# Nitrate-Polluted Waterbodies Remediation: Global Insights into Treatments for Compliance
## 1 Introduction
The presence of nitrate in waterbodies is a consequence of the natural nitrogen cycle; the problem is that in certain areas, there has been an alteration of this cycle, causing an increase in the concentration of nitrates, mainly due to the excessive use of fertilizers and their subsequent run-off by rainwater or irrigation [12]. Excessive nutrient inputs (typically nitrates and phosphates) into the water and exposure to solar radiation promote excessive growth of organic matter and the development of phytoplankton, algae, and other green plants [13]. The proliferation of these organisms is the early stage of eutrophication; it causes a turbidity in the water, resulting in a murky green colour that prevents light from penetrating to the bottom of the ecosystem, and the vegetation is unable to photosynthesize and dies. Bacteria and other microorganisms feed on the dead matter, depleting the levels of dissolved oxygen in the water. This hypoxia causes fish kills, inhibits the development of other living organisms, and leads to the development of toxic and hazardous substances that compromise human health [14; 15]. The concern is not only in the environment, but nitrate can also constitute a severe hazard to human health. Nitrate is non-toxic to human health. In fact, it has a positive protective effect on the stomach and an antimicrobial effect on gut pathogens. When the amount of nitrate is elevated, some of it may be converted into its harmful metabolites (nitrite ions) by bacterial reduction during food processing or intestinal transit. The ingestion of water with excessive nitrate concentrations disables human erythrocytes as oxygen carriers, especially in children, causing a fatal condition of methemoglobinemia [16; 17]. Nitrate may also be responsible for the synthesis of N-nitrosamines and N-nitrosamides, with potential carcinogenic effects [18; 19]. As a result of this background, there is concern among major international organizations such as the World Health Organization (WHO) and the Council of European Union that have set a limit on NO\({}_{3}\)\({}^{-}\) concentration in drinking water of 50 mg/L [20]. The quality standard of the Food and Agriculture Organization of the United Nations (FAO) in water for irrigation is a level of NO\({}_{3}\)\({}^{-}<\) 22 mg/L for unrestricted use, and with a slight to moderate degree of restriction, if the concentration ranges from 22 to 133 mg/L [21]. Reducing nitrate pollution is therefore a key issue, and this requires restoring the balance of the nitrogen cycle to achieve improvements in water quality [22]. Therefore, it is of great interest to adequately minimize diffuse pollution from agriculture and further integrate nutrient control technologies to limit eutrophication and protect the water environment [23]. This paper takes an in-depth look at the current leading technologies and some recent alternatives for remediation of nitrate-polluted waters. The aim is to provide a thorough knowledge of modern control technologies for the effective environmental remediation. The challenge is to find cost-efficient and energy-efficient technologies that will be both economically and environmentally sustainable.