Fariba Rezvani, Mohammad-Hossein Sarrafzadeh
UNESCO Chair on Water Reuse, Biotechnology Group, School of Chemical Engineering, College of Engineering, University of Tehran, Iran
Access to safe drinking-water along with climate change forces each country to invest a water supply infrastructure for water treatment as well as greenhouse reduction.
Several types of drinking water contaminants may be of concern for people especially children’s health. Examples include microorganisms, (e.g., E. coli, Giardia, and noroviruses), inorganic chemicals (e.g., fluoride, lead, arsenic, nitrates, and nitrites), organic chemicals (e.g., atrazine, glyphosate, trichloroethylene, and tetrachloroethylene), and disinfection byproducts (e.g., chloroform). Although the great majority of evident water-related health problems are the result of microbial (bacteriological, viral, protozoan or other biological) contamination, an appreciable number of serious health concerns may occur as a result of the chemical contamination of drinking-water.
The presence of nitrate in water drinking resources has been considered as the most challenging contaminants because of high solubility of it in water. Nitrate may arise from the excessive application of fertilizers or from leaching of wastewater or other organic wastes into surface water and groundwater. High levels of nitrates and nitrites can cause the blood disorder methemoglobinemia (blue baby syndrome) and have been associated with thyroid dysfunction in children and pregnant women.
As a result, United States Environmental Protection Agency (USEPA) has established a maximum contaminant level (MCL) of 10 mg nitrate–nitrogen (NO3−–N)/L, whereas the World Health Organization (WHO) and European Economic Community (EEC) have established a standard of 11.3 mg NO3−–N/L; to prevent the exceed of nitrate level in groundwater resources.
Several developed and industrial technologies have been applied for nitrate removal from drinking water resources, including physicochemical and biological techniques that are primarily classified into separation-based and elimination-based methods according to the fate of the nitrate in water treatment.
Elimination-based methods are generally preferred to separation-based methods as they completely remove nitrate by converting it into nitrogen gas; however, current treatment technologies and the development of emerging technologies for nitrate removal from drinking water require additional optimization Separation-based processes, including reverse osmosis, ion exchange, electrochemical reduction, electrodialysis, and activated carbon adsorption, which merely separate and transfer nitrate to a waste stream have expensive operating costs, and the subsequent disposal of the generated waste brine presents another problem. In contrast, chemical and biological nitrate removal facilitates the complete removal of nitrate by conversion it to harmless nitrogen gas during these processes. However, a full-scale system of chemical denitrification has not been reported, owing to the formation of ammonia and the potential health hazards of exposure to chemical compounds, such as electron donors and active catalysts. Hence, biological nitrate removal can be considered as a cost-effective and promising method for treatment of nitrate-contaminated drinking water resources. Among the biological nitrate removal carried out by both autotrophic and heterotrophic microorganisms, applying microalgae and hydrogen consumer denitrifies in a consortium is a promising way to reduce both CO2 via autotrophic cultivation and nitrate as their N-source for microbial growth. This approach can improve previous strategies by addressing both challenges of supplying a safe water and reducing greenhouse gases from the atmosphere.