Aging of RO membranes processing swine wastewater

There is an increased interest in the application of reverse osmosis (RO) technology to treat agricultural wastewaters because RO membranes can produce reusable water and recover valuable nutrients. With highly charged wastewater, however, membrane replacement could represent an important fraction of the operating costs. The objective of this project was to study the aging process of spiral-wound RO elements (BW30 and SW30) processing swine wastewater. The membrane elements were subjected to 21 h concentration-filtration (CF) cycles followed by a 1 h chemical cleaning and a weekly 3 d soaking period. The BW30 element experienced a 22% increase in intrinsic membrane resistance (R m), defined as resistance to water flux through the membrane, after the first four CF cycles with swine wastewater. This rapid increase was mainly caused by irreversible compaction of the membrane under high pressures. The SW30 membrane had a lower compressibility, and Rmonly increased by 7% in the first four cycles. After this initial period, small but steady increases in Rm were mainly attributed to the accumulation of foulants on or within the membranes. However, a 40% increase in Rm after 42 CF cycles with the BW30 membrane had little impact on permeate flux during swine wastewater filtration because permeate flux was mainly controlled by fouling and substrate-related resistances. All membrane elements maintained their ionic retention efficiency throughout the experiment, indicating no damage to the integrity of the membrane during the CF and cleaning cycles. Projection based on a total of 42 and 20 CF cycles for the BW30 and SW30 membranes, respectively, suggested that Rm would rapidly increase in the initial 12 CF cycles of swine wastewater filtration, by 29% and 11% for the BW30 and SW30 membranes, respectively, mainly due to compaction. Between cycles 12 and 624, R mwould further increase by 32% and 16% for the BW30 and SW30 membranes, respectively. This number of cycles corresponds to three years of operation using the same operational procedures as those described in this study. With proper care, the membrane elements may not need to be replaced for at least three years. However, these predictions remain to be verified in a commercial setting. © 2013 American Society of Agricultural and Biological Engineers ISSN 2151-0032.