Waste Water Management in Cities: Notes from Bengaluru and Nelamangala

Treating waste water is vital in a rapidly urbanising world, where freshwater is under stress. Centralised sewage treatment plants (STPs) are often ineffective in treating waste generated by cities and towns. Lack of underground drainage network, poor capacity building, frequent power failures, and the presence of industrial effluents in waste water are the main reasons behind the inefficacy of STPs (Jamwal et al 2015). Hence, untreated or partially treated sewage contributes significantly to the surface and groundwater contamination.

To address the surface water quality issues in rapidly growing and emerging cities, the focus of the state and non-state actors has been slowly shifting towards decentralised waste water management solutions. Many organisations and start-ups have demonstrated the applicability of low-cost decentralised green infrastructure in flood control and in the treatment of urban runoff in open storm drains (El Hattab and Mijic 2019). 

Using the examples of Bengaluru and Nelamangala (a town located on the outskirts of Bengaluru city), we demonstrate the potential of deploying an innovative and low-cost provisional green infrastructure (PGI), which also require low energy, to improve the water quality of lakes and rivers in cities and towns across India. This article describes a “first generation” PGI innovation currently in development by a transdisciplinary team of researchers, engineers, and designers. This approach is referred to as strategic in-stream treatment systems (STRAINS). The STRAINS model proposes modest modifications to improve flows in the existing concrete stormwater channels. We argue that PGI approaches are highly suitable for application in rapidly growing cities, peri-urban towns, and emerging cities, where treatment capacity gaps in conventional waste water management practices have been proving insufficient to keep pace with the growing development pressure and domestic sources of waste water contamination. These interventions are intended to offer low-cost, low-tech, decentralised supplementary functions to top-down waste water management practices, such as STPs. This helps in lowering the quantum of harmful biological/chemical contaminants from mixed (domestic and industrial) effluents and greywater, which currently contribute to the poor surface water and groundwater quality in specific regions. 

In the following sections, we highlight the gaps in the waste water treatment and management by taking a case study of Bengaluru city (a rapidly urbanising city) and Nelamangala town (a rapidly growing peri-urban town). We also describe the potential of deploying PGI, a bottom-up approach to address water quality woes in these regions. 

Waste Water Management in Megacities and the Case of Bengaluru

Bengaluru, India’s fourth largest megacity, is in the midst of a severe urban waste-water crisis.  Rare among major metropolitan population centres, Bengaluru is not intersected by a perennial water source, such as a major river. Instead, surface water flows through a complex system of around 200 lakes interconnected by a network of open stormwater channels (Nagendra 2010). Through these channels, the urban run-off and waste water follow the natural sloping terrain of the landscape. Taken in total, this urban hydrological network is often referred to as “tank cascade system.” The city also comprises three sub-watershed basins and many interconnected “lake chains” within its municipal boundaries.  

Although these systems had worked effectively for storing runoff in the past, the recent explosion of (largely unregulated) urban development has put immense pressure on them. The stormwater channels currently double up as de-facto open sewers, receiving a daily deluge of untreated domestic and industrial effluents. The contamination accumulates, as it makes its way through the interconnected channels, and causes a range of impacts to the local ecosystems, livelihoods, and public health. These include notorious burning of lakes, toxic foam, fish kills, and downstream impacts on human health and food systems. An estimated 700 million litres per day (MLD) sewage treatment capacity gap (CSE 2012), compounded by a drastic reduction in natural wetlands, leaves an estimated 90% of local waterbodies, particularly lakes (historically referred to as tanks), directly fed by sewage (CSE 2012; Ramachandra et al 2016). This has led to the widespread pollution of surface water and groundwater, rendering both the sources unfit for human consumption and propagation of wildlife respectively (Figure 1). 

Figure 1: Contamination within Bengaluru Watershed

Jamwal et al (2015) has conducted a study to assess the treatment efficiency and efficacy of a centralised STP located in Bengaluru. Vrishabhavathi Valley Treatment Plant (VVTP), which is one of the oldest and the largest STP, has been selected for this study. The study has concluded that effluents from VVTP have not been able to meet discharge standards set by the Central Pollution Control Board (CPCB), and they have not shown any significant impact on the quality of surface water (Figure 2). Poor coverage, lack of urban drainage infrastructure, and discharge of untreated/partially treated industrial effluents have led to the poor performance of STPs on both fronts. 

Despite the inadequacies reflected from various independent studies, the typical responses to address water quality issues in urban spaces have been that of a top-down approach. This has led to the establishment of seven additional STPs in Bengaluru (Menezes 2016). Currently, there are 25 STPs in Bengaluru with a treatment capacity of 1,067.5 MLD. In addition to STPs, civil works for upgrading of the existing urban drainage network have also been undertaken by the Bangalore Water Supply and Sewerage Board (BWSSB) (Deccan Herald 2015). Despite all these efforts by the authorities, the surface and groundwater quality in the region has continued to decline. Bangalore Development Authority’s revised master plan for 2031 shows that even with new STPs in the future, nearly 378 MLD of untreated waste water will continue to be released into stormwater channels by parts of the city that are unconnected to the underground drainages (BDA 2017). 

Figure 2: The Evaluation of Vrishabhavathi Valley Treatment Plant

Waste Water Management in Peri-urban Towns and the Case of Nelamangala

Many peri-urban towns in India are set to become more densely integrated with nearby megacities as they continue to expand. Currently, these towns depend significantly on groundwater to meet industrial, agricultural, and domestic needs (Banerjee and Chaudhuri 2012). Sanitation management occurs mainly at the household level through on-site systems, such as pit toilets and septic tanks. In these regions, the segregation and treatment of black water (toilet waste) often take place at the household level. Soakpits are constructed and used for the disposal of black water, and grey water (kitchen waste) is diverted and released into the open storm drains instead of the soakpits to avoid additional costs incurred in frequent cleaning. Over a period, waste water from soakpits and untreated greywater leak leading to the contamination of groundwater and surface water. 

Nelamangala is an example of a rapidly growing peri-urban town that is entirely dependent on groundwater sources for its water needs. Unlike Bengaluru, where both black and grey water are released into centralised systems through underground drainage network, in Nelamangala, households release the grey water into the open drains, and the black water into the soakpits.
The study Groundwater and Sanitation Nexus in Peri-Urban Small Towns of Bangalore, which was conducted in 2017–18 to explore the groundwater and sanitation link in Nelamangala town (located at the outskirts of Bengaluru city) by Ashoka Trust for Research in Ecology and Environment (ATREE), has shown that grey water flows in open storm drains have led to the contamination of groundwater and surface water (ATREE nd). The water quality data has shown an increase in fecal coliform (FC) levels, as water flows downstream in an open storm drain.  Also, high levels of fecal coliforms (>100 most probable number [MPN]/100 millilitres [ml]) have been frequently observed in the borewells located close to the open storm drains, indicating the impact of grey water discharges on groundwater quality. High levels of nitrates (> 45 milligrams/litres) have been observed in the borewells located within the densely populated wards of the town. The nitrate levels observed in the borewells have been correlated with the soakpit density, indicating the impact of a large number of soakpits on groundwater quality.  

Green Infrastructure: A Solution for Sustainable Development 

The Sustainable Development Goal (SDG) 6 of the United Nations is to “provide universal access to safe drinking water and sanitation for all by 2030” (Griggs et al 2013). It also explicitly mentions that water quality has to be improved by addressing both biological and chemical contaminants. The need for alternative surface water management approaches is particularly urgent in urbanising India, where immense development pressure, ongoing capacity building gaps, and delays in conventional waste-water infrastructure, combined with persistent widespread contamination, continue to place immense stress on local ecosystems, such as lakes, wetlands, and even groundwater sources, while threatening human health. 

As stormwater drains have become conduits of pollution, low-cost and low-resource green infrastructure offers great potential to address the pollution loads in these drains, especially in expanding megacities and emerging towns, where the volume of waste water continually outweighs the total capacity of STPs. 

Against the backdrop of such a scenario, alternative typologies of green infrastructure are capable of responding to a unique range of spatial, social, political, and economic conditions. PGI framework, examining the viability of bottom-up approaches, emphasises decentralised, low-tech, low-cost, low-maintenance, and culturally responsive designs.  PGIs are adaptable to both peri-urban towns, where grey and black water are segregated at the source (household), and also in those regions of large cities where STPs are inefficient and work below capacity.

Green infrastructure typically refers to the use of natural or semi-natural (designed) landscape conditions to produce a range of socioecological benefits within cities. A growing body of applied research and practice focuses on the role of green infrastructure in managing both the quantity and quality of urban waste water (El Hattab and Mijic 2019). Till date, the majority of green infrastructure innovation has taken place within economically shrinking "legacy" cities in North America, in established urban centres in the developed world, such as Europe and East Asian countries with strong centralised governance (Galbraith et al 2015; Siegrist 2017). Yet, there is a growing opportunity to extend, adapt, and apply these approaches in the rapidly growing "megacities" of South Asia.

Is PGI a viable strategy for improving watershed health and resilience in highly contaminated, rapidly growing cities?  If so, how, where, what types, and at what scales can PGI be most effective?   

The city of Bengaluru has been employed as both a case study and as an active laboratory for design development and experimentation. Research is aimed at assessing the viability of deploying PGI as an affordable and scalable decentralised decontamination strategy throughout the urban watershed. Factors such as population density, surface and groundwater quality, underground drainage coverage data  are utilised to develop a preliminary PGI suitability matrix for Bengaluru city (Figure 3). This matrix can be further modified by including factors such as the economics of materiality (for example, the necessity of utilising only affordable and readily available materials in the construction process) to hydro geophysical processes (such as, the realities of persistent solid waste dumping and seasonal flow variation within channelised nallahs [drains]). It is expected that these findings will also be broadly applicable to other megacity regions and emerging urban centres throughout South Asia. A specific focus has been placed on defining and exploring a range of unique constraints and opportunities that remain virtually unexamined within existing scholarship and practice.

Figure 3: Bengaluru Provisional Green Infrastructure Suitability Analysis

Figure 4: A Stormwater Drain in Bengaluru

The first-generation PGI approach developed by the authors and their team is referred to as STRAINS. STRAINS is targeted at first- and second-order open stormwater drains also called as “channelised nallahs,” which contain a minimum of waste water flows (either mixed effluents or grey water) (Figure 4). It is conceived as a modification to the existing channelised condition, and comprises three basic stages aimed at: (a) diverting and collecting solid waste, (b) slowing and settling sediment and suspended solids, and (c) lowering biochemical oxygen demand (BOD5)^[1] and trace metals levels through biofiltration using locally available aggregate materials (Figure 4). 

The development of this strategy till date has included iterative design; lab-based material performance testing, using various aggregates and synthetic waste water; physical and hydrological modelling; initial city-wide suitability analysis, and relationship building with the local partners (Biome Environmental Solutions and Mahadevapura Parisara Samrakshane Mattu Abhivrudhi Samiti). Our initial findings indicate that these systems could be capable of being deployed and scaled at a low cost with an immediate positive impact on the localised water quality. A lab-based study conducted to test the suitability of low-cost material for the treatment of waste water at ATREE's Water and Soil Lab has shown that out of three aggregate materials (gravel, cinder and terracotta), terracotta aggregate material has given the maximum contaminant removal efficiency (Jamwal et al 2019). 

We have initiated a pilot project and an experiment at Sowl Kere lake in Bengaluru. The objective of the experiment is to standardise the STRAINS system design for scaling up the deployment at the catchment level. To do this, we have to set up a full-scale STRAINS system at the lake. The plan is to assess the decontamination performance of the STRAINS system over time. This involves conducting water quality monitoring  at the inlet and outlet of the intervention. The final goal is to demonstrate^[2] “proof of concept” and inform future design iterations. 

A Scalable Model 

Stormwater channels are often neglected as a major point of intervention in cities and towns when devising strategies to treat the rising levels of waste water. Relatively, little focus has been placed on the status and importance of urban stormwater channels that serve as critical arteries which link hydrological systems. Focusing specifically on storm drains, streams, and channels is an important but underexplored facet of the large urban waste water challenge in megacities and their peri-urban emerging towns and cities. Therefore, we hypothesise that focusing on the stormwater channels offers a viable alternative form of green infrastructure to improve the health of local waterbodies. By focusing on the development of viable new typologies, suitable for the adoption in South Asian megacities, we believe this research will contribute in translating the theory and practice of green infrastructure to new cultural frontiers.