Monochloramine dissipation mechanisms in storm sewer systems

• Author / Creator

  Zhang, Qianyi

• Many municipalities in Canada and all over the world use chloramination for drinking water secondary disinfection to avoid DBPs formation from conventional chlorination. However, the long-lasting monochloramine (NH2Cl) disinfectant can pose a significant risk to aquatic life through its introduction into municipal storm sewer systems and thus fresh water sources by residential, commercial, and industrial water uses. To establish guidelines for total active chlorine (TAC) containing water discharge in storm sewers, the stormwater TAC concentration was monitored in Edmonton, Alberta, Canada, during the summers of 2015 and 2016. The results showed that TAC concentration varied from 0.02 to 0.77 mg/L in summer 2015, which exceeds the discharge effluent limit of 0.02 mg/L. As compared to 2015, the TAC concentrations were significantly lower during summer 2016 (0 to 0.24 mg/L), most likely because of the higher precipitation during summer 2016, which probably reduced outdoor tap water uses. Other physicochemical characteristics of stormwater and biological community distribution of sewer pipe biofilm were analyzed, and no significant difference was found during these two years. The statistical analysis of NH2Cl decay laboratory experiments illustrated that natural organic matter (NOM) concentration is the dominant factor in determining the NH2Cl decay rate in stormwater samples. The NH2Cl dissipation mechanisms were first studied in the presence of tap water, as it is the major source of TAC in storm sewers. A good model allowing prediction of NH2Cl loss in tap water can assist in the understanding of NH2Cl dissipation mechanisms in stormwater. In tap water, the NH2Cl loss rate can be influenced by temperature, pH, Cl/N molar ratio, the initial NH2Cl and NOM concentrations. In this research, a kinetic model was developed to predict the NH2Cl loss under various conditions. A temperature-dependent model was also developed. As NOM is the dominant factor that contributes to the NH2Cl decay in stormwater, to study the NH2Cl dissipation mechanisms, the reactions between NOM and active chlorine species were first studied. In this research, it is proposed that NOM reacts with both NH2Cl and free chlorine released from NH2Cl auto-decay. Based on this assumption, a kinetic model was developed and applied to estimate the NH2Cl decay in stormwater samples, and the modeling results matched well with the experimental data under all the conditions. Further, the stormwater dissolved organic matter (SWDOM) collected from various neighborhoods were analyzed by FTIR and fluorescence EEM techniques. Humic substances were found to be dominant in SWDOM both before and after chloramination. To study the NH2Cl biological decay, stormwater biofilms were cultured in annular reactors on PCV and cement materials under operational conditions similar to the storm sewer environment. The results indicate that under the same operational condition, higher abundances of total bacteria, ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria functional gene copies could be detected on cement slides as opposed to those on PVC materials. Further, batch experiments were conducted to study the NH2Cl dissipation kinetics in the presence of stormwater biofilms. Three pathways that contribute to NH2Cl decay were evaluated: (i) direct NH2Cl reaction with biofilm, (ii) AOB cometabolism, and (iii) the NH2Cl reaction with AOB utilized associated products, and a kinetic model was developed to predict these dissipation processes in storm sewers. The modeled results showed good matches with the experimental data, which is suggested that this model can be used to describe the NH2Cl dissipation under various stormwater conditions. Finally, the NH2Cl auto-, chemical and biological dissipation pathways were summarized in this research. Field tests were conducted to study the NH2Cl dissipation with continuous tap water discharge into storm sewers. The results showed a significant decrease of NH2Cl concentration from the discharge point to the sampling point at the beginning of discharge, while the decreases reduced with discharge time. To describe this continuous discharge process, a time coefficient f was introduced into the model. With the calibration by f, the modeled results can describe well the sampling data under various discharge times. The field sample analysis and model development in this research not only can be applied to the regulation of tap water outdoor discharge in Edmonton, but also can provide useful information for the stormwater chloramination studies in other regions.

• Subjects / Keywords

  • Storm sewer
  • Dissipation
  • Monochloramine

• Graduation date

  Spring 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R39K4678H

• License

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