Insight into the adsorption mechanisms of trace organic carbon on biological treatment process

Abstract

Presence of recalcitrant dissolved organic matter (DOM) could have a significant effect on the adsorption mechanism and capacity of the sludge for many trace organic carbons (TrOCs), especially for the hydrophobic and/or positively charged compounds. In this study, adsorption of three TrOCs on the sludge and humic acid was investigated. The results revealed that neutral hydrophilic compounds had an insignificant interaction with both sludge and humic acid.Positively charged compounds like Fluoranthene, had more affinity toward humic acid than sludge with solid/liquid partitioning of 57, and 3.2 L/gTS for HA and sludge, respectively.Adsorption mechanism of negatively charged TrOCs, was largely determined by strong interaction between adsorbate and adsorbent. Therefore, adsorption intensity (Kf) of Di 2-ethyl hexyl phthalate was 0.5 and 1.13 for the humic acid and the sludge, respectively. By introducing the sludge to the solution of humic acid and TrOCs that already reached equilibrium, the ability of sludge to uptake TrOCs from DOM was also investigated. The findings showed that at the lower concentration, adsorption of humic acid on the sludge was considered as the main removal pathway for the adsorbed emerging contaminants, as 70 mg of HA adsorbed by a gram of sludge.For the higher concentration, desorption of TrOCs from DOM into the sludge comprised 15 to 30% of total removal efficiency.