THE BIOGAS PLANT AT BALLYTOBIN
Site: The Camphill Community, Ballytobin, Callan, County Kilkenny, Ireland
Start-up date: December 1999
Owner: Bio-Energy & Organic Fertiliser Services (BEOFS) – a company established by the
Camphill Community to design, build and operate the biogas plant.
SUMMARY
In this small-scale centralised anaerobic digestion plant, slurry collected from local farms is
co-digested with kitchen refuse and food-industry wastes brought from as far as Dublin and
Cork; the biogas produced fuels a small district heating system. The liquid digestate is returned
to the farmers as fertiliser, and the solid residues are composted for use as soil conditioner.
AIMS of the PROJECT
To satisfy the energy requirements of a small community whilst making a positive environmental
impact.
To demonstrate centralised anaerobic digestion for the first time in Ireland.
To create work opportunities for persons needing a supportive work environment.
BACKGROUND
Founded in Scotland by some refugees from Nazi-occupied Austria, the Camphill movement
cares for young persons with special needs. At the Camphill Community in Ballytobin between
80 and 100 people with multiple disabilities and their volunteer helpers live, learn, work and
relax in a traditional farmhouse and in modern purpose-built accommodation. There are
classrooms, art and craft workshops, and a large hall used for community activities, religious
services, local events and seminars. About eleven hectares of land are used for grazing and
gardening.
The community farms organically and is strongly committed to caring for the environment, and
Ireland's first Centralised Anaerobic Digestion plant was commissioned here in 1999. The
"Genesis Project" was encouraged and actively supported by Kilkenny County Council,
Tipperary Rural Business Development Institute, FAS, and the Barrow-Nore-Suir Development
Board; technical assistance came from UCG Environmental Science Section, Teagasc, and SolEarth Architects, of Dublin.
DESCRIPTION
A novel arrangement of two digesters operating in series forms the core of the installation.
Food waste (mixed with some slurry to increase fluidity if necessary) is fed into one end of a
150m3 horizontal steel 'plug-flow' reactor along which it is slowly moved by a rotating spiral
impeller, reaching the discharge point after about 20 days. The contents are maintained at a
temperature of 55oC, resulting in the destruction of most pathogens and parasites. (New
regulations will require a pre-treatment stage where the food waste is heated at 70OC for one
hour before digestion, to ensure complete sterilisation).
The partially digested material displaced from the plug-flow digester together with undigested
slurry is pumped into the second 'stirred' digester; this is a 450 m3 tank covered by a flexible
double membrane which acts as a gasholder to accommodate small fluctuations in gas
production and demand. In this vessel digestion takes place at 37OC, and retention time is about
30 days.
Spent liquor leaving the second digester is separated into solid and liquid phases, the liquid
being returned without charge to the farms where it is spread as fertiliser, and the solids are
composted and air-dried for sale or use on-site as a peat-free soil conditioner.
About 14 tonnes of slurry are collected free from four local farms every day. On average 6 to 8
tonnes of kitchen and food-industry wastes are also received daily, and 'gate fees' are charged to
the waste management companies concerned.
Periodically sludge removed from the community's sewage settlement tanks is also digested (the
filtrate from these tanks passes into reed-beds for neutralisation).
Biogas production is estimated at 600m3 per day, and it is utilised in either an 85kW or a 200kW
hot water boiler to supply the community district heating system, and also in a second 85 kW
boiler which heats the digesters.
A gas engine and 105 kVA generator set with combined-heat-and-power capability is installed.
Unfortunately, BEOFS was not successful in obtaining a contract under recent AER rounds, and
the unit is retained only as an emergency standby generator; consequently, about 100m3 of
surplus gas has to be flared daily during the summer months.
INVESTMENTS & FINANCING
Support for the capital cost of the initial phase of construction was received from the Rural
Development Programme, and for the second phase from the European 'Leader Programme II'.
A grant towards non-capital costs (design, project management, etc.) came from the European
'Horizon' scheme, supporting projects creating employment for persons with disabilities.
As a demonstration project, funding for dissemination of information (including a seminar held
on-site in June 2000) came from the EU 'Altener' programme.
Four persons are employed full-time in operating and maintaining the biogas plant, collecting
slurry, delivering digestate, and processing compost; residents of the community assist as
required. The wages of the manager (who is a qualified gasfitter) and one labourer are met
entirely from revenues ( mainly gate fees), whilst those of two other local persons are subsidised
by a social employment scheme.
RESULTS & ENVIRONMENTAL IMPACT
Energy content of the biogas produced is circa 5 000 GJ (gross CV) per annum; some
500 GJ is lost in flared surplus gas, and an estimated 2 000 GJ per year is used for digester
heating, so that net annual energy production is about 2 500 GJ. Used in the district heating
boilers, this energy displaces approximately 55 000 litres of gas-oil, avoiding the emission of 165
tonnes of carbon dioxide of fossil-fuel origin every year.
The destruction of many pathogens and parasites reduces the risk of diseases being passed
between animals, and between animals and humans. Weed seeds are also killed.
The separated liquid digestate contains less than 5% solid matter and is easily spread using
simple spraying techniques; containing most of the nitrogen, phosphorus and potassium of the
original slurry, it is rapidly absorbed in to the soil (minimising run-off into watercourses) and is
readily taken up by plants. The liquid is practically odourless, obviating the unpleasant smells
associated with spreading raw manure.
LESSONS LEARNED
Centralised co-digestion of farm slurry with mixed food wastes has been successfully
demonstrated.
Rigorous monitoring of food wastes has proven necessary to ensure that digestion is not inhibited
e.g. by adverse pH values.
Maintenance of the plug-flow digester has proven more difficult than with the stirred reactor, due
to the need to empty the vessel to effect any repairs to the impeller.
REPLICABILITY
This small, centralised biogas plant might be replicated wherever a sufficient local demand for
heat exists (e.g. residential communities, swimming pools & leisure centres, or rural industrial
operations). Co-digestion of manure with other organic materials enhances gas production, and
the acceptance of such wastes from waste management companies would provide additional
revenues.
The relatively small size of Irish farms imposes economic and logistical difficulties in collecting
large amounts of slurry, so inhibiting the development of large scale centralised digesters. Except
where there is a local requirement for large amounts of heat or there is a potential purchaser of a
medium grade gaseous fuel (such as a brickworks), such plants would have to operate as
combined heat-&-power generators and maximise their sales of electricity.
MAIN MANUFACTURER & SUPPLIER
Biogas Nord of Germany designed and constructed the plant.
Biogas Nord GmbH
Kreuzstrasse 12
D – 33602 Bielefeld
Germany
tel: +49 521 55 44
fax: +49 521 48
www.biogas-nord.de
MORE INFORMATION
Further information may be obtained from -Mark Dwan
Camphill Community
Ballytobin
Callan
Co. Kilkenny
Ireland
tel: +353 (0)56 25114
fax: +353 (0)56 25849
markdwan@ballytobin.ie