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⁻²h⁻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.

Keywords:

• Anaerobically-digested manure wastewater
• Reverse osmosis
• Ammonia
• Purification

Acknowledgment

The research was supported in part by the IMUS fund provided by the biowaste utilization group, Alberta Research Council, Canada, and the Fundamental Research Funds for the Central Universities (No. 2009SD-8).