WP7
The Objectives: |
|
The Results: |
|
Participants: SDU (KR, Ulla Gro Nielsen, Elvis Genbo Xu and Theis Kragh), AU (AMS), AAU (MLC, JM), DTU (LMO).
P is a limiting nutrient for global food production and, at the same time, a costly pollutant in freshwater systems. In addition, carbon is a valuable component in soils, ensuring retention of cations as well as improving soil structure and the water holding capacity of soils (Kiani et al. 2021). It has been estimated that approximately 200 million cubic meters of sediment is being excavated from water bodies in the EU per year (Bartone et al. 2004). Often sediments contain an elevated concentration of both nutrients and organic matter compared to agricultural soils (Kiani et al. 2021). Hence, dredging sediment from the water bodies may not only be an effective way of lake restoration, but also provide the potential for recycling of nutrients in crop production. Only few studies have tested the effect of sediments as fertilizers and soil improvers, and often in less realistic setups without use of polymers for dewatering the sediment, sediments with low heavy metal concentrations and often only in short time experiments (Kiani et al. 2021; Canet et al. 2003). Therefore, we will test the value of lake sediment as a P fertilizer but also as a means of improving the soil quality in general as a carbon source. This will be conducted both in laboratory experiments as well as long-term field experiments. In addition, we will focus on the potentially detrimental effects of using dewatered sediment as a P fertilizer, with a particular focus on nanoplastic and heavy metals, which has recently been shown to negatively affect plant growth (Sun et al. 2020).
Objectives:
1. State-of-the-art analysis of the potential for reusing lake sediment
2. Test suitable synthetic polymers and biopolymers for effective and environmentally friendly dewatering of the sediment (in collaboration with WP2).
3. Conduct laboratory-scale plant experiments with substrates produced (WP3,4,5,6)
4. Conduct long-term field experiments with different types of dewatered sediment treatments to test different dewatering strategies (WP2,5,6)
5. Develop a protocol for identifying and quantifying micro(nano)plastic in sediments and soils
6. Test mobility of heavy metals in different types of soils and dewatered sediments
Research tasks
Task 7.1. State-of-the-art analysis for the potential for reusing lake sediment
Conduct a literature review of peer-reviewed as well as grey literature on experiences with reuse of lake sediment. If possible, this will be synthesized into a review article or a viewpoint on the potential for sediment reuse.
Task 7.2. Laboratory pre-screening of dewatered sediment for best-suited polymers
Conduct laboratory soil experiments and analytical chemical analysis to do pre-screening of different types of dewatered and modified sediment treatments. Based on these, we can select the most promising treatments in collaboration with WP2 and use these for in situ long-term plant experiments.
Task 7.3. Laboratory evaluation of fertilizer value and soil improvement of dredged sediment treatments
We will evaluate the mobility of nutrients and metals in laboratory-scale soil systems to estimate the fertilizer value of the different sediment treatments produced in the other WPs. We will scale up and conduct pot trial experiments for the most promising sediment treatments and compare biomass output and nutrient levels in different crop types, e.g. ryegrass and barley.
We will evaluate the fertilizer value by analyzing total P and metals (ICP-OES analysis) in above ground biomass and compare these to control treatments with added commercial P fertilizer. We will test relevant soil parameters (nutrients, metals and heavy metals, soil carbon, water holding capacity etc.) and conduct state-of-the-art analytical chemistry to identify the P compounds and their transformations over time. Hence, organic P species will be analyzed by 31P NMR spectroscopy, whereas iron phosphates (especially vivianite) will be analyzed by Mössbauer spectroscopy in collaboration with Delft University, Netherlands. We will apply for synchrotron beam time for P-XANES spectroscopy to do further characterization of inorganic P species. We will study the mobility of elements such as P, iron and as well as heavy metals such as Cadmium (Task 7.5) (in collaboration with WP 4) by Diffusive Gradients in Thin films (DGT). A modified sequential extraction scheme will be used to extract and quantify functional pools of P and iron from the sediment and will allow us to compare these with a more detailed analytical chemical analysis described above. Further, sediment extracted sequentially will be added to soil experiments to get knowledge on the most plant-available P fractions in the sediment or dewatered products. In general, these laboratory-scale experiments will also allow us to test different post-treatments of the sediment treatments produced in the WP(2,4-6), such as e.g. acidification, plant, and soil specific nutrient uptake etc.
Task 7.4. In situ long-term field trials to evaluate the fertilizer value of sediment treatments and identify potential environmental hazards
In this task, we will upscale from the laboratory experiments described in Task 7.2. We will test the long-term effect (3 years) of 3-4 sediment treatments under in situ and close to natural conditions by conducting plant experiments collaborating with a research group from the University of Copenhagen (KU). Here we will add sediment treatments identified from the laboratory test and deploy these to soil plots (1 m2), where ryegrass will be grown/harvested during a 3 years period. By this setup, we can follow the biomass production of ryegrass and fertilizer value of the sediment treatments and compare these to control groups with commercial fertilizers added. The fertilizer value of the sediments will be evaluated by biomass production relative to commercial P fertilizers and by measuring chlorophyll fluorescence, which will be used to identify the performance of photosynthesis for plant growth during the growth phase. Greenhouse gases (CH4, CO2, and N2O) will be monitored by newly developed automatic champers and sensors that can measure the gas flux in high resolution over long periods of time. Information on gas flux will enable us to quantify the effect on greenhouse gas production when adding sediment to the fields. In general, these sites will serve as valuable test systems, where all WPs will be able to interact and participate on relevant specific scientific topics (e.g., micro(nano)plastics, heavy metals, fertilizer value of HTC and water treatment products).
We expect the following treatments:
1. Sediment dewatered by the best performing biopolymer
2. Sediment dewatered by a commonly used synthetic polymer
3. Sediment dewatered by HTC or another of the above-mentioned dewatering strategies showing
the largest potential for commercialization
Task 7.5. Development of a protocol for detection of micro(nano)plastics in soil and sediments
In general, very little is known about the behavior of micro(nano)plastics in agricultural environments and the potential ecological effects and implications for agricultural sustainability and food security. However, it has recently been shown that charged nanoplastics can accumulate and inhibit the growth of small herb Arabidopsis thaliana (Sun et al. 2020). In addition to the direct impacts, both micro-and nano-sized plastics can influence the soil microbial communities and subsequently inhibit the growth of plants (Matthews et al. 2021). We will therefore initiate the development of protocols for the characterization and identification of micro(nano)plastics in soils and sediments by using FTIR and micro-RAMAN spectroscopy. These protocols will allow us to study the potential bioaccumulation in plant tissues and assess the adverse effects of micro(nano)plastics on plant growth. Hence, plant exposure experiments will be conducted in the laboratory with soils spiked with micro(nano)plastics of different concentrations, particle sizes, and polymer types, representing the detected plastic particles in the dewatered lake sediments (WP2).
Task 7.6. Evaluation of mobility of heavy metals in the dewatered sediment treatments
The polymer dewatered sediment and sediment processed by, e.g., electrodialysis (WP4) or HTC (WP5) will still contain some heavy metals such as cadmium. We will use DGT´s to measure the potential mobility of cadmium in the different types of dewatered sediments and the soils from the laboratory experiment (Task 7.2) and in situ plant experiments (task 7.3). This task will allow us to ensure safe utilization of the dewatered sediment products.
Expected scientific publications
P1: A review article on the potential for reuse of lake sediment
P2: Publication on suitable biopolymers for sediment dewatering
P3: Evaluating phosphate mobility in soils of various sediment derived fertilizers
P4: Long-term fertilizer effect of sediment amendments to agricultural soils
P5: Identification and quantification of micro(nano)plastics in lake sediments
P6: Effect of micro(nano)plastics from synthetic polymers on plant growth
P7: Mobility of heavy metals in dewatered lake sediments
WP structure
The research in the WP will be delivered by a postdoc student hosted and supervised at SDU, with the other partners as collaborators when relevant as co-supervisors. In addition, SDU will co-finance a PhD student for 1 year to help conduct the Task 7.1-7.4 in collaboration with AAU. The main workplace will be at SDU Odense, but the students will frequently visit the relevant partners during the project. In addition, we expect that several project students (Bachelors/Masters) will be involved in the WP.
Risks associated with work package
One risk is the failure to identify the suitable biopolymer and/or dewatered sediment produced by HTC in due time for the long-term field experiment. In this case, we will use our international network and choose the biopolymer and/or HTC dewatered sediment most likely to be used in sediment dewatering based on the present state of the art.