Algal biofilm technology is recently supposed to be a promising method to produce algal biomass as the feedstock for the production of biofuels. However, the carrier materials currently used to form algal biofilm are either difficult to be obtained at a low price or undurable. Commercialization of the biofilm technology for algal biomass production extremely requires new and inexpensive materials as biofilm carriers with high biomass production performances. Four types of lignocellulosic materials were investigated to evaluate their performance of acting as carriers for algal cells attachment and the relevant effects on the algal biomass production in this study. The cultivation of algal biofilm was processed in a self-designed flat plate photo-bioreactor. The biofilm production and chemical composition of the harvested biomass were determined. The surface physics properties of the materials were examined through a confocal laser-scanning microscopy. Algal biomass production varied significantly with the variation of the carriers (P < 0.05). All the lignocellulosic materials showed better performances in biofilm production than poly methyl methacrylate, and the application of pine sawdust as the carrier could gain the maximum biofilm productivity of 10.92 g m−2 day−1 after 16-day cultivation. In addition, 20.10–23.20% total lipid, 30.35–36.73% crude proteins, and 20.29–25.93% carbohydrate were achieved from the harvested biomasses. Biomass productivity increased linearly as the increase of surface roughness, and Wenzel’s roughness factor of the tested materials, and surface roughness might significantly affect the biomass production through the size of surface morphology and the area of surface (P < 0.05). The results showed that lignocellulosic materials can be efficient carriers for low-cost cultivation of algal biofilm and the enhancement of biomass productivity.

Background: Microalgae protein is considered as a sustainable alternative to animal protein in the future. Using waste for microalgal culture can upgrade low-value raw materials into high-value products, helping to offset the cost of microalgal protein production. In this study we explored the feasibility of using microalgae heterotrophic fermentation to convert broken rice hydrolysate (BRH) into protein. Results: The results showed that the increase of BRH supplemental ratio was beneficial to the increase of biomass production but not beneficial to the increase of intracellular protein content. To further improve protein production, the effect of C/N ratio on intracellular protein accumulation was studied. It was found that low C/N ratio was beneficial to the synthesis of glutamate in microalgae cells, which in turn promoted the anabolism of other amino acids and further the protein. When the C/N ratio was 12:1, the biomass productivity and protein content could reach a higher level, which were 0.90 g/L/day and 61.56%, respectively. The obtained Chlorella vulgaris biomass was rich in essential amino acids (41.80%), the essential amino acid index was as high as 89.07, and the lysine content could reach up to 4.05 g/100 g. Conclusions: This study provides a theoretical basis and guidance for using Chlorella vulgaris as an industrial fermentation platform to convert broken rice into products with high nutritional value.