Feasibility and constraints of edible fungi bio-flocculating microalgae

Microalgae are a promising source of carbon-neutral food and animal feed, but their own properties make isolation from the medium challenging. Fungi assisted microalgae harvesting is an emerging strategy for microalgae harvesting. However, most of the fungi reported are inedible or even poisonous, making harvested microalgae unsuitable for human or animal consumption. In this work, the performance of edible fungus Ganoderma lucidum on bio-flocculating microalgae Chlorella sp. was systematically investigated. By optimizing the fungi growth condition and fungi-microalgae flocculation condition, the highest harvesting efficiency of 39.7 % was achieved when the agitation rate of fungal culture was 50 rpm and 40 mg/ml of fungi pellet (wet weight) was used at pH 9, mixing speed 100 rpm and 23 degrees C. For Ganoderma lucidum, found that the mycelial morphology, rather than the surface charge neutralization, plays a key role in fungi-microalgae aggregation. The lipid content of the copolymer decreased after flocculation, while fungal-microalgal interactions led to an increase in polysaccharide content. Furthermore, the cost of using Ganoderma lucidum as the bio-flocculant was analyzed and its economic feasibility was discussed. These results provided an evidence-based boundary of the efficiency of edible fungi bio-flocculating microalgae, which had pointed to the cultivation cost of fungi and added value of biomass as the targets for future optimization.