Embracing the natural cycle
Colin Brade and Aidan Cumiskey of Monsal look at the positive benefits of using biosolids in agriculture and why the water industry should do more to promote organic recycling
The focus of environmental concerns has shifted from water to waste management.
Landfill opportunities for waste disposal will reduce significantly because
of its unpopularity and regulatory restrictions. European waste policy is based
on a hierarchy of management priorities: minimisation, recycling, incineration
(with energy recovery) and landfill. Food waste, the organic fraction of municipal
solid waste, animal and sewage sludge are all biogenic materials and should
be used as a resource not treated as waste.
The alternatives to beneficial recycling are the waste disposal routes of incineration,
gasification and landfill. These pose many environmental, technical and public
acceptance problems and do not contribute to sustainable development. Despite
all of this, over the last few years, the long-term viability of the agricultural
route has been questioned and the resulting uncertainty poses a major risk to
the water utilities in their biosolids recycling operations and associated sludge
treatment processes. This in turn has a negative effect on investment in treatment
technology by water utilities and sludge technology companies who need to have
an opportunity to realise a return on their capital investment projects.
This uncertainty has arisen as a result of specific sector and general public
concerns relating to farming and food production practices in the UK. The recent
outbreaks of BSE in cattle, Salmonella and Campylobacter in poultry,
and Escherichia coli type 0157 in meat products have increased public
awareness of food hygiene and the food chain as a major route for pathogen transmission.
Whilst there is little evidence of disease in man or animals resulting from
sludge applications to land, the need for more fundamental research was acknowledged
by the industry to allow these concerns to be fully addressed.
Worldwide there is a huge amount of research into wastewater sludge and its
use on land, relating to both risks and benefits. In the US the Environmental
Protection Agency (USEPA) Code of Regulations part 503, which cover use of biosolids
in land applications, was based on an 11-year study costing $15M and covering
14 pathway risk assessments from pathogens and metals. In the UK a major research
programme was commissioned by UK Water Industry Research (UKWIR) in 1998, with
an annual budget of about £3M funded by its member water companies and
authorities plus additional funding from other sources including the Water Environment
Research Foundation (WERF), American Water Works Association Research Foundation
(AWWARF), Department of the Environment, Transport and the Regions (DETR), Ministry
of Agriculture, Fisheries and Foods (MAFF), Department of Health (DoH) and the
Environment Agency (EA).
The UK research is only a part of the work being undertaken in Europe and in
October 2002 the European Commission organised a Researching the Sludge Directive
workshop in Brussels. It was reported that the workshop found: “Overall,
the research studies demonstrate that sewage sludge can be used safely in agriculture
in the EU and contributes to the pursuit of sustainability, with minimal risk
to the environment or the food chain. Sewage sludge makes a very minor contribution
to metal levels and organic contaminants in soil and plants. The risk of pathogen
transfer to the food chain can be substantially minimised through treatment
and cropping and harvesting restrictions. Conversely, the benefits are compelling
for using the nutrient, organic matter and essential elements found in sludge
to improve soil quality and stimulate plant growth.”
The results of the UK research and other related studies were presented in
London on January 9, 2002 at the Chartered Institution of Water and Environmental
Management (CIWEM) conference, Biosolids the Risks and Benefits – an Update
on the Latest Research. Although much of the work has been separately published
this was possibly the first opportunity for so much of it to be reviewed in
public by the experts involved. Whilst most of the presentations dealt with
risk assessment, Dr Chris Rowlands in his presentation of the joint work undertaken
by ADAS, SAC, WRc and UKWIR, Biosolids Benefits to Soil Quality and Fertility,
focused on the positive benefits of biosolids use. Dr Rowlands was clear in
his view that: “With all the research undertaken and risk analysis in place,
the industry should now be taking a proactive approach rather than the conservative
and defensive position it has taken in the past, extolling the benefits offered
The authors were left with the clear view that, subject to adherence to the
Code of Practice, the use of biosolids in agriculture represents best environmental
practice in most cases, contributes to sustainable development and provides
many direct benefits to the farmer and consumer with negligible risk.
In the US, where various lobby groups have campaigned over many years against
sludge recycling, the USEPA 503 regulations which have been in use since 1993
have provided a firm scientific basis so that biosolids can be positively and
confidently marketed. Assisted by the implementation of these regulations the
percentage of facilities using sludge to land has increased from 35% in 1988
to 54% in 1997.
The US regulations classify sludge as Class A (below pathogen detection level)
and Class B (conventional) in a similar way to the new UK Code of Practice’s
enhanced and treated sludge classification. In the US there is a large asset
base in recycling technologies including anaerobic digestion, chemical stabilisation,
composting and heat drying amongst others. Already 12% of biosolids treatment
facilities in the US now produce Class A sludge and that number is increasing.
Where does that leave us? Well, the UK also already has a large asset base
in recycling technologies – mostly mesophilic anaerobic digestion supported
by thickening, dewatering and thermal drying facilities. It has long been established
that proper treatment of sludge to reduce microbiological hazards, odour, volume
and mass is essential in the production of biosolids suitable for use on land.
Existing technologies with refurbishment and enhancement as necessary, have
the capability to meet the requirements for high quality biosolids and in particular
to satisfy the new UK Code of Practice classifications for treated and enhanced
sludges, and also the requirements of the forthcoming upgrade of the European
Directive on Sludge to Land 1986.
With sensible refurbishment incorporating technical improvements existing plants
can be expected to provide many years of service at low cost with a high level
of operability and maintainability. Furthermore, existing manpower, familiar
with conventional sludge treatment processes, will also be comfortable in operating
Anaerobic digestion, pre-pasteurisation, thermophilic operation and thermal
drying provide a suite of environmentally friendly modular processes which can
complement each other and be combined to meet particular site requirements.
Biological processes based on the intensification of naturally occurring pathways
are inherently environmentally friendly and minimise risk and costs. The right
combination of modular process units in the overall treatment flowsheet will
allow energy consumption to be minimised and thus contribute further to environmental
In the US there is increasing activity in the application of two-stage digestion,
some incorporating a thermophilic stage. This promotes pathogen destruction
and offers the prospect of enhanced process stability, gas production and solids
destruction. Others are looking at bolt-on thermal pre-pasteurisation or chemical
stabilisation, both of which can provide an immediate short-term fix. All of
these process options can be achieved with relatively low capital investment,
however revenue costs vary considerably with biological processes coming up
trumps. The lesson from the US is that the regulatory and market needs can be
addressed using existing assets. The industry needs long-term sustainable solutions
and with pressure on de-manning, robust biological processes start to sound
very attractive when faced with the alternatives.
On a broader note the industry can do more to promote recycling – a solution
which many in the water industry believe is right in the long-term. At the 65th
European Biosolids and Organic Residuals Conference, Dr Norman Lowe announced
an initiative by the EA which will investigate how partnerships can be developed
to promote recycling of organic wastes, recognising the success of the US approach.
This initiative aims to protect the practice of recycling of organic wastes
to land for the future. This will involve a change from, “you can recycle
if you wish – that is up to you and if you do these are the rules” to,
“we all think that recycling is good and we will help you to do that but
these are the rules which have to be met as a minimum”. Whilst this may
initially seem like a minor change in policy, the effect is very positive in
favour of recycling.
The practice of recycling sludge to land following effective treatment to stabilise
and reduce pathogens in line with the new Code of Practice will in most cases
provide best environmental practice and will contribute to sustainable development
in the long-term. Public confidence can be reassured with the industry taking
a proactive and positive approach to promote and provide high quality biosolids
for beneficial use.
The authors would like to thank the following for their contributions in
the preparation of this article: Dr Tim Evans, Tim Evans Environmental; Dr Peter
Matthews, EA/Monsal and Dr Chris Rowlands, Severn Trent Water.
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