Effects of Waste Activated Sludge Extracellular Polymeric Substances on Biosorption

Abstract

Extracellular polymeric substances (EPS) reportedly make up approximately half of the organic matter in activated sludge (AS), and therefore strongly influence AS properties. This study evaluated the component fractions of EPS normalized to volatile suspended solids (VSS) in waste activated sludge (WAS) from a trickling-filter-solids contact process (TF/SC) and its ability to biosorb organic matter from raw wastewater with 30 min of contact time. Biosorption is the process in which organic matter (carbohydrates, proteins, humic acids, DNA, uronic acids, and lipids) in a sorbate, such as raw wastewater, sorbs onto a sorbent such as WAS. A statistically significant correlation was found between both the total concentration of EPS and the proteins component of the EPS and the biosorption removal of soluble chemical oxygen demand (sCOD) and truly soluble COD (ffCOD). Thus, the biosorption of soluble forms of COD can accurately be predicted by quantifying just the amount of proteins in WAS-associated EPS. No significant correlations were found for the biosorption of colloidal COD (cCOD). WAS biosorbed 45–75 mg L−1 of COD in 30 min. WAS absorbed or stored the proteins fraction of the soluble microbial products (SMP) during the biosorption process. Higher concentrations of humic acids were found in the biosorption process effluent than in the untreated wastewater, which warrants further study. Longer cation exchange resin (CER) extraction times yielded more total EPS from the sludge: 90 ± 9, 158 ± 3, and 316 ± 44 mg g−1 VSS, for 45-min, 4-h, and 24-h extraction times, respectively. Thus, EPS extracted represented only 9%, 15.8%, and 31.6% of the VSS, respectively, raising questions about whether the accurate characterization of EPS can be performed using the typical extraction time of 45 min due to different extraction rates for different components. It was found that the humic acids fraction was extracted much more slowly than the other fractions.