| N-chloramines, which are oxidants produced in chlorine-disinfected wastewaters, were determined using liquid chromatography (LC) and flow injection analysis (FIA). A detector selective for N-chloramines was constructed based on post column derivatization in acidic iodide solution followed by electrochemical detection of the I2/I3- product. N-chloramine recoveries were evaluated as a function of LC separation parameters, with the highest recoveries obtained using a reverse-phase (C18) column with a mobile phase consisting of 25--60% acetonitrile/aqueous phosphate solution (pH 7). The detection limits obtained are in the low 10-7 mol/L range, which is 10--1000 fold lower than total residual chlorine concentrations typically found in disinfected water and wastewater.; To study more effective wastewater dechlorination, reduction rates of NH2Cl, N-Cl-piperidine, N-Cl-leucylalanine and N-Cl-alanylalanine were determined by a series of ten alternate dechlorination agents and compared to the commonly employed agent sulfite. Notably, reduction of N-chloroleucylalanine (N-Cl-LeuAla) by thiosulfate was approximately 3 times faster than by sulfite under controlled conditions, while ascorbic acid was found to be 5 times slower. When present in ten times molar excess, iodide was found to be a redox mediator for reduction of N-Cl-LeuAla by sulfite. A packed bed of metallic iron completely reduced N-Cl-LeuAla within 20 sec. A surface-normalized rate constant for reduction by iron was found to be 0.0015 L min-1 m -2 at pH 7.4.; Wastewater samples were collected from a municipal treatment facility and evaluated by LC and FIA. Although individual identities were not determined in LC, wastewater N-chloramine products could be roughly grouped by size and hydrophobicity. Compounds that are hydrophilic and have molecular weights less than 2200 daltons were found to be quickly (<2 min) chlorinated and quickly dechlorinated. Conversely, compounds that are moderately to very hydrophobic and have molecular weights greater than 2200 daltons were found to be slowly chlorinated and slowly dechlorinated. This behavior was observed for all five dechlorination agents evaluated on wastewater samples. Thiosulfate, iron metal, and iodide mediation of sulfite were kinetically more effective dechlorinating agents than sulfite alone. The compounds that were slowly chlorinated/dechlorinated in wastewater exhibit behavior that is similar to the model peptide N-chloramines investigated. |
