Diffuse phosphorus input to surface waters - new concepts in removal, recycling and management (P-TRAP)

Project Information

P-TRAP

Grant agreement ID: 813438

DOI

10.3030/813438

Project closed

EC signature date 20 August 2018

Start date 1 March 2019

End date 31 August 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 2 911 106,16

EU contribution

€ 2 911 106,16

Coordinated by

UNIVERSITEIT UTRECHT
Netherlands

Periodic Reporting for period 2 - P-TRAP (Diffuse phosphorus input to surface waters - new concepts in removal, recycling andmanagement (P-TRAP))

Reporting period: 2021-03-01 to 2023-08-31

Summary of the context and overall objectives of the project

Identifying mitigation strategies for reducing phosphorus (P) losses from soils and sediments to surface waters in order to improve water quality continues to represent a challenge in Europe. Despite the reduction of nutrient losses from the agricultural sector, release of P from inventories in soils and sediments, which have been accumulated in the past, remains a persistent source of P export into surface waters. The Marie Skłodowska-Curie Doctoral Training Network P-TRAP, running from 2019 to 2023, aimed to develop mitigation measures to reduce the P loading from drained agricultural areas and lake sediments to surface waters and to recover the retained P by converting the retained P into fertilizers.
P-TRAP focused on:
• P retention in agricultural areas with tile drainage by using filter systems based on iron(Fe)-containing by-products from water treatment or by taking profit from the natural Fe dynamics.
• Converting the P-loaded Fe-materials into P-containing Fe minerals and test their suitability as fertilizers.
• Improving the quality of lake waters by adding Fe-containing by-products
• Determining the mechanisms and rates of Fe mineral formations and constrain the consequence for P uptake and release by these minerals..
P-TRAP aligned with Sustainable Development Goals (SDGs), including SDG 2 (Zero Hunger) by addressing the role of P in food production and SDG 15 (Life on Land) by conserving terrestrial ecosystems. It also supported SDG 12 (Responsible Consumption and Production) by emphasizing circular economy principles for sustainable P management.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Given the focus of P-TRAP, the following work was performed and results achieved:

a) Retaining and Recovering P in Agricultural Drainage Systems:
Understanding P reservoirs in drained agricultural areas is the prerequisite for the development of mitigation measures. P budgets and fluxes were studied on a representative farm, revealing significant P reservoirs in topsoil that are slowly leaching into lower layers. Field experiments on adjusting groundwater levels with hydraulic measures revealed the risk of enhanced P export when ground water levels reach the topsoil. Various systems for removing dissolved P using Fe-containing by-products were explored. The possibility of using P-loaded materials as fertilizers or converting them into marketable fertilizers through microbial processes, like bio-vivianite, was investigated at laboratory scale. To test the suitability of vivianite and P-loaded Fe minerals as fertilizers, pot experiments were conducted using a variety of soils, crops and cultivation techniques.

b) P Binding in Lake Sediment:
The objective was to stabilize P in lake sediments using Fe-containing by-products from water treatment. Field tests at two sites showed that Fe addition can effectively reduce P release into the water from sediments. However, care must be taken to maintain the right P to Fe ratio to avoid unintended consequences, such as increased P flux during anoxic conditions.

c) Fe Mineral Transformation:
Laboratory experiments aimed to understand Fe mineral transformations and their kinetics in various systems, including soils, sediments, drainage systems, and bioreactors. Advanced techniques were used to characterize the interactions between Fe and P in detail. This work informed modeling for predicting P-containing Fe phases' behavior across different contexts. Fe-containing by-products from water treatment were studied for reactivity, particularly in P binding and sediment treatments. Results included the influence of silicic acid and cations on recrystallization rates and P release and the formation and dissolution of vivianite, a phosphate mineral. Mathematical models were developed to predict P release under various conditions.

Overall, this research provided critical insights into complex Fe-P interactions in different environments, contributing to the understanding and application of P-TRAP technologies.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The P-TRAP project has delivered promising results, showcasing the effectiveness of Fe-containing water treatment residuals in retaining dissolved phosphorus (P) in drained agricultural areas and lake sediments. These findings offer valuable insights for optimising the use of filter systems with these residuals, potentially enabling large-scale implementation in drained agricultural regions. Regarding P immobilisation in lake sediments, the project demonstrates that adding Fe can effectively prevent P leaching into overlying water. However, the introduction of Fe-containing water residuals requires careful assessment of biogeochemical reactions in the sediment and their consequences for the long-term binding of P by the added Fe.
It was demonstrated, that Fe oxides can be transformed into the phosphate mineral vivianite through microbial reactions when sufficient P is introduced. The efficiency of vivianite and Fe phosphates as P fertilizers showed varying results depending on factors such as grain size and preparation of the materials. Promising results were obtained with vivianite as a P fertilizer when it is applied to slightly acidic soils, which are submersed in water, such as rice paddies. This opens the door to P recovery, potentially reducing the dependence on mined phosphorus. The mechanisms and rates for the dissolution, precipitation and transformation of multiple Fe minerals were established, creating the basis to develop quantitative models for designing and evaluating innovative approaches developed within P-TRAP. Beyond its scientific contributions, P-TRAP has fostered collaborations among research groups, consulting firms, governmental stakeholders, and fertiliser companies in Europe. This has provided early-stage researchers with opportunities to develop academic and non-academic skills and expand their professional networks, facilitating career advancement within and beyond academia.

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