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Title: Nitrogen Balances in Landfills
Author: S Burton
Author: I Watson-Craik
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_377, Representation ID: 573, Object ID: 1721
This study was commissioned by the former Wastes Technical Division of the Department of the Environment under contract no. EPG 1/7/16. The project transferred to the Environment Agency and became part of the Waste Regulation and Management R and D Programme in April 1996. Objectives The objectives of this two year project are: a to review and report the current understanding of the role and metabolism of nitrogen in the various processes appropriate to landfill wastes. a to interview local landfill operators and determine their views pertaining to landfill nitrogen and ascertain how the research should be directed to best meet their requirements. a to investigate the distribution, role and fate of nitrogen within landfill sites using laboratory based landfill models. a to suggest suitable methods of landfill management likely to lead to the rapid and permanent reduction of the ammonia content of landfill leachate. Background The research programme was set against the need for a greater understanding of the basic microbiological processes which occur during the decomposition of landfill refuse and their relevance to the sustainable management of landfills. Main Findings A study of the current understanding of the role of nitrogen in the various processes pertaining to landfilled waste was completed. Information was obtained from the current literature and consultation with landfill site operators. The review of the current scientific literature revealed fundamental gaps in our knowledge regarding the role of nitrogen and nitrogenous compounds during refuse decomposition which the research programme addressed. What was previously reported in the literature was that the protein present in the organic components of refuse was the source of the ammonia concentrations in landfill leachate. The research approached the study of nitrogen in refuse using three different methodologies, by refuse incubation studies, refuse columns and multi-vessel fermenter systems. To quantify the nitrogenous content in each of the systems novel analytical techniques were devised which pioneered the measurement of the nitrogenous content of decomposing waste. Ammonia is the most important nitrogenous compound in landfill refuse. It persists in landfill refuse because the microbiological and physiological processes which produce it (ammonification) do so at a rate which cannot be met by its utilisation during the growth of microorganisms. Experiments suggested limited uptake of ammonia by bacteria in landfill laboratory models. There was consequently no major route for the removal of ammonia from refuse other than the aerobic treatment of leachate taken from the landfill and treated in aeration lagoons. R and D TECHNICAL REPORT P1-217/TR iii The proportion of ammonia in refuse compared to the total organic nitrogenous pool (3.86% N dry weight), the source of ammonia, was relatively small, between 5% to 10%, indicating that by the end of the active phase of ammonia production the bulk of ammonia was retained in the refuse and only a small proportion (5%) was released into the leachate during anaerobic decomposition. Increasing the ammonia concentrations could reduce the methane production by landfill refuse and may be important in determining the rate of refuse decomposition. Acclimatisation of decomposing refuse to high ammonia concentrations was not seen in laboratory experiments but may be operational over longer time scales. Nitrate and nitrite were not found in the refuse studied and presumably have no role in the mineralisation of landfilled refuse. Treatment of the ammonia in landfill leachate by traditional methods leads to the production of the nitrogenous compound nitrate. Recirculation of nitrate containing leachate could be a viable method for the removal of nitrogen from landfill leachate and may accelerate the decomposition of landfill refuse. Experiments on landfill refuse and nitrate revealed rapid consumption of nitrate and its removal to nitrogen gas after 6 days. The production of methane was inhibited at concentrations of 500 and 1000 mg NO3--N l-1 but recovered rapidly after the consumption of 50 mg NO3--N l-1. The bacterial process of methanogenesis could coexist with the microbial processes which remove nitrate (denitrification) in liquid systems at 5.7 mg NO3--N l-1. Nitrate addition encouraged the removal of certain volatile fatty acids and increased the pH of the leachate. Experiments containing 50 mg NO3--N l-1 revealed that a small proportion of the nitrate (4-7%) was converted back to ammonia and was retained in the refuse. Main Conclusions Anaerobically decomposing landfilled refuse rapidly removes nitrate and represents an effective method of removing nitrate from treated nitrified leachate by recirculation, without the expense of secondary anaerobic leachate treatment. The addition of nitrate to a landfill will inhibit methane production in the short term if applied in similar concentrations to nitrified or treated acetogenic landfill leachate. Rates of consumption of nitrate suggest the stratification of refuse into zones of denitrification and methanogensis during the recirculation of nitrified leachate. Concentrations of 50 mg NO3--N l-1 will allow the rapid recovery of methanogenesis in refuse once the nitrate has been denitrified. High ammonia concentrations may affect the rates of methane production by refuse. Better rates of methane production and anaerobic degradation could come from controlling the ammonia concentration in refuse. The anaerobic decomposition by refuse cultures was not phosphate or nitrogen limited. A reductive nitrogen transformation pathway which converted nitrate to ammonia was found during incubation of refuse cultures. This was capable of reducing 4 -7% of the nitrate added. This may have been caused by the highly reduced conditions of landfill refuse combined with reduction on the surfaces of metals or by microbial enzymes. The reductive pathway competed with the denitrification of nitrate. Greater proportions were reduced when the indigenous bacteria were destroyed by gamma irradiation. Autoclaving prevented significant loss of nitrate following incubation, suggesting that a biotic or cell associated biochemical transformation was involved. R and D TECHNICAL REPORT P1-217/TR iv Binding of ammonia to refuse in refuse cultures appeared to be controlled by pH value, suggesting greater leaching at higher pH values. Incorporation into biomass of the ammonia produced during decomposition appeared insignificant in experiments using heavy isotopes in model landfill systems. Leachate ammonia accumulated during anaerobic decomposition in batch cultures. Nitrogen in refuse did not accumulate significantly during the growth of anaerobic bacteria in refuse columns when supplied with combinations of ammonia and volatile fatty acids. Utilisation of ammonia during bacterial growth is probably not an important route for the nitrogenous components in decomposing landfill refuse. Acknowledgements The authors kindly acknowledge Mr. Ian Wilson and colleagues at Cunninghame District Council for access to their landfill site at Shewalton. We would also like to thank Dr Tom Preston and Dr H. M. Banford at the Scottish Universities Research and Reactor Centre for assistance in the analysis of natural nitrogen isotopes and the irradiation of samples. Two students, Marc Jacobs and Cheryl Posnett, helped on aspects of the project whilst studying for their degrees. We also acknowledge the assistance of the staff at the DoE and ETSU. R and D TECHNICAL REPORT P1-217/TR v R and D TECHNICAL REPORT P1-217/TR vi 1.
Publisher: Environment Agency
Subject Keywords: Ammonia; Landfill; Nitrogen; Bacteria; Leachate; Balance; Wastes; Biomass; Anaerobic; Decomposition
Extent: 137
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