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 us ed as a growth substrate at 15, 50, and 100 mg/L. Variations in piezom etric head, substrate concentration, and biomass measured as volatile solids, were monitored in space and time. Reductions in hydraulic cond uctivity 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 concentratio n 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 w ere 96% for 0.3 mm, and 98% for 0.2 mm sand. Phenol removal efficienci es varied from 88% to 94% depending on influent concentration and sand size. Hydraulic conductivity reduction correlated with average biomas s density when biofilm density is high and was adversely affected by r eduction in specific surface area. Anaerobic biofilms developed at phe nol concentrations of 50 and 100 mg/L markedly reduced hydraulic condu ctivities of all three sand sizes by virtue of their gaseous biodegrad ation end products. At phenol concentrations of 50 and 100 mg/L hydrau lic conductivity correlated with biomass densities per unit mass of sa nd and was less affected by biofilm thickness and specific surface are a.