Closing the loop on nutrient losses from agriculture and cities – a review of ecotechnologies, best practices

Closing the loop on nutrient losses from agriculture and cities – a review of ecotechnologies, best practices

Authors: Arno Rosemarin (SEI) and Filippa Ek (SEI)


In the agricultural sector, ecotechnologies for recovery of nitrogen and phosphorus were more prevalent than for carbon recovery. The most common way of reusing carbon and nutrients was through manure-based ecotechnologies. Animal manure on its own is the principal source of recovery of nutrients or carbon. Among manure-based ecotechnologies, anaerobic digestion was the most frequent, followed by combinations/systems of technologies and struvite crystallization. The second largest group of studies was classified as ‘mixed’ which refers to manure mixed with plant biomass (e.g. crop residues). The most common ecotechnologies in this category were: composting/vermicomposting, pyrolysis/biochar production as well as anaerobic digestion/co- digestion. Two least frequent types of ecotechnologies were those relying only on plant biomass (e.g. crop residues) and those associated with water as the recovery source. Nitrogen recovery was overall slightly more common than phosphorus recovery, which in turn was significantly more common than carbon recovery.

For the wastewater sector, the body of evidence on ecotechnologies for energy recovery is larger than that of nutrient recovery, indicating that ecotechnologies for recovering energy are potentially more mature. The most common way of reusing nutrients is through biosolids or treated wastewater, both of which include organic carbon, nitrogen and phosphorus. Recovery of phosphorus is more common than nitrogen, especially when done through chemical processes. The higher representation of energy recovery over nutrient recovery, and of phosphorus recovery over nitrogen recovery, is in line with current paradigms within the wastewater sector.

The implementation and scaling up of technologies recovering and reusing nutrients and carbon is determined to a large extent by the global market price of phosphate rock, natural gas (for ammonia and biogas production) and other fuels and energy systems (for energy-based carbon and heat reuse) all of which ultimately affect the revenue and profitability of any technology. Strictly following the market costs and benefits, recovered nutrients must therefore be supplied with the same or lower market price to be economically feasible. Of course, there are significant societal drivers that go beyond just market drivers. The need to increase sovereign sources of phosphorus is a driver that promotes reuse of P. Another significant driver that affects the reuse of organic material in both agriculture and wastewater is the need to close the loop on carbon in order to reduce greenhouse gas emissions. Also, the banning of ocean dumping and landfills for the disposal of sludge and manure has created new drivers for extraction of nutrients and reuse.

The report also summarizes the policy and governance structures that could facilitate or impede the transformation of the agriculture and wastewater sectors towards a more circular economy.

Although the Circular Economy Package has been adopted by the European Parliament in 2018, most EU policies and regulations are still dominated by linear resource-waste thinking and not circular economy concepts. Priority areas for changing this are packaging, plastics and climate-related measures. Phosphorus has yet to be included in the EU Nitrates Directive in order to better harmonize the reuse of P with N in agriculture systems. HELCOM works under the umbrella of the EU as a regional coordination body that produces recommendations on nutrient emissions from each member country as well as recommendations to promote best practices in order to recycle nutrients. Implementation is carried out by national governments. As a result, phosphorus recycling within the EU and the Baltic Region is governed by fragmented decision-making in regional administrations. Active regulatory support, such as recycling obligations or subsidies, is lacking in most countries. Legislation harmonisation, inclusion of recycled phosphorus in existing fertiliser regulations and support of new operators would speed up market penetration of novel technologies, reduce phosphorus losses and safeguard European quality standards.