Part 2: Water Tankers and the Wastewater Opportunity
This case study shows how excess treated wastewater from apartments can be transported for construction activities, saving freshwater and limiting discharge into drains.
Sahana Balasubramanian and Shreya Nath
Water tankers to transport treated wastewater are an important part of solving the treated wastewater reuse problem. In Part 1 of this blog series, we detailed how water tankers are on an unsustainable path, which has huge implications on the future of their business and, more importantly, on the freshwater needs of densely-populated cities.
We also explained that there are government rules in places that mandate 100% reuse of treated wastewater at apartments. Despite this, there are hurdles.
Our wastewater research brief details six key reasons why treated wastewater is not being effectively reused.
One of them, the focus of this blog, is the reluctance among tanker companies to transport treated wastewater. But this roadblock could in fact be an opportunity to tackle this multifaceted problem.
In Part 2, we delve into a unique case study in another big metropolitan city, Mumbai, that testifies the viability of the treated wastewater reuse and transport option, focusing on the construction sector as the end-user. The ideation part of the project took about a month and the transactions were initiated in February 2022.
This example shows switching to wastewater helped achieve 46% savings in the cost of freshwater for the builder and save 150–200 kilolitres (KL) of freshwater.
The opportunity
Like in Bengaluru, the Brihanmumbai Municipal Corporation (BMC) has mandated the installation of STPs in apartments. The Zero Liquid Discharge (ZLD) policy is also in place here, in a bid to ensure 100% of the treated wastewater is reused and not released into stormwater drains.
One part of our case study site is Celeste Apartment in Mira Bhayandar, Mumbai, where treated wastewater is being reused mainly for toilet flushing and minimally for landscaping. About 100–150 KL of the excess treated wastewater from this apartment is discharged; this is illegal and liable to heavy penalties.
Clearly, there’s a resource here that has to be put to use. But where?
One kilometre away is a construction site. Construction is one of the sectors that consume large quantities of fresh water, right from preparing the foundation to compaction, concreting, and curing. It is estimated that for constructing a square meter, 27 KL of water is required. Their freshwater demands were being met by tankers, which brought water from other locations, and groundwater, through borewells dug at the site. They have been buying 10–15 tankers per day (1 tanker capacity- 10KL) at a cost of Rs. 900/tanker.
So, there’s an opportunity here. One, is for the construction site, to use recycled water instead of expensive freshwater. This helps the builder reduce the consumption of freshwater, thereby reducing costs as well. And two, from the apartment’s point of view, they are able to give away their excess treated wastewater and thus adhere to ZLD.
Given this context, replacing freshwater with wastewater is not only logical but also necessary. But as mentioned in Part 1, there are hurdles to making this switch. Here, we explain how this case study worked successfully and what lessons can be taken forward to replicate this model elsewhere.
Highlights of the case study
The buyer of the freshwater at the construction site, i.e. the builder, was concerned about the consumption of large quantities of freshwater and the costs involved in it. He identified the potential source of treated wastewater, Celeste Apartment nearby, and approached Green Lantern Engineering Pvt. Ltd., an environmental consulting company based in Bengaluru that specialises in STPs, waste-to-energy solutions. Green Lantern was responsible for transporting treated wastewater from the apartment to the construction site.
The table outlines information about the apartment, the source of excess treated wastewater:
A key learning from this case study is that multiple stakeholders need to come together to carry out this exercise successfully.
One of them is apartment residents. Initially, there was resistance among apartment residents about transporting and reusing the treated wastewater for secondary applications. They were not keen on giving the treated water away for free because they pay for the operation and maintenance (O&M) of the STP. Through awareness-building programmes that demonstrated the significant environmental impact in terms of cost and freshwater savings, the support of the Residents’ Welfare Association (RWA) was won over.
The tankers used for transportation are facilitated by Green Lantern’s logistics team, another important stakeholder. The tankers used for transporting wastewater are labelled as ‘STP treated water’. There is continuous availability of wastewater and transport schedules are based on the construction site’s requirements. The builder has installed a tank for temporarily storing the treated wastewater. The treated wastewater is consumed immediately at the construction site (within 24 hours), so no quality checks are carried out.
Stakeholders involved in the process
As mentioned above, the distance between source and sink is selected in such a way as to minimize fuel costs and time is taken. In this case, the distance between the source and sink is 1 km. Operating hours are between 8 am — 6 pm.
The time taken for one transaction is summarised in the table below:
Currently, the treated wastewater is being reused for curing (providing moisture and time for the concrete to develop its intended properties) and compaction (expels entrapped air from freshly prepared concrete and packs the aggregate particles to increase the density of concrete) at the construction site.
About 10–15 tanker trips are made every day. The builder was paying Rs. 900 per tanker (capacity 10KL) of freshwater. With this excess treated wastewater, the costs have been cut down to Rs. 486 per tanker. This results in 46% savings in cost for the builder and also 150–200 KL of freshwater is being saved.
This case study shows how treated wastewater can be transported from the source (the apartment) to the sink (the construction site) through the collective efforts of various stakeholders.
Finally, we draw lessons from this experience to highlight some of the key takeaways that can help make wastewater transportation economically viable.
- Number of loads carried by the tanker per day
It is essential to maintain sufficient tanker trips per day. Based on our financial analysis, an average of 7–8 tanker trips per day is required to make it economically viable.
- Distance between source and sink
The distance between the source and sink should be kept less than 5 km. As the distance between source and sink increases, the fuel costs will increase. Keeping the source and sink nearby will also help reduce the time taken to complete transactions.
- Distinction between tankers transporting freshwater and wastewater
It’s important to colour code the tankers carrying treated wastewater for them to be easily distinguishable from the freshwater tankers. In Part 1, we wrote about the reluctance among tanker operators to ply wastewater because they don’t want to entirely lose their business of transporting freshwater. Because of the ‘yuck factor’, operators fear that their usual customers will turn to another agency because they perceive the same trucks are being used for both, and that freshwater and treated wastewater gets mixed during transportation. Creating a physical distinction is a possible solution that can overcome suspicion.
Additionally, it is necessary to find ways to ensure a sustained business for wastewater tanker operators through solutions like digital platforms that help sellers and buyers find each other more easily. The tankers are also important in the context of building trust among end-users such as residents and builders. Adding GPS trackers and water quality sensors to the vehicle goes a long way in allaying these fears.
Under CSEI ‘s Green Cities Initiative, we are studying how to use excess treated wastewater outside the apartment fence. To enable this, CSEI is collaborating with Karnataka Pollution Control Board (KSPCB) to pilot the use of excess treated wastewater from apartments for the greening of the public parks and gardens in the Yelahanka zone.
Edited by Kaavya Kumar
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