NUI Galway – UL Alliance First Annual ENGINEERING AND - ARAN ...

Assessment of the Suitability of Co-Mixed and Composted Separated Solids of
Pig Manure for Use as a Solid Fuel
Shane Troy ab , Tereza Nolan a , James J. Leahy c , Witold Kwapinski c , Peadar G. Lawlor a and
Mark G. Healy b .
a Teagasc, Pig Development Department, Moorepark, Fermoy, Co. Cork, Ireland
b Civil Engineering, National University of Ireland, Galway, Co. Galway, Ireland
c Chemical and Environmental Science, University of Limerick, Limerick, Ireland
E-mail: shane.troy@teagasc.ie
Abstract
The aim of this project is to investigate the use of the
solid portion of separated pig manure mixed with
various bulking agents as a both a compost and a solid
fuel. Composting experiments showed sawdust to be the
best of the bulking agents studied. An initial carbon
(C): nitrogen (N) ratio of 16:1 was used to produce
stable compost using separated pig manure and
sawdust. The three products of pyrolysis; biochar, biooil
and gas are being investigated. The bio-oil and
gases will be characterised as a fuel to provide the
energy needs of the pyrolysis process. The biochar is
being characterised as a fertiliser and soil addendum.
The effects of composting of the swine manure solids
before pyrolysis and the addition of C-rich bulking
agents is also being investigated.
1. Introduction
Management of pig manure is becoming an
expensive problem for pig farmers as new legislation to
prevent environmental pollution reduces the spreadlands
available. Practical and economically viable on-farm
solutions for swine wastewater treatment are needed to
tackle this growing problem. The aim of this research is
to investigate (a) composting, (b) pyrolysis and (c) both
composting and pyrolysis as methods of treating pig
manure in an economically viable manner, while also
providing environmental benefits. Composting stabilises
organic matter, destroys pathogens, and decreases water
content and odours. Pyrolysis of swine manure may
reduce waste disposal costs and provide cost effective
energy to be used on the farm. Pyrolysis is a process
whereby a biomass feedstock is thermally degraded at
high temperatures in an oxygen-free atmosphere. The
products of this process are biochar, bio-oil and gases.
The bio-oil and gases can be used as fuels or to provide
the energy needs of the pyrolysis process. Biochar may
also be used as a fuel, or as a fertiliser and soil
addendum, for C sequestration and for gas scrubbing.
2. Composting Experiments
Four composting trials were undertaken using
separated pig manure solids and a variety of C-rich
bulking agents. Trials 1 and 2 investigated the effect of
the addition of different bulking agents on the quality of
compost produced. Greenwaste, sawdust, woodchip and
straw were the bulking agents studied. Results showed
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that sawdust was the bulking agent which produced the
best quality compost. Trials 3 and 4 investigated the
effect of different quantities of sawdust addition. The
aim was to show if a C:N ratio lower than the
recommended 25-30 could be used to produce stable
compost. It was found that an initial C:N ratio of 16
resulted in stable compost, thus reducing the cost of the
process for farmers.
2. Characterisation of biochar
Proximate and ultimate analyses have been
undertaken on feedstock and biochar from 24 different
biomass mixtures. Six samples (anaerobically digested
pig manure with added sawdust, both before and after
composting) have been further analysed to investigate
surface area, pyrolysis energy requirements and pore
structure. Analysis has shown that pre-composting of
biomass before pyrolysis results in decreased heating
values, fixed carbon content and surface area. Product
yield is also changed for pre-composted samples;
biochar and bio-oil yield increases, while gas yield
decreases. The addition of bulking agents to pig manure
before pyrolysis results in increased heating values,
fixed carbon contents and surface areas.
3. Ongoing experiments
Further studies investigating the fuel characteristics
of the bio-oil and gases produced by the six feedstocks
described above are ongoing. An energy balance will be
conducted using experimental data from the separation,
composting and pyrolysis studies. The aim is to identify
the viability of an on-farm pyrolysis plant producing
biochar from pig manure with the energy requirements
provided by the bio-oil and gases. The impact of precomposting
will also be assessed in this energy balance.
The effect of sawdust addition on the energy balance
will show whether it is worthwhile for pig farmers to
import sawdust onto their farm to use as a co-feedstock.
4. Future Experiments
Landspreading analyses are planned using pig
manure, pig manure compost and artificial fertiliser with
and without the addition of pig manure biochar under
medium rainfall conditions. These analyses will quantify
the nutrient leaching from the three fertilisers and also
the nutrient retention capacity gained when biochar is
added to soil.