Simulation of in-situ bioremediation of phenol contaminated sandy aquifers: 1. Effect of sand sizes

Laboratory scale porous media biofilm reactors were used to evaluate the effect of biofilm thickness on media porosity and permeability. Media tested consisted of three different sizes of sand (0.4, 0.3, and 0.2 mm). A set of fifteen columns was used in this experiment, five columns for each size of sand. Columns were operated under constant piezometric head (2.5 m) conditions, resulting in a decreasing flow rate with biofilm development. During the experiment, variations in the piezometric head, substrate concentration, and growth in biomass as well as volatile solids were monitored in space and time. Phenol (15 mg/L) was used as a growth substrate. The reductions in hydraulic conductivity were found to be 97% for the coarse sand (0.4 mm), 96% for the medium size sand (0.3 mm), and 93.7% for the fine sand (0.2 mm). The respective removal of phenol in these columns was 96% for the coarser sand, 97.9% for the medium size sand, and 98.8% for the finer sand. Steady-state effluent phenol concentrations occurred simultaneously with uniform hydraulic conductivity reduction after 50 days of operation. The concentration of volatile solids near the column inlets and outlets, after 58 days of operation, ranged between 9.8 and 4.04 mg/g for the coarse sand, 11.2 and 6.2 mg/g for the medium size sand, and 11.8 and 6.2 mg/g of sand for the fine sand, respectively. The number of colonies near the column inlets and outlets was 2800 × 10¹⁰/mL and 1480 × 10¹⁰/mL for the coarse sand, and 2840 × 10¹⁰/mL and 1520 × 10¹⁰/mL for the medium sand, and 2890 × 10¹⁰/mL and 2120 × 10¹⁰/mL for the fine sand.