Intervention for wastewater management and water source protection

Intervention for wastewater management and water source protection

Sminu T. V. and Anjali V. Raj

Water is life, Currently, our water resources are vulnerable to contamination from numerous anthropogenic sources including agricultural and stormwater runoff, onsite sanitation systems and domestic wastewater. The massive surge in wastewater generation in urban and rural areas poses a potential threat to water resources and needs to be addressed quickly. Conventionally, sewage and stormwater runoff were managed through grey infrastructures like sewage treatment plants and stabilisation ponds. However, they are primarily centralised infrastructures requiring high capital costs and maintenance. Recently nature-based solutions (NbS) have gained more attention over grey infrastructures as low-cost, decentralised and sustainable alternatives for treating domestic wastewater, stormwater runoff, agricultural runoff, and industrial wastewater. NbS involves different ecosystem-based landscape approaches such as constructed wetlands, floating treatment wetlands, rain gardens, bioswales, retention basins, green roofs and green gardens designed to mimic natural ecosystems. NbS provides many ecosystem services, such as flood hazard mitigation, water quality treatment, thermal reduction and urban biodiversity enhancement. It also delivers cultural services such as recreation, education and aesthetic appreciation. The NbS focuses on natural treatment systems for sustainable wastewater management. These systems are applicable in both urban and rural contexts. 

Renaturing Bengaluru with natural-based solutions

Bengaluru, once abounded with pristine lakes and lush gardens, is now tussling with water stress and related public health hazards. Economic factors and growth dynamics throw up significant challenges to the health of the city's lakes and their rich green cover. This situation is provoked by human activities such as improper land use management, rapid groundwater extraction, industrial effluent and greywater discharge. Population growth and migration have led to an increase in water consumption and consequently increased wastewater generation in urban areas. The tank cascade system in Bangalore, designed for stormwater storage and agriculture irrigation, is now full of open sewers receiving domestic and industrial effluents. Furthermore, lakes in Bangalore receive partially treated/ untreated sewage, resulting in the ingress of nutrients in the water and hence eutrophication of urban lakes. While seeking to address the consequences of rapid and unplanned urbanisation, Bangalore Development Authority (BDA) developed Master Plan 2050 that envisioned sustainable growth and development of the city. Nature-based solution (NbS) is an impetus for city planners and developing authorities to support environmental restoration for resilient growth in cities by working with nature and setting up solutions with stakeholders. 

Natural treatment systems are nature-based solutions that mimic and represent natural treatment in a controlled environment. Strategic instream treatment systems (STRAINS) are one such engineered systems that are designed and constructed to mimic the natural process of wetlands operating with design features similar to modified horizontal flow constructed wetlands. These interventions can reduce contaminant load from dry weather flows in open drains before they flow into downstream receiving waters. A semi-controlled field experiment was conducted near the inlet of a small urban lake known as Sowlkere in Bangalore. At Sowlkere, a small-scale ‘model nallah’ condition was developed, which mimics the dimensions and materials of a typical concretized stormwater channel found throughout the city. Two different filter materials, gravel and terracotta, were tested in the setup planted with Canna lilies. Urban wastewater from a manhole, receiving nearby commercial and domestic sewage, was fed into the setup. The system was successful in removing 77% organic matter and 20–50% nutrients from the urban wastewater flow. The study opens up the possibility of using inexpensive, locally available aggregate materials (gravel and terracotta rubble) to reduce downstream water source contamination from open stormwater drains without the use of specialised or mechanical technology. To move towards the Master Plan 2050, Bengaluru needs to focus on NbS to tackle water management challenges in all sectors. Upscaling NbS in our city can accelerate by promoting research and policies, legal regulations and funding and improving cross-sectorial collaborations and knowledge base.

Semi-controlled, experimental ‘model nallah’ field setup deployed at Sowlkere in Bangalore

Solving rural wastewater issues with natural treatment systems

In rural areas, wastewater (greywater and blackwater) appears to be an emerging challenge that has not been given enough attention. The Swachh Bharat Mission (SBM) and Open Defecation Free (ODF) schemes have been promoting the deployment of onsite sanitation infrastructures like soak pits and pit latrines in rural India. The contaminants from blackwater leach through these systems, polluting the groundwater and surface water streams in the vicinity. The number of on-site sanitation facilities has increased tremendously after the implementation of SBM and ODF schemes, posing a potential threat to shallow groundwater sources from high nitrates and microbial contamination. With the provision of piped water supply through Jal Jeevan Mission, rural wastewater generation is expected to increase in the coming years. This, along with the existing problem of contaminant leaching from pit latrine/soak pits, poses a great threat to groundwater and surface water sources in rural areas. Due to the dispersed nature of households, centralised treatment facilities are not feasible in such situations. Natural treatment systems like constructed wetlands can serve as decentralised, effective and affordable choices for secondary treatment of sewage/blackwater and safely dispose of treated effluent in an environmentally sound manner. 

Constructed wetland system deployed at Berambadi school in Gundlupet

As a part of ATREE’s collaborative work with James Hutton Institute, a constructed wetland system was deployed at a rural school in Berambadi to polish effluents from the septic tank system before final discharge. The constructed wetland system at Berambadi receives primary, treated blackwater from the school toilet. The septic tank effluent receives secondary treatment/polishing as it moves through the system. Out of the two constructed wetlands in the school, one system was planted with Canna lilies to test the influence of vegetation in the constructed wetland system. The Canna lilies in the system facilitate contaminant reduction through nutrient assimilation and enhancement of microbial activity. The system improved the quality of effluent by offering over 60% reduction in organic matter and over 10% reduction in nutrients. The effluents from the constructed wetland system complied with the CPCB discharge standards and hence were safe to be discharged into the environment. These systems can be scaled up and adopted in rural areas to provide decentralised solutions for wastewater management. The involvement of local stakeholders is crucial for the successful implementation and smooth functioning of such systems. Hence active community participation was ensured from the planning through the deployment stage of the project to encourage and embed knowledge about safe water and sanitation in the community while also ensuring the sustainability of these systems. With proper incentivization, natural treatment systems can be sustainable community-managed solutions for rural wastewater issues.

Despite all the above-listed benefits and success stories, mainstreaming NbS in developing plans remains a challenge today. The barriers to implementing NbS for water and wastewater management can be viewed from technical, social, political and financial perspectives. Firstly, there is a lack of operational clarity and the absence of guidelines for evaluating the efficacy of the NbS system. Secondly, there is the negligence of nature conservation topics on the political agenda and the dominance of grey infrastructure over NbS. Thirdly, there is a lack of proper mechanisms and funding, and stakeholder participation slows down the adoption and scaling up of NbS. The dire need is to adopt a collaborative approach in developing an integrated action plan tailored to the local context. The uncertainties around the deployment of NbS can be overcome by a) accounting for the overall benefits or services (improvement in water quality, biodiversity benefits, climate change mitigation, etc.) and b) costs and potential risks associated with their implementation. However, this attempt could be limited by financial constraints and a lack of infrastructure. Moreover, it leads to an insignificant increase in doubts regarding the effectiveness of NbS and decision-making for long-term projects compared to conventional approaches.