Recycling Human Waste Could Redefine Global Fertilizer Justice

Every grain harvest on Earth depends on a handful of chemical elements, yet the way those elements move through the global economy is strikingly unjust. Nitrogen, phosphorus and potassium are mined, synthesized, shipped and applied in wildly uneven patterns, leaving some regions drowning in nutrient pollution while others cannot afford enough fertilizer to keep their soils productive. A new Perspective published in Nature Reviews Earth & Environment argues that this imbalance is not merely a technical failure of agriculture but a structural inequality embedded in access to fertilizers, sanitation and waste-management infrastructure. The international team, led by Chuan Liao of Cornell University together with Shuai Zhou, Seongmin Shin, Danning Lu, Yujin Lee, Shuai Xu, Ying Tu, Krisztina Mosdossy, Lucinda Li, Rebecca Nelson and Johannes Lehmann, proposes that a circular bionutrient economy, in which nutrients are recovered from organic waste streams and redirected into agrifood systems, could simultaneously advance sustainability and equity, but only if paired with deliberate governance and redistribution mechanisms.

The scale of the mismatch is enormous. According to the authors’ global mapping, roughly 75 percent of the world’s cropland is nitrogen limited and approximately 90 percent is phosphorus limited when measured against the nutrients that could be recovered locally from human and livestock waste. In other words, most farms on the planet sit within reach of a recoverable nutrient supply that is currently being flushed into waterways, vented into the atmosphere or landfilled. Critically, the analysis finds that substantial recovery potential exists in many lower-income and middle-income regions, where unmet fertilizer demand and recoverable waste streams are often co-located. This spatial coincidence is a rare piece of good news in global environmental accounting: the places that most need nutrients are frequently the same places generating recoverable organic waste, which means circular systems could shorten supply chains, reduce import dependence and build local nutrient sovereignty.

The technical core of the Perspective is a systematic comparison of three families of nutrient recovery pathways: physicochemical, thermochemical and biological. Physicochemical approaches include struvite precipitation from wastewater, membrane separation and ammonia stripping, which can yield concentrated mineral fertilizers from liquid streams. Thermochemical pathways center on pyrolysis and related processes that convert organic residues into biochar and ash rich in phosphorus and potassium, with biochar also contributing to soil carbon sequestration. Biological routes encompass composting, anaerobic digestion, vermicomposting and insect bioconversion, notably the use of black soldier fly larvae to transform food waste and excreta into protein-rich feed and nutrient-dense residue. The authors emphasize that no single technology is universally superior. Each pathway differs in nutrient concentration, contaminant load, energy demand, capital intensity and logistical requirements, and their real-world benefits depend on context, governance and existing infrastructure.

That contextual dependence extends to scale. The Perspective frames nutrient recovery along a continuum from fully centralized to fully decentralized configurations. Large centralized wastewater treatment plants can exploit economies of scale and sophisticated process control, but they presuppose sewer networks that much of the world lacks. Decentralized options, including urine-diverting dry toilets, container-based sanitation, community composting and farmer-scale pyrolysis kilns, can operate where sewers are absent and can keep nutrients circulating close to the fields that need them. The authors draw on case studies from Uganda, Ghana, Niger, Kenya, Bolivia and beyond, where ecological sanitation and urine recycling have been tested with farmers, including innovations developed by women farmers in Niger who produced sanitized urine fertilizer known locally as Oga. These examples show that recovery technologies can be adapted to radically different infrastructural and cultural settings, but they also reveal persistent challenges of legitimacy, financing and social acceptance.

Contaminants loom large among those challenges. Recycled organic materials can carry heavy metals, pharmaceutical residues, microplastics and pathogens, and the authors stress that contaminant management is essential if recovered nutrients are to be safe and trusted. Source separation, thermal treatment and careful quality control can mitigate many risks, but regulatory frameworks for excreta-derived and waste-derived fertilizers remain patchy across jurisdictions. Public perception adds another layer of complexity: surveys in England and Japan and studies of farmer attitudes in multiple countries indicate that acceptance of human-excreta-based fertilizers varies widely and is shaped by trust, framing and demonstrated safety. The Perspective argues that these social and regulatory dimensions are not afterthoughts but core determinants of whether circular bionutrient systems scale beyond pilot projects.

The equity argument is where the article makes its most distinctive contribution. Previous scholarship has framed nutrient circularity largely as an efficiency and environmental problem, focusing on extending phosphate reserve lifetimes, curbing nitrogen pollution and reducing the greenhouse gas and eutrophication footprint of food production. Liao and colleagues broaden the lens to nutrient justice, asking who benefits from recovery systems, who bears their costs and who controls the resulting nutrient flows. They connect the circular economy literature to environmental justice scholarship, food sovereignty frameworks and just-transition debates, noting that circularity initiatives can reproduce existing inequalities if, for example, recovery enterprises extract value from poor neighborhoods while profits accrue elsewhere, or if women, who often manage household waste and sanitation, are excluded from decision-making about new systems.

Global market shocks sharpen the stakes. Recent analyses of fertilizer supply chains highlight how geopolitical conflict, export restrictions and energy price volatility have sent fertilizer prices soaring, devastating farm profitability and food security in importing countries, particularly across sub-Saharan Africa, where low soil fertility already reinforces chronic poverty in a self-perpetuating feedback loop identified more than a decade ago. A circular bionutrient economy cannot insulate any region entirely from global markets, but locally recovered nutrients offer a buffer, converting an expensive import dependency into a domestic resource. The authors also note that recycling can extend the lifetimes of finite phosphate rock reserves, a strategic concern given the concentration of phosphate mining in a small number of countries and the environmental damage associated with extraction.

Yet the Perspective is notably candid about the limits of circularity. Local circular economies, the authors conclude, have genuine potential to improve efficiency, reduce pollution and strengthen nutrient sovereignty, but they cannot overcome entrenched global nutrient inequalities in the absence of supportive infrastructure, institutions and redistribution mechanisms. Nutrients generated in wealthy, urbanized regions will not spontaneously flow to nutrient-deficient farmland elsewhere; markets alone will not finance sanitation for the billions of people who lack safely managed services; and technological fixes will not dismantle the political economy that concentrates fertilizer access among large, capitalized farms. The authors call for research that identifies which combinations of technologies, governance arrangements and implementation scales can align nutrient recovery with justice goals, including polycentric governance, participatory design of sanitation infrastructure, and policy instruments ranging from nutrient planning to financial support for inclusive sanitation.

The message for policymakers, technologists and farmers is ultimately one of disciplined optimism. The raw materials for a more equitable nutrient system already exist in every city and village, in sewage, manure, food scraps and crop residues, and the technical repertoire for recovering them is mature and diversifying. What remains scarce is not phosphorus in the ground but the institutional imagination to route recovered nutrients to the fields and farmers who need them most. As the authors put it in their framing, global nutrient flows are profoundly imbalanced, and correcting that imbalance requires treating nutrients not merely as commodities to be efficiently cycled but as resources to which people hold a claim. A circular bionutrient economy, designed with justice at its center rather than bolted on afterward, offers a credible pathway toward that goal, provided the infrastructure, institutions and redistribution mechanisms catch up with the chemistry.

Subject of Research: Circular bionutrient economy and global nutrient justice through recovery of nitrogen and phosphorus from organic waste streams

Article Title: Towards global nutrient justice via a circular bionutrient economy

Article References: Liao, C., Zhou, S., Shin, S., Lu, D., Lee, Y., Xu, S., Tu, Y., Mosdossy, K., Li, L., Nelson, R., & Lehmann, J. (2026). Towards global nutrient justice via a circular bionutrient economy. Nature Reviews Earth & Environment. https://doi.org/10.1038/s43017-026-00831-w

Image Credits: AI Generated

DOI: 10.1038/s43017-026-00831-w

Keywords: circular bionutrient economy, nutrient justice, nitrogen, phosphorus, nutrient recovery, sanitation, fertilizer access, organic waste, food sovereignty, biochar, decentralized wastewater treatment, global nutrient flows