Sanitary landfill is the most common municipal solid waste disposal in Colombia; however, one of the main problems related to the management of sanitary landfills are leachates generated due to high concentration of different contaminants. The characteristics of the landfill leachate can usually be represented by the basic parameters COD, BOD, BOD/COD ratio, pH, suspended solids (SS), total ammonia nitrogen (TAN) and heavy metals; nevertheless, the leachate composition may vary widely from different sanitary landfills. According to Renou et al (2008), there are many factors affecting the quality of leachates, e.g. the age of landfill, precipitation, seasonal weather variation and waste type and composition; being the age of landfill is the most important of these factors. The early-age leachate contains high concentration organic matters and has high carbon/nitrogen ratios, while the mature leachate (under landfilling for at least 5 years) contains fewer biodegradable organic matter and high ammonia concentration. Landfill leachate, especially mature leachate, is difficult to treat using conventional biological processes due to its complex composition, high concentration of ammonia, high pH, and low carbon/nitrogen ratio. In this study, the performance of anaerobic ammonium oxidation process (ANAMMOX process) was analyzed as a promising alternative for reducing the total ammonia nitrogen (TAN) content in mature leachates. The main purpose of this study was to analyze the influence of pH on the performance of the process. The influence of pH over ANAMMOX process has been studied through the observation of four leachate pH effects (6.5, 7.5, 8.2 and 9.2 units in the influent) in a bench-scale sequential batch reactor, using a mature leachate with an ammonia and COD influent concentration of 2793 ± 520 mg/L and 4057 ± 150 mg/L, respectively. The results show that the high (9.2 units) and low (6.5 units) pH influent, have serious influence on the performance of ANAMMOX reactor, because they cause an inhibitory effects in the biological activity and reduction of biomass concentration. During the operation with pH in the influent of 7.5 and 8.2 units, better system behaviors for ammonia removal were observed. For 7.5 units of pH an ammonia removal efficiency of 54.5 ± 12.4% was obtained, and for 8.2 units, an ammonia removal efficiency of 54.0 ± 5.4% was obtained.
The effect of low pH on ANAMMOX reactor is mainly caused by the inhibitions of acidity and free nitrous acid, between them. On the other hand, the influence of high pH on the performance of the system is related to the toxicity of ammonium, because the pH above 9.0 units predominates free ammonia (NH3), which has a toxic effect on microorganisms, in both cases, the problem can be controlled by taking strategies of stopping the feeding of the reactor and adjusting the pH of the influent to a range between 7.5 and 8.2 units.
Keywords: Biological landfill leachate treatment, ammonium oxidation process.
References: Renou, S.; Givaudan, J. G.; Poulain, S.; Dirassouyan, F.; Moulin, P. Landfill leachate treatment: Review and opportunity. Journal of Hazardous Materials. Volume 150, Issue 3, 2008, Pages 468-493.
6d. Water and sanitation
