Micropollutant and Sludge Characterization for Modeling Sorption Equilibria

Abstract

The sorption of hydrophobic micropollutants in sludge is one of the major mechanisms which drive their fate within wastewater treatment systems. The objective of this study was to investigate the influence of both sludge and micropollutant characteristics on the equilibria of sorption to particles and to dissolved and colloidal matter (DCM). For this purpose, the equilibrium constants were measured for 13 polycyclic aromatic hydrocarbons, 5 polychlorobiphenyls and the nonylphenol, and five different sludge types encountered in treatment systems: a primary sludge, a secondary sludge, the same secondary sludge after thermal treatment, after anaerobic digestion, and after both treatments. After thermal treatment, no more sorption to DCM was observed. Anaerobic biological treatment was shown to enhance micropollutants sorption to particles and to DCM of one logarithmic unit, due to matter transformation. Partial least-squares linear regressions of sorption data as a function of micropollutant and sludge properties revealed that sludge physical and chemical characteristics were more influential than micropollutant characteristics. Two models were provided to predict the sorption of such micropollutants in any sludge. To our knowledge, this is the first time that a three-compartment approach is used to accurately model micropollutant sorption in sludge and to understand the driving mechanisms.

Influence of feed characteristics on the removal of micropollutants during the anaerobic digestion of contaminated sludge

“…In SupSS, DCM proportion was enhanced without the denaturing phenomenon reported for thermal treatment [29]. According to the bioavailability hypotheses previously mentioned in Section 3.4, micropollutant bioavailability may have been increased.…”

“…Extraction from inlet and outlet sludge samples and quantification in all extracts were performed in accordance with Barret et al. [29].…”

“…Studies concerning the impact of such pre-treatment on the fate of organic micropollutants are scarce. Whereas ozonation was demonstrated to solubilise PAHs [35], probably because of PAH sorption to the solubilised dissolved and colloidal matter, no PAH transfer into the aqueous phase was detected after thermal treatment [35], or the aqueous fraction was found to decrease in both feed sludge and digested sludge on account of the denaturing of the dissolved and colloidal matter [29]. Usually, the aqueous fraction of micropollutants is assumed to be bioavailable to microorganisms [14,40,41].…”

“…In the first place, hydrophobic material may not be readily accessible for microorganisms, and thus it lowers the overall co-metabolism. Furthermore, it favours the sorption of micropollutants to particles [29] and may thus lower bioavailability. Both these effects may account for the strong negative impact of lipids.…”

Influence of nitrifying conditions on the biodegradation and sorption of emerging micropollutants

“…In most cases, only overall removal efficiencies were determined (Simonich et al, 2002;Clara et al, 2005;Gö bel et al, 2007;Vieno et al, 2007;Smook et al, 2008;Radjenovic et al, 2009), while few studies identified and quantified the removal efficiencies related to the different mechanisms Carballa et al, 2007a;Hoori et al, 2007;Wick et al, 2009;Xue et al, 2010). Activated sludge has proved to achieve a significant removal of many micropollutants (Joss et al, 2005), mostly due to biodegradation or to sorption on solids or colloids (Barret et al, 2010), but little is known about the influence of operational parameters on both mechanisms, which might explain the disparity of removal efficiencies found for similar technologies in the literature (Onesios et al, 2009). Hydraulic retention time (HRT) together with sludge retention time (SRT) govern both reaction time and loading (McAdam et al, 2010), thus affecting biomass activity and concentration.…”