Overview of in-situ applicable nitrate removal processes

Nitrate contamination of groundwater has became an environmental and health problem in developed and developing countries. Nitrate pollution is caused by the intensive use of nitrogen fertilizers, crop irrigation with domestic wastewater and use of manure, therefore, it is concern of diffuse pollution. The non-point sources of nitrate contamination make really difficult to apply the ex-situ approach to groundwater remediation. Nevertheless, best available technologies to treat nitrate-contaminated water such as reverse osmosis, ion exchange and electrodialysis developed for drinking water production cannot be used in in-situ application, which cause their technological complexity. Other alternative processes can be potentially used in in-situ application such as chemical reduction, adsorption and biological denitrification. These approaches can be applied in different ways such as a permeable reactive barrier or direct injection of liquid and gaseous reactive compounds in groundwater. Particular attention should be given to the process which allows simultaneous in-situ removal of nitrate and other priority pollutants because it is an effective topic of a groundwater remediation field. One of these was recently proposed by our group for combining heterotrophic and autotrophic denitrification based on cotton as the organic carbon source and support material and zero-valent iron (ZVI) for cathodic hydrogen gas favouring autotrophic growth. This process showed better performance than the simple heterotrophic one, and it is proposed to be simultaneously effective for removal of nitrate, chlorinated ethanes and chromium (VI). This study, overviewing the latest developments in nitrate removal, proposes the most proper process(s) by means of economic, technical and design prospects for in-situ application regarding sustainable development strategy in the developing, in particular, Mediterranean countries.