Chapter 7 summary

Opportunities for recovering phosphorus from residue streams

Chapter authors: Ludwig Hermann, John W. McGrath, Christian Kabbe, Katrina A. Macintosh, Kimo van Dijk, Will J. Brownlie • 10min read

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Chapter highlights

Currently large amounts of phosphorus are lost in waste streams. A global commitment to recycling nutrients in wastes and residues is needed. Phosphorus recovery provides the opportunity to recover a contaminant free, high purity source of phosphorus that can be used to create customised products, and substitute effectively for phosphorus derived from phosphate rock. Phosphorus recovery and recycling will catalyse new circular economy opportunities in line with national and international policies and directives.

Introduction

How can we make better use of the phosphorus currently lost in our waste streams through phosphorus recovery and recycling?

A significant increase in the recovery and recycling of phosphorus lost in organic wastes is vital if we are to improve global phosphorus sustainability. There is great potential to recycle phosphorus (and other nutrients) by applying phosphorus-rich organic wastes and manures to agricultural soils. However, in some cases phosphorus must be recovered, detoxified, and modified from wastes, in order to recycle it safely and effectively and to reach higher levels of nutrient use efficiency.

Phosphorus recovery refers to processes used to isolate high-quality phosphorus from organic matter (including after an intermediate step of incineration leading to inorganic ash) into recovered products that can be recycled without further processing (e.g. struvite), or recovered phosphorus materials (e.g. calcium phosphates, phosphoric acids, white phosphorus) that can be used to make recovered phosphorus fertilisers. Phosphorus recovery provides the opportunity to recover a ‘safe’ (i.e. low-in or free-from contaminants), high purity source of phosphorus that can be used to create customised products, and substitute effectively for phosphorus derived from phosphate rock. Most customised products made using recovered phosphorus are fertilisers, however, recovered phosphorus materials can be used to manufacture a range of other products (e.g. flame retardants, feedstocks).

Phosphorus recovery may be particularly suitable in situations where large distances separate phosphorus-rich organic waste production (e.g. in livestock-dominated areas) from croplands where they can be recycled. Transporting large volumes of bulky organic material to croplands is often not economically feasible. In these situations, phosphorus recovery processes (including solid/liquid separation) can produce recovered phosphorus materials and/or fertilisers that are cheaper and easier to store and transport. In other situations, contaminant levels in the phosphorus-rich organic wastes and residues, even after treatment, are too high for their desired use. Processes such as composting and vermicomposting can reduce contaminants in wastes. Pathogens, hormones, antibiotics, heavy metals, and micro-plastics may persist and can accumulate in soils/biota after repeated manure/biosolid application. Depending on the desired use of the waste, this can pose a risk to human, animal, and environmental health. In some industrial applications, even trace levels of contaminants are not tolerated. Most phosphorus recovery processes produce materials that contain low to no contaminants.

There are more than 30 different technologies available to recover phosphorus from waste streams and new ones continue to emerge. Selecting the most effective phosphorus recovery process depends on the type of waste treated, the resources available and the products that are required. Commercially established processes of phosphorus recovery exist mainly for sewage sludge and digestate, with phosphorus recovery predominantly practised in the European Union (EU), Japan and North America. Industrial phosphorus recovery processes have also been applied to abattoir wastes (e.g. blood, meat and bone meal), poultry litter, livestock manure, food processing wastes and industrial waste streams. Some recovered phosphorus fertilisers are more sustainable than mineral phosphorus fertiliser, but with similar phosphorus content and bioavailability, allowing phosphorus inputs to soils to be carefully managed to optimise plant uptake and yield, whilst avoiding phosphorus losses to the environment.

In the following section, we discuss the challenges and solutions for making better use of the phosphorus currently lost in our waste streams through phosphorus recovery and recycling.

Key issue 7.1

Many waste streams represent a significant untapped phosphorus resource

The challenge

The phosphorus in many organic waste streams and residues, including food wastes, biosolids and abattoir wastes, is commonly lost to the environment. In a global assessment of phosphorus flows in 2013, it was estimated that ~85% of the phosphorus in human excreta and other human wastes (equivalent to ~6 Mt phosphorus) were not recycled. Whilst data is not available for the phosphorus lost in abattoir wastes globally, in the EU alone, each year ~4 Mt of animal bone biomass is produced (bones are extremely high in phosphorus). Most of this is incinerated, and waste ashes often landfilled or used in building materials without recovering the phosphorus they contain. Indeed, many phosphorus-rich wastes are managed as pollution rather than valuable phosphorus resources. Phosphorus losses are not just confined to organic waste streams; opportunities to recover phosphorus in industrial wastes, such as steelmaking wastes, are also often ignored. There are significant opportunities to increase phosphorus recovery in all regions.

The solution

A global commitment to recycling nutrients in wastes and residues is needed. Over the last couple of decades, the importance of using phosphorus-rich organic wastes as a sustainable phosphorus resource has been widely acknowledged in the literature. There is a need to shift the focus from phosphorus removal to phosphorus recovery in a ‘usable’ form to facilitate recycling. To make significant improvements nations should commit to ambitious targets to recover and recycle nutrients from livestock manure, wastewaters, abattoir wastes and industrial waste streams, whilst discontinuing landfilling phosphorus-rich ashes and their displacement into building materials. This must be underpinned by clear targets to increase phosphorus recovery and phosphorus recycling, within specified time ranges. A significant increase in phosphorus use efficiency, in conjunction with good management practices to reduce and mitigate phosphorus losses is also critical.

Key issue 7.2

Recovered phosphorus materials must have a competitive commercial value

The challenge

The economic viability of phosphorus recovery is dynamic and depends on many factors, however, a current lack of economic incentives to stimulate phosphorus recovery remains a significant challenge globally. Phosphorus recovery processes that do not generate industry compatible raw materials (e.g. as an alternative to phosphate rock), or a finished product (i.e. a recovered phosphorus fertiliser) with a clearly defined market potential may fail to contribute to phosphorus recycling. Whilst there are markets for recovered phosphorus products for use as niche fertilisers sold at a small scale, these companies are unlikely to compete with the mineral phosphorus industry, which is characterised by huge volumes and established trade networks. Indeed, a key challenge for phosphorus recyclers is producing relevant volumes and homogeneous quality to meet demand. Furthermore, where recovered phosphorus fertiliser match mineral phosphorus fertiliser in terms of performance, systems to support large scale production, transport and handling are currently insufficient.

The solution

Phosphorus recovery technologies must produce commercially viable materials with a defined market potential or that are industry compatible as a raw material for fertilisers and other products. However, determining which technologies are the most commercially viable, and hence should receive investment depends on region-specific factors. An integrated systems framework should be used to guide decision-making by identifying the phosphorus that is available for recovery and examining logistics such as regional spatial phosphorus demands. Failure to take a systems approach could result in investing in costly technologies that do not deliver. The market price of recovered phosphorus products/fertiliser alone should not define the economic feasibility of phosphorus recovery. When compared with the mining of phosphate rock and the manufacture of mineral phosphorus fertilisers, phosphorus recovery processes have the potential to do far more than just supply a product; they are more of a ‘service’, combining decreased emissions to the environment (i.e. soil, air and water) and a reduction in waste generation with the production of high-quality phosphorus fertilisers. Opportunities to produce co-value products and services (i.e. produce energy, other nutrients), and the environmental sustainability of recovery processes, should be optimised.

Key issue 7.3

There is a lack of policy and market support for phosphorus recovery

The challenge

There is a global lack of tangible policy support for phosphorus recovery, which has hindered the building of commercial markets for renewable phosphorus products, including financial instruments such as subsidies, tax incentives, or support for farmers to adopt sustainable measures. Certifying recovered phosphorus products as fertilisers can provide a significant challenge for phosphorus recovery enterprises. In most regions, farmers are often not compensated for investing in more sustainable practices, including a transition from mineral phosphorus fertiliser to recovered phosphorus fertiliser use. Whilst farmers are key players in the production of raw materials, they tend to have the least power in the food-value chain, and a limited ability to demand higher food prices (to cover potential costs of more sustainable practices).

The solution

Critical policy needs to include a regulatory framework to boost the use of recovered phosphorus materials as an alternative to phosphate rock as the primary source of phosphorus in mineral fertilisers. In some regions, the necessary infrastructure to collect wastes and residues is still required. In most nations, the establishment and implementation of stringent regulations to enforce time-bound targets for phosphorus recovery (and recycling) are required. Regional targets should be developed and integrated, with existing agricultural policy to ensure sufficient support is in place for targets to be achieved. For many high-income countries, the fertiliser market itself poses a problem, requiring a regulatory framework to provide a level playing field between mineral and recovered phosphorus fertilisers. Global advocacy and awareness-raising of the environmental benefits of phosphorus recovery and recycling will help to improve public and political support. The next step could be global binding agreements and a paradigm change: taxing the consumption of natural resources and related externalities and reducing the tax burden of renewable resources and labour.

Conclusion

Phosphorus recovery and recycling will catalyse new circular economy opportunities in line with national and international policies and directives. Considering global warming and finite resources - globally acknowledged by the Paris Climate Change Agreement (COP21) and the United Nations Sustainable Development Goals agreed in 2015 - the Circular Economy is a must, with ‘business as usual’ not an option. The European Commission selected phosphorus for implementation within its “Circular economy: A zero waste programme for Europe”, due to it being a critical and non-replaceable element in agriculture. The feasibility of phosphorus-recovery within the prevailing socio-economic system could create a convincing narrative for introducing circular principles in other economic activities.

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Suggested citation for this chapter: L. Hermann, J.W. McGrath, C. Kabbe, K.A. Macintosh, K. van Dijk, W.J. Brownlie. (2022). Chapter 7. Opportunities for recovering phosphorus from residue streams, in: W.J. Brownlie, M.A. Sutton, K.V. Heal, D.S. Reay, B.M. Spears (eds.), Our Phosphorus Future. UK Centre for Ecology and Hydrology, Edinburgh. doi: 10.13140/RG.2.2.16366.08006

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Consumption: the missing link towards phosphorus security