J. Donald Johnson

Modeling and efficiency of ultraviolet disinfection systems

Abstract Modeling can play a particularly useful role in ultraviolet (u.v.) disinfection because of difficulties in measuring u.v. dose and the immediate results of disinfection. This model predicts bacterial survival in flow-through systems. The calculation takes into account the complex intensity patterns, non-ideal flow patterns, and non-linear curves of log survival vs u.v. dose. Based on the organismal dose-response, the number of survivors in each fraction of the residence time distribution is calculated separately and summed to calculate the average survival. The model uses as input data: the average u.v. intensity within the system, the residence time distribution, and an experimentally determined dose-survival curve in a simplified system where dose can be directly measured. The predictions of the model corresponded well with measured survival in a u.v. pilot plant study. The model was used to show the effects of flow dispersion on average survival by varying residence time distribution. Measures of capacity and efficiency of u.v. systems were derived and illustrated experimentally in simple cylindrical batch units and in two multiple lamp units.

Evaluation of the efficiency of ultraviolet disinfection systems

One problem in using ultraviolet light (u.v.) for full scale wastewater disinfection is the difficulty in measuring the dose of u.v. and in monitoring the immediate results of disinfection. A bioassay method for measuring the average u.v. intensity and the residence time distribution (RTD) was tested on two small and two large multiple-lamp u.v. systems. Spore suspensions of u.v. resistant Bacillus subtilis were injected into the u.v. units as a spike and collected at a known time from injection in the effluent so that the exposure time was known. The survival could be related to a standard curve of survival vs u.v. dose. In one unit the bioassay measurements of intensity corresponded well with the predictions of a method of calculating intensity across a wide range of fluid u.v. absorbance values. The problems with interpreting the results of a continuous flow of the bioassay spores were demonstrated. The measurement of average intensity, RTD, volume of the chamber and the lamp u.v. output enabled us to assign measures of capacity and efficiency to the systems. The analysis illustrated a means of quantitatively isolating the factors involved in the overall efficiency of the disinfection system and a means of comparing different systems.

The reaction of ozone with isolated aquatic fulvic acid

Abstract Aquatic fulvic acid, isolated from a North Carolina bay lake, was reacted with ozone, an alternative oxidant in drinking water treatment. Ozonated samples were acidified, extracted with ether, dried, concentrated, and methylated prior to GC-MS analysis. Identified reaation products include mono-, di- and tribasic aliphatic acids and benzene tricarboxylic acids. The products with the highest relative concentrations were succinic and malonic acid, although all products were at relatively low concentration levels. Many of the products identified in this study have also been seen among the reaction products of fulvic acid and other oxidants, such as Cl 2 , CIO 2 and KMnO 4 .

Effect of monochloramine on isolated fulvic acid

Abstract Monochloramine is interesting both as a selective oxidant of fulvic acid and as a drinking water disinfectant. In this study, the controlled reaction of aquatic fulvic acid with monochloramine did not result in products detectable by ether extraction-gas chromatography-flame ionization detection techniques. Evidence of a reaction was shown by bleaching of the fulvic acid solution (decreased absorbance at 465 nm) and chlorine substitution. Chlorine-containing products were quantified by the total carbon adsorbable organic halide (TOX) parameter. Bleaching and organic chlorine formation were much less extensive than in the reaction of free chlorine with fulvic acid. Monochloramine was shown to produce an organic chlorine fraction more hydrophilic and with higher molecular size than that produced by chlorine and fulvic acid. Results suggest that monochloramine may be useful tool for the investigation of certain humic functionalities because it reacts rather selectively and to a small extent with aquatic fulvic acid.