Chlorination of aqueous solutions containing organic nitrogen: Analysis and detection with MIMS

In most “real-world” applications of chlorine to aqueous systems, the interactions between chlorine and organic N-compounds are of concern in terms of both disinfection efficacy and analytical interference. The organic chloramines that are formed in these reactions are much less effective than inorganic chloramines in terms of antimicrobial potential. Conventional analytical techniques for “active” chlorine measurements have demonstrated potential interference by organic chloramines. Therefore, it is necessary to develop a more accurate technique for chlorination process control so as to provide adequate disinfection while limiting the toxicity associated with residual chlorine and DBPs. A membrane introduction mass spectrometric (MIMS) method for differentiation and quantification of free chlorine and inorganic chloramines in aqueous solution was developed based on a low cost mass spectrometer. Several factors were examined for system optimization. Linearity of the response and limits of detection of all inorganic chlorine and chloramines were evaluated. System performance was evaluated with comparison of DPD/FAS titration from chlorination of ammoniacal water, aqueous solutions containing glycine and samples of potable water and wastewater. The MIMS system was applied for purposes of studying the chlorination of aqueous solutions containing model organic N-compounds and pure bacterial cultural solutions. DPD/FAS pure bacterial cultural solutions. DPD/FAS titration was performed in parallel for comparison. DPD/FAS titration yielded false-positive measurements of chloroorganic N-compounds as “apparent” chloramines, while little or no inorganic chloramines were detected by MIMS. in the cases of model organic N-compound chlorination, the breakpoint chlorination curve shape and by-product formation were evaluated and found to be strongly dependent on Cl:N molar ratio, as well as the structure of the compounds. In the cases of bacterial solution chlorination, the results indicated that residual chloramines existed in the form of organic chloramines and the bacterial cells were the source of organic-N. The kinetic study showed a pattern in chlorination of the bacterial suspensions of rapid initial free chlorine consumption, followed by slow free chlorine consumption with trace quantities of inorganic chloramines being formed