A parametric study of electrocoagulation as a recovery process of marine microalgae for biodiesel production

Sustainable development and environmental protection has become a major global concern. Biofuels are an alternative transport fuel that can reduce the consumption of non renewable carbon resources and greenhouse gas emissions. Biodiesel is a type of biofuel that is made from renewable lipid containing biological resources and is non toxic. Current feedstocks for biodiesel production include vegetable oils and animal fats, which are vital components of the human food chain, and this makes them less suitable for biofuel production. Lipid-containing microalgal biomass is another feedstock for biodiesel production and has the potential to replace the conventional sources. Microalgae could have many advantages over traditional feedstocks, such as fast photosynthetic growth rates and high lipid content, and these have triggered interest in microalgae bioprospecting. However, one of the main disadvantages of microalgae-to-biofuel process engineering is the high energy consumption and operational costs associated with the culture dewatering stage for biomass creation. This is due to the small size of microalgae cells and the extremely dilute nature of the microalgae culture even at the late exponential phase of the cultivation process. In order to make biodiesel production from microalgae sources commercially viable, the dewatering step must be technologically and economically effective. Current dewatering technologies such as centrifugal recovery and filtration are highly energy intensive. Cell aggregation induced by either flocculation or coagulation is another commonly used dewatering technique that has the advantage of using less energy under optimum conditions. These techniques have found numerous applications in industrial wastewater treatment, and hence could have a potential application for microalgae removal. The work conducted in this research investigated two dewatering techniques for microalgae under the umbrella of bioseparation by induced cell aggregation; flocculation and electrocoagulation. A series of batch experiments were carried out under varying experimental conditions using two marine microalgae species; Chlorococcum sp. and Tetraselmis sp. The key assessment criterion, the microalgae recovery, was quantified by determining the amount of microalgae recovered, that is, the amount of microalgae that settled due to flocculation or floated due to electrocoagulation. Two types of flocculants were used in this research; polyelectrolytes and aluminium sulphate (alum). All flocculants were able to achieve successful microalgae flocculation to varying degrees. Contrary to literature, the results from this research showed that anionic and non-ionic polyelectrolytes were able to adequately flocculate marine microalgae. It was also found that alum flocculation was possible at doses that were comparable to those used for freshwater microalgae flocculation, where previous literature had stated that the doses required for marine microalgae flocculation required were in the range of 5 to 10 times larger. The polyelectrolyte flocculants were able to achieve up to 90 % recovery at doses between 2 to 10 mg/L. Alum was able to achieve up to 99 % recovery at doses under 100 mg/L. Flocculation recovery was seen to increase with pH, and the zeta potential showed that the microalgae become more electropositive with decreasing pH. The recovery of microalgae was also seen to increase with increasing temperature. Electrocoagulation was carried out with two sacrificial anode materials; aluminium and ferritic stainless steel type 430, and a carbon inert anode. The maximum recovery obtained was 99, 90 and 38 % for electrocoagulation with the stainless steel 430, aluminium and carbon anodes, respectively. In order of efficiency, the optimum anode was aluminium, stainless steel 430 and then carbon. The microalgae recovery increased with increasing applied voltage and electrocoagulation time. The valencies of dissolved metal ions from the anode were investigated for multivalent species and confirmed with a metallic and ionic mass balance of the dissolution and electrocoagulation process. The pH of the solution did not appear to have a significant effect on recovery. The zeta potential of the microalgae after electrocoagulation was seen to become more electropositive with increasing experimental run time. An increase in temperature increased recovery whilst a reduction in salinity resulted in reduced microalgal recovery. The theory of the mechanism of electrocoagulation was proven with the results of the experimental work conducted in this research. Evidence was shown of the three main steps involved in the electrocoagulation mechanism; coagulation, charge neutralisation and flotation. The results demonstrated that coagulation of microalgae occurs in the bulk of solution, and not at a specific location such as in the vicinity of an electrode. The rate limiting step of the electrocoagulation process was found to be the rate of coagulation of microalgae cells, induced by the binding of metal ions onto the microalgae surface. A mathematical model was developed in order to predict the recovery of microalgae at predetermined electrocoagulation conditions such as the applied current, time, microalgae species and electrode material. The mathematical model was able to accurately predict microalgae recovery for all microalgae systems. This model made it possible to optimise the electrocoagulation process for conditions that required a low energy demand and accomplished high microalgae recovery. These optimum conditions enabled a comparison between alum flocculation and the aluminium anode electrocoagulation. Such a comparison is interesting as the two processes have a similar flocculation mechanism. A techno-economic and carbon assessment was performed on the unit operation of microalgal culture dewatering operation as part of the microalgal biodiesel production process. This involved estimating the operation costs, carbon dioxide emissions and energy consumption. Three different dewatering technologies were investigated; centrifugation, electrocoagulation/centrifugation and alum flocculation/centrifugation. The analysis showed that both electrocoagulation and flocculation require significantly less energy to dewater in comparison to centrifugation. However, when the energy to produce the raw materials was taken into account, electrocoagulation was found require a greater energy demand. The operational cost of continual replacement of the anodic material significantly increased the overall economics of electrocoagulation compared to alum flocculation. In terms of energy requirements, carbon dioxide emissions and overall costs, alum flocculation showed to be the most promising dewatering technique with genuine potential to be used as the main dewatering technology in microalgae sourced biodiesel production. Future work may involve the investigation of electrocoagulation as a continuous process and also the combination of alum flocculation and electrocoagulation as a single dewatering method.

Microalgal biomass is a potentially attractive source of several bioproducts, such as carbonic anhydrase, the enzyme responsible for catalyzing the reversible hydration of CO2. This biomolecule has been studied for its application in enzymatic systems of CO2 capture and sequestration. Therefore, the aims of this study were to evaluate the production of carbonic anhydrase in the culture of marine and freshwater microalgae and to monitor the growth in terms of biomass and pH. The marine microalgae Dunaliella tertiolecta, Tetraselmis suecica, Phaeodactylum tricornutum, Isochrysis galbana and Nannochloropsis oculata, and the freshwater microalgae Chlorella vulgaris and Scenedesmus obliquus were cultured in Erlenmeyer flasks at 25 °C. The freshwater microalga that had the highest enzyme production was C. vulgaris: its maximum activity was 44.0 U/L. Among the marine microalgae, P. tricornutum stood out as the best producer, with a maximum activity of 19.9 U/L. In terms of specific activity, the highest values were obtained from D. tertiolecta (44.6 U/g) and P. tricornutum (24.5 U/g). These results show the potential of microalgae to produce the carbonic anhydrase enzyme. Microalgal biomass represents an attractive source of this biomolecule.

Application of metal-air fuel cell electrocoagulation for the harvesting of Nannochloropsis salina marine microalgae

Butanol is a four carbon alcohol commonly used in the chemical industry and also as a transportation fuel additive. Acetone-butanol-ethanol (ABE) fermentation is one of the processes used to produce butanol through biological conversion. The current fermentation process that uses lignocellulosic materials or food-based feedstock is not favourable because it requires high energy for the pretreatment due to the presence of lignin in lignocellulosic materials. Therefore, fermentation using an alternative feedstock such as microalgal biomass, which is a non-food based material and contains low lignin content, is considered as one of the approaches to overcome these issues. This study, therefore, was undertaken to evaluate the potential of ABE fermentation using microalgal biomass from two microalgae species, a freshwater microalgae Chlorella sp. and a marine water microalgae T. suecica. This research involves the investigation of the entire process consisting of biomass production, pretreatment, and enzymatic saccharification for reducing sugar production and ABE fermentation. A preliminary study on the thermochemical conversion of microalgal biomass was also carried out in this research. A microalgal cultivation and carbohydrate accumulation study indicated that microalgal growth rate and carbohydrate content were significantly influenced by the cultivation conditions such as light intensity, temperature, pH, salinity and carbon dioxide concentration (CO2). The maximum biomass production, specific growth rate (µ) and carbohydrate content for Chlorella sp. were 0.567 gL-1, 0.252 d-1, and 32.41% of dried biomass respectively, attained at 2000 lux, 30°C in a medium with initial pH of 7 without addition of NaCl. The maximum biomass production, µ and carbohydrate content for T. suecica of 0.54 gL-1, 0.22 d-1, and 20.6% of dried biomass respectively, were attained at 3000 lux, 30°C in a medium with initial pH of 7 and 30 gL-1 of NaCl. This study also indicated that both microalgae were able to grow in a medium supplied with 15% CO2. Comparison of indoor and outdoor microalgal cultivation was performed at two different temperature ranges, low temperature: 10 - 20°C and high temperature range: 20 - 32°C. It was observed that higher microalgal biomass production and growth rate were obtained from the indoor cultivation compared than that of outdoor cultivation. The results suggested that the ambient temperature and natural light intensity fluctuation have a significant influence on the microalgal growth in outdoor cultivation. The biomass obtained from the cultivation was pretreated prior to hydrolysis and ABE fermentation. Dilute alkaline pretreatment, which is a less harsh and more environmentally friendly approach compared to acid pretreatment, was applied to pretreat the microalgal biomass and the process was optimised. The pretreatment conditions (alkaline agent, alkali concentration, temperature and reaction time) were found to influence the pretreatment performance. A quadratic model that describes interaction of pretreatment conditions was developed and successfully fitted to the experimental results (r2=0.92 for Chlorella sp. and r2=0.96 for T. suecica). This pretreatment method is able to disrupt the microalgal cell structure and preserve the chemical compound of the microalgal cell. The results also demonstrated that the dilute alkaline pretreatment was able to enhance the enzymatic saccharification of microalgal biomass. The enzymatic saccharification condition for reducing sugar production was optimised by varying the temperature, pH, enzyme concentration and biomass concentration in order to obtain the maximum sugar concentration from microalgal biomass. It was found that ≈90% saccharification yield of both pretreated microalgal biomass was achieved from the saccharification at the optimum conditions (temperature: 40°C, pH: 4.5 and biomass concentration: 5-10 gL-1). A high amount of glucose (50%) and xylose (45%) in both microalgal hydrolysate indicates that it can be used as chemical platform for biofuel production through the fermentation process. This study also demonstrates that a combination of dilute alkaline pretreatment followed by enzymatic saccharification can be applied to pretreat microalgal biomass prior to ABE fermentation. Subsequently, the ABE fermentation of microalgal biomass was performed using four different forms of these two microalgal biomass; (1) untreated, (2) alkaline pretreated, (3) lipid extracted, and (4) lipid extracted followed by alkaline treated biomass. Each of the samples was subjected to enzymatic saccharification for reducing sugar production prior to the ABE fermentation. The highest ABE concentration was obtained from the fermentation of the dilute alkaline pretreated Chlorella sp. (0.161 gL-1) and T. suecica (0.126 gL-1) biomass. It was found that the butanol conversion yield from the fermentation of alkaline pretreated Chlorella sp. and T. suecica was 0.3% and 0.7% dried biomass respectively. A preliminary study on thermochemical conversion of both microalgal biomass was also undertaken through pyrolysis and gasification process. The lipid extracted microalgal biomass exhibited low activation energy, which is favourable to be used in thermochemical conversion. In addition, the gasification of microalgae at 800°C and time of around 20 min were suitable conditions to complete the conversion in a thermogravimetric analyser. The findings from this study generate significant information on the production of biofuel in an environmentally friendly manner. This has the potential to be applied not only for butanol production, but also for the production of various types of microalgal carbohydrate-based biofuel such as bioethanol, biohydrogen and biomethane.

Microalgae have been considered a promising option to provide food, feed and biofuel based on their high areal productivity and their ability to be cultured on non-arable land with different water sources (fresh, brackish or seawater). This research thesis work evaluated different cultivation systems for growing the marine microalga Tetraselmis sp. (M8) and optimised dispersed air flotation (DiAF) as a separation and harvesting method using the research facilities in the Algae Biotechnology Laboratory and Mineral Processing Laboratory at the University of Queensland’s St. Lucia campus. Current algae cultivation systems are threatened by contamination with other algae or algal grazers resulting in the need for significant improvement in cultivation and harvesting systems. So far, not much work has been carried out on flotation methods, a process widely used for recovery of particles in mining, for harvesting of marine microalgae. To address these issues, we have developed an efficient two-stage cultivation system using the marine microalga Tetraselmis sp. M8. This hybrid system combines exponential biomass production in positive pressure air lift-driven bioreactors with a separate synchronised high lipid induction phase in nutrient deplete open raceway ponds. A comparison to either bioreactor or open raceway pond cultivation systems suggests that this process potentially leads to significantly higher productivity of algal lipids that can serve as a feedstock for biodiesel production. Nutrients are only added to the closed bioreactors and open raceway ponds have turnovers of only a few days, thus avoiding the critical issue of contamination. Once the cultivation of marine species was optimised, the focus of this study was directed towards optimisation of DiAF method. An initial study was carried out to harvest freshwater microalgae (Chlorella sp. BR2) and marine microalgae (Tetraselmis sp. M8) from dilute culture with and without a collector, tetradecyl trimethylammonium bromide (C14TAB). The surface hydrophobicity of microalgae was measured by using a modified adherence-to-hydrocarbon method. If no collector was added, BR2 showed high hydrophobicity, and its flotation tests in a mechanically agitated cell produced an algal concentrate with an enrichment ratio of 13.5 and 90.3% algae recovery. The natural hydrophobicity of M8 was low, so was its flotation recovery (6.4%). Addition of C14TAB improved M8 recovery to 71.1% but with a low enrichment ratio of 3.4 times. Overall, the flotation performance correlated well with algal hydrophobicity. In search of more effective collectors for marine algae flotation, the hydrophobicity of M8 in aqueous solutions of varying surfactant type and concentration and pH was measured. It was found that addition of dodecylammonium hydrochloride (DAH) at 25 ppm and pH 6 significantly enhanced the hydrophobicity of M8. Subsequent flotation results confirmed that at this chemical condition, M8 enrichment ratio was increased to 6.6 with 80.5% algae recovery. Further improvement was achieved by using a Jameson cell with relatively small air bubbles. The Jameson flotation for M8 gave an enrichment ratio of 11.4 times with 97.4% algae recovery. To make the process more cost effective it was necessary to carry out DiAF as close to the growth medium’s natural pH as possible. On testing separation of marine microalga M8 from seawater with various 12-carbon chain collectors, such as dodecyl pyridinium chloride (DPC), N-dodecylpropane-1,3-diamine hydrochloride (DN2), dodecyl amine hydrochloride (DAH), and sodium dodecyl sulphate (SDS) were added. DPC at natural growth medium pH (9.5) outperformed DAH, DN2 and SDS. For DPC, the use of a Jameson cell further improved the flotation performance from 16 times to a final enrichment ratio of 23 times, with over 99% marine microalgae recovered. The present study helped to refine the flotation process and led to a deeper understanding on how marine microalgae can be harvested by using DiAF. During the study it was also found that hydrophobicity plays a key role in microalgae recovery. Different microalgae have different natural hydrophobicity. Generally, collector chemicals are required to increase the efficiency of the flotation process. However, the use of chemicals restricts the application of harvested biomass and makes it unfit for feed or food purposes. During the hydrophobicity testing of different microalgae, some were found to possess naturally higher hydrophobicity. Hence a comparative study was needed to identify the microalgal species that can be flotated without the addition of chemicals. The study showed that freshwater strains Chlorella sp. BR2 and Scenedesmus sp. NT8c possess hydrophobicity values of up to 28.85% and 23.88% which indicated that they can be harvested effectively without the addition of collector chemicals. The DiAF study showed that 85.69% and 66.29% of Chlorella sp. BR2 and Scenedesmus sp. NT8c could be recovered using a mechanical cell with enrichment ratios of 21.98 and 17.43. Although these values are lower than those obtained with collectors, the harvested biomass would be suited for animal feed, while the remaining uncollected algae can be used as a continued culture. In conclusion, this study has demonstrated that DiAF is a suitable technique for effective and large-scale harvesting of both freshwater and marine microalgae.

Microalgae biomass is considered as one of the promising alternative feedstock for biofuel production. The biomass productivity of some of the microalgae can exceed an order of magnitude compared to any other terrestrial plant. Apart from nitrogen and phosphorus, iron is one of the major elements that must be provided to microalgae culture for high density biomass production. The amount of iron that is required per cell or per unit of microalgae biomass will vary among microalgae strains. Depending on the concentration of iron in the cultivation media, the microalgae will accumulate different amount of iron and this process may alter the compositions of other major metabolites. In order to be competitive the cost of microalgae biomass production should be lower and the desired metabolites should be present in higher percentages; therefore, the appropriate concentration of iron should be determined. On the contrary, there are very limited study on the microalgal iron requirement. The first objective of this study is to determine the minimum concentration of iron requirement by some of the locally isolated potential microalgae. The second objective of this study is to characterize the lipid accumulation under different iron concentrations. Gillard f/2 and BG-11 are the two common nutrients composition used to culture marine and freshwater microalgae respectively. In these two nutrients media, the concentrations of iron are 0.65 mg/l and 1.24 mg/l for Guillard F/2 and BG-11 media respectively. Due to some limitations, in most of the cases the concentrations of phototrophic microalgae in large scale biomass production doesn't exceed 0.5 g/L. If these two media are to be used in large scale, iron requirement can be calculated as 1.3 kg (6.3 kg as FeCl3.6H2O) and 2.4 kg (12 kg as FeCl3.6H2O) respectively for each ton of biomass production. Therefore, the cost of the iron fertilizer can be significant for low cost feedstock; furthermore, if there is residual iron in the discharge water it will require additional treatment steps. Three local marine microalgae (Nannochloris sp., Tetraselmis sp., Chlorocystis sp.) and three local freshwater microalgae (Scenedesmous sp., Chlorella sp., Neochloris sp.) were selected to study their iron requirement. Apart from iron, all the nutrients were added as per f/2 or BG-11 media concentrations. However, for the marine microalgae, the range of iron concentration was 0 to 1 mg/L while for the freshwater microalgae it was 0 to 3 mg/L. All the experiments were conducted in triplicates. 10 ml of culture was inoculated in 90 ml containing any culture media in a 250 ml flask; the flasks were kept in an orbital shaker which was maintained at 120 rpm speed, 25°C, 12 hours photoperiod. The growth period for any strain was kept fixed at 7 days. It was found that marine Naanochloris sp. didn't require the addition of iron; the available iron in the seawater is sufficient to produce 0.5 g/L biomass density. The other two strains had also smaller iron requirement compared to f/2 media. For the three freshwater microalgae, there was also minor requirement for iron (1 mg/L) which was much lesser than iron concentration in BG-11 media. Iron deficiency, during the cultivation process, resulted in bleaching and changes in metabolites (especially in pigments). Nannochloris sp. and Scenedesmous sp. will be later grown in outdoor small raceway tanks (1000 liter) to verify the indoor small scale results.

Microalgae are one of the most effective sources of renewable energy production. It can grow at high rates and capable of producing oil along the year. Microalgae biomass was first suggested as a feedstock for biofuel production and received early attention for commercial application. Microalgae are expected to be a vital raw material for amino acids, vitamins and productions of valuable byproducts. The cultivation of microalgae is known to be the most gainful business in the biotechnological industry. It is a waste less, environmentally pure, energy and resource saving route. Biodiesel production from algal lipid is non-toxic and highly biodegradable. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into: thermal, chemical and biochemical methods, in addition to the large number of different agents for decomposing and hydrolysing. We can obtain the low-cost energy production from the wastewater treatment by using microalgae. Finally, biodiesel production by microalgae in Egypt is not practical at the economical level. In order to improve biodiesel fuel quality, the alga must be subjected to genetic engineering for up-regulation of fatty acid biosynthesis and/or by down-regulation of β-oxidation. Economically, the algal biomass must be processed for bio-refinery to maximize its utilization for different applications.

Due the worldwide need to improve care for the environment and people, there is a great demand for the development of new renewable, sustainable, and less polluting technologies for food, health, and environmental industries. The marine environment is one of the main areas investigated in the search for alternatives to the raw materials currently used. Thereby, cyanobacteria and marine microalgae are microorganisms that are capable of producing a diverse range of metabolites useful for their cellular maintenance, but that also represent a great biotechnological potential. Due its great potential, they have an enormous appeal in the scientific research where, the biological activity of metabolites produced by these microorganisms, such as the antioxidant action of sterols are, some examples of biotechnological applications investigated around the world. Thereby, Brazil due to its extensive biodiversity, has high potential as a raw material supplier of marine waters, researching cyanobacteria and microalgae metabolites and their applications. Thus, this rapid review intends to present some important contributions and advances from Brazilian researchers, using the biomass of Brazilian cyanobacteria and marine microalgae, in order to illustrate the value of what has already been discovered and the enormous potential of what remains unexplored so far.

Cultivation, photobioreactor design and harvesting of microalgae for biodiesel production: A critical review

Marine microalgae have been used for a long time as food for humans such as Chlorella vulgaris, Spirulina platensis and Nannochloropsis bacillaris and for animals in aquaculture. The biomass of these microalgae and the compounds they produce have been shown to possess several biological applications with numerous health benefits. The three marine microalgae (Chlorella vulgaris, Spirulina platensis and Nannochloropsis bacillaris) were collected from Vellar estuary, South east coast of India. These three microalgae were cultivated in respective media (BG11, Conway, and Zarrouk) and estimated their biochemical composition (Protein content, Carbohydrate (CHO) analysis, Total lipids, Chlorophyll, Carotenoids and antibacterial activity. Simultaneously, these cultures were cultivated in flask containing 500 ml of respective media at lab condition for a period of one month and their growth, pH, biomass, CO2 fixation and carbon content were determined. Based on the growth rate, the pH of three microalgae in media was observed at lab condition. During maximum growth and biomass, the pH was found to be ranged between 9 and 11 for Spirulina platensis; 7 and 9 for Chlorella vulgaris; 8 and 9 for Nannochloropsis bacillaris. The Spirulina platensis and Chlorella vulgaris reached maximum growth rate and produced maximum biomass. Further, Chlorella vulgaris and Spirulina platensis attained maximum biomass in media at lab condition, also fixed highest level of carbon dioxide in media but they did not produce maximum biomass, though the growth of Nannochloropsis bacillaris were found high in media at lab condition. Among the three microalgae, Chlorella vulgaris and Spirulina platensis produced highest biochemical (Protein estimation) compounds. Hence, Chlorella vulgaris and Spirulina platensis were selected as efficient microalgae for antibacterial activity against human pathogen. This study revealed that certain green algae and blue green microalgae having high growth, pH, CO2 fixation, carbon content and biochemical composition paves the way for pharmaceutical activity. Antibacterial activity against human pathogen (Klebsiella pneumoniae, Proteus mirabilis, Vibrio cholera, Salmonella typhi and Escherichia coli) was evaluated.The crude and fractionated extraction of Chlorella and Spirulina were dissolved in different solvents like ethanol, methanol, chloroform and diethyl ether. The extracts were applied to 6 mm dry sterile disc in aliquots of 30 μL of solvent, allowed to dry at room temperature and placed on agar plates seeded with microorganisms. The bacteria were maintained on nutrient agar plates and incubated at 37˚ C for 24 hrs. Zones of growth inhibition were measured after incubation from all the extracts and tested twice at a concentration of 30 mg disc-1 was evaluated for Chlorella and Spirulina with their potential health benefits. Keywords: Chlorella vulgaris, Spirulina platensis, Nannochloropsis bacillaris, CO2 fixation, Biochemical composition, Pharmaceutical activity

Whole-cell microalgae biomass and their specific metabolites are excellent sources of renewable and alternative feedstock for various products. In most cases, the content and quality of whole-cell biomass or specific microalgal metabolites could be produced by both fresh and marine microalgae strains. However, a large water footprint for freshwater microalgae strain is a big concern, especially if the biomass is intended for non-food applications. Therefore, if any marine microalgae could produce biomass of desired quality, it would have a competitive edge over freshwater microalgae. Apart from biofuels, recently, microalgal biomass has gained considerable attention as food ingredients for both humans and animals and feedstock for different bulk chemicals. In this regard, several technologies are being developed to utilize marine microalgae in the production of food, feed, and biofuels. Nevertheless, the production of suitable and cheap biomass feedstock using marine microalgae has faced several challenges associated with cultivation and downstream processing. This review will explore the potential pathways, associated challenges, and future directions of developing marine microalgae biomass-based food, feed, and fuels (3F).

Simple SummaryMicroalgae are increasingly recognized as a source of valuable biomass with numerous health benefits. Cleaning of marine microalgal biomass is very crucial for microalgal studies as the salt on the microalgae cells will lead to overestimation of biomass determination. Incomplete washing of salt from microalgae could also interfere with the nutritional analyses. The biomass, especially dry weight, has been utilized for nutritional or compositional evaluation. Although standard methods of marine microalgal dry weight determination are available, these methods did not provide comprehensive details, and the parameters vary among themselves. Without a standard method, a comparison of results among previous studies can be misleading and unreliable. Therefore, the current study aimed to investigate and determine the ideal setting of several parameters in the marine microalgal dry weight determination for laboratory-scale culture. The present findings could assist in developing a standardized protocol to ensure a high quality of biomass for microalgal studies. Microalgal biomass is one of the crucial criteria in microalgal studies. Many reported methods, even the well-established protocol on microalgal dry weight (DW) determination, vary greatly, and reliable comparative assessment amongst published results could be problematic. This study aimed to determine the best condition of critical parameters in marine microalgal DW determination for laboratory-scale culture using four different marine microalgal species. These parameters included the washing process, grades of glass microfiber filter (GMF), GMF pretreatment conditions, washing agent (ammonium formate) concentrations, culture: washing agent ratios (v:v) and washing cycles. GMF grade GF/A with precombustion at 450 °C provided the most satisfactory DW and the highest ash-free dry weight (AFDW)/DW ratio. Furthermore, 0.05 M ammonium formate with 1:2 culture: washing agent ratio and a minimum of two washing cycles appeared to be the best settings of microalgal DW determination. The present treatment increased the AFDW/DW ratio of the four respective microalgae by a minimum of 19%. The findings of this study could serve as a pivotal reference in developing a standardized protocol of marine microalgal DW determination to obtain veracious and reliable marine microalgal DW.

Biomass and lipid production of marine microalgae using municipal wastewater and high concentration of CO 2

Microalgae can contribute to the decarbonization of wastewater treatment by municipalities, industries and agriculture, by substituting sunlight for energy intensive conventional treatment processes, while capturing nutrients and carbon in the algal biomass. The carbon fixed into the algal biomass can be converted to renewable natural gas (RNG) using anaerobic digestion or into renewable diesel and sustainable aviation fuel (SAF) using hydrothermal liquefaction (HTL), with greatly reduce the carbon footprints compared to conventional fuels. Bioplastics, biofertilizers and other bioproducts from microalgae biomass also provide potential benefits in greenhouse gas (GHG) reduction and domestic supply chains. Microalgae technologies can counter eutrophication caused by harmful algal blooms by recovering nutrients, N and P, from wastewaters, and even from very low nutrient concentrations found in surface waters. CO2 is required in microalgae cultivation and wastewater treatment to support maximal rates of the photosynthesis, with the CO2 obtained from the wastes themselves, other local sources or even atmospheric CO2. Greenhouse gas mitigation with microalgae processes is based on life cycle assessments, comparing such green processes with current energy intensive wastewater treatment, and nutrient reduction technologies. Microalgae technologies are specifically relevant to smaller, often disadvantaged, communities, where currently about 5,000 algae wastewater treatment ponds are operated by public utilities with many more are operated by industries. However, many, if not most, of these pond facilities require urgent technology upgrades to achieve the potential and goals of low cost GHG mitigation and efficient nutrient recycling. MicroBio Engineering Inc. is developing and has demonstrated several technologies that combine innovative carbon mitigation and decarbonization technologies for a circular economy, with longer-term potential for large-scale biofuels and biofertilizer production.

Microalgae can contribute to the decarbonization of wastewater treatment by municipalities, industries and agriculture, by substituting sunlight for energy intensive conventional treatment processes, while capturing nutrients and carbon in the algal biomass. The carbon fixed into the algal biomass can be converted to renewable natural gas (RNG) using anaerobic digestion or into renewable diesel and sustainable aviation fuel (SAF) using hydrothermal liquefaction (HTL), with greatly reduce the carbon footprints compared to conventional fuels. Bioplastics, biofertilizers and other bioproducts from microalgae biomass also provide potential benefits in greenhouse gas (GHG) reduction and domestic supply chains. Microalgae technologies can counter eutrophication caused by harmful algal blooms by recovering nutrients, N and P, from wastewaters, and even from very low nutrient concentrations found in surface waters. CO2 is required in microalgae cultivation and wastewater treatment to support maximal rates of the photosynthesis, with the CO2 obtained from the wastes themselves, other local sources or even atmospheric CO2. Greenhouse gas mitigation with microalgae processes is based on life cycle assessments, comparing such green processes with current energy intensive wastewater treatment, and nutrient reduction technologies. Microalgae technologies are specifically relevant to smaller, often disadvantaged, communities, where currently about 5,000 algae wastewater treatment ponds are operated by public utilities with many more are operated by industries. However, many, if not most, of these pond facilities require urgent technology upgrades to achieve the potential and goals of low cost GHG mitigation and efficient nutrient recycling. MicroBio Engineering Inc. is developing and has demonstrated several technologies that combine innovative carbon mitigation and decarbonization technologies for a circular economy, with longer-term potential for large-scale biofuels and biofertilizer production.