Optimization of the landfill leachate treatment by the Fenton process

The Fenton process was used with the objective of improving the biodegradability of the leachate pretreated biologically up to a value compatible with a subsequent biological treatment. The optimum reaction and settlement pH was 3, both for the organic matter removal and for the improvement of the biodegradability. The chemical oxygen demand (COD) removal increased at increasing Fe²⁺ dosages, from 75.6% for 300 mg/L to 89.0% for 1400 mg/L. The most significant enhancement (84.8%) was obtained with 800 mg Fe²⁺/L. However, the biological oxygen demand/chemical oxygen demand ratio (BOD/COD) was almost the same at all the Fe²⁺ dosages, around 0.29. Moreover, varying the H₂O₂ concentration between 600 and 3600 mg/L, COD removal percentages were between 85.9 and 89.0%. However, the BOD/COD ratio increased at increasing H₂O₂ dosage up to 3000 mg/L, from 0.12 at 600 mg/L to 0.29 at 3000 mg/L.     

Inhibition of the activities of β-galactosidase and dehydrogenases of activated sludge by heavy metals

Heavy metal inhibitions of the activities of β-galactosidase and dehydrogenases in activated sludge were studied.The activities of β-galactosidase and dehydrogenases were strongly inhibited by Cd and Hg. To produce 50% inhibition of β-galactosidase by Cd and Hg required 1.3 and 0.004 mmol g⁻¹ MLSS, respectively. In the case of dehydrogenase, 50% inhibition appeared by Cd 0.16 and Hg 0.04 mmol g⁻¹ MLSS, respectively.The inhibitions of the activities of β-galactosidase and dehydrogenases with Cd and Hg were easily recovered with the addition of thiol compounds. Reactivation by thiols suggested that Cd and Hg form reversible mercaptides with SH groups of β-galactosidase and dehydrogenases.The inhibitions of the activities of β-galactosidase and dehydrogenases by Cd and Hg gave reversible non-competitive type of kinetics. The inhibitor constant (K_i) values of β-galactosidase for Cd and Hg were calculated to be 1.6 mM (1.7 mmol g⁻¹ MLSS) and 0.005 mM (0.005 mmol g⁻¹ MLSS), respectively. K_i values of dehydrogenases for Cd and Hg were 0.6 mM (0.3 mmol g⁻¹ MLSS) and 0.02 mM (0.01 mmol g⁻¹ MLSS), respectively.     

Removal of 17α‐ethinylestradiol,salicylic acid,trimethoprim, carbamazepine and nonylphenol through biological carbon and nitrogen removal processes

This study investigated five different trace organic contaminants (TOrCs) (one hormone: 17α‐ethinylestradiol (EE2), two pharmaceuticals: salicylic acid (SA) and trimethoprim (TMP), one analgesic drug: carbamazepine (CBZ), and one surfactant metabolite: nonylphenol (NP)) removal efficiency at a full‐scale Advanced Wastewater Treatment Plant (AWTP). The AWTP achieved average EE2, SA and NP removal over 80% at the biological carbon removal stages. The results also showed a 66% removal of TMP at the nitrogen removal stages. CBZ was recalcitrant throughout the plant, due to its high solubility and low distribution coefficient between wastewater and sludge. Batch experiments were conducted on active and inactive secondary, nitrification and denitrification sludge by adding TOrCs to understand the removal mechanism through sorption and biodegradation. Sorption was the dominant mechanism to remove EE2, SA and NP in secondary treatment processes. In nitrification and denitrification processes, higher percentage of TOrCs removal through biodegradation were observed compared to removal through sorption.