A Review on In-Situ Denitrification Technology for Consideration in Jaffna Peninsula Aquifer Remediation

The groundwater nitrate levels in the Jaffna peninsula of Sri Lanka are well above the World Health Organization limit of 10 mg/L as N and recent studies point to the high use of chemical fertilizers and the close proximity of septic systems to drinking water wells as probable causes. Since aquifers in the peninsula are primarily porous, and shallow karstic Miocene limestone, they provide high levels of infiltration. If the current situation continues unabated, the public may suffer the harmful effects of nitrate toxicity.  This paper discusses in-situ bioremediation processes, along with other possible mitigation measures, to remove nitrate and improve the quality of the drinking water. Five in-situ denitrification projects conducted in the Northern USA and Canada are presented, using carbon sources such as ethanol, methanol, and acetate. Treatment was achieved by a) injecting carbon and phosphorus or b) infiltrating treated water with excess carbon and phosphorus into groundwater. Nitrate-nitrogen concentrations as high as 60 mg/L have been reduced to below the limit of 10 mg/L with no ill effects. Pump-and-treat methods are conventional techniques and comparatively high-cost solutions. Furthermore, greener solutions such as controlling inorganic fertilizer addition and implementing long-term protective measures are inexpensive, but the minimal threat continues to exist. In addition, sustainable solutions such as banning agrochemicals, switching to organic farming, and establishing groundwater source protection zones have no negative impacts on the environment, but they are highly expensive to implement. In addition, restorative methods such as in-situ bioremediation and carbon farming, cultural or reconciliatory practices such as mulching seaweeds as organic fertilizer and using organic Neem-based pesticides, and regenerative solutions such as agroforestry or permaculture (includes intercropping with symbiotic nitrogen fixing crops) and holistic farming are less expensive and highly resilient or systemically vital methods suggested by this review.