Effects on greenhouse gases of the application of MBT output, biosolids and compost on land
MSc Thesis Summary by Anna-Maria Skartsila: September 2010
Supervisors: Dr Nick Voulvoulis and Dr Martin Head
Objectives:
This project aimed to investigate the effect on greenhouse gases emitted by soil, following the application of
bio-solid wastes to the soil’s surface. Four main project objectives were identified:
1. to gain primary data of the GHG concentrations emitted
after the application of MBT output, quality compost and
biosolids on land;
2. to
study
the
effects
on
greenhouse
gas
(GHG)
concentrations, of the application of compost, biosolids
and MBT output to soil
3. to research the way that different soil PHs may affect
these concentrations.
4. to research the way that different soil moisture contents
may affect these concentrations.
Introduction:
Atmospheric concentrations of the three main greenhouse gases: carbon dioxide (CO 2), methane (CH4) and
nitrous oxide (N2O) have increased since the industrial revolution due to anthropogenic activities. Population
growth and an observed change in life style during the last decades, have led to an increasing rate of waste
generation. 70% of the generated Municipal Solid Waste goes to landfill, the most dominant method of waste
disposal which contributes 25% of total emissions of CH4.
Increasing concerns about the negative effects of landfill emissions on human health and the natural
environment have led to the introduction of European directives.
The Kyoto Protocol sets binding policies and
practices for 37 industrialised countries and
the European community, which target the
reduction of greenhouse gas emissions. The
UK and other Member States also have to
meet stringent targets under the EU Landfill
Directive for the reduction of the amount of
biodegradable municipal waste going to
landfill.
Mechanical Biological Treatment (MBT) is a
method that processes a wide variety of
waste and can leave a large proportion of
Mechanical Biological Treatment options
(DEFRA, 2007)
residue
with
uncertain
biodegradability
potential, which may be applied to land as a
soil conditioner. MBT is preferred by many local authorities as it holds a good public perception (DEFRA,
2007) and has potential energy and materials recovery.
While the use of MBT plants may have beneficial effects on meeting the Landfill Directive targets, soil
sequestration of atmospheric CO2 through land application of organic residues may have beneficial effects
as a strategy to offset the increase in the concentration of GHGs in the atmosphere. However, only limited
scientific data is available on this subject. This project will form part of a bigger Life Cycle Analysis (LCA) for
treated organic waste and will aim to cover the impacts that application to land of MBT output quality
compost and biosolids will have on gaseous emissions.
Methodology
First of all a literature review was managed to illustrate the drivers for this thesis and to show the necessity of
the specific study, while reviewing what is already known about applications of organic treated waste.
Next, the experimental part of this study, took place in Silwood Park campus, and a research was made prior
the experiment in order to define the three most suitable sites that would be used for the experiment, in
terms of differences in soil pH.
Compost, biosolids and MBT output samples were obtained from
different facilities of organic waste treatment, and were described in
terms of pH, moisture content, treatment method and feedstock
material used for their generation. These samples were then applied
to soil; in dedicated closed chambers that were placed in the three
sites with the different soil pHs that were selected in the campus.
Flux measurements by gas sample collection and analysis for CO2,
CH4, O2, N, H2, Ethylene, Ethane and Acetylene through gas
chromatography, took place.
After the concentrations of these gases were
known, an effort to interpret the factors that were
responsible for different concentrations was
made. Soil PH and moisture, and treatment
method used for the production of each of the
treated organic samples were the parameters
that were studied during the analysis.
Results

No CH4, Ethylene, Ethane and Acetylene emissions were observed through soils with pH 4.56, pH
5.67 and pH 6.7 after the application of MBT output, biosolids and compost.

No significant variations in the N and O2 content of the atmosphere were observed after the
application of MBT output, biosolids and compost on land.

After the application of MBT output on soil with pH 5.67 & soil moisture=7.9%, 0.1% of CO 2 was
emitted 30 minutes after the closure of the chamber that enclosed this soil. This concentration was
eliminated within 30 minutes.

After the application of biosolids on soil with pH 4.56 & soil moisture=4.5%, 0.1% of CO 2 was emitted
at closure and 30 minutes later this concentration increases to 0.2%.

After the application of biosolids on soil with pH 5.67& soil moisture=5.3%, 0.2% of CO 2 was emitted
30 minutes after closure. This concentration was eliminated within 30 minutes.

After the application of biosolids on soil with pH 6.7 & soil moisture=4%, 0.1% of CO2 was emitted 60
minutes after closure.

After the application of compost on soil with pH 5.67 & soil moisture=5.3%, 0.2% of CO2 was emitted
60 minutes after closure.
Discussion, Conclusions and Implications:
After the analysis of the results the following trends were observed:

CO2 was the only gas that was emitted through soil after the application of MBT output, biosolids and
compost

Outputs from different facilities have a different behaviour in terms of gas emissions after application
on soil

Soil with pH 5.67 was observed to be the soil that enhances CO 2 emissions through soil respiration

Soil with pH 6.7 seemed to be the soil with the less emissions after the application of MBT output,
biosolids and compost on soil

Biosolids was the sample that when applied on soil had the most significant emissions compared
with the other two samples

MBT output was the sample that when applied on soil had the most optimum behaviour in terms of
gas emissions through soil
However, it should be mentioned that the data obtained should be used keeping in mind the implications
related to this study. First of all, there are numerous parameters that may interact during the application of
such samples onto soil. A major problem of researching the application of treated organic material on soil is
that the experimental conditions and the tested organic samples are so different that it is difficult to
concentrate results into general conclusions. Chemical and physical properties of the applied samples
include several factors that may affect the emitted gases after their application on soil. Chemical and
physical properties of the soil as well as the fact that micro-populations of the soil may be disturbed by this
application made the analysis of the results extremely challenging. Apart from these, external factors such as
seasonal effect and atmospheric pressure as well as soil management techniques also have an effect on
gas production and emission. These techniques include tillage, irrigation and organic matter application.
Other factors affecting gas generation and emission through soil are also the available C and N content in
soil. Another point to consider in terms of implications related to this study is the limited scientific data
available on this subject for comparison to the data obtained. Indeed, there is a lack of scientific knowledge
in terms of effects on the environment of the application of CLOs on land and this is mainly due to the fact
that long-term field experiments would be required for this study that should involve a major number of
variables.
Thus, good quality scientific evidence needs to be gathered which should involve:

The effect that the different properties of pre-treated waste in terms of new generation engineering
might have on gas emissions.

The way that gas emissions after such application on soil would be affected by seasonal effect and
atmospheric pressure as well as soil management techniques.

The effect that such application would have on soil fertility and productivity