Hybrid membrane process for nutrient recovery and sodium reduction in aquaculture wastewater

The swift growth of the aquaculture industry has exacerbated nutrient discharge, leading to eutrophication, while low nutrient but high sodium content impedes effective nutrient recovery and reuse. This study presents a novel hybrid membrane-based treatment sequence comprising ammonia stripping (AS), vacuum membrane distillation (VMD), and nanofiltration in diafiltration mode (NF), designed to efficiently recover ammonia and phosphate and reduce sodium from mixed aquaculture effluents. The process achieved ammonia and phosphate recovery efficiencies of 88.74 % and over 99 %, respectively, with a corresponding sodium reduction of 99.04 wt %. The AS stage concentrated ammonia from 20.37 mg/L to 2046.67 mg/L, whereas the subsequent VMD and NF stages produced phosphate-rich (rose from 10.33 mg/L to 50.50 mg/L) and sodium-reduced retentates (decreased from 510 mg/L to 44.50 mg/L). Long-term testing over eight consecutive batches showed robust performance with ammonia flux decline by only 2.81 %, permeate flux reduction by 4.30 %, and minimal inorganic fouling, maintaining consistent permeate quality that met environmental standards. These findings underline the proposed hybrid process's potential for sustainable aquaculture wastewater management, offering substantial enhancement in nutrient and water recycling.