Role of Iron-Carbon Micro-Electrolysis in Constructed Wetlands for Nitrate Removal: A Review

Abstract

Nitrate (NO- 3), as one of the main causes of eutrophication in water body, has contaminated seriously groundwater and surface water due to the excessive discharge of nitrogenous wastewater from agriculture and industry. Compared to other nitrate removal techniques, constructed wetlands (CWs) are frequently used to reduce nitrate to nitrogen gas (N2). Among the numerous methods of enhancing nitrate removal performance in CWs, iron-carbon Micro-Electrolysis (Fe/C-M/E) system, provides a unique occasion of waste material (iron scrap) for handling wastewater containing nitrate. Currently, the introduction of Fe/C-M/E structure could enhance nitrate removal rates by 20 % ~ 50 % in different types of CWs. Although the application of iron as the special substrate in nitrogenous wastewater treatment is intensively investigated with a large variety of CWs, research about Fe/C-M/E impact on the removal of nitrogen in CWs so far is very limited. Particularly, the information about the comprehensive interaction of biological and electrochemical effects with several distinct factors is inadequate, making it hard to obtain essential and universal conclusions. This paper offers a summary of research regarding Fe/C-M/E system in CWs used to remove nitrogen, discussing nitrogen removal pathways and mechanism via the effect of microorganism or Fe/C system. It also mainly focuses on the influence in the converting NO- 3 to N2 process by different operation parameters such as the type of carbon, the iron-carbon doping ratio, dissolved oxygen (DO), hydraulic retention time (HRT) and pH. It is worth noting that Fe/C-M/E CWs have not only high nitrate remove rate, but also relatively very little emissions of nitrous oxide (N2O), which as one of the main potential sources of greenhouse gases. Finally, this paper proposed some suggestions on future study and application.