Investigation of methane formation processes during waste disposal in the northern territories

Zabelina Alexandra Victorovna Practice teacher, ITMO University 197101, Russia, Saint Petersburg, Kronverksky ave., 49 zabelina-eco@mail.ru

1. Introduction

One of the zones in the Russian Federation for which the actual problem of correct accounting of methane and other emissions of pollutants and greenhouse gases in landfill gas is the Arctic zone. Despite the low population density, the need for highly efficient facilities for the treatment of MSW is quite relevant here. The climatic features of the location region, the geoecological features of the structure of MSW landfills, the technologies used in the placement of MSW, taking into account the best available technologies (BAT), together should be taken into account when calculating the formation and rationing of emissions.

According to the data of the consolidated reporting 2-TP (waste), formed by the Federal Service for Supervision of Environmental Management, as of the end of 2022, the disposal of production and consumption waste, in general, remains the main type of solid municipal waste management (hereinafter referred to as MSW) ^[1-4].  

Currently, the normalization and calculation of emissions from landfills of MSW is carried out according to the "Methodology for calculating the quantitative characteristics of emissions of pollutants into the atmosphere from landfills of solid household and industrial waste" approved in 2004 ^[5-8]. It calculates landfill gas emissions based on the amount of waste disposed with an increasing total for each calendar year. Emissions are calculated based on the content of the organic component, fat-like, carbohydrate-like and protein substances in organic matter, as well as taking into account the average humidity of waste.

The period of active methane release does not take into account the geochemical and climatic features of the region where the landfill is located; the last two years of waste disposal can be excluded from consideration due to the lack of stable methane release in the surface layers of the landfill body ^[9-13].

In addition, the 2004 methodology does not take into account the heterogeneity of the landfill body, the different density of waste depending on the depth of their occurrence and, accordingly, the uneven accumulation of landfill gas ^[14-16].

In order to confirm the hypothesis that the heterogeneity of the landfill body structure at the stage of post-operational maintenance and completion of the life cycle as a waste disposal facility leads to heterogeneity of landfill gas accumulations and emissions in the summer of 2022, a study of volume-density characteristics was conducted; in 2023, a gas-geochemical survey of the studied waste disposal facilities in the Leningrad Region and in the city of Norilsk. The studied polygons are approaching the period of reclamation.

The purpose of this study is to analyze the features of methane formation processes at MSW landfills.

2. Methodology and methods of research.

At the first stage of the research using the RTK (Real Time Kinematic) method, which consists in satellite positioning with a high degree of accuracy (up to 1 cm), in the mode of static definitions and movements from point to point during one study session with connection to the Geospider network ^[17], a topographic survey of the relief and contour was performed polygon bodies with a section of the relief horizontally through one meter. The received data was uploaded to the AutoCAD program.

At the second stage, drilling of pits for sampling was performed to study the volume-density characteristics of the MSW landfill ^{[18, 19]}. The volumetric density study was carried out only on the horizontal surface of the landfill, the lateral slopes were not studied due to the technical impossibility of installing drilling equipment on them. Samples were taken from the landfill body:  from the surface layer of waste and in layers at a depth of up to 51 meters. Such a sample was taken as a representative sample, which, when passing the well to a given depth, completely filled the volume of the core pipe, and when lifting which there was no loss of a significant part of the sample volume. To determine the volume of the sampled sample, measurements of the core pipe and the depth of the face were performed.

At the third stage, in order to study the composition of landfill gas in the surface layers of the spent landfill maps, a gas-geochemical survey of the territory was performed using the method of surface drilling of spent landfill maps with the installation of observation points. Air samples were taken from boreholes and the volume fraction of landfill gas components – CH4 and CO2 - was measured.

On the body of the polygon, access to the measurement point was carried out using a GPS navigator, measurement conditions and hindering factors were assessed. The study of the gas-air mixture obtained as a result of sampling was carried out at each point with a gas analyzer, the duct of which was connected through silicone nozzles to the borehole pipe.

The hole was driven to a depth of 0.8 meters, which corresponds to the depth of the last year of waste disposal. The research was carried out on an area of 5.7 hectares in 23 locations. The hole has a perforation at the depth of the sampling point for free air flow into the measuring path. The data obtained during the measurements were recorded in a field journal.

The measurements were carried out under meteorological conditions corresponding to the operating parameters of the measuring instruments. The surveys were carried out using devices PGA-1, PGA-300, MAG-6 P-V, which have operating manuals and valid verification certificates. The meteorological conditions during the measurements corresponded to acceptable ones.

3. The results of the study

The results of the study of the volume-density characteristics of the MSW landfill body are presented in Table 1.

The results of the experiment on measuring the volume-density characteristics of the MSW landfill showed that the density in the lower layers of waste disposal significantly exceeds the density in the surface layers of landfill masses.  

The results of the gas-geochemical study (Figure 2) and the measurement of concentrations of individual components of landfill gas showed the absence of detectable concentrations (below the detection limit), which allows us to conclude that waste disposed of more than 15 years ago does not participate in the formation of landfill gas.

Due to the natural processes of settling of the landfill body under the influence of gravity, landfill gas moved from the waste layers placed more than 15 years ago to the upper layers through natural man-made ruptures. The implementation of active degassing contributed to the release of landfill gas from the lower layers of waste, which currently represent a stable and inert base of the landfill body.

Figure 2. The process of gas-geochemical research at the municipal solid waste disposal facility^[20].

During the experiment, data were also obtained on significant concentrations of methane in the upper layers of waste disposed over the last two years of operation of the MSW landfill, which are not taken into account when calculating, rationing and controlling emissions from waste disposal facilities.  The results of a gas-geochemical survey with data on the volume fractions of methane and carbon dioxide concentrations are presented in Table 2.  

Table 2 – Results of gas-geochemical studies

The waste that is placed in the landfill begins to emit methane within a few months after its placement. In the first year, methane release usually reaches a peak, as the biological decomposition of organic materials begins in the absence of oxygen. In the future, the rate of methane release decreases, but methane continues to be released for many years, sometimes decades after the landfill is closed. According to the results of the field study, the presence of methane in the waste of the first year of placement in a volume fraction from 0 to 61%, carbon dioxide in a volume fraction from 0 to 11.88% was found. According to European climate standards ^[12-15], such methane release is considered significant and can have an impact on the greenhouse effect. Thus, these landfills of MSW can be considered as a significant source of greenhouse gas emissions.

4. Conclusions.

As the results of volume-density studies and gas-chemical examination have shown, the density in the lower layers of municipal solid waste is significantly higher than in the layers later in time of placement, the amount of landfill gas released is not significant. At the same time, active methane formation occurs in the upper layers of the waste mass at the depths corresponding to the first year of waste disposal.

The current methodology for calculating emissions from MSW landfills does not consider the features of methane extraction at different stages of the landfill life cycle. Emissions from the decomposition of waste over the last two years of disposal are not taken into account in the calculations of emissions, which creates prerequisites for adjusting the methodology based on the results of instrumental measurements.

In general, it can be argued that clarifying information on landfill gas emissions at MSW landfills based on instrumental measurements will allow for more reliable results in calculating emissions and determining possible carbon units when introducing BAT.  Accurate calculation of landfill gas emissions and their disposal fully meets the goals of environmental protection and rational nature management in the Arctic zone.