Pretreatment using UV combined with CaO₂ for the anaerobic digestion of waste activated sludge: Mechanistic modeling for attenuation of trace organic contaminants

Trace organic contaminants (TOrCs) in waste active sludge (WAS) have caused many concerns due to their recalcitrance and detriment to the performance of anaerobic digestion (AD). In this study, UV (2 h) combined with calcium peroxide (CaO₂, 0.1 g g⁻¹-VSS (VSS, volatile suspended solid) was proposed as a suitable sludge pretreatment to enhance the AD performance with an increase in the production of maximum total short-chain fatty acids (421.3 %) and methane (119.2 %). Meanwhile, above 50 % removal efficiency for 19 detected TOrCs was achieved. UV and CaO₂ had a synergistic effect on the subsequent AD of WAS. Both UV and Ca(OH)₂ produced by CaO₂ played important roles in the dissolution of WAS and the subsequent AD, while UV-direct and ^[rad]OH-indirect photolysis accounted for TOrCs attenuation. In order to predict TOrCs attenuation by UV/CaO₂ treatment, a TOrCs photolysis model was tentatively established using carbamazepine as an indicator. This predictive model expressed a good prediction with adj-R² = 0.94, and the difference of predicted and measured values was within 27.3 %. This work evaluates a sludge pretreatment for simultaneously TOrCs attenuation and methane accumulation, laying foundation for promotion of sludge resource recycling.