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Project description:

Project no:
Hydrothermal treatment of cyanobacteria with focus on nitrogen and phosphorus recovery
1st project leader:
Hornung, Ursel - Institute of Catalysis Research and Technology (IKFT) at Karlsruhe Institute of Technology (KIT), Karlsruhe
2nd project leader
Dahmen, Nicolaus - Institute of Catalysis Research and Technology (IKFT) at Karlsruhe Institute of Technology (KIT), Karlsruhe

Lake eutrophication due to cyanobacteria in over-fertilized lakes and marine water is a huge environmental problem and topic of research in China as well as in Germany. On one hand side the monitoring of water and weather conditions are performed in long term measurements to analyze water bloom by aggregation of cyanobacteria, on the other hand reutilization of cyanobacteria is of interest and will be the focus of this project. Both research fields have been investigated more than 15 years by Prof. Zhu from Hohai University regarding Taihu Lake.
The proposed PhD work at KIT will be performed in collaboration with Prof. Zhu. Concerning the usage of Taihu Lake cyanobacteria salvage, Prof. Zhu applies supercritical water gasification [1], extraction by DME, and the recovery of phosphorus and nitrogen by mild oxidative hydrolysis in order to cultivate microalgae [2]. Only a few studies [3-5] were performed concerning hydrothermal liquefaction (HTL) of native cyanobacteria. Due to the low lipid and high protein content a relative low biocrude yields between 7 and 21 wt% with high nitrogen content have been observed during HTL. Huang et al. [5] achieved maximum yields of HTL biocrude of about 21 wt% and observed nitrogen contents up to 7.5 wt%. Borgol et al. [6] applied HTL at relative mild conditions between 240-260 °C with the aim to gain viscoelastic materials for road binders. Under these conditions he could achieve up to 50 wt% yield.

The proposed work at KIT will concentrate on near critical HTL of cyanobacteria in order to recover nitrogen and phosphorus as main product in aqueous phase and gain HTL biocrude for fuel applications as side product. The fate of nitrogen during HTL of model compounds was already investigated by KIT [7]. Although, HTL of cyanobacteria is not recommended as sole conversion method for biofuel production, it is promising as post-treatment for remaining biomass after extraction of valuables, like proteins or amino acids. A similar procedure was worked out for the protein rich microalgae Scenedesmus Almeriensis and Chorella Vulgaris by KIT [8, 9]. Enzymatic hydrolysis to amino acids and direct protein extraction was applied prior to HTL and successfully supported by pulsed electric fields (PEF) resulting in higher biocrude yields from HTL as well as better quality of biocrude concerning nitrogen content. In addition to enzymatic hydrolysis and protein extraction, the mild oxidative hydrolysis [2] will be applied to cyanobacteria and its impact on HTL be analyzed, because it might decrease the carbohydrate content of the residual biomass fraction as well and, therefore, have a positive effect on biocrude yields of HTL.

The proposed PhD work shall evaluate an optimized processing route for Taihu Lake cyanobacteria salvage focusing on the recovery of nitrogen as well as phosphorus and the HTL of those. Finally, the proposed processing route should be compared to other procedures like supercritical water gasification and hydrothermal carbonization.

Thesis will be submitted in the faculty of Chemical Engineering at KIT, therefore, faculty might demand attendance of one lecture in Chemical Engineering from chemists
[1] Chen, C., Zhu, W., Wang, C., Zhang, H., Lin, N.; Transformation of phosphorus during sub- and supercritical water gasification of dewatered cyanobacteria and one-step phosphorus recovery (2019) Journal of Supercritical Fluids, 147, pp. 188-193.

[2] Ruochen Wang, Wei Zhu, Siyuan Hu, Ganyu Feng, Zongpu Xue, Huaimin Chen; Hydrothermal pretreatment of salvaged cyanobacteria and use of pretreated medium for cultivating Scenedesmus obliquus, Bioresource Technology (2019),294,pp. 122120.

[3] Nava Bravo, I., Velásquez-Orta, S.B., Cuevas-García, R., Monje-Ramírez, I., Harvey, A., Orta Ledesma, M.T.; Bio-crude oil production using catalytic hydrothermal liquefaction (HTL) from native microalgae harvested by ozone-flotation (2019) Fuel, 241, pp. 255-263.

[4] Zhang, B., He, Z., Chen, H., Kandasamy, S., Xu, Z., Hu, X., Guo, H.; Effect of acidic, neutral and alkaline conditions on product distribution and biocrude oil chemistry from hydrothermal liquefaction of microalgae (2018) Bioresource Technology, 270, pp. 129-137.

[5] Huang, Y., Chen, Y., Xie, J., Liu, H., Yin, X., Wu, C.; Bio-oil production from hydrothermal liquefaction of high-protein high-ash microalgae including wild Cyanobacteria sp. and cultivated Bacillariophyta sp. (2016) Fuel, 183, pp. 9-19.

[6] Borghol, I., Queffélec, C., Bolle, P., Descamps, J., Lombard, C., Lépine, O., Kucma, D., Lorentz, C., Laurenti, D., Montouillout, V., Chailleux, E., Bujoli, B.; Biosourced analogs of elastomer-containing bitumen through hydrothermal liquefaction of: Spirulina sp. microalgae residues (2018) Green Chemistry, 20 (10), pp. 2337-2344.

[7] Fan, Y., Hornung, U., Dahmen, N., Kruse, A.; Hydrothermal liquefaction of protein-containing biomass: study of model compounds for Maillard reactions (2018) Biomass Conversion and Biorefinery, 8 (4), pp. 909-923.

[8] Guo, B., Yang, B., Silve, A., Akaberi, S., Scherer, D., Papachristou, I., Frey, W., Hornung, U., Dahmen, N.; Hydrothermal liquefaction of residual microalgae biomass after pulsed electric field-assisted valuables extraction (2019) Algal Research, 43, art. no. 101650,

[9] López Barreiro, D.; Samorì; Terranella, G., Hornung, U.; Kruse, A.; Prins, W.; Assessing microalgae biorefinery routes for the production of biofuels via hydrothermal liquefaction, Bioresource Technology 174 (2014) 256–265.
Methods that will be used:
Hydrothermal liquefaction in batch and continuous autoclaves
Reaction of cyanobacteria in hot compressed water, reaction with model compounds
chemical analysis: GC-MS, GC-FID, NMR, FTIR, TGA, elemental analysis, ICP etc
pretreatment: extraction, enzymatic hydrolysis, mild oxidative hydrolysis
Collaboration partners:
Prof. Zhu from Hohai University
Expected candidate‘s qualification:
Chemical Engineer with a very good back ground in Chemistry
Chemist with background in organic chemistry and analytical chemistry
Hydrothermal liquefaction (HTL), reaction in water under near critical condition, cyanobacteria, amino acid extraction, protein extraction