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.
