Treatment of mariculture wastewater by an integrated ultrasonic stripping-membrane distillation (US-MD) system: Effect of operating parameters on effluent quality and membrane fouling mitigation

Abstract

The actual application of membrane distillation (MD) in the mariculture industry is faced with two challenges of substandard ammonia removal and membrane fouling. Therefore, an integrated ultrasonic stripping (US)-MD system is built to efficiently purify mariculture wastewater in this study. US-MD technique exhibited outstanding purification for NH4+-N (86.8 %) compared to sole MD (76.2 %). US pretreatment coupled with a phase of setting ahead of MD could notably remove organics and salts from sewage, finally mitigating membrane fouling in subsequent MD (normalized flux (NF), 96.0 h, 0.77) compared sole MD (0.19). Ultrasonic cavitation effect in US unit largely promoted the protein denaturation and salt crystallization, causing a considerable removal efficiency for proteins (54.0 %∼68.8 %) and phosphate (7.1 %∼8.7 %) before MD unit. The operating parameters of US-MD system posed remarkable impacts on its purification efficiency, and proper increment of pH, operation time, and ultrasonic power in US unit partly facilitated the US-MD operation. US-MD operation was also enhanced by slightly raising the US temperature to around 35 °C. Furthermore, the higher temperature (80–90 °C) and flow velocity (10.48–15.72 mm/s) of feed in MD unit also contributed to the efficient purification of mariculture wastewater.