Integrating bioengineering approaches and precipitation techniques for phosphorus recovery from eutrophic marine sediments
Time: Tue 2025-09-02 10.00
Location: Kollegiesalen, Brinellvägen 8, Stockholm
Video link: https://kth-se.zoom.us/j/67610573472
Language: English
Subject area: Biotechnology
Doctoral student: Fengyi Zhu , Industriell bioteknologi
Opponent: Professor David Weissbrodt, Norwegian University of Science and Technology
Supervisor: Universitetslektor Zeynep Cetecioglu, Industriell bioteknologi; Doktor Frederico M. Penha, Resursåtervinning
QC 2025-07-29
Abstract
Phosphorus (P) is an essential nutrient for all living organisms, yet its availability is limited within the European Union (EU), leading to a complete reliance on imports to meet the region’s P demand. This dependency highlights the urgent need to explore alternative P sources, with recovery from secondary resources emerging as a viable solution. Concurrently, marine eutrophication, particularly in the Baltic Sea, has become a global environmental crisis due to decades of nutrient over-enrichment. According to Baltic Marine Environment Protection Commission’s (HELCOM) eutrophication assessment, over 97% of the Baltic Sea region fails to meet good environmental status, with 12% classified as being in the worst condition. Addressing these dual challenges, P resource scarcity and P-driven eutrophication, requires innovative approaches. Recovering P from eutrophic Baltic Sea sediments presents a promising strategy, offering the dual benefits of P recycling and eutrophication mitigation. This Ph.D. research aims to develop a chemical bioengineering-method for P release and recovery from Baltic Sea sediments, contributing to both resource sustainability and environmental restoration.
Anaerobic batch experiments demonstrated that among various carbon sources, propionic acid and glucose exhibited significantly higher stimulation of P release, indicating their stronger potential for promoting P mobilization under anaerobic conditions. Subsequent long-term sequencing batch reactor (SBR) operations further verified that supplementation with propionic acid at 200 mg/L chemical oxygen demand (COD) effectively facilitated both P anaerobic release and aerobic uptake from marine sediments, while selectively enriching polyphosphate-accumulating organisms (PAO)-related family (Rhodocyclaceae), whose abundance increased from 0% to 16% within 42 days.
Building on these findings, optimized operational conditions were applied to achieve enhanced PAO enrichment and P concentration for subsequent struvite precipitation. Cyclic anaerobic-aerobic cultivation promoted PAO abundance at the genus level from 0.06% to 7.1%, while achieving satisfactory P release (8.61 mg P/g VSS·h-1) and uptake (8.43 mg P/g VSS·h-1) within the sediment-inoculated SBR. Additionally, extended anaerobic operation enabled the concentration of low-P solutions into high-P supernatants (up to 99.5 mg/L), facilitating efficient P recovery with a rate exceeding 95%. Notably, this P extraction process further accelerated PAO enrichment at the genus level, increasing their abundance from less than 15% to 52.1% by the end of the operation.
Furthermore, a combined strategy involving PAO inoculation and ethylenediaminetetraacetic acid (EDTA) addition was proposed to further enhance P release from marine sediments. This approach achieved a final P release efficiency exceeding 80% within 13 days, with the P concentration reaching approximately 150 mg/L and PAO abundance increasing rapidly from <13% to over 65%. PHREEQC simulations and precipitation experiments confirmed the feasibility of recovering the released P via precipitation.
Overall, this study provides new insights into the microbial mechanisms and engineering strategies for P release and recovery from marine sediments, offering a promising approach for sustainable P resource management and eutrophication mitigation.