What is riverbank filtration?

Introduction

Most rivers in developing countries serve as waste water conduits, contaminated with high loads of pathogenic microorganisms released from sewage, agriculture runoff and other hazardous compounds from industrial effluents. India's huge and growing population is putting a severe strain on the country's natural resources. India has made progress supplying safe water to its people, but gross disparity in coverage still exists. World Bank estimates that 21% of communicable diseases in India are related to unsafe water. Hence, treating surface water and minimizing groundwater constrains is crucial. Devising sustainable, resilient and affordable technologies for cleaning polluted water and which are readily replicable and easily adopted by rural communities will be required to meet the increasing water demand.

What is Riverbank Filtration?

Riverbank Filtration (RBF) is a technology that operates by pumping out water from borewells drilled along the banks of a river. During the pumping process, river water infiltrates into and passes through the riverbed sediments. As the raw surface water travels towards the RBF well, dissolved and suspended contaminants, as well as pathogens are potentially removed or significantly reduced in numbers resulting from a combination of the physical, chemical and biological processes.

How does it work?

In an RBF system, water is withdrawn from one or more wells near a river or lake. Wells may either be vertical or horizontal and typically, RBF wells are drilled within a few hundred meters of a surface water body so that when the well is pumped, surface water is drawn through the underlying sediments. By pumping an RBF well, the groundwater potential is lowered and river water (together with groundwater) is induced to flow through the porous riverbed sediments. Several studies carried out by researchers say that bacterial removal efficiencies are almost up to 99.82%. A TERI study revealed that heavy metal concentrations were significantly reduced, such as zinc (82%), copper (51%), lead (75%), chromium (94%), and cadmium (75%). In general, the degree of pollutant removal depends largely on the properties of the materials through which the flow takes place. There is evidence that much of the contaminant removal occurs at the interface between the river and the sediments. This zone is known as the colmation zone or schmutzdecke and is characterized by high microbial activity and small grain size. It is thought that periodic scouring during flood events regenerates the treatment activity of the colmation layer. Due to these auto-regenerative natural treatment processes, properly engineered RBF systems can maintain essentially unlimited treatment durations.

Why RBF technology?

There are a number of reasons why RBF technology is well suited for use in both, developing and industrial countries. For instance, an RBF:

• an be implemented along most rivers and even lakes;
• Is a mechanically simple, easily understood technology that can be inexpensively designed and built; and
• Is scalable so it can meet the needs of small farms, rural villages or even larger urban areas. In fact, RBF might be the only viable option for many remote villages that cannot afford more complex and expensive water treatment technologies, such as reverse osmosis.

Additionally, given favourable hydrogeological conditions, installing RBF systems might be an appropriate first response to natural disasters that disrupted conventional water treatment systems.

DID YOU KNOW?

Central Pollution Control Board (CPCB) is the apex body, monitoring the water quality of aquatic resources across the country under a three-tier programme i.e. Global Environmental Monitoring System (GEMS), Monitoring of Indian National Aquatic Resources System (MINARS) and Yamuna Action Plan (YAP).

The present water quality monitoring network comprises of 2500 stations covering 28 States and 6 Union Territories across the country.

Sustainable Tips

• Have effective sewage treatment plants for housing colonies to control water pollution and avoid sewage discharge into rivers. Do not dump plastic and other dry waste into waterbodies.
• Use water wisely - recycle grey water for gardening instead of letting it flow into the drain.