Dry matter losses and methane emissions during wood chip storage: the impact on full life cycle greenhouse gas savings of short rotation coppice willow for heat

A life cycle assessment (LCA) approach was used to examine the greenhouse gas (GHG) emissions and energy balance of short rotation coppice (SRC) willow for heat production. The modelled supply chain includes cutting multiplication, site establishment, maintenance, harvesting, storage, transport and combustion. The relative impacts of dry matter losses and methane emissions from chip storage were examined from a LCA perspective, comparing the GHG emissions from the SRC supply chain with those of natural gas for heat generation. The results show that SRC generally provides very high GHG emission savings of over 90 %. The LCA model estimates that a 1, 10 and 20 % loss of dry matter during storage causes a 1, 6 and 11 % increase in GHG emissions per MWh. The GHG emission results are extremely sensitive to emissions of methane from the wood chip stack: If 1 % of the carbon within the stack undergoes anaerobic decomposition to methane, then the GHG emissions per MWh are tripled. There are some uncertainties in the LCA results, regarding the true formation of methane in wood chip stacks, non-CO2 emissions from combustion, N2O emissions from leaf fall and the extent of carbon sequestered under the crop, and these all contribute a large proportion of the life cycle GHG emissions from cultivation of the cro

The fate of toluene, acetone and 1,2-dichloroethane in a laboratory-scale simulated landfill

The objective of this research was to study the fate of toluene, acetone and 1,2- dichloroethane (DCA) in refuse excavated from a municipal solid waste landfill contaminated with organic solvents. Refuse excavated from the landfill was used to fill multiple 8-1 simulated landfill reactors that were operated with and without moisture addition to simulate the absence and presence of an engineered cover, respectively. An average of 31.3% of the added C-14-toluene was converted to (CH4)-C-14 and (CO2)-C-14 in reactors that received water additions, while only 12% was mineralized in the absence of water addition. Up to 30% of the added C-14 was recovered in humic and fulvic acid fractions and up to 12% of the C-14 was not extractable with dichloromethane (DCM) followed by 0.5 N NaOH. The non-extractable fraction may represent strongly sorbed toluene or toluene metabolites covalently bound to humins. From 21.6 to 40.3% of the added C-14-acetone was converted to (CH4)-C-14 and (CO2)-C-14 although there was no consistent effect associated with water. This is likely explained by the high solubility of acetone as considerably more acetone was present in the reactor leachate relative to toluene. Reductive dehalogenation of 1,2-DCA to ethylene was measured in all reactors. This study suggests that remediation activities designed to reduce moisture infiltration could adversely affect contaminant biodegradation at the source and that moisture infiltration must be balanced against the potential increase in contaminant release due to leaching. Further, the association with humic matter in decomposed refuse may represent an alternative mechanism for contaminant sequestration

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

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

Development Of An Enzymatic Assay For The Determination Of Cellulose Bioavailability In Municipal Solid Waste

As there is a constant need to assess the biodegradation potential of refuse disposed of in landfills, we have developed a method to evaluate the biodegradability of cellulosic compounds (cellulose and hemicellulose) in municipal solid waste. This test is based on the quantification of monosaccharids released after the hydrolysis of solid waste samples with an optimised enzyme preparation containing commercially available cellulases and hemicellulases. We show that the amounts of monosaccharids could be related to the biodegradability of the cellulosic material contained in the samples. This enzymatic cellulose degradation test was assayed on 26 samples originating from two Belgian landfills and collected at different depths. As results correlated well with those obtained with a classical biochemical methane potential assay, this new and rapid test is sufficiently reliable to evaluate cellulose bioavailability in waste samples.Confinement de centres d'enfouissement technique à l'aide de barrières argileuse

Methane production and microbial community structure in single-stage batch and sequential batch systems anaerobically co-digesting food waste and biosolids

Anaerobic co-digestion of food waste and biosolids was carried out in sequential batch and single-stage batch systems in four treatments. Methane yield, which was used as a functional process parameter, differed between treatments, with the single-stage batch system generating lower volumes than the sequential batch systems. Volatile fatty acid (VFA) concentrations and pH in the leachate also differed between treatments. VFA concentrations were highest and methane generation yields lowest in the single-stage batch system in comparison to the sequential batch systems. The anaerobic microbial community structure of the domains Archaea and Bacteria, determined by denaturing gradient gel electrophoresis, differed between treatments and was correlated to a number of environmental parameters such as pH, VFA concentration and methane generation rate. Methane generation rate was significantly correlated to the community structure of Bacteria but not Archaea. This indicated that the substrates that are produced by acetogens (Bacteria) are important for the growth and community structure of the methanogens (Archaea). Community structure of Archaea changed over time, but this had no observable effect on functional ability based on methane yields. Microbial diversity (H′) was shown to be not important in developing a functionally successful anaerobic microbial community.B. Dearman, P. Marschner and R. H. Bentha