Grantee Research Project Results
Final Report: Integrated Approach for the Control of Cryptosporidium parvum Oocysts and Disinfection By-Products in Drinking Water Treated with Ozone and Chloramines
EPA Grant Number: R826830Title: Integrated Approach for the Control of Cryptosporidium parvum Oocysts and Disinfection By-Products in Drinking Water Treated with Ozone and Chloramines
Investigators: Mariñas, Benito J. , Minear, Roger A.
Institution: University of Illinois Urbana-Champaign
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 1998 through August 31, 2002 (Extended to March 31, 2003)
Project Amount: $367,427
RFA: Drinking Water (1998) RFA Text | Recipients Lists
Research Category: Water , Drinking Water
Objective:
The overall objective of this research project was the development of process design recommendations for the simultaneous control of Cryptosporidium parvum oocysts and disinfection by-products (DBPs) during ozone/chloramines sequential disinfection of natural waters. Because the main objective of the study was to develop an integral control strategy, the scope of work focused on a limited number of selected DBPs (bromate, formaldehyde, and cyanogen halides) associated with the ozone/chloramines sequential disinfection process.
Approach:
The scope of work of the project includes experimental tasks designed for the simultaneous study of C. parvum oocyst inactivation and selected DBP formation/decomposition in natural waters treated with ozone and chloramines using both batch and flow-through reactors. An integrated predictive model will be developed and calibrated with these experimental results. The model will be used to determine optimum process design, and verified in full-scale systems using fluorescent-dyed polystyrene microspheres as non-biological surrogate indicators for C. parvum oocyst inactivation.Summary/Accomplishments (Outputs/Outcomes):
Activities under this research project have produced three major contributions toward the understanding of sequential ozone/monochloramine disinfection and associated DBP formation kinetics.
Synergistic effects associated with the inactivation of C. parvum oocysts during sequential application of ozone and monochloramine were investigated. The inactivation kinetics of C. parvum oocysts with ozone and monochloramine used as single disinfectants were characterized by a lag phase followed by a region of pseudo-first order kinetics. The lag phase was found to increase and the rate of C. parvum inactivation to decrease as temperature decreased. The inactivation rates under all conditions were consistent with the Arrhenius equation for the temperature range investigated of 1 to 20°C. Thus, for process design purposes, the Arrhenius equation could be used to predict inactivation kinetics at temperatures for which experimental data are unavailable; however, the application of safety factors should be considered because of the variability in oocyst resistance to disinfectant.
Synergy was observed for ozone/monochloramine sequential disinfection at all temperatures studied. Because of the weaker temperature dependence of the rate constant for secondary inactivation with monochloramine after ozone pre-treatment, the synergy was found to increase as temperature decreased. The inactivation rate with monochloramine after ozone pre-treatment was 5 times faster at 20°C and 22 times faster at 1°C than the corresponding rates of inactivation with monochloramine when no ozone pre-treatment was applied. The synergy levels observed for ozone/monochloramine sequential disinfection at low temperature present a potential solution for the inactivation of C. parvum oocysts in regions where the water temperature may approach the freezing point.
The low apparent activation energy observed for secondary monochloramine disinfection after ozone pre-treatment suggests that the secondary inactivation step may be the result of permeation within oocyst wall layers with relatively lower reactivity. In contrast, in single-step disinfection and in the first step of a sequential process, inactivation may be a permeation process within more reactive oocyst wall layers. Unfortunately, these are just qualitative explanations. A need remains for improving the understanding of disinfection mechanisms.
Integrated models for the simultaneous prediction of C. parvum inactivation and bromate formation were developed for three ozone reactors having different hydrodynamic conditions: true batch; bench-scale flow-through ozone bubble-diffuser contactor with external recirculation (plug flow-side plug flow reactor or PFR-side PFR); and lab- and pilot-scale ozone bubble-diffuser contactors (axial dispersion reactors or ADRs). The various models developed included the following key elements: (1) ozone decomposition kinetics and mechanism; (2) bromate formation mechanism; (3) C. parvum inactivation kinetics; (4) empirical estimation of ozone mass transfer; and (5) hydrodynamic model.
The various models were evaluated with actual experimental data. The mechanistic predictive model for ozone decomposition and bromate formation, which incorporated more than 30 chemical species and more than 50 chemical reactions, was validated with data obtained with a batch ozone contactor operated with synthetic waters. Experiments with a lab-scale flow-through ozone contactor with external recirculation also were performed with laboratory synthetic waters, which were spiked with C. parvum oocysts to verify the integrated model for hydrodynamic conditions. The mechanistic predictive model was further improved by incorporating empirical reactions for natural organic matter to simulate the bromate formation in natural water (i.e., treated Ohio River water). The model was evaluated with experimental data obtained with natural water in a batch reactor based on the concentrations of not only ozone and bromate but also those of the OH-radical probe, para-dichlorobenzoic acid (p-CBA).
The model for natural water was combined with the ADR model to simultaneously predict C. parvum inactivation and bromate formation in a lab-scale flow-through ozone contactor with two chambers in series. The applicability of the ADR model to represent the hydrodynamic condition in ozone bubble-diffuser reactor was verified with a model with empirical ozone decomposition kinetics by successfully simulating the inactivation levels of C. parvum and C. muris oocysts in a pilot-scale ozone contactor operated with a selected natural water (i.e., treated Ohio River water). In all cases, semi-batch experiments to obtain the inactivation kinetics of C. parvum oocysts preceded the prediction of C. parvum inactivation levels in flow-through ozone contactors. Tracer tests also were performed with each reactor to provide the validity of hydrodynamic models that were used for different ozone contactors.
The model is expected to provide a useful tool to predict both C. parvum inactivation and bromate formation in flow-through ozone bubble-diffuser contactors. Once the parameters that determine the kinetics of ozone decomposition, bromate formation, and C. parvum inactivation are determined from bench-scale batch and semi-batch tests, the model can be used to predict the performance in flow-through systems.
The model can be further utilized to find an optimum design criteria and operating conditions for ozone disinfection systems with respect to inactivation of C. parvum oocyst and control of bromate formation. In this study, the following recommendations could be made for the design and operation of ozone contactors to achieve the above two countering goals:
- A hydrodynamic condition with less back-mixing is more favorable because short-circuiting through continually stirred tank reactor-like hydrodynamic condition has much greater negative effect on C. parvum inactivation than on bromate formation.
- A source water pH has much greater impact than mixing conditions on bromate formation, whereas C. parvum inactivation does not depend on pH. Therefore, lowering the pH of the source water will be a more efficient way to suppress the formation of bromate than changing the hydrodynamic condition of the existing process.
- For the natural water used in this study (treated Ohio River water), it was suggested that the oxidation of key bromine species such as bromide was mostly responsible for the formation of bromate.
- Meeting inactivation requirements for C. parvum oocysts would be more challenging at lower temperatures because the temperature dependence of C. parvum inactivation kinetics was great enough to compensate for the other effects, which would favor the higher level of inactivation at lower temperature. Unfortunately, the effect of temperature on bromate formation was not discussed in this study because of the limitations of information and knowledge about the temperature dependence of most of the chemical reactions involved in ozone decomposition and bromate formation.
It is important to note that the trends observed for the effects of various operating and water quality parameters on the inactivation efficiency of C. parvum and C. muris oocysts in the pilot-scale ozone contactor should not be generally extended to other microorganisms or to contactors with different design. The same is true for the model simulation results and corresponding hypotheses made for the specific natural water. The inability of the model to simulate such other cases originates not from limitations of model itself, but from the lack of the information to represent, for example, inactivation kinetics of other types of microorganisms, mathematical predictions of the bubble sizes in different types of diffusers, and other parameters. The model presented in this study, however, could be considered as a prototype that could be adapted to simulate the performance of ozone disinfection systems with respect to inactivation of any pathogenic microorganism and control of formation of other types of DBP. For example, this model can be applied to predict any microorganism inactivation in any water if ozone decomposition and ozone inactivation kinetics are available from bench-scale tests. As another example, the model can be coupled with mechanisms of formation of other halogenated DBPs verified in bench-scale testing and used to simulate its formation in the flow-through ozone contactor. In addition, the model can be used to predict the performance of ozone contactors with other configurations.
Ozone disinfection results in the formation of aldehydes among which formaldehyde (HCHO) is typically formed at the highest concentration. Monochloramine (NH2Cl), and monobromamine (NH2Br) formed in the presence of bromide, can then react with HCHO, undergoing a number of reactions which ultimately form cyanogen halides (e.g., cyanogen chloride and cyanogen bromide). The formation mechanism of cyanogen chloride (ClCN) from NH2Cl and HCHO has been reported in the literature. A similar mechanism for the formation of cyanogen bromide (BrCN) from NH2Br and HCHO, the main focus of this study, was investigated in two stages: bromamine decomposition kinetics and the reaction kinetics between bromamines and HCHO.
Bromamine decomposition in the pH range of 6.7 to 9.5 was investigated with ammonia always in excess to bromine. A simplified bromamine decomposition model was proposed and validated. Good agreement was found between model predictions and experimental data. The first reaction in the model was an equilibrium reaction: 2 NH2Br ó NHBr2 + NH3, in which the total bromamines were conserved. This reaction underwent general acid catalysis by H+, H2PO4-, NH4+, HCO3-, and H2O in both forward and backward directions consistent with the Brønsted relationship. The two bromamine species then underwent decomposition according to the following two reactions: 2 NHBr2 ð products, and NHBr2 + NH2Br ð products. Both of these decomposition reactions were found to undergo base catalysis. HPO42- was the only species found to catalyze the first reaction, and OH-, CO32- and H2O all showed some catalytic effect on the second reaction under the range conditions investigated in this study. The base catalysis rate constants were found to be consistent with the Brønsted relationship.
Cyanide ion (CN-), formed as an intermediate compound, reacted with bromamines to produce cyanogen bromide. The reaction between NH2Br and CN- was general acid catalyzed by H+, H2PO4-, H3BO3, NH4+, HPO42- and H2O according to the Brønsted relationship. The resulting Brønsted expressions were used to predict reaction rate constants in solutions buffered by other species, especially those that may not be realistic to characterize experimentally because of the need to use extreme pH conditions or other limitations. An overall kinetic model was developed to predict BrCN formation from the chain of reactions initiated by reaction between monobromamine and formaldehyde.
BrCN formation from the pathway elucidated in this study may be used to provide information for future assessment regarding the control of cyanogen halides in the event that these DBPs undergo further regulatory scrutiny. Even though bromamine is not commonly applied in drinking water treatment, conditions that favor the formation of bromamines (i.e., combined chlorine disinfection of bromide containing waters) are usually encountered and formaldehye is a common DBP in drinking water treated with various disinfectants, including ozone and combined chlorine. According to this mechanism, the formation of BrCN is strongly pH dependent because of the occurrence of general acid catalysis for the rate limiting step and the faster decomposition of bromamines through NH2Br disproportionation. Other water quality parameters of specific natural waters also could affect the overall formation of BrCN and the role played by pH. Additional research is needed to elucidate such effects.
Expected Results:
It is anticipated that this research project will result in a better and more integral understanding of the kinetics of DBP formation/decomposition and C. parvum oocyst inactivation in water supply systems using ozone and chloramines as primary and secondary disinfectants. A predictive model incorporating this information will be available for the overall optimization of both C. parvum and DBP formation control.Journal Articles on this Report : 8 Displayed | Download in RIS Format
Other project views: | All 23 publications | 8 publications in selected types | All 8 journal articles |
---|
Type | Citation | ||
---|---|---|---|
|
Driedger AM, Rennecker JL, Marinas BJ. Inactivation of Cryptosporidium parvum oocysts with ozone and monochloramine at low temperature. Water Research 2001;35(1):41-48. |
R826830 (1999) R826830 (2000) R826830 (2001) R826830 (Final) |
Exit Exit |
|
Kim J-H, Rennecker JL, Tomiak RB, Marinas BJ, Miltner RJ, Owens JH. Inactivation of Cryptosporidium oocysts in a pilot-scale bubble-diffuser contactor. II: model validation and application. Journal of Environmental Engineering 2002;128(6):522-532. |
R826830 (2002) R826830 (Final) |
Exit |
|
Kim J-H, von Gunten U, Marinas BJ. Simultaneous prediction of Cryptosporidium parvum oocyst inactivation and bromate formation during ozonation of synthetic waters. Environmental Science & Technology 2004;38(7):2232-2241. |
R826830 (Final) |
Exit Exit |
|
Lei H, Marinas BJ, Minear RA. Bromamine decomposition kinetics in aqueous solution. Environmental Science & Technology 2004;38(7):2111-2119. |
R826830 (Final) |
Exit Exit Exit |
|
Rennecker JL, Corona-Vasquez B, Driedger AM, Marinas BJ. Synergism in sequential disinfection of Cryptosporidium parvum. Water Science and Technology 2000;41(7):47-52. |
R826830 (2000) R826830 (Final) |
Exit |
|
Rennecker JL, Corona-Vasquez B, Driedger AM, Rubin SA, Marinas BJ. Inactivation of Cryptosporidium parvum oocysts with sequential application of ozone and combined chlorine. Water Science & Technology 2001;43(12):167-170. |
R826830 (2002) R826830 (Final) |
|
|
Rennecker JL, Kim J-H, Corona-Vasquez B, Marinas BJ. Role of disinfectant concentration and pH in the inactivation kinetics of Cryptosporidium parvum oocysts with ozone and monochloramine. Environmental Science & Technology 2001;35(13):2752-2757. |
R826830 (2002) R826830 (Final) |
Exit Exit |
|
Rennecker JL, Driedger AM, Rubin SA, Marinas BJ. Synergy in sequential inactivation of Cryptosporidium parvum with ozone/free chlorine and ozone/monochloramine. Water Research 2000;34(17):4121-4130. |
R826830 (1999) R826830 (2000) R826830 (2001) R826830 (Final) |
Exit Exit Exit |
Supplemental Keywords:
chloramination, drinking water, monochloramine, ozonation, analytical chemistry, drinking water, environmental chemistry, epidemiology, DBP risk management, alternative disinfection methods, bromate formation, brominated DBPs, chloramines, Cryptosporidium parvum oocysts, disinfection byproducts, microbial risk management,, RFA, Scientific Discipline, Water, Environmental Chemistry, Chemistry, Analytical Chemistry, Drinking Water, alternative disinfection methods, cryptosporidium parvum oocysts, public water systems, integrated approach, disinfection byproducts (DPBs), treatment, bromate formation, brominated DPBs, cyanogen halides, microbial risk management, chloramines, DBP risk management, monochloramine, drinking water contaminants, drinking water systemProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
- 2002 Progress Report
- 2001 Progress Report
- 2000 Progress Report
- 1999 Progress Report
- Original Abstract
8 journal articles for this project