What is it about?
Treatment of arsenic-contaminated shallow groundwater upon extraction has become imperative to provide safe drinking water in remote villages in West Bengal, India. Arsenic removal plants (ARPs) stabilising arsenic-rich waste water ‘in situ’, despite saving valuable time and money, require high technical expertise for operation and maintenance, which is difficult to facilitate in rural communities lacking the necessary infrastructural support. Contrarily, arsenic removal units (ARUs) have been widely accepted by the society for their user-friendliness. However, most of them produce a high volume of hazardous sludge, safe commercial reuse of which can be done by ‘ex situ’ stabilisation with clay bricks. Based on the number of ARPs and ARUs needed to help households seeking remedy, a cost–benefit analysis of the remediation and waste-management aspects is performed by system dynamics modelling. For a major arsenic-affected district of the state, the simulation results suggest that in lieu of ARPs, installation of ARUs is deemed to be financially sustainable for at least 15 years from now, if the arsenic-laden bricks are sold at a price 20% higher than normal. Future projections of groundwater draft and stress in the region commensurately confirm the economic and environmental sustainability of the arsenic remediation.
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Why is it important?
Throughout the developing world, where rural habitations rely on groundwater for drinking, geogenic arsenic contamination of aquifers is a major public health problem. Millions of households living in arsenic-affected regions in the state of West Bengal in India are vulnerable to arsenic exposure by relying heavily on groundwater to obtain drinking water. With the exponential increase in the number of such households over time, SWSSs must be set up on a continuous basis to provide relief. Although distribution of arsenic-free river water and deep groundwater through PWS is the best scheme, installation of community-based ATUs (which treat arsenic-contaminated shallow groundwater upon its extraction) is necessary to provide safe drinking water to households living in the remote locations where laying a PWS network is not possible due to logistic constraints. Using a system dynamics modelling framework, this study estimates the number of such units that will have to be installed during 2021–2035, for helping such households in North 24 Parganas District, who otherwise have no choice but to depend on hand-pump-fitted STWs for drawing drinking water. Meanwhile, stabilisation of toxic sludge, generated by backwash cleaning of the ATUs, is also crucial to quarantine the strenuously removed arsenic, to prevent re-contamination of the local environment. Certain ATUs, called ARPs (developed by the PHED), which are designed to benefit more than 1000 households, have in situ arrangements for effective stabilisation of sludge with iron-rich sand filters and are hence often perceived to be fiscally and environmentally appropriate for arsenic mitigation. However, their O&M requires high technical expertise, which is an impediment in rural communities lacking requisite skills and resources. In contrast, ARUs, each designed to cater to at most 600 households, are likely to remain socially reliable for their user- friendliness. Also, the voluminous wet sludge, which is scrupulously stored and detained in their premises, can be safely reused off-site by ex situ stabilisation with clay bricks, for long- term sequestration of the arsenic. At 1–10% addition of wet sludge by volume, the AsL bricks have been found to be safe and equally efficient as normal clay bricks in usage as a construction material. A CBA of the in situ and ex situ aspects in two separate scenarios for North 24 Parganas District suggests that in lieu of the ARPs, fiscal investments in installation of the ARUs and stabilisation of sludge in a government-run brick manufacturing factory of the region will be sustainable (B/C > 1) for the government, for at least 15 years from now. However, this will hold true on the condition that an AsL brick is sold at a price 20% higher than that of a normal brick.
Perspectives
By availing potable water from the SWSSs (with the ARUs being the sole new ATUs for installation) and paying nominal water tariff in return, the society will stay as the principal beneficiary (B/C > 15), with a household saving more than 250 INR/month in avoiding harmful exposure to arsenic. Moreover, future projections of groundwater draft and stress in the district uphold the economic and environmental sustainability of the arsenic remediation schemes. This study shows that the concurrent withdrawal of groundwater in the region for domestic consumption and agricultural irrigation will remain within ecologically safe limits (stage development < 70%), with low impact on arsenic mobilisation in the aquifers (GS < 1). This allows installation of new ATUs and other groundwater-based SWSSs at fiscal expenses that do not abate their sustainability. Such a comparative analysis between arsenic mitigation scenarios would assist policymakers in devising other plausible frameworks for the arsenic waste disposal aspect in future remedial measures and to decide which of the two scenarios provides long-term benefits to the government and society. This methodology is therefore also suitable for sustainability assessment of similar water-management projects in other major arsenic-affected Asian countries. In line with the growing body of research to identify sustainable water- and wastewater-management techniques in the developing world, this paper makes a novel endeavour to resolve a prevalent socio-environmental problem in India. In summary, two important issues have been discussed to address the arsenic crisis in the state of West Bengal. Firstly, a non-hazardous and financially beneficial arsenic-waste-management project has been proposed for sustainable mitigation in a critically affected district. Secondly, the total groundwater draft in the district has been estimated to evaluate the ecological aptness in implementation of associated mitigation schemes. Although based on the local factors of India, the system dynamics model formulated for this research nominates parameters that exist in similar patterns in other Asian countries as well, with the population of the study area as the central parameter, the simulation results of the model are sensitive mainly to the data on the status of water-supply schemes and brick production market. The dependency of the model on a smaller number of static data corroborates its analytical and qualitative robustness for decision making. This also enables a policymaker to regulate the model under volatile circumstances created by disaster events and economic crises, particularly in a post coronavirus disease 2019 world. The model can therefore be trusted, and customised readily, for sustainability appraisal of similar water-management projects in other nations facing arsenic calamity. However, the model does not consider geopolitical factors that come into play while analysing international water-management projects involving transboundary co-operation and hence is applicable to policy studies on regional ecosystems only.
Soumyajit Koley
Indian Institute of Technology Kanpur
Read the Original
This page is a summary of: Sustainability appraisal of arsenic mitigation policy innovations in West Bengal, India, Infrastructure Asset Management, March 2023, ICE Publishing,
DOI: 10.1680/jinam.21.00021.
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