Application of a hybrid ultrasonic stripping-membrane distillation (US-MD) system for the treatment of mariculture wastewater

Abstract

Membrane distillation (MD) is presently regarded as a superior technique for the advanced purification of mariculture wastewater, while membrane fouling and unsatisfactory removal efficiency of NH4+-N are two major barriers to its massive application. Hence, a hybrid ultrasonic stripping-membrane distillation (US-MD) system was established in this work for efficient purification of mariculture wastewater. Compared to sole MD (71.7 %), a considerable removal ratio of 86.8 % for NH4+-N was obtained in US-MD system without pH adjustment. US pretreatment obviously promoted protein denaturation and salt crystallization before the MD treatment, contributing to the fouling mitigation in subsequent MD unit. With a period of standing treatment (40 min) between US and MD unit, these denatured protein floccules and salt crystals could be effectively removed outside sewage, with a considerable removal efficiency of 58.7 % and 8.6 % for protein and phosphate, respectively. Hence, a retarded fouling behavior (NF of 0.38, 384 h) was seen for US-MD system compared to sole MD (0.17, 384 h). Without setting treatment, the flux drop of US-MD system (0.11, 288 h) was even sharper than that of sole MD, suggesting that a period of standing treatment was essential in US-MD system.