The Organic Factor

Diverting organic wastes, especially foodwaste, from landfills is a top priority of many local governments and environmental organizations. Even such federal agencies as the United States Environmental Protection Agency (EPA) and the United States Department of Agriculture (USDA) support the diversion of foodwaste from landfills.

Organics are the low-hanging fruit (and vegetables) for recovery in the solid wastestream. Foodwaste is an issue that draws passionate responses from a wide variety of stakeholders, some even calling for “A War Against Food Waste” (Dylan Walsh, “A War Against Food Waste,” The New York Times, September 15, 2011). Why would anyone be concerned about diverting of organic waste from landfills?

One group that may be concerned with organic waste diversion includes the developers of landfill gas-to-energy (LFGTE) projects. Billions of dollars have been spent on the development of LFGTE systems that include expensive piping networks, blowers, gas cleaning systems, engines, and generators. These LFGTE systems rely on an expected quantity of methane-rich landfill gas over the life of the systems. In most landfills, organic materials decompose anaerobically, creating methane. It goes without saying, therefore, that the removal of organic materials from landfills will reduce the quantity, and possibly the quality, of landfill gas. But is this, or should this be, a concern of LFGTE system owners or developers?

The goal of this article is to explore the possible implications of organics diversion on LFGTE projects. This article will consider landfill gas modeling conducted by others, and will provide insight with respect to organics diversion and landfills.

The Nature of Foodwaste

According to the Huffington Post, half of the world’s food production, over 2 billions tons, ends up as foodwaste (“Food Waste: Half of all Food Ends Up Thrown Away,” Huffington Post UK, October 1, 2013. Retrieved October 20, 2014). But what exactly is foodwaste? EPA defines foodwaste as “uneaten food and food preparation wastes from residences and commercial establishments such as grocery stores, restaurants and produce stands, institutional cafeterias and kitchens, and industrial sources like employee lunchrooms” (“Terms of Environment: Glossary, Abbreviations and Acronyms,” USEPA, last update June 18, 2009. Retrieved October 20, 2014).

Foodwaste in the US is primarily disposed of in landfills. EPA’s Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures for 2012 indicates that close to 54% of MSW ends up in landfills (USEPA, Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures for 2012, EPA-530-F-14-001, February 2014). And the largest component of landfilled MSW is foodwaste at 21%.

With the exception of yard trimmings, efforts in the US to reduce the amount of organics in the wastestream have not been successful. In comparing waste composition from 1992 to 2012, foodwaste has actually increased substantially as a percentage of discarded materials, from 8.4% in 1992, to 21.1% in 2012 (USEPA, Characterization of Municipal Solid Waste in the United States: 1995 Update and USEPA, Municipal Solid Waste Generation, Recycling, and Disposal in the United States: Facts and Figures for 2012, EPA-530-F-14-001, February 2014).

Efforts to Divert Foodwaste From Landfills

As mentioned earlier, diverting organics and especially foodwaste from landfills remains a top priority of many governments and organizations. EPA has developed a foodwaste hierarchy that, in addition to source reduction, considers the feeding of people and animals as high priorities ahead of such management methods as composting or landfilling (USEPA, Food Recovery Challenge, www.epa.gov/foodrecoverychallenge. Recovered October 20, 2014).

The USDA, in collaboration with EPA, has developed the US Food Waste Challenge (USDA, US Food Waste Challenge, www.usda.gov/oce/foodwaste. Recovered October 20, 2014). Among the goals of the challenge:

• Reduction of foodwaste by improving product development, storage, shopping/ordering, marketing, labeling, and cooking methods

• Recovery of foodwaste by connecting potential food donors to such hunger relief organizations as food banks and pantries

• Recycling of foodwaste to feed animals or to create compost, bioenergy, or natural fertilizers

Other organizations working to keep foodwaste out of landfills include the Food Waste Reduction Alliance, the US Composting Council, and the Sierra Club.

In addition to voluntary programs by the US government, several states have enacted legislation targeting food and organic waste diversion from disposal. The states that have enacted bans on landfill disposal of organics are summarized in the table to the left. Several US cities have also enacted programs or bans on organics disposal, including New York City, Portland, San Francisco, and Seattle.

Organics and Landfill Gas

Landfill gas (LFG) is created by biological decomposition of the organic fraction of solid waste in a landfill. Bacteria decompose the organic fraction of landfill waste in four phases. The composition of the gas produced by these bacteria changes with each of the four decomposition phases (The Agency for Toxic Substances and Disease Registry, Landfill Gas Primer: An Overview for Environmental Health Professionals, November 2001).

Phase I Aerobic— Phase I involves the decomposition of organic materials by aerobic bacteria (bacterial that live in the presence of oxygen). When waste is initially deposited in a landfill, it will likely contain oxygen. In addition, until the waste is buried and oxygen sources have been depleted, the aerobic bacteria will continue to live and feed on the organic materials. Phase I may last for several days or several months, depending on the amount of oxygen initially in the waste and the landfill cover material conditions.

Phase II Anaerobic (non-methanogenic)—Phase II decomposition begins after the depletion of oxygen in Phase I. In this anaerobic (without oxygen) phase, bacteria convert compounds created by aerobic bacteria primarily resulting in carbon dioxide and hydrogen.

Phase III Anaerobic (methanogenic, unsteady)—Phase III is also an anaerobic decomposition phase in which the environmental conditions support the growth of methanogenic bacteria. These bacteria in turn consume organic compounds and produce methane gas. In Phase III, the composition and production rates of LFG are unsteady.

Phase IV Anaerobic (methanogenic, steady)—During Phase IV, methanogenic bacteria continue to consume organic compounds and produce LFG in a relatively steady state. Phase IV LFG usually contains approximately 45% to 60% methane by volume, 40% to 60% carbon dioxide, and 2% to 9% other gases, such as sulfides. During Phase IV, LFG may be produced at a relatively steady state for approximately 20 years or more.

Landfills often accept waste over a 20- to 30-year period, so waste in a landfill may be undergoing several phases of decomposition at once. This means that older waste in one area might be in a different phase of decomposition than more recently buried waste in another area.

The Effect on LFG From Organics Diversion

Burlington County, NJ—Robert Simkins has considered the relationship of organic waste and landfills for many years. As the solid waste coordinator for Burlington County, Simkins has overseen the development of the county’s comprehensive integrated solid waste program, including single-stream recycling collection and processing, biosolids composting, bioreactor landfill, and 7.1-MW LFGTE system. Burlington County invested millions of dollars in the LFGTE system, which was designed, built, and operated
by DCO Energy LLC.

Burlington County has been on the forefront of innovation with other uses of LFG for energy, including heating an onsite greenhouse and a demonstration LFG to liquefied natural gas (LNG) production and truck fueling facility. Simkins has a vision for the Burlington County Landfill to become a closed-loop solid waste system in which waste collection vehicles are fueled with biogas produced from the solid waste delivered in their trucks.

In 2008, Burlington County evaluated the potential LFG loss by a theoretical 15-year foodwaste diversion program. The county’s evaluation assumed that 43,000 tons per year of foodwaste would be diverted from the county’s approximate 300,000 tons per year of MSW entering the landfill. During the 15-year period, the expected LFG loss was calculated to grow from 147 cubic feet per minute (cfm) in year 1 to approximately 550 cfm in year 15. At 550 cfm of LFG, the power production could be approximately 1.3 MW, which at $40 per megawatt-hour, would result in a loss of almost $450,000 per year to the county. This loss in electricity revenues would be on top of the loss in tipping fee revenues, which at the county’s current fee of $76.41 per ton equals $3.3 million per year.

Landfill Gas Modeling for the US—At the 2014 Solid Waste Association of North America (SWANA) Landfill Gas Symposium, Alex Stege of SCS Engineers presented a paper titled “The Effects of Organic Waste Diversion on LFG Generation and Recovery from US Landfills.” The paper investigated the effects of various organics waste diversion scenarios on LFG generation and recovery landfills in California and elsewhere in the US over a 25-year period (2000–2024).

Stege used a modified version of the Intergovernmental Panel on Climate Change (IPCC) model to evaluate LFG generation scenarios based on different organics diversion rates. The three general scenarios included (1) a baseline scenario, (2) a moderately accelerated organics diversion scenario, and (3) an aggressively accelerated organics diversion scenario. The baseline scenario assumed organics recovery and diversion consistent with trends from 2009 to 2012. The moderately accelerated organics diversion scenario assumed organics recovery and diversion between one-and-a-half and two times (depending on the organic material) the baseline recovery and diversion scenario. The aggressively accelerated organics diversion scenario assumed organics recovery and diversion two to three times (depending on the organic material) the baseline recovery and diversion scenario.

From the modeling scenarios, Stege forecasted LFG generation through 2025 and concluded the following:

• Continuing baseline organic diversion trends suggest that annual increases in LFG generation will decline over time, but continue until at least 2025.

• Moderately accelerated organics diversion will cause LFG generation to be less than baseline projections by 9% (California landfills) to 9.4% (other US landfills) by 2025. Annual increases in LFG generation are projected to approach 0% by 2025 under this scenario.

• Aggressively accelerated organics diversion will cause LFG generation to be less than baseline projections by 17.3% (California landfills) to 18.5% (other US landfills) by 2025. Annual increases in LFG generation are projected to stop after 2020, after which LFG generation is projected to slowly decline under this scenario.

The State of LFGTE in the US

EPA’s Landfill Methane Outreach Program (LMOP) is a voluntary assistance program that helps to reduce methane emissions from landfills by encouraging the recovery and beneficial use of landfill gas as an energy resource. LMOP tracks operational and under-construction LFGTE projects in the US. As of July 22, 2014, there were 636 operational LFGTE systems in the US, producing 1,978 MW of electricity. There were also approximately 440 candidate LFGTE projects with an estimated 885 MW of electricity potential.

If you assume an LFGTE system capital cost at $1.5 million per installed MW, there is currently close to $3 billion in infrastructure associated with LFGTE in the US, which could grow to $4.2 billion from the candidate landfills. As an industry, we have invested a significant amount of capital investment into our LFGTE systems. Those LFGTE investments were based on anticipated LFG quantities.

The Impact on LFGTE From Organics Diversion

It is clear and intuitive that diversion of organic materials from landfills will reduce the quantity of LFG generation. LFG is only generated from the anaerobic degradation of organic materials, so removal of those material from the landfill will have the effect of reducing LFG quantities.

Stege’s study demonstrated a potentially significant impact on LFG quantities from organics diversion rate increases. Moderately accelerated organics division programs would yield a 9% LFG reduction from baseline projections and aggressively accelerated organics diversion programs would yield up to 18.5% LFG reduction from baseline projections and cause LFG generation to start to decline after 2020.

When it comes to considering the impact of organics diversion on LFGTE systems, it is important to note:

• Landfills currently contain millions of tons of organic waste.

• The organic wastes currently in landfills will likely degrade over many years in the anaerobic, methanogenic, steady state.

• Organics diversion programs will likely take time to develop and mature.

It is also interesting to note that, from a policy perspective, the EPA LMOP program does not consider organics diversion and LFGTE to be in conflict. LMOP’s position on the compatibility of organics diversion and LFGTE is summed up in the following statement:

The promotion of LFG energy is not in conflict with promotion of waste diversion and does not compete with waste reduction, recycling, and composting. LFG energy projects use methane that is generated from waste that has not been successfully diverted from landfills. The goal of LFG energy projects is to promote beneficial utilization of LFG collected from MSW landfills that have already disposed waste. It is possible to support the diversion of the organic fraction of discards from landfills so that uncontrolled methane is not generated and also support LFG energy projects that utilize methane generated from organic waste already disposed in landfills (USEPA Landfill Methane Outreach Program, Frequent Questions, LFG Energy Projects, www.epa.gov/lmop/faq/lfg.html. Recovered October 21, 2014).

On a practical level, I agree with the LMOP position. We can, and should, embrace the foodwaste management hierarchy and find the highest and best use of foodwaste, reserving landfills as a last resort.

However, there is, and should be, a real concern about the financial security of the $3 billion that we, as solid waste management professionals, have already invested to generate renewable energy from LFG. Fortunately for the LFGTE systems we have in place, changes to organic waste diversion in the US will likely happen over time, and we can take this time to plan and adapt to the coming changes.

John G. Carlton, P.E., BCEE, is senior vice president, Gershman, Brickner & Bratton Inc.