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Several media have been used in treatment plants, however, their efficiency for turbidity removal, which is determined by qualitative indices, has been considered. Current qualitative indices such as turbidity and escaping particle number could not completely measure the efficiency of the filtration system; therefore defining new qualitative indices is essential. In this study, the efficiency of two different dual media filters in turbidity removal was compared in different operating condition using qualitative indices. The pilot consisted of a filter column (1-m depth) in which the filter-1 was consisted of a layer of anthracite (450-mm depth) and a layer of silica sand (350-mm depth); and filter-2 had the same media characteristics except for the first layer that was light expanded clay aggregates (LECA). Turbidities of 10, 20, and 30 NTU, coagulant concentrations of 4, 8, and 12 ppm and filtration rates of 10, 15, and 20 m/h were considered as variables. Results showed that the media of filter-2 is a suitable substitute for the media of filter-1 (P value \ 0.05). Turbidity removal efficiencies in different condition were 79.97 ± 1.79 to 91.37 ± 1.23% for the filter-2 and 75.12 ± 2.75 to 86.82 ± 1.3% for the filter-1. The LECA layer efficiency in turbidity removal was independent of filtration rates and due to its low head loss; LECA can be used as a proper medium. Results also showed that the particle index was a suitable index as a substitute for turbidity and escaping particle number as indices.

In assessing the quality of drinking water in transmission and distribution lines, the study on chlorine reactions is of particular importance. Chlorine decay happens in bulk and wall and it is mainly affected by the water age which depends on the transmission line length. Residual chlorine concentration in Isfahan water transmission line (IWTL) is simulated through three decay models, namely the first order, parallel first order and second order single reactant (SR model) which incorporated in EPANET and EPANET MSX, respectively. The results of the models are compared through two approaches, one is the one-part approach (OPA) whereby chlorine decay simulation is performed taking into account the whole line as one section and the second is multi-part approach (MPA) whereby the line is divided into two sections and decay coefficients of chlorine for each section are separately determined. Results show that in the OPA, the SR model in summer and the parallel model in winter are the best kinetic models. While in the MPA, the results of first order model has the same order of accuracy as the more complex models of parallel and SR models. In general, the simple first order model in the MPA applied by EPANET2.0 s/w provides acceptable level of accuracy in compare to the complex models applied in EPANET MSX s/w. The average RMSE volumes are reduced from 0.078 in OPA to 0.029 in MPA in summer and from 0.059 to 0.015 in winter, indicating that the dividing the line in simulation procedure and considering the individual decay coefficient for each part, considerably improves the results, more effectively than the application of advanced decay models.

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