Removal of Phenols in Table Olive Processing Wastewater by Using a Mixed Inoculum of Candida boidinii and Bacillus pumilus: Effects of Inoculation Dynamics, Temperature, pH, and Effluent Age on the Abatement Efficiency

Abstract

The main goal of this paper was to assess the ability of a combination of Candida boidinii and Bacillus pumilus to remove phenol in table olive processing water, as a function of some variables, like temperature, pH, a dilution of waste and the order of inoculation of the two microorganisms. At this purpose C. boidinii and B. pumilus were sequentially inoculated in two types of table olive processing water (fresh wastewater, FTOPW and wastewater stored for 3 months-aged wastewater, ATOPW). pH (6 and 9), temperature (10 and 35 °C) and dilution ratio (0, 1:1) were combined through a 2^k fractional design. Data were modeled using two different approaches: Multifactorial Analysis of Variance (MANOVA) and multiple regression. A higher removal yield was achieved by inoculating B. pumilus prior to the yeast (192 vs. 127 mg/L); moreover, an increased efficiency was gained at 35 °C (mean removal of 200 mg/L). The use of two statistic approach suggested a different weight of variables; temperature was a global variable, that is a factor able to affect the yield of the process in all conditions. On the other hand, an alkaline pH could increase the removal of phenol at 10 °C (25-43%).

Keywords: Bacillus pumilus; Candida boidinii; bioremediation; phenols; table olive processing wastewater.

Figure 1

Decomposition of the statistical hypothesis for the effects of inoculation (A); p-level, < 0.0001), combinations of the design (B), p-level, < 0.0001) and time of sampling (C); p-level, < 0.0001) on the removal of phenols on FTOPW (fresh table olive processing water). Mean value ± 95% confidence interval; test 1: inoculum of C. boidinii followed 3 days after by B. pumilus; test 2: inoculum of B. pumilus and 3 days after C. boidinii.

Figure 2

Decomposition of the statistical hypothesis for the effects of inoculation (A); p-level, <0.0001) and combinations of the design (B); p-level, <0.0001) on the removal of phenols on ATOPW (aged table olive processing water). Mean value ± 95% confidence interval. Test 1: inoculum of C. boidinii followed 3 days after by B. pumilus; test 2: inoculum of B. pumilus and 3 days after C. boidinii.

Figure 3

3D plots for the interaction pH/temperature on phenol reduction (test 1: inoculum of C. boidinii followed 3 days after by B. pumilus) in ATOPW (aged table olive processing water) after 3 (A) and 8 days after (B). Test A and B of Table 3.

Figure 4

3D plots for the interaction pH/temperature on phenol reduction (test 1: inoculum of C. boidinii followed 3 days after by B. pumilus) in FTOPW (fresh table olive processing water) after 3 days. Test C of Table 3.

Figure 5

3D plots for the interaction pH/temperature on phenol reduction (test 2: inoculum of B. pumilus followed 3 days after by C. boidinii) in ATOPW (aged table olive processing water) (A) and FTOPW (fresh table olive processing water) (B) after 8 days. Test F and H of Table 3.