Effects On Particle Retention In Water Of Deep Bed Filtration

The new sanitary standard for drinking water came into effect on July1,2012andthe turbidity of treated water should be less than1.0NTU. Conventional turbidityinstrument is sensitive to particles under1μm while particle counter is sensitive toparticles larger than1μm, so it will be an important means to improve the water qualitysafety by combining the turbidity instrument with the particle counter together due topathogenic organisms in water is larger than1μm. Filter production monitoring andmodel filter experiments were carried out for filter intercept effects of particulate matterin water as the core content. The main research results of this paper included thefollowing three aspects:(1) The dirt holding capacity of homogeneous sand media was higher than that ofgraded filtering media. The particle removal efficiency was better for the filter mediawith smaller effective media grain size. Homogeneous sand media could effectivelyremove particles in water large than2μm, while graded filtering media of0.5~1.2mmcould retain particles large than10μm well.(2) The particles size, bed depth and configuration of filter media play a key role infiltration process. Homogeneous sand media taken some advantages in head-lossincreasing control, filtered water average turbidity, particles removal efficiency, filternet production ratio and performance index F value. The particle count control mainlydepended on the bed depth, the effect of filter media equivalent depth L/d on particleremoval didn’t be proved. The size range of the particles most difficult to be removedwas3~5μm. The less size and depth of media configuration means higher head lossincreasing, higher filtered water turbidity and particles count, although this configuration could avoid the detrimental effect from turbidity increasing at the end ofrun. All of above, the media configuration with deeper bed depth and more uniform sizedistribution along depth should be regarded as the prior alternative choice for filterdesign and prompting in the future.(3) Actual production monitoring showed that homogeneous sand media couldremove particles larger than2μm well and activated carbon media could retain particlesbetween2~10μm effectively. The result of pilot tests showed that the intercept effect ofturbidity and particle counts ranges: sand filter <anthracite filter <activated anthracitefilter <activated carbon-quartz sand filter.