Abstract
This work was undertaken to investigate the effect of variations of the feed rate on a fed-batch set-up used to degrade xenobiotics. The mixture of substrates was composed of PCP, 2,4,6 TCP and 2,3,5,6 TeCP (pentachlorophenol, 2,4,6 trichlorophenol and 2,3,5,6 tetrachlorophenol respectively). Two acclimated bacteria isolated from soil were used: Pseudomonas aeruginosa and Achromobacter sp. nov. The different flow rates tested were: I: 0.5 ml∙min -1 , II: 1.67 ml∙min -1 and III: 2.00 ml∙min -1 . Our results show that during fed-batch operation the 2,4,6 TCP exhibits an earlier degradation than the other compounds, for all of the flow rates tested. This indicates that in this case the degradation of the most recalcitrant compounds (PCP and 2,3,5,6 TeCP) is benefited by the increase in biomass of bacteria, due to the metabolisation of a less recalcitrant compound (2,4,6 TCP). The defined parameter, specific degradation rate (SDR), was demonstrated to be very useful for comparing the degradation abilities at different flow rates of a fed-batch system. The degradation efficiencies were shown to be higher than 90% for all of the cases and to decrease as the feed rate increases. However, the SDR, a parameter that involves the rate of degradation and the biomass, increases as the flow rate increases. At a feed flow rate of 2 ml∙min -1 SDR reaches a maximum of 12.476 x 10 -10 mgCP∙h -1 ∙CFU -1 . Finally, among the feed flows tested, taking into account both the degradation efficiency and the SDR, 2 ml∙min -1 is the most convenient flow rate for chlorophenol degradation in fed-batch systems. An even higher degradation efficiency (97%) can be achieved by using the feed rate of 2 ml∙min -1 followed by an additional batch post-treatment of 2 h, with a SDR of 13.136 x 10 -10 mg CP∙h -1 ∙CFU -1 . Keywords: Chlorophenol; fed batch system; aerobic degradation; waste treatment; microbial biocatalysis
Highlights
Microbial biodegradation processes in aerobic or anaerobic reactors are among the most widely used biological methods for removing chlorinated phenolic compounds (CP) from contaminated waters
DV .substrate i of concentration (Si) dt dV .Si dt Results and discussion The mixed culture constituted of Pseudomonas aeruginosa where: and Achromobacter marplatensis was able to simultaneously t is the operation time degrade the mixture of highly-substituted chlorophenols PCP, V is the actual volume of reactor
The first term ([dVS/dt]acc) represents the net accumulation of the component i in the control volume V, while F∙Sif represents the input of compound i to the volume control, and the last concentrations were much higher in B than in the fed-batch assays when they were close to zero (Table I)
Summary
Microbial biodegradation processes in aerobic or anaerobic reactors are among the most widely used biological methods for removing chlorinated phenolic compounds (CP) from contaminated waters. The exploration of new cultures capable of degrading xenobiotics without the addition of ancillary carbon sources is an approach that may result in significant cost reductions in the decontamination process. While most researchers have studied biological treatment in batch reactors, several authors have proposed alternate configurations to improve the industrial application of CP degradation (Mun et al, 2008), including fed-batch reactor systems (Bali and Sengül, 2002; De Los Cobos-Vasconcelos et al, 2006). Contrary to the continuous systems, the effluent is not withdrawn until the reactor is full. In this way, high concentrations of organic and toxic compounds are diluted in a large reaction volume, reducing inhibitory/toxic effects. Biological oxidation of these compounds usually takes place at a higher rate (Bali and Sengül, 2002)
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