Resource recovery from liquid digestate of swine wastewater by an ultrafiltration membrane bioreactor (UF-MBR) and reverse osmosis (RO) process

Abstract

Biogas production is an important method for treating manure and wastewater produced in swine farms, but the liquid digestate generated by this process poses an issue due to the high costs of both in-situ standard treatment for discharge and off-site transportation for fertilizer. Membrane technology plays an important role in combining the standard treatment process with resource recovery from liquid digestate. In this study, an ultrafiltration membrane bioreactor (UF-MBR) and reverse osmosis (RO) system was used to treat and reuse the liquid digestate produced from swine wastewater. The bioreactor component of the system was able to reduce the pH of the liquid digestate to 6.5. A dissolved oxygen (DO) concentration of 4.0 mg/L was found to lead to the highest quality of effluent. The UF component of the MBR had an obvious effect on removing suspended solids and reducing turbidity, protecting the subsequent RO membrane. Under 90% water recovery, RO permeate water was found to meet the standard requirements for discharge and reuse of the water. Higher concentrations of nutrients and humic acid were found in the RO concentrate; the fate analysis of the substances showed that the UF-MBR and RO system was not conducive to the recovery of N and P, but could be used for recovering K, Ca, Mg, and humic acid for the production of water-soluble fertilizers.