Harvest and dewatering poses a significant economical burden for industrial algae biomass production. To mitigate these effects, energy efficient techniques for these process steps have to be developed. Flocculation of the microalgae Scenedesmus obtusiusculus in salt based medium was induced by pH-shift and alternatively by addition of two biological flocculants, chitosan, and the commercial tannin CFL-PT. This is the first time that CFL-PT is used as an algae flocculant particularly focusing on harvesting of halophilic strains. The method was characterized and subsequently optimized. In comparison to biological flocculants, induction by pH shift is far cheaper, but due to buffering effects of the brackish cultivation medium infeasible amounts of base are required to raise the pH-value. tannin appears to be superior compared to chitosan not only in the absence of algae organic matter (AOM), but tannin-based harvest is also more robust regarding culture pH in presence of AOM. A higher flocculant-demand for modified tannin compared to chitosan is offset by the lower price. Given the employed strain and cultivation conditions, cultivation time had no pronounced effect on flocculation efficiencies (FE) while algae zeta-potential and bacterial communities also remained stable.

Harvest of the Oleaginous Microalgae Scenedesmus obtusiusculus by Flocculation From Culture Based on Natural Water Sources.

Application of chitosan and PASS for the removal of turbidity and colour from water

Chitosan a versatile adsorbent in environmental remediation in the era of circular economy-a mini review

The thesis comprises the characterization and genetic engineering of the non-conventional, oleaginous yeast Cutaneotrichosporon oleaginosus as well as the optimization of harvest by flocculation of the microalgae Scenedesmus obtusiusculus. In the first part, the screening of oleaginous yeast, overexpression of two genes of enzymatic bottlenecks for triglyceride synthesis and the effect of target-of-rapamycin 1 (TORC1) inhibition are described. In the second part, effects and relationships in the process of algae harvest by flocculation as well as the complexity of their interactions are explored.

Screening and Characterization of Oleaginous Yeasts and Modeling of Flocculation-based Algae Harvest

Chitosan (1,4,2-amino-2-deoxy-β-D-glucan), a component of the shell of marine crustaceans, is one of the most abundant organic polymers present in nature. Because of its positive charge and molecular structure, chitosan possesses valuable properties as a metal-recovering and water-purifying agent. Given the increasing use of chemical coagulants to improve the water treatment process, studying chitosan has become very important. The goal of this study was the performance of chitosan as a primary coagulant for the removal of copper (Cu 2+ ) and turbidity from wastewater. The removal of zinc by chitosan was also investigated. Coagulation-flocculation-sedimentation experiments were performed by jar tests (Phipps and Bird, USA) on drinking water mixed with sanitary sewage, with industrial wastewater and with a bentonite suspension. The results showed that chitosan is superior to alum when used as a primary coagulant in a mixture of drinking water with industrial wastewater. 40 mg/L of chitosan permitted 100% elimination of copper from drinking water mixed with industrial wastewater at proportions of 35 and 47%. The use of chitosan as a primary coagulant is more effective than the other classical coagulant in term of toxicity and waste disposal. Chitosan is superior to alum especially when the turbidity and alkalinity of water is high. In our study, the main factors affecting the coagulation-flocculation by chitosan were the physico-chemical characteristics of raw water and the type and concentration of different chemical compounds present in the water.

M.-B. Gidas

Papers

Performance of chitosan as a primary coagulant for the wastewater treatment