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Setting the scene
Geopolitics and rising prices
Russia’s invasion of Ukraine had economic knock-on effects throughout the world.
This included impacts on the farming industry in the UK.
After the war began, prices for ammonium nitrate – the most commonly used fertiliser in Britain – rose by a staggering 230%.
While prices haven’t reached the heights seen in 2022 in the wake of the conflict in Iran, fertiliser costs have once again spiked. That means biosolids produced from sludge look more like a bargain than ever: a cheap, low-carbon means of enriching farmland.
In fact, most sludge produced in the UK is used for this purpose. According to DEFRA, just under 95% of sludge processed by English water and wastewater companies is reused on agricultural land as a source of nutrients and organic matter.
Amount the price of ammonium nitrate rose on the outbreak of the war between the US and Iran
Amount of sewage sludge processed for agriculture in the UK
Farmers use biosolids, derived from water company sewage sludge (or dewatered sludge cake), because they enrich soil as well as helping to grow crops. “Chemical fertilisers are great for delivering the nutrients, but what they don't do is add any organic matter to the soil,” explains Jenny Grant, head of organics and natural capital at the Renewable Energy Association (REA).
Biosolids provide farmers with phosphate, nitrogen, sulphur and organic matter, and a small amount of magnesium. Organic matter helps drain the land when it is wet and retain water when it is dry. The nitrogen and phosphorous from biosolids is gradually released. Because of this, farmers who use organic materials often see a long-term increase in soil fertility.
Biosolids have another big advantage: they are cheap.
Water companies tend to provide biosolids at nominal prices. “Costs vary depending on if the service includes delivery and spreading, however many companies may supply at low or no cost," Grant explains. As a rule of thumb, biosolids cost about a tenth of the equivalent tonnage of synthetic fertiliser. Farmers located close to water treatment works stand to gain.
Where there’s muck, then, there’s brass.
But how are water companies ensuring the sludge they process is fit for consumption on agricultural land?
Read on to learn how Welsh Water is tackling the issue.
Sludge for farming: A brief history
Sludge – both from people and animals – has been spread on farmland for centuries. When sewer systems were initially built in the mid-1800s, one of the solutions to the problem of what to do with all the waste was to pipe untreated sewage on to large expanses of land.
In the early 20th century, engineers began to treat sewage in treatment works. Sludge treatment became standard, producing large quantities of separated sludge. Farmland was one of several recovery options, along with landfill, incineration and dumping at sea (this latter option was outlawed by the European Union in 1998).
In the later years of the last century, spreading sludge on farmland grew in importance, and regulations were brought in to establish quality standards. These included the Sludge (Use in Agriculture) Regulations 1989, which includes controls on metals and pathogens where sludge is used in farming. The voluntary Safe Sludge Matrix (agreed with supermarkets in 2001) banned the use of untreated sludge on food crops. And in 2015, the Safe Sludge Matrix and other regulations were brought together by the launch of the Biosolids Assurance Scheme (BAS), which was set up by 11 UK water and wastewater utility companies as a quality-assurance scheme for sludge spread on farmland.
The objective of the BAS is to give farmers, food companies and consumers confidence that biosolids are safe to use on land that grows food. Matt Taylor, technical director at Assured Biosolids, which owns and operates the BAS, explains more: “There’s loads of different rules, regulations, codes of practice and industry guidance [about spreading sludge on farmland]. One of the benefits of the BAS is formalising them in one place, and getting consistency across the industry.” Being certified by the BAS ensures water and wastewater companies are meeting regulatory standards, he adds.
Under the BAS, biosolids are tested for nutrients, metals and pathogens such as E. coli and Salmonella to confirm they’ve been treated properly and are safe to use on farmland. Water companies are subject to mandatory three-monthly independent testing at a laboratory to ensure the biosolids they produce don’t contain levels of harmful pathogens. E. coli is mainly used as an indicator organism: because it is present in large numbers in sewage sludge, its levels show how effectively treatment has reduced faecal pathogens overall. Salmonella levels are tested because it’s a pathogen in its own right.
Technology helps to ensure levels of both E. Coli and Salmonella are safe.
