Carbamazepine improves hydrogen production from anaerobic fermentation of waste activated sludge

Abstract

The widespread use of pharmaceuticals sparked concerns about their potential environmental effects. Previous studies demonstrated that most of the pharmaceuticals investigated had detrimental effects on wastewater or sludge treatment. However, it was found in this work that carbamazepine at environmentally relevant levels increased hydrogen production from anaerobic fermentation of waste activated sludge (WAS). Experimental results exhibited that with an increment of carbamazepine from 7 to 51 mg/kg VSS, the maximal hydrogen yield increased from 14.9 ± 0.6 to 23.5 ± 0.3 mL/g VSS. Mechanism analysis showed that carbamazepine accelerated the release of organics from solid to liquid phase, offering more substrates for hydrogen production. Carbamazepine did not affect hydrogen producing processes but inhibited the processes relevant to hydrogen consumption. Molecular docking demonstrated that carbamazepine and sulfite reductase protein were joined by hydrogen bond and ASP-597 and VAL-598 were the active sites. These contributed to the contact between carbamazepine and sulfite reductase, thereby affecting the hydrogen consumption process. The reduced α -helix ratio and α -helix / (β -plate + random coil) values indicated that the presence of carbamazepine led to the destroy of the hydrogen network, leading the collapse of protein structure. Further investigation revealed that carbamazepine reduced the corresponding genes with hydrogen consumption, especially involved in the steps of CO2 → fmdA → Formyl-MFR → 5,10-Methylere-THMPT → mer → 5,10-Methyl-THM(S)PT (CO2-reduction), 5,10-Methyl-THM(S)PT → mtrD/E → Methyl-CoM → mcrA/B → CH4 (CO2-reduction and aceticlastic reaction) and Sulfate → sat → APS → aprB → Sulfite → cysJ → Sulfide (sulfate reduction).