Removal of Constituents of Emerging Concern by Ozone and Advanced Oxidation Process – a Bench-Scale Approach

摘要

Bench-scale ozone (O_3) and O_3 in combination with hydrogen peroxide (H_2O_2) tests wereconducted to evaluate the removal of selected constituents of emerging concern (CECs) added toMetropolitan Water District of Southern California’s (Metropolitan’s) source waters. Whendetected, CECs in Metropolitan’s source and finished waters have been in the low ng/L range-levels at which there has been no evidence of human health risks. Despite these lowconcentrations, testing was conducted to evaluate the effectiveness of ozonation processes atMetropolitan’s water treatment plants to further limit CECs and their potential risks using StateProject water (SPW), Colorado River water (CRW) and SPW/CRW blends. The five CECsselected for evaluating included atrazine, caffeine, carbamazepine, primidone, and tris(2-chloroethyl) phosphate (TCEP).Prior to evaluating CEC removal, the removal of taste and odor compounds (2-methylisoborneol[MIB] and geosmin) using the bench-scale O_3 and O_3/H_2O_2 apparatus was conducted to establishbench-scale ozonation conditions that would result in similar oxidation conditions and removalsas found in Metropolitan’s full-scale plants. These studies evaluated MIB and geosmin removalfrom potential stripping by oxygen gas flow and oxidation.Initial results indicated that the bench-scale system could be operated to achieve similaroxidation conditions and removals for MIB and geosmin as seen in full-scale plants. Phase Ⅰbench-scale studies showed that over a range of ozonation conditions for waters spiked withCECs at 100 ng/L, ozone was effective for removing carbamazepine at greater than 99 percent,caffeine at greater than 82 percent, and primidone at greater than 47 percent; atrazine removalwas limited showing less than 54 percent removal. Ozonation was not effective for TCEPremoval.Results for Phase Ⅱ of the bench-scale studies, which included O_3/H_2O_2 testing, showed thatunder the same ozone dosages used in Phase Ⅰ studies, O_3 and O_3/H_2O_2 were effective forremoving carbamazepine at greater than 99 percent and primidone at greater than 47 percent;caffeine at greater than 70 percent; atrazine removal was limited below 56 percent removal. O_3and O_3/H_2O_2 was not effective for TCEP removal. However, increasing the H_2O_2 dose mayincrease TCEP removal. In general, O_3/H_2O_2 enhanced primidone and atrazine removals.Results also showed that O_3 and O_3/H_2O_2 oxidation of primidone and atrazine resulted in slightlyhigher percent removals in SPW than in CRW and SPW/CRW blends.