Roles of bacterial cell and extracellular polymeric substance on adsorption of Cu(II) in activated sludges: A comparative study

Abstract

Activated sludge adsorbs heavy metals in the water during the water treatment process, which brings trouble to the subsequent treatment of the waste sludge. However, the role of bacterial cell and extracellular polymeric substance (EPS) on adsorption of heavy metal remains elusive. Here, we found the anammox sludge possessed the highest Cu(II) adsorption capacity (14.68 mg/g SS), followed by the activated sludge and denitrifying sludge. The Cu(II) adsorption capacities of sludges increased when sludge dosages and initial Cu(II) concentrations increased. These sorption processes were all well explained by Langmuir isotherms. Analysis of the Cu(II) distribution found that Cu(II) adsorbed by bacterial cells (35 %) were much higher than the Cu(II) adsorbed by EPS (4–11 %). This implied that bacterial cells were the most important carrier for the sludge to adsorb Cu(II). Additionally, the difference in Cu(II) adsorption of sludge was due to the inconsistent Cu(II) content adsorbed by EPS. Correlation analysis showed that the EPS content highly positively correlated with the Cu(II) content adsorbed by EPS, which indicates that the EPS content was crucial factor causing the difference in Cu(II) adsorption. FITR analysis shows that another key factor for disparate Cu(II) adsorption was functional groups, including amide I and amide II of protein, C–H from aliphatic, as well as OH and CO from carboxylic acid. This study provides more information for understanding the role of the bacterial cell and EPS in the adsorption of heavy metals, which might provide a theoretical basis for the treatment of heavy metals-containing sludge.