PHOSPHORUS IN THE ENVIRONMENT – WHY SHOULD RECOVERY BE
A POLICY ISSUE?
R. Dils, S. Leaf, R. Robinson, N. Sweet
1.
Introduction and background
The environmental concern – aquatic eutrophication
As one of the main macronutrients, phosphorus plays an important role in the health and
functioning of both terrestrial and aquatic ecosystems. An adequate supply of nutrients is essential
for the production of food crops both for animal and human consumption. However, an excess
supply of nutrients (particularly phosphorus (P) and nitrogen (N) compounds) with subsequent
losses to the aquatic environment can lead to adverse effects on both the ecology and uses of
receiving waters. The process of accelerated enrichment and its impacts, arising from human
activities, is termed cultural eutrophication and has been recognised internationally as a
significant environmental problem/challenge for a number of decades, particularly since the
influential OECD reports and cooperative programme of the early 1980s (Vollenweider and
Kerekes 1982).
More recently, at European level, the European Environment Agency (EEA) report Europe’s
Environment: The Dobris Assessment (EEA, 1995) identified eutrophication (of fresh and saline
waters) as a pan-European problem of major concern, a finding reiterated in more recent EEA
reports (EEA 1998, EEA 1999a). The EEA has called for more effective and co-ordinated policies in
this area. In the UK, eutrophication has been identified as an important environmental issue in
Northern Ireland (as it is in the Republic) and Scotland, particularly in fresh waters. In England and
Wales, the importance of eutrophication, as a national water quality issue, was highlighted in the
Agency’s 1998 report on the state of fresh waters (Environment Agency, 1998a). This identified
nutrient enrichment as one of ten priority issues requiring attention in order to achieve a more
sustainable balance between the needs of society and the health of freshwater ecosystems. The
Agency has since issued a consultative report and final strategy on the management of aquatic
eutrophication (Environment Agency 1998b and Environment Agency 2000).
2.
Sources of phosphorus inputs to surface waters
Nutrient sources can be broadly segregated into two categories: readily identifiable point sources (such
as sewage treatment works) and diffuse sources (such as the runoff from agricultural land). The
contributions, in any given catchment, of nutrient inputs from different sources, are variable and
depend on the nature of the catchment, environmental conditions and the impact of human activities.
However, approximate national estimates of the relative contributions from the main nutrient sources
give a useful overall indication. The contributions (in percentage terms) of the main sources of
phosphorus (as total P) entering surface waters in the EU (average for 12 countries including the UK)
are shown in Figure 1 (Morse et al., 1993). Forms of P are also an important consideration. Sewage
effluent discharges are generally the most significant source of bio-available P entering surface waters.
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Industry
7%
Background
source
9%
Human and
household
w aste
24%
Fertiliser
16%
Detergents
10%
Livestock
34%
Figure 1. Sources of P entering surface waters (after Morse et al., 1993)
This phosphorus (other than background sources) originates as mined phosphorus rock which is
processed and used in the production of fertilisers, animal feeds, detergents and other products. Losses
to the water environment occur when these products are used and/or become wastes, primarily via
waste water collection/treatment systems and from agricultural activities. Annual national inputs of P
to surface waters have been estimated to range from 13,000 to 106, 000 tonnes of P for European
countries (Morse et al, 1993), of which background sources comprise only around 9%. Thus modern
society has largely replaced the natural scarcity of P in ecosystems, and its re-cycling via traditional
agricultural practices, with a linear throughput system based on the extraction of some 140 million
tonnes of phosphate rock per annum world wide (CEFIC/CEEP l988).
2.1
Natural phosphate reserves
Deposits of phosphate in sedimentary and igneous rock are widespread across the world, but high grade
reserves for commercial exploitation are geographically limited. Most of Europes requirements come
from North Africa (particularly Morocco), with Russia, the United States, South Africa and China also
having substantial reserves. Phosphate rock is mined, refined and purified and then used in agricultural
fertilisers, detergents, antifreezes, baking powder, toothpaste, soft drinks, yeast and numerous other
products used in daily life. The global fertiliser market accounts for approximately 80% of all
phosphate rock production, with the remainder divided between detergents (12%), animal feeds (5%)
and speciality applications eg food. Current estimates suggest that at current exploitation rates (c. 40
million tonnes P2O5 annually), global phosphate reserves will only last another 100 years. Continued
exploitation is, however, not sustainable as despite P being the 11 th most abundant element in the
earth’s crust, it is a finite resource and is declining in both quality and accessibility. There is an urgent
need to close the phosphorus cycle in order to achieve a sustainable system.
2.2
Phosphorus use in agriculture
Phosphorus is an essential element for plant growth, and is applied to agricultural soils as commercial
inorganic fertiliser, organic manure or sewage sludge. A certain critical soil P level is necessary for
economic crop production, but above this level, there is little increase in yield and risks of
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environmental loss increase. The widespread use of fertilizers, particularly since the 1950s, has
increased the soil-P status of agricultural land from very low levels to generally medium and high
levels. Further increase in soil-P status is, however, not economically or environmentally sustainable.
Sustainable agriculture requires fertilisation strategies that give profitable production but minimise
adverse environmental effects. Recycling of animal manures offers a very efficient alternative source
of P, and over the past decade this has been reflected in a trend towards greater reliance on organic
manures. This is despite the inherent problems of availability (usually local surplus in relation to P
requirement of agricultural land), handling and variable nutrient content of organic manures.
2.2.1
Commercial inorganic fertilisers and their use
Commercial production and use of superphosphate in the UK started in the middle of the last century
(Johnston and Poulton, 1992). Since then, the build up and maintenance of soil P levels through
fertiliser use has enabled agricultural production to increase dramatically. World annual phosphate
fertiliser consumption figures show an increase from 4.4 Tg P 2O5 in 1960 to 12.6 Tg in 1993-94
(International Fertilizer Association, 1997). In many Western European countries, however, the use of
commercial inorganic P is now declining (Bertilsson and Forsberg, 1997). The decline can be attributed
to the increase in fertiliser price, greater recognition of the nutrient value of animal manures, changes
in land use and greater environmental awareness. In the UK, inorganic phosphate (P 205) fertiliser use
decreased by 24% between 1987 and 1999, from 456,000 to 347,000 tonnes (FMA, 2000).
2.2.2
Nutrient value of animal manures and sewage sludges
Approximately 67 million tonnes of animal manure (cattle, pig, poultry and sheep) are collected
annually from farm buildings and yards in England and Wales (Chambers et al., 2000). Of this amount,
30.7 million tonnes (46%) are solid based manures. These manures require handling, storage and
subsequent land application. An additional 45 million tonnes of excreta are deposited directly on fields
by grazing animals. The potential fertiliser value of handled manures is estimated at over £150m
annually (at current fertiliser prices), as they contain 340,000 tonnes of nitrogen (N), 90,000 tonnes of
phosphorus (P) and 250,000 tonnes of potassium (K). These manures, if carefully managed and
recycled, represent a substantial resource. The nutrient value gained from recycling animal manures,
however, is critically dependent on the method and timing of applications, in particular in relation to
weather conditions. Applications made during winter months have limited value to the crop and are a
high environmental risk. Farmers perception of the nutrient value of organic manures is still poor
relative to that of commercial inorganic fertilisers which are easy to handle and more predictable in
terms of nutrient availability. In particular, the problem of manures having smaller N:P ratios (2-6:1)
than most crop requirements (7-11:1) leads to the requirement of a farm-based manure or nutrient
management plan to avoid significant soil P enrichment over time.
In addition to manures, the agricultural recycling route is also very important for the recovery of
sewage sludges. The last survey of sludge recovery and disposal which was undertaken in the UK in
1999 (Environment Agency 1999) revealed that 47% of sewage sludges were applied to agricultural
land. Assuming average N and P contents of 3.8 and 2.2% respectively, approximately 20 000 t of N
and 11 000t of P are recycled to farmland each year. This equates to a monetary value of approximately
£15M (Smith, 1996). However, when sewage sludges are applied to agricultural land, it is important to
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remember that the P requirement of agricultural crops is only 10-25% of the quantity of N removed by
crop plants from soil (Cooke, 1982). Consequently, applying sewage sludges according to the N
requirements will supply P in excess of crop needs. A single application of dewatered sludge cake
could supply sufficient P for most 3-4 year crop rotations.
2.2.3
National and farm nutrient balances
National agricultural P balances reveal significant differences across Europe for the potential for P
accumulation in agricultural systems. Phosphorus is imported onto farms via fertiliser, bedding and
concentrates, plus a small amount from the atmosphere, and exported in milk, livestock, crop off-take
and to the water environment. The data in Table 1 for 1994-95 (Steén, 1997) clearly demonstrates that
European agriculture is currently operating on an annual P surplus. For the UK, Withers et al. (1998)
estimated an annual surplus of approximately 16 kg P ha -1, in line with most other European countries.
Until recently, this annual accumulation was seen as beneficial by improving soil fertility, however,
large P surpluses can have major impacts on water quality.
Phosphate surplus in European agriculture (1994/95)
<10
Austria
Germany
Sweden
Phosphate surplus (kg P ha-1 yr-1)
10-20
>20
Denmark
Netherlands
Finland
France
Greece
Ireland
Norway
Crude national estimates are useful indicators of temporal trends, however, farm scale nutrient
budgeting is a more accurate approach for quantifying nutrient imbalances and for identifying where
management changes would be most effective in addressing the imbalance. Haygarth et al. (1997), for
example, calculated that for a 57ha intensive dairy system in the west of England, the imbalance
between annual P import (2.48 t) and annual P export (0.98 t) resulted in an accumulation rate of 27 kg
P ha-1 yr-1. This surplus occurs despite a fertiliser input of only 16 kg P ha -1 yr-1, and suggests
management should be targeted at reducing the P imported in feed concentrates.
2.3
Sewage as a source of phosphorus
Sewage generated by the water industry is a significant source of phosphorus, with approximately 40
million tonnes of domestic sewage (organic waste prior to dilution with tap or rain water) produced
annually in the UK (CEFIC/CEEP, 1998b). These wastes are estimated to contain around 45,000
tonnes of phosphorus (as P), largely derived from human wastes (average of 0.44 kg P/capita) and
other household activities, including contributions from household detergents (a further 0.48-0.68 kg
P/capita). Regulatory and socio-environmental pressures are advancing phosphorus recovery and
recycling from sewage, however, many technological, economic and logistical challenges still need
addressing. Phosphorus recovery, for example, is only possible if biological phosphorus removal is
carried out, but current practice is based on chemical phosphorus removal. Biological P removal can be
successful, although for most sites backup chemical dosing is required during the winter months.
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3.
Environmental Impacts
The main impacts of aquatic eutrophication in Europe are summarised in the EEA report Nutrients in
European Ecosystems (EEA, 1999b). The state of European lakes and reservoirs is reported as heavily
affected by anthropogenic nutrient pollution, the (ecological) condition of many lakes and reservoirs
being far from satisfactory, with widespread impacts on recreational and other water uses. Concentrations
of phosphorus, which is generally the limiting nutrient in freshwater situations, were found to be elevated
in many areas. As regards rivers, while P concentrations were found in general to have fallen significantly
in recent years, they were still excessive at practically all monitoring stations, generating unwanted plant
growth and giving rise to blue-green algal blooms in slow-flowing waters. For transitional (estuaries) and
marine waters, where P is one of the key factors controlling plant growth, whilst recognising the
difficulties in understanding changes due to natural causes, eutrophication was considered a widespread,
transboundary phenomenon, affecting marine biodiversity, fish and shellfish stocks, human health and
recreational uses of coastal zones.
4
How do we do something about the issues?
4.1
The European regulatory framework for eutrophication control
In parallel with the findings of state of the environment reports, a range of international and national
strategies and legal measures has been introduced, particularly in the last decade, aimed at controlling
point and diffuse nutrient inputs to the water environment, to reduce the risks and impacts of
eutrophication. These include the Urban Waste Water Treatment Directive (91/271/EEC), which
addresses P and N inputs from sewage treatment works of greater than 10,000pe to waters identified as
affected by, or at risk from, eutrophication, and the Nitrate Directive (91/676/EEC), which addresses
nitrogen inputs to such waters from agricultural sources. The Habitats Directive (92/43/EEC) requires
controls on activities affecting waters of high nature conservation value, including control of nutrients in
discharges where appropriate. The more recent Water Framework Directive (2000/60/EC) is likely to be a
future driver for both point and diffuse source nutrient control in catchments where eutrophication is a
concern. In 1998, under the OSPAR Convention, a strategy to combat eutrophication in marine waters
was adopted and is likely to drive measures to control point and diffuse nutrient inputs to waters identified
as “problem areas”. In addition, the 1992 Convention on Biological Diversity, signed at Rio, is giving rise
to national habitat and species action plans that include measures to control eutrophication.
The control regimes outlined above are mainly aimed at controlling nutrients at the point of release
to waters affected by, or at risk from, eutrophication. They are indirect, rather than direct drivers for
action to reduce nutrient inputs to water (directly and via the land) by complementary or alternative
approaches of a more “global” nature (rather than targeted at identified waters). Examples of the
latter include manipulation of P/N in animal diets, measures to reduce P in detergents, and removal
and recovery of P from sewage and animal wastes.
4.2
Eutrophication in the UK -The Environment Agency’s Environmental Vision
Identifying environmental problems is one thing: solving them is quite another. It is obvious that the
causes of eutrophication are varied and complex and that any solutions will require us to use an
integrated and long term approach. The formation of the Agency brought together the many ways in
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which we consider and manage our environment, from dealing with pollution to minimising risk.
We have also sought to develop a more equitable approach to environmental problems, not just in
terms of cost benefits but also in terms of all the values that society places upon them. The Agency
feels that it has already been able to achieve a great deal of success in using this approach, but that a
more ambitious and demanding Vision is now needed.
In January 2001, the Agency published its Environmental Vision (EA 2001), setting out the
organisation’s contribution to sustainable development and its long term vision and goals for the
environment. The key elements of the thematic approach in the Vision are outlined below, with
those of particular relevance, in the context of P removal, recovery and recycling, shown in italics.
Fundamental goals:

A better quality of life

An enhanced environment for wildlife
Environmental outcomes to strive for:

Cleaner air for everyone

Improved and protected inland and coastal waters

Restored and protected land with healthier soils
Changes to be sought:

A “greener” business world

Wiser, sustainable use of natural resources
Risks and problems to be managed, prevented and overcome:

Limiting and adapting to climate change

Reducing flood risk
4.3
Taking forward the vision - The Agency’s Strategy on Aquatic Eutrophication and its
relevance to P recovery/recycling
In order to take forward the Vision, the Agency is assessing the activities required to move towards its
goals in the medium term. As regards the control of eutrophication, which is a specific feature of the
theme on inland and coastal waters, the main action will be the implementation of the Agency’s
strategy on aquatic eutrophication (EA 2000). The strategy is wide ranging, but some of the main
elements of relevance here are:

the promotion of a partnership approach to eutrophication management, at both local and national
level, since solutions are generally beyond the remit of any one regulatory body or other party;

a two-pronged approach whereby measures to reduce nutrient inputs to the water environment
nationally, are complemented by more comprehensive, catchment-based management action, for waters
most at risk from or affected by eutrophication;
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
the adoption of a range of mechanisms (regulatory, voluntary, collaborative, educational and
economic) by the Agency and others, as appropriate, in order to reduce nutrient inputs to environmental
waters and manage local problems;

the promotion of wise use of non-renewable resources.
As part of its proposals on reducing P inputs to water nationally, the strategy includes a specific action
to work with others to promote the development and uptake of P recovery and recycling technologies
and practice within the UK. The introduction of such practices is seen to have the following potential
benefits of relevance to eutrophication control and progress towards the Agency’s Vision:

reduced use of a non-sustainable resource (mined phosphorus rock), with replacement by a
renewable raw material;

re-introduction of a cyclical use of P by society, rather than the current linear throughput system;

reduced P loadings to environmental waters (directly and via the land) from sewage/industrial
effluents and sludge disposal;

reduced sludge production and challenges of using/disposing of P and metal rich sewage sludges;

an uptake route for excess quantities of agricultural wastes, particularly from intensive livestock
operations and less pressure on other uptake/disposal routes;

greening of phosphate, water and agricultural industries;

reduced inputs to the water environment from detergent P contributions.
These potential benefits, delivered by widespread adoption of P removal, recovery and re-cycling
practices, would appear to be a useful complement to more traditional (often locally targeted) controls on
nutrient emissions in sewage effluents, sewage sludges and from agricultural practices. The approach
could serve the objectives of both national/international eutrophication control measures and broader
strategies aimed at the achievement of sustainable development.
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