Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all halogenated organic disinfection byproducts (DBPs) in a water sample. TOX performs like “a master parameter”, and its significance to DBP studies cannot be overestimated. TOX can be measured with the adsorption–pyrolysis method based on Standard Method 5320B. This method involves concentration of organic halogens from water by adsorption onto activated carbon (AC), and removal of inorganic halides present on the AC by competitive displacement by nitrate ions. Since AC can also act as a reductant, this work first studied whether the reduction of chlorinated DBPs by AC occurs during the TOX measurement, to what extent the reduction affects the measurement of TOX, what types of chlorinated DBPs can be re...[ Read more ]

Total organic halogen (TOX) is a collective parameter and a toxicity indicator for all halogenated organic disinfection byproducts (DBPs) in a water sample. TOX performs like “a master parameter”, and its significance to DBP studies cannot be overestimated. TOX can be measured with the adsorption–pyrolysis method based on Standard Method 5320B. This method involves concentration of organic halogens from water by adsorption onto activated carbon (AC), and removal of inorganic halides present on the AC by competitive displacement by nitrate ions. Since AC can also act as a reductant, this work first studied whether the reduction of chlorinated DBPs by AC occurs during the TOX measurement, to what extent the reduction affects the measurement of TOX, what types of chlorinated DBPs can be reduced by AC, and how the TOX measurement can be improved.

Chlorinated Suwannee River fulvic acid samples were prepared and pretreated with precipitation/dialysis/ultrafiltration to minimize the chloride levels in the samples. It was found that the fractions of “TOX” in the precipitated, dialyzed and ultrafiltered samples that were reduced by AC in 5-min contact were ~13%, 20% and 24%, respectively. The formation of some N-chloroamino compounds and their reactivity with AC were examined. The results indicate that organic chloramines are one type of DBPs in TOX that can be reduced by AC. It was demonstrated that slight oxidation of AC with ozone (OAC) inhibited its reduction for TOX and meanwhile maintained its adsorption capacity for TOX.

The development of the TOX method in recent years lies in the differentiation of total organic chlorine (TOCl), total organic bromine (TOBr) and total organic iodine (TOI) by detecting halides with off-line ion chromatography. Whether the reduction of brominated/iodinated DBPs by AC occurs during the TOBr/TOI measurement was also examined. The results show that TOBr was sometimes reduced by AC to bromide, but the reduction was not as significant as that of TOCl; the reduction of TOI to iodide was not significant. The results suggested that 10% or less of brominated Suwannee River fulvic acid was reduced to bromide. The method for the TOBr measurement was improved by using OAC when reduction occurred on AC. The improved method was also evaluated on treated wastewater and swimming pool water samples. The effect of quenching time on the TOCl/TOBr measurement was also studied. The appropriate quenching time was found to be 15-60 min.

The improved TOX method was used to determining the TOCl and TOBr levels from different disinfection processes, including chlorination, chloramination, ozonation, and chlorine dioxide treatment. Depending on the NOM sources and disinfection processes, the increments of TOCl and TOBr measured with OAC were 10-20% and 5-10%, respectively. Because of the low TOCl and TOBr concentrations in the chlorine dioxide and ozone treated samples, the differences measured with AC and OAC were not significant. Therefore, the use of OAC in the TOCl/TOBr measurement may give more accurate results for chlorinated and chloraminated samples.

The penetration of (highly) polar brominated DBPs through AC or OAC columns were explored with six simulated drinking water samples and two chlorinated wastewater effluent samples. Both known and unknown polar brominated DBPs were selectively detected with a novel precursor ion scan method using electrospray ionization-triple quadrupole mass spectrometry. The results show that 5-25% of polar brominated DBPs in the drinking water samples penetrated through AC, and higher percentages of polar brominated DBPs in the chlorinated wastewater effluent samples penetrated through AC. Compared with AC, OAC was demonstrated to be an improved adsorbent which can significantly minimize the penetration of polar brominated DBPs during the TOBr analysis.