Guidance

Sewage sludge in agriculture: code of practice for England, Wales and Northern Ireland

Published 23 May 2018

Applies to England, Northern Ireland and Wales

Read this code if you produce or use sewage sludge in agriculture in England, Wales and Northern Ireland.

If you produce or use sludge in agriculture in Scotland, you should read guidance for Scotland.

Contact the Scottish Environment Protection Agency (SEPA) for more advice.

You’re a sludge producer if you’re a:

• water company
• private business that produces sludge

You’re a sludge user if you’re a:

• farmer
• owner or manager of agricultural land

In this code users are referred to as farmers.

Use this code to show you’ve taken steps to follow the Sludge (Use in Agriculture) Regulations 1989 Great Britain and Northern Ireland 1990.

It helps you understand how to:

• follow good agricultural practice
• look after the land so you can continue to farm it in the future
• avoid public nuisance
• avoid causing pollution
• protect human, animal and plant health

In this code sewage sludge means ‘residual sludge from sewage plants that treat domestic or urban waste waters’.

1. Benefits and hazards of sludge

Sewage sludge is solid matter that’s left when you treat waste water. It’s mainly human wastes but also includes:

• industrial effluents
• effluents from animal and vegetable processing
• storm water run-off

Some contents of sewage sludge are good for soil and plants. Others contain potentially toxic elements (PTE) which are only safe if they’re below set limits.

1.1 Benefits

Sewage sludge can supply a large part of the nitrogen or phosphorus that most crops need. It’s also a good source of organic matter that improves soils.

Treated sludge contains fewer pathogens, and is less fermentable. The treatment processes also change how sludge releases nitrogen.

To get the most benefit from sludge, you should use it:

• when the crop you’re growing can make the best use of it
• in the right amount for the crop you’re growing

If you apply dewatered sludge cake, the organic content can improve the water-retaining capacity and structure of soil.

Liquid anaerobically digested sludge releases ammonia nitrogen which is easily taken up by plants and benefits grassland.

1.2 Hazards

Sludge contains potentially toxic elements (PTE). High levels of PTE can risk the health of plants, animals and people.

If you produce sludge, you must monitor PTE levels in sludge and in the soil.

As the farmer or landowner, you must know these levels before you spread the sludge, or before you agree to it being spread on your land.

Sludge also contains viruses, bacteria and other disease-causing organisms known as pathogens.

The pathogens often found in sludge are:

• salmonellae
• beef tapeworm eggs
• potato cyst nematodes

The risk from toxins and pathogens in sludge depends on:

• how the sludge has been treated
• the levels of PTE already in the soil
• how the sludge is applied to the soil - if it’s spread,injected or worked into it
• the type of crop and what it’s used for – for example whether it’s grazed or harvested
• existing micro-organisms in the soil
• the weather

2. Producers and farmers: before you use sludge

You must know the existing PTE levels in the sludge and soil, and how much you will be adding.

As a producer you’re responsible for testing PTE levels in the sludge and soil.

As a farmer, you must know what’s recently been spread on the soil and give this information to the producer.

You must take precautions before using sludge, if:

• there are unresolved animal health issues
• tests have shown there’s a mineral imbalance in the soil, crops or livestock
• you could pollute groundwater or surface water
• you could damage the soil structure by using inappropriate spreading equipment
• the soil type is not suitable
• you could cause a nuisance from heavy traffic or odour to nearby homes, industry or other road users
• the weather and conditions are not suitable – such as frozen ground, waterlogged fields or an adverse weather forecast

3. Producers: treat sludge

You can treat sludge by using:

• biological, chemical or heat treatments
• long-term storage
• other appropriate processes

3.1 Untreated sludge

You must not spread untreated sludge on land. You must inject or work it into the soil.

Untreated liquid sludge and dewatered treated sludge release nitrogen slowly and the benefits to crops are realised over a relatively long period.

Contents of septic tanks and sludge from secondary biological treatment are not considered to be biologically treated. These include:

• humus sludge
• surplus activated sludge
• residual sludge from extended aeration plants

3.2 Examples of effective sludge treatment processes

Treatment process	Method
Sludge pasteurisation	Minimum of 30 minutes at 70°C or minimum of 4 hours at 55°C (or appropriate intermediate conditions), followed by primary mesophilic anaerobic digestion
Mesophilic anaerobic digestion	Mean retention period of at least 12 days primary digestion at 35°C ±3°C or at least 20 days at 25°C ±3°C followed by a secondary stage which provides a mean retention period of at least 14 days
Thermophilic aerobic digestion	Mean retention period of at least 7 days digestion and subjected to a minimum of 55°C for at least 4 hours
Composting (windrows or aerated piles)	The compost must be maintained at 40°C for at least 5 days including 4 hours at a minimum of 55°C followed by a period to complete the compost reaction process
Lime stabilisation of liquid sludge	Addition of lime to raise pH to above 12 for at least 2 hours
Liquid storage	Storage of untreated liquid sludge for a minimum of 3 months
Dewatering and storage	Conditioning of untreated sludge with lime or other coagulants followed by dewatering and storage for a minimum of 3 months. If sludge has been subject to primary mesophilic anaerobic digestion, storage to be for a minimum of 14 days

4. Producers: check what goes into sewage sludge

You must check if effluent from a new business could affect sludge quality before you allow it to be drained into the sewer.

You should be aware that effluent from:

• metal finishing and electronics businesses may contain large amounts of PTE
• abattoir and other animal processing plants may contain pathogens
• industries such as those producing chemicals or treating carpet materials are examples of potential sources of organic contaminants.
• chemical industries may contain synthetic organic contaminants – you must get specialist advice about how they could affect sludge
• animal hide-processing may contain anthrax spores (if hides are sourced from endemic areas) –you must get specialist advice before you supply sludge

You may receive veterinary advice if there are significant discharges to sewer of wastes from animal or poultry processing plants. This advice may include monitoring treated sludge for microbiological quality.

You must monitor your treatment processes to make sure they’re operating efficiently.

5. Producers: test sewage sludge

You must test sludge at least every 6 months or when there’s a change in the quality of the sewage treated at the works. You must test it for:

• dry matter (%)
• organic matter (% dry solids)
• pH
• nitrogen - total and ammoniacal (% dry solids)
• phosphorus total (% dry solids)

You must also test levels of potentially toxic elements (PTE). PTE include:

• chromium (mg/kg dry solids)
• zinc (mg/kg dry solids)
• copper (mg/kg dry solids)
• nickel (mg/kg dry solids)
• cadmium (mg/kg dry solids)
• lead (mg/kg dry solids)
• mercury (mg/kg dry solids)

You must also test levels of the elements in the table below, every 6 months. If the levels are consistently no higher than set out in this table, you can reduce how often you test to every 5 years.

Potentially Toxic Element (PTE)	Reference Concentration (mg/kg dry solids)
Molybdenum	3
Selenium	2
Arsenic	2
Fluoride	200

6. Producers: test the soil

There are 2 types of testing required:

• statutory - testing you must do before sludge is used for the first time
• operational - testing you should do as part of good farming practice

PTE limits are different for arable soil and grassland. You must test the soil’s pH and PTE levels for these elements.

6.1 Statutory testing

You must get a representative sample of soil which is a mixture of 25 separate core samples. This should be tested:

• before sludge is used for the first time
• at least once per 5 hectares(ha)
• at least every 20 years since sludge was first used
• at 25cm deep or the depth of the soil, whichever is less

6.2 Operational testing

Operational samples must be taken at 15cm deep for arable soil or 7.5cm on grassland.

If you inject sludge, you must sample soil to the depth of injection.

When you take samples, you must check with the farmer the quality and quantity of other materials used on the site.

Dedicated sites have specific legal requirements which may affect how and when you carry out further tests on those sites.

6.3 PTE limits in soil used for arable farming

If you produce sludge, you must test soil for the PTE set out in these tables.

Potentially toxic elements (PTE)	Maximum permissible concentration of PTE in soil (mg/kg dry solids)				Maximum permissible average annual rate of PTE addition over 10 years (kg/ha)
	pH 5<5.5	pH 5.5<6.0	pH 6.0-7.0	pH >7.0
Zinc	200	200	200	300	15
Copper	80	100	135	200	7.5
Nickel	50	60	75	110	3

Potentially toxic element (PTE)	Maximum permissible concentration of PTE in soil (mg/kg dry solids) if pH 5.0 and above	Maximum permissible average annual rate of PTE addition over 10 years (kg/ha)
Cadmium	3	0.15
Lead	300	15
Mercury	1	0.1
Chromium	400	15
Molybdenum	4	0.2
Selenium	3	0.15
Arsenic	50	0.7
Fluoride	500	20

You must not apply sludge on arable soil if it will cause soil PTE levels to exceed the limits set out in the table. The table also shows the maximum average amount of each PTE in sludge you can apply each year over 10 years.

The higher PTE concentrations in soils with a pH greater than 7.0, only apply to soils containing more than 5% calcium carbonate.

The accepted safe level of molybdenum in agricultural soils is 4 mg/kg. In areas where a higher concentration is found naturally, you should get advice from an agricultural specialist before you use sludge.

This advice will take account of existing molybdenum levels and current arrangements to provide copper supplements to livestock.

6.4 PTE limits in soil used as grassland

If you produce sludge, you must test soil under the grass to a depth of 7.5cm for PTE as set out in these tables.

Potentially toxic element (PTE)	Maximum permissible concentration of PTE in soil (mg/kg dry solids)
	pH 5<5.5	pH 5.5<6.0	pH 6.0-7.0	pH >7.0
Zinc	200	200	200	300
Copper	130	170	225	330
Nickel	80	100	125	180

Potentially toxic element (PTE)	Maximum permissible concentration of PTE in soil (mg/kg dry solids) for pH 5.0 and above
Cadmium	3
Lead	300
Mercury	1.5
Chromium	600
Molybdenum	4
Selenium	5
Arsenic	50
Fluoride	500

The higher PTE concentrations in soils with a pH greater than 7.0, only apply to soils containing more than 5% calcium carbonate.

You must not use sludge on the surface of grassland if it will cause soil PTE levels to exceed the limits set out in the table.

The table for arable soils shows the maximum average amounts of each PTE in sludge you can apply yearly over 10 years.

For lead, cadmium and fluoride, you can apply no more than 3 times the average annual limit of PTE in a single year. This is to control how much of these elements your livestock can ingest.

See the rules for PTE concentrations in soils of pH greater than 7.0 and molybdenum.

You must not apply sludge to grassland if soil PTE levels could exceed the limits set out in the table.

6.5 Soil pH

Soil pH affects how plants take up elements in the soil. In acidic (low pH) soils, PTE are more likely to damage crops.

Most PTE become harder for crops to take up as soil pH increases. But selenium and molybdenum are taken up more easily as pH increases.

You must not apply sludge to land with a pH of less than 5.0.

As a producer, you must get advice if the pH value of the representative sample is less than 5.2.

If you’re the farmer, you must follow this advice when you use sludge.

6.6 PTE concentration limits in sludge used on grassland

You must not spread sludge on the surface of grassland if it contains more than:

• 1200mg/kg dry solids of lead
• 1000mg/kg dry solids of fluoride

There are no set PTE concentrations in the sludge that you can use on arable soils.

7. Dedicated sites

A site is known as a ‘dedicated site’ if the Secretary of State gave permission on 17 June 1986 for it to be used for sludge disposal as well as for commercial agricultural activities, including growing crops.

PTE limits for arable soil and grassland don’t apply to these sites.

You must get approval from the Secretary of State:

• before you apply sludge on these sites
• if you want to return a dedicated site to normal agricultural use

You may have to meet certain conditions such as monitoring the quality of the soil,crops or livestock you produce.

7.1 Growing crops for animal consumption only

If the levels of PTE or rates of application of PTE exceed the values for arable soil or grassland and you want to continue to apply sludge, you can only grow crops for animal consumption.

8. Farmers: plan when to use sludge

You must plan when you should use sludge to fit in with planting, grazing or harvesting timetables.

You must not spread treated or use untreated sludge:

• on growing fruit and vegetable crops
• under permanent glasshouses or polytunnels

You must not use untreated sludge:

• in orchards
• on land used for growing nursery stock, including bulbs

You must not spread untreated sludge on land, you must inject it or work it into the soil.

You must not spread untreated, dewatered sludge on grassland. You must treat it by composting it or storing it until it’s ready to be spread. It’s ready when it’s broken down to a finely divided material.

You must make sure that livestock aren’t at risk of ingesting the material when it’s spread.

8.1 When you can use treated sludge

On growing crops	Restrictions
Cereals, oil seed rape	No restrictions
Grass	No grazing or harvesting within 3 weeks of use
Turf	Not less than 3 months before harvest
Fruit trees	Not less than 10 months before harvest

Before planting crops	Restrictions
Cereals, grass, fodder, sugar beet, oilseed rape, fruit trees	No restrictions
Soft fruit and vegetables	Not less than 10 months before harvest if crops are normally in direct contact with soil and may be eaten raw
Potatoes	Not less than 10 months before harvest. Don’t spread on land that’s used or will be used for a cropping rotation that includes basic seed potatoes or seed potatoes for export
Nursery stock	Don’t spread on land that’s used or will be used for a cropping rotation that includes basic nursery stock or nursery stock (including bulbs) for export

9. When you can use untreated sludge

Injected into soil with growing crops	Restrictions
Grass	No grazing or harvesting within 2 weeks of application
Turf	Not less than 6 months before harvest

Worked or injected into soil before planting crops	Restrictions
Cereals, grass, fodder, sugar beet, oilseed rape, fruit trees	No restrictions
Soft fruit, vegetables	Not less than 10 months before planting if crops are normally in direct contact with soil and may be eaten raw
Potatoes	Not less than 10 months before planting if crops are normally in direct contact with soil and may be eaten raw. Don’t spread on land that’s used or will be used for a cropping rotation that includes seed potatoes

9.1 Tomato seeds in sludge

If you want to grow a crop to feed to livestock before winter frosts, you must not use sludge between March and August in the year you plant the crops.

This is to stop tomato plants growing from hardy tomato seeds contained in the sludge. Adult tomato plants are toxic to livestock.

10. Producers: keep records

If you produce sludge, you must record:

• how much sludge you produce
• how much sludge you supply
• the sludge test results
• the type of sludge treatment you use
• soil test results
• estimates of soil metal concentrations where 25cm samples haven’t yet been taken

You must give the test results to the person you supply to. For each person you supply to, you must also record the:

• name, address and location of each site
• quantity and quality of sludge you supply
• type of sludge treatment you used
• quantity and quality of other sludge the farmer has used from other suppliers

If other producers have supplied sludge to the site, you must agree with them who has overall responsibility for monitoring.

A site is each field or part of a field where sludge is used.

You must also keep records of:

• written advice you receive from Department for Environment Food and Rural Affairs (Defra) on using sludge on dedicated sites
• relevant soil or crop analyses

10.1 Records you must give to farmers

You must give farmers all relevant records including:

• sludge test results
• soil test results
• how much sludge you used on each site

11. Producers and farmers: protect the environment and avoid public nuisance

If you transport or use sludge you should take steps to protect the environment and avoid public nuisance. Using sludge incorrectly can:

• cause harm to the environment
• cause a pollution risk to water
• be offensive to the public

You should discuss with local authorities:

• your transport routes
• locations of sludge application
• methods of delivery and application

Before you use sludge, you must inspect each site to identify potential problems.

As a producer, you must also remove as much non-degradable material (such as plastics) as possible, before it’s spread.

11.1 Producers: transport sludge

To reduce the risk of nuisance on the road, you should:

• make sure the delivery vehicle is suitable for the route
• make sure all sludge loads are contained and covered
• avoid cross contamination with treated and untreated sludge - clean vehicles thoroughly after carrying untreated sludge
• choose delivery routes to minimise public nuisance
• clear up spillages immediately taking care to avoid polluting watercourses
• speak to the local authority before you transfer sludge from vehicles on the roadside
• avoid carrying mud onto the road from the farm
• make sure field access points don’t cause traffic hazards

11.2 Farmers & producers: avoid sludge run-off

You must make sure liquid sludge doesn’t run off onto roads or adjacent land, or into rivers or waterways.

You must stop spreading if it rains heavily enough to cause run-off.

To reduce the risk of run off from sloping land, you must avoid spreading:

• on frozen, waterlogged or very dry ground
• on very dry or clay soils over land drains covered by permeable fill
• near water supply sources

You should consider stopping or reducing your spreading rates if run-off starts happening

11.3 Protect water

You should take precautions to prevent run off if the soil is dry, or if clay soils are at, or close to field capacity.

You should take precautions to prevent liquid sludge from leaching through permeable soils and polluting groundwater and land drains.

You mustn’t store or apply sludge close to water supply sources.

You should use good farming practices to reduce the risks of water pollution. For example, you can reduce the risk of nitrogen getting into water supplies by adjusting the timing and rates of application according to the demands of the crop.

If your site is in a sensitive location, you may need to follow special rules when you use sludge.

11.4 Reduce offensive odour

You can use some effective controls to reduce odour problems from sludge. You can:

• inject it or work it into the soil as soon as possible
• use treated sludge

Treatment processes will help you to reduce odours but some treated sludges can still be offensive.

You need to consider:

• how close you are to populated areas including properties and recreational areas
• wind direction and strength

You should spray liquid sludge as close as possible to the ground so that fine spray isn’t carried away on the air.

If you can’t do this and you have to use a high trajectory spray gun, you should tell local environmental health officers and follow their advice.

11.5 Producers and farmers: storing sludge on a farm

If you store sludge on a farm, it can be easier to plan:

• deliveries of sludge
• when you’re going to apply it to the land

You must design and build the sludge storage unit so that it:

• is secure from public access
• doesn’t cause public nuisance from odour
• doesn’t leak and cause pollution