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Controlling Methane Production in Groundwater Proximal to Landfill Settings
Controlling Methane Production in Groundwater Proximal to Landfill Settings
Jim Mueller, PhD (Provectus Enviromental Products, Inc – Freeport IL), and
Ramon Rivera (Diamond Systems, LLC –Titusville, FL)
Introduction
Over the past 25 years, various remedial amendments have been used to treat groundwater impacted by chlorinated solvents and other VOC, pesticides, and heavy metals that have, presumably, emanated from landfill sources. A very common problem, however, is that indigenous methanogens often bloom following the addition of the organic hydrogen donors thereby liberating large amounts of methane gas. This is because methanogens are the most ubiquitous indigenous microbes in anoxic aquifer settings. This problem can be greatly exacerbated by methane also being produced proximal to the landfill areas.What is the Problem with Methane?
There are recognized benefits to methanogens and of limited methanogenesis. For example, methanogens play important roles in synergistic microbial ecology, and they support natural degradation of landfill contents and managed gas production. However, extended production of methane can result in elevated groundwater concentrations (as high as >100 ppm have been reported) which can lead to accumulation in soil gas subsequently impacting indoor air. While this is perhaps more relevant in urban settings where methane can accumulate in basements, under slabs/foundations and/or migrate along utility corridors, excessive methane production has also been observed in more rural settings and other open spaces. Accordingly, elevated methane concentrations can exceed current and pending regulations of < 10 to <28 ppm in groundwater and/or 0.5% v/v methane in soil gas (e.g., 10% of the LEL) and/or indoor air (methane is flammable between 5% and 15% v/v). Many remedial practitioners proactively design contingencies for implementation in the event that methane exceeds a threshold level ranging from 1 to 10 ppm groundwater. These contingencies often entail expensive and extensive systems for treating methane in soil gas/vapor captured via SVE systems. Moreover, from a sustainability perspective, it can be argued that controlling methane production has a positive impact on greenhouse gases. The comparative impact of CH4 on climate change is about 20x greater than that of CO2 when averaged over a 100-year period (US EPA, 2014).Technical Solution
Provect-CH4â„¢ is a genuinely new, antimethanogenic reagent that contains natural statin compounds with the unique ability to block protein and enzyme systems specific to methanogens thereby controlling their growth and proliferation (Woese and Fox, 1977). The technology has been widely used in the cattle industry for many years to manage rumen microbiology (Henderson et al, 2010)), but is being newly applied to the environmental industry as a remedial supplement, a landfill gas management tool, et cetera. The methane inhibitor itself can be used as a stand-alone supplement, or it can be added to myriad amendments used during remedial actions to make them safer and to greatly improve their overall efficacy in a predictable manner (US Patent Office Scalzi et al, 2013, 2014).
Proof of Concept
There are at least two scenarios where methane inhibitors can be used: i) “preemptivelyâ€, or in a proactive effort to prevent excesses methane production, or ii) “curativelyâ€, in an attempt to ameliorate a situation where excessive methanogenesis has been established. Laboratory work documented that the methane inhibitors (40 ppm) yielded rapid (within 2 to 3 days) and significant (>90%) reduction of methane production by an active, adapted culture of Archaea in a closed bioreactor system (Figure 1). Laboratory work using simulated aquifer microcosms (soil and groundwater) inoculated with an active culture of methanogens also demonstrated rapid (within 1 to 3 days) and significant (>90%) reduction of methane in the presence of ca. 100 ppm inhibitor (data not shown).Figure 1. Changes in Methane Concentrations over Time.
