Conversion of Scenedesmus rubescens Lipid into Biodiesel by Biochar of Different Origin

One of the most recent applications studied in recent years is the use of biochar as a catalyst for the conversion of oils into biodiesel. The scope of this work was to evaluate the efficiency of biochars as heterogeneous catalysts for the conversion of Scenedesmus rubescens lipids into biodiesel. Biochar from different materials were employed, namely, malt spent rootlets (MSR), coffee spent grounds (CSG), and olive kernels (OK). Materials were charred at two temperatures (400 and 850 °C) in order to examine the effect of pyrolysis temperature. Homogeneous catalysts such as sulfuric acid and sodium hydroxide were also employed for comparison purposes. In order to explain the different performance of biochar as catalyst, we conducted detailed characterization of these materials. The results of this study showed that homogeneous catalysts (H2SO4 and NaOH) had similar results to the CSG biochar at 400 °C, which was the most productive tested biochar. The pyrolysis temperatures affected the FAMEs recovery of OK and CSG biochar.

The Potential Risk of Electronic Waste Disposal into Aquatic Media: The Case of Personal Computer Motherboards

Considering that electronic wastes (e-wastes) have been recently recognized as a potent environmental and human threat, the present study aimed to assess the potential risk of personal computer motherboards (PCMBs) leaching into aquatic media, following a real-life scenario. Specifically, PCMBs were submerged for 30 days in both distilled water (DW) and artificial seawater (ASW). Afterwards, PCMBs leachates were chemically characterized (i.e., total organic carbon, ions, and trace elements) and finally used (a) for culturing freshwater (Chlorococcum sp. and Scenedesmus rubescens) and saltwater (Dunaliella tertiolecta and Tisochrysis lutea) microalgae for 10 days (240 h), (b) as the exposure medium for mussel Mytilus galloprovincialis (96 h exposure), and (c) for performing the Cytokinesis Block Micronucleus (CBMN) assay in human lymphocytes cultures. According to the results, PCMBs could mediate both fresh- and marine algae growth rates over time, thus enhancing the cytotoxic, oxidative, and genotoxic effects in the hemocytes of mussels (in terms of lysosomal membrane impairment, lipid peroxidation, and NO content and micronuclei formation, respectively), as well as human lymphocytes (in terms of MN formation and CBPI values, respectively). The current findings clearly revealed that PCMBs leaching into the aquatic media could pose detrimental effects on both aquatic organisms and human cells.

Long-Term Toxicity of ZnO Nanoparticles on Scenedesmus rubescens Cultivated in Semi-Batch Mode

The scope of this study was to investigate the toxic effects of zinc oxide (ZnO) nanoparticles (NPs) on freshwater microalgae, in long-term semi-batch feeding mode at two different hydraulic retention times (HRTs) (20 and 40 days). A freshwater microalgae, Scenedesmus rubescens, was employed and exposed to a semi-continuous supply of ZnO NPs at a low concentration of 0.081 mg/L for a period of 28 d. Experiments were conducted under controlled environmental conditions. Τhe impact of ZnO NPs on S. rubescens, which was assessed in terms of nutrient removal, biomass growth, and algal lipid content. Semi-batch mode cultures showed that low ZnO NP concentrations at an HRT of 40 d did not have any negative effect on microalgae growth after the fourth day of culture. In contrast, algal growth was inhibited up to 17.5% at an HRT of 20 d in the presence of ZnO NPs. This might be attributed to the higher flow rate applied and ZnO NPs load. A positive correlation between nutrient removal and microalgae growth was observed. The algal lipid content was, in most cases, higher in the presence of ZnO NPs at both HRTs, indicating that even low ZnO NPs concentration cause stress resulting in higher lipid content.

Evaluation of Scenedesmus rubescens for Lipid Production from Swine Wastewater Blended with Municipal Wastewater

This study examined the feasibility of using non-sterilized swine wastewater for lipid production by an isolated microalga, Scenedesmus rubescens. Different dilution ratios using municipal wastewater as a diluent were tested to determine the suitable levels of microalgal growth in the wastewaters, its nutrient removal, and its lipid production. The highest lipid productivity (8.37 mg/L/d) and NH4+ removal (76.49%) were achieved in swine wastewater that had been diluted to 30 times using municipal wastewater. Various bacteria coexisted in the wastewaters during the cultivation of S. rubescens. These results suggest the practical feasibility of a system to produce lipids from swine wastewater by using microalgae.

Nitrogen Deficiency-Dependent Abiotic Stress Enhances Carotenoid Production in Indigenous Green Microalga Scenedesmus rubescens KNUA042, for Use as a Potential Resource of High Value Products

The microalgal strain Scenedesmus rubescens KNUA042 was identified in freshwater in Korea and characterized by evaluating its stress responses in an effort to increase lipid and carotenoid production. Under a two-stage cultivation process, the algal strain that generally exhibits optimal growth at a nitrate (source of nitrogen) concentration of 0.25 g L−1 was challenged to different exogenous stimuli—salinity (S), light intensity (L), combined L and S (LS), and nitrogen deficiency (C)—for 14 days. Lipid production and carotenoid concentration increased in a time-dependent manner under these physicochemical conditions during the culture periods. Lipid accumulation was confirmed by thin layer chromatography, BODIPY staining, and fatty acid composition analysis, which showed no differences in the algal cells tested under all four (C, S, L, and LS) conditions. The quality of biodiesel produced from the biomass of the algal cells met the American Society for Testing and Materials and the European standards. Total carotenoid content was increased in the LS-treated algal cells (6.94 mg L−1) compared with that in the C-, S-, and L-treated algal cells 1.75, 4.15, and 1.32 mg L−1, respectively). Accordingly, the concentration of canthaxanthin and astaxanthin was also maximized in the LS-treated algal cells at 1.73 and 1.11 mg g−1, respectively, whereas lutein showed no differences in the cells analyzed. Conversely, chlorophyll a level was similar among the C-, S-, and LS-treated algal cells, except for the L-treated algal cells. Thus, our results suggested that S. rubescens KNUA042 was capable of producing carotenoid molecules, which led to the maximum values of canthaxanthin and astaxanthin concentrations when exposed to the combined LS condition compared with that observed when exposed to the salinity condition alone. This indicates that the algal strain could be used for the production of high-value products as well as biofuel. Furthermore, this article provides the first evidence of carotenoid production in S. rubescens KNUA042.

A Novel Microalgae Harvesting Method Using Laser Micromachined Glass Fiber Reinforced Polymers

Microalgae are an ideal source for next-generation biofuels due to their high photosynthetic rate. However, a key process limitation in microalgal biofuel production is harvesting of biomass and extraction of lipids in a cost-effective manner. The harvesting of the algal biomass amounts to approximately 20 to 30% of the total cost of the cultivation; hence, developing an efficient and universal harvesting method will make the commercialization of microalgal bio-cultures sustainable. In this study, we developed, demonstrated, and evaluated a novel harvesting method based on Glass Reinforced Fiber Polymer (GFRP) panels, suitable for industrial-scale installations. The proposed method was based on previous observations of preferential micro-algae development on glass surfaces, as well as in the assumption that the microalgae cells would prefer to attach to and grow on substrates with a similar size as them. At first, we developed a laser micromachining protocol for removing the resin and revealing the glass fibers of the GFRP, available for algal adhesion, thus acting as a microalgae biomass harvesting center. Surface micromachining was realized using a ns pulsed ultraviolet laser emitting at 355 nm. This laser ensured high machining quality of the GFRP, because of its selective material ablation, precise energy deposition, and narrow heat affected zone. A specially built open pond system was used for the cultivation of the microalgae species Scenedesmus rubescens, which was suitable for biofuel production. The cultivation was used for the experimental evaluation of the proposed harvesting method. The cultivation duration was set to 16 days in order for the culture to operate at the exponential growth phase. The biomass maximum recovery due to microalgae attachment on the GFRP surface was 13.54 g/m2, a yield comparable to other studies in the literature. Furthermore, the GFRP surfaces could be upscaled to industrial dimensions and positioned in any geometry dictated by the photobioreactor design. In this study, the glass fiber reinforced polymer used was suitable for the adhesion of Scenedesmus rubescens due to its fiber thickness. Other microalgae species could be cultivated, adhere, and harvested using GFRP of different fiber sizes and/or with a modified laser treatment. These very encouraging results validated GFRPs’ harvesting capabilities as an attachment substrate for microalgae. Additional studies with more algae species will further strengthen the method.