Water--Purification--Reverse osmosis process

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.

The problem of solute transport through saturated porous media is considered in this thesis. The end application of this study is to evaluate the option of spray irrigation as a means of disposing reverse osmosis effluent. Reverse osmosis effluent was sprayed on an experimental field composed of typical area soil. The changes in groundwater quality were monitored at intervals of ten to twenty days. Applying the experimentally obtained data to a basic numerical model, which uses the convection-diffusion equation, the key parameter of the soil, D* the diffusion coefficient, is obtained for the Myakka sand. While the numerical model can predict the qualitative behavior of hardness and conductivity, hysteresis is observed for the response of the total organic carbon (TOC) content. Further studies are needed to understand and model the inherent capacitance of the soil for hardness and the observed hysteresis in TOC response.