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Case study 2: DEWATS in India – A sustainable approach to wastewater treatment

DEWATS in India: A sustainable approach to waste water treatment
In this video, we’re going to look at a case study of how to approach the challenge of SDG 6. I will be talking to Jan Knappe, who spent several years working as a sanitation expert for a German NGO, BORDA, in India. His work explored effective sanitation in a densely-populated city with rapidly rising population. It lacks adequate infrastructure to deal with the increasing amount of waste water, which creates a significant public health risk. Hello. So far, we’ve focused mainly on traditional centralised and on-site systems for the treatment of wastewater.
A centralised system would probably be what comes to most people’s mind when thinking of wastewater treatment, a large-scale system with an extensive underground sewer network where all the wastewater from an entire city is treated. You will find this in most well-developed urban environments. On-site systems, on the other hand, are more common in rural areas where people live in individual houses or small villages, where the operation of an extensive treatment system is not feasible. Such systems rely on individual solutions for single households and are sometimes called off-the-grid solutions.
But for many situations, especially in rapidly-expanding urban areas and the outskirts where the more traditional categorizations of urban areas and rural areas merge into something we call peri-urban areas, neither of those two approaches really suit. In those areas, traditionally landscape uses become mixed and sometimes clash with the increased pressure from rapid urbanisation and a heavy influx of new people. We can see in these examples from India and Nepal how former agricultural areas become surrounded by dense urban pockets. We’ve seen the extent of such areas expand massively in the last few years, especially in low- and middle-income countries. Considering those challenges, how can we provide appropriate sanitation to a growing population and achieve as SDG 6?
Should we continue to build extensive sewer networks and centralised treatment plants, or are there other more suitable and sustainable approaches we could explore? For a long time, centralised systems such as the one we see here– in fact, this is one of the world’s largest treatment systems in the world– were believed to be the gold standard. Operationally, it is easier to collect all the waste water produced in a city or part of the city and pump it to a common collection point where it gets treated and released back into nearby rivers, lakes, or the sea. But this also comes at a cost.
First of all, such systems are expensive– both the planning and construction of the facility itself, land acquisition, the sewer networks, but also the continuing operational costs. This might not always be a problem as long as sufficient funding is guaranteed. But if we think of the areas that are experiencing the highest population growth globally, we see that the high-tech solutions are not always appropriate and affordable. Centralised systems also tend to be rather inflexible when it comes to dealing with extreme weather events like heavy rainfall or, say, large-scale power outages due to storm events. As they heavily rely on the use of electricity and complex machinery to operate, a de facto power outage will affect the entire catchment area.
This will especially pose tremendous challenges when we start looking at the potential for increasing uncertainties of global and local weather patterns following climate change. Before joining Trinity College Dublin, I have been working for a number of years in South Asia, mostly in India, with the German NGO BORDA. BORDA is, among other things, specialised in providing basic needs and services in low- and middle-income countries. As such, they are actively developing and implementing so-called decentralised wastewater treatment systems, or short DEWATS. DEWATS is not a technology per se. It is rather an approach to wastewater treatment, and the idea is fairly simple. Avoid using electrical equipment which can be switched off, and avoid using moving parts which can break.
DEWATS treatment in turn depends of natural biochemical and physical processes, including the degradation of organic material until the point at which chemical or biological reactions stop, the physical separation and remove solids from the liquid, and finally the removal of toxic or otherwise problematic substances which are likely to distort sustainable biological cycles. As in conventional systems, the various natural treatment processes require different boundary conditions to function efficiently. DEWATS are comprised of a series of treatment modules each providing an ideal environment for the removal of certain groups of pollutants. The systems are broadly based on the combination of four different treatment technologies.
Firstly, sedimentation in the second chamber to remove solids that come with the wastewater, similar to a septic tank, followed by multiple-chamber biological treatment through microbes naturally occurring in the wastewater stream who start feeding on the organic pollutants. Next, excessive nutrients are reduced and oxygen levels improved in constructed wetlands using locally-available plants that can tolerate growing in wastewater. And finally, an optional treatment in artificial lakes or lagoons that mimic natural treatment processes and could even include different aquatic species such as water plants, algae, or even fish for fish farming. The resulting treated water can then either be discharged or reused locally for irrigation and landscaping purposes or even recirculated as flush water for toilets.
Because of the modular nature, decentralised treatment systems can be constructed and operated successfully almost anywhere because they can be built from locally available material or pre-fabricated. They rely solely on natural processes without the need for specialised equipment, chemicals, or energy supply. This decentralised wastewater treatment system, for example, was constructed in the central Indian state of Maharashtra in 2007 to serve approximately 125 people. Here, we find all the modules we just discussed except for the artificial lake. Instead, the treated water is collected in an underground tank and used for irrigation of the surrounding areas. In coastal areas, which are more prone to flooding, we often face additional challenges when it comes to planning wastewater treatment systems.
In this example we clearly see how all underground modules are raised above ground level to prevent surface water from entering into the system. A flooded system would easily spread the wastewater in the area and pose a serious health and safety hazard. Because constructed wetlands are by design open systems, we see an additional biological treatment step being implemented here instead. But decentralised systems can also be scaled to accommodate small and medium-sized enterprises, organisations like schools or, as in this case, a hospital. Built in 2003, the system at this hospital in Tamil Nadu was designed to treat more than 300,000 litres of wastewater every single day.
You can see the beautiful canna plants growing in the constructed wetlands just in front of the main entrance to the hospital here. Most of the patients and visitors will most likely not even know that the artificial lake that you pass on the way in or the slabs on the ground where you might park your car are part of the wastewater treatment system of the hospital.
I hope you have seen that the modular approach of decentralised wastewater treatment systems can work in many different settings, especially in areas where a direct connection to conventional centralised system is not feasible or not desired. This and many other innovative approaches to solving sanitation-related challenges to SDG 6 in rapidly-expanding urban areas are implemented worldwide. As traditional centralised wastewater treatment systems might seem to offer a perfect solution on first glance, the high cost and construction, maintenance, as well as potentially severe impact on the environment in case of system malfunctions are often prohibitive when it comes to implementation in low- and middle-income countries, but not only here.
There are strong reasons to consider moving away from centralised systems towards decentralised solutions that offer efficient and effective technologies that require lower long-term investments and are easier to maintain while providing a comparable level of treatment if properly managed. The scalability and modular nature allow them to be readily adaptable and more flexible when it comes to changing population patterns, especially in rapidly-developing peri-urban areas. They offer the potential for local resource reuse and can play a vital role in protecting the environment and human health. This approach could be the way forward to overcome challenges to achieving SDG 6.

In the outskirts of rapidly expanding urban areas, peri-urban areas are emerging. In these areas, as Jan explains in the video, there can be many challenges to achieving clean water and sanitation. Should we continue to build extensive sewer networks and centralised treatment plants? Or are there other, more suitable and sustainable approaches we could explore?

In the video, Jan describes some solutions to these sanitation challenges in the form of modular decentralised wastewater treatment system, or short, DEWATS.

Thinking about your own community:

  • What type of wastewater treatment system does your neighborhood use?
  • Is it a centralised, decentralised, or on-site system?
  • Would a decentralised system be more sustainable? Why / Why not?

In the next step, we will be moving to the challenge of rapid urbanization. As we will see, this is an area that has a major impact on the provision of basic needs services, such as the supply of improved water and sanitation.

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