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The rise of the global mean temperature as a consequence of incessant anthropogenic greenhouse gas (GHG) emissions, led by CO2, is one of the direst challenges faced by humankind today. The need of the hour is to minimize fossil fuel usage and capture the atmospheric CO2. Broadly, the CO2 mitigation strategies employ carbon capture and storage (CCS) and biological carbon capture and utilization (bio-CCU) technologies. A critical comparative summary of the prevalent CCS and bio-CCU methods has been presented in this study. Among all the CO2 capture technologies, the microalgal bio-CCU in a biorefinery model is more environment and economy-friendly. Microalgal biorefinery can potentially serve as a platform not only for bio-CCU but also for producing third-generation biofuels and commercially important value-added products as means of wealth generation from waste CO2. Alongside reducing the world's reliance on fossil fuels, this approach also directly or indirectly addresses most of the UN's sustainable development goals (SDGs). To enhance the microalgal CO2 capture efficiency and consequent biomass productivity, smart bioprocess design and reactor engineering performed by researchers are summarized to understand the progress in this direction. Recent advances, innovations, and existing challenges in the design and development of microalgal cultivation processes and systems, including CO2 delivery mechanisms, have been critically discussed and assessed in terms of carbon capture efficiency. The futuristic vision for the fourth-generation microalgal biorefinery-based bio-CCU has also been outlined to make some practical recommendations for its successful implementation or adaptation by the thermal power plants and cement industries. [ABSTRACT FROM AUTHOR]

BACKGROUND: Natural photosynthesis, utilizing intelligent molecular machinery to harness sunlight, stands as the benchmark for efficient energy generation. Despite its high quantum efficiency compared to synthetic methods, challenges persist due to dynamic nutritional and light requirements in plant, microalgae, and cyanobacteria‐driven processes. Reported microalgae CO2 uptake rates rely on biomass dry cell weight measurement after certain incubation period and systematic study of required CO2 concentrations for optimal photobioreactor operation remaining unexplored. This research is thus aimed at evaluating the critical dissolved CO2 (Ccrit ∙ CO2) concentration and specific CO2 uptake rates (SCUR) of Chlorella minutissima (CM) culture in the presence of surplus light and other nutrients by online monitoring and measuring the dynamic CO2 uptake rates which will help in maintaining the optimal rate of CO2 delivery for continuous cultivation of microalgae while minimizing the escape of CO2. RESULTS: Dissolved Ccrit ∙ CO2 was determined to be in the range of 16–20 mg/L, and the maximum SCUR in BBM (Bold Basal Medium) was found to be 0.73 mg CO2 (mg dcw ∙ h)−1. Interestingly, this SCUR value is nearly three times greater than that of the most efficient in vitro artificial photosynthetic novel pathway reported so far. CONCLUSION: From the calculated SCUR values, it may be noted that 9.6 g of biomass can be obtained from 1 g of microalgal inoculum in a day, thereby setting a benchmark for the scientists working in the areas of bioprocess engineering, synthetic biology, and metabolic engineering to comply. © 2024 Society of Chemical Industry (SCI). [ABSTRACT FROM AUTHOR]

Global warming is induced partly by rising atmospheric carbon dioxide levels, calling for sustainable methods to sequester carbon. Here we review carbon capture, usage, and storage with microalgae, with focus on methods to improve carbon dioxide uptake, systems combining wastewater and flue gases, machine learning for strain identification, artificial intelligence and automation, and the circular bioeconomy. Carbon dioxide uptake by microalgae can be improved by using modified photobioreactors, membranes, chemical methods, solvents, adapted strains, genetically engineered strains, omics, and nanotechnology. We also discuss the economic viability of microalgae-based carbon capture and bioenergy generation. On an average, microalgal farming on 13 million acres area can sequester approximately 0.5 gigatons of CO2 to generate more than 300 tons of biomass. [ABSTRACT FROM AUTHOR]

Algal biotechnology has received significant attention over the past two decades in fields ranging from biofuels to cosmeceuticals. However, the development of domesticated or genetically engineered microalgal strains for commercial applications depends on accurate and reliable growth data. To this end, several companies have developed lab-scale photobioreactors (PBRs) that enable precision control of conditions and automated growth recording. Whilst the transition from manual control of conditions and measurements to automated systems has allowed researchers to greatly improve the accuracy and scope of cultivation experiments, it has also presented novel challenges. The most pertinent of these being the analysis of the copious quantities of data produced. A standard PBR experiment can contain tens or even hundreds of thousands of data points, and often features outliers, noise, and a requirement for datasets to be calibrated with a standard curve or merged with replicates. Furthermore, complex analysis of multiple curves may be required in order to extract information such as the gradient or fit to a growth model. This can be laborious, time consuming and is not standardized between research groups. Proprietary software provided with most PBRs tends to lack these more advanced features and is typically unable to process data from other PBR manufacturers. To address these issues, we have developed the Algal Data Analyser (ADA), an open-source software platform providing the tools to rapidly plot and analyse microalgal data. ADA can simultaneously interpret datasets from three major PBR suppliers (Algenuity, Industrial Plankton, Photon Systems Instruments), and can also incorporate data from manual readings. Users can rapidly produce standardized, publication ready plots, and analyse multiple growth curves in parallel. Future iterations of ADA will include compatibility with datasets from other PBR suppliers as they become available, with the aim of making it a universal platform for all PBR data.

Microalgal cultivation for biodiesel and feed requires recycled nutrient resources for a sustainable long‐term operation. Whey permeate (WP) from dairy processing contains high organic load (lactose, oils, and proteins) and nitrogen (resources tested for microalgal cultivation) and organic phosphorus (P) that has not yet been tested as a P source for microalgal cultivation. We explored the potential of green algae strains (brackish) and polyculture (freshwater) in exploiting P from WP added to a medium based on either seawater (7 psu) or landfill leachate. Both strains showed a capacity of using organic P in WP with equal growth rates (0.94–1.12 d−1) compared with chemical phosphate treatments (0.88–1.07 d−1). The polyculture had comparable growth rate (0.25–0.57 d−1) and biomass yield (152.1–357.5 mg L−1) and similar or higher nutrient removal rate in the leachate–WP medium (1.3–6.4 mg L−1 day−1 nitrogen, 0.2–1.1 mg L−1 day−1 P) compared with the leachate–chemical phosphate medium (1.2–4.7 mg L−1 day−1 nitrogen, 0.3–1.4 mg L−1 day−1 P). This study showed that WP is a suitable P source for microalgal cultivation over a range of salinities. To date, this is the first study demonstrating that raw WP can replace mineral P fertilizer for algal cultivation. Practitioners Points: Whey permeate is a comparable phosphorus source to standard fertilizers used in algal cultivation.Green algae removed phosphorus effectively from whey permeate.Microalgal cultivation is a good approach for treatment of whey permeate in combination with a nitrogen‐rich wastewater. [ABSTRACT FROM AUTHOR]

In the present study swine wastewater diluted at the different percentages (10%, 20%, 60%, and 100%) was used to cultivate the red alga Porphyridium purpureum to evaluate microalgal growth, nutrient removal and the production of polysaccharide and phycoerythrin. The results showed the dilution level significantly affected algal growth and nutrient removal. The best growth was in the swine wastewater diluted at 60% resulting in the highest biomass concentration of 9.44 ± 0.44 g L−1, and the corresponding removal efficiency of COD, total nitrogen (TN), total phosphorus (TP), and ammonia nitrogen (NH4+-N) reached up to 94.85 ± 0.08%, 92.69 ± 0.09%, 96.08 ± 0.02%, and 100 ± 0.00%, respectively. Moreover, the algal cells cultured in the wastewater produced high concentration of polysaccharide and phycoerythrin. Microalgae cultured in 10% swine wastewater produced the highest polysaccharide concentration of 2.16 ± 0.02 g L−1. The highest phycoerythrin concentration of 54.45 ± 4.76 mg L−1 was observed in the 60% swine wastewater group. The results showed that P. purpureum has great potential in treating wastewater and producing high-value byproducts, which is conducive to the development of the bio-circular economy. [ABSTRACT FROM AUTHOR]

Microalgae and cyanobacteria are photosynthetic microorganisms capable of synthesizing several biocompounds, including polysaccharides with antioxidant, antibacterial, and antiviral properties. At the same time that the accumulation of biomolecules occurs, microalgae can use wastewater and gaseous effluents for their growth, mitigating these pollutants. The increase in the production of polysaccharides by microalgae can be achieved mainly through nutritional limitations, stressful conditions, and/or adverse conditions. These compounds are of commercial interest due to their biological and rheological properties, which allow their application in various sectors, such as pharmaceuticals and foods. Thus, to increase the productivity and competitiveness of microalgal polysaccharides with commercial hydrocolloids, the cultivation parameters and extraction/purification processes have been optimized. In this context, this review addresses an overview of the production, characterization, and potential applications of polysaccharides obtained by microalgae and cyanobacteria. Moreover, the main opportunities and challenges in relation to obtaining these compounds are highlighted.

Nannochloropsis is widely used in aquaculture as a feed source. However, large-scale cultivation of Nannochloropsis usually fails due to rotifer contamination. In order to identify an effective technique for reducing rotifer contamination, the effect of Brachionus plicatilis contamination on photosynthetic characteristics in Nannochloropsis oculata and the efficacy of the celangulin (CA):toosendanin (TSN) (1:9) combination for rotifer extermination were investigated using chlorophyll a fluorescence transient. B. plicatilis could directly devour microalgal cells and sharply reduced N. oculata density to very low levels. B. plicatilis also inhibited activities of PSII reaction centers, both acceptor and donor side, thereby damaging the photosynthetic performance of surviving N. oculata cells. However, the CA:TSN (1:9) combination could completely eliminate B. plicatilis, thereby preventing rotifers from devouring microalgae cells and protecting the photosynthetic performance of the surviving algal cells against rotifers damage. Therefore, the binary combination of CA:TSN (1:9), is considered to be a good candidate of botanical pesticide for controlling rotifer contamination.

Microalgal biofuel production is a useful process to produce sustainable and carbon-neutral biofuels. The choice of microalgal species and the processes adopted in various production stages determine biofuel production. In this review, recent technological advancements made in various stages of microalgal biofuel production are discussed. This review also discussed the recent progress made in harvesting microalgal biomass and lipid extraction. In addition, the viability of using wastewater as a nutrient source for microalgae and its nutrient removal capabilities has been discussed in detail. This is the first study that enlists and compares the minimum achievable cost of biofuel produced in different studies. Also, process optimization strategies adopted to minimize the cost are discussed. The reported biofuel production cost varied from 0.14 $/L to 24.33 $/L based on the variation in the microalgae strains, production method, and optimization strategies. [ABSTRACT FROM AUTHOR]

The aim of the study was to investigate the potential of microalgal cultivation on anaerobic liquid digestate as a growth medium. The two methods of liquid digestate treatment including centrifugation and distillation and the two algal strains (Chlorella vulgaris and Arthrospira platensis) were compared. Additionally, the volume of the liquid digestate used to prepare the culture medium constituted from 10 to 50% of the medium volume. The study demonstrated that the highest C. vulgaris and A. platensis biomass productions of 2490 mg TS/L and 2990 mg/L, respectively, were obtained by adding 50% of distilled digestate to a growth medium. Regarding centrifuged liquid digestate, only 10% dilution was required to obtain the maximum final biomass concentration. A. platensis removed 81.1% and 66.4% of the total nitrogen from medium prepared on distilled and centrifuged digestate, respectively, while C. vulgaris ensured 64.1% and 47.1% of removal, respectively. The phosphorus removal from both culture media was higher than 94.2% with A. platensis, while it was 70.4% from distilled and 87.4% from centrifuged media with C. vulgaris. The study confirmed a great potential of microalgal biomass production on anaerobic liquid digestate with a high treatment efficiency of digestate. [ABSTRACT FROM AUTHOR]

Microalgae and cyanobacteria are photosynthetic microorganisms capable of synthesizing several biocompounds, including polysaccharides with antioxidant, antibacterial, and antiviral properties. At the same time that the accumulation of biomolecules occurs, microalgae can use wastewater and gaseous effluents for their growth, mitigating these pollutants. The increase in the production of polysaccharides by microalgae can be achieved mainly through nutritional limitations, stressful conditions, and/or adverse conditions. These compounds are of commercial interest due to their biological and rheological properties, which allow their application in various sectors, such as pharmaceuticals and foods. Thus, to increase the productivity and competitiveness of microalgal polysaccharides with commercial hydrocolloids, the cultivation parameters and extraction/purification processes have been optimized. In this context, this review addresses an overview of the production, characterization, and potential applications of polysaccharides obtained by microalgae and cyanobacteria. Moreover, the main opportunities and challenges in relation to obtaining these compounds are highlighted. [ABSTRACT FROM AUTHOR]

Microalgae offer a promising source of biofuel and a wide array of high-value biomolecules. Large-scale cultivation of microalgae at low density poses a significant challenge in terms of water management. High-density microalgae cultivation, however, can be challenging due to biochemical changes associated with growth dynamics. Therefore, there is a need for a biomarker that can predict the optimum density for high biomass cultivation. A locally isolated microalga Cyanobacterium aponinum CCC734 was grown with optimized nitrogen and phosphorus in the ratio of 12:1 for sustained high biomass productivity. To understand density-associated bottlenecks secretome dynamics were monitored at biomass densities from 0.6 ± 0.1 to 7 ± 0.1 g/L (2 to 22 OD) in batch mode. Liquid chromatography coupled with mass spectrometry identified 880 exometabolites in the supernatant of C. aponinum CCC734. The PCA analysis showed similarity between exometabolite profiles at low (4 and 8 OD) and mid (12 and 16 OD), whereas distinctly separate at high biomass concentrations (20 and 22 OD). Ten exometabolites were selected based on their role in influencing growth and are specifically present at low, mid, and high biomass concentrations. Taking cues from secretome dynamics, 5.0 ± 0.5 g/L biomass concentration (16 OD) was optimal for C. aponinum CCC734 cultivation. Further validation was performed with a semi-turbidostat mode of cultivation for 29 days with a volumetric productivity of 1.0 ± 0.2 g/L/day. The secretomes-based footprinting tool is the first comprehensive growth study of exometabolite at the molecular level at variable biomass densities. This tool may be utilized in analyzing and directing microalgal cultivation strategies and reduction in overall operating costs. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel integrated recirculating aquaculture systems (RAS) using microalgae is suggested. • Microalgae decarbonate RAS by mitigating energy-demanding water treatment processes. • Microalgae provide O 2 and sequester CO 2 , boosting RAS efficiency and sustainability. • Phycoremediation mitigates the growth-inhibiting factors of fish in RAS. • Coupled hydrothermal liquefaction of fecal waste provides bioavailable nutrients. In recirculating aquaculture systems (RAS), waste management of nutrient-rich byproducts accounts for 30–50% of the whole production costs. Integrating microalgae into RAS offers complementary solutions for transforming waste streams into valuable co-products. This review aims to provide an overview of recent advances in microalgae application to enhance RAS performance and derive value from all waste streams by using RAS effluents as microalgal nutrient sources. Aquaculture solid waste can be converted by hydrothermal liquefaction (HTL), then the resultant aqueous phase of HTL can be used for microalgae cultivation. In addition, microalgae generate the required oxygen while sequestering carbon dioxide. The review suggests a novel integrated system focusing on oxygenation and carbon dioxide capture along with recent technological developments concerning efficient microalgae cultivation and nutrient recovery techniques. In such system, microalgae-based biorefineries provide environmentally-conscious and economically-viable pathways for enhanced RAS performance and conversion of effluents into high-value products. [ABSTRACT FROM AUTHOR]

Foodwaste leachate (FWL) is often generated during foodwaste treatment processes. Owing to its high nutrient content, FWL has high potential for phycoremediation, a microalgal technology application for water treatment while acting as CO2 fixation tank. Additionally, the end product of microalgal from phycoremediation can be potentially used for biodiesel production. Therefore, the phycoremediation has drawn a lot of attention in recent decades. This study evaluates the performance of microalgal foodwaste leachate treatment and the potential of utilizing FWL as medium for microalgal biodiesel production. Two microalgal species, Dunaliella tertiolecta and Cyanobacterium aponinum, were selected. For each species, two experimental levels of diluted FWL were used: 5 and 10% FWL. The partial inhibition growth model indicates that some inhibit factors such as ammonia; total suspended solids and oil and grease (O&G) content suppress the microalgal growth. Most of the nutrient such as nitrogen and phosphorus (> 80%) can be removed in the last day of phycoremediation by D. tertiolecta. C. aponinum also show considerable removal rate on total nitrogen ammonia and nitrate (> 60%). Biomass (0.4–0.5 g/L/day) of D. tertiolecta and C. aponinum can be produced though cultivated in diluted FWL. The bio-CO2 fixation rates of the two species were 610.7 and 578.3 mg/L/day of D. tertiolecta and C. aponinum. The strains contain high content of saturated fatty acid such as C16 and C18 making them having potential for producing good quality biodiesel. [ABSTRACT FROM AUTHOR]

Functionally uniform monocultures have remained the paradigm in microalgal cultivation despite the apparent challenges to avoid invasions by other microorganisms. A mixed microbial consortium approach has the potential to optimize and maintain biomass production despite of seasonal changes and to be more resilient toward contaminations. Here we present a 3-year outdoor production of mixed consortia of locally adapted microalgae and bacteria in cold temperate latitude. Microalgal consortia were cultivated in flat panel photobioreactors using brackish Baltic Sea water and CO2 from a cement factory (Degerhamn, Cementa AB, Heidelberg Cement Group) as a sustainable CO2 source. To evaluate the ability of the microbial consortia to maintain stable biomass production while exposed to seasonal changes in both light and temperature, we tracked changes in the microbial community using molecular methods (16S and 18S rDNA amplicon sequencing) and monitored the biomass production and quality (lipid, protein, and carbohydrate content) over 3 years. Despite changes in environmental conditions, the mixed consortia maintained stable biomass production by alternating between two different predominant green microalgae (Monoraphidium and Mychonastes) with complementary tolerance to temperature. The bacterial population was few taxa co-occured over time and the composition did not have any connection to the shifts in microalgal taxa. We propose that a locally adapted and mixed microalgal consortia, with complementary traits, can be useful for optimizing yield of commercial scale microalgal cultivation.

A dynamic coarse-grained model of microalgal growth considering light availability and temperature under discontinuous bioprocess operation was parameterized using experimental data from 15 batch cultivations of Nannochloropsis granulata in a pilot-scale tubular photobioreactor. The methodology applied consists of a consecutive two-step model parameter estimation using pooled, clustered and reorganized data to obtain initial estimates and multi-experiment fitting to obtain the final estimates, which are: maximum specific growth rate μmax = 1.56 d−1, specific photon half-saturation constant KS,ph = 1.89 molphgX-1d-1, specific photon maintenance coefficient mph = 0.346 molphgX-1d-1 and the cardinal temperatures Tmin = 2.3°C, Topt = 27.93°C and Tmax = 32.59°C. Biomass productivity prediction proved highly accurate, expressed by the mean absolute percent error MAPE = 7.2%. Model-based numerical optimization of biomass productivity for repeated discontinuous operation with respect to the process parameters cultivation cycle time, inoculation biomass concentration and temperature yielded productivity gains of up to 35%. This optimization points to best performance under continuous operation. The approach successfully applied here to small pilot-scale confirms an earlier one to lab-scale, indicating its transferability to larger scale tubular photobioreactors.

Dwindling fossil fuels, and the rise in energy demand have urged us to explore alternative renewable energy forms. An integrated process of dark fermentation and microalgal cultivation to deliver biofuels are gaining momentum in recent times. In this study, in the first stage, the starchy wastewater (SWW) with poultry manure (PM) was treated to produce a maximum hydrogen yield of 4.11 mol H2/Kg COD reduced to 5.03 mol H2/Kg COD reduced. The reutilization of soluble spent wash for the cultivation of Chlamydomonas reinhardtii yielded a biomass concentration of 1.45–1.02 g/L. The potentiality of algae to produce biodiesel was checked effectively, and it was reported that a biodiesel of 90.34 g/Kg Algal Biomass to 119.61 g/Kg Algal was yielded. The integration of the process enhanced the overall energy with an efficient removal of organic content. In conclusion, the valorisation of PM with SWW through dark fermentation and microalgal cultivation will open avenues to generate sustainable bioenergy forms. [ABSTRACT FROM AUTHOR]

Purpose: Microalgae present promising green economy applications in the energy and biorefinery sectors. The work concerns a pilot study on the integration of anaerobic digestion with microalgae cultivation for managing at the same time emissions and digestate from the dry anaerobic treatment of organic waste. Methods: Biogas produced was used to feed Solid Oxide Fuel Cell after a filtering step for removing toxic compounds. The exhausts and digestate were used for providing carbon and nutrients for microalgae growth. The experimental workflow includes the characterization of both for defining their suitability in the microalgal growth (Chlorella vulgaris) tests. Results: The exhausts of Solid Oxide Fuel Cells showed relatively stable concentration of CH4 (4–7%) and CO2 (93–96%) and low concentrations (sub ppm(v)) of sulphur, carbonyl and carboxyl, and aromatic compounds and terpenes, making it particularly suited for algae growing as compared with internal combustion engines. The challenging growing conditions are a compromise between carbon recovery and use of digestate. A good microalgae growth has been obtained (22.31 mm3 mL−1 of biovolume corresponding to 151 dry mg L−1 day−1) exploiting ammonia and phosphate from dilute digestate (removal efficiency 94% and 30% respectively) as well as a good carbon recovering (310 mg CO2 L−1 day−1). Conclusions: Based on our data, the integration of microalgae growth and anaerobic digestion process seems a viable solution to achieve (i) reduced emissions due to carbon recovery; (ii) optimum integrated management of anaerobic digestion waste and (iii) biomass production by low-cost nutrients and carbon. [ABSTRACT FROM AUTHOR]

The non-airtight digestion technology is emerging to be applied in the acidogenic phase for two-stage methane production. However, in this study, it was used to pretreat screened dairy manure (SDM) in order to provide microalgae cultivation with a substrate that might be more suitable for nutrient reduction, especially phosphorus. SDM was firstly underwent non-airtight digestion applying different dilution folds, i.e., blank (no dilution), 5-fold, 10-fold, and 15-fold. Total solids (TS), total dissolved solids (TDS), and chemical oxygen demand (COD) of the SDM were mostly reduced when there was no dilution applied. Five-fold dilution is the most beneficial one for ammonia reduction. Total phosphorus (TP) was reduced the most efficiently in the blank SDM. After the non-airtight digestion, 5-fold diluted original SDM, 5-fold diluted digested original SDM, and digested 5-fold diluted SDM were used to grow microalgae for 8 days. Microalgae grown in 5-fold diluted digested original SDM and digested 5-fold diluted SDM had better removal efficiencies in COD and NH4-N. From the monitoring of pH and TP during the 8-day culture period, it is found that pHs were peaked on the 4th day for microalgae grown in 5-fold diluted digested original SDM and digested 5-fold diluted SDM, corresponding to the maximal TP removal. Non-airtight digestion of SDM could help achieve better nutrient removal by microalgal cultivation in a shorter time span. [ABSTRACT FROM AUTHOR]

A number of dairies in southern Idaho employed stationary inclined screens to separate large solid particles out of liquid dairy manure. In this way, the total solid content of the liquid dairy manure can drop about 20%. Solids in dairy wastewater cause high turbidities, which could block the incident light, a key factor in the microalgae cultivation process using wastewaters as culture media. In this study, screened liquid dairy manure was used as the microalgae Chlorella vulgaris culture media. The aim was to optimize the dilution folds for the best growth of Chlorella vulgaris and nutrients' reduction with a special focus on phosphorus removal and recovery. Four folds of dilution, designated as 5*, 10*, 15*, 20*, were applied to the liquid dairy manure to alleviate hindrance of the high turbidity together with the high ammonium. Microalgal cultivation removed a significant amount of turbidity and major nutrients. For differently diluted liquid dairy manures, although the initial turbidities varied a lot, the final removal rates were not significantly different, falling in the range of 88.11–91.73%. Chemical oxygen demand (COD) in the 5-fold diluted liquid dairy manure dropped from 6700 to 1200 mg/L, corresponding to a removal rate of 79.81%. For the 10-fold, 15-fold, and 20-fold diluted manures, Chlorella removed around 67–69% of the initial CODs. Total Kjeldahl nitrogen (TKN) was removed at rates ranging from 70.84 to 73.99% from the four differently diluted liquid dairy manures without significant differences. NH4-N was removed most efficiently by 88.92% from the 20-fold diluted liquid dairy manure, and the least at 68.65% from the 5-fold diluted one. Although the original total phosphorus (TP) concentrations were distinctive for each group, the TP removal rates stayed in the range of 52.16 to 65.22%. Scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS) analysis of the precipitates harvested from the microalgal cultivation suggested possible phosphate precipitate forms. The chelation of Ca or Mg cations by dissolved organic matter (DOM) under alkaline conditions caused by microalgae cultivation could explain the unsatisfactory phosphorus removals observed in this study. [ABSTRACT FROM AUTHOR]

Conventional microalgal cultivation method relied on suspended growth or attached growth that uses inert solid surfaces, requiring the addition of external carbon sources to promote microalgal growth. The inert solid substrates for attached microalgae pose constraints on the maximal capabilities of these microorganisms as it does not possess the ability to provide the necessary nutritional support required for optimal microalgal growth. As a result, microalgae are obliged to only rely on the solid substrate as a means of attachment, without any further nutritional provisions. Slower growth rates, larger resource requirements, and exorbitant operating expenses had prompted the exploration of an alternative strategy, i.e; the innovative use of solid organic waste as nutritional source cum attachment platform. The findings of this review unveil key insights into microalgae cultivation system, offering a solution to economic challenges in the production phase. This innovation not only promotes economic feasibility and sustainability, but also contributes to economically viable and environmentally sustainable biofuel production. [Display omitted] • New breakthroughs for conventional attached microalgal cultivation system. • Intrinsic environmental and nutrient factors to spur attached microalgal growth. • Organic solid wastes exude nutrients for populating attached microalgal cells. [ABSTRACT FROM AUTHOR]

Contamination by the predatory zooplankton Poterioochromonas malhamensis is one of the major threats that causes catastrophic damage to commercial-scale microalgal cultivation. However, knowledge of how to manage predator contamination is limited. Previously, we established a phosphite (Pt)-based culture system by engineering Synechococcus elongatus, which exerted a competitive growth advantage against microbial contaminants that compete with phosphate source. Here, we examined whether Pt is effective in suppressing predator-type contamination. Co-culture experiment of Synechococcus with isolated P. malhamensis revealed that, although an addition of Pt at low concentrations up to 2.0 mM was not effective, increased dosage of Pt (~20 mM) resulted in the reduced grazing impact of P. malhamensis. By using unsterilized raw environmental water collected from rivers or ponds, we found that the suppression effect of Pt was dependent on the type of environmental water used. Eukaryotic microbial community analysis of the cultures using environmental water samples revealed that Paraphysomonas, a colorless Chrysophyceae, emerged and dominated under high-Pt conditions, suggesting that Paraphysomonas is insensitive to Pt compared to P. malhamensis. These findings may provide a clue for developing a strategy to reduce the impact of grazer contamination in commercial-scale microalgal cultivation.

Nannochloropsis is widely used in aquaculture as a feed source. However, large-scale cultivation of Nannochloropsis usually fails due to rotifer contamination. In order to identify an effective technique for reducing rotifer contamination, the effect of Brachionus plicatilis contamination on photosynthetic characteristics in Nannochloropsis oculata and the efficacy of the celangulin (CA):toosendanin (TSN) (1:9) combination for rotifer extermination were investigated using chlorophyll a fluorescence transient. B. plicatilis could directly devour microalgal cells and sharply reduced N. oculata density to very low levels. B. plicatilis also inhibited activities of PSII reaction centers, both acceptor and donor side, thereby damaging the photosynthetic performance of surviving N. oculata cells. However, the CA:TSN (1:9) combination could completely eliminate B. plicatilis, thereby preventing rotifers from devouring microalgae cells and protecting the photosynthetic performance of the surviving algal cells against rotifers damage. Therefore, the binary combination of CA:TSN (1:9), is considered to be a good candidate of botanical pesticide for controlling rotifer contamination. [ABSTRACT FROM AUTHOR]

The prospect of using constructed communities of microalgae in algal cultivation was confirmed in this study. Three different algal communities, constructed of diatoms (Diatom), green algae (Green), and cyanobacteria (Cyano), each mixed with a natural community of microalgae were cultivated in batch and semi‐continuous mode and fed CO2 or cement flue gas (12–15% CO2). Diatom had the highest growth rate but Green had the highest yield. Changes in the community composition occurred throughout the experiment. Green algae were the most competitive group, while filamentous cyanobacteria were outcompeted. Euglenoids, recruited from scarce species in the natural community became a large part of the biomass in semi‐steady state in all communities. High temporal and yield stability were demonstrated in all communities during semi‐steady state. Valuable products (lipids, proteins, and carbohydrates) comprised 61.5 ± 5% of ash‐free biomass and were similar for the three communities with lipids ranging 14–26% of dry mass (DM), proteins (15–28% DM) and carbohydrates (9–23% DM). Our results indicate that culture functions (stability, biomass quality) were maintained while dynamic changes occurred in community composition. We propose that a multispecies community approach can aid sustainability in microalgal cultivation, through complementary use of resources and higher culture stability. [ABSTRACT FROM AUTHOR]

Vampirovibrio chlorellavorus is an obligate, predatory bacterial pathogen of the genus Chlorella. It is recognized as an important pathogen of Chlorella sorokiniana, field isolate DOE 1412, a highly-favored microalga for cultivation in outdoor reactors in the arid USA Southwest for feedstocks used in biofuel production. To determine the V. chlorellavorus titer, based on gene copy number, required to cause infection and mortality of C. sorokiniana in an experimental outdoor reactor, a multiplexed quantitative polymerase chain reaction (qPCR) assay was developed for pathogen detection, based on the 16S and 18S ribosomal RNA gene of V. chlorellavorus and C. sorokiniana, respectively. The assay was further used to establish the optimal effective concentration of benzalkonium chloride required to achieve a below "disease-threshold"-bacterial titer, while minimizing biocidal effects on algal growth and enable economic biomass production. Reactors treated with 2.0 ppm benzalkonium chloride at four-day intervals throughout the cultivation cycle experienced runs of 22 days or longer, compared to 12 days for the untreated control. The qPCR assay was used to estimate disease severity over time using the Area Under the Disease Progress Stairs (AUDPS) metric, indicating a severity rating of 0.016 and 62.308 in biocide-treated and untreated cultures, respectively. The near-real time assay detected as few as 13 copies of V. chlorellavorus, allowing for the recognition of its presence in the reactor just before algal cell density decreased, an indication of pathogen attack, while also informing the timing of biocide applications to minimize DOE 1412 infection such that harvestable biomass could be produced. [ABSTRACT FROM AUTHOR]

Stress state of microalgal cells is caused under unfavorable conditions such as disordered light regime and depleted nitrogen. The stress state can impair photosynthetic efficiency, inhibit cell growth and result in the accumulation of triacylglycerol (TAG) from protective mechanisms. Continuous light or nitrogen starvation was applied on microalgae and performed effectively on inducing TAG production. To evaluate the light regime effect on inducing TAG production, the effect of different light regimes on nitrogen-starved Isochrysis zhangjiangensis was investigated in this work. The continuous light and nitrogen starvation elevated TAG content of biomass by 73% and 193%, respectively. Furthermore, the TAG accumulation of I. zhangjiangensis cell under nitrogen starvation decreased under aggravated stress from continuous illumination. Our results demonstrated that culturing the cells with 14L: 10D light regime under nitrogen starvation is the optimal mode to achieve maximal accumulation of TAG. A recovery in light regime was necessary for I. zhangjiangensis cultivation. [ABSTRACT FROM AUTHOR]

Microalgae are promising cell factories for producing value-added products. Large-scale microalgal cultivation suffers from invasion by contaminating microorganisms. Since most contaminating organisms cannot utilize phosphite as a unique phosphorus source, phosphite-utilizing ability may provide a growth advantage against contaminating organisms and solve this problem. Studies showed that microorganisms, typically unable to metabolize phosphite, can utilize phosphite by expressing exogenous phosphite dehydrogenase. Here, we constructed Cyanidioschyzon merolae strains introduced with the phosphite dehydrogenase gene, ptxD, from Ralstonia sp. 4506. The ptxD-introduced strains grew in a phosphite-dependent manner, with the phosphite-related growth rate almost matching that with phosphate as sole phosphorus source.

With the aim of identifying an effective and safe technique for reducing contamination by the ciliate, Stylonychia mytilus, in microalgal cultivation, the toxic effects of the natural triterpenoid toosendanin and ammonium bicarbonate on S. mytilus were studied. Toxicity tests showed that toosendanin and ammonium bicarbonate were highly toxic to S. mytilus, with 24 h LC50 values of 6.4 μg L−1 and 0.8 g L−1, respectively. The population density of S. mytilus decreased significantly when exposed to ≥ 2 μg L−1 toosendanin or ≥ 0.4 g L−1 ammonium bicarbonate. In addition, the S. mytilus control effects of toosendanin and ammonium bicarbonate and their safety in Chlorella pyrenoidosa were evaluated. It was found that ≤ 14 μg L−1 toosendanin had no obvious influence on photosynthesis and growth of C. pyrenoidosa and even increased the final cell density, with the highest being 12.3% over that of untreated cultures. Ammonium bicarbonate is the most widely used optimization technique for controlling contamination, but it has limited ability to reduce S. mytilus. Furthermore, ≥ 0.8 g L−1 ammonium bicarbonate inhibited photosynthesis and growth of C. pyrenoidosa, causing a 5.1% reduction in cell density or even a complete crop failure. Based on its high toxicity to S. mytilus and its relative safety to C. pyrenoidosa, together with its low commercial price and ecological acceptability, toosendanin is considered to be a good potential botanical pesticide for controlling S. mytilus contamination in microalgal mass cultivation. [ABSTRACT FROM AUTHOR]

Anaerobic digestion has emerged as the preferred treatment for organic fraction of municipal solid waste. Digestate management strategies are devised not only for safe disposal but also to increase the value and marketability. Regulations and standards for digestate management are framed to address the pollution concerns, conserve vulnerable zones, prevent communicable diseases, and to educate on digestate storage and applications. Regulations and the desired end uses are the main drivers for the enhancement of digestate through pretreatment, in vessel cleaning, and post-digestion treatment technologies for solid and liquid fractions of digestate. The current management practice involves utilization of digestate for land application either as fertilizer or soil improver. Prospects are bright for alternative usage such as microalgal cultivation, biofuel and bioethanol production. Presently, the focus of optimization of the anaerobic digestion process is directed only towards enhancing biogas yield, ignoring the quality of digestate produced. A paradigm shift is needed in the approach from 'biogas optimization' to 'integrated biogas–digestate optimization'. [ABSTRACT FROM AUTHOR]

Anaerobic digestion is an established technology to produce renewable energy as methane-rich biogas for which microalgae are a suitable substrate. Besides biogas production, anaerobic digestion of microalgae generates an effluent rich in nutrients, so-called digestate, that can be used as a growth medium for microalgal cultures, with the potential for a closed nutrient loop and sustainable bioenergy facility. In this study, the methane potential and nutrient mobilization of the microalga Scenedemus dimorphus was evaluated under continuous conditions. The suitability of using the digestate as culture medium was also evaluated. The results show that S. dimorphus is a suitable substrate for anaerobic digestion with an average methane yield of 199 mL g −1 VS. The low level of phosphorus in digestate did not limit algae growth when used as culture medium. The potential of liquid digestate as a superior culture medium rather than inorganic medium was demonstrated. [ABSTRACT FROM AUTHOR]

Light is the most important factor involved in the growth of photosynthetic organisms, and low efficiency of artificial light systems imposes higher cultivation costs. Phosphorescent paints can emit light for a few hours, and so may be appropriate to accumulate scattered light. In this study, the effects of blue and green phosphorescent paints on growth rate, biomass production and chlorophyll content of three different microalgae, Scenedesmus dimorphus, Chlamydomonas reinhardtii and Chlorella vulgaris were investigated. These strains were cultivated in broth medium in three glass bowls. Half of the first two bowls was stained with blue or green phosphorescent paints (B and G treatment), while the third one was unstained and used as the control (C treatment). All measured parameters were higher in B. The results indicate that partial staining of culturing bowls by blue phosphorescent paint can be an economic approach to increase light efficiency in cultivating microalgae. [ABSTRACT FROM AUTHOR]

To improve the antifouling (AF) properties of photobioreactors (PBR) for microalgal cultivation, using trihydroxymethyl aminomethane (tris) as the linking agent, a series of polyethylene (PE) films grafted with sulfobetaine (PE-SBMA) with grafting density ranging from 23.11 to 112 μg cm−2were prepared through surface-initiated atom transfer radical polymerization (SI-ATRP). It was found that the contact angle of PE-SBMA films decreased with the increase in the grafting density. When the grafting density was 101.33 μg cm−2, it reached 67.27°. Compared with the PE film, the adsorption of protein on the PE-SBMA film decreased by 79.84% and the total weight of solid and absorbed microalgae decreased by 54.58 and 81.69%, respectively. Moreover, the transmittance of PE-SBMA film recovered to 86.03% of the initial value after cleaning, while that of the PE film recovered to only 47.27%. The results demonstrate that the AF properties of PE films were greatly improved on polySBMA-grafted surfaces. [ABSTRACT FROM PUBLISHER]

Functional genomics of microalgae have undergone tremendous progress and have a huge impact for streamlining the algal cultivation technology; however, the rational utilization of algal genomes for discovering the strategies to combat algal culture contamination remain unexplored. Genome comparison of fungi and microalgae allowed us to find insights into the possible distinctions of key enzymes and genetic structural of sterol biosynthetic pathway, which are the targets for commercial fungicides. By further screening and characterizing chemical inhibitors targeting selected sterol biosynthetic enzymes, a species-specific contamination control method tailored to oleaginous Nannochloropsis oceanica has been developed. With a concentration of as low as 1 μg/ml, triticonazole, a sterol 14-demethylase inhibitor, was capable of effectively eliminating contaminated fungi and potential invasive algal strains, and able to stimulate the growth of desired microalgal species. These findings suggest that the crossing kingdom genome comparison helps to identify genetic distinctions which can be utilized to select appropriate and customized microbial contamination control approach for culturing individual microalgal species with desired production traits. [ABSTRACT FROM AUTHOR]

In response to the energy crisis, global warming and climate changes, microalgae have received increasingly global attention as a renewable, alternative and sustainable source for the production of biodiesel. Much original research regarding microalgal biodiesel production has been reported. However, microalgal biodiesel faces plenty of challenges that current cultivation and biodiesel conversion is economically unfeasible for industrial applications on a large scale. This perspective paper first briefly discusses the latest advances in liquid transportation biodiesel production from microalgal biomass, including microalgal growth, biomass harvesting and drying, lipid extraction and biodiesel conversion. Subsequently, strategies for the future development of microalgal biodiesel have been proposed and discussed, in an attempt to reduce the cost gap. From the microalgal biodiesel production chain perspective, genetic and metabolic engineering, isolation of suitable species, high-efficiency bioreactor development, efficient culturing system development, optimal harvest process design, high-efficiency lipid extraction and transesterification method development will have critical roles to play. It is worthy of note that the increase of the outcome credits can also realize the reduction of the economic gap, and the main measures include appropriate glycerol recovery and reutilization, integration with wastewater treatment and CO 2 mitigation together with microalgal biorefinery for the production of multiple co-products with high values. Finally, concluding remarks are put forward. [ABSTRACT FROM AUTHOR]

Galdieria sulphuraria 074G (Rhodophyta) was grown heterotrophically in defined medium and on amylolytic and proteolytic hydrolysed food waste from restaurants and bakeries. Substrate uptake, growth, and phycocyanin content were quantified in the cultures. The alga utilised carbohydrates and amino acids from the waste but ammonium and other inorganic nutrients were needed to stimulate phycocyanin synthesis. Highest specific phycocyanin contents (20–22 mg g −1 ) were observed in cells grown at 25 °C or 34 °C on the food wastes. Growth inhibition was observed when the hydrolysates were used in quantities resulting in glucose concentrations of 10 and 50 g L −1 for bakery and restaurant waste, respectively. Still, G. sulphuraria 074G grew and produced phycocyanin efficiently on food waste under adequate conditions and may potentially be utilised for synthesise of high-valuable products from food waste. [ABSTRACT FROM AUTHOR]

The ability of phototrophs to colonise different environments relies on robust protection against oxidative stress, a critical requirement for the successful evolutionary transition from water to land. Photosynthetic organisms have developed numerous strategies to adapt their photosynthetic apparatus to changing light conditions in order to optimise their photosynthetic yield, which is crucial for life on Earth to exist. Photosynthetic acclimation is an excellent example of the complexity of biological systems, where highly diverse processes, ranging from electron excitation over protein protonation to enzymatic processes coupling ion gradients with biosynthetic activity, interact on drastically different timescales from picoseconds to hours. Efficient functioning of the photosynthetic apparatus and its protection is paramount for efficient downstream processes, including metabolism and growth. Modern experimental techniques can be successfully integrated with theoretical and mathematical models to promote our understanding of underlying mechanisms and principles. This review aims to provide a retrospective analysis of multidisciplinary photosynthetic acclimation research carried out by members of the Marie Curie Initial Training Project, AccliPhot, placing the results in a wider context. The review also highlights the applicability of photosynthetic organisms for industry, particularly with regards to the cultivation of microalgae. It intends to demonstrate how theoretical concepts can successfully complement experimental studies broadening our knowledge of common principles in acclimation processes in photosynthetic organisms, as well as in the field of applied microalgal biotechnology. [ABSTRACT FROM AUTHOR]

This report constitutes the effect of microbial contaminants on the cultivation practices of microalgae. Its goal is the description of the types of microbial contaminants and extent of losses caused by them during the cultivation of microalgae at different levels. Systematic procedures to search, review and organize literature and to collect the necessary data were followed. Initially, a total of 1470 articles were gathered from three data base with the ultimate retention of 94 articles for data gathering. The data was analysed first through meta-analysis using the metafor package in R- software to estimate the effect-sizes. The Mean Difference approach together with the random effects model with tau squared estimator of DL (Der Simonian-Laird estimator) were chosen as they were more pertinent to the current data structure. Then, descriptive statistics using excel spreadsheet was used to characterize the type and percentage of losses encountered as a result of contamination. The most frequently cultivated microalgae were Chlorella spp., Scenedesmus spp. and Nannochloropsis spp. The results highlighted a significant amount of losses caused by microbial contamination during cultivation of microalgae at laboratory, photobioreactor and open-pond levels. Significant losses were quantified by 70 % loss of microalgal cell density, 56 % of chlorophyll content and 28 % of lipid content for open-pond cultivation systems, where, the loss is pronounced as ponds are more susceptible to microbial contamination. On the other hand, the loss in pigments were more pronounced in photobioreactors owing to their closed nature, and hence lack of exposure to direct natural sunlight irradiation. Thus, efforts in designing photobioreactors towards improving the prevention of contamination and enhancement of the illumination system might be a promising avenue for microalgal cultivation practices. Regarding the types of microbial contaminants, bacteria were by far the most frequently encountered contaminating agents followed by protozoa. The most frequent bacterial contaminants included Pseudomonas spp., Vampirovibrio chlorellavorus , Flavobacterium spp., Escherichia coli , Proteobacteria spp., • Residual maximum likelihood meta-analysis model described the variability in biocontamination. • Bacteria followed by protozoa were the most frequently reported bio contaminants • Production losses were more pronounced in open ponds than in photobioreactors [ABSTRACT FROM AUTHOR]

Polyhydroxyalkanoates (PHAs) are promising alternatives that accumulate as energy and carbon storage material in various microorganisms, including bacteria and microalgae, being biodegradable and suitable for a wide variety of applications. Among these compounds, the most prevalent and well-characterized biopolymer is polyhydroxybutyrate (PHB), which belongs to the short-chain PHAs. The present study was designed to evaluate algae-based PHB production in two Chlorophyta (Desmodesmus communis and Chlorella vulgaris) under a two-phase nutritional mode of cultivation, namely a phototrophic growth phase (PGP) and a mixotrophic stress phase (MSP) with N,P-depleted media and organic carbon supply (i.e., glucose or sodium acetate, NaOAc). The highest PHB productivity (0.11 g PHB/g biomass/d; 0.015 g PHB/L/d), corresponding to 32.1 % w/w of intracellular PHB, was observed for D. communis after 3 days of cultivation under mixotrophic conditions in batch cultures (e.g., low light, phosphorus-free medium, 1 g/L of NaOAc). A scaled-up cultivation (10 L) was set up to evaluate for the first time PHB yields and biomass composition in a semi-continuous system. A PHB content of 34 % w/w was achieved on day 8, corresponding to a maximum PHB productivity of 0.10 g PHB/g biomass/d (or 0.011 g PHB/L/d), which increased up to 54 % w/w on day 15. The biomass was composed of about 30 % w/w proteins, 6 % w/w polysaccharides, and 11 % w/w lipids, which can be valorised from a biorefinery perspective. The scaled-up D. communis cultivation in 10 L PBRs confirmed the potential utilization of this algal species for PHB production with productivity up to 2-times higher than those reported for several cyanobacterial species and similar to the maximum value obtained with batch cultures in previous works performed with Scenedesmaceae. • Desmodesmus communis resulted able to produce PHB under mixotrophic conditions. • D. communis cultivation gave a PHB productivity up to 0.11 g PHB/g biomass/d. • A semi-continuous cultivation for PHB production in Chlorophyta yielded up to 50 % (w/w). • The algal biomass resulted exploitable also for proteins valorisation. [ABSTRACT FROM AUTHOR]

The microalgal species Chlorella pyrenoidosa was cultivated in synthetic wastewater of initial chemical oxygen demand (COD), nitrate, and phosphate concentrations of 5000, 100, and 40 mg/L, respectively. The aim of the study was to find out the tolerance of microalgae to different COD concentrations and the extent of COD degradation at those concentrations. Three dilutions of wastewater (initial COD concentrations 5000, 3000, and 1000 mg/L) and three inoculum sizes (0.1, 0.2, and 0.3 g/L) were considered for the study. The experimental parameters such as total organic carbon, total inorganic carbon, COD, optical density, total solids, nitrate, and phosphate were measured on a daily basis. Biodegradation kinetics was determined for all cases using first-order reaction and Monod degradation equations. Optimal results showed that up to 90% reduction in TOC was obtained for 1000 COD wastewater while only 38% reduction in total organic carbon (TOC) was achieved for 5000 COD wastewater. Over 95% reduction in nitrate and nearly 90% removal of phosphate were obtained with the lowest microalgal inoculum concentration (i.e., 0.1 g/L) for all COD dilutions. This study showed that microalgal species C. pyrenoidosa can successfully degrade the organic carbon source (i.e., acetate) with significant removal efficiencies for nitrate and phosphate. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO) gas is a major carbon source for microalgal cultivation. It is usually sparged into photobioreactors in the form of bubbles. The behaviour of the bubbles significantly affects mass transfer, distribution and microalgae growth. In this study, the dynamic behaviour of the CO bubbles was compared between a microalgal suspension and pure water. These investigations were carried out via visual methods. The movement and distribution of microalgae at the gas-liquid interface were observed. The effects of gas flow velocity, CO concentration and capillary orifice size were analysed. The results indicated that much of the microalgal cells adsorbed onto the surface of the CO bubbles in the microalgal suspension, when compared with that in pure water. This resulted in an easier detachment of the bubbles in the microalgal suspension. The growth status of the bubbles were divided into two states according to changes in the Eötvös number and the behaviour of the CO bubbles as influenced by gas flow velocity: steady and unsteady state. The critical gas velocity between the two states was achieved. The CO bubble rising trajectory can be divided into three main phases: the vertical acceleration phase, the transition phase, and the oscillatory rising phase. During the oscillatory rising phase, the amplitude of the bubble rising trajectory was approximately two times greater than the bubble diameter. In addition, the wavelength of the bubble rising trajectory was approximately 16-18 times the bubble diameter in the microalgal suspension. A smaller capillary orifice size and larger CO concentration led to a decrease in the bubble detachment diameter, an increase in velocity and an enlargement in the zone of bubble influence in the horizontal direction. These are advantageous for CO transportation. These findings are beneficial for optimizing the design and operation of microalgal photobioreactors. [ABSTRACT FROM AUTHOR]

Sustainable microalgal cultivation at commercial scale requires nitrogen recycling. This study applied hydrothermal carbonization to recover N of hot-water extracted Arthrospira platensis biomass residue into aqueous phase (AP) under different operation conditions and evaluated the N utilization, biomass yield and quality of A. platensis cultures using AP as the sole N source. With the increase of temperature at 190–210 °C or reaction time of 2–3 h, the N recovery rate decreased under nitrogen-repletion (+N) cultivation, while contrarily increased under nitrogen-limitation (−N) cultivation. Under +N biomass accumulation in the cultures with AP under 190 °C was enhanced by 41–67% compared with that in NaNO 3 , and the highest protein content of 51.5%DW achieved under 200 °C-2 h was also 22% higher. Carbohydrate content of 71.4%DW under −N cultivation achieved under 210 °C-3 h was 14% higher than that in NaNO 3 . HTC-algal cultivation strategy under −N mode could save 60% of conventional N. [ABSTRACT FROM AUTHOR]

Nowadays, microalgae-based bioenergy has been commonly considered as a potential substitute of the non-renewable traditional energy resources with increasing attention. Nevertheless, microalgal cells will secrete/release some Soluble Algal Products (SAPs) into the culture medium during microalgal biomass cultivation. Studies on the influences, especially the negative ones, of SAPs in large-scale cultivation of microalgae for biomass/bioenergy production remain limited. The negative effects, properties, production and treatments of SAPs were therefore investigated and summarized in this paper. It was found that SAPs may inhibit microalgal growth, raise the cost of microalgal recovery and lower the performance of the downstream discharged water treatment process after microalgal cultivation, among others. The production of SAPs could be as high as 70 mg/L in terms of dissolved organic carbon (DOC), causing substantial environmental issues. The chemical properties of SAPs significantly varied among different microalgal species, growth phases and nutrient concentrations. The distribution of molecular weight of SAPs varied from less than 1 kDa to more than 100 kDa, meanwhile the hydrophilic/hydrophobic property of SAPs showed a consistency. All studies showed that more than 60% of SAPs are hydrophilic. After comparing three different SAPs treatment methods, it was concluded that biodegradation could be a feasible and economical process to remove SAPs based on the properties of SAPs. The mechanisms of SAPs formation and the mitigation of their undesirable effects are still not clear. Therefore, a systematic and deep study on those topics is urgently needed. [ABSTRACT FROM AUTHOR]