Optimization of freshwater microalgal biomass harvest using polymeric flocculants

Although microalgae show a great potential in the biotechnology sector, high production costs have limited industrial applications. Biomass harvest is one of the major bottlenecks in microalgae cultivation due to high energy inputs which are needed to separate the cells from the surrounding media. Chemical flocculation is considered to be a reliable resource to improve cost-effectiveness in the downstreaming processing. Flocculation efficiency is dependent on several factors such as the polymer type and charge as well as on the microalgae species. In the present study, 15 polyelectrolytes were tested for their potential to harvest algal biomass. Cationic, anionic and nonionic flocculants were tested in different amounts at varying incubation times to determine the adequate conditions needed. By testing the three chlorophytes, Chlorella sp., Scenedesmus acuminatus and Chlamydomonas reinhardtii, the influence of different sizes, morphologies and motilities of the flocculation efficiency was verified. Furthermore, the biocompatibility of an efficient flocculant was tested in a recycling experiment over a period of 8 weeks.