Decentralized Water Sanitation Systems (DEWATS): Exploring Opportunities for Urban Innovation

With cities all over the world growing at an explosive pace there is a growing need for efficient and adaptive approaches to waste water treatment and using wastewater as a resource. Rapid urbanisation and growing population increases the demand on a local municipality’s water resources. With the growing awareness for the need for sustainability, small scale sanitation systems in cities are gathering pace over recent years (Mortiz et al. 2015). Traditional approaches of water management utilizes potable water for irrigation,? washing and toilet flushing activities even though these actions do not require high physical or chemical quality standards (Bernal, Restrepo and Casquete 2021). Majority of the emerging economies utilize centralized treatment systems for wastewater, however, experience shows that centralized systems have been particularly poor at reaching peri-urban areas, particularly those that fall outside municipal boundaries and have not been responsive to local needs and resources. Decentralized systems are gaining popularity overtime due to the possibility of reducing long term expenditures and its potential for wastewater reuse. Decentralized water treatment involves the treatment of wastewater in close proximity to the point of generation. Having a relatively small footprint and the ability to treat large volumes of water, these systems fundamentally operate on solar, force of gravity, physio-chemical and? biological processes which drastically reduce the energy requirement? for the sanitation process. (See Annex)

In contrast to centralized wastewater treatment systems, a decentralized system offers potential to reduce costs as transport sewers that include lifting stations and storage infrastructures that handle combined sewage flow are not needed.? Often when centralized systems are established in urban centers, they are oversized and subsequently with increase in population and demand they become undersized. Small scale decentralized systems can help with? the precise matching of the growing water requirements therefore increasing efficiency of water usage. Furthermore, centralized water sanitation systems tend to combine and treat heterogeneous water streams i.e. household, industrial and stormwater? making the treatment process difficult and hence results in an increase in cost. Decentralized wastewater treatment systems treat relatively homogenous streams of wastewater and are also capable of treating special contaminants with the appropriate type of technology for the respective type of wastewater in particular areas. (Mortiz et al. 2015) Large collection systems tend to have infiltration ,inflow and outflow problems in the event of a storm and also end up treating stormwater. Decentralized water sanitation systems have smaller networks of wastewater collection which are usually pressure controlled sewers which reduces the chances of infiltration and inflow even in the case of a storm making them more climate resilient. (Ahuja et al. 2014).

Decentralized WATSAN system options have been successful in places such as Vietnam, where treatment of wastewater done by baffled septic tanks with anaerobic filters proved to be the most viable option for residents. Additionally, suitable technologies are being applied in Colombia, Brazil and India. In Brazil, anaerobic treatment as an option for decentralized treatment systems for various districts is increasing. However, many scholars while analyzing the potential of decentralized water sanitation systems have also paid attention to ‘governance issues’, and the importance of proper governance in megacities when it comes to quality of water (Verma et al. 2020).

In order to ensure the success of such a system in cities, an enabling environment must be created. The following recommendations will attempt to enhance the performance of decentralized WATSAN systems keeping in mind social, environmental and economic parameters-

a.????? Site Specific management strategies are essential and must account for cultural and economic conditions of the target municipality.

b.????? Usage of “Appropriate Technology”? that is economically viable for the specific form and type of wastewater.

c.????? Centralized management of decentralized systems is important to ensure regular inspection and maintenance.

d.????? Capacity building for the local people in the municipalities by prioritising access to information and resources.

e.????? Training modules for municipality representatives will aid with the monitoring of water quality and maintenance of equipment.

f.????? Institutional Strengthening through administrative reforms that reduces bureaucratic involvement and government control and increases user participation through suitable planning and policy.

Components and Principles of Decentralised WATSAN systems:

The? three main treatment processes along with their principles are as follows:

a.???? Primary Treatment ?

This step? is based on the principles of Sedimentation and biological treatment. A Settler or a septic tank is used and they usually have two chambers; the first one is used for the retention of scum and sludge via anaerobic sludge????? digestion and the second chamber further filters the waste water.

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b.???? Secondary Treatment

Anaerobic Baffled Reactors have multiple chambers that help increase biological degradation by making the waste water go through active sludge beneath chamber separating. A Biogas Digester can be used as a setter as well; it provides anaerobic treatment of wastewater with a higher organic load which produces biogas as a useful by-product.

c.???? Combined Secondary and Tertiary Treatments

In this step suspended solids and dissolved solids are removed from the pre-treated water. Anaerobic Filters are used to treat non settleable solids by bringing in them with close contact to active microbial mass. For wastewater with a low percentage of suspended solids, Horizontal Gravel Filters are used to filter water based on the principles of biological conversion, physical infiltration and chemical absorption.

Sources:

Gutterer, Bernd. 2009. Decentralised Wastewater Treatment Systems (DEWATS) and Sanitation in Developing

Countries: A Practical Guide. Germany: BORDA.

BRODA. (2017). DEWATS Implementation by BRODA.

Moglia, Magnus, Kim Alexander, and Ashok Sharma. 2011. “Discussion of the Enabling Environments for Decentralised Water Systems.” Water Science and Technology?: A Journal of the International Association on Water Pollution Research 63 (June): 2331–39. https://doi.org/10.2166/wst.2011.443.

Yu, C, R Brown, and Peter Morison. 2012. “Co-Governing Decentralised Water Systems: An Analytical Framework.”Water Science and Technology?: A Journal of the International Association on Water Pollution Research 66 (October): 2731–36. https://doi.org/10.2166/wst.2012.489.

Massoud, May A., Akram Tarhini, and Joumana A. Nasr. 2009. “Decentralized Approaches to Wastewater Treatment and Management: Applicability in Developing Countries.” Journal of Environmental Management 90 (1): 652–59. https://doi.org/10.1016/j.jenvman.2008.07.001.

?Konig, Moritz, Julius Jacob, Tariq Kaddoura, and Amro M. Farid. 2015. “The Role of Resource Efficient Decentralized Wastewater Treatment in Smart Cities.” In 2015 IEEE First International Smart Cities Conference (ISC2), 1–5. Guadalajara, Mexico: IEEE. https://doi.org/10.1109/ISC2.2015.7366155.

?PramitVerma2020.“UrbanEcology-1stEdition.”n.d.AccessedJune2, 2021. https://www.elsevier.com/books/urban-ecology/verma/978-0-12-820730-7.

Ahuja, S., Larsen, M. C., Eimers, J. L., Patterson, C. L., Sengupta, S., & Schnoor, J. L. (2014). Comprehensive water quality and purification. Elsevier/Academic Press.

All image sources -? BRODA. (2017). DEWATS Implementation by BRODA.