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

Abstract

Membrane 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−2 h−1 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 NH3 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 two-pass RO treatment afforded a complete rejection of Cl−. 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.