Master of Science (MSc)
Faculty of Science
D. S. Smith
Current regulations for sensitive receiving waters are approaching the limit of technology for phosphorus removal and improved methods are required. Existing methods target removal of the orthophosphate form of phosphorus, but to achieve low effluent limits other non-reactive (NRP) forms, such as condensed phosphate and organic phosphorus, must be removed as well. This could be accomplished by developing a quaternary step in wastewater treatment that utilizes reverse osmosis (RO) followed by advanced oxidation processes (AOP) on the produced brine (RO concentrate). The objective during advanced treatment is to convert NRP in the brine to reactive phosphorus for removal by traditional chemical addition methods; however, the various antiscalants utilized for RO membrane maintenance can contribute phosphorus to the brine. To test brine treatment as a viable alternative to achieve low effluent phosphorus, antiscalant-free brine, demonstration facility-produced brine, four commercially available antiscalants and various representative model phosphorus compounds were evaluated for treatment effectiveness. For antiscalant addition experiments the dosage of antiscalant was designed to match the necessary concentration for effective RO membrane maintenance. The advanced oxidation processes evaluated were 100 ppb peroxide for 30 minutes, 50 ppm bleach for 30 minutes, pH 2 for 30 minutes, and 100 ppb peroxide at pH 2 for 30 minutes. The use of chemical addition as a pretreatment was also evaluated. Treatment effectiveness was determined by measuring residual total phosphorus post AOP treatment after a subsequent 6 ppm alum treatment. The use of 30 ppm alum chemical addition as a pretreatment effectively improves the use of AOPs for P removal from 57% up to 73% for a 100 ppb peroxide at pH 2 treated antiscalant free brine. The most effective chemical AOP after a 30 ppm alum pretreatment was 100 ppb peroxide at pH 2 which achieved 73% TP removal for the antiscalant-free brine, 84% TP removal in the demonstration facility produced brine, 66-82% TP removal for the brine amended with the three commercially available antiscalants, and 3-92% TP removal for the various phosphorus standards. A comparison removal using a multiphase treatment which employs UV digestion with 3000 ppm peroxide at pH 2 and 80-90°C for 1 hour was also evaluated and achieved 81-94% TP removal in the two brines and four antiscalant-dosed brines, as well as 73-84% TP removal in the various phosphorus standards. The effectiveness of treatments at converting NRP seems to be bond type dependent, such that phosphate-esters, followed by phospho-esters are the most convertible, whereas phosphonate bonds seem to be resilient to conversion. Therefore RO shows potential for quaternary treatment to achieve low phosphorus levels. The RO brine can concentrate nutrients (whether naturally occurring or contributed by antiscalants), which can be removed by chemical addition as well as via AOP processes.
Patton, Petrease, "Treatment of Reverse Osmosis Brine with Advanced Oxidative Processes for Enhanced Phosphorus Removal" (2013). Theses and Dissertations (Comprehensive). 1617.