A review of volatile fatty acids production from organic wastes: Intensification techniques and separation methods.

High value-added products from organic waste fermentation have garnered increasing concern in modern society. VFAs are short-chain fatty acids, produced as intermediate products during the anaerobic fermentation of organic matter. VFAs can serve as an essential organic carbon source to produce substitutable fuels, microbial fats and oils, and synthetic biodegradable plastics et al. Extracting VFAs from the fermentation broths is a challenging task as the composition of suspensions is rather complex. In this paper, a comprehensive review of methods for VFAs production, extraction and separation are provided. Firstly, the methods to enhance VFAs production and significant operating parameters are briefly reviewed. Secondly, the evaluation and detailed discussion of various VFAs extraction and separation technologies, including membrane separation, complex extraction, and adsorption methods, are presented, highlighting their specific advantages and limitations. Finally, the challenges encountered by different separation technologies and novel approaches to enhance process performance are highlighted, providing theoretical guidance for recycling VFAs from organic wastes efficiently.

A review of lipid accumulation by oleaginous yeasts: Culture mode.

Microbial lipids have attracted considerable interest owing to their favorable environmental sustainability benefits. In laboratory-scale studies, the factors impacting lipid production in oleaginous yeasts, including culture conditions, nutrients, and low-cost substrates, have been extensively studied. However, there were several different modes of microbial lipid cultivation (batch culture, fed-batch culture, continuous culture, and other novel culture modes), making it difficult to comprehensively analyze impacting factors under different cultivation modes on a laboratory scale. And only few cases of microbial lipid production have been conducted at the pilot scale, which requires more technological reliability assessments and environmental benefit evaluations. Thus, this study summarized the different culture modes and cases of scale-up processes, highlighting the role of the nutrient element ratio in regulating culture mode selection and lipid accumulation. The cost distribution and environmental benefits of microbial lipid production by oleaginous yeasts were also investigated. Our results suggested that the continuous culture mode was recommended for the scale-up process because of its stable lipid accumulation. More importantly, exploring the continuous culture mode integrated with other efficient culture modes remained to be further investigated. In research on scale-up processes, low-cost substrate (organic waste) application and optimization of reactor operational parameters were key to increasing environmental benefits and reducing costs.

Adsorption of crystal violet on activated bamboo fiber powder from water: preparation, characterization, kinetics and isotherms.

Biomass-activated carbon has made a great contribution as an adsorbent in the field of dye wastewater treatment. In this study, the response surface method (RSM) based on the Box-Behnken design was used to optimize the preparation process. Bamboo fiber activated carbon (BAC) with a specific surface area of 2892 m2 g-1 and a pore volume of 1.80 cm3 g-1 was prepared. Various characterization methods (SEM, XPS, XRD, and Raman spectroscopy) were used to analyze the micro-structure of BAC. In the microscopic state, the BAC is fibrous and maintains the originally connected pores of the bamboo fiber. After high-temperature activation, the microcrystallinity of BAC decreases, and the degree of graphitization is low, indicating the presence of amorphous carbon. The adsorption capacity of BAC to crystal violet in simulated wastewater was evaluated via an adsorption experiment. Under the following conditions: the dosage of BAC was 0.04 g, the concentration was 600 mg L-1, the adsorption temperature and time were 25 °C and 30 min, respectively, and the as-prepared BAC had a 99.96% removal rate. The adsorption process conformed to the pseudo-second-order kinetic model and Langmuir adsorption isotherm model, indicating that the adsorption process of CV on BAC belonged to monomolecular layer adsorption. The adsorption process occurs spontaneously and is accompanied by heat release, and the maximum adsorption capacity of BAC within a given concentration range could reach 1353.09 mg g-1. SEM-EDS characterization before and after adsorption showed that ion exchange and the presence of oxygen-containing functional groups played an important role in promoting the adsorption process. The results show that BAC considerably affects CV removal, which has great application prospects.