How does the pre-treatment of landfill leachate impact the performance of O3 and O3/UVC processes?

In this study, O-3 and O-3/UVC processes were evaluated for the treatment of landfill leachate after biological nitrification/denitrification, coagulation, or their combinations. The O-3-driven stage efficiency was assessed by the removal of color, organic matter (dissolved organic carbon (DOC) and chemical oxygen demand (COD)), and biodegradability increase (Zahn-Wellens test). Also, fluorescence excitation-mission matrix (EEM) and size exclusion chromatography coupled with OC detector (SEC-OCD) analysis were carried out for each strategy. The bio-nitrified-leachate (L-N) was not efficiently mineralized during the O-3-driven processes since the high nitrites content consumed ozone rapidly. In turn, carbonate/bicarbonate ions impaired the oxidation of the bio-denitrified-leachate (L-D), scavenging hydroxyl radicals (HO center dot) and inhibiting the O-3 decomposition. For both bio-leachates, only O-3/UVC significantly enhanced the effluent biodegradability (>70%), but COD legal compliance was not reached. EEM and SEC-OCD results revealed differences in the organic matter composition between the nitrified-coagulated-leachate (L-NC) and denitrified-coagulated-leachate (L-DC). Nonetheless, the amount of DOC and COD removed per gram of ozone was similar for both. Cost estimation indicates the O-3-driven stage as the costliest among the treatment processes, while coagulation substantially reduced the cost of the following ozonation. Thus, the best treatment train strategy comprised L-DC (with methanol addition for denitrification and coagulated with 300 mg Al3+/L, without pH adjustment), followed by O-3/UVC (transferred ozone dose of 2.1 g O-3/L and 12.2 kJ(UVC)/L) and final biological oxidation, allowed legal compliance for direct discharge (for organic and nitrogen parameters) with an estimated cost of 8.9 (sic)/m(3) (O-3/UVC stage counting for 6.9 (sic)/m(3)). (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

In the study, O-3 and O-3/UVC processes were evaluated for treating landfill leachate. O-3/UVC significantly improved effluent biodegradability, but COD legal compliance was not reached. Analysis revealed differences in organic matter composition between nitrified-coagulated and denitrified-coagulated leachate.