Membranes (Technology)

This study evaluated the technical feasibility o f increasing the typical water
recovery of a pilot scale membrane system (85-90%) to 97% by treatment of
nanofiltration concentrate with low-pressure reverse osmosis. The study used Biscayne
aquifer water (freshwater), and determined that it may be technically feasible to increase
the recovery up to approximately 95% when the RO flux is —10 gfd, the feed water pH is
reduced to -6.1 with H2 SO4 , and antiscalant in the NF process. The tested membranes
showed stable and similar performance under the pilot conditions. However, pilot tests
were sensitive to pH variations (pH>6.2). The main barrier for increasing the water
recovery was fouling caused by iron, carbonate hardness, and iron bacteria. A
preliminary cost analysis showed that there is an apparent econom ic advantage when the
recovery is greater than 90%. Estimated water cost at 95% recovery is $1.99 compared
with $2.69 at the typical 85% recovery.

This paper presents the results of the spike tests performed in the alternative water supply pilot testing program for the City of Pembroke Pines. It establishes the effectiveness of a protocol that can be used to gain further insight on the rejection capacities of RO membranes. An in-depth study of the molecular descriptors affecting rejection by RO membranes is presented and used in the development of a discriminant function analysis. This analysis proved to be an effective way to predict the passage of Emerging Substances of Concern (ESOCs) through RO membrane. Further, a principal component (PC) analysis was performed to determine which factors accounted the largest variation in RO permeability. Additionally, this paper defines the groundwork for a discriminant analysis model that, if further developed, could serve as an important tool to predict the rejection capabilities of RO treatment when handling with ESOCs.