Utilization of ammonium by the hydrocarbon-producing microalga, Botryococcus braunii Showa

Biomass and hydrocarbon production from Botryococcus braunii: A review focusing on cultivation methods

Botryococcus braunii has garnered significant attention in recent years due to its ability to produce high amounts of renewable hydrocarbons through photosynthesis. As the world shifts towards a greener future and seeks alternative sources of energy, the cultivation of B. braunii and the extraction of its hydrocarbons can potentially provide a viable solution. However, the development of a sustainable and cost-effective process for cultivating B. braunii is not without challenges. Compared to other microalgae, B. braunii grows very slowly, making it time-consuming and expensive to produce biomass. In response to these challenges, several efforts have been put into optimizing Botryococcus braunii cultivation systems to increase biomass growth and hydrocarbon production efficiency. This review presents a comparative analysis of different Botryococcus braunii cultivation systems, and the factors affecting the productivity of biomass and hydrocarbon in Botryococcus braunii are critically discussed. Attached microalgal growth offers several advantages that hold significant potential for enhancing the economic viability of microalgal fuels. Here, we propose that employing attached growth cultivation, coupled with the milking technique for hydrocarbon extraction, represents an efficient approach for generating renewable fuels from B. braunii. Nevertheless, further research is needed to ascertain the viability of large-scale implementation.

A simple method for the preparation of single cells and regeneration of colonies of Botryococcus braunii NIES836

Botryococcus braunii, a colonial alga, is known for notably slow growth; however, the growth rate and hydrocarbon productivity are expected to be improved using genetic modification techniques. Nevertheless, B. braunii has a hydrocarbon-rich extracellular matrix (ECM), and the ECM is a major barrier to DNA transformation. To analyse and utilize genetically modified B. braunii, it is essential to regenerate genetically homogeneous colonies derived from single cells. In this study, we developed a novel, simple method for harvesting viable single cells of B. braunii by centrifugation of the culture and subsequent filtration alone. The harvest of single cells was made possible by culturing B. braunii colonies in AF6 medium until the depletion of nitrogen and phosphorus sources and then releasing the single cells in colonies into the medium. Twenty-day culture of single cells in a 96-well plate resulted in 96% regeneration of colonies, and the regeneration of colonies was also confirmed on agar medium. This is the first report of colony regeneration from single cells of B. braunii. We believe that our method developed in this study will contribute greatly to the advancement of genetic modification techniques for B. braunii.

Screening of the dominant Chlorella pyrenoidosa for biofilm attached culture and feed production while treating swine wastewater

This research 12 microalgal species were screened for biofilm attached culture in the treatment of anaerobically digested swine wastewater (ADSW). The influence of ADSW on biomass productivity and removal efficiencies were evaluated using biofilm attached culture with the selected Chlorella pyrenoidosa. The variation of nutritional components from algal cells were further analysed to evaluate the potential applications of C. pyrenoidosa. The results showed that C. pyrenoidosa had the highest tolerance to ADSW, and the highest removal efficiencies for wastewater pollutants were reached when cultured in 5 times diluted ADSW. These test conditions resulted in an algal cell biomass composed of 57.30% proteins, 14.87% extracellular polysaccharide, 3.08% crude fibre, 5.57% crude ash, 2.85% moisture. Amino acids in proteins contained 21.73% essential amino acids and the EAA/NEAA value was 0.64. The essential amino acid score indicates that the selected C. pyrenoidosa could be a good protein source for feed addition.

Cultivation of Microalgae and Cyanobacteria: Effect of Operating Conditions on Growth and Biomass Composition

The purpose of this work is to define optimal growth conditions to maximise biomass for batch culture of the cyanobacterium Arthrospira maxima and the microalgae Chlorella vulgaris, Isochrysis galbana and Nannochloropsis gaditana. Thus, we study the effect of three variables on cell growth: i.e., inoculum:culture medium volume ratio (5:45, 10:40, 15:35 and 20:30 mL:mL), light:dark photoperiod (8:16, 12:12 and 16:8 h) and type of culture medium, including both synthetic media (Guillard’s F/2 and Walne’s) and wastewaters. The results showed that the initial inoculum:culture medium volume ratio, within the range 5:45 to 20:30, did not affect the amount of biomass at the end of the growth (14 days), whereas high (18 h) or low (6 h) number of hours of daily light was important for cell growth. The contribution of nutrients from different culture media could increase the growth rate of the different species. A. maxima was favoured in seawater enriched with Guillard’s F/2 as well as C. vulgaris and N. gaditana, but in freshwater medium. I. galbana had the greatest growth in the marine environment enriched with Walne’s media. Nitrogen was the limiting nutrient for growth at the end of the exponential phase of growth for C. vulgaris and N. gaditana, while iron was for A. maxima and I. galbana. The growth in different synthetic culture media also determines the biochemical composition of each of the microalgae. All species demonstrated their capability to grow in effluents from a wastewater treatment plant and they efficiently consume nitrogen, especially the three microalga species.

The effects of refractory pollutants in swine wastewater on the growth of Scenedesmus sp. with biofilm attached culture

Microalgae have been widely used for treatment of swine wastewater. However, the research on combined treatment of refractory pollutants ammonia nitrogen, Cu (II) and antibiotics from swine wastewater was still scattered. This study, the growth and removal efficiency of NH₄Cl, CuSO₄, tetracycline, norfloxacin and sulfadimidine with selected Scenedsmus sp. was investigated by biofilm attached culture. The results showed that low concentration of ammonia nitrogen had little effect on algae growth. The highest biomass productivity was 6.2 g/(m²d) at the concentration of NH₄Cl of 50.0 mg/L, which was similar to that of a standard growth medium BG 11. Cu (II) concentration of 1.0 mg/L could accelerate the growth of Scenedsmus sp., and the highest biomass was 57.2 g/m² in 8 days. Moreover, the highest biomass mean values was 59.5 g/m², 57.1 g/m^2, and 58.1 g/m², respectively, when tetracycline concentration was 20.0 mg/L, norfloxacin concentration was 100.0 mg/L and sulfadimidine concentration was 10.0 mg/L. The removal efficiency of ammonia nitrogen, copper, tetracycline, norfloxacin and sulfadimidine with Scenedsmus sp. at their optimal initial concentration by biofilm attached culture was 85.2%, 64.6%, 74.6%,71.2%, and 62.3%, respectively. This study provides a theoretical basis for the purification of refractory substances from swine wastewater.