Predicting biogeochemical calcium precipitation in landfill leachate collection systems.
Clogging of leachate collection systems within municipal solid waste landfills can result in greater potential for contaminants to breach the landfill barrier system. The primary cause of clogging is calcium carbonate (CaCO3(s)) precipitation from leachate and its accumulation within the pore space of the drainage medium. CaCO3(s) precipitation is caused by the anaerobic fermentation of volatile fatty acids (VFAs), which adds carbonate to and raises the pH of the leachate. An important relationship in modeling clogging in leachate collections systems is a yield coefficient that relates microbial fermentation of VFAs to precipitation of calcium carbonate. This paper develops a new, mechanistically based yield coefficient, called the carbonic acid yield coefficient (Y(H)), which relates the carbonic acid (H2CO3) produced from microbial fermentation of acetate, propionate, and butyrate to calcium precipitation. The empirical values of Y(H) were computed from the changes in acetate, propionate, butyrate, and calcium concentrations in leachate as it permeated through gravel-size material. The theoretical and empirical results show that the primary driver of CaCO3(s) precipitation is acetate fermentation. Additionally, other non-calcium cations (e.g., iron and magnesium) precipitated with carbonate (CO3(2-)) when present in the leachate. A common yield between total cations bound to CO3(2-) and H2CO3 produced, called the calcium carbonate yield coefficient (Yc), can reconcile the empirical yield coefficient for synthetic and actual leachates.
GeoEngineering Centre at Queen's-RMC, Department of Civil Engineering, Queen's University, Kingston, ON, Canada K7L 8J9.
Jamie F
JF
VanGulck
R Kerry
RK
Rowe
Bruce E
BE
Rittmann
Andrew J
AJ
Cooke
D000465:Algorithms; D002118:Calcium / Q000737:chemistry*; D002119:Calcium Carbonate / Q000737:chemistry; D002255:Carbonic Acid / Q000737:chemistry; D005285:Fermentation; D005544:Forecasting; D006859:Hydrogen / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D008697:Methane / Q000737:chemistry; D010100:Oxygen / Q000737:chemistry; D012037:Refuse Disposal; D012989:Soil Pollutants / Q000032:analysis*; D013054:Spectrophotometry, Atomic
D007202:Indicators and Reagents; D012989:Soil Pollutants; D002255:Carbonic Acid; D006859:Hydrogen; D002119:Calcium Carbonate; D008697:Methane; D010100:Oxygen; D002118:Calcium