Use of dual-media filters consisting of sand and biological activated carbon

Biological filtration is a treatment process that allows to reduce both the concentrations of biodegradable organic matter and precursors of disinfection by-products. To improve this technique, the effects caused by (i) variations of the duration of filtration cycles, (ii) height of submersion above the filtering materials, and (iii) the mixture of the filtering materials were observed on a pilot system of 2 m(3)/h. The head loss, turbidity, degree of expansion of the filtering materials during backwash as well as the level of mixing of the filtering materials in the filter were measured during the test. The results have shown that when the temperature of the raw water is higher than 10 degrees C, it might be necessary to increase the frequency at which the filters are backwashed to control the growth of higher level microorganisms. The height of submersion above the filters does not have any effect on the rate of load loss in sand and activated carbon biological filters. Conversely, when these two materials are not well separated. Lye have observed higher rates of head loss.