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The stability of calcium alginate beads for microalgae immobilization in wastewater treatment has been a concern due to the potential exchange of Ca2+ ions from the bead surface with the environment. To overcome this constraint, adding biopolymers might improve the properties of alginate gel. The purpose of the study is to immobilize Chlorella vulgaris in blends of sodium alginate with carboxymethylcellulose (CMC) or pectin in different concentrations (1%, 1.5%, and 2%) to evaluate the microalgae growth and nutrient removal from culture media. The microalgae growth was assessed by cell counting and chlorophyll content using a fluorescent excitation–emission matrix. Nutrient removal was conducted by measuring the phosphate and nitrate concentration using ion chromatography. The characterization of beads, such as size, shrinkage degree, swelling ratio, water content, and dry weight, was also investigated. Compared to alginate-only beads, the results present better performance for cell growth and, similarly, for removing nutrients in the presence of pectin and CMC blends. Microalgae in alginate with 1.0% of pectin grew 26% more than in alginate-only beads on day 8. The blends with CMC showed faster removal of nutrients compared to pectin blends and alginate-only in only 3 days. For phosphate, the highest removal was by immobilized microalgae of 95% for 2.0% of CMC and 86% for 2.0% of pectin. For nitrate, the immobilized microalgae removed 100% in 1.0% and 1.5% of CMC and 98% in 1.0% of pectin. [ABSTRACT FROM AUTHOR]

Diatoms (Bacillariophyceae) are important to primary productivity of aquatic ecosystems. This algal group is also a valuable source of high value compounds that are utilised as aquaculture feed. The productivity of diatoms is strongly driven by light and CO2 availability, and macro- and micronutrient concentrations. The light dependency of biomass productivity and metabolite composition is well researched in diatoms, but information on the impact of light quality, particularly the productivity return on energy invested when using different monochromatic light sources, remains scarce. In this work, the productivity return on energy invested of improving growth rate, photosynthetic activity, and metabolite productivity of the diatom Chaetoceros muelleri under defined wavelengths (blue, red, and green) as well as while light is analysed. By adjusting the different light qualities to equal photosynthetically utilisable radiation, it was found that the growth rate and photosynthetic oxygen evolution was unchanged under white, blue, and green light, but it was lower under red light. Blue light improved the productivity return on energy invested for biomass, total protein, total lipid, total carbohydrate, and in fatty acids production, which would suggest that blue light should be used for aquaculture feed production. [ABSTRACT FROM AUTHOR]

A matrix of photobioreactors integrated with metabolic sensors was used to examine the combined impact of light and temperature variations on the growth and physiology of the biofuel candidate microalgal species Nannochloropsis oculata. The experiments were performed with algal cultures maintained at a constant 20°C versus a 15°C to 25°C diel temperature cycle, where light intensity also followed a diel cycle with a maximum irradiance of 1920 µmol photons m−2 s−1. No differences in algal growth (Chlorophyll a) were found between the two environmental regimes; however, the metabolic processes responded differently throughout the day to the change in environmental conditions. The variable temperature treatment resulted in greater damage to photosystem II due to the combined effect of strong light and high temperature. Cellular functions responded differently to conditions before midday as opposed to the afternoon, leading to strong hysteresis in dissolved oxygen concentration, quantum yield of photosystem II and net photosynthesis. Overnight metabolism performed differently, probably as a result of the temperature impact on respiration. Our photobioreactor matrix has produced novel insights into the physiological response of Nannochloropsis oculata to simulated environmental conditions. This information can be used to predict the effectiveness of deploying Nannochloropsis oculata in similar field conditions for commercial biofuel production. [ABSTRACT FROM AUTHOR]

Abstract: Development of the capacity to produce hydrogen economically from renewable energy resources is of critical importance to the future viability of that fuel. The inexpensive and widely available green alga Chlamydomonas reinhardtii has the ability to photosynthetically synthesise molecular hydrogen. Green algal hydrogen production does not generate any toxic or polluting bi-products and could potentially offer value-added products derived from algal biomass. The growth of dense and healthy algal biomass is a vital requirement for efficient hydrogen production. Algal cell density is principally limited by the illumination conditions of the algal culture and by the availability of key nutrients, including the sources of carbon, nitrogen, sulphur and phosphorus. In this study, the effect of different light regimes and carbon dioxide feeds on Chlamydomonas reinhardtii growth were investigated. The objective was to increasing the algal growth rate and the cell density, leading to enhanced biohydrogen production. State-of-the art photobioreactors were used to grow algal cultures, and to measure the pH and optical density of those cultures. Under mixotrophic growth conditions, using both acetate and carbon dioxide, increasing the carbon dioxide feed rate increased the optical density of the culture but reduced the growth rate. Under autotrophic growth conditions, with carbon dioxide as the only carbon source, a carbon dioxide feed with a partial pressure of circa 11% was determined to optimise both the algal growth rate and the optical density. [Copyright &y& Elsevier]