臭氧应用英文文章33
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Pergamon PII: soo43-1354(%)ooo71-1
War.Res. Vol. 30,No. 9, pp.21W2170,1996 Copyright 0 1996Elsevier Science Ltd
Printed in Great Britain. All rights reserved
1985). Many drinking water treatment facilities add large amounts (3-6 mg/L) of chlorine as an
anti-fouling agent before transporting their source waters from reservoirs/aqueducts to treatment plants to avoid bacterial growth and corrosion in pipelines. Ozonation is practiced widely for treatment of drinking water to improve taste, remove color, enhance coagulation and to improve the biodegradability of organic impurities. During drinking water treatment, ozonation can potentially oxidize residual chlorine to ClO; . ClO; formation during ozone treatment of water containing residual chlorine has caused a growing concern about the possible health significance of the presence of ClO; and chlorite (ClO;) in drinking water. ClO; and ClO; have been shown to cause hemolytic anemia in laboratory animals (Condie, 1986; Daniel ef al., 1990; Stettler, 1977). The effects of ClO; and CIO; in mammals arise from oxidative damage to red blood cells resulting in hemolytic anemia and methaemoglobin formation. The World
Health Organization (WHO) under the revisions of its Drinking Water Guidelines has proposed a guideline value of 200 pg/L for ClO; , but it was considered that there was insufficient data available to make an assessment of CIO; (FWR, 1993). Under acidic biological conditions, the reduction of ClO; to ClO; is feasible. In the U.K. the total concentration of chlorine dioxide, ClO; and ClO; in treated water is limited to 500 p/L (FWR, 1990). ClO; is also individually regulated in the U.K. as a by-product of the on-site electrolytic production of chlorine, with a limit of 7OOp/L in the final water. In the U.S. the EPA has set a maximum contaminant level (MCL) for chlorite at lOOOflg/L with an MCL goal of 80 pg/L (USEPA, 1994) and an MCL for ClO; may be forthcoming. This limit is based on what is achievable with current technology rather than being based solely on health data. Future limits may be much lower than these numbers and elucidation of accurate formation mechanisms is crucial for its control and minimization. This article discusses the various pathways for the formation of ClO, and the effect of several water quality and treatment (pH, DOC, alkalinity, ozone dose, ammonia and peroxide addition) variables on the formation and minimization of ClO; . METHODS
0043-1354/96 $15.00 + 0.00
CHLORINE-OZONE
INTERACTIONS: CHLORATE
FORMATION
OF
MOHAMED S. SIDDIQUI Department of Civil Engineering, University of South Alabama, EGCB 280 Mobile, AL 36688 U.S.A.
2160
Formation of chlorate
Ozos were performed in 500 mL completely mixed glass reactor fitted with a syringe to which a single ozone dose was added by injection of a concentrated ozone stock solution. Ozone gas was produced from a 0.45 lb/d ozone generator which uses pure oxygen. Concentration stock ozone solution was produced by bubbling ozone gas through a DOC-free water until the concentration of ozone in liquid phase was between 3540 mg/L (= pH = 6.0). The samples for analysis were periodically withdrawn using a syringe. Ozone demand experiments were performed by spiking incremental doses of ozone in a series of serum vials and measuring its concentration after 5 minutes using indigo method (APHA, 1989). The ozone dose for which there was a measurable amount of dissolved ozone in the sample was taken as the dose required to meet the ozone demand. UV absorbance method was not employed to measure dissolved ozone in DOC containing waters as background dissolved organic matter interferes with dissolved ozone measurement.
INTRODUCTION The mechanism of chlorine and ozone interaction has not been studied extensively even though these chemicals are widely used for disinfection. Chlorate (CLO;) is not naturally present in waters but is a secondary product formed from ozone-chlorine reactions. ClO; can also form during the manufacture and storage of hypochlorite solutions. Chlorine dioxide, which is often applied as a water disinfectant/oxidant reacts with a relatively high rate constant with ozone to form ClO< (Hoigne et al.,
(First received September 1995; accepted in revised form February 1996)
Abstract-The chlorate ion is one of the contaminants being considered for regulation in drinking water under the disinfection by-product rule. In addition to its presence in water as a result of chlorine dioxide
Source waters
Dissolved organic carbon (DOC)-free Milli-Q water (MQW) and natural source waters containing a wide ranging background characteristics were evaluated for CIO, formation (Table 1).
use, chlorate may be formed during intermediate ozonation if residual chlorine is present. The majority of chlorate forms through a free radical pathway in natural source waters as opposed to by both molecular ozone and free radical pathways in low-DOC waters. The monitoring of OH radicals using p-chlorobenzoic acid indicated that the formation of chlorate is proportional to OH radical generation. The increase in pH favored chlorate formation and the presence of alkalinity enhanced chlorate formation due to secondary reactions between carbonate radicals and chlorine species. The addition of ammonia and peroxide before ozonation reduced chlorate formation whereas the simultaneous addition of peroxide during ozonation enhanced chlorate formation. Copyright 0 1996 Elsevier Science Ltd Key words--chlorate, ozone, PEROXONE (ozone plus peroxide), chlorine dioxide
War.Res. Vol. 30,No. 9, pp.21W2170,1996 Copyright 0 1996Elsevier Science Ltd
Printed in Great Britain. All rights reserved
1985). Many drinking water treatment facilities add large amounts (3-6 mg/L) of chlorine as an
anti-fouling agent before transporting their source waters from reservoirs/aqueducts to treatment plants to avoid bacterial growth and corrosion in pipelines. Ozonation is practiced widely for treatment of drinking water to improve taste, remove color, enhance coagulation and to improve the biodegradability of organic impurities. During drinking water treatment, ozonation can potentially oxidize residual chlorine to ClO; . ClO; formation during ozone treatment of water containing residual chlorine has caused a growing concern about the possible health significance of the presence of ClO; and chlorite (ClO;) in drinking water. ClO; and ClO; have been shown to cause hemolytic anemia in laboratory animals (Condie, 1986; Daniel ef al., 1990; Stettler, 1977). The effects of ClO; and CIO; in mammals arise from oxidative damage to red blood cells resulting in hemolytic anemia and methaemoglobin formation. The World
Health Organization (WHO) under the revisions of its Drinking Water Guidelines has proposed a guideline value of 200 pg/L for ClO; , but it was considered that there was insufficient data available to make an assessment of CIO; (FWR, 1993). Under acidic biological conditions, the reduction of ClO; to ClO; is feasible. In the U.K. the total concentration of chlorine dioxide, ClO; and ClO; in treated water is limited to 500 p/L (FWR, 1990). ClO; is also individually regulated in the U.K. as a by-product of the on-site electrolytic production of chlorine, with a limit of 7OOp/L in the final water. In the U.S. the EPA has set a maximum contaminant level (MCL) for chlorite at lOOOflg/L with an MCL goal of 80 pg/L (USEPA, 1994) and an MCL for ClO; may be forthcoming. This limit is based on what is achievable with current technology rather than being based solely on health data. Future limits may be much lower than these numbers and elucidation of accurate formation mechanisms is crucial for its control and minimization. This article discusses the various pathways for the formation of ClO, and the effect of several water quality and treatment (pH, DOC, alkalinity, ozone dose, ammonia and peroxide addition) variables on the formation and minimization of ClO; . METHODS
0043-1354/96 $15.00 + 0.00
CHLORINE-OZONE
INTERACTIONS: CHLORATE
FORMATION
OF
MOHAMED S. SIDDIQUI Department of Civil Engineering, University of South Alabama, EGCB 280 Mobile, AL 36688 U.S.A.
2160
Formation of chlorate
Ozos were performed in 500 mL completely mixed glass reactor fitted with a syringe to which a single ozone dose was added by injection of a concentrated ozone stock solution. Ozone gas was produced from a 0.45 lb/d ozone generator which uses pure oxygen. Concentration stock ozone solution was produced by bubbling ozone gas through a DOC-free water until the concentration of ozone in liquid phase was between 3540 mg/L (= pH = 6.0). The samples for analysis were periodically withdrawn using a syringe. Ozone demand experiments were performed by spiking incremental doses of ozone in a series of serum vials and measuring its concentration after 5 minutes using indigo method (APHA, 1989). The ozone dose for which there was a measurable amount of dissolved ozone in the sample was taken as the dose required to meet the ozone demand. UV absorbance method was not employed to measure dissolved ozone in DOC containing waters as background dissolved organic matter interferes with dissolved ozone measurement.
INTRODUCTION The mechanism of chlorine and ozone interaction has not been studied extensively even though these chemicals are widely used for disinfection. Chlorate (CLO;) is not naturally present in waters but is a secondary product formed from ozone-chlorine reactions. ClO; can also form during the manufacture and storage of hypochlorite solutions. Chlorine dioxide, which is often applied as a water disinfectant/oxidant reacts with a relatively high rate constant with ozone to form ClO< (Hoigne et al.,
(First received September 1995; accepted in revised form February 1996)
Abstract-The chlorate ion is one of the contaminants being considered for regulation in drinking water under the disinfection by-product rule. In addition to its presence in water as a result of chlorine dioxide
Source waters
Dissolved organic carbon (DOC)-free Milli-Q water (MQW) and natural source waters containing a wide ranging background characteristics were evaluated for CIO, formation (Table 1).
use, chlorate may be formed during intermediate ozonation if residual chlorine is present. The majority of chlorate forms through a free radical pathway in natural source waters as opposed to by both molecular ozone and free radical pathways in low-DOC waters. The monitoring of OH radicals using p-chlorobenzoic acid indicated that the formation of chlorate is proportional to OH radical generation. The increase in pH favored chlorate formation and the presence of alkalinity enhanced chlorate formation due to secondary reactions between carbonate radicals and chlorine species. The addition of ammonia and peroxide before ozonation reduced chlorate formation whereas the simultaneous addition of peroxide during ozonation enhanced chlorate formation. Copyright 0 1996 Elsevier Science Ltd Key words--chlorate, ozone, PEROXONE (ozone plus peroxide), chlorine dioxide