This paper, presents a simplified model for predicting chemical chloramine loss in ultrapure water as a function of various measurable parameters, which otherwise requires the simulation of a complex mechanistic model involving the implementation of a number of ordinary differential equations (ODE), using specialised software. The complexity of the mechanistic model is evidenced by its lack of use outside chemical reaction modelling academics. We developed a simplified model as a single-line equation with eight fixed coefficients to predict the first-order decay coefficient. The developed model accurately predicts the first-order chloramine decay coefficient as a function of the water pH (7.5-8.5), chlorine-to-ammonia mass ratio (3.0-4.5), initial chloramine dose (1.5-5.0 mg/L), and alkalinity (up to 200 mg/L CaCO3) at 25 °C in ultrapure water samples. The user either has to input all the above mentioned water quality parameters or can evaluate the relative effect of water quality parameters individually or collectively, by using a relative model. The decay coefficient for temperature between 4 and 35 °C can be obtained by applying Arrhenius equation. To predict the chloramine profile, the initial chloramine concentration has to be decreased slightly (4% when pH < 7.8 to no adjustment at pH > 8.2) before the first order model is applied. Such a model will help in adding the effect of other parameters such as NOM, bromide, and microbiological decay in the future to facilitate easy adaptation by the water utilities.

This work aimed to study the kinetics of arsenic absorption by Eichhornia crassipes and Lemna valdiviana under pre-established conditions of pH phosphate and nitrate in the nutrient solution. Additional aims were to evaluate the conversion kinetics between As(III) and As(V), and the effect of arsenic concentrations on development of the species. The plants were cultivated in nutrient solutions containing different arsenic concentrations: 0, 0.56, 0.89 and 1.38 mg L-1 for the water-hyacinth, and 0, 0.13, 0.48, 0.99 and 1.4 mg L-1 for Lemna. Monitoring of arsenic removal by the plants was performed by sampling at intervals of 0, 4, 8, 16, 24, 48, 96, 144, 192 and 240 h for the water hyacinth, and 0, 4, 8, 16, 24, 48, 96, 144 and 168 h for Lemna. The samples were submitted to analysis of total arsenic, As(III), As(V) and phosphorus. The first-order kinetics was fit to the arsenic removal kinetics by the plants, and it was observed that the decay coefficient (k) decreased with the increase of its initial concentration in the nutrient solution. For the, absorption was observed after 96 h of culture, the time coinciding with the greatest As(V) concentrations. For Lemna, the metal was only absorbed by the plant after decay of the phosphate levels of the medium, which occurred at 48 h. Concentrations above 1 mg L-1 implied deleterious effects in both plant species and in the phytoremediation process, and the bioaccumulation factor decreased for concentration above this for both E. crassipes and L. valdiviana.