TY - JOUR
T1 - Ozonation of phosphonate antiscalants used for reverse osmosis desalination
T2 - parameter effects on the extent of oxidation
AU - Greenlee, Lauren F.
AU - Freeman, Benny D.
AU - Lawler, Desmond F.
N1 - Funding Information:
The authors thank the U.S. National Science Foundation Graduate Research Fellowship and International Research and Education in Engineering programs for funding (CBET 0553957). The authors acknowledge the Water Research Foundation (Project #4061). The views herein are those of the authors and not of NSF or WaterRF.
Copyright:
Copyright 2014 Elsevier B.V., All rights reserved.
PY - 2014/5/15
Y1 - 2014/5/15
N2 - The recovery of usable product water in brackish water reverse osmosis (RO) desalination is limited by the potential for membrane scaling. This limited recovery results in high costs of disposal of the concentrate (waste) stream. Concentrate treatment to improve recovery is vital, and treatment that includes antiscalant oxidation prior to precipitation and solid/liquid separation might allow increased precipitation through antiscalant deactivation. Ozone and hydrogen peroxide were used to oxidize phosphonate-type antiscalants under varying conditions of water composition, pH, ozone dose, and antiscalant type; orthophosphate (P) is an oxidation product and was used to measure the extent of oxidation. Antiscalant oxidation increases with ozone dose (1-10mg/L O3) and in the presence of calcium, from 1mg/L P to 7mg/L P for an antiscalant concentration of 27mg/L as P. The addition of hydrogen peroxide causes only minor increases in antiscalant oxidation. The extent of oxidation varies with pH as a function of metal-ligand speciation, with the doubly-protonated metal-ligand species dominating the reactivity of the antiscalant. In the presence of calcium, the primary oxidation pathway for phosphonate antiscalants is through direct reaction with ozone (70-80% of measured P). In the absence of calcium, ozone and hydroxyl radicals appear to contribute relatively equally to oxidation. These results suggest phosphonate antiscalants can be oxidized with relatively low ozone doses, thereby deactivating the chelating behavior of the antiscalant and allowing increased precipitation of scaling salts such as calcium and magnesium.
AB - The recovery of usable product water in brackish water reverse osmosis (RO) desalination is limited by the potential for membrane scaling. This limited recovery results in high costs of disposal of the concentrate (waste) stream. Concentrate treatment to improve recovery is vital, and treatment that includes antiscalant oxidation prior to precipitation and solid/liquid separation might allow increased precipitation through antiscalant deactivation. Ozone and hydrogen peroxide were used to oxidize phosphonate-type antiscalants under varying conditions of water composition, pH, ozone dose, and antiscalant type; orthophosphate (P) is an oxidation product and was used to measure the extent of oxidation. Antiscalant oxidation increases with ozone dose (1-10mg/L O3) and in the presence of calcium, from 1mg/L P to 7mg/L P for an antiscalant concentration of 27mg/L as P. The addition of hydrogen peroxide causes only minor increases in antiscalant oxidation. The extent of oxidation varies with pH as a function of metal-ligand speciation, with the doubly-protonated metal-ligand species dominating the reactivity of the antiscalant. In the presence of calcium, the primary oxidation pathway for phosphonate antiscalants is through direct reaction with ozone (70-80% of measured P). In the absence of calcium, ozone and hydroxyl radicals appear to contribute relatively equally to oxidation. These results suggest phosphonate antiscalants can be oxidized with relatively low ozone doses, thereby deactivating the chelating behavior of the antiscalant and allowing increased precipitation of scaling salts such as calcium and magnesium.
KW - Antiscalant
KW - Calcium complexation
KW - Hydroxyl radical
KW - Ozone
KW - Phosphonate
KW - Reverse osmosis desalination
UR - http://www.scopus.com/inward/record.url?scp=84894361740&partnerID=8YFLogxK
U2 - 10.1016/j.cej.2014.02.002
DO - 10.1016/j.cej.2014.02.002
M3 - Article
AN - SCOPUS:84894361740
VL - 244
SP - 505
EP - 513
JO - Chemical Engineering Journal
JF - Chemical Engineering Journal
SN - 1385-8947
ER -