Study on Vacuum Membrane Distillation Process for RO Drained Wastewater from Iron and Steel Industry

摘要

Novel hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membrane was used in the treatment of a reverse osmosis (RO) concentrated water from iron and steel industry via vacuum membrane distillation (VMD) method and air-blowing vacuum membrane distillation (AVMD) method. Based on the characteristic of the industrial wastewater, the hardness removal method and proportion of the hardness removal agents were studied. Waste water with hardness removal was applied in both VMD and AVMD as feed water. The results were compared with those of raw water without pretreatment It was found that the hardness removal method of NaOH is better than that of Ca(OH)2-Na2CO3 both in hardness removal rate and cost When the RO drained wastewater was pretreated, the flux of VMD process reached nearly 18kg/(m2·h) before the water was concentrated up to 15 times, the flux of AVMD process reached nearly 20kg/ (m2 ·h) before the water was concentrated up to 7 times. Thereafter, with the increase of the concentration fold, the flux decreased gradually. As the concentration fold arrived at 30, salt crystallization was observed. However, when the wastewater without pretreatment was taken as the feed, the flux of both VMD process and AVMD process declined drastically.