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Waste Reduction

Landfills underestimate waste disposal

The landfill’s closure and the fact that it no longer received new waste was the most important factor in determining the efficiency of the gas collection system. Closed sites were 17 percentage points more efficient at collecting gas than open sites actively receiving waste.

New targets for methane

The US EPA has proposed new regulations that align with the goal of reducing emissions at landfills. The proposed modifications of the municipal landfill rules pursuant to the Clean Air Act aim to lower the emission threshold at which a dump is required to design and construct an active gas collection system.

The US is not the only country that has adopted improved waste management practices, such as enhancing existing sites that will continue to operate for many years. The Pope’s Encyclical urged the reduction of “…the pollutants produced by residues, including…waste in different areas”, and the UN’s Sustainable Development Goalsfor 2030 contains multiple goals that are in line with how we manage waste in the US.

The US has plenty of space to store its garbage. Jon Powell, Author provides

Our research clearly shows that in the US, landfilling will be the dominant waste management method in the near future.

Our new study quantified US disposal capacity, a far cry from the widespread concern in the 1980s and 90s about the depletion of space.

Our analysis showed that the disposal capacity had increased over the past few years. In fact, we found that from 2010 to 2013, there was a new capacity of about 2.7 additional years available each year. In other words, the US can continue to generate waste at its current rate and still find space to dump it in landfills for decades.

Better data, better landfill disposal estimate

We used a large amount of data from a recently published data set by the US EPA in its Greenhouse Gas Reporting Program law.

The GHGRP, passed in 2009, requires that facilities in certain sectors – including municipal solid waste dumps – collect and report electronically a variety of data used to calculate total CO2 emission at the facility. In our analysis, we were able to leverage a huge amount of data from all landfills that are subject to the rule. We had more than 1,200 datasets in total.

More than 1,200 US landfills generate methane. Jon Powell is the author.

Our estimate of the amount disposed of in the US in 2013 ranged between 266 million tons and 264 million in 2010.

Why are our estimates higher than the municipal data that are published by the US EPA and are often reported? It’s all about the methodology.

Prior to the GHGRP, the best way to estimate the municipal waste management in the US consisted of examining material flows within the US Economy, which led to a final estimate of the amount of waste that was disposed, combusted, and recycled. The GHGRP data, on which our estimate is based, contains data that has been measured and quality-assured from each reporting facility.

The standard practice for landfills is to weigh each truckload at arrival and departure. The difference between the two weights represents the amount of waste placed in the landfill.

Add up the weight of each truckload over the course of a year to get the information reported by each landfill. To develop our estimate, we aggregated the data reported by each facility. Some landfills are too small to be covered by the GHGRP, and some wastes are not municipal waste but are still disposed at municipal landfills. We calculated that the amounts of construction waste and other non-municipal waste are relatively small in comparison to our total calculated disposal.

Environmental informatics

A second key conclusion, supported by data collected from hundreds of landfills in operation, is that efforts to reduce emissions must be focused on landfills that accept waste.

Gas collection is a serious business, as landfills have open spaces that make it difficult to collect gas using traditional methods. Also, faulty gas collection systems may cause problems. Gas is usually collected from landfills by installing a series perforated pipes vertically or horizontally in the waste, once there is enough waste to fit the wells. Gas collection problems, such as conditions of high temperature within the waste can cause pyrolysis and fires.

A landfill in Wisconsin captures and treats the methane emissions. Wisconsin Department of Natural Resources CC-BY-ND

We recommend a focus on new gas collection methods that capture gas as soon as waste is placed in the landfill. Early gas collection can have other benefits than reducing methane emissions. The energy content of landfill gas collected at several hundred sites in the US is used to produce electricity or fuels.

We hope this will be the first of many analyses that utilize large data sets that are quality-assured in the waste management and materials domain. They can be used to inform the current performance and pinpoint targets for short-term and longer-term improvements. This will usher in a new era of environmental informatics.

Future studies should use our data mining methodology to uncover additional relationships and insights regarding how disposal facilities actually operate. This will help inform policymakers and improve analytical tools like life-cycle assessments, as well as bring about a sustainable future for materials management.

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Jane S. King

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