Shiqing Sun

Performance of three microalgal strains in biogas slurry purification and biogas upgrade in response to various mixed light-emitting diode light wavelengths

The three microalgal strains were cultivated, namely, Chlorella vulgaris, Scenedesmus obliquus, and Neochloris oleoabundans, by applying mixed light-emitting diode wavelength treatments to biogas slurry in a photobioreactor bag. This study aims to compare the growth and nutrient removal efficiency of the algae and determine their roles for biogas upgrading. At red:blue=5:5, S. obliquus and C. vulgaris efficiently removed COD and TP, respectively. S. obliquus demonstrated high N removal efficiency at red:blue=7:3. The same strain significantly improved removal capacity for all nutrients compared with C. vulgaris and N. oleoabundans, particularly at red:blue=5:5, 7:3, and 3:7. For biogas upgrade, CH4 contents were higher than 75% (v/v) for all strains. The algae exhibited particularly good CH4 enrichment at red:blue=7:3, 5:5. Results show that microalgal biomass production offers real opportunities for addressing issues, such as nutrient reduction, CO2 removal, and biogas enrichment.

Simultaneously upgrading biogas and purifying biogas slurry using cocultivation of Chlorella vulgaris and three different fungi under various mixed light wavelength and photoperiods

In order to purify biogas slurry and biogas simultaneously, three different fungi, Pleurotus geesteranus (P. geesteranus), Ganoderma lucidum (G. lucidum), and Pleurotus ostreatus (P. ostreatus) were pelletized with Chlorella vulgaris (C. vulgaris). The results showed that the optimal light wavelength ratio for red:blue was 5:5 for these three different fungi-assisted C. vulgaris, resulting in higher specific growth rate as well as nutrient and CO2 removal efficiency compared with other ratios. G. lucidum/C. vulgaris was screened as the best fungi-mialgae for biogas slurry purification and biogas upgrading with light/dark ratio of 14h:10h, which was also confirmed by the economic efficiency analysis of the energy consumptions. These results will provide a theoretical foundation for large-scale biogas slurry purifying and biogas upgrading using microalgae.

Effects of influent C/N ratios and treatment technologies on integral biogas upgrading and pollutants removal from synthetic domestic sewage

Three different treatment technologies, namely mono-algae culture, algal-bacterial culture, and algal-fungal culture, were applied to remove pollutants form synthetic domestic sewage and to remove CO2 from biogas in a photobioreactor. The effects of different initial influent C/N ratios on microalgal growth rates and pollutants removal efficiencies by the three microalgal cultures were investigated. The best biogas upgrading and synthetic domestic sewage pollutants removal effect was achieved in the algal-fungal system at the influent C/N ratio of 5:1. At the influent C/N ratio of 5:1, the algal-fungal system achieved the highest mean chemical oxygen demand (COD) removal efficiency of 81.92% and total phosphorus (TP) removal efficiency of 81.52%, respectively, while the algal-bacterial system demonstrated the highest mean total nitrogen (TN) removal efficiency of 82.28%. The average CH4 concentration in upgraded biogas and the removal efficiencies of COD, TN, and TP were 93.25 ± 3.84% (v/v), 80.23 ± 3.92%, 75.85 ± 6.61%, and 78.41 ± 3.98%, respectively. These results will provide a reference for wastewater purification ad biogas upgrading with microalgae based technology.