Livestock manure management between useful resources and pollution
Published on 3 November 2026 at 03:05 GMT
By Editorial Team SDG6
A tank of pig slurry can supply crop nutrients, produce renewable gas or contaminate a river. The outcome depends on its containment, treatment and destination. Intensive livestock farms concentrate excreta where animals are housed, while imported feed brings nutrients from elsewhere. Energy recovery leaves much of that nutrient content in the remaining material.
Manure types and pollution risks
Solid manure contains dung and often bedding, with enough dry matter to stack. It can improve soil organic matter and fertility, directly or after composting. Exposed heaps can nevertheless generate contaminated runoff; poorly managed composting can lose nitrogen to air.
Liquid slurry is pumpable dung and urine, sometimes diluted with washwater. It is common in housed pig and dairy systems. Oxygen-poor storage produces methane, while leaks and overflows transport nutrients and microbes. Farm wastewater, including parlour washings and contaminated yard runoff, is often more dilute but highly variable. Dilution increases handling volume without eliminating pollution. Clean rainwater is a separate stream until contaminated.
Cattle farming is not a single system: bedded housing and scraped beef yards produce different materials from flushed dairies. Manure deposited during grazing is also distinct from collectable waste. Consequently, technologies suited to intensive liquid systems cannot automatically treat all livestock excreta.
What the figures actually measure
England’s February 2026 Farm Practices Survey, published by the Department for Environment, Food and Rural Affairs, reports that 79% of holdings spread manure or slurry on grassland or arable land. Fifteen per cent processed some waste, crops or feedstocks through anaerobic digestion; specifically, 6% processed slurries or manures. These are shares of holdings, not percentages of manure tonnes, and cover agriculture generally rather than intensive pig and cattle farms alone.
The categories overlap: digestion can precede spreading. The remaining 94% cannot be labelled dumped or untreated, and spreading itself does not establish compliance with crop requirements. The survey provides no mass-based allocation between beneficial fertilisation, excessive application, composting, advanced recovery and unlawful disposal.
For the United States, the Environmental Protection Agency reports more than 400 operating livestock digesters in 2024 and over 70 under construction. It estimates technical feasibility at over 8,000 dairy and hog operations. Dividing these numbers would not establish a national treatment rate: installed projects and potentially suitable operations are different populations, and throughput varies.
The sources examined here do not provide a comparable global inventory of illegal dumping or uncontrolled discharges. Recorded incidents cannot reveal the undetected total. They therefore do not establish a percentage for every manure destination. Fresh weight, dry matter and nutrient mass also produce different percentages.
When fertilisation becomes pollution
Agricultural recycling supplies nutrients at rates and times compatible with crop uptake, soil nutrient stocks and site conditions, accounting for other fertilisers. Applying enough manure to satisfy nitrogen demand can oversupply phosphorus. Repeated surpluses can accumulate in soil and increase losses; field application alone does not establish that nutrients are being used by crops.
Disposal into drains or watercourses is a different pathway from fertilisation. Uncontrolled releases also arise from failed stores or storm-driven overflows, without proving intentional dumping. Whether an incident is unlawful depends on the applicable rules and evidence. Excessive field application can create diffuse pollution even without a visible pipe discharge.
Nitrate can move below roots into groundwater. Phosphorus and nitrogen entering rivers can promote eutrophication, while decomposing organic matter consumes oxygen. Manure can also carry pathogens, antibiotic residues and metals, adding risks beyond nutrients. These pathways connect livestock waste directly with SDG 6 (Clean Water and Sanitation).
Ammonia from housing, storage and spreading contributes to fine particulate pollution and deposits nitrogen elsewhere. Methane from anaerobic storage and nitrous oxide from nitrogen transformations add climate impacts. Nearby residents can face odour, contaminated water and treatment costs; workers face additional hazards from concentrated gases during slurry handling. Pollution exposure depends on distance, weather, hydrology and management, rather than farm size alone.
Biogas does not remove the nutrients
Anaerobic digestion is established technology: microbes convert part of the organic matter into methane-rich biogas. It can fuel heat and electricity generation or undergo cleaning and carbon dioxide removal to produce biomethane. Capturing methane that would otherwise escape from liquid storage can reduce emissions. Actual performance depends on leakage, operation, energy use and the storage system being replaced.
The remaining digestate retains fertiliser nutrients and substantial water. It is not clean discharge water. Covered storage, nutrient testing and controlled application remain relevant; solids can be separated for further processing. Digestion changes nitrogen availability and can increase ammonia-loss potential. Pathogen reduction varies with treatment conditions, so digestion is not automatic sterilisation.
Large, regularly supplied liquid-manure systems offer economies of scale. Smaller farms can operate digesters, but capital, maintenance, skilled operation and gas connections constrain economics. Food-waste co-digestion can improve gas output while importing additional nutrients. Energy income and environmental performance consequently answer different questions.
Recovery technologies beyond energy
Mechanical separation is commercially established and moves particulate nutrients into a smaller solids stream, potentially easing transport. It leaves much dissolved ammonium in the liquid. Ammonia stripping with capture produces nitrogen fertiliser; struvite precipitation recovers phosphorus with some nitrogen. Both are commercially available, although manure composition, chemical inputs and product markets constrain deployment.
A 2026 review by McKenzie Burns and colleagues reports nitrogen recovery costs across assessed technologies of US$3.40 to more than US$26.20 per kilogram of nitrogen recovered. Its comparison gives US synthetic fertiliser prices of approximately US$0.50–2.50 per kilogram of nitrogen during 2010–2024. These estimates vary by technology and scale and are not universal farm quotations. The authors identify the price gap as a barrier to financing recovery through fertiliser sales alone.
Membranes can produce concentrates, with electricity, pretreatment, fouling and replacement costs. Experimental electrochemical and microbial electrochemical systems can recover ammonium; laboratory efficiencies do not establish economical, continuous farm operation. Biological nitrogen removal can reduce pollution by converting nitrogen to gas, but that is removal rather than fertiliser recovery. Comparable full-scale cost evidence remains limited for emerging recovery methods.
Biochar offers another route. Pyrolysis converts dried solids under oxygen-limited conditions, concentrating phosphorus and retaining some carbon. The 2025 review by Jesper Knijnenburg and colleagues finds that hotter processing can reduce phosphorus solubility, potentially reducing losses while also limiting crop availability. Feedstock composition and processing determine performance. Drying wet slurry consumes energy; metals remain a product-quality concern. Commercial pyrolysis equipment does not establish that every manure-derived product has demonstrated agronomic or climate benefits.
How much can become useful
The sources describe opportunities for fertilisation and targeted energy or nutrient recovery, but do not establish a universal conversion percentage. Collection limits, crop demand, transport, energy requirements, contaminants and markets determine the usable fraction. Several products can emerge from the same tonne, so their recovery percentages cannot simply be added.
For intensive pig and cattle farms, resource recovery depends partly on the capacity of receiving land and buyers to use the resulting nutrients. Digestion can recover energy while leaving a nutrient surplus to manage. Assessing circularity therefore involves accounting for residual nutrients, emissions and disposal streams as well as the products recovered.
Written by a human author, edited with AI assistance.
Further information:
Department for Environment, Food and Rural Affairs, Farm Practices Survey February 2026. The introduction and digestion results establish England’s holding-based figures and their scope.
Environmental Protection Agency, Frequent questions about livestock biogas projects. This supports US deployment figures, technical potential and scale constraints.
Environmental Protection Agency, AgSTAR Project Development Handbook, third edition. This explains biogas, digestate, project economics and operational hazards.
Burns and colleagues, Environmental Science and Technology, 2026. This reviews manure nitrogen losses, commercial and emerging recovery methods, and economic limitations.
Knijnenburg and colleagues, RSC Sustainability, 2025. This examines manure pyrolysis, phosphorus availability and biochar limitations.
