Landfill conditions are usually oversimplified, or even misrepresented, when described by laymen. Occasionally, biodegradable substances are found preserved in landfills. This has been held out as evidence that landfills are 'dry tombs.' However, the elevated heat in landfills and the generation of millions of tons of biogas prove otherwise.
Landfills with leachate (moisture from rainfall and groundwater,) which is almost all of them, are very biologically active, and as was mentioned above, there are two very obvious signs of this - an elevated temperature, between 90 degrees Farenheit and 155 degrees Farenheit, and the production of biogas, a mixture of methane and carbon dioxide. Methane is the chemical name for natural gas, which is methane found underground. This is why landfills are now being tapped to retrieve methane. Even the very dry landfill for Tucson, Arizona, produces useful amounts of methane.
Another mischaracterization one hears about landfills is that they are anaerobic, or completely free of oxygen. In fact, scientific studies which measured landfill gases have been published. What these studies find is that once landfills are covered, the oxygen content falls over a period of time from that of the atmosphere, to microaerophillic conditions. This slow decline typically takes about 21 months. Microaerophillic conditions are conditions of low, but not zero, oxygen. Landfills have between .1% and 1% oxygen as a permanent condition, according to the American EPA, after the slow decline in oxygen which follows covering of the landfill. This percentage has actually been measured by many scientists in many different studies. ( See the landfill gas composition table in, "Landfill Gas Basics; Sources; Crawford and Smith 1985; DOE 1995; EPA 1993;" posted at Landfill gas basics )
The significance of this for biodegradation in landfills is that biodegradation in landfills is caused by a very wide variety of microbes. The kinds of microbes found in landfills are microaerophiles, which require some oxygen, but less than that found in the atmosphere; aerotolerant anaerobes, which do not use air, but which are not harmed by it; facultative anaerobes, which can function with or without oxygen, by virtue of having two completely different methods of respiring, and switching between them as needed; and obligate anaerobes, which are harmed by oxygen, but which are protected from the oxygen by biofilms, sometimes called EPS, or exopolysaccharides.
A bare-bones model of events in landfills is as follows: First aerobic, facultative anaerobic, aerotolerant anaerobic, and obligate anaerobic bacteria produce carbon dioxide and acetate in landfills, and then methanogens (a class of anaerobic bacteria, some of which are aerotolerant,) produce methane using the carbon dioxide or acetate as food sources. 1/3 of the methane is generated from hydrogen / carbon dioxide digestion, and 2/3 is generated from acetate digestion. Then microbes that eat methane consume it, and there are both aerobic and anaerobic microbes that eat methane. Furthermore, some microbes that eat methane (Methylomirabilis oxyfera,) liberate oxygen from nitrites, and this may well be why there are always between .1% and 1% of oxygen in landfills. Though I have described it as a sequence, in fact all of these processes occur simultaneously and continuously, after the initial 'start up' of this sequence. This process also occurs in a technology that is growing in importance, anaerobic digesters, which turn organic substances such as manure and crop residues into methane for use as a fuel.
I have identified many microbes, aerobic, anaerobic, facultatively anaerobic, and microaerophillic, which are capable of biodegrading plastic, given assistance from my Earth Nurture additives.
As far as the fate of methane produced in landfills goes, it is increasingly being tapped for the same uses as natural gas. In smaller landfills, up to 100% of the methane produced is eaten by methanotrophs. In large landfills, up to 50% of the methane generated is eaten by methanotrophs. In the past, this fact was unknown, and thus earlier estimates of the methane which would enter the atsmosphere were much higher than the reality. It also turns out that we get less methane out of landfills when we tap them than theory led us to expect, because we are competing with methanotrophs for the methane. In fact, some landfills actually consume more methane than they produce, as they suck methane from the atmosphere to consume it. The methane consumed is not a dead loss, however - the bodies of countless trillions of methanotrophs enrich the soil with their bodies, forming humus, contributing to the life of our biosphere.
Bacteria and protozoa populations in groundwater in landfill area in São Carlos; Rev. Microbiol. vol.30 n.3 São Paulo July/Sept. 1999; http://dx.doi.org/10.1590/S0001-37141999000300003; SP; Roberta Fusconi; Mirna Januária Leal Godinho
Occurrence of microaerophilic bacteria in the water and sediment of a grass carp culture pond; Aquaculture; Volume 103, Issue 2, 1 May 1992, Pages 135-140; doi:10.1016/0044-8486(92)90407-C; H. Sugita, M. Takayamaa, T. Ohkoshib, Y. Deguchia
Landfill Gas Basics; Sources; Crawford and Smith 1985; DOE 1995; EPA 1993; http://www.atsdr.cdc.gov/hac/landfill/html/ch2.html
Methane Generation In Landfills; Renewable Energy, Volume 32, Issue 7, June 2007, Pages 1243-1257, :10.1016/j.renene.2006.04.020 Nickolas J. Themelis, Priscilla A. Ulloa, Earth Engineering Center and Department of Earth and Environmental Engineering, Columbia University, New York, NY 10027, USA
Anaerobic Digestion Fundamentals; a lecture by Dr. Christina Cavinato; posted online at http://www.valorgas.soton.ac.uk/Pub_docs/JyU%20SS%202011/CC%201.pdf
Environ. Sci. Technol. 1998, 32, 2233-2237
Characterization of Landfill Gas Composition at the Fresh Kills
Municipal Solid-Waste Landfill
B A R T E K L U N D , * E R I C P . A N D E R S O N , B A R R Y L . W A L K E R , † A N D
DON B . B U R R O W S ; Radian International, LLC, P.O. Box 201088, Austin, Texas 78720-1088
...Over 250 separate landfill gas samples were collected from emission sources at the Fresh Kills
landfill n New York City and analyzed for approximately 150 different analytes...
TABLE 3. Average Landfill Gas Composition
carbon dioxide 37.14%
[Just shy of 1% oxygen, from 250 separate samples, in an environment often wrongly claimed to be anaerobic. This level of oxygen is called microaerophilic. -TD]
Compost Science Utilization (2007)Volume: 15, Issue: 3, Pages: 184-190 * ISSN: 1065657X
Effect of oxygen concentration on the composting process and maturity
by WeiDong Wang, XiaoFen Wang, JianBin Liu, M Ishii, Y Igarashi, ZongJun Cui
The goal of this research was to investigate the effects of oxygen concentration on the composting process in China. The compost system was composed of cattle manure, chicken manure, and wheat straw combined at a ratio 1:3:6 for a period of 60 days. Microaerobic treatment was attained by manual turning, while aerobic treatment was performed by forced air plus turning. The fermentation parameters such as C/N ratio, composting temperature, liginocellulose content and O2 concentration were determined. Results showed that oxygen concentration of compost in the microaerobic treatment was always lower than 1.5% during composting periods except for the first four hours and oxygen concentration was more than 4.0% in the aerobic treatment at all times. The duration of the thermophilic phase above 50C under microaerobic treatment was 23 days, compared to 15 days under the aerobic treatment. However, the composting temperature at the later phases declined more slowly under aerobic conditions than under microaerobic conditions. The hemicellulose content decreased from 13.9% to 8.0% in the microaerobic treatment, compared to 8.5% in the aerobic treatment. The cellulose content decreased from 21.5% to 16.1% in the microaerobic treatment, compared to 18.0% in the aerobic treatment at the end of composting process. When C/N ratio, NO3 to evaluate compost maturity, the compost matured in 35 days in the microaerobic treatment, compared with 45-50 days in the aerobic treatment. Laboratory culture experiment with compost samples taken at the thermophilic phase corroborated that cellulose degradation was more rapid under microaerobic conditions.
[Oxygen concentration in the atmosphere is about 21%, so this finding means that microaerobic degradation at less than 1/14 the oxygen atmospheric levels at sea level causes much faster and slightly more complete composting than highly aerobic conditions. -TD]
FEMS Microbiology Letters
Volume 114, Issue 3, 15 December 1993, Pages 317-323
Methanogenesis in granular sludge exposed to oxygen
Mario T. Kato Corresponding Author Contact Information, Jim A. Field, Gatze Lettinga
Department of Environmental Technology, Wageningen Agricultural University, Bomenweg 2, 6703 HD Wageningen, the Netherlands
Substrate competition between methanogenic and facultative bacteria under highly aerobic conditions was investigated in batch experiments. Natural mixed cultures of anaerobic bacteria immobilized in granular sludge were able to concurrently utilize oxygen and produce methane when supplied with ethanol as substrate. The most oxygen tolerant sludge converted 3 to 25% of substrate chemical oxygen demand to methane after 3 days while 23 to 2 mg l -1 of dissolved oxygen were present in the media. The tolerance of methanogens to oxygen and their coexistence with facultative bacteria were evident even after long periods of oxygen exposure. Eventually, methane oxidizing bacteria developed in the co-culture. The consumption of oxygen by facultative bacteria, creating anaerobic microniches inside the granules, is hypothesized to protect the methanogens.
[Contrary to popular belief, methanogens (bacteria which generate methane,) can flourish and generate methane in low oxygen conditions, and live in the same environment as bacteria which are using oxygen. -TD]
Volume 18, Issue 2, April 1998, Pages 107-116
Feasibility and benefits of methanogenesis under oxygen-limited conditions
D.H. Zitomera, Corresponding Author Contact Information, a, J.D. Shrouta
Purchase,a Civil and Environmental Engineering, Marquette University, Milwaukee, WI 53201, USA
Methanogenic and aerobic (or microaerophilic) biological processes are often considered mutually exclusive and separated as biological wastewater treatment options. However, under oxygen-limited conditions, both aerobic respiration and methanogenesis can be practically accomplished by a single mixed culture. This paper describes sustained batch culture, oxygen-limited methanogenic serum bottle and bench-scale systems. Serum bottle cultures exhibited methanogenic activity similar to or greater than that of a strictly anaerobic culture maintained in parallel. The COD removal efficiencies of anaerobic, oxygen-limited, and aerobic bench-scale reactors receiving 30,000 mg/l of sucrose were all greater than 93%, a system receiving 1 g O2/LR-day achieved a lower final effluent COD than the strictly anaerobic reactor. After a shock-load of sucrose, the pH recovered in low-aeration batch reactors in 28 to 34 days, whereas anaerobic pH did not recover after 52 days of observation. In the future, methanogenesis under limited-aeration may be employed as an energy efficient treatment option to achieve low final COD concentrations, minimal biosolids generation, and mineralization of a broad range of specific organic chemicals.
[Methanogenic bacteria create just as much, or even more methane, in a microaerophilic environment than they do in an anaerobic environment, contrary to statements which deny that methanogens can even survive in microaerophilic environments. -TD]
Volume 102, Issue 10, May 2011, Pages 5685-5691
Electrolysis-enhanced anaerobic digestion of wastewater
B. Tartakovsky Corresponding Author Contact Information, E-mail The Corresponding Author, P. Mehta, J.-S. Bourque, S.R. Guiot
Biotechnology Research Institute, National Research Council, 6100 Royalmount Av., Montreal, QC, Canada H4P 2R2
This study demonstrates enhanced methane production from wastewater in laboratory-scale anaerobic reactors equipped with electrodes for water electrolysis. The electrodes were installed in the reactor sludge bed and a voltage of 2.8–3.5 V was applied resulting in a continuous supply of oxygen and hydrogen. The oxygen created micro-aerobic conditions, which facilitated hydrolysis of synthetic wastewater and reduced the release of hydrogen sulfide to the biogas. A portion of the hydrogen produced electrolytically escaped to the biogas improving its combustion properties, while another part was converted to methane by hydrogenotrophic methanogens, increasing the net methane production. The presence of oxygen in the biogas was minimized by limiting the applied voltage. At a volumetric energy consumption of 0.2–0.3 Wh/LR, successful treatment of both low and high strength synthetic wastewaters was demonstrated. Methane production was increased by 10 to 25% and reactor stability was improved in comparison to a conventional anaerobic reactor.
[Once again we see that methanogenesis is actually increased by microaerophilic conditions. -TD]
The effect of the supplementation with a primary carbon source on the resistance to oxygen exposure of methanogenic sludge
C. Estrada-Vázquez*, H. Macarie**, M.T. Kato***, R. Rodríguez-Vázquez*, F. Esparza-García* and H.M. Poggi-Varaldo* * CINVESTAV-IPN, Dept. Biotechnology and Bioengineering, Environmental Biotechnology R&D Group, P.O. Box 14-740, México D.F., 07000, México. (E-mail: email@example.com) ** IRD, Marseille, France *** Federal University of Pernambuco, Recife, Brazil
Anaerobic methanogenic consortia have a considerable resistance to oxygen exposure. Yet, most research has been focused on the study of the tolerance to oxygen of anaerobic immobilized biomass. Less is known on the potential of the anaerobic suspended biomass for withstanding exposure to oxygen and the effect of a primary degradable substrate on such resistance. Thus, the objective of this work was to determine the effect of the amount of a primary degradable substrate (sucrose) on the resistance of a methanogenic suspended biomass to oxygen exposure. It was found that the inhibition of disperse anaerobic sludge by oxygen exposure decreases when the concentration of the supplemented carbon source increases. This is in agreement with the fact that aerobic respiration of the added substrate by the facultative heterotrophic bacteria, always present in this type of sludge, has been found in previous studies as one of the main mechanisms protecting methanogens against O2. From a practical point of view, this suggests that aeration of anaerobic systems should be possible without inhibiting the activity of methanogenic bacteria if an adequate ratio between oxygen and COD feeding is maintained. Such a ratio will depend however on the wastewater initial COD concentration.
[Note that the study comments that the co-existence of aerobic bacteria with methanogens protects the methanogenic bacteria more when there is an organic carbon source to nourish the aerobically functioning bacteria. In landfills, this would be everything from rotten tomatoes to wood. -TD]
The Open Waste Management Journal, 2011, 4, 1-19 1 1876-4002/11 2011 Bentham Open Open Access
Oxygen Effects in Anaerobic Digestion - A Review
Deshai Botheju* and Rune Bakke Telemark University College, Norway
This article reviews the experimental and theoretical studies conducted on the possible effects of oxygen in biogas generating anaerobic digesters. The interactions of oxygen with various biochemical processes associated with anaerobic digestion are discussed together with other relevant aspects. The conventional perception of oxygen being merely toxic in anaerobic digestion (AD) is refuted. Digesters can withstand significant levels of oxygenation without drastic negative impacts. Limited quantities of oxygen can even lead to improved AD reactor performance under certain operating conditions. Co-existence of anaerobic and aerobic cultures in a single bioreactor environment has been demonstrated. It is shown that the partial aeration assisted AD can serve as a beneficial treatment strategy for simultaneous waste treatment and energy generation, for a multitude of organic waste categories.
[Once again, the co-existence of aerobic and anaerobic methanogens is acknowledged, demonstrating once again that the production of methane is not a proof of an anaerobic environment, and that the presence of oxygen can actually increase the methane output of methanogenic bacteria. -TD]
Nature. 2010 Mar 25;464 (7288):543-8 20336137 Cit:32
Nitrite-driven anaerobic methane oxidation by oxygenic bacteria.
Katharina F Ettwig, Margaret K Butler, Denis Le Paslier, Eric Pelletier, Sophie Mangenot, Marcel M M Kuypers, Frank Schreiber, Bas E Dutilh, Johannes Zedelius, Dirk de Beer, Jolein Gloerich, Hans J C T Wessels, Theo van Alen, Francisca Luesken, Ming L Wu, Katinka T van de Pas-Schoonen, Huub J M Op den Camp, Eva M Janssen-Megens, Kees-Jan Francoijs, Henk Stunnenberg, Jean Weissenbach, Mike S M Jetten, Marc Strous
Radboud University Nijmegen, IWWR, Department of Microbiology, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands. firstname.lastname@example.org
Only three biological pathways are known to produce oxygen: photosynthesis, chlorate respiration and the detoxification of reactive oxygen species. Here we present evidence for a fourth pathway, possibly of considerable geochemical and evolutionary importance. The pathway was discovered after metagenomic sequencing of an enrichment culture that couples anaerobic oxidation of methane with the reduction of nitrite to dinitrogen. The complete genome of the dominant bacterium, named 'Candidatus Methylomirabilis oxyfera', was assembled. This apparently anaerobic, denitrifying bacterium encoded, transcribed and expressed the well-established aerobic pathway for methane oxidation, whereas it lacked known genes for dinitrogen production. Subsequent isotopic labelling indicated that 'M. oxyfera' bypassed the denitrification intermediate nitrous oxide by the conversion of two nitric oxide molecules to dinitrogen and oxygen, which was used to oxidize methane. These results extend our understanding of hydrocarbon degradation under anoxic conditions and explain the biochemical mechanism of a poorly understood freshwater methane sink. Because nitrogen oxides were already present on early Earth, our finding opens up the possibility that oxygen was available to microbial metabolism before the evolution of oxygenic photosynthesis.
[This is the paper that introduced an extraordinary discovery - there is a microorganism which generates oxygen in anaerobic environments, without using photosynthesis, by breaking down nitrites. Landfill leachate, which is chemical infused water in landfills, contains a great deal of nitrite.-TD]
Appl Microbiol Biotechnol. 2011 Jun 11;: 21667086
Diversity and enrichment of nitrite-dependent anaerobic methane oxidizing bacteria from wastewater sludge.
Francisca A Luesken, Theo A van Alen, Erwin van der Biezen, Carla Frijters, Ger Toonen, Christel Kampman, Tim L G Hendrickx, Grietje Zeeman, Hardy Temmink, Marc Strous, Huub J M Op den Camp, Mike S M Jetten
Department of Microbiology, Institute for Water and Wetland Research, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands.
Recently discovered microorganisms affiliated to the bacterial phylum NC10, named "Candidatus Methylomirabilis oxyfera", perform nitrite-dependent anaerobic methane oxidation. These microorganisms could be important players in a novel way of anaerobic wastewater treatment where ammonium and residual dissolved methane might be removed at the expense of nitrate or nitrite. To find suitable inocula for reactor startup, ten selected wastewater treatment plants (WWTPs) located in The Netherlands were screened for the endogenous presence of M. oxyfera using molecular diagnostic methods. We could identify NC10 bacteria with 98% similarity to M. oxyfera in nine out of ten WWTPs tested. Sludge from one selected WWTP was used to start a new enrichment culture of NC10 bacteria. This enrichment was monitored using specific pmoA primers and M. oxyfera cells were visualized with fluorescence oligonucleotide probes. After 112 days, the enrichment consumed up to 0.4 mM NO (2)(-) per day. The results of this study show that appropriate sources of biomass, enrichment strategies, and diagnostic tools existed to start and monitor pilot scale tests for the implementation of nitrite-dependent methane oxidation in wastewater treatment at ambient temperature.
[Microorganisms that create oxygen in anaerobic conditions are quite common, and despite not being deliberately seeded into anaerobic digesters, they were found in 9 out of 10 anaerobic digesters sampled. -TD]
The gas entering the gas collection system is saturated with water, and that water must be removed prior to further processing. The typical dry composition of the low-Btu gas is 57 percent methane (natural gas), 42 percent carbon dioxide, 0.5 percent nitrogen, 0.2 percent hydrogen, and 0.2 percent oxygen. In addition, a significant number of other compounds are found in trace quantities. These include alkanes, aromatics, chlorocarbons, oxygenated compounds, other hydrocarbons and sulfur dioxide.
[The State of California, which has very low rainfall, says that its landfill gas is .2% oxygen, which is more than enough for microorganisms to function aerobically -TD]
Analysis of the landfill gas collected at the flare provided the following information: 41.5 Percent Methane Gas 34.3 Percent Carbon Dioxide 2.5 Percent Oxygen 21.5 Percent Balanced Gases (Mainly Nitrogen)
[Reviewing the locations sampled, the trend is that rainier locations have more oxygen in landfill gas than dryer locations, but even the dry locations have ample oxygen for aerobic functioning of microbes. -TD]
"Sampling of Landfill Gas Monitoring Wells" A proper reading should have 2 percent oxygen by volume or less. If levels of oxygen are higher, it may indicate that air is being drawn into the system giving a false reading of the true soil gas concentrations.
[The State of Missouri considers landfill oxygen readings of below 2% to be ordinary. It is routine for the managers of landfills to monitor the landfill gas composition. -TD]