Jun Li

Status PhD

• PhD successfully defended
• Final title of the PhD thesis: Selenium and zinc enriched bioproducts generated from wastewater as micronutrient feed supplements and biofertilizers
• Supervisors / promoters: Gijs Du Laing, Piet Lens, Ivet Ferrer
• Place and date of PhD defense: Gent, 31/05/2021
• PhD degree awarding institutions: Ghent University, UPC Barcelona

Publications arising from the PhD

• Li, J., Otero-Gonzalez, L., Lens, P.N.L., Ferrer, I., Du Laing, G. (2022). Assessment of selenium and zinc enriched sludge and duckweed as slow-release micronutrient biofertilizers for Phaseolus vulgaris growth. Journal of Environmental Management, 324, 116397. https://doi.org/10.1016/j.jenvman.2022.116397
• Li, J., Otero-Gonzalez, L., Parao, A., Tack, P., Folens, K., Ferrer, I., Lens, P.N.L., Du Laing, G. (2021). Valorization of selenium-enriched sludge and duckweed generated from wastewater as micronutrient biofertilizer. Chemosphere 281, 130767. https://doi.org/10.1016/j.chemosphere.2021.130767
• Li, J., Otero-Gonzalez, L., Michiels, J., Lens, P.N.L., Du Laing, G., Ferrer, I. (2021). Production of selenium-enriched microalgae as potential feed supplement in high-rate algae ponds treating domestic wastewater. Bioresource Technology, 333, 125239. https://doi.org/10.1016/j.biortech.2021.125239
• Li, J., Lens, P.N.L., Ferrer, I., Du Laing, G. (2021). Evaluation of selenium-enriched microalgae produced on domestic wastewater as biostimulant and biofertilizer for growth of selenium-enriched crops. Journal of Applied Phycology, 33, 3027-3039. https://doi.org/10.1007/s10811-021-02523-y
• Li, J., Lens, P.N.L., Otero-Gonzalez, L., Du Laing, G. (2020). Production of selenium- and zinc-enriched Lemna and Azolla as potential micronutrient-enriched bioproducts. Water Research, 172, 115522. https://doi.org/10.1016/j.watres.2020.115522
• Li, J., Loi, G., Otero-Gonzalez, L., Du Laing, G., Ferrer, I., Lens, P.N.L. (2020). Selenate and selenite uptake, accumulation and toxicity in Lemna minuta. Water Science and Technology, 81, 1852-1862. https://doi.org/10.2166/wst.2020.214

Link to PhD thesis

https://biblio.ugent.be/publication/8709138

Short abstract/summary

Selenium (Se) is an essential micronutrient for humans and animals with a narrow window between deficiency and toxicity levels. Dietary Se intake of humans and animals is not adequate in some regions. On the other hand, Se toxicity also frequently occurs worldwide, due to water or soil contamination, as Se is widely applied in or released from industrial and agricultural activities. The trace element zinc (Zn) is also often present in too low concentrations in agricultural soils, but is also toxic at elevated concentrations. Improvement of the dietary Se and Zn intake through enrichment of food and feed crops (named biofortification) is currently being explored as a possible solution for Se and Zn deficiency. Supplementation of feed and food products with Se and Zn is another solution. In biofortification, the application of conventional chemical Se/Zn fertilizers to increase the Se/Zn content in crops could result in secondary soil and water contamination due to the low utilization efficiency of Se/Zn and fast leaching. Slow-release Se/Zn-enriched fertilizers may therefore be beneficial. Moreover, the use of Se/Zn originating from primary mining for the production of Se/Zn enriched-feed/food supplements is not considered economically and environmental-friendly, taking into account that external Se/Zn is being used and the excess chemicals are currently being discharged as waste. It may thus be beneficial from an economic and environmental point of view to produce slow release Se/Zn-enriched biofertilizers or Se/Zn-enriched feed supplements locally from Se/Zn-bearing water while partially cleaning the water. This may contribute to the worldwide drive for resource recovery and circular economy. Therefore, this thesis aimed to explore the potential of Se/Zn-enriched bioproducts produced from wastewater treatment processes by eco-technologies (phytoextraction, bioreduction and microalgae-based systems) as Se/Zn feed supplements and biofertilizers. Chapter 1 and Chapter 2 present the motivation, objectives and background information on the occurrence of Se and Zn in human and animal diets and their deficiency and toxicity for humans and animals. Current studies regarding micronutrient biofortification and the production of Se and Zn supplements to tackle micronutrient deficiency are discussed. This is followed by a discussion on the paradigm shift from waste treatment to resource recovery, highlighting the potential of biobased technologies for micronutrient recovery from wastewater, while producing micronutrient-enriched feed/food supplements and biofertilizers. Since Se can replace sulfur in amino acids and Zn can also be complexed by functional groups in proteins, protein-rich plants have an immense potential for the bioaccumulation/biofortification of these micronutrients. Thus, two aquatic plants (Lemna and Azolla) with substantial protein content were applied in Chapter 3 to evaluate the possibility of Se and Zn bioaccumulation/removal from wastewater while producing micronutrient-enriched dietary proteins (for feed/food supplements) and biofertilizers. Nutrient-medium spiked with different concentrations of Se and Zn was used to mimic wastewater. Results of Chapter 3 demonstrated that both Lemna and Azolla can accumulate high levels of Se and Zn, while they take up around 10 times more Se(IV) than Se(VI) from the medium. Besides, high transformation to organic Se forms and accumulation in plants after taking up Se(IV), together with the high protein content and fast growth rate, makes Lemna (also named duckweed later on) and Azolla good candidates for the production of Se- and Zn-enriched biomass, which can be used as crop fertilizers or protein-rich food/feed supplements or ingredients. Considering that a synergetic effect between Se and Zn in Lemna, but an antagonistic effect in Azolla was observed in Chapter 3, Lemna loaded with Se/Zn was selected for the subsequent experiments in Chapter 4 and Chapter 5. Subsequently, Chapter 4 and Chapter 5, respectively, evaluated the valorization potential of the produced micronutrient-enriched duckweed as well as sludge generated in wastewater treatment processes containing single Se or Se combined with Zn as micronutrient biofertilizers. This was conducted in pot experiments using green beans (Phaseolus vulgaris). Micronutrient-enriched sludge dominated by the presence of Se in zero oxidation state (Se(0)) was found to be the preferred slowrelease Se biofertilizer and an effective Se source to produce Se-enriched beans for Se-deficient populations. This was motivated by the higher Se bioavailability and lower organic carbon content released into the soil from micronutrient-enriched sludge in comparison with micronutrient-enriched duckweed, enabling a higher soil Se supply. The remarkably higher organic carbon content in the soil could result in Se immobilization. On the contrary, the Zn content in the seeds of beans was not successfully improved through the application of micronutrient-enriched biofertilizers in comparison with the control. This could be attributed to the lower Zn translocation rate from plant roots to seeds, and the lower Zn amount applied into soils as Se/Zn-enriched biomaterials. Additionally, microalgae have a great capacity to assimilate/remove excess nutrients from the corresponding growth medium (or wastewater) and metabolize them into valuable compounds such as protein, fatty acids, vitamins and carbohydrates. Microalgae are thus a potential protein source to substitute common animal and plant proteins (e.g. soybean). Chapter 6 explored the potential of Se removal in high rate algal ponds (HRAPs) treating domestic wastewater, while producing high-value Seenriched biomass that may be used as feed supplement (dietary protein) or biofertilizer. Results indicated that the wastewater treatment performance of the HRAPs was effective. The produced Se-enriched microalgae in HRAPs fed with domestic wastewater contained a high content of crude protein (48% of volatile suspended solids) and the selenoamino acid selenomethionine (SeMet) (91% of total Se). Besides, the essential amino acid content of the microalgae was comparable to that of soybean, an animal feed protein. This Chapter also highlighted that Se may potentially induce the production of the polyunsaturated fatty acids omega-3 (ω3) and omega-6 (ω6), and eicosapentaenoic (EPA) in microalgae, although further research is still needed to confirm this. Therefore, the production of Se-enriched microalgae in HRAPs may offer a promising alternative for upgrading low-value recovered resources into high-value feed supplements. Chapter 7 aimed to evaluate the Se-enriched microalgae generated in Chapter 6 as a potential biostimulant and/or biofertilizer to enhance crop growth and improve the Se content of the crops. Raw Se-enriched microalgal biomass and an extract thereof were applied in the production of green beans (Phaseolus vulgaris) through soil and foliar application. This study demonstrated that the application of raw Se-enriched microalgae biomass to soil (1-10%, soil application) and its extract to leaves (1%, foliar spray) enhanced plant growth, which confirmed that Se-enriched microalgae act as a biostimulant. Besides, a higher Se content in the plant and soil (for soil application) was achieved after the application of Se-enriched microalgae or its extract. This indicated that Se-enriched microalgae cultivated during wastewater treatment can be valorized as a biostimulant and biofertilizer to improve both the seed yields and Se content of beans, leading to a higher market value of the beans. Chapter 8 concluded and discussed the key findings of this thesis, taking also economic aspects into account. It also highlighted the limitations of the study. The whole thesis contributes to offering an environmentally friendly and sustainable way for micronutrient biofortification/supplementation in Se/Zn-deficient areas, while recovering nutrients from wastewater.