Combining thermophilic aerobic reactor (TAR) with mesophilic anaerobic digestion (MAD) improves the degradation of pharmaceutical compounds.

The removal efficiency of nine pharmaceutical compounds from primary sludge was evaluated in two different operating conditions: (i) in conventional Mesophilic Anaerobic Digestion (MAD) alone and (ii) in a co-treatment process combining Mesophilic Anaerobic Digestion and a Thermophilic Aerobic Reactor (MAD-TAR). The pilot scale reactors were fed with primary sludge obtained after decantation of urban wastewater. Concerning the biodegradation of organic matter, thermophilic aeration increased solubilization and hydrolysis yields of digestion, resulting in a further 26% supplementary removal of chemical oxygen demand (COD) in MAD-TAR process compared to the conventional mesophilic anaerobic digestion. The highest removal rate of target micropollutants were observed for caffeine (CAF) and sulfamethoxazole (SMX) (>89%) with no substantial differences between both processes. Furthermore, MAD-TAR process showed a significant increase of removal efficiency for oxazepam (OXA) (73%), propranolol (PRO) (61%) and ofloxacine (OFL) (41%) and a slight increase for diclofenac (DIC) (4%) and 2 hydroxy-ibuprofen (2OH-IBP) (5%). However, ibuprofen (IBP) and carbamazepine (CBZ) were not degraded during both processes. Anaerobic digestion affected the liquid-solid partition of most target compounds. Sorbed fraction of pharmaceutical compounds on the sludge tend to decrease after digestion, this tendency being more pronounced in the case of the MAD-TAR process due to much lower concentration of solids.

Modelling PAHs removal in activated sludge process: effect of disintegration.

The removal of polycyclic aromatic hydrocarbons (PAHs) in activated sludge was evaluated using two laboratory-scale bioreactors, coupled or not with a disintegration system (sonication). Mass balances performed on each system underlined that PAHs removal was significantly improved after sludge disintegration, especially for the higher molecular weight PAHs studied, which tended to adsorb to suspended matter. A model was developed in order to study the effect of sludge disintegration on the content of dissolved and colloidal matter (DCM), and to predict the potential impacts on PAHs availability and degradation. Results showed that this new model was efficient for capturing apparent degradation improvement trends and for discriminating between the involved mechanisms. This study showed that DCM content increased after sludge disintegration, and proved to be the main driver for improving PAHs apparent degradation.

Modelling PAH partitioning during sludge disintegration: The key role of dissolved and colloidal matter.

The partitioning between solids and the aqueous phase largely controls the fate of PAH compounds in biological treatment. The prediction of PAH sorption behaviour into activated sludge was investigated here. The suitability of a three-compartment model to describe partitioning in such a complex matrix was first evaluated by adding increasing quantities of dissolved and colloidal matter (DCM) (from 0 to 34.9% of the total matter). In a range of DCM concentrations varying from 0 to 1.4 g L-1, the PAH aqueous fraction, including both freely dissolved and sorbed to DCM molecules, increased from 9.9% to 33% for naphthalene (the most soluble PAH) and from 0.29% to 13.3% for indeno(1,2,3,c,d)pyrene (the least soluble PAH tested). The sorption of PAHs on dissolved and colloidal matter (DCM) was assessed by determining two partitioning constants (KPART and KDCM) for the 16 PAHs listed by the US EPA. New experiments were carried out for model validation and show that the model properly predicts the PAH partitioning following sludge disintegration by sonication.