USE OF DUAL-MEDIA FILTERS CONSISTING OF S AND AND BIOLOGICAL ACTIVATED CARBON

Biological filtration is a treatment process that allows to reduce bot h the concentrations of biodegradable organic matter and precursors of disinfection by-products. To improve this technique, the effects caus ed 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 materia ls during backwash as well as the level of mixing of the filtering mat erials in the filter were measured during tile test. The results have shown that when the temperature of the raw water is higher than 10 deg rees C, it might be necessary to increase the frequency at which the f ilters are backwashed to control the growth of higher level microorgan isms. The height of submersion above the filters does not have any eff ect on the rate of load loss in sand and activated carbon biological f ilters. Conversely, when these two materials are not well separated. L ye have observed higher rates of head loss.