Utilization of ammonia-containing wastewater by combining membrane absorption and vacuum membrane distillation

Background: In this study, membrane absorption and vacuum membrane distillation were integrated to recover ammonia and water, respectively, from saline ammonia-containing wastewater discharged by metallurgical plants. Results: Ammonia was removed by membrane absorption with a parallel hollow fiber membrane (HFM) module to decrease the ammonia content to below 5mgL^-1. Then the wastewater was concentrated by vacuum membrane distillation with a cross-flow HFM module to maximize fresh water recovery, while maintaining higher permeate flux levels. The Taguchi method was used for experiment designs and contributions of operating parameters were determined over the specified parameter ranges through variance analysis. Recovery of ammonia and fresh water reached 99.8% and 80% within 250min and 160min, respectively. Membrane fouling in the membrane distillation process could be mitigated at lower concentrate rate in semi-batch running mode, while permeate flux was maintained at high levels for a longer time. Permeate flux was greatly restored through a cleaning technique consisting of alkaline cleaning, acid picking, EDTA washing and drying. Permeate flux loss due to irreversible membrane fouling was 0.7%. Conclusion: The experimental results demonstrate the potential for resource utilization of saline ammonia-containing wastewater by combining membrane absorption and vacuum membrane distillation.