Bioregeneration Of Granular Activated Carbon Loaded With Phenol And P-Nitrophenol: Effects Of Physico-Chemical And Biological Factors
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Date
2015-09
Authors
Chan, Poh Ying
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Abstract
Bioregeneration is defined as a process during which the adsorbent surface is renewed by living microorganisms for further adsorption. The effects of acclimated biomass concentration, adsorbent dosage, type of granular activated carbon (GAC) and biomass acclimation concentration on the efficiency and rate of bioregeneration of GAC loaded with phenol and p-nitrophenol (PNP) were investigated by determining the time courses of adsorbed substrate amount and residual substrate concentration during bioregeneration under the sequential adsorption and biodegradation approach. The mean bioregeneration efficiencies of phenol- and PNP-loaded GAC were found to be 78 ± 2 % and 77 ± 1 %, respectively. The results revealed that increasing the acclimated biomass concentration and adsorbent dosage did not have an observable effect on the bioregeneration efficiencies of phenol- and PNP-loaded GAC. Additionally, bioregeneration efficiencies of phenol-loaded GAC 830 and GAC 1240+ did not show any observable difference but the bioregeneration efficiency of PNP-loaded GAC 1240+ was greater than that of PNP-loaded GAC 830. This indicates that the improvement of bioregeneration efficiency of spent GAC through further chemical activation was dependent on the type of adsorbate. As for the bioregeneration of phenol-loaded GAC using biomasses acclimated to 350 and 600 mg/L, the bioregeneration efficiencies were found to be almost similar at the same GAC dosage. Two kinetic models incorporating the first-order (Model 1) and Haldane (Model II) biodegradation kinetics, as well as first-order desorption kinetics were developed to describe the time courses of bioregeneration under sequential adsorption and biodegradation approach. The results showed that Model II gave a relatively better fit than Model I in all cases. The desorption rate constant for phenol- and PNP-loaded GAC increased with increasing initial biomass concentration and decreasing GAC dosage, but was not dependent on the types of GAC and biomass acclimation concentration employed in the study. Under biotic conditions, the values of desorption rate constant were greater than those under abiotic conditions at higher initial biomass concentration indicating that the effect of biologically induced desorption was more distinct at higher initial biomass concentrations. Overall, the first-order desorption rate constant was observed to be much smaller than first-order biodegradation rate constant demonstrating that the desorption process was the rate-determining step in the bioregeneration of phenol- and PNP-loaded GAC.
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Chemistry