Single and Mixed Surfactants-aided Removal of Mixed Toxic Metals and Petroleum Hydrocarbons in Contaminated Soil: Batch and Column Studies

摘要

Indiscriminate disposal of different kinds of wastes on soil at auto-repair sites in Makurdi, Nigeria is becoming an environmental issue and the restoration of impacted soil is a challenge. The potential of single surfactants and their binary blends to remove mixed contaminants were evaluated via bench scale soil washing experiments. Impacted soil samples from auto-repair site, located in Makurdi Nigeria was assayed for Cd, Cu, Ni, Pb, Zn and total petroleum hydrocarbon (TPH) concentrations. Batch and column soil washing experiments were designed to assess the effectiveness of the single surfactants (sodium dodecyl sulphate (SDS) and Triton x-100 or their binary blends to remove the mixed contaminants with the view to optimizing operating conditions such as surfactant initial concentration (10-150 mm), surfactant initial pH (3-12), soil/liquid ratio (1:50-1:1 g/mL), washing time (30-240 min) and % w/w of surfactant in blend. Prior to soil washing, the critical micelle concentration (CMC) of the surfactants were measured to be: SDS (8.50 mm) and Triton x-100 (0.25 mm. Results of batch soil washing experiments for the two surfactants showed that % contaminants removal increases as the initial surfactants concentration increases, decreases as pH increases, increases as S/L ratio decreases and increases as washing time increases. Results of column experiment showed that % contaminants removal decreases with time. Synergism parameter showed more synergistic effects in the binary blend and hence was more effective than the individual surfactants. Reasons for these behaviors have been suggested.