Cadmium transfer and distribution in a multi-species biofilm and the impact on naphthalene removal

Biofilm technology is being introduced into bioremediation of contaminated soils and underground water, in the form of biofilm barriers. However, the low availability of polycyclic aromatic hydrocarbons (PAHs) and toxicity of the frequently accompanying heavy metals may limit its application. The objective of this study was to investigate the mass transfer and distribution of cadmium (Cd) into the biofilm matrix and the impact caused by it. The influences of pH value, presence of an alternative substrate and increased dissolved oxygen were examined. As the pH value increased, cadmium sorption in the biofilm increased and naphthalene removal decreased. Ten mg/L of cadmium was enough to show a significant impact on biofilm when the pH was above 7.5. The cadmium minimum inhibition capacity was determined to be 5μgCd/mgVS. Acetate, added as an alternative substrate, competed with naphthalene and did not demonstrate the ability to reduce cadmium toxicity. Hydrogen peroxide, added to supplement the dissolved oxygen, accelerated the cadmium uptake/efflux cycle, making the biofilm more vulnerable to cadmium attack. Cadmium was shown to transfer faster than naphthalene into biofilm, and the removal of naphthalene in the presence of cadmium was retarded and reduced.