Enhanced Microalgal Biomass Research Articles

Biomass Accumulation, Contaminant Removal, and Settling Performance of Chlorella sp. in Unsterilized and Diluted Anaerobic Digestion Effluent

Microalgae demonstrate significant efficacy in wastewater treatment. Anaerobic digestion effluent (ADE) is regarded as an underutilized resource, abundant in carbon, nitrogen, phosphorus, and other nutrients; however, the presence of inhibitory factors restricts microalgal growth, thereby preventing its direct treatment via microalgae. The purpose of this study was to dilute ADE using various dilution media and subsequently cultivate Chlorella sp. to identify optimal culture conditions that enhance microalgal biomass and water quality. The effects of various dilution conditions were assessed by evaluating the biomass, sedimentation properties, and nutrient removal efficiencies of microalgae. The results demonstrate that microalgal biomass increases as the dilution ratio increased. The microalgae biomass in the treatments diluted with simulated wastewater was significantly higher than that with deionized water, but their effluent quality failed to meet discharge standards. The treatment diluted with deionized water for 10 times exhibited abundant microbial biomass with strong antioxidant properties. The corresponding total phosphorus concentration in the effluent (6.96 mg/L) adhered to emission limits under the Livestock and Poultry Industry Pollutant Emission Standards (8 mg/L), while ammonia nitrogen concentration (90 mg/L) was near compliance (80 mg/L). The corresponding microbial biomass, with a sludge volume index (SVI30) of 72.72 mL/g, can be recovered economically and efficiently by simple precipitation. Its high protein (52.07%) and carbohydrate (27.05%) content, coupled with low ash (10.75%), makes it a promising candidate for animal feed and fermentation. This study will aid in understanding microalgal growth in unsterilized ADE and establish a theoretical foundation for cost-effective ADE purification and microalgal biomass production.

Effect of iron oxide nanoparticles on mixotrophic cultivation of Chlorella spp. for biofuel production

The current study investigated the effect of iron oxide nanoparticles (IONPs) on mixotrophic microalgae cultivation in wastewater for biofuel production. Optimal IONPs doses of 10 and 20 mg L−1 increased Chlorella pyrenoidosa growth by 16% and lipid accumulation by 53 %, respectively, compared with the control group. Conversely, the protein content declined drastically, while carbohydrates remained relatively unchanged. A maximum of 15% rise in biomass growth was observed for Chlorella sorokiniana IITRF at an IONPs dose of 20 mg L−1, with no significant variation in biochemical composition. Microalgae grown under mixotrophic conditions with IONPs in a biofilm reactor were more suitable for biogas production than biodiesel, increasing biogas and methane content by 38 and 48%, respectively. The findings suggest that low doses of IONPs can enhance microalgal biomass, biogas production and methane content. Further, metabolomics studies are warranted to investigate the interaction between microalgae and nanoparticles to achieve high-quality biodiesel.

Enhanced microalgal biomass and lipid production with simultaneous effective removal of Cd using algae-bacteria-activated carbon consortium added with organic carbon source

Recently, using microalgae to remediate heavy metal polluted water has been attained a huge attention. However, heavy metals are generally toxic to microalgae and consequently decrease biomass accumulation. To address this issue, the feasibility of adding exogenous glucose, employing algae-bacteria system and algae-bacteria-activated carbon consortium to enhance microalgae growth were evaluated. The result showed that Cd2+ removal efficiency was negatively correlated with microalgal specific growth rate. The exogenous glucose alleviated the heavy metal toxicity to algal cells and thus increased the microalgae growth rate. Among the different treatments, the algae-bacteria-activated carbon combination had the highest biomass concentration (1.15 g L−1) and lipid yield (334.97 mg L−1), which were respectively 3.03 times of biomass (0.38 g L−1) and 4.92 times of lipid yield (68.08 mg L−1) in the single microalgae treatment system. Additionally, this algae-bacteria-activated carbon consortium remained a high Cd2+ removal efficiency (91.61%). In all, the present study developed an approach that had a great potential in simultaneous heavy metal wastewater treatment and microalgal lipid production.

Enhancing microalgal biomass production in lab-scale raceway ponds through innovative computational fluid dynamics-based electrode deflectors

The design of novel electrode deflector structures (EDSs) introduced a promising strategy for enhancing raceway ponds performance, increasing carbon fixation, and improving microalgal biomass accumulation. The computational fluid dynamics, based flow field principles, proved that the potency of arc-shaped electrode deflector structures (A-EDS) and spiral electrode deflector structures (S-EDS) were optimal. These configurations yielded superior culture effects, notably reducing dead zones by 9.1% and 11.7%, while elevating biomass increments of 14.7% and 11.5% compared to the control, respectively. In comparison to scenarios without electrostatic field application, the A-EDS group demonstrated pronounced post-stimulation growth, exhibiting an additional biomass increase of 11.2%, coupled with a remarkable 23.6% surge in CO2 fixation rate and mixing time reduction by 14.7%. A-EDS and S-EDS, combined with strategic electric field integration, provided a theoretical basis for promoting microalgal biomass production and enhancing carbon fixation in a raceway pond environment to similar production practices.

Mechanism of enhanced microalgal biomass and lipid accumulation through symbiosis between a highly succinic acid-producing strain of Escherichia coli SUC and Aurantiochytrium sp. SW1

Microalgae, known for rapid growth and lipid richness, hold potential in biofuels and high-value biomolecules. The symbiotic link with bacteria is crucial in large-scale open cultures. This study explores algal-bacterial interactions using a symbiotic model, evaluating acid-resistant Lactic acid bacteria (LAB), stress-resilient Bacillus subtilis and Bacillus licheniformis, and various Escherichia coli strains in the Aurantiochytrium sp. SW1 system. It was observed that E. coli SUC significantly enhanced the growth and lipid production of Aurantiochytrium sp. SW1 by increasing enzyme activity (NAD-IDH, NAD-ME, G6PDH) while maintaining sustained succinic acid release. Optimal co-culture conditions included temperature 28 °C, a 1:10 algae-to-bacteria ratio, and pH 8. Under these conditions, Aurantiochytrium sp. SW1 biomass increased 3.17-fold to 27.83 g/L, and total lipid content increased 2.63-fold to 4.87 g/L. These findings have implications for more efficient microalgal lipid production and large-scale cultivation.

Polyphenols modulate microalgae metabolism with a particular increment in lipid accumulation

The development of an affordable strategy to concurrently enhance microalgal biomass and biocomponents is warranted for commercial applications. Here, we reported that a cheap and natural polyphenol, tannic acid, regulated the metabolic and physiological properties of the oleaginous microalga Phaeodactylum tricornutum to overproduce biocompounds. Tannic acid provision regulated the key metabolic pathways to enhance algal biomass and lipids in a dose-dependent manner without having a direct impact on photosynthesis. It reduced oxidative stress and reallocated carbon precursors toward lipogenesis. Lipidomic analyses showed that tannic acid provision unprecedentedly regulated the key lipogenic pathways, enhancing glyco- and neutral-lipids by 1.29- and 1.54-fold, respectively, whereas phospholipids were significantly altered. Tannic acid facilitated polyunsaturated fatty acid overproduction with a specific increment of EPA and DHA of 1.18- and 2.25-fold, respectively. Transcriptomic analysis demonstrated that tannic acid upregulated the expression of multiple genes involved in lipogenesis. Here, we dissected the potential of tannic acid, a natural and cheaper polyphenol, for simultaneously enhancing lipids and PUFAs without impairing physiological properties in P. tricornutum. The findings provide novel insights into the mechanistic roles of polyphenols as potential chemical modulators.

The effects of light intensity and nitrogen concentration to enhance lipid production in four tropical microalgae

The manipulation of nutritional and culture parameters is one of the most promising methods for enhancing microalgal biomass and biofuel production. An earlier study analysed the ability of eight locally isolated microalgae to utilize standard nutrient sources in culture media to produce lipids. Four microalgae, Ankistrodesmus falcatus, Chlorella emersonii, Chaetoceros muelleri, and Isochrysis galbana, showed the desired biofuel properties (lipid/mass productivity, lipid content, and fatty acid profiles) and were selected for the present study. In this study, light intensity and nitrogen concentration were optimised to increase the growth rate, biomass, and lipid content of the four selected microalgae. Under optimal conditions of 135 μmol/m2/s light intensity and 5 g/l nitrogen, the isolates exhibited biomass productivity of 0.31–0.56 g/l/day, lipid content of 20.30–40.95% dry weight, and lipid productivity of 85.26–180.18 mg/l/day. Using the optimised parameters, the microalgae was further cultured with an upscaled volume of 5 L. The study found that C. muelleri and I. galbana produced the most promising results, with the highest lipid content, up to 43.40% dry weight, and the desired fatty acid profiles, which included a high concentration of saturated fatty acids (43.89–48.00%) and monounsaturated fatty acids (35.30–38.44%). Regardless, C. muelleri was chosen as a promising candidate for biodiesel application because of its high oleic acid proportion (27.68%), which was significantly higher than the other three microalgae (only 2.37–3.62% oleic acid). The study demonstrates the potential use of the tropical marine microalga C. muelleri as a feedstock for the production of biofuels.

A cleaner and smarter way to achieve high microalgal biomass density coupled with facilitated self-flocculation by utilizing bicarbonate as a source of dissolved carbon dioxide

Microalgae feedstock-based bioprocesses are increasingly unfolding as promising futuristic technologies towards achieving some of the sustainable development goals, mostly pertaining to clean energy and environment. The current technologies that involve sparging flue-gas carbon dioxide (CO2) directly into closed or open photobioreactors suffer from very limited bioavailability of sparingly soluble CO2 in dissolved form leading to less algal biomass production. Thus, the present study was designed to assess the ability of Chlorella vulgaris as a model microalga to capture carbon from a dissolved inorganic carbon (DIC) source like sodium bicarbonate (NaHCO3) and grow in photobioreactors to high biomass density. With the aim to develop a proof of this concept, Chlorella vulgaris was grown in minimal medium supplemented with varying doses of initial bicarbonate (50–250 mM). The results demonstrated that with increasing initial bicarbonate (HCO3−) concentration, CO2 fixation rate and algal biomass productivity were enhanced. At 150 mM initial HCO3−, biomass concentration and CO2 fixation rate were increased by about 145% and 38%, respectively, as compared to minimal medium. Biomass concentration was further improved by implementing a smart intermittent bicarbonate feeding strategy, which resulted in an overall enhancement by about 255%, as opposed to the case of minimal medium. It was interesting to observe that Chlorella vulgaris facilitated its own harvesting by self-flocculation-cum-settling mechanism within a short period of time in presence of HCO3−. The efficiency of self-flocculation was found to increase by about 55% in presence of 150 mM initial HCO3−, when compared with minimal medium. High resolution microscopic analyses revealed that microalgal cells were embedded within a self-produced matrix of extracellular polymeric substances (EPS) and underwent alterations in topological complexity that may have facilitated nutrient uptake and gaseous exchange across the cell surface, thereby resulting in enhanced biomass production and self-settling. Therefore, strategic utilization of bicarbonate as a source of DIC convincingly establishes the novelty of our rational approach towards enhancing microalgal biomass coupled with efficient CO2 fixation and self-harvesting. This innovative and smart process may be scaled up and translated to efficiently sequester flue-gas CO2 released by thermal power plants and other fossil fuel-based industries through algal cultivation.

Boosting the yields of microalgal biomass and high-value added products by phytohormones: A mechanistic insight using transcriptomics

Addition of phytohormones (diethyl aminoethyl hexanoate and indole acetic acid) at 10−5 M significantly increased the growth of a green microalga, Chlorella pyrenoidosa up to 62.25% achieving cell concentrations of 5.13╳107 cells ml−1. Yielding of high-value added byproducts (pigments, carbohydrate, proteins, and fatty acids) was more in presence of phytohormones comparing to the control. Further transcriptomics analysis demonstrated phytohormones upregulated numerous genes involved in DNA replication and repair pathways, and energy metabolisms (glycolysis, citrate cycle, and oxidative phosphorylation). Moreover, genes in purine metabolism, and porphyrin and chlorophyll metabolism were also more expressed by up to 6.49 times with phytohormones. These pathways can supply more cellular signaling molecules and antioxidant contents. This study carried new insights on the key driving factors in phytohormone enhanced microalgal biomass production processes, which can help to find more feasible application solutions of phytohormones in microalgal biofactories.

Optimization of nutrient composition for enhanced microalgal biomass and macromolecules using RSM: An integrated approach towards improving microalgal biodiesel feasibility

Optimization of nutrient composition for enhanced microalgal biomass and macromolecules using RSM: An integrated approach towards improving microalgal biodiesel feasibility

ITRAQ-based proteome profiling revealed the carbon metabolism regulation for mariculture wastewater treatment with Bacterial-Algal Coupling Technology

Acidogenic fermentation coupled with microalgae cultivation is efficient for mariculture wastewater (MW) treatment and energy recovery, but there is limited information regarding carbon metabolic networks as a response to varied broth composition at the proteome level. In this study, ethanol-type, propionate-type, and butyrate-type fermentation effluent of MW were applied to microalgae cultivation. The carbon source composition of different types of acidogenic fermentation was optimized to enhance microalgal biomass production and nutrients removal. Compared with ethanol-type fermentation effluent, higher efficiency in biomass accumulation and ammonia assimilation of Chlorella pyrenoidosa was observed in propionate-type and butyrate-type. Lipid accumulation in microalgae was enhanced with ethanol-type fermentation effluent, and the maximum lipid content reached 513.3 and 546.7 mg/L at an inorganic carbon/organic carbon (IC/OC) ratio of 3:1 and 2:1, respectively. The increasing ratio of IC/OC improved the expression of key enzymes related to the photosynthetic system, which had a positive effect on carbohydrate production and microalgal growth. The upregulation of magnesium chelatase with bicarbonate supply was revealed by iTRAQ analysis, thereby promoting chlorophyll production in microalgal cells. In response to an increasing proportion of IC, more energy and precursor substances for lipid production were generated with the enhancing expression of glycolysis and pyruvate metabolism.

Heterologous mannitol-1-phosphate dehydrogenase gene over-expression in Parachlorella kessleri for enhanced microalgal biomass productivity

BackgroundMicroalgae have tremendous potential in CO2 sequestration, bioenergy, biofuels, wastewater treatment, and high-value metabolites production. However, large-scale production of microalgae is hampered due to photo-inhibition in outdoor cultivation. Mannitol, as an osmolyte, is known to relieve the stress produced under different abiotic stress conditions during the growth of a photosynthetic organism. ResultsIn the present study, Mannitol-1-phosphate 5-dehydrogenase (Mt1D) was over-expressed to study the effect of mannitol over-production in Parachlorella kessleri under high-light induced stress. Over-expression of Mt1D led to 65% increased mannitol content in the transformed P. kessleri compared to that of wild type. Mannitol transformant demonstrated > 20-fold reduction in reactive oxygen species generation and 15% higher biomass productivity when grown in outdoor cultivation with high-light irradiance of 1200 μmol photons m−2 s−1. ConclusionsThe current study establishes that a higher mannitol concentration provides stress shielding and leads to better acclimatization of transgenic microalgae against high-light generated stress. It also led to reduced ROS generation and improved growth of microalga under study. Thus, overexpression of the Mt1D gene in microalgae can be a suitable strategy to combat high-light stress.

Glucose-assisted trophic conversion of Chlamydomonas reinhardtii by expression of glucose transporter GLUT1

The use of genetic engineering techniques to alter the nutritional patterns of microalgae is a key means of enhancing microalgal biomass, as it enables the highly efficient heterotrophic growth of microalgae via the utilisation of organic carbon sources, especially glucose. To investigate the effects of the expression of the glucose transporter on the growth of the model alga, Chlamydomonas reinhardtii, we transformed C. reinhardtii using the human GLUT1 gene, regulated by the Hsp70, PsaD, and Arg7 promoters, and obtained engineered algae after screening. The engineered algae showed better growth than the control algae under both heterotrophic and mixotrophic growth conditions. The engineered alga in which the GLUT1 gene was regulated by the Arg7 promoter exhibited the best growth. Although the engineered algae exhibited heterotrophic growth in complete darkness by using glucose as the carbon source, their growth rates and biomass were relatively low compared to those of the control. Analysis of the glucose transport ability of the engineered algae revealed that glucose was successfully transported to the cytoplasm via the glucose transporters, but was unable to enter the chloroplasts, which could explain the slow heterotrophic growth of the engineered algae.

Influence of Symbiotic Probiont Strains on the Growth of Amphora and Chlorella and Its Potential Protections Against Vibrio spp. in Artemia.

The emerging aquaculture industry is in need of non-antibiotic-based disease control approaches to minimize the risk of antibiotic-resistant bacteria. Bacterial infections mainly caused by Vibrio spp. have caused mass mortalities of fish especially during the larval stages. The objectives of this study were to verify the potential of symbiotic probiont strains, isolated from microalgae (Amphora, Chlorella, and Spirulina) for suppressing the growth of Vibrio spp. and at the same time ascertain their abilities to enhance microalgal biomass by mutualistic interactions through microalgae-bacteria symbiosis. In addition, in vivo studies on Artemia bioencapsulated with probiont strains (single strain and mix strains) and microalgae were evaluated. The selected potential probionts were identified as Lysinibacillus fusiformis strain A-1 (LFA-1), Bacillus sp. strain A-2 (BA-2), Lysinibacillus fusiformis strain Cl-3 (LFCl-3), and Bacillus pocheonensis strain S-2 (BPS-2) using 16s rRNA. The cell densities of Amphora culture supplemented with BA-2 and Chlorella culture supplemented with LFCl-3 were higher than those of the controls. Artemia bioencapsulated with mix strains (LFA-1 + BA-2 + LFCl-3 + BPS-2) and Amphora demonstrated the highest survival rate compared to the controls, after being challenged with V. harveyi (60 ± 4%) and V. parahaemolyticus (78 ± 2%). Our study postulated that BA-2 and LFCl-3 were found to be good promoting bacteria for microalgal growth and microalgae serve as a vector to transport probiotic into Artemia. Moreover, mixture of potential probionts is beneficial for Artemia supplementation in conferring protection to Artemia nauplii against pathogenic Vibrios.

Trophic Transition Enhanced Biomass and Lipid Production of the Unicellular Green Alga Scenedesmus acuminatus.

Microalgal heterotrophic cultivation is an emerging technology that can enable producing high cell-density algal cell cultures, which can be coupled with photoautotrophic cultivation for valuable chemicals such as lipids manufacturing. However, how the heterotrophically grown algal cells respond to the lipid-inducing conditions has not been fully elucidated so far. In this study, when the heterotrophically grown Scenedesmus acuminatus cells were subjected to the high light (HL) and nitrogen-limited (NL) conditions, both the biomass and lipid productivity were enhanced as compared to that of the photoautotrophically grown counterparts. The chlorophyll a fluorometry analysis showed that the Fv/Fm and Y(II) of the heterotrophically grown cells subjected to the HL and NL conditions was recovered to the maximum value of 0.75 and 0.43, respectively, much higher than those of the photoautotrophically grown cells under the same stress conditions. Transcriptomic analysis revealed that heterotrophically grown cells fully expressed the genes coding for the photosystems proteins, including the key photoprotective proteins D1, PsbS, light-harvesting-complex (LHC) I and LHC II. Meanwhile, downregulation of the carotenoid biosynthesis and upregulation of the glycolysis/gluconeogenesis, tricarboxylic acid (TCA) cycle and oxidative phosphorylation pathways were observed when the heterotrophically grown cells were subjected to the HL and N-limited conditions for lipid production. It was deduced that regulation of these pathways not only enhanced the light utilization but also provided the reducing power and ATP by which the biomass accumulation was significantly elevated. Besides, upregulation of the acetyl-CoA carboxylase/biotin carboxylase, digalactosyl diacylglycerol synthase and diacylglycerol acyltransferase 2 encoding genes may be attributable to the enhanced lipid production. Understanding the cellular responses during the trophic transition process could guide improvement of the strength of trophic transition enhancing microalgal biomass and lipid production.

Exploration of applying growth-promotion bacteria of Chlorella sorokiniana to open cultivation systems.

Nowadays, artificial construction of bacteria-algae consortia to enhance microalgal biomass is prevalent in enclosed systems, while few are built in an open culture. In this study, Achromobacter sp. and Rhizobium sp., isolated from an open pond of Chlorella sorokiniana, were the microalgal growth-promotion bacteria and selected to build the bacteria-algae consortia with axenic C. sorokiniana in open cultivation systems. To examine the performance of these two artificial bacteria-algae consortia in open culture under stable cultivation conditions, the co-cultivation experiments were conducted under constant temperature and light intensity indoors. It was found that Achromobacter sp. gradually lost the dominance of the population in the co-culture and failed to promote the growth of C. sorokiniana during open cultivation. However, the Rhizobium sp. maintained its dominant population of bacterial community in open culture and could promote the growth of C. sorokiniana, with an enhancement of 13.76%. To further evaluate the effects of Rhizobium sp. on microalgae under variations of temperature and sunlight intensity conditions, the open co-cultivation experiments were built outdoors. Results showed that the growth of C. sorokiniana could rise 13.29% only when Rhizobium sp. was added to the culture continuously, and addition of bacterial solution in log-phase of microalgae could help Rhizobium sp. dominate in the bacterial community. In this way, addition of Rhizobium sp. in the log-phase of C. sorokiniana should be an effective process to be applied to open ponds cultivation. Our findings are a step toward applying growth-promotion bacteria for C. sorokiniana for applications in open cultivation systems.

Identification and Biotechnical Potential of a Gcn5-Related N-Acetyltransferase Gene in Enhancing Microalgal Biomass and Starch Production.

Microalgae are promising feedstocks for starch production, which are precursors for bioenergy and chemicals manufacturing. Though starch biosynthesis has been intensively studied in the green alga Chlamydomonas reinhardtii, regulatory mechanisms governing starch metabolism in this model species have remained largely unknown to date. We proposed that altering triacylglycerol (TAG) biosynthesis may trigger intrinsic regulatory pathways governing starch metabolism. In accordance with the hypothesis, it was observed in this study that overexpression of the plastidial lysophosphatidic acid acyltransferase gene (i.e. LPAAT1) in C. reinhardtii significantly enhanced TAG biosynthesis under nitrogen (N)-replete conditions, whereas the starch biosynthesis was enhanced in turn under N depletion. By the exploitation of transcriptomics analysis, a putative regulatory gene coding Gcn5-related N-acetyltransferase (GNAT19) was identified, which was up-regulated by 11–12 times in the CrLPAAT1 OE lines. Overexpression of the cloned full-length CrGNAT19 cDNA led to significant increase in the starch content of C. reinhardtii cells grown under both N-replete and N-depleted conditions, which was up to 4 times and 26.7% higher than that of the empty vector control, respectively. Moreover, the biomass yield of the CrGNAT19 OE lines reached 1.5 g L-1 after 2 days under N-depleted conditions, 72% higher than that of the empty vector control (0.87 g L-1). Overall, the yield of starch increased by 118.5% in CrGNAT19 OE lines compared to that of the control. This study revealed the great biotechnical potentials of an unprecedented GNAT19 gene in enhancing microalgal starch and biomass production.

Enhancing microalgal biomass productivity with an optimized flow field generated by double paddlewheels in a flat plate photoreactor with CO2 aeration based on numerical simulation

Computational fluid dynamics were used to analyze the flash light effect and CO2 bubble behavior in an optimized flow field generated by double paddlewheels in a flat plate photoreactor to enhance microalgal biomass productivity. The increased D/w ratio significantly enhanced the average turbulent kinetic energy and flash cycle frequency. However, the effects became weak when the D/w ratio was over 0.67. Appliance of double paddlewheels increased flash cycle frequency from 0.035 to 0.121 Hz and increased light time ratio from 8.3% to 31.5%. Meanwhile, the bubble dynamic behavior was characterized using population balance model. The average bubble size reduced by 24.4% and the bubble rising velocity reduced by 10.6%, which facilitated CO2 mixing and mass transfer in microalgal solution. Therefore, biomass accumulation of microalgae Chlorella in the photoreactor with double paddlewheels increased by 62.3% under 15% CO2.

Sustainable and stepwise waste-based utilisation strategy for the production of biomass and biofuels by engineered microalgae

Waste streams have emerged as potential feedstocks for biofuel production via microbial bioconversion. Metabolic engineering of the microalga Phaeodactylum tricornutum in its lipid biosynthetic pathways has been conducted with an aim to improve lipid production. However, there has been only limited achievement in satisfying biofuel demands by utilising extracellular organic carbons from low-cost waste streams. Herein, we present a successive staged cultivation mode, based on a previously engineered strain that co-overexpresses two key triacylglycerol biosynthesis genes. We first optimised microalgal biomass and lipid production by using food waste hydrolysate and crude glycerol as the cultivation media. Food waste hydrolysate (5% v/v) is a low-cost organic carbon source for enhanced microalgal biomass production, and the resulting lipid concentration was 1.08-fold higher with food-waste hydrolysate than that of the defined medium. Additionally, the resultant lipid concentration after using crude glycerol (100 mM) was 1.24-fold higher than that using the defined medium. Two carbon feeding modes (hybrid and sequential) were also performed to investigate the potential of engineered P. tricornutum with preliminary mechanistic analyses. The biodiesel properties of lipids produced in the hybrid mode were evaluated for potential application prospects. Collectively, this study demonstrates a waste stream utilisation strategy for efficient and sustainable microalgal biofuel production.

Low concentration of zeolite to enhance microalgal growth and ammonium removal efficiency in a membrane photobioreactor

ABSTRACT The aim of this work was to study the growth and nutrient removal efficiency of a mixed microalgal culture with and without the addition of low concentrations (0.5, 1, and 5 g L-1 of total liquid volume in the reactor) of natural zeolite. A control test in which only zeolite was added into a similar membrane photobioreactor was also conducted. The addition of 0.5 g L−1 zeolite to a continuously-fed membrane photobioreactor increased the microalgal biomass concentration from 0.50 to 0.90–1.17 g particulate organic carbon per L while the average ammonium removal efficiency increased from 14% to 30%. Upon microscopic inspection, microalgal cells were observed growing on the surface of zeolite particles, which indicates that zeolite can support attached microalgal growth. With higher zeolite doses (1 and 5 g L−1) inside the reactor, however, the breaking apart of added zeolite particles into finer particles dramatically increased solution turbidity, which likely was not beneficial for microalgal growth and ammonium removal due to reduced light penetration. This work shows that low doses of zeolite can be used as microcarriers to enhance microalgal biomass concentration and ammonium removal efficiency, while minimizing zeolite dose would likely reduce the turbidity effects.