High efficient assimilation of NO₃⁻-N with coproduction of microalgal proteins by Chlorella pyrenoidosa / 生物工程学报

The aim of this study was to establish a novel technology using microalgae for NO₃⁻ removal from high concentration wastewater and conversion to algal proteins. The effects of cultivation modes and illumination modes on the biomass yield, NO₃⁻ assimilation rate and algal protein yield were first investigated in shaking flasks for mixotrophic cultivation of Chlorella pyrenoidosa, and subsequently the scale-up verification in 5-L photo fermenter was successfully conducted. Fed-batch cultivation without medium recycling was the best cultivation mode in shaking flask system, in which the highest biomass yield (35.95 g/L), the average NO₃⁻ assimilation rate (2.06 g/(L·d)) and algal protein content (up to 42.44% of dry weight) were achieved. By using a staged increase of light intensity as illumination modes, the specific growth rate of cells could be significantly promoted to the highest (0.65 d⁻¹). After a 128-hour continuous cultivation in a 5-L photo fermenter, the highest biomass yield and the average NO₃⁻ assimilation rate were reached to 66.22 g/L and 4.38 g/(L·d) respectively, with the highest algal protein content at 47.13% of dry weight. Our study could provide a photo fermentation technology of microalgae for highly efficient treatment of waste industrial nitric acid and/or high concentration nitrate wastewater. This microalgae-based bioconversion process could coproduce protein-rich microalgal biomass, which facilitates the resource utilization of these type wastewater by trash-to-treasure conversion.

The physiological and biochemical mechanism of nitrate-nitrogen removal by water hyacinth from agriculture eutrophic wastewater

ABSTRACT Large amount of agriculturl wastewater containing high level nitrate-nitrogen (NO3 --N) is produced from modern intensive agricultural production management due to the excessive use of chemical fertilizers and livestock scale farming. The hydroponic experiment of water hyacinth was conducted for analyzing the content of NO3 --N, soluble sugar content, N-transported the amino acid content and growth change in water hyacinth to explore its purification ability to remove NO3 --N from agriculture eutrophic wastewater and physiological and biochemical mechanism of this plant to remove NO3 --N. The results showed that the water hyacinth could effectively utilize the NO3 --N from agriculture eutrophic wastewater. Compared with the control, the contents of NO3 -change to NO3 --N in the root, leaf petiole and leaf blade of water hyacinth after treatment in the wastewater for a week was significantly higher than that in the control plants treated with tap water, and also the biomass of water hyacinth increased significantly, indicating that the accumulation of biomass due to the rapid growth of water hyacinth could transfer some amount of NO3 --N.13C-NMR analysis confirmed that water hyacinth would convert the part nitrogen absorbed from agriculture eutrophic wastewater to ammonia nitrogen, which increased the content of aspartic acid and glutamic acid, decreased the content of soluble sugar, sucrose and fructose and the content of N-storaged asparagine and glutamine, lead to enhance the synthesis of plant amino acids and promote the growth of plants. These results indicate that the nitrate in agriculture eutrophic wastewater can be utilized by water hyacinth as nitrogen nutrition, and can promote plant growth by using soluble sugar and amide to synthesis amino acids and protein.