Remediation of sediments contaminated with PAHs and heavy metals using a sequential bioslurry reactor

A lab-scale sequential slurry reactor was developed to remediate sediments contaminated with both polycyclic aromatic hydrocarbons (PAHs) and heavy metals. The sediment was first treated with an aerobic bioslurry reactor containing a PAH-degrading mixed culture and subsequently treated with a sulfur oxidizing bacterium, Thiobacillus thiooxidans AZ11 in a second bioleaching slurry reactor. The results showed that 82.6% of naphthalene and 92.6% of phenanthrene, in solid phase, were removed in 21 days. However, significant fractions of PAHs, 40.0% of naphthalene and 10.3% of phenanthrene were volatilized. No detectable levels of PAHs were found in the liquid phase after 3 days and the highest MPN counts occurred at Day 3 and decreased thereafter. These results suggest that biodegradation was limited by the dissolution of PAHs from sediments. The optimum culture conditions for T. thiooxidans AZ11 were studied. With the decrease in the initial pH, the time to reach a steady state was shortened. The optimum sulfur/sediment ratio was determined to be ! 0.04 W/W, and solid content ! 30% was inhibitory due to the buffering capacity of the sediment. Under the optimum conditions, the PAH treated sediment was treated in a bioleaching slurry reactor. Results showed that 94% of 3500 mg/kg Zn, 70% of 420 mg/kg Cu, 54% of 105 mg/kg Pb, and 46% of 8.5mg/kg Cd were removed from the sediment in 8 days.