- from Sewage
Works to Composting Plant
The rate of adoption of
composting - especially of kerbside collected green waste - has
been accelerating over the past few years, but finding suitable
sites can be a limiting factor. The site chosen for this Enviros
designed project - and the extent to which existing infrastructure
has been modified and re-used -makes this project a remarkable example
of sustainable re-use on a large scale.
The Scottish Water Waste Services (SWWS) sewage treatment
works which was used had been standing idle since 2003.
It has now been converted by civil engineering contractor,
Mackenzie Construction into a very successful composting plant,
with design and project management provided by the Compost
Team of consultants, Enviros.
To convert a sewage works into a composting plant
might seem an unlikely transformation, but draining the sewage treatment
tanks and converting them into compost reception areas, windrow
slab areas and soon - under a second stage contract which commenced
in December - into in-vessel tunnels, has brought many advantages,
as well as significant cost-savings.
The Deerdykes Composting Plant, Cumbernauld, Scotland,
which has been taking green waste from three local authorities for
the past 9 months, lent itself very well to this transformation.
The project also attracted Scottish Executive support from the outset
and won a grant of approximately £600,000 (0.9M Euros) from the
Waste and Resources Action Programme (WRAP) Organics Capital Support
Programme, through funding provided by the Scottish Executive.
This funding helped Scottish Water produce and pre-sell the
first 500 tonnes of high quality compost, during the autumn
of 2005 to a local land restoration scheme.
Most of the future (PAS100) compost production for 2006 has
also been pre-sold for local industrial site restoration schemes.
Deerdykes was built in the 1970s and was originally
known as the Cumbernauld Sewage Purification Works. The Kelvin Valley
Sewer now serves the area, taking sewage past the site to a much
larger and more modern plant downstream.
Clearly, reuse - where possible - is the most sustainable
option for redundant civil engineering structures. Enviros Consulting
recommended reusing the works which were in good structural condition,
despite 30 years of use. In addition to structural elements, the
condition of the drainage system was also found to be very good
and has needed little more than a thorough cleaning - and only minor
modification - for its new role. Most of the original structures
are, to varying degrees, being recycled -
- The original activated sludge process plant, with inner walls
demolished, has become the compost reception, mixing, and pre-screening
- The original rectangular sedimentation tanks make excellent
in-vessel composting tunnels with their end walls demolished -
once a central dividing wall has been installed - and roofed.
- One of the two circular clarifier tanks has also been used to
store sludge press washwater and a gently sloping access ramp
has been added to lead vehicles down what were once tanks, but
are now composting bays.
Sedimentation Tank before commencement of
Demolition materials were crushed on site and were also reused
in the formation of the new slabs constructed for the maturation
At present, the plant operates on the open windrowing principle.
However, construction of in-vessel composting facilities is
underway and in-vessel composting will start when these are
complete in the summer of 2006. This further development of
the facility will enable the acceptance of a wide variety
of kitchen and catering wastes, requiring compliance with
the Animal By-Products Regulations (ABPR), while still providing
a high quality fully accredited PAS100 compost product.
The production of premium quality compost from a wide
range of organic waste materials requires a highly controlled in-vessel
environment. Deerdykes will use a forced-air, in-vessel process,
providing an initial sanitisation and stabilisation process over
an initial composting period, followed by maturation in the open.
This will be similar to the existing system already
in place at the Beddington Farmlands composting plant in Beddington,
Surrey - operated by Viridor Waste Management - and also designed
Blowers and fans will circulate air through pipes
into the composting tunnels, while a series of probes, set within
the composting mass, monitors the temperature. A biofilter will
provide a very high level of control on atmospheric discharges and
prevent the generation of odours.
It was fortuitous that the site was so well suited
to composting. The choice of alternative uses for the site had previously
highlighted a number of potential development challenges. The site
was not suited to housing development, being within an industrial
zone. However, finding an industrial tenant would not have been
easy, as several other industrial sites of a similar size were standing
vacant nearby. Furthermore, those properties could be utilised for
industry without the need for - and cost of - demolition of the
substantial existing sewage treatment works structures.
It is often time consuming and expensive to apply
for the necessary licences and consents to operate waste processing
facilities, such as composting plants. Here again, there were advantages
at this site. Discussions with the planning authority were simplified
for development as a waste management centre, based upon the previous
established use as a waste site.
|The suitability of the site was also recognised
as ideally situated for the delivery of green waste generated
in the main centres of population - it being located between
the main population centres of Scotland - e.g. the city of Glasgow
to the west (14Km) and Edinburgh (50Km) to the east. The site
is also directly accessible from a junction of the A80 dual
carriageway and, thus, readily accessible to the three neighbouring
unitary authorities comprising Glasgow City, East Dunbartonshire
and North Lanarkshire Councils.
Composting plant slab construction in progress
So, it was not surprising that the Deerdykes site
was highlighted when business managers at Scottish Water Waste Services
(SWWS) began to look for possible locations for the construction
of a new composting facility. The Deerdykes site rapidly became
the prime choice to be operated as a profitable venture on a commercial
basis. This would also assist the Scottish Executive (SE) and the
Waste Resources Action Programme (WRAP), tasked with promoting the
development of new waste facilities throughout Scotland.
A feasibility study by Enviros in early summer of
2004, showed that there would be strong initial demand from local
authorities for facilities to accept large quantities of green waste,
which could be economically processed on the site by windrow composting
on open slabs.
The need for this facility was also urgent - with
kerb side collections of green (garden) waste due to start in January
2005 - so there was very little time to design and construct the
facility to offer to the local authorities on a term contract basis.
Enviros was engaged in early autumn 2004 to obtain competitive
quotations and to supervise the commencement of demolition
of those parts of the works not destined to be reused, while
simultaneously designing the plant.
With only 4 months to the opening date, fast-tracking the
design process on an initial stage (30,000tpa) green waste
plant was essential, so that construction works could commence
as soon as the demolition contractor departed.
SWWS also has a growing number of clients in industries,
such as food production, that require additional sludge processing
capacity - for dewatering and treating liquid sludges, as well as
treatment of industrial sludge arriving on site in cake form. Disposal
of sludge cake solids by co-composting has been shown to be successful
elsewhere if in-vessel composting technology is utilised to ensure
a high degree of control of composting conditions, as well as odours
and bio-aerosols. Therefore, sludge press facilities have been included
within the initial design stages and subsequent construction contracts.
It has been recognised from the start that the composting
industry will develop in Scotland.
Furthermore, there will be a growing demand for the
more sophisticated composting techniques required for -
- Sludge co-composting with other (mostly green/garden) wastes;
- In vessel composting, to reduce emissions and, especially, to
avoid odours and provide a more controllable environment for the
- Accepting waste - which would be subject to the Animal By-Products
Regulations - from industry and from the planned segregation and
collection of additional organic waste streams, such as the introduction
of household kitchen waste collections which are being planned
by the unitary authorities.
The Deerdykes Facility will, in time, meet all these requirements.
The project was a first of its kind in Scotland and has provided
much needed composting capacity in the region. The existence of
this plant should lead to the development of others elsewhere in
The project has turned a liability into an asset for
the owner - Scottish Water Waste Services - and attracted a grant
of approximately £600,000 from The WRAP Organics Capital Support
Programme, through funding provided by the Scottish Executive.
It has been shown that sustainable and innovative
re-uses can be found for large redundant civil engineering structures.
The high quality compost produced is being sold successfully and,
as Scottish compost market requirements become more sophisticated,
SWWS will progress from the present simple, but effective open windrow
systems, to state-of-the-art in-vessel systems to process a wide
variety of organic materials and serve premium areas of the compost
To view a recent paper presented about the project
in November 2005 - click
For further information -