Free Chlorine Consumption Research Articles

Chlorination of pure bacterial cultures in aqueous solution

The fate and distribution of chlorine in aqueous solutions containing four pure bacterial cultures was studied. Solutions were subjected to chlorination at different initial free chlorine concentrations. Resulting concentrations of residual chlorine were determined by both DPD/FAS titration and membrane introduction mass spectrometry (MIMS). In all cases, false-positive breakpoint chlorination curves, probably attributable to the formation of chloroorganic-N compounds, were observed by DPD/FAS titration, while little or no inorganic residual chloramine was found by MIMS. Free chlorine was observed in similar quantities by both methods after chlorine demand by bacterial cellular materials in solution was satisfied. These results indicated the residual chloramines existed in the form of organic chloramines; these compounds are generally recognized as being poor antimicrobial agents. Further investigation confirmed that the bacterial cells were the source of organic-N compounds. The kinetics of chlorination of pure bacterial suspensions was also studied. The pattern of residual chlorine decay following chlorination of the bacterial suspensions indicated rapid initial free chlorine consumption, followed by slow free chlorine consumption, with trace quantities of inorganic chloramine being formed.

Modeling of the cast iron/drinking water system by electrochemical impedance spectroscopy

Among the various causes of free chlorine consumption in drinking water distribution networks, the internal corrosion of pipes has not been so far seriously considered. This work focused on the corrosion study of cast iron, as a representative material of those networks, in non-chlorinated and chlorinated waters, by both electrochemical impedance spectroscopy and classical photographic observations. The results collected with cast iron rotating disk electrodes show that the behavior of cast iron depends only on the presence or absence of free chlorine and not on its concentration. Moreover, they lead to a scheme of different corrosion products layers based on the porous electrode theory of de Levie. This physical model describes the behavior of cast iron with and without free chlorine and at any time of immersion. The experimental impedance diagrams were at first fitted by the measurement model developed by Orazem et al. in order to identify the stochastic error and to delete non-stationary points. Then the regression of the physical model to the data provided the value of the anodic charge transfer resistance and, in this way, the value of the corrosion current. As the anodic charge transfer resistance was found to have the same order of magnitude as the polarization resistance, a simpler technique than the electrochemical impedance can be used to assess the corrosion rate.

Free chlorine consumption induced by cast iron corrosion in drinking water distribution systems

Among the various causes of chlorine consumption in drinking water distribution networks, corrosion has not been so far seriously considered. This work focused on the corrosion study of cast iron, as a representative material of those networks, by both electrochemical methods (steady-state curves, corrosion potential and electrochemical impedance data) and classical photograph observations in the absence and in the presence of chlorine. From impedance results and photographs, a scheme of the different corrosion products layers, that is based on the de Levie's theory, is proposed. By fitting this physical model to experimental impedance diagrams, the anodic charge transfer resistance can be extracted and thus a reliable value of the corrosion rate can be given. The general conclusion is that free chlorine is not electrochemically consumed at the metal surface though it is more easily reducible than oxygen. Therefore, the corrosion of cast iron pipes induces only a chemical decay of chlorine corresponding to its reaction with ferrous ions released by iron dissolution and the total consumption rate is exactly obtained from the corrosion current density.

Relative importance of the phenomena responsible for chlorine decay in drinking water distribution systems

Free chlorine consumption in distribution systems is due both to chemical reactions occurring in the bulk phase and at the pipe walls. Knowledge of the relative importance of these various reactions is needed in order to improve chlorine decay modeling. Experimental results carried out in this study make it possible to propose a hierarchical classification of the main parameters involved in the free chlorine decay observed in distribution systems. Corrosion of metallic pipe appears to be a major parameter, while synthetic materials are of little influence. The rate of chlorine decay in bulk phase can be estimated according to the TOC and the temperature. Influence of biofilms depends on the BDOC content of water, and on the pipe diameter. Chlorine decay due to corrosion phenomena must be modeled according to a zero order kinetics, while chlorine decay due to other parameters can be modeled according to a first order kinetics with respect to chlorine.

Relative importance of the phenomena responsible for chlorine decay in drinking water distribution systems

Free chlorine consumption in distribution systems is due both to chemical reactions occurring in the bulk phase and at the pipe walls. Knowledge of the relative importance of these various reactions is needed in order to improve chlorine decay modeling. Experimental results carried out in this study make it possible to propose a hierarchical classification of the main parameters involved in the free chlorine decay observed in distribution systems. Corrosion of metallic pipe appears to be a major parameter, while synthetic materials are of little influence. The rate of chlorine decay in bulk phase can be estimated according to the TOC and the temperature. Influence of biofllms depends on the BDOC content of water, and on the pipe diameter. Chlorine decay due to corrosion phenomena must be modeled according to a zero order kinetics, while chlorine decay due to other parameters can be modeled according to a first order kinetics with respect to chlorine

Formation, evolution and modeling of trihalomethanes in the drinking water of a town: II. In the distribution system

Six sampling points located at different distances, two by two (near-far), from the three main supply reservoirs, were selected in the distribution system of the drinking water network of the city of Salamanca in order to follow the evolution of trihalomethanes (THMs). Data obtained were correlated statistically with the chlorination dosages in the treatment plants and the distribution system, the distances run by the water, residual free chlorine and total chlorine, the total organic carbon (TOC), pH and temperature. The prechlorination dosage did not correlate strongly ( P = 0.1268) with chloroform content at the first point of the distribution system, while that of postchlorination and rechlorination did not correlate at all. The organic matter, measured as the TOC, showed a positive correlation ( P = 0.0322), with a consumption of free chlorine ( R = −0.327, P = 0.0190) and total chlorine ( R = −0.290, P = 0.0393) that was proportional to the content in THMs. However, the distance among the six points of the distribution system—an approximate means of estimating the reaction time—yielded conflicting results. Temperature and pH proved to be the parameters with the strongest influence. Temperature alone did not show linear dependence, while pH did ( R = 0.665, P = 0.0001), showing a dramatic increase in THM levels on two sampling dates with exceptionally high pH levels. Functions of these two parameters permitted the elaboration of a predictive mathematical model ( R = 0.995, P <0.0001) in which increasing values of pH and temperature are seen to increase the level of chloroform up to a given temperature value ( T c = 17.30°C) after which a sharp decrease in the chloroform content occurs. This value was comparable with that obtained with a similar model in the finished water treatment plants. A global modeling of both systems (treatment plants and distribution system) was also possible ( R = 0.827, P = 0.0001), with a T c value of 18.74°C for each pH.

The reaction of nucleotides with aqueous hypochlorous acid

It has been found that the rate of consumption of hypochlorous acid by the nucleotides cytidine monophosphate (CMP) and adenosine monophosphate (AMP) increases with decreasing pH. At pH 5.6, CMP and AMP are the primary consumers of free chlorine; at pH 7.6 guanosine monophosphate (GMP), as well as CMP and AMP, react readily with hypochlorous acid. At pH 10, the only consumer of hypochlorite is GMP. A parallel was found between the rate of inactivation of virus and the rate of consumption of free chlorine by two of the nucleotides; both the rate of virus inactivation and the rate of consumption of chlorine by AMP and CMP increase with decreasing pH. Under conditions of virus disinfection, uridine monophosphate (UMP) is quite unreactive with aqueous hypochlorous acid.