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Microalgae present a viable mechanism for purifying aquatic environments through the absorption of organic pollutants. In this paper, Chlorella protothecoides was cultured in a tetracycline environment, and biochar was added during the cultivation process. Compared with conventionally cultured Chlorella protothecoides, the addition of biochar for cultivation under a tetracycline environment increased the biomass of Chlorella protothecoides by 13.26 %. Moreover, the adsorption of tetracycline by biochar alone was not complete, but when mixed with Chlorella protothecoides, tetracycline was completely removed, which proved the biosorption of Chlorella protothecoides for low concentrations of tetracycline. Finally, the cultured Chlorella protothecoides was used further to prepare electrode materials, and it was found that the specific capacitance of the material reached 233.15F/g at a current density of 1 A/g. In this study, the use of biochar and Chlorella protothecoides to jointly adsorb tetracycline is of great significance for environmental protection and microalgae cultivation., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

Immobilized microalgae have great potential on the nutrient removal during wastewater treatment. However, their applications are challenged by how to cost-effectively maintain and preserve large number of viable and active microalgal cells. In this study, the cells of Chlorella sacchrarophila were immobilized in the agar containing with algal nutrient, encapsulated in a transparent package and preserved at room temperature. After the preservation for 200 days, microalgal cells with viability of 47-52% were maintained and could be quickly revived after the cultivation in fresh algal medium. Based on the agar-immobilized microalgae, the NH 4 + -N and PO 4 3- -P were efficiently removed from batch and continuous cultures, with the highest removal efficiencies ranging from 96% to 99% were observed. Even being recycled for eight times, the agar-immobilized microalgae were still able to remove 94% of NH 4 + -N and 66% of PO 4 3- -P. Moreover, more than 60% of the nutrient removal efficiency was determined even the agar-immobilized microalgae being preserved for 120 days at room temperature. This work provides a simple, cost-effective and practicable method for the long-term preservation of microalgae at room temperature, which makes the application of microalgal species on the nutrient removal during wastewater treatment more convenient and useful., Competing Interests: Declaration of competing interest No interest conflict to declare., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

A cost-effective and environmentally friendly method for biofuel production was developed, by utilizing duckweed as feedstock for biohydrogen production through dark fermentation and simultaneously using the fermentative waste to produce microalgal lipids. The results suggested that acid hydrolysis (1% H 2 SO 4 ) was more suitable for the pretreatment of duckweed biomass. Maximum hydrogen production of 169.30 mL g -1 dry weight was determined under a temperature of 35 °C and an initial pH of 7.0. After the dark fermentation, the volatile fatty acids (VFAs) including acetate and butyrate, were detected in the waste, with concentration determined as 1.04 g L -1 and 1.52 g L -1 , respectively. During the mixotrophic cultivation of Chlorella sacchrarophila FACHB-4 using waste as feedstock, the maximum microalgal biomass and the lipid productions were about 2.8 and 33 times higher with respect to the autotrophic growth. The simultaneous biohydrogen production and waste utilization method provided a green strategy for biofuel production., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)