Biomass Lipid Content Research Articles

Nutrients recovery from dairy wastewater by Chlorella vulgaris and comparison of the lipid's composition with various chlorella strains for biodiesel production.

Microalgae biomass is regarded as a promising feedstock for biodiesel production. The biomass lipid content and fatty acids composition are among the main selective criteria when screening microalgae strains for biodiesel production. In this study, three strains of Chlorella microalgae (C. kessleri, C. sorokiniana, C. vulgaris) were cultivated nutrient media with different nitrogen contents, and on a medium with the addition of dairy wastewater. Moreover, microalgae grown on dairy wastewater allowed the removal of azote and phosphorous. The removal efficiency of 90%, 53% and 95% of ammonium nitrogen, total nitrogen and phosphate ions, respectively, were reached. The efficiency of wastewater treatment from inorganic carbon was 55%, while the maximum growth of biomass was achieved. All four samples of microalgae had a similar fatty acid profile. Palmitic acid (C16:0) was the most abundant saturated fatty acid (SFA), and is suitable for the production of biodiesel. The main unsaturated fatty acids (UFA) present in the samples were oleic acid (C18:1 n9); linoleic acid (C18:2 n6) and alpha-linolenic acid (C18:3 n3), which belong to omega-9, omega-6, omega-3, respectively.

Efficient Production of Microalgal Biomass—Step by Step to Industrial Scale

The production of microalgal biomass on a commercial scale remains a significant challenge. Despite the positive results obtained in the laboratory, there are difficulties in obtaining similar results in industrial photobioreactors. Changing the cultivation conditions can affect not only the growth of microalgae but also their metabolism. This is of particular importance for the use of biomass for bioenergy production, including biofuel production. The aim of this study was to determine the biomass production efficiency of selected microalgal strains, depending on the capacity of the photobioreactor. The lipid and ash content of the biomass were also taken into account. It was found that as the scale of production increased, the amount of biomass decreased, irrespective of the type of strain. The change in scale also affected the lipid content of the biomass. The highest values were found in 2.5 L photobioreactors (ranging from 26.3 ± 2.2% for Monoraphidium to 13.9 ± 0.3% for Chlorella vulgaris). The least favourable conditions were found with industrial photobioreactors, where the lipid content of the microalgal biomass ranged from 7.1 ± 0.6% for Oocycstis submarina to 10.2 ± 1.2% for Chlorella fusca. The increase in photobioreactor capacity had a negative effect on the ash content.

Moringa oleifera seed extract-mediated flocculation as an efficient method for harvesting Chlorella lewinii biomass

The aim of this research was to investigate the potentials of harvesting Chlorella lewinii through flocculation by Moringa oleifera seed extract. Water, ethanol, and sodium chloride solution were used to extract flocculating agents from both whole and de-fatted Moringa oleifera seeds and their ability to flocculate C. lewinii cells were evaluated. The effects of extracting solvents, extract concentration, incubation period and culture age on flocculation efficiency were investigated. The lipid contents of the biomass harvested by flocculation using M. oleifera seed extract were compared with those harvested by centrifugation. The results showed that 1M sodium chloride solution was the most effective solvent for extracting M. oleifera active ingredient. The optimum extract concentration was 600±0.10 mg/L with approximately 60±0.46 % efficiency, while the optimum length of period for incubating a mixture of cell culture and seed extract was 80±0.26 min. Defatted Moringa oleifera seed extract was more efficient than whole seed extract with an efficiency of 50%. The percentage lipid content of biomass harvested by centrifuge and moringa extracts decreased in the following order: Centrifugation-(22.55%) > de-fatted seed extract (16.63%) > whole seed extract (14.42%). These results indicate that M. oleifera seed extract is a reliable method of harvesting microalgae biomass.

Revealing the role of phosphorus supply on the phosphorus distribution and lipid production in Scenedesmus obliquus UTEX 393 during nitrogen starvation

Microalgal-based processes offer promise for addressing two sustainability challenges: recovering phosphorus (P) from wastewater and producing biofuel feedstock. This study investigated the role of phosphorus supply on microalgal growth, lipid yield, and P distribution for Scenedesmus during nitrogen starvation. Extracellular polymeric substances and intracellular polymeric substances were the most important pools for inorganic phosphorus (IP) and organic phosphorus (OP), respectively. The main P pool for microalgae with low phosphorus supply was EPS, which accounted for 57 % of the total biomass phosphorus; while under high P concentrations, 79 % of the phosphorus was stored in IPS. A high concentration of orthophosphate stimulated rapid P uptake as IP and promoted the transformation of IP to OP associating with biomass synthesis. The highest P content of microalgal biomass was 6.5 % of dry weight when the phosphorus concentration in medium was 113 mg/L, and the OP content was 4.9 % of dry weight. High phosphate-P enhanced the biomass's lipid content by 60 %, and the distribution of fatty acid methyl esters was not altered by P concentrations. Collectively, high phosphate-P availability could promote microalgal biomass synthesis, lipid production and P accumulation.

Validated Growth Rate-Dependent Regulation of Lipid Metabolism in Yarrowia lipolytica.

Given the strong potential of Yarrowia lipolytica to produce lipids for use as renewable fuels and oleochemicals, it is important to gain in-depth understanding of the molecular mechanism underlying its lipid accumulation. As cellular growth rate affects biomass lipid content, we performed a comparative proteomic analysis of Y. lipolytica grown in nitrogen-limited chemostat cultures at different dilution rates. After confirming the correlation between growth rate and lipid accumulation, we were able to identify various cellular functions and biological mechanisms involved in oleaginousness. Inspection of significantly up- and downregulated proteins revealed nonintuitive processes associated with lipid accumulation in this yeast. This included proteins related to endoplasmic reticulum (ER) stress, ER–plasma membrane tether proteins, and arginase. Genetic engineering of selected targets validated that some genes indeed affected lipid accumulation. They were able to increase lipid content and were complementary to other genetic engineering strategies to optimize lipid yield.

Biodiesel production potential of an indigenous South African microalga, Acutodesmus bajacalifornicus

In this study, a South African indigenous microalga Acutodesmus bajacalifornicus was evaluated in different cultivation media. Eleven potential cultivation media were identified and tested on A. bajacalifornicus, a potential source for biodiesel production. A. bajacalifornicus had the highest growth rate in the JG medium (in-house formulation), with a competitive average specific growth rate of 0.47 d−1. The highest biomass productivity was in the Hase medium, but with relatively low productivity of 53.1 mg.L−1.d−1.Analysis of the biomass lipid content and profile of each cell culture, using fatty acid methyl ester (FAME) gas chromatography (GC) showed that the lipid content varied between cultivation media, with minimum lipid content of 20% (w/w) and an average close to 47% (w/w). Utilising biodiesel property predictive formulas, and the lipid profiles obtained in this study, it was possible to predict the properties of biodiesel that could be generated from A. bajacalifornicus. It was found that biomass from eight of the media adhered to South African summer grade biodiesel standards.As such, A. bajacalifornicus is a potential candidate for microalgal biodiesel production in South Africa. However, the bioenergy yield rate would need to be improved to have a similar attractiveness to other studies.

Machine learning aided bio-oil production with high energy recovery and low nitrogen content from hydrothermal liquefaction of biomass with experiment verification

Hydrothermal liquefaction (HTL) of biomass with high moisture (e.g., algae, sludge, manure, and food waste) is a promising and sustainable approach to produce renewable energy (bio-oil) and protect the environment. However, the production of bio-oil with high yield and preferable properties such as low nitrogen content (N_oil) is time/labor-consuming using the traditional HTL experimental method. To this context, machine learning (ML) algorithms were employed to aid the bio-oil production with the consideration of related factors in HTL, including biochemical and elemental compositions of biomass, process parameters, and solvents. Results showed that the random forest (RF) algorithm was the best one (average R2 = 0.80) for the multi-task prediction of bio-oil yield (Yield_oil), N_oil, and energy recovery (ER_oil), hence employed for post feature interpretation and optimization. Feature importance indicates that both Yield_oil and ER_oil follow the trend of lipid content in biomass > temperature > retention time, while N_oil follows the trend of N content in biomass > temperature > retention time. Then ML-based optimization was conducted to guide the experimental research to produce bio-oil with high yield and low N content. The HTL experiment verification based on the optimal solutions from the ML-based Particle Swarm Optimization achieved the maximum Yield_oil (54.30%) and minimal N_oil (2.60%) from model biomass (composed of protein content 28%, lipid 48%, and carbohydrates 21%) at 300 °C and 30 min. The experiment verification was successful as the results were comparable to the modeling results, with errors of less than 7% for Yield_oil and ER_oil, and 23% for N_oil, and the N_oil of the experiment N_oil (2.60%) was interestingly lower than the modeled one (3.37%). This work provides new insight and strategy to accelerate the engineered HTL for desired bio-oil production.

Economic perspective of ethanol and biodiesel coproduction from industrial hemp

In this study, the economics of producing biofuels from an industrial hemp (Cannabis sativa) genotype – 19m96136 was investigated. A lignocellulosic biofuel plant, hourly consuming 85 metric tons of hemp biomass was modeled in SuperPro Designer®. The integrated bioenergy plant produced hemp biodiesel and bioethanol from lipids and carbohydrates, respectively. The structural composition of the industrial hemp plant was analyzed in a previous study. The data obtained was used to simulate feedstock composition in SuperPro Designer®.The simulation results indicated that Hemp containing 2% lipids can yield up to 3.95 million gallons of biodiesel annually. On improving biomass lipid content to 5 and 10%, biodiesel production increased to 9.88 and 19.91 million gallons, respectively. The breakeven unit production cost of hemp biodiesel with 2, 5, and 10% lipid containing hemp was $18.49, $7.87, and $4.13/gallon, respectively. The biodiesel unit production cost when utilizing 10% lipid-containing hemp was comparable to soybean biodiesel at $4.13/gallon. Furthermore, sensitivity analysis revealed the possibility of a 7.80% reduction in unit production cost upon a 10% reduction in hemp feedstock cost. Furthermore, industrial hemp was capable of producing between 307.80 and 325.82 gallons of total biofuels per hectare of agricultural land than soybean.

Sustainable Production of Monoraphidium Microalgae Biomass as a Source of Bioenergy

Microalgae are a renewable source of unconventional biomass with potential application in the production of various biofuels. The production of carbon-neutral fuels is necessary for protecting the environment. This work determined the possibility of producing biomass of microalgae belonging to Monoraphidium genus using saline wastewater resulting from proecological salmon farming in the recirculating aquaculture system. The tests were carried out in tubular photobioreactors using LED light. As a part of the analyses, the growth and productivity of microalgal biomass, cell density in culture, and lipid concentration and ash content in biomass were determined. In addition, the concentration of selected phosphorus and nitrogen forms present in wastewater corresponding to the degree of their use by microalgae as a nutrient substrate was determined. The biomass concentration estimated in the tests was 3.79 g·L−1, while the maximum biomass productivity was 0.46 g·L−1·d−1. The cells’ optical density in culture measured at 680 nm was 0.648. The lipid content in biomass was 18.53% (dry basis), and the ash content was 32.34%. It was found that microalgae of the genus Monoraphidium effectively used the nitrogen as well as phosphorus forms present in the wastewater for their growth. The total nitrogen content in the sewage decreased by 82.62%, and total phosphorus content by over 99%. The analysis of the individual forms of nitrogen showed that N-NO3 was reduced by 85.37% and N-NO2 by 78.43%, while orthophosphate (V) dissolved in water was reduced by 99%. However, the content of N-NH4 in wastewater from the beginning till the end of the experiment remained <0.05 mg·L−1.

Inulin as a Promising Alternative Feedstock for Docosahexaenoic Acid Production by Schizochytrium sp. ATCC 20888

AbstractSchizochytrium sp. is considered as a promising alternative commercial source of docosahexaenoic acid (DHA), but the production is hindered by the high feedstock cost. In this study, inulin is used as a cheap and readily available feedstock for Schizochytrium sp. ATCC 20888 to produce DHA. The strain could not utilize inulin directly and therefore inulin first needed to be hydrolyzed. Compared with the acidic hydrolyzate by HCl and hydrolyzate by endo‐inulinase, the hydrolyzate by exo‐inulinase serves as the most effective carbon source for microalgal growth. Hydrolysis of inulin by exo‐inulinase is further optimized, and up to 97.8% of inulin conversion is obtained under the optimal conditions of 40 °C, pH 7.0, substrate concentration of 80 g L−1 and exo‐inulinase loading of 2 g kg−1 substrate for 12 h. The resulting hydrolyzate containing mainly fructose is used for the DHA production by the microalga. The lipid content in biomass, DHA content in total fatty acids, DHA yield, and DHA productivity at 72 h reach 45.26%, 35.59%, 5.64 g L−1 and 1.88 g L−1 d−1, respectively. The results suggest that inulin is an excellent feedstock for Schizochytrium sp. suitable for commercial DHA production.Practical Applications: DHA is an essential nutrient for human health and is widely used in infant formula and functional food. As a reserve carbohydrate, inulin present in plants represents a cheap, abundant, and readily available bioresource. This study describes the suitability of inulin as a promising alternative to glucose for DHA production by Schizochytrium sp. Hence, a practical bioprocess for commercial DHA production from inulin by Schizochytrium sp. could be developed. As far as it is known, this is the first report of inulin as a feedstock for Schizochytrium sp. to produce DHA.

Isolation of a freshwater microalgae and its application for the treatment of wastewater and obtaining fatty acids from tilapia cultivation.

In the present study, isolated strains of the microalgae Chlamydomonas sp. (CH) and Chlorella vulgaris (CV) were used to treat aquaculture wastewater and to obtain fatty acids and from a fattening culture of tilapia. The microalgae were cultivated for 11days in tubular photobioreactors with an operating volume of 2L, constant aeration and illumination. High removal rates of NO3- and PO43- were achieved for both Chlamydomonas sp. (84.7% and 96%, respectively) and Chlorella vulgaris (94.6 and 97.9%, respectively). The maximum biomass productivity achieved by Chlamydomonas sp. was 0.06 and 0.10 gL-1d-1 for Chlorella vulgaris. Therefore, tilapia wastewater contained the necessary nutrient concentration for algal growth and development. Chlamydomonas sp. biomass lipid content was 69%, while that of Chlorella vulgaris was 40%. The lipid profile of both microalgae was abundant in palmitic acid (78% for Chlamydomonas sp. and 35% for Chlorella vulgaris). This fatty acid is suitable for biodiesel production. Tilapia wastewater is low-cost alternative culture medium as it contains the necessary nutrient concentration for microalgae development and growth.

The effect of diverse nitrogen sources in the nutrient medium on the growth of the green microalgae Chromochloris zofingiensis in the batch culture

The effect of three nitrogen (N) sources in the nutrient medium – sodium nitrate (NaNO3), urea (CO(NH2)2), and ammonium chloride (NH4Cl) – on the morphological and physiological characteristics of the green microalga Chromochloris (Chlorella) zofingiensis, a potential commercial producer of lipids and a ketocarotenoid astaxanthin, was studied. The alga was batch-cultivated in glass conical flasks from starting cell density (n) around 2.3·106 per mL and dry weight (DW) content of 0.06 g·L−1 in all variants at 120 μmol·m−2·s−1 PAR, +20…+21 °C, and air bubbling at a rate of 0.3 L·min−1·L−1. The concentration of nitrogen sources (as elemental N) in the modified BBM nutrient medium was 8.83 mmol·L−1, the cultivation duration was 17 days. The dynamics of n and cell volumes, DW content, chlorophylls a and b (Chla and Chlb), total carotenoids (Car), and lipids (Lip) in the cultures, concentration of N sources in the nutrient medium, and its pH were recorded. It was shown that the growth rate, size distribution of the cell populations, and the biomass chemical composition depended significantly on the nitrogen source in the nutrient medium. Using NH4Cl as N source caused on the second day growth inhibition, cell swelling, aggregation, and discoloration; by the seventh day, it caused culture crash. C. zofingiensis cells took up NaNO3 and CO(NH2)2 from the medium at a similar rate (0.626 and 0.631 mmol N·L−1·day−1, respectively), but the growth of the culture fed with CO(NH2)2 lagged; its cell volume and Chla, Chlb, and total Car contents declined profoundly. The average dry matter productivity (PDW) in the culture grown on CO(NH2)2 [(0.086 ± 0.004) g·L−1·day−1] was 32.6 % lower than in the culture grown on NaNO3 [(0.114 ± 0.005) g·L−1·day−1]. At the same time, lipid productivity (PLip) of the urea-fed culture was comparable with that of the nitrate-fed culture (PLip of 28 and 26 mg·L−1·day−1, respectively). The lipid DW percentage of the former exceeded significantly that of the nitrate-fed culture (31.6 % vs 23.1 %, respectively). From the standpoint of profitability, the lag in biomass accumulation recorded in the urea-fed culture on PDW is not critical since it is compensated by lowering the cost of nitrogen source for the nutrient medium (approximately by 230 %) and a higher biomass lipid content. C. zofingiensis grown in media with urea as the only N source deserves further investigation.

Lipid production by the yeast Lipomyces starkeyi grown on sugars and oil palm empty fruit bunch hydrolysate

Lipid accumulation by the yeast Lipomyces starkeyi grown on various carbon (C) sources (glucose, xylose, hydrolysate of oil palm empty fruit bunch (OPEFB)) is reported. In media with glucose as the main C-source, a glucose concentration of 60–80 g L−1 was optimal for producing microbial biomass and lipids. Glucose at 60 g L−1 afforded a final dry biomass concentration of 21.2 g L−1 with a 35.8% lipid content. The biomass concentration was reduced to 18.7 g L−1 if the glucose was 80 g L−1 and the lipids were reduced to 11.8%. With pure xylose (80 g L−1), the final biomass concentration was 14.0 g L−1 and the lipid content of the biomass was 42.1%. A 4:1 by mass mixture of glucose and xylose was used to simulate a typical hydrolysate of OPEFB. With this mixture (glucose = 64 g L−1, xylose = 16 g L−1), the maximum biomass concentration was 17.9 g L−1 and the lipids in the biomass exceeded 37.9%. A hydrolysate of OPEFB was prepared by enzymatic hydrolysis of the alkali-pretreated OPEFB. With this hydrolysate as the main C-source, the final yeast biomass concentration was 14.9 g L−1, but the lipid content in the biomass was only 6%. The lipid content of the yeast biomass could be raised to >40% by using a hydrolysate diluted with distilled water. Apparently, dilution alleviated the effects of inhibitory compounds that formed during hydrolysis of lignocellulosic biomass with the commercial enzymes. The lipid yield on C-sources was 0.162 g g−1 in a medium with a C:N mole ratio of 71.7:1.

Identification of microalgae from waste stabilization ponds and evaluation of electroflotation by alternate current for simultaneous biomass separation and cell disruption

ABSTRACT This work aimed to investigate algal diversity at the genus level in stabilization pond systems treating domestic wastewater and to evaluate the feasibility of an electroflotation by alternate current (EFAC) system for simultaneous microalgae separation and cell disruption. Evaluation of algal diversity showed that the genera Euglena and Chlorella were present in relatively high frequencies in five of the six effluents analyzed. The use of EFAC on an effluent that presented bloom of Chlorella achieved turbidity and chlorophyll-a removal efficiencies higher than 70 and 90%, respectively, after 70 minutes of operation. Total lipid yield for the Chlorella-rich biomass was 21.4±2.02%. Such high biomass lipid content demonstrates the potential for obtaining lipid-based biofuels from wastes. The current paper describes the first attempt, with promising results, at using electroflotation by alternate current for low cost, simultaneous microalgae harvesting and disruption.

Bioenergy from wastewater resources: Nutrient removal, productivity and settleability of indigenous algal-bacteria polyculture, and effect of biomass composition variability on methane production kinetics and anaerobic digestion energy balance

Algal-bacteria high-rate ponds represent an energy-efficient wastewater treatment approach and a source for affordable and sustainable biomass feedstock for production of renewable energy through anaerobic digestion (AD). However, there is still a need for more data on wastewater treatment efficiency, biomass productivity and settleability from outdoor treatment facilities, as well as on impact of variability in biomass composition and digestibility on methane yield and energy output. Hydraulic retention time (HRT) and wastewater quality fed into 30 m2 raceway ponds had a major effect on algal-bacteria polyculture productivity, settleability, phylogenetic and biochemical compositions, digestibility and methane yield. While Micractinium, Scenedesmus, Chlorella, and pennate diatoms were always among the key species observed, the gross productivity and 2-hour settleability during summer cultivation varied in the first-stage ponds treating primary wastewater from 29 ± 5 to 54 ± 12 gAFDW/m2/d and from 88 ± 8 to 94 ± 4% for HRT of 3 and 2 days, respectively. For these conditions, the effluent had csBOD of 3.4 or 3.3 mg/L and Ntotal (mostly NO3−-N) of 9.2 or 8.2 mg/L, respectively. The second-stage algal ponds (HRT 3 days) showed lower productivity of 16 ± 6 gAFDW/m2/d, settleability of 84 ± 11%, and effluent csBOD 3.7 mg/L and Ntotal 0.8 mg/L. Biomass composition from different ponds was 34–38% protein, 18–28% total lipids and 6–14% FAME. The methane yield varied about 30% with largest value of 0.34 ± 0.01 L/gVS and showed a positive correlation with biomass lipid content (R2 = 0.93). First-order and pseudo-parallel first-order rate kinetic models exhibited a better fit for methane production (most R2 > 0.993) than the modified Gompertz model. The variation in biomass composition led to significant differences in energy output (varied by about 60%), Net Energy Ratios (ranged from 1.6 to 2.2) and Net Energy Efficiency (from 60% to 70%) when projecting the energy balance for a large-scale continuous AD process with an optimal HRT of 20–30 days.

Carbon biofixation and lipid composition of an acidophilic microalga cultivated on treated wastewater supplied with different CO2 levels

ABSTRACTThis study evaluated productivity, CO2 biofixation, and lipid content in biomass of the acidophilic microalga Chlamydomonas acidophila LAFIC-004 cultivated with five different carbon dioxide concentrations. The influence of carbon dioxide concentration on nutrient removal and pH was also investigated. Treated wastewater (secondary effluent) was used as culture medium. Five experimental setups were tested: T-0% – injection of atmospheric air (0.038% CO2), T-5% (5% CO2), T-10% (10% CO2), T-15% (15% CO2) and T-20% (20% CO2). The T-5% and T-10% experiments showed the highest values of productivity and CO2 biofixation, and maximum biomass dry weight was 0.48 ± 0.02 and 0.51 ± 0.03 g L−1, respectively. This acidophilic microalga proved to be suitable for carbon biofixation and removal of nutrients from secondary effluent of wastewater treatment plants with high CO2 concentration. All assays were performed without pH control. This microalga species presented high lipid content. However, fatty acid methyl esters (FAME) are not suitable for biodiesel use.

Assessment of the scalability of a microtiter plate system for screening of oleaginous microorganisms

Recent developments in molecular biology and metabolic engineering have resulted in a large increase in the number of strains that need to be tested, positioning high-throughput screening of microorganisms as an important step in bioprocess development. Scalability is crucial for performing reliable screening of microorganisms. Most of the scalability studies from microplate screening systems to controlled stirred-tank bioreactors have been performed so far with unicellular microorganisms. We have compared cultivation of industrially relevant oleaginous filamentous fungi and microalga in a Duetz-microtiter plate system to benchtop and pre-pilot bioreactors. Maximal glucose consumption rate, biomass concentration, lipid content of the biomass, biomass, and lipid yield values showed good scalability for Mucor circinelloides (less than 20% differences) and Mortierella alpina (less than 30% differences) filamentous fungi. Maximal glucose consumption and biomass production rates were identical for Crypthecodinium cohnii in microtiter plate and benchtop bioreactor. Most likely due to shear stress sensitivity of this microalga in stirred bioreactor, biomass concentration and lipid content of biomass were significantly higher in the microtiter plate system than in the benchtop bioreactor. Still, fermentation results obtained in the Duetz-microtiter plate system for Crypthecodinium cohnii are encouraging compared to what has been reported in literature. Good reproducibility (coefficient of variation less than 15% for biomass growth, glucose consumption, lipid content, and pH) were achieved in the Duetz-microtiter plate system for Mucor circinelloides and Crypthecodinium cohnii. Mortierella alpina cultivation reproducibility might be improved with inoculation optimization. In conclusion, we have presented suitability of the Duetz-microtiter plate system for the reproducible, scalable, and cost-efficient high-throughput screening of oleaginous microorganisms.

Techno-economic evaluation of simultaneous production of extra-cellular polymeric substance (EPS) and lipids by Cloacibacterium normanense NK6 using crude glycerol and sludge as substrate.

This study used the technical, economic analysis tool, SuperPro designer in evaluating a novel technology for simultaneous production of extracellular polymeric substance (EPS) and biodiesel using crude glycerol and secondary sludge. As renewable energy sources are depleting, the process utilizes municipal sewage sludge for production of EPS and biodiesel along with crude glycerol, which is a waste byproduct of biodiesel industry providing an alternate way for disposal of municipal sludge and crude glycerol. Newly isolated Cloacibacterium normanense NK6 is used as micro-organism in the study as it is capable of producing high EPS concentration, using activated sludge and crude glycerol as the sole carbon source. The technology has many environmental and economic advantages like the simultaneous production of two major products: EPS and lipids. Sensitivity analysis of the process revealed that biomass lipid content is a most significant factor where unit cost production of biodiesel was highly sensitive to lipid content during bioreaction. B7 biodiesel unit production cost can be lowered from $1 to $0.6 if the lipid content of the biomass is improved by various process parameter modifications.

The experimental validation of a large-scale compact tubular microalgae photobioreactor model

Summary A dynamic mathematical model is developed to estimate microalgae growth in medium- and large-scale compact tubular photobioreactors (PBRs). Besides cell and other chemical species concentrations, temperature and local solar irradiation are important variables to be assessed. Three different experiments were conducted to adjust and validate the mathematical model for which a methodology based on the coefficient of determination is introduced. The first experiment was performed in a 100 L prototype PBR, the second in a column 78.5 L air-lift PBR, and the third in a 12,000 L compact tubular PBR. Initially, cell growth numerical simulation curves were directly compared with data from the first experiment, which resulted in a coefficient of determination R2 = 0.4043, showing that model adjustment was needed. As a result, 3 adjustment parameters were defined: (i) local solar irradiation (Ψ1); (ii) medium CO2 concentration (Ψ2); and (iii) nutrient concentration (Ψ3). Then, the first experiment data set was used to solve an inverse problem of parameter estimation, obtaining Ψ1 = 1.05, Ψ2 = 0.95, and Ψ3 = 0.18, which resulted in R2 = 0.98584. Next, cell growth numerical simulation curves were compared with measured data from the second and third experiments, obtaining R2 = 0.9862 and R2 = 0.82969, respectively. With the experimentally validated model, a 29 day (or 696 hours) simulation of microalgae cultivation was conducted to calculate the 12,000 L PBR microalgae-derived oil production, which allowed for the projection of the microalgae species Acutodesmus obliquus oil productivity as approximately 2300 L ha−1 yr−1, considering 11.4% microalgae dry biomass lipid content. Such low production demonstrates that achieving an economically viable process for microalgae-derived biofuels will require more technological advances and the development of highly optimized processes.

Using straw hydrolysate to cultivate Chlorella pyrenoidosa for high-value biomass production and the nitrogen regulation for biomass composition

Heterotrophic cultivation of Chlorella pyrenoidosa based on straw substrate was proposed as a promising approach in this research. The straw pre-treated by ammonium sulfite method was enzymatically hydrolyzed for medium preparation. The highest intrinsic growth rate of C. pyrenoidosa reached to 0.097h−1 in hydrolysate medium, which was quicker than that in glucose medium. Rising nitrogen concentration could significantly increase protein content and decrease lipid content in biomass, meanwhile fatty acids composition kept stable. The highest protein and lipid content in microalgal biomass reached to 62% and 32% under nitrogen excessive and deficient conditions, respectively. Over 40% of amino acids and fatty acids in biomass belonged to essential amino acids (EAA) and essential fatty acids (EFA), which were qualified for high-value uses. This research revealed the rapid biomass accumulation property of C. pyrenoidosa in straw hydrolysate medium and the effectiveness of nitrogen regulation to biomass composition at heterotrophic condition.