The efficacy of sand-immobilized organoclays as filtration bed materials for bacteria

Abstract Previous research has shown that montmorillonite clays exchanged with cationic surfactants including cetylpyridinium (CP), hexadecyltrimethylammonium (HDTMA), and cetyldimethylethylammonium (CDEA) were effective in reducing Salmonella enteritidis colony counts in bulk antibacterial assays. In order to increase the porosity (and hydraulic conductivity) of these materials for use in filtration beds, organoclays were tightly adhered and immobilized onto the surface of sand. Bulk antibacterial assays performed with 10 mg of the sand-immobilized organoclay (S/IOC) showed that the composite materials retained their antibacterial activity after processing. Reductions in plate colony counts ranged from 16.5% for sand-immobilized CP-exchanged sodium montmorillonite to 83.9% for immobilized CDEA-exchanged low pH montmorillonite. The sand/adhesive matrix and sand-immobilized activated charcoal failed to produce any significant decreases. Pilot studies with columns containing 1.0 g of S/IOC showed that maximal filtration efficiency was obtained at a filtration rate of 1.0 ml/min. Initial column studies with Salmonella suspensions at a concentration of 3.0×10 8  cfu/ml, produced reductions in colony plate counts varying from 28.5% for immobilized CP-exchanged calcium montmorillonite to 59.5% for immobilized CDEA-exchanged low pH montmorillonite. The sand/adhesive matrix and immobilized activated charcoal yielded much lower reductions (7.6% and 10.4%, respectively). Studies with Escherichia coli suspensions (3.0×10 7  cfu/ml) indicated reductions varying from 59.3% for immobilized CP-exchanged calcium montmorillonite to 99.9% for immobilized CDEA-exchanged low pH montmorillonite. These initial results suggest that S/IOC can be effective in reducing microbial numbers in wastewater following some modifications.