Simultaneous ammonia recovery and water reclamation from brackish aquaculture effluent via reactive vacuum membrane distillation

Due to the high volatility of ammonia and contemporaneous condensation of water and ammonia on permeate side, it remains a challenge to obtain a high concentration of ammonia or high-quality water using conventional vacuum membrane distillation (VMD). In this study, a reactive VMD (RVMD) with a two-stage downstream system was developed for simultaneous recovery of ammonia and water from brackish aquaculture effluent with dilute ammonia content. Notably, the RVMD system allowed for complete recovery of dilute ammonia in acid solution. Compared to a conventional VMD system, both the separation factor (SF) and concentration factor (CF) were intensified by 16 times within 2 h using the RVMD system. In the RVMD system, ammonia was first dis-solved in acid solution without chilling using immersed trap tube; followed by water vapor condensation under chilling to obtain clean water. It was found that more diluted acid (0.0025 M of sulphuric acid or 0.005 M of phosphoric acid) could be applied to absorb the same amount of ammonia by using this system. Through this system, the recovered ammonia from brackish aquaculture effluent could be concentrated by 23 times (from 19.83 to 465 mg/L) with an SF of 148, while very low ammonia content (0.04 mg/L) was detected in the recovered water. These findings demonstrate that RVMD with a two-stage downstream system outperforms conventional VMD in concentrating ammonia and purifying water.

Automated summary

Due to the challenges posed by the volatility of ammonia and the condensation of water and ammonia, obtaining high concentration ammonia or high-quality water using conventional vacuum membrane distillation (VMD) is difficult. This study developed a reactive VMD (RVMD) with a two-stage downstream system to simultaneously recover ammonia and water from brackish aquaculture effluent with dilute ammonia content. The RVMD system allowed for the complete recovery of dilute ammonia in acid solution, intensifying the separation factor (SF) and concentration factor (CF) by 16 times within 2 hours compared to a conventional VMD system. The RVMD system dissolved ammonia in acid solution without chilling using an immersed trap tube, followed by water vapor condensation under chilling to obtain clean water. The recovered ammonia could be concentrated by 23 times with an SF of 148, while the recovered water had a very low ammonia content of 0.04 mg/L. These findings highlight the superior performance of RVMD with a two-stage downstream system in concentrating ammonia and purifying water.