Membrane filtration with rapid pretreatment using adsorbent of submicron particle size

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Normal manufacturer-supplied powdered activated carbon (PAC) was pulverized to reduce the PAC particle size to less than 1 μm; we call the pulverized PAC super-powdered activated carbon (S-PAC). Advantages of S-PAC over normal PAC, mainly in terms of adsorptive removal of natural organic matter (NOM) and geosmin (musty-earthy taste and odor compund), were studied. Batch adsorption kinetic tests and tubular flow reactor tests revealed that S-PAC rapidly adsorbed NOM from water samples. NOM concentration rapidly decreased after S-PAC addition and reached a plateau of practically attainable removal in a contact time of 5 s. Next, S-PAC adsorption as a pretreatment for microfiltration (MF) was studied by using laboratory-scale and bench-scale pilot plants. Use of S-PAC could decrease significantly the detention time for adsorption pretreatment before MF. A detention time of 2.4 s yielded the same NOM concentration in the MF permeate as a detention of 15 min. Use of S-PAC could also decrease the dosage compared with normal PAC by a factor of 1/4. The dosing sequence, PAC followed by coagulant and then MF, showed slightly better NOM removal than the sequence, coagulant followed by PAC and then MF, suggesting that flocculation of PAC particles somewhat hinders adsorbate uptake into PAC particles. Adsorption pretreatment by using this S-PAC removed the geosmin with vastly greater efficiency than by normal PAC. Removal was attained in a much shorter contact time and at a much lower dosage. The S-PAC was also beneficial in attenuating the trans-membrane pressure rises that occurred between both physical backwashings and chemical cleanings. No membrane fouling effect was observed as a result of S-PAC addition before MF.