Black odorous water concentrating by forward osmosis: rejection performance of characteristic pollutants based on...

This study aimed to investigate pollutant concentration and nitrogen interception characteristics of a forward osmosis (FO) process for concentrating black odorous water. The membrane cell was operated in active layer facing feed solution (AL-FS) mode with aquaporin (AQP) as the membrane material and NaCl solution as the draw solution (DS). The organic pollutants (COD), TP, NH+4-N, NO-3-N, TN, Fe and Mn in black odorous water were concentrated non-intermittently for 24 h, and their interception characteristics were investigated. The results showed that the average interception rates of COD, TP, NO- 3-N, TN, Fe and Mn were 97.2%, 98.0%, 58.7%, 54.3%, 61.8% and 60.0%, respectively, while the average interception rate of NH⁺₄-N was only 1.27%-3.47%. To explore the characteristics of nitrogen interception, a comparison was conducted between AQP membrane and thin film composite (TFC) membrane. Because the surface electronegativity of AQP membrane was stronger than that of TFC, the effect of cation exchange on ammonia nitrogen interception was more serious with AQP membrane. With NaCl solution as DS, the reverse osmosis flux of Na⁺ was (0.53 ± 0.02 mol·m^-2·h^-1), which was significantly higher than that of Cl^- (0.29 ± 0.03 mol·m^-2·h^-1) (P < 0.05). The interception effect of AQP membrane on TN was related to the proportion of NH⁺₄-N in TN. The pretreatment of black odorous water by aeration could transform part of NH⁺₄-N into NO^-3-N, and reduce the negative effect of cation exchange effect on nitrogen interception. The TN interception rate increased from 54.3% to 66.1%.