6. c. The brine seal consists of a gasket around the outside of the RO membrane element that seals the element to the external housing and prevents water from by-passing the element.
7. b. The feedwater spacing material promotes water turbulence as it conducts the feedwater between the envelopes of spiral wound membranes. Greater feedwater turbulence, as well as greater flow velocity, through the element means that there is greater shear placed on potential foulants at the membrane surface. This tends to subject the element to a lesser fouling rate.
8. d. Percent recovery is defined as the ration of permeate flow rate to feedwater flow rate, expressed as a percentage. It is used to describe how efficiently the system is being operated, and is also used to determine the extent of concentration of constituents in the feedwater, or in other words, the likelihood of scales or foulant formation on the concentrate side of membrane envelopes.
9. b. The higher the percentage of feedwater that permeates to product water, the higher becomes the concentration of solutes in concentrate water, and higher concentrations of salts will thereby permeate the membrane.
10. e. In using RO systems to reduce TDS in water supplies, the maximum recovery should be limited by the scaling potential of the RO concentrate, which will potentially foul the membrane and limit the membrane's useful life. Even with one or more pretreatment methods for controlling salt solubilities (such as softening, acid injection or injection of a scale inhibitor), there will always be an upper limit to the recovery beyond which the risk of scale formation is too great.