The global livestock industry is chock full of chemical byproducts that could be processed into higher-value products. Yet among EU biorefineries, animal waste is still among the least used feedstocks, according to a Mission Innovation survey.
Without enough processing capacity in place to mop up the surplus, huge amounts of livestock byproducts are being incinerated each year, including valuable materials like the keratin in feather waste.
Resource security is not the only benefit of valorising these abundant feedstocks. There are also environmental benefits to keeping waste matter circulating in the economy for as long as possible.
Currently, livestock agriculture contributes hugely to global greenhouse gas emissions. Decomposition of animal waste in particular is responsible for about 403 million tonnes of carbon dioxide worldwide, with cattle the leading source of this.
Aside from global warming, animal byproducts pose other environmental threats since improper disposal leads to soil nutrient overload, lake and river eutrophication, and the spread of pathogenic organisms. Building a biobased and circular industry to use up livestock waste could go some way to solving the pollution associated with animal farming.
Waste-powered energy
In terms of sheer volume, animal faeces are difficult to dismiss as a circular feedstock: abundant and relatively evenly distributed, this organic matter hosts a lot of potentially valuable resources if scalable methods are developed.
Animal manure is already relatively widely used in certain applications. In the EU, manure is already a key feedstock for biomethane, so far the most scaled end-use for valorising animal waste. Similarly in the US, 72% of digesters under construction in 2021 were fitted out to draw on animal waste feedstock.
Biomethane can be used as a fuel for vehicles and is made by decomposing organic matter like manure without oxygen. The process relies on a consortium of microorganisms working together to break down the waste. The biogas that results is approximately 60% biomethane and then 40% carbon dioxide. These can be converted into heat and electricity through a purpose-built heat and power unit. To obtain pure biomethane, the biogas is upgraded by removing contaminants and carbon dioxide.
One 2021 estimate stated that if all animal waste globally were converted into biogas, it could meet the energy demand of India and China. The process has the added benefit of keeping methane out of the atmosphere.
Of course, practical considerations like losses during the manufacturing process and the greenhouse gases released while building the plants means the actual sustainability profile of this route may be less impressive. However, the estimate does give a rough idea of the scope of the feedstock available and how much of it is being under-utilised.
Biogas plants can also power themselves using the products that they make, meaning the industry can support carbon reduction policies on two fronts: both by producing an alternative to fossil fuel products and by achieving some measure of energy efficiency. Over 90% of the 273 digesters operating on US waste either produce electricity or use biogas for its own activities.
Feeding the world
One of the most widely recognised end use markets for animal waste is fertiliser. Yet there is still far more potential for growth in this circular use. One study estimated that globally, there is enough human-animal faecal mass to provide large, low-cost quantities of phosphorus (21–91 billion kg/year), potassium (7–28 billion kg/year), calcium (15–17 billion kg/year), magnesium (4–5 billion kg/year), and iron (786 billion kg/year).
North Carolina startup Phinite is one of the most recent manure-processing startups to emerge. Its process starts with removing hog waste from lagoons – the term for a hole that collects water, pig excrement, and carcasses – and turns it into phosphorus fertiliser. The founder hit upon the idea after seeing that farmers lacked access to low-cost methods for drying their livestock waste into a lighter product ready for transport and sale.
Of course, human waste counts as animal waste too. In premodern Japan and more recently in other parts of Asia like Singapore it was common practice to collect human waste from urban centres for use in surrounding farmland. Reviving this circular practice would take time yet would go a long way to solving the problem of cropland nutrient depletion.
Another startup trying to change our relationship to faecal matter and the nutrient cycle is Wasted, which bagged $7.5 million in 2023 from the Collaborative Fund.
Wasted is a Vermont startup that has developed a porta-potty that separates human waste into solid and liquids, which are then collected and taken to a decentralised processing plant for turning into fertiliser. Currently, the startup has been developing the tech for processing urine but eventually wants to bring their poop-processing capabilities in-house too.
The company’s revenue flow depends on renting their modular waste-separating toilets to clients as well as selling on the fertiliser created from the waste. It is first targeting clients in construction but hopes to eventually supply disaster relief zones and refugee camps.
The problem of water
Animal waste is everywhere and holds potentially valuable energy and nutrients. Anaerobic digester facilities for animal wastes are a relatively well-understood piece of infrastructure. So why does the use of animal waste remain relatively rare?
Moisture is the biggest enemy of scaling the animal waste circular industry. The moisture content of animal waste is high – between 95 to 98% – meaning that only a tiny portion of its weight is capable of fetching high returns. As a result, operators are generally not incentivised to transport waste, knowing that most of its haulage consists of a low-value product.
This means that animal waste processing facilities that do exist tend to be built on-site or very close to farms – at least those that perform the initial processing step, where the water is extracted and the waste begins to be converted into valuable substances.
As a result, the focus of research and industry has been in developing cost-effective on-site tech for farmers to reduce the waste’s water weight. This makes the waste feedstock more transportable, enhancing its market appeal. Simple on-site processing means the farmer gets an initial draw of valuable fertiliser material from their waste before they sell the feedstock to other processors.
Ideally, on-farm waste processing technologies should extract as much high-value substance from the fresh waste as quickly as possible in a way that reduces the volume of the waste product, making it cheaper to transport to the next processing plant where it will be further converted into other kinds of fertiliser like phosphorus.
Ways of stripping moisture from the waste to leave nitrogen have been investigated including solid liquid separation (SLS), which extracts nitrogen from the manure by up to 20% of the total contained in animal waste, allowing the solid portion of waste to be concentrated in small volumes ripe for transport. Ammonia stripping is one of the simplest ways of obtaining nitrogen, where ammonia is removed from waste with an airstream, absorbed in an acid solution, and converted into an ammonium salt.
Biomass Controls is a startup geared around solving the moisture barrier in valorising livestock waste, pitching itself as a specialist in building biorefineries that get high-value end products from manures but also agricultural residues and food waste.
Fur and feathers: nature’s protective packaging
Manure is not the only circular feedstock that comes out of the livestock sector. The startup Aeropowder has developed a process to create high-performance insulation materials from surplus feathers from the poultry industry, 3 million tonnes of which are generated in Europe alone each year. The chemical at the heart of Aeropowder’s process is keratin, a natural fibre that is a good insulator. Their flagship product PlumoPlus exploits keratin’s natural properties to function as a circular replacement for expanded plastics polystyrene in packaging. The circular material is insulating enough to protect heat-sensitive life science and pharmaceutical products from high temperatures in transit.
Woola is another company using livestock waste to produce new forms of non-plastic packaging. Using leftover sheep wool sourced from farmers in Estonia, the company creates what it calls the Wool Envelope, which stands in for traditional plastic bubble wrap packaging. The type of wool it says it draws on is too coarse for textile weaving and would otherwise end up getting burned or buried, meaning that it is not diverting raw materials away from other industries.
The binding agent that the company has used so far to create its protective packaging material is also biodegradable, synthesised from corn. However, the company stated that this year their product will only contain wool going forwards.
Waste for security
The circular animal waste sector can contribute to a less fossil-reliant world by offering a biobased source of fertiliser and energy, which are huge contributors to greenhouse gas emissions currently.
At the same time, agricultural livestock itself is a major source of greenhouse gases. To meet global climate goals, there must be a reduction in overall livestock and meat consumption meaning that the waste feedstock pool associated with these industries should ideally shrink over time.
Nonetheless, the biobased industries around animal wastes are still so small that they still have great potential to scale, regardless of any limits posed by decarbonisation. Even under the most ambitious carbon emissions reduction scenarios, poultry and cattle will also likely remain significant enough for their waste byproducts to pose other ecological hazards such as nitrate and phosphorus pollution. Under any scenario then, the re-use and recovery of materials from livestock waste should form an integral part of climate and environmental policy.
Aside from sustainability targets, economic security has become a key motivator for adopting circular solutions like this. As policymakers place greater emphasis on recovering high-value chemicals and materials after the supply shocks of the pandemic and Ukraine war, animal waste processing may attract more interest than ever.