Farming-out reed technology
Stewart Moir of Scottish Agricultural College's consultancy department, Heartland Environmental, explores the potential for reed beds in treating agricultural effluent
Reed beds are best known for the treatment of domestic sewage. They are a proven
and accepted technique by the Environment Agency (EA) and the Scottish Environment
Protection Agency (SEPA) for the treatment of domestic sewage in rural areas
where connection to the mains sewer is not available.
The Scottish Agricultural College (SAC) is actively involved in the treatment
of effluents which issue from rural communities and industries. As Scotland’s
largest reed bed designer, SAC has built a reputation over the years as being
a UK leader in the development of reed bed technology.
Since 1985 SAC has been involved in an advisory capacity on many reed bed systems
and since 1993 the company has been designing and building reed bed systems
commercially. Reed beds, however, form only a part of its overall service to
rural communities, industry and agriculture under its ‘Effluent Treatment Services’
SAC advises on and specifies a range of systems available for developments
that do not have access to a local authority mains sewer. Reed beds form the
bulk of its business, however, and to-date SAC has designed in excess of 90
systems. Around 70% of these systems are for domestic clients. SAC systems treat
sewage from developments which range from between one house and several hundred
houses. The other 30% are reed bed systems for rural businesses and industries.
These reed beds serve developments such as caravan parks, hotels, visitor centres
and effluents from various industries such as vegetable processing, lorry park
run-off and leachate from landfill sites. Currently, SAC reed bed systems service
over 8,000 people, which is about 1.5M litres of effluent every day. This equates
to over 35,000m² of reed beds or about five football pitches in surface
One of SAC’s largest reed bed systems is for Cardrona village, a new rural
development in the Scottish Borders three miles south of Peebles. Cardrona Village
will consist of over 200 houses and a 150 bed four star hotel. The treatment
system is designed for a population equivalent of 1,400 and consists of four
large septic tanks followed by four large reed beds. This configuration is designed
to accommodate further development over the coming years. Two reed beds are
now fully operational, the first completed in early 2000, the second in October
The design process was challenging as not only had the legal requirements of
the discharge consent to be met, the system had to fit into the overall site
layout. This meant consultation with several house builders and the golf course
designer. The 340 acre Cardrona village site includes a new 18-hole golf course,
which surrounds the development on three sides. The reed bed system had to be
designed around several of the fairways, tees and greens. SAC also designed
the storm water run-off system for the village and the treatment pond had to
be landscaped within the golf course.
From the outset sustainability was a key design criteria for Cardrona, believed
to be the first new rural village in the Scottish Borders for over 200 years.
The system for Cardrona Village was designed for Scottish Borders Council in
consultation with East of Scotland Water (EoSW). The latter will be responsible
for operation and maintenance in the future. As well as providing an environmentally-sound
treatment system, the reed beds are actually built using over 7,000 tonnes of
recycled gravel, graded out from soil materials used in the construction of
the golf course.
Down on the Farm
SAC is not only involved in consultancy but also has an active programme of
research and development on the treatment of agricultural effluents and also
using waste materials as growing media. In the past SAC’s research has looked
at nutrient removal and pesticide degradation within reed bed systems. In 1999
SAC secured funding from the Scottish Executive Environment & Rural Affairs
Department (SEERAD) to investigate and develop a reed bed system which could
treat effluents from the dairy unit at SAC’s Auchincruive farm, near Ayr.
There are only a handful of systems in the UK designed for agricultural effluents
and most of them were built for research purposes. The very high strengths of
agricultural effluents have precluded them from being suitable for treatment
by reed bed systems. When comparing a typical rural stream which has a BOD in
the region of 3mg/l with silage effluent for example, with a BOD of anything
between 20,000 and 80,000mg/l, the challenge is clear. Any release of agricultural
effluent into a stream will result in a serious pollution incident.
The main aims of the research were to produce an effluent suitable for recycling
on the farm, achieve an effluent suitable for discharging to a watercourse and
ensure cost-effective construction, operation and maintenance.
Farms have many types of effluent which arise from many different activities
but they can be grouped into washings and contaminated waters. Washings can,
for example, arise from washing down machinery or milking equipment. Contaminated
waters are a pollutant and unsuitable for discharge. These waters can be from
yards where livestock is collected or moved across, or from clamps which store
livestock manures prior to application on the land. The strongest contaminated
waters come from silage clamps (where grass is stored for winter fodder).
These washings and contaminated waters are normally collected, stored and applied
to the land with livestock slurries thereby recycling nutrients. However, these
effluents can pose problems when stored and applied with slurries and removing
them from the system, by treating them separately, could provide several benefits.
At SAC’s Auchincruive farm they separated the washings from the dairy unit
and fed them into a treatment system. These washings arise from the sterile
part of the milking process. The cows are milked twice a day and after each
milking the pipe work and tanks, in which the milk is stored prior to collection,
are flushed and cleaned. The dairy washings, therefore, consist of water, milk
residue and disinfectants. Treating these washings is a challenge as they are
generally around pH12 and are sterile in addition to having a BOD of between
1,000 and 2,000mg/l. Dairy washings are a true waste product to the farmer as
they have negligible nutrient content.
The dairy washings are collected and pre-treated in an aerobic sequence batch
reactor (SBR). The washings are then discharged into a number of reed beds for
final treatment. Both the SBR and the reed beds work in sequence with the scheduled
milking of the cows. The farm runs a large herd of over 200 cows and each day
the washings account for approximately 3m3 of wastewater which is equivalent
to 1,100m³ per annum.
Pre-treating the washings means that the footprint of the reed beds can be
kept to an absolute minimum so as not to use valuable land. Hence the reed beds
have a total footprint area of only 52m².
The system has been running since January 2000 and results have been excellent.
SAC has consistently achieved a standard issue from the reed beds below the
typical UK watercourse discharge standard of 20mg/l BOD and 30mg/l suspended
solids. This type of system is now ready to be used by dairy farmers all over
the UK. This research is also applicable to food processors producing milk-based
Following on from this success SAC is now looking at treating silage effluent
currently collected with other yard run-off and irrigated onto the land at Auchincruive
separate from the livestock slurry. This effluent poses a completely different
problem in that pH4 is an average value and BOD varies between 5,000 and 30,000mg/l.
SAC is using similar technology in that it is aerating the collecting tank and
discharging into the reed bed system which has been extended to a total footprint
area of 130m2. Since May 2001 the extended reed bed system has been receiving
3m³ of dairy washings plus 3m³ of silage effluent each day.
Preliminary results are encouraging but would not at this stage allow the discharge
of the effluent into a watercourse. SAC is confident that this can be achieved
in the future.
The benefits of treating agricultural effluents, rather than applying them
to land, are significant. If washings and waters are not stored with the slurry
more storage space is available. The slurry will be thicker and therefore less
likely to run-off the land. This may go some way to reducing diffuse pollution
Farmers will also get better value for money. Less volume to spread means reduced
costs and each load of slurry that is spread will have a greater concentration
of nutrients per m³ when not diluted by nutrient-deficient washings.
Depending on the farm set-up other benefits such as reducing storage costs,
reducing water bills by recycling treated water and freeing-up land to increase
production are all possible spin-offs from treating effluents rather than storing
them prior to land application.
This programme of research runs until March 2003. Both the dairy washings and
the silage effluent systems are full scale, farm size demonstration units. Further
information on the pollution of water from agricultural sources can be found
in the Ministry of Agriculture, Fisheries and Food (MAFF, now Department of
the Environment, Food and Rural Affairs, DEFRA) 1998 publication ‘Code of
Good Agricultural Practice for the Prevention of Water‘, commonly called
The Water Code and also in the Scottish Office Agriculture, Environment and
Fisheries Department (SOAEFD, now SEERAD) 1997 publication ‘Prevention of
Environmental Pollution from Agricultural Activity‘, commonly called The
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