Valuable nutrients such as ammonium and phosphate exist in teensy concentrations in marine-culture wastewater (MCW), causing their recovery challenging with inefficient conventional methods. Air gap membrane distillation (AGMD) is systematically explored for the first time to recover nutrients and pure water from low-nutrient MCW. This study assessed the AGMD performance in resource recovery by conducting a thorough investigation and optimization of various parameter conditions. Concerning the findings, AGMD satisfactorily inhibits ammonia transfer from the feed stream to the permeate stream by optimizing operating parameters specifically feed temperature and pH. A higher feed temperature improves water recovery, and feed pH is critical in nutrient recovery. In particular, high pH promotes the transformation and transport of ammonia through the membrane, whereas low pH inhibits ammonia transport, encouraging the creation of pure water. Maintaining an acidic feed solution decreases membrane fouling by increasing the solubility of calcium phosphate, hence boosting water recovery. Nevertheless, higher pH levels encourage fouling by allowing solid phosphate particles to form more readily. While at lower pH, ammonium phosphate fertilizers might be generated in the retentate solution by improving NH4+ and PO43- recovery under optimal conditions. The findings reveal that the AGMD system provides a novel method for treating MCW while also improving nutrient and pure water recovery.
Keywords: Air gap membrane distillation; Ammonia recovery; Marine-culture wastewater; Phosphate recovery.
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