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Bengaluru is grappling with a severe water crisis. Image Credit: rawpixel.com
Many parts of India are facing a water shortage. Both surface and underground water sources are stressed. As cities grow, people rely more on underground water. But taking too much water out and not handling sewage properly has made the water quality worse.
Scientists from the Korean Institute of Science and Technology and Korea University wrote an article in the Water Research journal in February 2024. They say they found a way to help store water underground and make it better.
Their idea is called aquifer storage and recovery (ASR). They say it could help in a world where the climate is risky. They put water from the surface into the ground through special wells or shafts. Then, it's kept there for later use.
States try storing water underground
Some states in India, like Karnataka, Tamil Nadu, Maharashtra, Rajasthan, and Telangana, have tried out ASR projects to help manage water better. They've tested it to see if it works.
Other states are also looking into whether ASR could work for them. According to Nandakumaran P, a former chairman of the Central Groundwater Board, it's important to study ASR in different situations to make sure it helps with water problems.
In Bihar, districts like Nalanda and Rajgir have shown that ASR could be a good idea. But there's a big concern: if the water we put into the ground is already dirty, it could make the groundwater worse. This happens especially when the water has a lot of dissolved organic matter, which is a complex mix of stuff in the water.
Too much of this dissolved organic matter can make the water acidic, carry other bad stuff like heavy metals, and make the water taste and smell bad. It also helps bad bacteria grow. If this bad water gets into lakes and ponds, it can mess up the water there too.
Dirty water can harm the quality of underground water. Microbes help clean it by breaking down harmful substances. Iron also plays a role in this process.
Iron gives microbes something they need to clean the water. It acts like a meal for them. This process, called Dissimilatory Iron Reduction (DIR), is important for cleaning up water during ASR.
The type of iron available affects how well this process works. Some types of iron, like goethite and hematite, are better at helping microbes clean water than others.
Study: Nitrate speeds up cleaning
In a recent study, experts conducted a 10-day experiment in conditions without oxygen. They found that adding nitrate to the water helped speed up the cleaning process. It also helped turn less effective types of iron into better ones, improving the overall water quality during ASR.
According to the study report, samples with nitrate showed higher microbial activity compared to those without it. This led to the emergence of a new genus of bacteria called Nitrate-Dependent Ferrous Oxidation bacteria, which were abundant in nitrate-containing samples.
During the DIR process without oxygen, microbes use nitrate as electron acceptors for their metabolism, reducing its concentration. These microbes work to break down organic carbon in the water.
The report highlighted that the biochemical reactions during DIR, in the presence of nitrate, transform amorphous ferric hydrite into crystalline ferric oxides, increasing the availability of crystalline compounds essential for DIR. This dual process, where nitrate and iron compounds serve as electron acceptors for microbes, speeds up the degradation of organic carbon, thus improving water quality and making it suitable for consumption.
Although nitrate is a contaminant and can worsen water quality, its presence is crucial for faster reduction of dissolved organic carbon. Comparisons between tests with and without nitrate showed that DIR without nitrate yielded slower and less effective results (7-8 percent), whereas samples with nitrate achieved DOC attenuation rates of 15-50 percent.
The concept of ASR presents a solution to emerging water issues by blending surface and groundwater. Ensuring both quality and quantity of water is essential in this process. The study's findings can be scaled up for ASR implementation in vulnerable areas to enhance water security.
Sudhir Srivastava, senior scientist at Central Groundwater Board, endorsed the study, stating, "When reactor Dissolved Oxygen concentrations are low and nitrate is present, they may couple the oxidation of organic carbon compounds to CO2 with reduction of NO3− to N2 gas."
Ancient India: Varied rainwater harvesting
The study reveals that ancient India had various methods of rainwater harvesting. In the Trans and western Himalayan regions of Jammu and Kashmir, people used small tanks, ponds, or channels to collect melted glacial water and stream runoff. In the Eastern Himalayan region, they built earthen dams on valley slopes to gather rainwater.
In the North East, pond-like structures or bamboo pipes were used to capture runoff for agricultural use. In the Indo-Gangetic plains, square or circular reservoirs and step wells were common. Rajasthan favored covered underground circular wells with saucer-shaped catchment areas. Other regions, like Bundelkhand and parts of central, western, and southern India, utilized man-made lakes, check dams, and percolation tanks. In the eastern part of the country, strong earthen embankments were curved and built across drainage lines. South India employed small lake-like structures, check dams, and underground canals to connect groundwater and surface water bodies.
As of 2015, India had the highest reported Managed Aquifer Recharge (MAR) capacity globally, reaching 30.9%. This was documented in only five states: Andhra Pradesh (including Telangana), Gujarat, Jharkhand, Karnataka, and Uttarakhand.
Modern artificial recharge methods can be categorized into four main types: infiltration, direct injection, filtration, and rooftop rainwater harvesting.
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