Environmental applicability of chitosan and zeolite for amending sewage sludge

This study investigated the potential leachability of toxic heavy metals and pathogenic reduction in sewage sludge using chitosan and zeolite as adsorbing materials. Experiments were conducted on chitosan-sludge and zeolite-sludge mixtures in the application ratio of 0.1 : 10, 0.5: 10, 1.0: 10, 2.0: 10, 3.0: 10, and 4.0: 10, respectively, and examined their capacities to bind some heavy metals (Zn, Cu, Ni and Pb) deriving from sewage sludge. Acrylic columns packed with chitosan and zeolite-sewage sludge mixtures in optimum ratio 1.0: 10 and 3.0: 10, respectively, were leached with tap water and sewage effluent at different pH levels. Seven eluate fractions were collected from the leaching test at leachant/dry sludge (L/S) ratio fixed to 0.48, 0.95, 1.43, 1,90, 2.38, 2.85, and 3.33 L/kg, respectively, and monitored for heavy metal and fecal coliform reductions. Results from leaching test studies for amended sludge showed that the variation of the observed heavy metal contents were influenced by the pH and eluate fractions of leachants. It was found that from neutral to acid conditions, the mobility of heavy metals in amended sludge mixtures was increased with the decrement of pH value in leachants. Zeolite-sludge was found to have higher percentage of reduced metal bioavailability than chitosan-sludge. It can be seen in column studies, pathogenic reduction in amended sludge mixtures were dependent with eluate fractions and type of amended materials. It was also revealed that chitosan can reduce greater fecal coliform counts in sewage sludge than that of zeolite.