Remoual mechanisms of lnert particles in slow sand filters

Although slow sand filtration technology is now abouttwo hundred years old, a principle understanding of particleremoval mechanisms has not been developed. Many proposedmechanisms have been introduced, nevertheless, none ofhypotheses have been verif ied. The aim of this research was toinvestigate and verify the inert particles’ removal mechanism(s)in slow sand filters.Lab scale slow sand filters cells were used to test the effects ofdifferent filtration conditions on the removal of artificialturbidity formed by dispersing a set of mono-sized Latexparticles in raw water. In some of the experiments raw waterwas obtained from a raw water tap at Bolton Point WaterTreatment Plant, on Cayuga Lake, in New York, USA. In otherexperiments disti lied water from Cornell UniversityEnvironmental Engineering Laboratory, New York, was used asfilters influent. Filters biological maturity was checked bymeasuring the removal of added E- coli bacteria.Particle’s removal was monitored by a Particle Counter (CoulterMultisizer 10 and a ratio turbidimeter.Biological poison and a disinfectant (chlorine), had been used totest particle removal under no living biology conditions.Microscopic observations using Ebifluorescence Techniquewas used to confirm the results.Some of the major findings of the present research were- Inert particles’ removal in slow sand filtration is mainlyattributed to sticky biofilms below the dirty skin.- Non-screening physical removal mechanlsrnts) has almost noeffect in removing turbidity causing particles in a slow sandfilter.- There has been si ight difference between the eff iciency of abiologically active filter and a filter in which biologicalactivities were ceased.