filter. So far the treated water is being used for parks in the area but other uses can be envisioned once people are aware of the source.

Singapore Park The park across from the Singapore High Commission is the site of the fifth SBT plant. It is currently under construction and will have a capacity of 300 kld. The total construction cost is estimated around Rs 60-70 lakhs. The treated water will be used to water the gardens in the area and may even be used by the Singapore High Commission for toilet flushing. There are two slums nearby that house around 10,000 people. Those residents receive 9 tankers a day of potable water from the NDMC and draw groundwater from hand pumps for cleaning and washing. These residents are potential consumers for the treated water of the Singapore garden STP if they need water for non-body contact purposes. However slums generally consume less non-essential water than middle and upper income communities do, where gardening, washing houses and cars are more common.

Sanjay Lake Park This STP using the MBR technology is under construction and should be ready within two months. It draws raw wastewater from a nala manhole within the Sanjay Lake Park and will treat 300 kiloliters per day for horticulture in the area.

PPP arrangements At present, the NDMC is the sole client for the treated water produced through these plants. The PPP arrangement between the companies and the NDMC requires the company to pay all installation and operation and maintenance costs for 12 years. The NDMC pays for the system by guaranteeing to purchase the water from the company. They guarantee full purchase of water at around Rs 30-37 per kiloliter depending on the size of the plant.

The Future Apart from the current horticultural uses, there is scope for expanding the uses that can be made of this water. In middle and upper income homes, about half of total water consumption occurs in areas other than those that meet essential, bodily needs. Bathing, drinking, cooking and dishwashing take up 40% of the water budget, while toilet flushing, household washing, industrial processes and gardening take up a bit more than 50%. Slowly these non-essential needs which add up to 50% of the water budget in urban areas can be met by treated wastewater. This will save groundwater and raw river water for essential needs and also provide backup water in a time of disaster or emergency.

Granted, the NDMC territory is not a normal kind of city space and cannot act as a model for all cities. It is extremely privileged with open garden spaces and parks, wide roads and a low residential and office density compared to other urban centers. Its requirements for garden maintenance are enormous. It is in that sense an irregular kind of urban setting for testing out the utility and feasibility of these decentralized treatment systems. These plants have been built fairly quickly in New Delhi because the NDMC holds available land; the tighter land situation in other cities may restrict the creation of decentralized STPs.

Still, these examples allow the public to see what is possible and generate interest in experimenting with decentralized methods of wastewater treatment in other settings such as schools, golf courses, universities and other large institutions. Wastewater is abundant in every city and once treated with proven technologies can be a new source of water in almost any context. Experiments like those shown in this article can spawn local markets for wastewater and lead to the development of other technologies and uses. The two technologies used in these NDMC projects, namely the soil biotechnology and the membrane bioreactor methods, are performing well and offer hope for the future.

Dr Kelly D Alley & Nutan Maurya (alleykd@auburn.edu)