This Policy Position Statement outlines the main issues relating
to the treatment and use of wastewater biosolids, taking account of
legislation, practicability, risk management, resource
conservation, carbon reduction, soil protection, sustainability and
other matters of concern to legislators, regulators, the public and
other stakeholders, particularly in a UK context.
CIWEM calls for:
- A consistent and proportionate approach to policy for land
application of all organic resources
- A consistent and proportionate approach to policy for
production and use of biogas irrespective of feedstock so as to
enable [and not hinder] co-digestion. This should include
financial incentives for the renewable energy produced and rules
for the land application of digestate.
- Recognition by Government that the water industry has anaerobic
digestion assets and long experience of operating them and
electricity generation, which should be exploited for
- Government bodies to stop treating biosolids adversely, for
example the Quality Protocol for Compost excludes biosolids
although PAS100 'Specification for compost' on which it is based,
- Risk-based approach to legislation at the European level.
- Recognition that capturing phosphate from wastewater and using
it agronomically is a necessity because the world's reserves are
The Chartered Institution of Water and Environmental Management
(CIWEM) is the leading professional body for the people who plan,
protect and care for the environment and its resources, providing
educational opportunities, independent information to the public
and advice to government. Members in 98 countries include
scientists, engineers, ecologists and students.
Wastewater biosolids (sewage sludge) contain organic matter and
nutrients recovered from wastewater during its treatment.
Water is abstracted, cleaned, used and recovered to complete the
urban water cycle. Because most of the chemicals used in
society find their way into wastewater (see also Discussion 4, 6
and 7) there is need for risk assessment and risk management.
It is not merely the presence that matters; as Paracelsus said 500
years ago "the dose makes the poison" (i.e. concentration, pathway
and receptor). Understandably, sewage is emotive but in
reality the risks have been researched extensively and today's
practices are soundly based on science. Wastewater treatment
has improved the health of people and the water environment.
During the 1830s, half the children died before age 5 mainly from
diarrhoea, dysentery, typhoid and cholera because water used for
drinking was contaminated with sewage; wastewater collection and
treatment prevented these deaths. The UK's metropolitan
rivers contain more species of fish than at any time since before
the industrial revolution because of effective wastewater
collection and treatment.
In the 20th century, the world's human population increased from
1.6 billion to 6 bn, 2.6 bn of whom do not have access to
sanitation. The UN predicts the rate of increase will slow
from 2050 by which time the population will be 9 bn. For the
first time in history more people live in urban than rural
areas. Food with its embodied nutrients flows from rural to
urban areas. Food wastes, excreted organic matter and
nutrients are captured into biosolids, which can be used on farms
as biofertiliser to complete the nutrient cycles. Sewage
sludge can be digested to make biogas or incinerated, both yield
renewable energy though net energy from incineration alone is
marginal. By retrofitting enhancements to existing digesters
there is huge opportunity for co-digesting food and other
biodegradable waste as has been practised in Denmark for more than
10 years (Evans et al., 2002).
Phosphate is an essential nutrient and part of the DNA of all
organisms, it is thus irreplaceable. It is the least abundant
of the major plant nutrients. Adult human excrete 98% of the
phosphate consumed in their diets because they are turning over
cells rather than laying down new ones. There is already talk
of "peak phosphorus" (Cefic, 2008) and predictions that today's
resources will be exhausted in 65 years at the current rate of
exploitation; we might find another 200 years of reserves (Heffer
et al. 2006). Isaac Asimov summarised the consequences of
"…life can multiply until all the phosphorus is gone, and then
there is an inexorable halt which nothing can prevent…. We may be
able to substitute nuclear power for coal, and plastics for wood,
and yeast for meat, and friendliness for isolation - but for
phosphorus there is neither substitute nor replacement."
"Asimov on chemistry" (June 1974) Doubleday Company, New York
- The collection and treatment of municipal wastewater is one of
the most significant contributions to improved public health.
Sewage sludge contains the organic matter and nutrients separated
from and created during the transformation of wastewater into
treated, non-polluting water. Biosolids are the product of
treating sewage sludge so that it is safe to use on land.
- Wastewater biosolids treatment / use in the EU takes place
within the framework of the relevant directives (CEC, 1986 and CEC,
1991), implemented as national regulations, which may in turn be
complemented and amplified by national Codes of Practice. In
the UK these are the 1989 Sludge Use in Agriculture Regulations and
the 1996 Code of Practice; these are similar to the
"guidelines" (STC5, 1976 and STC20, 1981) that they replaced.
Thus there is more than 30 years' experience of using this risk
management model successfully and with no evidence of adverse
- When biosolids cannot be used on land, the only significant
alternative is thermal destruction, of which incineration is the
most established method; within the regulatory controls it is
safe. Disposal at sea was banned in 1998 and landfilling is
restricted within the EU. In general these alternatives
currently squander the phosphate in biosolids. However
phosphate could be extracted before incineration and/or the ash
could be stored pending the time when extracting phosphate from it
becomes economically viable.
- All of the chemicals used in society can be found in urban
wastewater at some concentration and therefore risk of excess must
be managed. A fundamental principle of risk management was
enunciated 500 years ago by Paracelsus: "the dose makes the
poison". For there to be a risk, there has to be a chain of
transmission from a source via a pathway to a receptor that can
deliver a harmful dose. If the dose delivered is too small to
be harmful; if there is no pathway; if there is no receptor, there
is no risk. When considering the source (see also 6 and 7),
one should recognise that some hazardous substances are persistent
and can accumulate in soil (if there is a succession of
applications of biosolids) and that an accumulated substance might
biodegrade or its bioavailability might change over time.
- In 1998, an agreement was reached between Water UK, farmers,
landowners and the British Retail Consortium, which developed
additional guidelines for the use of biosolids in agriculture. The
agreement has been adopted across the UK. As a consequence
sludge is treated according to the principles of HACCP (Hazard
Analysis Critical Control Point) and biosolids are applied
according to the "Safe sludge Matrix".
- The inputs of potential pollutants at point sources to sewer
(i.e. factories discharging into the urban wastewater collection
system) have been effectively controlled over the last 30 years so
that their concentrations in biosolids have been dramatically
reduced. For most wastewater treatment works further
reductions are now limited by contributions from diffuse sources
such as dental amalgam (mercury), cosmetics (zinc) and plumbing
- The manufacture, marketing and use of the substances considered
most dangerous (e.g. PCBs) has been reduced or eliminated by
legislation. They do not find their way into biosolids
because the source has been eliminated.
- The risk to health (i.e. the risk of pathogen transmission) is
controlled by biosolids treatment and/or restrictions on how land
is used after biosolids have been applied and the time delays
before harvesting, grazing, etc.,
- The risk of adverse environmental impact from potentially toxic
elements when biosolids are used on agricultural land is controlled
through the soil limit values set in the Sludge Regulations. These
limit values are based on sound science and are reviewed on the
basis of continuing R&D. CIWEM encourages continuation of
long-term field trials into the safety of these limit values.
- Compliance with the Sludge Regulations and the Nitrates
Directive are (Cross Compliance) obligations of the Single Payment
Scheme of the Common Agricultural Policy introduced in 2004 (Evans,
2005). However regulatory policy in the UK has not taken the
opportunity of this complementary requirement to simplify
- Biosolids treatment and their use or disposal account for
approximately half of the total cost of wastewater treatment.
- Biosolids contain organic matter and plant nutrients separated
from wastewater and concentrated during its treatment.
- The use of biosolids on land completes nutrient cycles and
conserves organic matter. It feeds the soil and promotes
better structure and life within the soil. It is thus a
component of sustainable development.
- Using biosolids on land to complete the phosphate cycle is
- The use of biosolids on land is, in many cases, the Best
Practicable Environmental Option (BPEO).
- When biosolids are used on land, they substitute for part of
the mineral fertiliser needs of crops, and because of the gradual
release properties of the nutrients the crops are frequently
healthier and therefore need fewer applications of crop protection
- CIWEM considers the term "sewage sludge" is really a misnomer
because 40%, or more, of the solids are excess biomass that has
grown during the wastewater treatment process and that was not
originally present in the sewage. CIWEM considers it should
be replaced with the term "wastewater biosolids" or
- Although the use of biosolids in agriculture is regulated,
there is no EU framework for the use of biosolids in forestry or
for land restoration. A more serious deficiency is with
regard to the spreading of manures and other residuals on
land. They can have similar environmental effects to
biosolids, but the quantities used are 40 times greater than
biosolids. Whilst supporting land application, CIWEM
considers that it is inconsistent to regulate 5% and not the
remaining 95% and encourages the Commission to reduce this
inconsistency by increasing the range of residuals and to consider
- CIWEM applauds the work of water utilities in the UK in using
such a large proportion (80% in 2005 for England and Wales) of the
biosolids on land to conserve organic matter and complete nutrient
- There is no documentary evidence of adverse effects on public
health where biosolids treatment and use have conformed to existing
- CIWEM considers no stakeholder should inhibit land application
of biosolids unless they have clear objective scientific evidence
of harm and challenges them to present such evidence.
- Nuisance may result if the operation of wastewater treatment
works or biosolids recycling sites cause offensive odours or
disruptive vehicle movements. However, implementation of good
practice can bring about substantial amelioration and often
elimination of such problems. CIWEM encourages everybody
involved with using organic resources on land to use practices that
do not cause offence.
- Whilst there are relatively few complaints about land
application of biosolids, odour is the root of nearly all of them;
CIWEM calls on Ofwat and water companies to move to treatments and
practices that do not cause odour nuisance and do not bring land
application into disrepute.
- CIWEM considers that any future policy changes should be
proportionate to risk and that their potential climate change
impacts should be balanced against potential benefits. In
general, increases in treatment standards have a consequential
climate change impact.
- CIWEM commends the application of HACCP (Hazard Analysis and
Critical Control Point) to the whole source-control, treatment and
- In CIWEM's view it is essential that the use of biosolids on
land remains an option for the recovery of biosolids. Other routes,
notably incineration and other methods of thermal destruction, may
be necessary in some situations but they are generally much more
expensive and squander phosphate unless additional conservation
measures are employed. Landfill capacity should not be wasted
on materials that can be used beneficially.
- CIWEM considers that the known risks from controlled use of
biosolids on land are very small; however, CIWEM considers that if
there are risks they should be borne by the producer of the
biosolids (or other organic soil treatments) and not by the
- CIWEM commends the British Retail Consortium (as lead body for
the UK food industry) and Water UK (representing the water
utilities in UK) for negotiating agreement on the use of biosolids
in agriculture. CIWEM considers this was a world
milestone. It commends the commitment to continuous
improvement in operation and to subjecting its operations to
independent audit. CIWEM recommends biosolids recyclers to
continue to take proactive measures to build and ensure stakeholder
acceptance and confidence.
- CIWEM considers that, in general, wastewater biosolids
treatment and use are being performed efficiently in the United
Kingdom. However, to ensure environmental, animal and human
health are protected, to guarantee the continued availability of
agricultural land for the beneficial use of biosolids and other
residuals, and to meet current and future stakeholder concerns,
there should be a consistent framework of controls for all
residuals applied to land.
- CIWEM considers the anaerobic digestion assets and operational
experience in the water industry could and should be used for
co-treating other organic residuals and biomass to produce
biofertiliser and biogas. CIWEM recommends government and
regulators to remove the regulatory barriers that currently inhibit
- The use of biosolids and other organic resources on land should
be viewed from the perspective of the soil rather than from the
origins of the materials. It is important to move to a
holistic view of all aspects of organic resource production, use,
soil protection, countryside stewardship, water protection, air
protection and crop and livestock production. There is
considerable opportunity to simplify the regulatory regime by
taking account of the cross compliance requirements of the single
farm payment scheme. The EU requires the Sludge Directive be
applied to sewage sludge but does not preclude its application to
other organic resources. CIWEM considers there is scope for
simplified, proportionate, science-based regulation of all organic
resources and for co-treatment.
CEC (1986) Council of the European Communities On the protection
of the environment, and in particular of the soil, when sewage
sludge is used in agriculture (86/278/EEC) Official Journal of the
European Communities No L 20/43-48
CEC (1991) Council of the European Communities Concerning
urban wastewater treatment (91/271/EEC) Official Journal of the
European Communities No L 135/40-52
Code of practice for agricultural use of sewage sludge. Second
Edition 1996 HMSO, London
Cefic (2008) Scope Newsletter 71 September 2008
Evans, T.D. (2005) Cap reform, cross-compliance, and biosolids and
biowastes Proc. 10th CIWEM AquaEnviro European Biosolids &
Biowastes Conference, Wakefield, UK
Evans, T.D., Jepsen, S.-E., Panter, K. P. (2002) A survey of
anaerobic digestion in Denmark. Proc. 7th CIWEM AquaEnviro European
Biosolids & Organic Residuals Conference, Wakefield, UK
Heffer, P., Prud'homme, M.P.R., Muirhead, B. and Isherwood, K.F.
(2006). Phosphorus fertilisation: issues and outlook. Proc.
586 International Fertiliser Society, York, UK. ISBN
"Safe sludge Matrix" http://www.adas.co.uk/media_files/Document%20Store/SSM.pdf.
STC5 Report of the working party on the disposal of sewage
sludge to land. (1976) HMSO, London
STC20 Report of the working party on the disposal of sewage sludge
to land. (1981) HMSO, London
The Sludge (Use in Agriculture) Regulations SI 1263, 1989 as
amended by The Sludge (Use in Agriculture) (Amendments) Regulations
1990, SI 880. HMSO, London.
Note: CIWEM Policy Position Statements (PPS) represent the
Institution's views on issues at a particular point in time. It is
accepted that situations change as research provides new evidence.
It should be understood, therefore, that CIWEM PPS's are under
constant review, and that previously-held views may alter and lead
to revised PPS's.