This study applied microwave-assisted extraction of chlorogenic acid (CGA) from Coffee liberica L. using ethanol as solvent. It sought to determine the effects of temperature, extraction time, solvent-to-solid ratio, and solvent concentration on the CGA yield expressed as gallic acid equivalent per litre (mg GAE L-1). The values of these factors were varied at three levels each and experiments were implemented using the L934 orthogonal array of the Taguchi design of experiment. Results showed that increasing the solvent-to-solid ratio from 2.5 to 7.5 mL g--1decreased the yield significantly. Conversely, increasing the solvent concentration from 0.6 to 0.7 (v v-1) increased the yield, but beyond this, lower yield was obtained. Likewise, yield increased when the extraction time was increased from 5 to 7 minutes but decreased subsequently when extraction was extended to 10 minutes. Temperature did not show significant effect on yield. Among the factors tested the solvent- to-solid ratio has the most significant effect on yield, followed by solvent concentration and extraction time while temperature had no significant effect. In the Taguchi design the highest yield of 304.90±0.58 mg GAE L-1 was obtained at 90°C, extraction time of 7 minutes, solvent-to-solid ratio of 2.5 mL g-1 and solvent concentration of 0.8 (v v-1). Using the same extraction temperature and time and solvent-to-solid ratio but lower solvent concentration, the confirmatory run resulted is significantly higher yield of 854.35±3.35 mg GAE L-1. Chlorogenic acid was identified in the extract at a concentration of 3152 mg L-1. By applying Soxhlet extraction using the same solvent concentration and solvent-to-solid ratio at the same temperature as that of the confirmatory run the yield was significantly lower at 570.42±5.3 mg GAE L-1.
The kinetics of polychlorinated biphenyl (PCB) degradation in a completely mixed three-phase fluidized-bed biofilm reactor was studied using an initial PCB concentration of 40 ppm. The mixed-culture biofilm grown on cement balls was gradually acclimatized to PCBs prior to the experimental runs. The time course of PCB concentration was monitored and the data obtained were fitted to first, second, and third order rate equations. Analysis of data was based on the assumptions that the PCB concentration was rate limiting and the mixed liquor volatile solids (MLVS) represents the active biomass. Linear regression analysis conducted for the 11 experimental runs show that PCB degradation does not follow first order kinetics. The best fit was obtained for second order in the first six runs when the overall PCB degradation was 80-85% (8-6 ppm final concentration). When the overall degradation increased to 89-92% (4-3 ppm final concentration) from run 7 onwards, the third order gave the best fit. The improved performance of the biofilm to degrade PCBs resulted in a kinetic rate pattern, which shifted from second to third order as the concentration of the PCBs dropped. The rate of PCB degradation was influenced by the presence of mixed culture whose combined attack on and long contact with PCBs resulted in PCB degradation that progressed from one batch to the next.
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