Hydrothermal Carbonization of Residual Algal Biomass for Production of Hydrochar as a Biobased Metal Adsorbent

Conversion of residual algal biomass to value-added products is essential for enhancing the economics of algae cultivation. Algal hydrochar produced via hydrothermal carbonization of lipid-extracted Picochlorum oculatum is a material rich in oxygen functional groups and carbon (up to 67.3%) and hence a promising candidate for remediation of wastewaters. The hydrothermal carbonization conditions were optimized and the adsorption capacity of the hydrochar was tested for metal removal. By the end of the remediation process, cumulative removal of Al3+, Cu2+, Fe2+, Mg2+, Mn2+, and Pb2+ reached 89, 98, 75, 88, 75, and 100%, respectively. The adsorption of all metals was found to follow pseudo second-order kinetics and the Langmuir isotherm. Overall, when hydrothermal carbonization is applied to lipid-extracted algae, it generates a promising biobased adsorbent with value-added potential in metal remediation.

Research technology of cultivation of spirulina algae with the use of CO2 hidden from the smoke of rice husk boiler

This paper presents an investigation of Spirulina algae cultivation by the CO2 gas emitted from the combustion of rice husk. The gas emitted from the rice husk combustion containing CO2 but no toxic gas of SOx. The CO2 molecules are absorbed into the micro-algae cultivation medium and then converted into the HCO3 by the assimilation of Spirulina. At the same time, the pH values are controlled to be from 8.5 to 9.5, which is suitable for Spirulina algae. At the first seven days of cultivation in Zarrouk medium the values of Spirulina algae biomass and pH increase from 0.05 g/l and 8.5 to 1.0 g/l and 10.2, respectively. On the 8th day, when the amount of 7,6 % CO2 v/v under 35–40 ºC and 1 atm is introduced into the above medium, the decrease of pH from 10.2 to 8.6 is observed. This pH value, which is maintained over the following days, is optimal for the growth yield of the Spirulina. As a result, the biomass concentration increases from 1.0 to 1.4 g/l. The obtained results are compared with those of the control sample from Zarrouk medium without gas introduction. For the latter case, the biomass reaches the maximum and then decreases. On the basis of the obtained results, the cultivation of Spirulina algae by using the CO2 molecules emitted from the combustion of rice husk can be applied practically.

Production of Biodiesel from Spirogyra elongata, a Common Freshwater Green Algae with High Oil Content

The need for exploring nonfood low-cost sustainable sources for biodiesel production is ever increasing. Commercial and industrial algae cultivation has numerous uses in biodiesel production. This study explores S. elongata as a new algal feedstock for the production of biodiesel that does not compete with food production. The major fatty acids identified in S. elongata oil were oleic (30.5%), lauric (29.9%), myristic (17.0%), and palmitic (14.2%) acids. Transesterification to FAME was conducted using basic (KOH), acidic (HCl), and Zeolitic catalysts for assessment. The yields with acidic (54.6%) and zeolitic (72.7%) catalysts were unremarkable during initial screening. The highest biodiesel yield (99.9%) was achieved using KOH, which was obtained with the optimum reaction conditions of 1.0% catalyst, 60 °C, 4 h, and an oil-to-methanol volume ratio of 1:4. The resulting S. elongata oil methyl esters exhibited densities, CNs, and IVs, that were within the ranges specified in the American (ASTM D6751) and European (EN 14214) biodiesel standards, where applicable. In addition, the high SVs and the moderately high CPs and PPs were attributed to the presence of large quantities of short-chain and saturated FAME, respectively. Overall, the composition and properties of FAME prepared from S. elongaae oil indicate that S. elongata is suitable as an alternative algal feedstock for the production of biodiesel.

Continuous measurements of volatile gases as detection of algae crop health

Algae cultivation in open raceway ponds is considered the most economical method for photosynthetically producing biomass for biofuels, chemical feedstocks, and other high-value products. One of the primary challenges for open ponds is diminished biomass yields due to attack by grazers, competitors, and infectious organisms. Higher-frequency observations are needed for detection of grazer infections, which can rapidly reduce biomass levels. In this study, real-time measurements were performed using chemical ionization mass spectrometry (CIMS) to monitor the impact of grazer infections on cyanobacterial cultures. Numerous volatile gases were produced during healthy growth periods from freshwater Synechococcus elongatus Pasteur Culture Collection (PCC) 7942, with 6-methyl-5-hepten-2-one serving as a unique metabolic indicator of exponential growth. Following the introduction of a Tetrahymena ciliate grazer, the concentrations of multiple volatile species were observed to change after a latent period as short as 18 h. Nitrogenous gases, including ammonia and pyrroline, were found to be reliable indicators of grazing. Detection of grazing by CIMS showed indicators of infections much sooner than traditional methods, microscopy, and continuous fluorescence, which did not detect changes until 37 to 76 h after CIMS detection. CIMS analysis of gases produced by PCC 7942 further shows a complex temporal array of biomass-dependent volatile gas production, which demonstrates the potential for using volatile gas analysis as a diagnostic for grazer infections. Overall, these results show promise for the use of continuous volatile metabolite monitoring for the detection of grazing in algal monocultures, potentially reducing current grazing-induced biomass losses, which could save hundreds of millions of dollars.

Self-Flocculation as an Efficient Method to Harvest Microalgae: A Mini-Review

The development of clean and renewable biofuels has been of wide concern on the topic of energy and environmental issues. As a kind of biomass energy with great application prospects, microalgae have many advantages and are used in the fields of environmental protection and biofuels as well as food or feed production for humans and animals. However, the high cost of microalgae harvesting is the main bottleneck of industrial production on a large scale. Self-flocculation is a cost-efficient and promising method for harvesting microalgal biomass. This article briefly describes the current commonly used technology for microalgae harvesting, focusing on the research progress of self-flocculation. This article explores the relative mechanisms and influencing factors of self-flocculation and discusses a proposal for the integration of algae cultivation and harvesting as well as the co-cultivation of algae and bacteria in an effort to provide a reference for microalgae harvesting with high efficiency and low cost.

Elliptic Array Luminescent Solar Concentrators for Combined Power Generation and Microalgae Growth

The full utilization of broadband solar irradiance is becoming increasingly useful for applications such as long-term space missions, wherein power generation from external sources and regenerative life support systems are essential. Luminescent solar concentrators (LSCs) can be designed to separate sunlight into photosynthetically active radiation (PAR) and non-PAR to simultaneously provide for algae cultivation and electric power generation. However, the efficiency of LSCs suffers from high emission losses. In this work, we show that by shaping the LSC in the form of an elliptic array, rather than the conventional planar configuration, emission losses can be drastically reduced to the point that they are almost eliminated. Numerical results, considering the combined effects of emission, transmission and surface scattering losses show the optical efficiency of the elliptic array LSC is 63%, whereas, in comparison, the optical efficiency for conventional planar LSCs is 47.2%. Further, results from numerical simulations show that elliptic array luminescent solar concentrators can convert non-PAR and green-PAR to electric power with a conversion efficiency of ~17% for AM1.5 and 17.6% for AM0, while transmitting PAR to an underlying photobioreactor to support algae cultivation.