Enhanced nitrogen removal from wastewater using MAP precipitation and SBR system

Abstract

A study to enhance nitrogen removal of high concentration wastewater was performed using MAP precipitation and SBR process. MAP was used for removing ammonia and phosphorus simultaneous as well as increase C/N ratio of wastewater. Following SBR process was designed to remove COD and residual ammonia for maintaining the effluent quality. By MAP precipitation, 83% of ammonia and 97% phosphorus were removed. Operating pH should be 9.5 or higher and the best pH was 10.5 for MAP precipitation. Reaction time should be longer than 10 minutes and 20 minutes of reaction time was preferred. However, more than 30 minutes was undesirable. Magnesium loading for MAP precipitation should be 1.0 to 2.0 mole/L for efficient MAP formation. Even though theoretical value was 1.0 mole/L, 1.5 mole/L was reasonable in practical use. Bittern, seawater, and $MgCl_2$ were studied for magnesium sources to compare the efficiency of magnesium sources with commercial magnesium sources. When bittern, sea water, and $MgCl_2$ were used as coagulants, 72%, 62%, and 83% of ammonia were removed and 99%, 95% and 97% of phosphorus were removed, respectively. Especially, bittern was proved a proper alternative instead of expensive $MgCl_2$ and it could also reduce transportation costs because the bittern contained a high magnesium concentration. Morphological study of MAP precipitate showed that the MAP crystal had a shape of hexagonal plate with white powder having good settling. MAP process had advantage of less sensitive to temperature change and of being as a fertilizer. Combined MAP precipitation and SBR process was tested for coke wastewater containing high ammonia. By MAP process, 22.1% of TCOD of coke wastewater was removed precipitation following 85% of residual TCOD was removed in SBR. In MAP process, the ammonium nitrogen was removed by 75% and then 61% of residual ammonia was removed again by SBR. The G value of raw coke wastewater was 197 and the G value of MAP treated coke wastewater w...