Optimization of operational conditions using the experimental design method to remove Escherichia coli from contaminated groundwater by an adsorbent material prepared from Moroccan oil shales

Abstract The aim of the present study is to investigate the removal of Escherichia coli (E. coli) strain from contaminated groundwater using an adsorbent material prepared from Moroccan oil shales extracted in the Timahdit region (layer X). Several factors were studied and optimized using the experimental design method based on the Plackett-Burman Experimental plan (PBE); namely, the bacterial suspension concentration (105-108 CFU/mL), the adsorbent mass (1-30 mg), the pH (3-9), the temperature (20-37°C), the contact time (5-360 min) and the stirring speed (45-150 rpm). Data analysis, by the PBE model, showed that the bacterial suspension concentration, the adsorbent mass and the stirring speed are the most significant factors that influence the removal of E. coli. The optimum process conditions were found with a suspension concentration below 5×107 CFU/mL, about 15.5 mg of the adsorbent material and a stirring speed over 97.5 rpm at 28.5°C and pH 6 during 182 min. Under these conditions, the adsorption efficiency of E. coli reached 70.57%.