Co-Fermentation of Chlorella vulgaris with Oleaginous Yeast in Starch Processing Effluent as a Carbon-Reducing Strategy for Wastewater Treatment and Biofuel Feedstock Production

Abstract

Low biomass yield and nutrient removal efficiency are problems challenging the employment of microorganisms for wastewater remediation. Starch processing effluent (SPE) was used as a fermentation substrate to co-culture Chlorella vulgaris and Rhodotorula glutinis for biofuel feedstock production. Co-culture options were compared, and the optimal conditions were identified. The result shows that microalgae and yeast should be inoculated simultaneously at the beginning of SPE-based fermentation to achieve high biomass yield and the optimal inoculation ratio, light intensity, and temperature should be 2:1, 150 μmol/m2/s, and 25 °C, respectively. Under the optimal conditions, the lipid yield of microorganisms was 1.81 g/L and the carbon–conversion ratio reached 82.53% while lipid yield and the carbon–conversion ratio in a monoculture fell in the range of 0.79–0.81 g/L and 55.93–62.61%, respectively. Therefore, compared to the monoculture model, the co-fermentation of Chlorella vulgaris and Rhodotorula glutinis in starch processing effluent could convert nutrients to single-cell oil in a more efficient way. It should be noted that with the reduced concentration of residual organic carbon in effluent and the increased carbon–conversion ratio, co-fermentation of microalgae and yeast can be regarded as a promising and applicable strategy for starch processing effluent remediation and low-cost biofuel feedstock production.

Cultivation of microalgae in food processing effluent for pollution attenuation and astaxanthin production: a review of technological innovation and downstream application

“…As reported by the previous study, genetically engineered Synechocystis sp. contained high content of astaxanthin, reaching 29.6 mg g -1 (dry cell weight) ( Lu et al, 2023b ). Hence, the development of genetic modification techniques is bringing new prospects of microalgae-based astaxanthin production.…”

“…Normally, such a wastewater treatment plant could treat the FPE produced by a large-sized food processing factory. Some data in previous studies were used to estimate the fate of carbon in FPE treatment ( Lu et al, 2023b ; Fajardo-Puerto et al, 2023 ). Concentration of organic carbon in FPE was set as 2,780 mg L -1 .…”

“…Nutrient removal efficiency is one of the important parameters, which are employed to assess the performance of wastewater remediation. It has been discovered that the co-culture of microalgae with heterotrophic microorganisms, particularly bacteria, yeast, and fungi, could promote the organics decomposition and nutrients removal in wastewater remediation ( Liu et al, 2017 ; Lu et al, 2023b ). As shown in Figure 2 , the synergistic cooperations between microalgae and heterotrophic microorganisms mainly include the interspecies exchange of O 2 and CO 2 , organics decomposition accelerated by extracellular enzymes, and secretion of growth promoting substances ( Lee C. et al, 2019 ).…”

“…This method, hence, can be employed to increase the ratio of C/N in FPEs, creating a suitable environment for microalgae-based astaxanthin production. However, ammonia stripping is accompanied with intensive emission of ammonia, not only reducing the utilization efficiency of TN in FPE, but also cause air pollution ( Lu et al, 2023b ). Besides, due to the low concentrations of TN and TAN in FPE after ammonia stripping, microalgae may suffer from the nitrogen deficiency in the later stage of exponential phase.…”

“…Firstly, the interspecies exchange of O 2 and CO 2 creates a "comfortable" environment for the growth of microalgae and heterotrophic microorganisms. In the co-culture system, CO 2 produced by heterotrophic microorganisms could be captured by microalgae for photosynthesis while O 2 released by microalgae is essential to the metabolisms of heterotrophic microorganisms (Lu et al, 2023a;Lu et al, 2023b). In contrast, without the interspecies exchange of O 2 and CO 2 between microalgae and heterotrophic Frontiers in Bioengineering and Biotechnology frontiersin.org microorganisms, algal cells would assimilate the atmospheric CO 2 , of which the low concentration and dissolution rate may limit the photosynthesis and biomass production.…”