Efficiency of EDTA, SDS, and NaOH Solutions to Clean RO Membranes Processing Swine Wastewater

The increasing use of membranes to treat a broad range of wastewaters requires the development of efficient cleaning strategies. The objective of this study was to optimize the efficiency of EDTA-SDS-NaOH solutions to recover flux and remove proteins and bacteria from RO membranes filtering swine wastewater. At 60-min cleaning time, flux recovery (FR) increased with SDS concentrations up to 18 mM, but decreased at 36 mM. Adding up to 20 mM EDTA to the SDS solutions did not improve FR. The SDS-NaOH solutions yielded higher FRs at pH 11/40°C and pH 12/33°C than pH 10/45°C, indicating that increasing pH had a greater impact on cleaning efficiency than increasing temperature. At pH 11/40°C and pH 10/45°C, increasing cleaning time from 60 to 120 min decreased FR at all SDS concentrations, probably because of surfactant adsorption on membrane surface, as opposed to inadequate foulant removal, since residual protein concentration was lower on membranes cleaned for 120 than 60 or 30 min. At pH 12/33°C, however, increasing cleaning time to 120 min improved FR at all SDS levels. The lower temperature or higher pH may have prevented surfactant attachment to the membrane. At pH 12/33°C and 120 min, a solution containing NaOH only yielded similar FRs than an 18-mM SDS solution after up to four consecutive fouling-cleaning cycles. Increasing cleaning time and pH would thus eliminate the need to add a surfactant to the cleaning solution.