RO Membrane Challenges
The RO membranes were challenged with each chemical in Table 3-1. The target challenge concentration for each chemical was 1 mg/L, which is much higher than most challenge levels in the NSF/ANSI Standards for POU devices. Only two membranes were challenged with each chemical. The organic chemical challenges were conducted one chemical at a time, but the inorganic chemicals were combined into one challenge. Each membrane was only tested with one of the ten organic chemicals, because of concern that some of them, especially benzene and chloroform, could damage the membranes or membrane seals at the high challenge levels. This approach eliminated the possibility that membrane performance against subsequent chemicals was negatively biased. TDS reduction was also measured during the challenges, to serve as a membrane performance benchmark, and also to evaluate whether any organic chemicals damaged the membrane or integrity of the membrane seals.
A total of twenty RO membrane units were tested, divided into ten pairs. The inorganic chemicals challenge was conducted first. The two systems used for the inorganic chemicals challenge were used again for an organic chemical challenge.
As discussed in section 1.2, each challenge period was only one day. The systems were operated for six tank-fill periods, and then were allowed to rest overnight. Influent and effluent samples were collected during the operation period, and also the next morning after the rest period. In addition to influent and effluent samples, reject water samples were also collected and analyzed in an attempt to determine whether any of the chemicals adsorbed onto or absorbed into the membrane material in significant amounts. See section 3.2.5.2 for RO membrane challenge protocol details.
