Simulation of in-situ bioremediation of phenol contaminated sandy aquifers .2. Effect of phenol concentration

Hydraulic conductivity reduction caused by enhanced biological growth in sand was investigated. Studies were conducted using columns packed with three different sand sizes of 0.2, 0.3, and 0.4 mm. Phenol was used as a growth substrate at 15, 50, and 100 mg/L. Variations in piezometric head, substrate concentration, and biomass measured as volatile solids, were monitored in space and time. Reductions in hydraulic conductivity due to microbial growth were found to be 72% for the 0.4 mm, 82% for the 0.3 mm, and 86% for the 0.2 mm sand at phenol concentration of 15 mg/L. Similarly of 50 mg/L, the reductions were 94% for 0.4 mm sand, and 96% for 0.3 mm sand. Finally, at 100 mg/L, the reductions were 96% for 0.3 mm, and 98% for 0.2 mm sand. Phenol removal efficiencies varied from 88% to 94% depending on influent concentration and sand size. Hydraulic conductivity reduction correlated with average biomass density when biofilm density is high and was adversely affected by reduction in specific surface area. Anaerobic biofilms developed at phenol concentrations of 50 and 100 mg/L markedly reduced hydraulic conductivities of all three sand sizes by virtue of their gaseous biodegradation end products. At phenol concentrations of 50 and 100 mg/L hydraulic conductivity correlated with biomass densities per unit mass of sand and was less affected by biofilm thickness and specific surface area.