Assessing methods to estimate emissions of non-methane organic compounds from landfills

Jovita M Saquing,Jeffrey P Chanton,Ramin Yazdani,Morton A Barlaz,Charlotte Scheutz,Don R Blake,Paul T Imhoff

doi:10.1016/j.wasman.2014.07.007

Abstract

The non-methane organic compound (NMOC) emission rate is used to assess compliance with landfill gas emission regulations by the United States Environmental Protection Agency (USEPA). A recent USEPA Report (EPA/600/R-11/033) employed a ratio method to estimate speciated NMOC emissions (i.e., individual NMOC emissions): speciated NMOC emissions=measured methane (CH4) emission multiplied by the ratio of individual NMOCs concentration relative to CH4 concentration (CNMOCs/CCH4) in the landfill header gas. The objectives of this study were to (1) evaluate the efficacy of the ratio method in estimating speciated NMOC flux from landfills; (2) determine for what types of landfills the ratio method may be in error and why, using recent field data to quantify the spatial variation of (CNMOCs/CCH4) in landfills; and (3) formulate alternative models for estimating NMOC emissions from landfills for cases in which the ratio method results in biased estimates. This study focuses on emissions through landfill covers measured with flux chambers and evaluates the utility of the ratio method for estimating NMOC emission through this pathway. Evaluation of the ratio method was performed using CH4 and speciated NMOC concentration and flux data from 2012/2013 field sampling of four landfills, an unpublished landfill study, and literature data from three landfills. The ratio method worked well for landfills with thin covers (<40cm), predicting composite NMOC flux (as hexane-C) to within a factor of 10× for 13 out of 15 measurements. However, for thick covers (⩾40cm) the ratio method overestimated NMOC emissions by ⩾10× for 8 out of 10 measurements. Alternative models were explored incorporating other chemical properties into the ratio method. A molecular weight squared (MW)2-modified ratio equation was shown to best address the tendency of the current ratio method to overestimate NMOC fluxes for thick covers. While these analyses were only performed using NMOC fluxes through landfill covers measured with flux chambers, results indicate the current USEPA approach for estimating NMOC emissions may overestimate speciated NMOC emission ⩾10× for many compounds.

Highlights

With 54–69% of municipal solid waste (MSW) discarded in landfills in 2008, landfill disposal remains a major waste management option in the United States
Similar vertical variations are observed in concentration ratios of speciated non-AP-42 non-methane organic compound (NMOC) to CH4 at SoutheasternUS (Fig. S1): higher CNMOCs/CCH4 ratios are generally observed on the landfill surface versus samples with depth
The current ratio method used in a recent United States Environmental Protection Agency (USEPA) Report (USEPA, 2012) uses CH4 flux measurements and measured CNMOCs/ CCH4 ratios from landfill header gas to estimate speciated NMOC fluxes from the landfill

Summary

Introduction

With 54–69% of municipal solid waste (MSW) discarded in landfills in 2008, landfill disposal remains a major waste management option in the United States The decomposition of MSW organics in landfills produces landfill gas (LFG) that contains methane (55–60 vol%), carbon dioxide (40–45 vol%), and traces of non-methane organic compounds (NMOCs) at pptv to ppmv levels including alkanes, alkenes, aromatics, chlorinated ethylenes, chlorinated methanes, halocarbons, alcohols, ketones, terpenes, chlorofluoro compounds (CFCs), and siloxanes (Staley et al, 2006; Brosseau and Heitz, 1994). Gas control at MSW landfills is regulated in the United States under the Clean Air Act (section 111) New Source Performance Standards (NSPS)/Emission Guidelines (EG) (40 CFR part 60) (USEPA, 1996). J.M. Saquing et al / Waste Management 34 (2014) 2260–2270 meters) or annual NMOC emissions >50 Mg are required to install gas control and collection systems. Estimates of annual NMOC emissions are important for compliance with environmental regulations.

Objectives

Results

Conclusion