GS Paper III

News Excerpt:

A research article published in the Water Research journal recently by the Korean Institute of Science and Technology and Korea University has claimed to have found a solution on improvement of aquifer storage and improvement of the quality of water.

More about the research:

• The researchers have advocated for the implementation of Aquifer Storage And Recovery (ASR), suggesting that it could offer a solution in a world increasingly threatened by climate-related risks. 

Aquifer Storage And Recovery (Asr):

• Aquifer storage and recovery (ASR) is a water resources management technique for actively storing water underground during wet periods for recovery when needed, usually during dry periods. 
• The water from surface sources is injected to the local aquifer through recharge wells / shafts and is stored there for future use.
• ASR has been piloted in some states of India, under the Managed Aquifer Recharge interventions. The states include Karnataka, Tamil Nadu, Maharashtra, Rajasthan and Telangana, which have done pilot work on ASR.
• Nalanda and Rajgir districts of Bihar have unveiled the feasibility of ASR with different types of aquifers and their characteristics.

Problems with Aquifer Storage And Recovery:

• Injecting surface water contaminated with physical, chemical, and organic pollutants into the aquifer can degrade groundwater quality and lead to contamination throughout the entire aquifer system.
• The problem is severe when injected surface water has high concentrations of dissolved organic carbon (DOC). 
• DOC is a fraction of the total organic matter in water. It has a very complex effect on the quality of water.
• If the groundwater high in DOC feeds the freshwater lakes and water bodies, it can result in eutrophication and deteriorating water quality.

Impact of Dissolved Organic Carbon on water quality: 

• High concentrations of DOC can reduce the pH of water, making it acidic, and also can act as a carrier for other contaminants, including heavy metals. 
• It also deteriorates the taste and odour of water, making it unfit for consumption.
• Enhanced levels of DOC act as breeding ground for harmful microbial growth. 
• The difference in concentration of DOC between the injected surface water and existing groundwater can deteriorate the overall water quality of the aquifer. 
• Hence, DOC attenuation is a must to improve the water quality during ASR. 
• During the DOC attenuation process, the microbes present in the water allow for biodegradation, which reduces the concentration of organic carbon.

Dissimilatory Iron Reduction (DIR):

• Dissimilatory Iron Reduction (DIR) facilitates the reduction of Dissolved Organic Carbon (DOC) by providing iron as an electron acceptor to the microbes / bacteria, which they use for their metabolism. 
• DIR is a process in which iron compounds act as electron acceptors to microbes for their microbial activity, in which ferric iron (Fe3) is reduced to ferrous iron (Fe2).

How Dissimilatory Iron Reduction (DIR) facilitates reduction in DOC?

• Dissimilatory Iron Reduction (DIR) utilizes organic carbon compounds as an energy source for iron-reducing bacteria.
• This process leads to the reduction of iron minerals, which can immobilize Dissolved Organic Carbon (DOC) by associating it with newly formed iron minerals.
• DIR also promotes microbial processes that degrade or transform DOC into less bioavailable forms.
• Overall, DIR facilitates the attenuation of DOC by promoting its removal or transformation within aquatic environments.

Availability of iron compounds for DIR:

• The natural availability of iron compounds affects the DIR process. 
• The higher bio-availability of crystalline iron hydroxides (goethite and hematite) improves the DIR process and vice versa. 
• The crystalline iron compounds are less naturally available than the amorphous ones (Iron hydrides) in aquifer systems. 
• In anoxic conditions where oxygen is not present for microbial activity, iron hydroxides are the compounds which the microbes use for their microbial activity. The entire process is important to improve the quality of water during ASR.

Key findings of the research:

• During the study, a 10-day batch experiment was conducted by the experts in anoxic (without dissolved oxygen) conditions. 
• The results from the experiment show that the presence of nitrate in the test samples not only enhances the DOC attenuation process, but also transforms the amorphous iron compounds into crystalline ones such as goethite and hematite.
• Goethite and hematite are more important for the DIR process during ASR.
• The samples containing nitrate had higher microbial activity than those without it. 
• In the samples containing nitrate, a new genus of Nitrate-Dependent Ferrous Oxidation bacteria appeared in high abundance.

• • Though nitrate is a contaminant and deteriorates the water quality, its availability is important to reduce the DOC at a faster rate. 
  • The comparison in tests with and without use of nitrate has shown that DIR without use of nitrate is slow and bears less results (7-8 per cent). 

• The reduction of organic carbon will improve the overall quality of water, making it fit for consumption.

Way Forward:

• Many states in India have started facing a water crisis. Surface and groundwater sources are under stress. As urbanization is increasing, so is the dependence on groundwater.
• The concept of ASR is a solution to the arising water problems. Since there is a mix of surface and groundwater in the process, it becomes important to improve the water quality along with the quantity. 
• The results from the study can be replicated at large scales in ASR for water security in vulnerable areas.