Purification of UF-treated anaerobically digested manure wastewater by two-pass reverse osmosis

Abstract

A B S T R A C TMembrane technology provides a potential promise towards manure treatment as well as nutrients concentration and recovery in the livestock industry. A two-pass reverse osmosis (RO) system was described in this study for the purification of UF-treated anaerobically digested manure wastewater (ADMW) with respect to permeate flux, ionic rejection, permeate quality, and membrane cleaning. The permeate flux fluctuated at 26.6-33.4 and 73.7-91.2 L m À2 h À1 for the first-and second-pass RO processing, respectively, at operating pressure of 1,500 kPa in the temperature range of 24-34˚C. The overall rejections of both Na + and K + by the two-pass RO were greater than 99%, whereas in case of ammonia, it was approximately 88%. The significant presence of molecular NH 3 at relatively high pH in ADMW solution probably induced a lower rejection of total ammonium, which also largely led to the low rejection of alkalinity and further pH increase in the RO permeate. The twopass RO treatment afforded a complete rejection of Cl À . The overall rejections of dissolved solids (DS) were estimated to be 94% with the first-pass RO and 98.8% after the two-pass RO resulting in product water containing only 45 mg/L of DS. Chemical cleaning of used membrane was successfully performed by successive flush of specific acid and base cleaning agents.