Emissions Management Services
From Landfill Sites
At a well designed and managed site, the collection and treatment of leachate along with the extraction and, where possible, utilisation of landfill gas are the most important emission management tasks. A biologically-based water treatment process can ensure that leachate can be released into the surface water without creating a risk to the environment. We have extensive experience in managing a range of types of water treatment processes at our landfill sites.
Methane, one of the constituents of landfill gas, is a powerful greenhouse gas. For that reason, it is important that landfill gas is extracted as much as possible and at least flared. If the recovery takes place in an efficient way, the gas can be used to generate electricity and heat. Landfill gas is then no longer a problem but actually becomes a source of energy.
Afvalzorg has years of experience in the field of quantifying methane emissions originating from landfills. Methane emission can be quantified by means of modelling or in in situ measurements.
Methane emission modelling
Over the last couple of years, Afvalzorg has compared six different emission models of which four models are used to register emission to regulation of the European Pollutant Release and Transfer Register (E-PRTR), versus measured emission data. The comparison of these models showed large differences in modelled methane emissions. Questions can be raised whether E-PRTR goals are going to be met if there is a large model dependency.
Afvalzorg believes that if we want to come to comparable, consistent and accurate European datasets, model dependency should be ruled out by applying harmonised guidance to quantify methane emission by modelling. In the paper “Comparison of methane emission models”, Afvalzorg made a first attempt towards achieving this goal.
In addition Afvalzorg since 2009 assits the European Commission in drafting improved guidance for landfill gas control. With support of the Dutch environment agency a new simple landfill gas generation and emission model based on IPCC recommended parameters has been developed.
Methane emission measurement
In cooperation with ECN (Dutch Energy Research Centre) Afvalzorg has developed a simple and cheap methane emission measurement method. The method was tested on a Dutch and Danish landfill and verified with measurement data from the scientifically approved Dynamic Plume Method (DPM).
The simple and cheap method is performed according to the “Static Plume Methodology”. During a measurement campaign evacuated gas bottles are used and via capillaries ambient air is sampled during a certain period of time. Gas bottles are positioned in the vicinity of the landfill, down wind and perpendicular to the wind direction. Once opened, the gas bottles are sampling ambient air at a known rate via the critical capillary. Next to ambient air also a tracer gas is sampled due to the fact that tracer gas is released from the landfill at a known rate.
Ambient air contains known oxygen and nitrogen concentrations, but down wind of the landfill, now air will also contain methane and tracer gas emitting from the landfill. After six hours of sampling, gas bottles are closed. Sampled gas is analysed for methane and tracer gas in a laboratory. Methane emission is determined solely by the ratio of released tracer gas (dilution) and the combined concentration of methane in all gas bottles. Various campaigns have shown that the simple and cheap measurement technique compares very well to more expensive DPM techniques.
In the summer of 2009 Afvalzorg has constructed two test fields for research of methane oxidation in cover soil. The research is carried out with support of Agentschap NL(programme Reduction of Other Greenhouse Gases), the Institute of Soil Science of the University of Hamburg and the Technical University of Hamburg-Harburg in the framework of the MiMethox project (www.mimethox.de).
Methane oxidation is the process through which soil microorganisms in a cover soil degrade methane from landfill gas into carbon dioxide. It is well known that methane is an important greenhouse gas. At some point it is no longer feasible to extract and utilise or flare landfill gas actively. In that situation a 'passive'approach to neutralise the remaining methane emission of the landfill is required. With a methane oxidising cover soil a significant reduction of the greenhouse gas emission of landfills can be realised. Insufficient knowledge on the effectiveness of methane oxidation hampers inclusion in green house gas accounting. The research contributes to recognition of methane oxidation as suitable option to reduce methane emission on landfills. In addition, knowledge is generated on the water balance in a cover soil and the optimisation of water storage of a cover soil.
In order to ‘evenly feed’ the soil microorganisms it is important to evenly distribute the landfill gas over the entire surface. Two aspects are very important. First of all a gas distribution layer is required. Secondly the soil needs to have a sufficient porosity for even gas transport through the soil. This imposes requirements on the composition and the construction of the cover soil. The soil needs to have a relatively high percentage of sand and it should not be compacted. The pore volume available for gas transport is strongly influenced by moisture. Rainwater has to flow down through the same pores as the gas has to flow up. Too much moisture means that the gas cannot find an even way out. Gas pressure increases and the gas will move through a 'preferential pathway'. The speed and the amount of landfill gas will be too high to give the microorganisms an opportunity to degrade the methane. An uncontrolled methane emission will occur. It is important to find the required pore volume that enables both adequate methane oxidation and adequate water holding capacity and water discharge under most of the conditions that can occur during the year. The research therefore addresses both methane oxidation and water balance.
The test fields are constructed on a membrane with sidewalls. This enables catchment and measurement of water flow through the cover soil. The membrane blocks the ‘natural gas supply’ from the landfill. A gas distribution unit has been installed to supply landfill gas to the test fields. This enables measurement of incoming and outgoing gas flows and establishment of the oxidation efficiency. Two test fields have been constructed with a different technique. One test field is constructed with a long-stick excavator. Thus a very 'fluffy' cover soil was constructed. The other test field is constructed in a more traditional way with a bulldozer.
Results after two years
In the first year a methane load to the cover soil of 0.25 liter methane per m2 and hour was imposed. In both testfields no methane emissions could be observed. Methane was not detectable in the soil profile except very deep. In the second year the methane load to the cover soil was increased to 1 liter methane per m2 and hour. After a short period of 'habituation' methane again could only be observed at significant depth in the soil profile. 94 - 97% of the injected methane was oxidised. At most Afvalzorg landfills gas generation is less then 1 liter per m2 and hour. Teh project can already be called succesful. The testfield built with the long-stick excavator did slightly better than the testfield built with the bulldozer. In july 2011 the methane load to the cover soil was increased to 2.5 liter methane per m2 and hour.