•Temperature and R/M ratio significantly affected yield and quality of the bio-oil.•Microalgae allows the conversion of WRT under milder conditions than WRT alone.•A positive synergistic effect was ...observed between the WRT and the microalgae.•ZnO and carbon black in the WRT improved the quality of the bio-oil.•HHVs of bio-oils were found to be in the range of 35.80–42.03MJ/kg.
Co-pyrolysis of microalgae and waste rubber tire (WRT) in supercritical ethanol was examined to investigate the effects of reaction temperature (290–370°C), time (10–120min), WRT/microalgae mass ratio (R/M, 5/0–0:5), and ethanol/feedstock ratio (EtOH/(R+M), 5:5–30:5). Temperature and mass ratio are two factors that significantly affect the yield and quality of bio-oil. Under optimal reaction conditions, the highest bio-oil yield achieved was 65.4wt%. The presence of microalgae allows the conversion of WRT to occur under milder conditions than WRT alone. The temperature needed for adequate conversion of WRT and microalgae in supercritical ethanol (330°C) is much lower than the co-pyrolysis temperature without a solvent. ZnO and carbon black in the WRT played catalytic roles in the conversion of the WRT and microalgae as well as the in situ denitrogenation and deoxygenation of the bio-oil. A positive synergistic effect between the WRT and the microalgae was observed. The highest value for the synergistic effect (37.8%) was observed at an R/M mass ratio of 1:1. The interaction of microalgae and WRT during co-pyrolysis also favored denitrogenation and deoxygenation, thus improving the quality of the bio-oil. The heating values of the bio-oils produced from the co-pyrolysis of WRT and microalgae were found to be in the range of 35.80–42.03MJ/kg. The main components in the gas phase are typically CO2, H2, and CH4. However, methods for improving the quality of bio-oil via co-pyrolysis will require further study.
•HRT has obvious impacts on biomass production and nutrient removal in MPBR.•An equation for the microalgae harvest rate was proposed based on nitrogen balance.•MPBR run stably for 130 days with an ...HRT and BRT of 2.0 d and 21.1 d, respectively.•Nutrients in the influent were effectively removed during the long-term operation.•Inner resistance contributed the main part of the total resistance in MPBR.
In this study, the effect of hydraulic retention time (HRT) on algal biomass production and nutrient removal was investigated in membrane photobioreactors (MPBRs) in which Chlorella vulgaris was cultured with secondary effluent. The results indicated that decreasing the HRT improved the algal biomass productivity. MPBR that operated at an HRT of 2.0 d obtained the largest productivity of algal biomass. For nutrient removal, MPBR that operated at longer HRT showed a greater reduction in influent nutrients. An MPBR that operated at an HRT of 2.0 d was then chosen to study the long-term operation of the reactor. Microalgae suspensions were continuously harvested from the MPBR at a certain rate, which was calculated using an equation based on the nitrogen balance of the reactor. Therefore, the MPBR ran stably for 130 days, with an HRT and biomass retention time (BRT) of 2.0 d and 21.1 d, respectively. The algal biomass concentration in the MPBR remained at a relatively stable level of 1.035–1.524 g L−1 throughout the cultivation period. The nutrient in the influent was also effectively removed, with effluent nutrient concentrations ranging from 1.76 to 3.82 mg L−1 and 0.01 to 0.14 mg L−1 for DIN and DIP, respectively. Our study of membrane fouling showed that the membrane resistance, cake resistance and inner resistance contributed 6.7%, 39.1%, and 54.2% of the total resistance in MPBR, respectively.
•Nutrient in digestate was reused through Chlorella 1067 amplification.•Chlorella 1067 was then co-digested with chicken manure (CM) in return.•Synergy between Chlorella 1067 and CM during ...co-digestion was verified.•Difference of microbial diversity in co- and mono-digestion was demonstrated.•Potential for a close-loop of nutrient reuse and energy production was indicated.
The present investigation targeted on a sustainable co-digestion system: microalgae Chlorella 1067 (Ch. 1067) was cultivated in chicken manure (CM) based digestate and then algae biomass was used as co-substrate for anaerobic digestion with CM. About 91% of the total nitrogen and 86% of the soluble organics in the digestate were recycled after the microalgae cultivation. The methane potential of co-digestion was evaluated by varying CM to Ch. 1067 ratios (0:10, 2:8, 4:6, 6:4, 8:2, 10:0 based on the volatile solids (VS)). All the co-digestion trials showed higher methane production than the calculated values, indicating synergy between the two substrates. Modified Gompertz model showed that co-digestion had more effective methane production rate and shorter lag phase. Co-digestion (8:2) achieved the highest methane production of 238.71mL⋅(g VS)−1 and the most significant synergistic effect. The co-digestion (e.g. 8:2) presented higher and balanced content of dominant acidogenic bacteria (Firmicutes, Bacteroidetes, Proteobacterias and Spirochaetae). In addition, the archaea community Methanosaeta presented higher content than Methanosarcina, which accounted for the higher methane production. These findings indicated that the system could provide a practicable strategy for effectively recycling digestate and enhancing biogas production simultaneously.
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Microalgae biomass is a sustainable source with the potential to produce a range of products. However, there is currently a lack of practical and functional processes to enable the ...high-efficiency utilization of the microalgae. We report here a hydrothermal process to maximize the utilizability of microalgae biomass. Specifically, our concept involves the simultaneous conversion of microalgae to (i) hydrophilic and stable carbon quantum dots and (ii) porous carbon. The synthesis is easily scalable and eco-friendly. The microalgae-derived carbon quantum dots possess a strong two-photon fluorescence property, have a low cytotoxicity and an efficient cellular uptake, and show potential for high contrast bioimaging. The microalgae-based porous carbons show excellent CO2 capture capacities of 6.9 and 4.2mmolg−1 at 0 and 25°C respectively, primarily due to the high micropore volume (0.59cm3g−1) and large specific surface area (1396m2g−1).
Microalgae cultivation, when compared to the growth of higher plants, presents many advantages such as faster growth, higher biomass productivity, and smaller land area requirement for cultivation. ...For this reason, microalgae are an alternative platform for carotenoid production when compared to the traditional sources. Currently, commercial microalgae production is not well developed but, fortunately, there are several studies aiming to make the large-scale production feasible by, for example, employing different cultivation systems. This review focuses on the main carotenoids from microalgae, comparing them to the traditional sources, as well as a critical analysis about different microalgae cultivation regimes that are currently available and applicable for carotenoid accumulation. Throughout this review paper, we present relevant information about the main commercial microalgae carotenoid producers; the comparison between carotenoid content from food, vegetables, fruits, and microalgae; and the great importance and impact of these molecule applications, such as in food (nutraceuticals and functional foods), cosmetics and pharmaceutical industries, feed (colorants and additives), and healthcare area. Lastly, the different operating systems applied to these photosynthetic cultivations are critically discussed, and conclusions and perspectives are made concerning the best operating system for acquiring high cell densities and, consequently, high carotenoid accumulation.
Although microalgae are a promising biobased feedstock, industrial scale production is still far off. To enhance the economic viability of large-scale microalgae processes, all biomass components ...need to be valorized, requiring a multi-product biorefinery. However, this concept is still too expensive. Typically, downstream processing of industrial biotechnological bulk products accounts for 20–40% of the total production costs, while for a microalgae multi-product biorefinery the costs are substantially higher (50–60%). These costs are high due to the lack of appropriate and mild technologies to access the different product fractions such as proteins, carbohydrates, and lipids. To reduce the costs, simplified processes need to be developed for the main unit operations including harvesting, cell disruption, extraction, and possibly fractionation.
A multi-product biorefinery is essential to make microalgal production of bulk commodities economically feasible.
Large-scale cultivation using closed photobioreactors makes microalgal harvesting a smaller economic hurdle in a multi-product biorefinery.
Techno-economic scenario studies show that a current multi-product biorefinery requiring multiple unit operations is complex and therefore too expensive.
Process simplification can be accomplished by reducing the number of unit operations (e.g., by integrating unit operations or by avoiding auxiliaries in the process chain), making a multi-product biorefinery economically feasible.
•Recent developments in wet oil extraction and biodiesel conversion from microalgae.•Direct transesterification omitting a separate oil extraction step for wet microalgae.•Needs for purification of ...microalgal oils and upgrading of biodiesel properties.
An interest in biodiesel as an alternative fuel for diesel engines has been increasing because of the issue of petroleum depletion and environmental concerns related to massive carbon dioxide emissions. Researchers are strongly driven to pursue the next generation of vegetable oil-based biodiesel. Oleaginous microalgae are considered to be a promising alternative oil source. To commercialize microalgal biodiesel, cost reductions in oil extraction and downstream biodiesel conversion are stressed. Herein, starting from an investigation of oil extraction from wet microalgae, a review is conducted of transesterification using enzymes, homogeneous and heterogeneous catalysts, and yield enhancement by ultrasound, microwave, and supercritical process. In particular, there is a focus on direct transesterification as a simple and energy efficient process that omits a separate oil extraction step and utilizes wet microalgal biomass; however, it is still necessary to consider issues such as the purification of microalgal oils and upgrading of biodiesel properties.
Energy and fuel demands, which are currently met primarily using fossil fuels, are expected to increase substantially in the coming decades. Burning fossil fuels results in the increase of net ...atmospheric CO2 and climate change, hence there is widespread interest in identifying sustainable alternative fuel sources. Biofuels are one such alternative involving the production of biodiesel and bioethanol from plants. However, the environmental impacts of biofuels are not well understood. First generation biofuels (i.e. those derived from edible biomass including crops such as maize and sugarcane) require extensive agricultural areas to produce sufficient quantities to replace fossil fuels, resulting in competition with food production, increased land clearing and pollution associated with agricultural production and harvesting. Microalgal production systems are a promising alternative that suffer from fewer environmental impacts. Here, we evaluate the potential impacts of microalgal production systems on biodiversity compared to first generation biofuels, through a review of studies and a comparison of environmental pressures that directly or indirectly impact biodiversity. We also compare the cultivation area required to meet gasoline and distillate fuel oil demands globally, accounting for spatial variation in productivity and energy consumption. We conclude that microalgal systems exert fewer pressures on biodiversity per unit of fuel generated compared to first generation biofuels, mainly because of reductions in direct and indirect land-use change, water consumption if water is recycled, and no application of pesticides. Further improvements of technologies and production methods, including optimization of productivities per unit area, colocation with wastewater systems and industrial CO2 sources, nutrient and water recycling and use of coproducts for internal energy generation, would further increase CO2 savings. Overall pollution reductions can be achieved through increased energy efficiencies, along with nutrient and water recycling. Microalgal systems provide strong potential for helping in meeting global energy demands sustainably.
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•60–100% removal of diclofenac, ibuprofen, paracetamol and metoprolol was achieved.•Biodegradation and photolysis are most important micropollutant removal mechanisms.•Sorption to ...solids accounted for <20% of micropollutant removal.•Removal of phosphorus and nitrogen was close to 100% by the end of the experiment.•No inhibition of C. sorokiniana in presence of micropollutants.
Micropollutant removal in an algal treatment system fed with source separated wastewater streams was studied. Batch experiments with the microalgae Chlorella sorokiniana grown on urine, anaerobically treated black water and synthetic urine were performed to assess the removal of six spiked pharmaceuticals (diclofenac, ibuprofen, paracetamol, metoprolol, carbamazepine and trimethoprim). Additionally, incorporation of these pharmaceuticals and three estrogens (estrone, 17β-estradiol and ethinylestradiol) into algal biomass was studied. Biodegradation and photolysis led to 60–100% removal of diclofenac, ibuprofen, paracetamol and metoprolol. Removal of carbamazepine and trimethoprim was incomplete and did not exceed 30% and 60%, respectively. Sorption to algal biomass accounted for less than 20% of the micropollutant removal. Furthermore, the presence of micropollutants did not inhibit C. sorokiniana growth at applied concentrations. Algal treatment systems allow simultaneous removal of micropollutants and recovery of nutrients from source separated wastewater. Nutrient rich algal biomass can be harvested and applied as fertilizer in agriculture, as lower input of micropollutants to soil is achieved when algal biomass is applied as fertilizer instead of urine.
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