About Us

Biosolids recycling

Each year, we generate more than 565,000 tonnes of biosolids from our sewage treatment works across the region.

For farmers, these biosolids are a high-quality alternative to manufactured fertilisers – at a competitive price –and play a vital role in enhancing soil quality and fertility and with improved treatment methods, we ensure that biosolids meet all regulatory requirements.

We operate under the Sludge (Use in Agriculture) Regulations 1989 which say soil must be analysed for heavy metals before biosolids can be spread on agricultural land, and ensure that soil heavy metal concentrations are kept below defined limits.

We also apply The Safe Sludge Matrix 2001 - an agreement between Water UK and the British Retail Consortium, which represents the major supermarkets. This deals with potential risks from pathogens when biosolids are spread on land. A wide range of crops are allocated to one of six categories within the matrix, with minimum intervals between spreading and harvest.

STW are also 100% certified participant in the Biosolids Assurance Scheme – our certification number is NSFBAS/002/1/15.

To help our customers find out more about biosolids, this page covers the key facts and frequently asked questions about application of biosolids to agricultural land.  

a sewage treatment factory

Our product

Organic matter

Biosolids contain organic matter which helps to maintain an open, porous, soil structure. It helps to improve the workability and drainage of heavy soils, reducing the risk of soil compaction. It also increases the water-holding capacity of light soils, reducing drought risk in periods of prolonged dry weather. It improves soil biological activity (such as bacteria, fungi, and the numbers of earthworms) and generally increases soil fertility all round.

Biosolids cake

Biosolids cake is typically spread at around 20 to 25 tonnes per hectare (8 to 10 tons per acre).

In the first year of application, a 23 tonnes/ha (9 tons/acre) dressing will supply approximately 20 to 30kg/ha of crop available nitrogen from an autumn application, 35 kg/ha if applied in winter and about 40 kg/ha when applied in spring. This application of biosolids cake will also release approximately 20 kg/ha of nitrogen in year two and another 10 kg/ha in year three.

Whether your land is in a Nitrate Vulnerable Zone or not, biosolids cake can be spread before a growing crop.

A 23 tonnes/ha (9 tons/acre) dressing will typically supply approximately 300 kg/ha of total phosphate (P2O5), of which half will be immediately available to the crop, with the remainder becoming available over future years. Typical offtake in crops is approximately 40 to 70 kg/ha P2O5 per year so after year one, a large amount of phosphate still remains in the soil for future crop use.

Cost benefits

Our biosolids cake is currently worth at least £10.63 per tonne in fertiliser replacement value. This means a typical dressing of around 23 tonnes/ha (9.3 tons/acre) isworth around £244/ha (Source: ADAS 20 June 2013).


One tonne of Severn Trent Water biosolids cake typically contains:

Nitrogen Phosphate Value*
Total (kg N/tonne)
Readily available (kg N/tonne) Total (kg P2O5/tonne) £/tonne  
1.5 13 10.63  

*Equivalent fertiliser value when UK ammonium nitrate can be purchased at £269 per tonne andtriple superphosphate at £335 per tonne (Source: ADAS 20 June 2013).


Do you qualify?

Which fields are the best to apply biosolids on?

Biosolids can be used on most fields, subject to soil analysis and where the soil phosphorus (P) level is Index 4 or below. For most arable crops and grassland, the optimum level of phosphorus in soil is ADAS Index 2; the use of biosolids is an economical way of gradually raising low soil phosphorus levels.

To minimise the risk of phosphorus entering watercourses, biosolids application at soil phosphorus (P) Index 5 or above is not recommended, although there could be benefit from other nutrients and organic matter in biosolids. Application of biosolids at high soil phosphorus (P) indices maybe interpreted as breeching the Sludge (Use in Agriculture) Regulations 1989 and Cross Compliance requirements for biosolids use (SMR 3).

The Safe Sludge Matrix  

It is essential that customers are aware of the rules for applying biosolids to agricultural land that are contained in the Safe Sludge Matrix.

Receiving Severn Trent Water biosolids

Key considerations in supplying biosolids are distance of your farm from our treatment works, the availability of biosolids within the treatment works, the characteristics of the field, and the crop to be grown.

Your FACTS trained local farm liaison officer will advise you on the suitability of your farm to receive biosolids.

A full environmental risk assessment will be undertaken of your fields, followed by soil analysis. You can contact us on 0800 917 7253.


a tractor

Recycling facts

Here are some fascinating facts and figures about the size and scope of Severn Trent Water’s biosolids operation – and the regulations which govern it.

  • We recycle 700,000 tonnes of biosolids to farmland each year
  • We require 34,000 hectares of farmland
  • We take 3,000 soil samples every year

Severn Trent Water fully complies with the following regulations:

We follow all relevant guidelines including:

Area contacts

If you have any questions on biosolids recycling at Severn Trent Water, please contact any member of our biosolids team through our central office. This office cannot help with domestic account inquiries.

Please contact us for current charges applicable to your area. Note the charges may vary depending on how far you are from a biosolids production site. Contact us at: Biosolids Recycling, Hattons Farm, Pendeford Hall Lane, Coven, West Midlands WV9 5BD

Telephone: 0800 917 7253 *Please note this a dedicated telephone number for Biosolids enquiries only. If you need to contact us about anything else please view our contact us page

Email: biosolids@severntrent.co.uk

Sewerage treatment works map