Long-term investigation of phosphorus removal by iron electrocoagulation in small-scale wastewater treatment plants

Abstract

Small-scale wastewater treatment plants (SWTPs), called Johkasou, are widely used as decentralized and individual wastewater treatment systems in sparsely populated areas in Japan. Even in SWTPs, nutrients should be removed to control eutrophication. An iron electrolysis method is effective to remove phosphorus chemically in SWTPs. However, it is necessary to determine the precise conditions under which phosphorus can be effectively and stably removed in full scale SWTPs for a long period. Therefore, long-term phosphorus removal from SWTPs was investigated and optimum operational conditions for phosphorus removal by iron electrolysis were analyzed in this study. Efficient phosphorus removal can be achieved for a long time by adjusting the amount of iron against the actual population equivalent. The change of the recirculation ratio had no negative effect on overall phosphorus removal. Phosphorus release to the bulk phase was prevented by the accumulated iron, which was supplied by iron electrolysis, resulting in stable phosphorus removal. The effect of environmental load reduction due to phosphorus removal by iron electrolysis was greater than the cost of power consumption for iron electrolysis.

Phosphate removal by ex situ generated Fe (hydr)oxides from scrap iron electrocoagulation: the critical role of coprecipitation

“…25 Ying et al 26 found that magnetite particles could form in NaCl solution regardless of the presence of Mg 2+ and Ca 2+ ions by electrocoagulation with carbon steel electrodes. Although some studies reported that the electrocoagulation process was efficient for in situ treatment of excess P in wastewater, [27][28][29] complexed wastewater components would lead to electrode passivation and energy increase. 30 Besides, wastewater of low electricity conductivity would lead to high energy consumption in the electrocoagulation process due to the high ohmic drop.…”