Evaluation of the duration of inoculation of a granular pozzolan biofilter from strains of indigenous bacteria and yeasts isolated from a rubber industry effluent
The purifying capacity of a granular biofilter depends on the time necessary for microorganisms to be fixed in the granular bed. This time depends only not on the microorganisms but also on environmental factors such as pH. This study was to investigate the influence of pH on the time required by four microbial strains isolated from the effluent of a natural rubber production plant to settle in the granular pozzolan bed. Two types of endogenous yeasts (LR and LB) and two types of bacteria (BB and BC) were fixed on the pozzolan grains having a size of 300-400 μm. The tests were conducted in a polyvinyl chloride (PVC) column (height 1 m, internal diameter 6 cm). After hydrodynamic characterization of the bed, binding tests of the microorganisms in the bed were carried out at different pH values (4, 5, 6 for yeast and 5, 7, 9 for the bacteria) and at a constant flow rate of 2.6 mL∙s‐1. The hydrodynamic study indicated that the flow state in our column was laminar and the flow was of a piston type. The porosity of the granular bed was 0.64. A pH of 5 was best for the binding and retention of the BC and BB bacteria strains, with a retention rate of 74 ± 2% for BC and 79 ± 1% for BB. This retention was achieved after 28 h for the BC strain and 25 h for the BB strain. However, at pH 9 we observed a reduction of the retained quantity by 20% and bacterial release after the 30th hour of operation. A period of 25 h was required for maximum binding of LB and LR yeast strains. A pH between 5 and 6 generated the best retention rate (80 ± 4%) but at pH 4 we observed a detachment of the yeast strains after the 20th hour of operation.