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Graphical abstract Highlights • Straw lignocellulose pretreated by ammonium sulfite was hydrolyzed as substrate. • Growth kinetics of Chlorella pyrenoidosa in straw hydrolysate was clarified. • Hydrolysate stimulated growth at low concentration and inhibited at high. • Han-Levenspiel model was well fit to explain the growth in hydrolysate medium. Abstract As the current bioconversion of lignocellulose mainly towards on bioenergy, a bioproduct with higher value would be promising to improve the profit output from the process. Straw lignocellulose, hydrothermally pretreated by ammonium sulfite, was used as the substrate to produce high-value microalgal biomass in this study. Medium based on the lignocellulose hydrolysate were prepared to cultivate four locally isolated microalgal strains, Chlorella and Scenedesmus species. All of the microalgal strains well adapted to the lignocellulose hydrolysate. Among the strains, C. ZTY4 had the highest growth rate in hydrolysate-based medium with a generation time of only 10.2 h, which was much shorter than that in glucose medium (16.7 h) and former reports. The polyunsaturated fatty acids (PUFA) content of C. ZTY4 reached to 66.4% in total fatty acids of C. ZTY4, which was well qualified for high-value applications. C. ZTY4 was identified as Chlorella pyrenoidosa by 18S rDNA sequencing. This research proposed a bioconversion approach from straw lignocellulose to high-value microalgal biomass and screened C. ZTY4 as a qualified strain. [ABSTRACT FROM AUTHOR]

Heterotrophic cultivation of Chlorella pyrenoidosa based on straw substrate was proposed as a promising approach in this research. The straw pre-treated by ammonium sulfite method was enzymatically hydrolyzed for medium preparation. The highest intrinsic growth rate of C. pyrenoidosa reached to 0.097 h −1 in hydrolysate medium, which was quicker than that in glucose medium. Rising nitrogen concentration could significantly increase protein content and decrease lipid content in biomass, meanwhile fatty acids composition kept stable. The highest protein and lipid content in microalgal biomass reached to 62% and 32% under nitrogen excessive and deficient conditions, respectively. Over 40% of amino acids and fatty acids in biomass belonged to essential amino acids (EAA) and essential fatty acids (EFA), which were qualified for high-value uses. This research revealed the rapid biomass accumulation property of C. pyrenoidosa in straw hydrolysate medium and the effectiveness of nitrogen regulation to biomass composition at heterotrophic condition. [ABSTRACT FROM AUTHOR]

Microalgae-based bioenergy has been long considered as a promising substitute to replace the fossil fuels at large-scale. After the decades of research, several bottlenecks remain to be overcome to make the large-scale production of microalgal bioenergy commercially viable. In this review, the bottlenecks that restrict the commercial production of microalgal bioenergy are summarized as “high cost” and “low efficiency” and then identified in detailed categories. Several solutions which aim to solve the bottlenecks are presented and discussed correspondingly. The solutions presented in this review including cultivating in wastewater, recycling water and nutrients, utilizing the whole biomass, selecting indigenous strains, cultivating mixed-species, supplementing low-cost organic substrates, mixing vertically in reactor, optimizing metabolic pathway and attaching the cells on suspended-solids. Furthermore, a novel system integrated with the solutions, which is combined with the wastewater treatment system and characterized as the mixed-species cultivation of wild-selected mixotrophic microalgal strains in suspended-solid phase bioreactor based on low-cost substrate, is proposed to promote the scale-up of the microalgal cultivation for bioenergy production. [ABSTRACT FROM AUTHOR]

Microalgae are potential candidates for the production of valuable products, such as renewable biodiesel, health products and pigments. However, low biomass productivity has restricted their large-scale applications. In this study, the effects of two auxins (one natural type of indole-3-acetic acid (IAA) and the other synthetic type of 2,4-dichlorophenoxyacetic acid (2,4-D)) on the growth and fatty acid methyl esters (FAMEs) production of a freshwater microalgae Scenedesmus sp. LX1 were investigated. Both auxins showed a “low dosage-promotion and high dosage-inhibition” effect on the growth and FAMEs accumulation. The optimum dosage of IAA and 2,4-D were 1 mg L −1 and 0.1 mg L −1 , respectively. Moreover, the IAA could increase the monounsaturated fatty acid content. The auxins may promote the growth by enhancing the photosynthetic activity through increasing chlorophyll contents. Therefore, auxin significantly enhanced microalgal growth and FAMEs accumulation, and has a potential for application in developing efficient microalgal cultivation. [ABSTRACT FROM AUTHOR]

Abstract: Using wastewater as resource for microalgal cultivation was seriously considered as a promising approach for sustainable biomass and lipid production. The proper selection of microalgal species is the foundation and key point to achieve this objective. This paper reviewed the recent status of microalgal cultivation in wastewater, including the characteristics of microalgal species used in recent studies, the performance of different microalgal species in different types of wastewater, the commonly-used isolation methods of microalgal species adaptable to the growth in wastewater, and the evaluation criteria of microalgal species. It was found that microalgal biomass and lipid production in wastewater were comparable to those in artificial culture medium, although most of the data was obtained in sterilized wastewater. Among all microalgal species involved in this review, Botryococcus braunii, Chlorella pyrenoidosa and Chlamydomonas reinhardtii showed superior performance in certain studies. However, no microalgal species has been demonstrated to meet all the requirements for large-scale biomass production in wastewater. Thus, the efforts on microalgal species isolation and characterization should still be promoted. On the basis of all the information, this review explored the limitations of recent studies and future research needs on this topic. [Copyright &y& Elsevier]

Highlights: [•] Solid carriers were added and kept suspended by aeration in this ssPBR. [•] Microalgae could attach and grow on the carriers. [•] By catching carriers, microalgae could easily be separated from liquid phase. [•] Biomass production in ssPBR was increased by adding solid carriers. [Copyright &y& Elsevier]

Microalgal growth is the key to the coupled system of wastewater treatment and microalgal biomass production. In this study, Monod model, Droop model and Steele model were incorporated to obtain an integrated growth model describing the combined effects of nitrogen, phosphorus and light intensity on the growth rate of Scenedesmus sp. LX1. The model parameters were obtained via fitting experimental data to these classical models. Furthermore, the biomass production of Scenedesmus sp. LX1 in open pond under nutrient level of secondary effluent was analyzed based on the integrated model, predicting a maximal microalgal biomass production rate about 20 g m −2 d −1 . In order to optimize the biomass production of open pond the microalgal biomass concentration, light intensity on the surface of open pond, total depth of culture medium and hydraulic retention time should be 500 g m −3 , 16,000 lx, 0.2 m and 5.2 d in the conditions of this study, respectively. [ABSTRACT FROM AUTHOR]