The use of magnetic bed conditioning and pH control to enhance filtration by natural titanomagnetite

The fine particle size and magnetic properties of natural titanomagnetite (TM) iron sand offer options for novel granular water filtration systems. The isoelectric points (IEPs) of a variety of natural and synthetic TMs were determined to be in the range from 3.60±0.06 to 4.01±0.06. TM beds (125–150 μm particle size) expanded by up to 28% were successfully conditioned with vertical fields of approximately 0.018 T and produced up to a three-fold increase in hydraulic conductivity. Filtration studies showed that the filtration efficiency decreased with bed expansion but that this reduction was more than compensated for by reducing the pH to below the IEP of TM. Backwash performance was improved by magnetic conditioning which allowed higher interstitial flow velocities at a given bed expansion.