| Reverse osmosis and nanofiltration membranes are used to remove dissolved contaminants in drinking water treatment facilities. A continuous flow of wastewater, usually called "concentrate" is discharged from this membrane process. This concentrate stream contains elevated concentrations of ions that frequently exceed the solubility product of compounds that can precipitate and foul the membrane surface. Antiscalants are applied to the membrane feed water to prevent fouling of the membrane surface. These antiscalants build up in the concentrate stream, and can inhibit processes used to treat the concentrate prior to discharge or reuse. In order to design concentrate treatment systems, the impacts of antiscalants on the behavior of the concentrate must be understood.;To examine the impact of antiscalants on membrane concentrate behavior, a hypothetical model membrane system was proposed, raw water data collected from the ten largest water systems in the state of South Dakota were used to create feed water characteristics of the hypothetical system used to model the membrane concentrate water quality characteristics. Based on the model membrane concentrate water quality a synthetic membrane concentrate was developed in laboratory.;Antiscalant behavior was assessed by measuring the ability of the antiscalants to sustain concentration (inhibit precipitation) of ions in the simulated concentrate solution. The simulated concentrate tests were performed under controlled temperature conditions in the laboratory. The parameters measured on the membrane concentrate during the study were alkalinity, calcium, magnesium, iron and manganese. The precipitation behaviors of these parameters were examined over the period of 48 hours at 100C and 20 0C. The five antiscalants investigated in this study were Flocon 260, Flocon 135, Itasca 98, polyphosphate and SpectraGuard SC.;The tests results revealed that temperature has a significant effect on the inhibiting characteristics of the antiscalants at lower doses of the antiscalants. At higher doses of the antiscalants, the temperature has very minimal effect on the inhibiting characteristics of the antiscalants. It was also observed that that different antiscalants effectively inhibit different elements. Not only can the antiscalants be selected based on their ability to serve its primary function as an antiscalant, but given the results of this work, the antiscalant can also be selected based on desired behavior of the membrane concentrate in the concentrate disposal or reuse processes. |
