Effects of Turbulence and Temperature on Leachate Chemistry

• Published in: Journal of environmental engineering (New York, N.Y.) N.Y.), 2012-05, Vol.138 (5), p.562-569
• Main Authors: Lozecznik, Stanislaw, Oleszkiewicz, Jan A, Clark, Shawn P, Sparling, Richard, VanGulck, Jamie F
• Format: Article
• Language: English
• Subjects: Applied sciences; Atmospheric pollution; Computational fluid dynamics; Evolution; Exact sciences and technology; General treatment and storage processes; Landfills; Leachates; Pollution; Reactors; Technical Papers; Turbulence; Turbulent flow; Wastes
• ISSN: 0733-9372; 1943-7870
• DOI: 10.1061/(ASCE)EE.1943-7870.0000507

AbstractThis study investigates the role of turbulence and temperature on changes in chemistry (dissolved Ca2+ and pH) of leachate within transmission pipes in bioreactor landfills, using synthetic and real leachate from the Brady Road Landfill in Winnipeg, Manitoba. Sealed reactors with rotating propellers were used to mimic leachate flow through the transmission pipes. The reactors were operated under turbulent conditions at 32, 83, and 180 rpm for 6 h on and 18 h off to represent the daily leachate injection operation of a general landfill. A control reactor was operated parallel to the reactors at 0 rpm. During the Off phase, the reactors were either sealed or open to the atmosphere. Under sealed conditions and pH values lower than 7.2, no significant changes in chemistry were observed for the synthetic or real leachate. However, for the mixers and control reactors containing real leachate at pH values higher than 7.4, pH dropped approximately by 0.3–0.4 units. This is explained by Ca2+ removal as CaCO3 decreasing the carbonate buffering capacity of the leachate, outcompeting the re-equilibration of CO2 evolved to the headspace of the reactors and its pH effect. The geochemical modeling software MINEQL+ was used to verify this interpretation, showing the same pH trend. Under open conditions, CO2 evolution, as it equilibrated with the atmospheric concentration, was responsible for increasing the pH by one unit for the synthetic leachate and between 0.35 to 0.45 units for the real leachate. The control reactor also exhibited an increased of pH under open conditions for the synthetic and real leachate. This shows that temperature had a significant impact on CO2 evolution and leachate pH, and may also affect the concentration of dissolved Ca2+ within the leachate, accumulating as inorganic solids similar to those clogging the leachate transmission pipes.