Advanced Phosphorus Removal from Membrane Filtrate and Filter Filtrate Using Packed Columns with Different Adsorptive Media
Abstract:This study investigated the potential of applying adsorptive media to further remove phosphorus in secondary and tertiary effluent to levels lower than the current limits of technologies in practice. On-site short-term bench scale adsorption column tests treating membrane microfiltration effluent were conducted in parallel with three different commercial adsorptive media including US filter GFH, ResinTech ASM-10-HP and Purolite Arsenex, at the city of Coeur d'Alene wastewater treatment plant. At influent TP concentrations ranging from 0.014 - 0.43 mg/L, effluent TP of 0.005-0.008 mg/L was achieved. Phosphorus fractionation analysis of influent and effluent through the column showed that soluble non-reactive P (sNRP), which likely consists of acid-hydrolysable P (poly-P) and dissolved refractory organic P (rDOP), is the dominant form of P in the membrane microfiltration (tertiary) effluent at a TP concentration of 0.014 mg/L. The particular P in the column effluent was negligible (<0.002 mg/L) for all tests, while effluent soluble P (sTP) ranged from 0.004 to 0.007 mg/L and consisted of 0.001 to 0.005 mg/L soluble non-reactive P (sNRP) and 0.002 mg/L ortho-P. The results demonstrated that the adsorption column process can effectively remove both soluble reactive ortho-P and soluble non-reactive P, such as dissolved refractory organic P in the wastewater. The three different adsorptive media tested exhibited comparable performance in terms of effluent P concentrations and fractionations, despite their composition differences. Addition of oxidants such as hydrogen peroxide to the influent seemed to negatively affect P removal via adsorption, and the final effluent TP concentrations were higher (0.013-0.017 mg/L) than those observed without any hydrogen peroxide addition (0.005-0.008 mg/L). P fractionation analysis showed that the effluent ortho-P remained the same (0.002 mg/L) compared to tests without pre-oxidation, whereas the effluent sNRP and sTP increased due to decreased removal efficiency of sNRP after H2O2 addition to the influent feed for all three media. A long-term pilot scale test with Kemira's CFH12 media-packed column was performed at the City of Las Vegas Water Pollution Control Facility for 6 months. The results demonstrated the potential of applying adsorption as a final polishing step to further reduce the effluent P to lower levels (TP<0.1 mg/L; orthoP<0.04 mg/L) than the limits of conventional P removal technologies. An average TP removal of 61% was achieved. Breakthrough did not occur at the end of six-month pilot testing, and the amount of P adsorbed per unit media based on the amount of ortho-P removed at the end of the pilot test was calculated to be 0.76 mgP/g media, which was much lower than the value estimated based on the P isotherm (by Genz et al.(2004)) of 5 mg/g at residual P concentration of 0.04 mg/L (pH 6-7). In this study, effluent ortho-P was below 0.04 mg/L after 41000 bed volumes at Empty Bed Contact Time (EBCT) of 5 minutes with influent ortho-P at 0.11 mg/L.
Document Type: Research Article
Publication date: 2007-10-01
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