Control of disinfection and halogenated disinfection byproducts by the electrochemical process.

The aim of this study was to investigate some aspects of the performance of electrochemical process as an alternative disinfection strategy, while minimising DBPs, for water purification. The study of electrochemical processes has shown free chlorine to be produced, but smaller amounts of stronger oxidants, such as ozone, hydrogen peroxide and OH radicals (*OH), were also generated. The formation of mixed oxidants increased with increasing electric conductivity, but was limited at conductivities greater than 0.6 mS/cm. Using several microorganisms, such as E. coli and MS2 bacteriophage, inactivation kinetic studies were performed. With the exception of free chlorine, the role of mixed oxidants, especially OH radicals, was investigated for enhancement of the inactivation rate. Additionally, the formation and reduction of DBPs was studied by monitoring the concentration of haloacetic acids (HAAs) during the process.

Role of disinfectant concentration and pH in the inactivation kinetics of Cryptosporidium parvum oocysts with ozone and monochloramine.

The objective of this study was to investigate the effect of disinfectant concentration and pH on the inactivation kinetics of Cryptosporidium parvum oocysts with ozone, monochloramine, and ozone/monochloramine at 20 degrees C. Experimental results revealed that the CT (product of disinfectant concentration and contact time) required to achieve a certain level of C. parvum inactivation was unique, thus demonstrating the validity of the CT concept for these single disinfectant and sequential disinfection processes for the range of experimental conditions investigated. Inactivation curves were represented accurately by a delayed Chick-Watson expression consistent with the CT concept. No pH dependence was observed for primary inactivation with ozone in the pH range of 6-10 or primary and secondary inactivation with monochloramine at pH values of 8 and 10. Oocyst resistance to chemical disinfectant attack was found to vary among oocysts lots as well as with oocyst aging within a given lot. The synergy observed for sequential disinfection with ozone/monochloramine suggested that monochloramine might be reacting with some of the same chemical constituents, both vital and nonvital, of the oocyst wall and/or cavity that also react with ozone. If so, partial completion of these reactions by the primary disinfectant would have resulted in the disappearance of the lag phase and the faster rate of inactivation observed for the secondary disinfectant.

Inactivation of Bacillus subtilis spores and formation of bromate during ozonation.

Inactivation of B. subtilis spores with ozone was investigated to assess the effect of pH and temperature, to compare the kinetics to those for the inactivation of C. parvum oocysts, to investigate bromate formation under 2-log inactivation conditions, and to assess the need for bromate control strategies. The rate of B. subtilis inactivation with ozone was independent of pH, decreased with temperature (activation energy of 42,100 Jmol(-1)), and was consistent with the CT concept. B. subtilis was found to be a good indicator for C. parvum at 20-30 degrees C, but at lower temperatures B. subtilis was inactivated more readily than C. parvum. Bromate formation increased as both pH and temperature increased. For water with an initial bromide concentration of 33 microgl(-1), achieving 2-logs of inactivation, without exceeding the 100 microg l(-1) bromate standard, was most difficult at 30 degrees C for B. subtilis and at midrange temperatures (10-20 degrees C) for C. partum. pH depression and ammonia addition were found to reduce bromate formation without affecting B. subtilis inactivation, and may be necessary for waters containing more than 50 microgl(-1) bromide.

Inactivation of Cryptosporidium parvum oocysts with sequential application of ozone and combined chlorine.

Single-step inactivation experiments with ozone and monochloramine revealed the presence of a CT lag followed by pseudo-first order inactivation kinetics. Sequential disinfection experiments with ozone followed by monochloramine revealed that ozone pretreatment resulted in the removal of a more prominent CT lag observed for monochloramine. In addition, the rate of inactivation for ozone-pretreated oocysts was approximately 2.5x greater than that observed for the post-lag phase portion of the monochloramine primary inactivation curve.

Inactivation of Cryptosporidium parvum oocysts with ozone and monochloramine at low temperature.

The rate of Cryptosporidium parvum inactivation decreased with decreasing temperature (1-20 degrees C) for ozone and for monochloramine applied alone as well as after pre-treatment with ozone. Synergy was observed at all temperatures studied for the ozone/monochloramine sequential disinfection scheme. The synergistic effect was found to increase with decreasing temperature. The inactivation rate with monochloramine after ozone pre-treatment was 5 times faster at 20 degrees C and 22 times faster at 1 degree C than the corresponding post-lag phase rates of inactivation with monochloramine at these temperatures when no ozone pre-treatment was applied. The CT required for achieving 2-logs of inactivation ranged from 11,400 mg min l-1 at 20 degrees C to 64,600 mg min l-1 at 1 degree C when monochloramine was applied alone. In contrast, the CT required for an overall sequential inactivation of 2-logs ranged from 721 mg min l-1 at 20 degrees C to 1350 mg min l-1 at 1 degree C when applying monochloramine after ozone pre-treatment. The presence of excess ammonia in the monochloramine solutions was not responsible for the synergy observed in ozone/monochloramine sequential disinfection.

The hydroxide-assisted hydrolysis of cyanogen chloride in aqueous solution.

The hydrolysis of cyanogen chloride (ClCN) was studied as a function of temperature and pH. Results were used to resolve discrepancies among previously reported kinetic constants. The pH dependence was studied over a range of 9.54-10.93 at a temperature of 21.0 degrees C. The effect of temperature was investigated over the range of 10-30 degrees C at a pH of approximately 10. Changes in the concentrations of ClCN and the reaction products cyanic acid and chloride ion were monitored with time. For the conditions corresponding to these experiments, the hydroxide-assisted hydrolysis pathway predominated. Collision frequency factor and activation energies recommended to represent the hydrolysis of ClCN in aqueous solution are A = 2.06 x 10(11) M-1 s-1 and Ea = 60,980 J mol-1 for the hydroxide-ion-assisted reaction, and A = 9.97 x 10(8) s-1 and Ea = 87,180 J mol-1 for the water-assisted reaction.