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The cheese industry produces substantial amounts of raw cheese whey wastewater (RW), which requires effective treatment prior to environmental disposal. This study presents an innovative sequential batch system that combines macrophyte and microalgal cultivation for RW remediation. The efficacy of Lemna minor MO23 in first-line photobioreactors (PBR-1) and Chlorella sp. MC18 (CH) or Scenedesmus sp. MJ23-R (SC) in second-line photobioreactors (PBR-2) for pollutant removal was evaluated. The nutrient removal capacity of L. minor, CH, and SC was assessed at optimal tolerance concentrations, alongside nutrient recovery from treated RW (TRW) by PBR-1 for microalgae biomass production. The results demonstrate that all three species effectively purified the cheese whey wastewater. L. minor efficiently removed COD, nitrate, phosphate, and sulfate from RW, producing TRW effluent suitable for microalgal growth. CH and SC further purified TRW, enhancing biomass production. CH outperformed SC with a 4.79% higher maximum specific growth rate and 20.95% higher biomass yield. Biochemical analyses revealed the potential of CH and SC biomass for applications such as biofuels and aquaculture. After treatment, the physicochemical parameters of the effluent were within the regulatory limits. This demonstrates that the PBR-1 and PBR-2 series-coupled system effectively purifies and recovers dairy effluents while complying with discharge standards. [ABSTRACT FROM AUTHOR]

The attached microalgal–bacterial consortium (microalgae–bacteria biofilm, MBBF) has been increasingly recognized in wastewater treatment for its superior pollutant removal efficiency, resilience to toxic substances, and improved harvesting performance. This review initially discusses the advantages of MBBFs compared to activated sludge and suspended microalgal–bacterial consortia. These advantages stem from the coexistence of pollutant removal pathways for the bacteria and microalgae in MBBFs, as well as the synergistic interactions between the microalgae and bacteria that enhance pollutant removal and resilience capabilities. Subsequently, the establishment of the MBBF system is emphasized, covering the establishment process, influencing factors of MBBF formation, and the utilization of photobioreactors. Lastly, the challenges associated with implementing MBBFs in wastewater treatment are deliberated. This study aims to present a detailed and comprehensive overview of the application of MBBFs for wastewater treatment and biomass production. [ABSTRACT FROM AUTHOR]

This study aims to reveal how height/diameter ratio of column photobioreactors affect the growth and lipid content of microalgae. For this purpose, Chlorella variabilis cells were grown in aerated column photobioreactors with height/diameter ratio of 1, 2, and 3 in defined (BG11) culture medium. Results obtained showed that maximum microalgae biomass concentration, cell productivity, cell doubling time, and lipid productivity were found to increase as the height/diameter of photobioreactor increased. After 15 days of cultivation, the highest cell productivity (0.139 gdw/L.day), cell lipid content (21.1%) and lipid productivity (29.33 mg/L.day) were obtained in the photobioreactor with the highest height/diameter ratio (3), whereas the highest specific growth rate (0.045 h-1) was obtained in the photobioreactor with the smallest height/diameter ratio (1). These findings contribute to the knowledge on photobioreactor design and pave way for more efficient use of column type photobioreactors in producing microalgae. [ABSTRACT FROM AUTHOR]

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The presented Fibonacci-type tubular photobioreactor represents a significant advancement over classical tubular photobioreactors. It exhibits notable flexibility in its geometric design with the ability to adapt its parameters to meet the specific photosynthetic requirements of microalgae, thereby achieving maximum efficiency. As a result, it emerges as a viable alternative to conventional tubular systems. Furthermore, the strategy utilized for optimizing the design of Fibonacci-type photobioreactors is also described. This strategy is applied to design a 5000 L reactor, serving as a potential approach to harnessing these reactors for the industrialscale production of high-value microalgae with commercial significance. [ABSTRACT FROM AUTHOR]

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

This review paper provides an overview of various types of photobioreactors (PBRs) that could be used for the production of polyhydroxyalkanoates (PHAs) using anoxygenic photoheterotrophs, with a focus on the design and operation of these systems. The paper highlights the potential of different PBRs based on reactor geometry and growth mode, and also examines the advantages and disadvantages of each PBR type and summarizes their suitability for PNSB-PHA production. The optimization of reactor design and operation is crucial for maximizing PNSB growth and PHA productivity. The self-immobilization of bacteria in granular sludge is a promising technology for wastewater treatment and the production of PHAs, while grooved-surface PBRs and porous-substrate PBRs have limitations due to difficult biomass harvesting in the former and the presence of aerobic conditions incongruent with PNSB culturing in the latter. Limitations exist with all solutions for maximizing rapid growth and maintaining high biomass concentrations due to the requirements of phototrophic growth. [ABSTRACT FROM AUTHOR]

In this research work, the performance of a Fibonacci-type photobioreactor scaled to 2500L to produce Chlorella sp.. is presented. The results show that this photobioreactor design kept the Chlorella culture at its optimal temperature, pH and dissolved oxygen levels. Despite the fact of being a closed reactor, the temperature was kept below 30 °C while the dissolved oxygen was maintained below 200 % Sat. under outdoor conditions at which the mean daily solar radiation ranged from 139 to 450 µE/m2s. Under these conditions, a maximum specific growth rate of 0.31 day−1, a biomass concentration of 1.9 g/L, and volumetric biomass productivity of 0.37 g/L day were achieved. The Fibonacci-type tubular photobioreactor presented here offers substantial advances compared to classic tubular photobioreactors, as it has proven to be flexible in its geometric design and it can adapt its parameters to the photosynthetic needs of the microalgae to ensure maximum efficiency, thus making it an alternative to conventional tubular systems. In addition, it is feasible to consider industrial production, since its costs have been estimated as 27.4 €/kg, at an annual production scale of 37 tons. Fibonacci-type photobioreactor. [Display omitted] • The performance of Fibonacci-type photobioreactors was demonstrated at a 2500L scale. • Fibonacci-type photobioreactors allow dissolved oxygen below 200 %Sat while controlling pH and temperature. • The V/S ratio is the key factor to scale-up Fibonacci-type photobioreactors. • The proposed technology allows producing high-quality biomass at a moderate cost. [ABSTRACT FROM AUTHOR]

Microalgal biomass is a promising alternative and renewable substrate for bioenergy production. The main problem for its commercial application is to obtain and keep a high level of production by providing microalgae with appropriate conditions for growth. The aim of this study was to determine optimal culture conditions such as temperature, photoperiod, and pH. The amount of biomass by gravimetry, optical density by spectrophotometry, and productivity were analyzed. Suitable values of cultivation parameters allowed for the increased growth and biomass productivity of Arthrospira platensis (4.24 g·L−1), Chlamydomonas reinchardtii (1.19 g·L−1), Chlorella vulgaris (2.37 g·L−1), and Dunaliella salina (4.50 g·L−1) and optical density for Ch. reinchardtii and C. vulgaris. These species had maximum biomass productivity of 0.72, 0.12, 0.36, and 0.77 g·L−1·d−1, respectively. Productivity was determined by cultivation temperature and for Ch. reinchardtii also by pH. [ABSTRACT FROM AUTHOR]

One of the main factors affecting hydrogen production and growth of photofermentative microorganisms is light; low light penetration and utilization are significant bottlenecks in photofermentative hydrogen production systems. In this study, light distribution in a thermosiphon photobioreactor operated with Rhodopseudomonas palustris was investigated. Radiation fields were modelled and simulated using computational fluid dynamics (ANSYS® Fluent, 2019 R2) and a reflector system was evaluated for the enhancement of light distribution in a thermosiphon photobioreactor. The effect of the reflector system was investigated experimentally in terms of hydrogen production, carbon substrate consumption and biomass circulation in the reactor. With the addition of the reflector system, hydrogen production was increased by 48% while glycerol consumption was increased from approximately 24% to 32%. After 336 h, the concentration of R. palustris cells still in suspension ranged from 0.13 to 0.18 g∙L−1, with no discernible difference in concentration between the systems with and without reflectors. Collectively, the reflector system was shown to be a viable option in enhancing light distribution in photobioreactors, with an associated increase in both hydrogen production as well as glycerol consumption. • Computational fluid dynamics can be used to model light in photobioreactors. • Reflectors can be used as a light distribution strategy in photobioreactors. • Reflectors can increase R. palustris hydrogen production and glycerol consumption. • Productivity of a thermosiphon photobioreactor can be increased with reflectors. [ABSTRACT FROM AUTHOR]

The biological treatment of source-separated human urine to produce biofuel, nutraceutical, and high-value chemicals is getting increasing attention. Especially, photoautotrophic microalgae can use human urine as media to achieve environmentally and economically viable large-scale cultivation. This review presents a comprehensive overview of the up-to-date advancements in microalgae cultivation employing urine in photobioreactors (PBRs). The standard matrices describing algal growth and nutrient removal/recovery have been summarized to provide a platform for fair comparison among different studies. Specific consideration has been given to the critical operating factors to understand how the PBRs should be maintained to achieve high efficiencies. Finally, we discuss the perspectives that emphasize the impacts of co-existing bacteria, contamination by human metabolites, and genetic engineering on the practical microalgal biomass production in urine. [ABSTRACT FROM AUTHOR]

Carbon dioxide production due to fossil fuels and their effects on global warming has prompted researchers to find ways to reduce and fix it. There are various biological and chemical methods to remove these contaminants. Using microalgae is one of the leading methods to absorbing carbon dioxide. During this process, microalgae absorb carbon dioxide in photobioreactors and convert it into biomass eventually. This study investigated bubble size, gas velocity, and photobioreactor structure as effective parameters on CO2 fixation for removing carbon dioxide by microalgae. Increasing CO2 concentration is inversely related to bubble growth, and it is due to the concentration gradient between the bubble and the microalgae suspension. Also, by examining the dimensions of the photobioreactor, we can obtain information about the dynamics of the bubble. The dimensions of the photobioreactor and the operating conditions of the process have an interaction. For example, whatever the H/D ratio is high, the gas velocity is more significant on bubble size. The result of examining the effect of bubble velocity on the volumetric mass transfer coefficient shows that the concentration of liquid and gas contact decreases with increasing bubble velocity and vice versa. Also, when the gas flow is higher, the bubbles grow faster and the contact time is shorter, and bubbles tend to grow in the vertical direction. To complete the previous research in this study, which focuses on mass transfer in the process of biological absorption of carbon dioxide, the bubble behavior of the suspension in microalgae is investigated. [ABSTRACT FROM AUTHOR]

In this experimental study, a novel cultivation mode in a conical annular photobioreactor (CAPBR) was proposed to enhance microalgae biomass production of Arthrospira platensis. Three operating factors under varying conditions of initial inoculum concentration (0.25-1.25 g.L-1), light intensity (6-180 µmols-1m-2) and surface/volume (S/V) ratios (94-112 m-1) were optimized. Box-Behnken design combining with response surface methodology was used to evaluate the effect of operating parameters on response variables (Volumetric productivity, Growth rate). Optimal parameters of the chosen variable were found by considering the quadratic model, as well as by evaluating the desirability function. The obtained results showed that the light intensity and S/V ratio were the most significant factors conditioning volumetric productivity and growth rate. Moreover, an important interaction between light intensity and S/V ratio (P < 0.05) on volumetric productivity and growth rate was reported. The maximum volumetric productivity and growth rate of 542 mgL-1day-1, 0.785 day-1 respectively was obtained at 180 µmols-1m-2, with inoculum concentration of 0.351 g.L-1 and S/V ratio of 112 m-1. According to ANOVA analysis, this model reasonably predicts match the experimental data. [ABSTRACT FROM AUTHOR]

This scientometric review and bibliometric analysis aimed to characterize trends in scientific research related to algae, photobioreactors and astaxanthin. Scientific articles published between 1995 and 2020 in the Web of Science and Scopus bibliographic databases were analyzed. The article presents the number of scientific articles in particular years and according to the publication type (e.g., articles, reviews and books). The most productive authors were selected in terms of the number of publications, the number of citations, the impact factor, affiliated research units and individual countries. Based on the number of keyword occurrences and a content analysis of 367 publications, seven leading areas of scientific interest (clusters) were identified: (1) techno-economic profitability of biofuels, bioenergy and pigment production in microalgae biorefineries, (2) the impact of the construction of photobioreactors and process parameters on the efficiency of microalgae cultivation, (3) strategies for increasing the amount of obtained lipids and obtaining biodiesel in Chlorella microalgae cultivation, (4) the production of astaxanthin on an industrial scale using Haematococcus microalgae, (5) the productivity of biomass and the use of alternative carbon sources in microalgae culture, (6) the effect of light and carbon dioxide conversion on biomass yield and (7) heterotrophy. Analysis revealed that topics closely related to bioenergy production and biofuels played a dominant role in scientific research. This publication indicates the directions and topics for future scientific research that should be carried out to successfully implement economically viable technology based on microalgae on an industrial scale. [ABSTRACT FROM AUTHOR]

The development of tools to predict the photobioreactors' (PBRs) productivity is a significant concern in biotechnology. To this end, it is required to know the light availability inside the cultivation unit and combine this information with a suitable kinetic expression that links the distribution of radiant energy with the cell growth rate. In a previous study, we presented and validated a methodology for assessing the radiative properties necessary to address the light distribution inside a PBR for varying illuminating conditions through the cultivation process of a phototrophic microorganism. Here, we sought to utilise this information to construct a predictive tool to estimate the productivity of an autotrophic bioprocess carried out in a 100 [L] tubular photobioreactor (TPBR). Firstly, the time-dependent optical properties over ten batch cultures of L. platensis were calculated. Secondly, the local volumetric rate of photon absorption was assessed based on a physical model of the interaction of the radiant energy with the suspended biomass, together with a Monte Carlo simulation algorithm. Lastly, a kinetic expression valid for low illumination conditions has been utilised to reproduce all the cultures' experimentally obtained dry weight biomass concentration values. Taken together, time-dependent radiative properties and the kinetic model produced a valuable tool for the study and scaling up of TPBRs. [ABSTRACT FROM AUTHOR]

Haematococcus pluvialis is a microalga of biotechnological interest due to its ability to produce astaxanthin, a carotenoid that is used as a pigment and a bioactive compound. It has applications in the pharmaceutical, cosmetic, nutraceutical, food, and aquaculture industries. This carotenoid is obtained when the microalgae is subjected to stress conditions such as light intensity, light color, nutrient deficiency, and salinity, and involves the use of photobioreactors (PBR). For this reason, this article is intended to show the type of PBR that has been used in its scaling and the related kinetic parameters that influence the performance of the process. PBRs facilitate the adjustment and control of the cultivation conditions, both in the green phase and in the red phase. Likewise, the use of the kinetic scaling parameters allows evaluating the process, thus, establishing the conditions that must be adjusted, to improve the cultivation of the microalgae and obtaining astaxanthin. The kinetic scaling parameters reviewed were biomass (cel/mL), biomass productivity (g/Lday), specific growth rate (µ/day), doubling time (day), astaxanthin content (mg/g) and its productivity. Thus, the technological feasibility of photobioreactors for the scaling of microalgae to produce astaxanthin is demonstrated. The most commonly used PBRs are tubular and cylindrical because they have a greater illumination surface and efficiency in light distribution, and because they report higher astaxanthin productivity; its downside may be the costs for their cleaning. [ABSTRACT FROM AUTHOR]

The freshwater green microalgae, Dictyosphaerium chlorelloides (CCALA 330), has the ability to produce extracellular polysaccharides (EPS). Conditions for optimum growth and EPS overproduction were determined in laboratory-scale tubular photobioreactors (PBR) with a working volume of 300 mL. Multiple limitations in nutrient supply were proven to be an effective method for EPS overproduction. Salinity stress was also applied to the culture, but no significant increase in EPS production was observed. The effects of different nitrogen sources were examined and the microalgae exhibited the fastest growth and EPS production in medium containing ammonium nitrate. Under determined optimal conditions, EPS concentration reached 10 g/L (71% of the total biomass) and a total biomass of 14 g/L at the end of 17 days cultivation. Pilot-scale cultivation was also carried out in a column type airlift photobioreactor (PBR) with a working volume of 60 L. A new and efficient methodology was developed for separating cells from the EPS-containing culture broth. Due to the strong attachment between cells and EPS, high-pressure homogenization was carried out before a centrifugation process. The EPS in the supernatant was subsequently purified using ultrafiltration. The green microalgae Dictyosphaerium chlorelloides may therefore be appropriate for the commercial production of EPS. [ABSTRACT FROM AUTHOR]

In recent years, researchers have been actively attempting to integrate biological materials into static building envelope systems. One promising approach is the integration of flat panel photobioreactors into building envelope systems and the BIQ (Bio-Intelligent Quotient) house is the state-of-the-art case building; however, the additional costs for glazing systems to contain photobioreactors, complexity of controlling cultures for microalgae growth, and difficulty of providing indoor environmental quality have kept flat panel photobioreactor systems from being applied widely. If we are able to bring about pleasant physical comforts for occupants through the use of shading devices capable of functioning as the photobioreactors, we can not only grow microalgae but also use less operational energy input to provide better IEQ for occupants. To this end, this study has explored a way to optimize the physical and functional properties of photobioreactor (for Chlorella sp.)-integrated shading devices (specifically vertical louvers). To find the optimal shape for static vertical louvers to be positioned on the west-facing facade, parametric design studies were conducted. To find the optimal vertical louver geometry among numerous alternatives, computer simulations were conducted in terms of three performance criteria (thermal balance by solar radiation, Daylight Autonomy, and microalgae growth rate) and an optimal option was found with the genetic algorithm optimization solver. To ensure reliability of the computer simulation (including numerical model) results, a series of experiments was conducted under the analogous climatic conditions; the computer simulation results were validated with the experimental data. When it comes to hourly indoor illuminance performance, the error between experimental data and computer simulation results was within a range of 5-20%; for average microalgae growth rate, the error was up to 19.9%. Despite the relatively high error between the simulation results and measurements, considering ever-changing light intensity conditions in our measurement compared to that of the computer simulation, it was justifiable to utilize the computer simulation results for the current parametric design study. Finally, the biofuel energy production from the proposed static envelope system was estimated to be 16.5 kWh/m²yr, which is smaller than the state-of-the-art annual biofuel energy production (30.0 kWh/m²yr) from the BIQ house. Nevertheless, the results are promising, given that we used the worst cultivation conditions for the microalgae in the current study. [ABSTRACT FROM AUTHOR]

Computational Fluid Dynamics (CFD) have been frequently applied to model the growth conditions in photobioreactors, which are affected in a complex way by multiple, interacting physical processes. We review common photobioreactor types and discuss the processes occurring therein as well as how these processes have been considered in previous CFD models. The analysis reveals that CFD models of photobioreactors do often not consider state-of-the-art modeling approaches. As a comprehensive photobioreactor model consists of several sub-models, we review the most relevant models for the simulation of fluid flows, light propagation, heat and mass transfer and growth kinetics as well as state-of-the-art models for turbulence and interphase forces, revealing their strength and deficiencies. In addition, we review the population balance equation, breakage and coalescence models and discretization methods since the predicted bubble size distribution critically depends on them. This comprehensive overview of the available models provides a unique toolbox for generating CFD models of photobioreactors. Directions future research should take are also discussed, mainly consisting of an extensive experimental validation of the single models for specific photobioreactor geometries, as well as more complete and sophisticated integrated models by virtue of the constant increase of the computational capacity. [ABSTRACT FROM AUTHOR]

[Display omitted] • A modelling visualised flow field changes in a photobioreactor was established. • Utilised 24 baffles to enhance hydrodynamic effects on an increase in cell numbers. • Achieved high growth rates for C.vulgaris in PBRM at airflow rates of 45−50L/h. • Observed composition variations in cells with CO 2 concentrations ranging from 5−20% • Introduced newly proposed PBRM featuring ordered vortex pairs that benefit cultures. Microalgae play a crucial role as bioresources, yet the culture systems of photobioreactors (PBR) encounter challenges. Many engineered PBRs tend to incorporate internals build-ups, serving photoautotroph production, and requiring substantial microalgal biomass. This study quantified the baffle effects on airlift flat plate PBRs based on the performance of Chlorella vulgaris. The impacts of baffle configurations, air velocity, and CO 2 contents, three dominant parameters, on microalgae culture were investigated using culture experiments, numerical simulations, and flow visualisation techniques. The results demonstrate that multiple baffle design strategies enhance microalgae growth and production. On the 11th cultivation day, airflow rates of 6, 45, or 90 L/h produced 1.5, 3.0, or 1.9 times the biomass weight and 1.76 × 107 cell numbers/mL in PBR M with 24 baffles, compared to 1.44 × 107 cell numbers/mL in PBR C without baffles. Furthermore, it revealed an intensification in the generation potential of biocomponents with C–H, C = O, and C–O–C functional groups at a 45−50 L/h airflow rate and CO 2 (20 %) aerated PBR M. Additionally, it presented the first visualisation explanation of the baffle-guided vortex flow pair symmetry PBR M. This study demonstrated enhancements by modelling newly proposed PBRs with baffles and high-valued bioproducts harvesting through the combination of culture parameters. [ABSTRACT FROM AUTHOR]

The potential of industrial applications for microalgae has motivated their recent fast development. Their growth dynamics depends on different factors that must be optimized. Since they get their energy from photosynthesis, light is a key factor that strongly influences their productivity. Light is absorbed and scattered in the liquid medium, and irradiance exponentially decreases towards the darkest part of the photobioreactor at a rate non-linearly depending on the biomass concentration. Maximizing productivity is then a tricky problem, especially when the growth rate is inhibited by an excess of light. Productivity optimization turns out to be highly dependent on how light is distributed along the reactor, and is therefore related to the extinction rate and the background turbidity. We propose a theoretical analysis of this problem, by introducing the concept of optical depth productivity for systems where background turbidity must be accounted for. A global optimum maximizing productivity is proposed, extending the concept of the compensation condition, consisting in compensating the algal growth rate at the bottom of the reactor by the respiration. This condition can drive the optimization of the surface biomass productivity depending on the minimum reachable depth. We develop a nonlinear controller and prove the global asymptotic stability of the biomass concentration towards the desired optimal value. [ABSTRACT FROM AUTHOR]

Global warming is a critical risk for the balance of nature, and its effects are increasing due to gases like CO2. One approach for CO2 capture is bringing together microalgae and buildings in esthetic bio-façade systems for obtaining environmentally friendly benefits. The aim of this study is to investigate the microalgae photobioreactors (PBR) as a potential bio-façade unit. Bio-façade concept focused on the multiple uses of water and nutrients, as well as CO2 capture, to highlight the sustainability and practicality. Chlorella vulgaris is selected as a model microalga due to its low doubling time and high biomass productivity. Experiments covered the dilutions of microalga medium (10%, 20%, 40%, 80%), recycling the cell separated medium and addition of CO2-enriched air (5% and 10%) focusing on their effects on various key factors like biomass and photosynthetic activity. PBR integrated laboratory scale house unit has also been constructed lastly. According to the preliminary results, up to 80% dilution, up to three cycles of medium and 5% CO2-enriched environment provided the high level of activity for bio-façade system. Interior air quality, changing of temperature and amounts of CO2–O2 with increasing of the biomass were investigated in PBR integrated laboratory scale house unit which depended on the outcomes of preliminary experiments (20% dilution and 5% CO2-enriched air). The results of unit showed the positive effects of the microalga integration with regards to its capability as a biofilter and a biocurtain for the sustainability. [ABSTRACT FROM AUTHOR]

Commercial applications of microalgae for biochemicals and fuels are hampered by their high production costs, and the use of conventional carbon supplies is a key reason. Bicarbonate has been proposed as an alternative carbon source due to its potential advantages in lower carbon supply costs, convenience for photobioreactor development, biomass harvesting, and labor and energy savings. We review recent progress in bicarbonate-based microalgae cultivation, which validated previous assumptions, suggested further advantages, and demonstrated potential to significantly reduce production cost. Future research should focus on improving production efficiency and reducing energy inputs, including optimizing photobioreactor design, comprehensive utilization of natural power, and automation in production systems. For microalgae production systems, bicarbonate is a better carbon supply than bubbled CO 2 gas in terms of carbon utilization efficiency, photobioreactor development, energy saving, and biomass harvesting. The carbon supply is the bottleneck in developing photobioreactors for low-cost microalgal biomass production, in contrast to the heterotrophic process, which is limited by oxygen supply. Recent progress suggests the potential of the bicarbonate-based integrated carbon capture and algae production system, to significantly reduce production costs and energy inputs in microalgae cultivation. Comprehensive utilization of natural power is a promising approach to further decrease energy consumption and improve the efficiency of the microalgae cultivation process in the future. [ABSTRACT FROM AUTHOR]

The Haematococcus pluvialis, a freshwater unicellular biflagellate microalga, is of great importance industrially as it is considered a source of natural production of astaxanthin, a carotenoid used as a colorant and a bioactive compound. This microorganism is the main producer of the best quality astaxanthin. The induction of carotene genesis is achieved when exposure to stress conditions is greater, and this is how the greatest accumulation of astaxanthin is generated. It has also been observed that, if cells are exposed to excess stress conditions, cell growth ceases completely and cells begin to die in a relatively short time, which makes their production difficult. The objective of this review is to show the models used to describe the growth kinetics of H. pluvialis and to establish the kinetic parameters that best explain the growth of the microalgae for use in laboratory culture and its scaling up in bioreactors or photobioreactors (PBR). The most applied mathematical models for monitoring the growth of microalgae are logistic, Baranyi-Roberts, exponential, and Monod. Kinetic growth models have been proposed considering parameters such as irradiance and light color. The kinetic parameters used are the maximum growth speed (µmax), the doubling time (td), the initial biomass (Xo), the final biomass (Xf) and the carotenoid productivity (Yp/Ys), to establish the optimal conditions for cultivating and producing the carotenoid, using the correlation coefficients generated by the model, in order to guarantee the cultivation of microalgae under the selected conditions and validate the data found. [ABSTRACT FROM AUTHOR]

Algae are not only a great source of natural bio energy but also they have the ability to capture CO2. ALGADISK refers to a biofilm reactor for algae biomass production that could compete with the current algae cultivation technologies, e.g., open-pond and tubular photo bioreactors. When algae-based biomass is grown on the surface attached biofilm as opposed to a suspended culture, then the biomass is concentrated and it can be more easily harvested. Automatic and continuous harvesting, increased efficiency and decreased water requirements indicate ALGADISK as a promising technology. Since it is in developing stage, it has its own disadvantages such as it is not recommended to operate in cold weather conditions. [ABSTRACT FROM AUTHOR]

It has been suggested that the energy-efficient production of microalgae biomass can be more easily obtained in short light path photobioreactors that can be operated at high biomass concentration. On the downside, however, high biomass concentrations also require an efficient gas exchange rate to avoid metabolic growth limitation or inhibition. A cascade photobioreactor featuring a thin liquid layer flowing down a sloping, wavy-bottomed surface can be operated at a biomass concentration that is much higher compared to most usual open-type equipment. Liquid flow, upon investigation, proved to exhibit peculiar “local recirculation” hydrodynamics, potentially conducive to the mixing of superficial and deep zones of the photobioreactor. Mass transfer coefficient represents a useful parameter to optimize the performance of a microalgal photobioreactor and its scale-up. The aim of the present article is to discuss the experimental mass transfer features of this novel type of photobioreactor and highlight expected opportunities and issues entailed by different ways of installing and operating such novel types of photobioreactors. [ABSTRACT FROM AUTHOR]

This work identifies shortcomings of conventional practices in unstructured modeling of microalgal growth, thereby exploring the possibility of improving simulation of algal cultures. Light- and nitrogen-limited growth of Chlorella vulgaris under CO2-replete conditions was modeled and simulated for a series of operating conditions in stirred-tank photobioreactors of bench scale. Based on the response of alga over a wide range of incident fluxes (50–400 µmol/(m2·s)) and nitrate levels (23–720 mg/L) in bubbled culture tubes, sixteen two-factor multiplicative models were developed by coupling suitable single-factor kinetic models for light and nitrate limited growth. Results suggest that the traditional use of Monod and Andrews kinetics in multi-factor modeling may not always be optimum as growth of the microalga was best described by other common models with a R2 of 0.93. Contrary to common belief, the study has demonstrated that biomass yield on nitrogen is a variable quantity and its reciprocal can be precisely modeled by Logistic/Gompertz function of nitrogen concentration. Common schemes to determine growth rate in attenuated light were also assessed. Local growth rates were found more appropriate than average intensity for estimation of net growth rate in steep light gradients. Simulations have also revealed that dissolved oxygen tension as high as 400% does not possess any threat to microalgal cultures as generally assumed. Model's predictability for scaled culture in geometrically similar photobioreactor was also examined. [ABSTRACT FROM AUTHOR]

The production of microalgal biomass and products derived thereof for a wide variety of applications is a hot research topic, with the number of facilities being built and products and biologically active molecules launched into the market increasing every year. The aim of the current study was to identify the attitudes of citizens in Almería (Spain) and Livorno (Italy) towards the construction of a microalgae production plant and a biorefinery in their cities and also their opinions about the microalgae-based products that could be produced. Overall, in Almería (Spain), a NIMBY (not in my back yard) attitude towards the construction of a microalgal production facility and especially towards a microalgal biorefinery was observed, despite the strong microalgal industry in the region and the higher knowledge of citizens about microalgae. In both locations, but especially in Livorno (Italy), microalgae-based biostimulants, biofertilisers, and aquafeeds were well accepted. Proximity was the main factor affecting the acceptance of a microalgae producing facility. Consumer knowledge about microalgal biotechnology and the health and environmental benefits of this valuable raw material are scarce, and opinions are based on drivers other than knowledge. After gaining more knowledge about microalgal biorefineries, most of the responses in Almería (47%) and Livorno (61%) were more positive. [ABSTRACT FROM AUTHOR]

Microalgae are photosynthetic microorganisms playing a pivotal role in primary production in aquatic ecosystems, sustaining the entry of carbon in the biosphere. Microalgae have also been recognized as sustainable source of biomass to complement crops. For this objective they are cultivated in photobioreactors or ponds at high cell density to maximize biomass productivity and lower the cost of downstream processes. Photosynthesis depends on light availability, that is often not constant over time. In nature, sunlight fluctuates over diurnal cycles and weather conditions. In high-density microalgae cultures of photobioreactors outdoors, on top of natural variations, microalgae are subjected to further complexity in light exposure. Because of the high-density cells experience self-shading effects that heavily limit light availability in most of the mass culture volume. This limitation strongly affects biomass productivity of industrial microalgae cultivation plants with important implications on economic feasibility. Understanding how photosynthesis responds to cell density is informative to assess functionality in the inhomogeneous light environment of industrial photobioreactors. In this work we exploited a high-sensitivity Clark electrode to measure microalgae photosynthesis and compare cultures with different densities, using Nannochloropsis as model organism. We observed that cell density has a substantial impact on photosynthetic activity, and demonstrated the reduction of the cell's light-absorption capacity by genetic modification is a valuable strategy to increase photosynthetic functionality on a chlorophyll-basis of dense microalgae cultures. • Microalgae biomass is a promising alternative to crops. • The impact of cultivation at scale on photosynthesis is still under-investigated. • The Photosynthesis-Irradiance (PI) relationship is informative. • High-sensitivity oxygen measurements for PI investigation was validated. • The effect of cell density on PI was studied in Nannochloropsis pale mutants. [ABSTRACT FROM AUTHOR]

Biomass of microalgae and the components contained in their cells can be used for the production of heat, electricity, and biofuels. The aim of the presented study was to determine the optimal conditions that will be the most favorable for the production of large amounts of microalgae biomass intended for energy purposes. The study analyzed the effect of the type of lighting, the time of lighting culture, and the pH of the culture medium on the growth of Chlorella vulgaris biomass. The experiment was carried out in vertical tube photobioreactors in three photoperiods: 12/12, 18/6, and 24/0 h (light/dark). Two types of lighting were used in the work: high-pressure sodium light and light-emitting diode. The increase in biomass was determined by the gravimetric method, by the spectrophotometric method on the basis of chlorophyll a contained in the microalgae cells. The number of microalgae cells was also determined with the use of a hemocytometer. The optimal conditions for the production of biomass were recorded at a neutral pH, illuminating the cultures for 18 h a day. The obtained results were 546 ± 7.88 mg·L−1 dry weight under sodium lighting and 543 ± 1.92 mg·L−1 dry weight under light-emitting diode, with maximum biomass productivity of 27.08 ± 7.80 and 25.00 ± 5.1 mg·L−1∙d−1, respectively. The maximum content of chlorophyll a in cells was determined in the 12/12 h cycle and pH 6 (136 ± 14.13 mg∙m−3) under light-emitting diode and 18/6 h, pH 7 (135 ± 6.17 mg∙m−3) under sodium light, with maximum productivity of 26.34 ± 2.01 mg·m−3∙d−1 (light-emitting diode) and 24.21 ± 8.89 mg·m−3∙d−1 (sodium light). The largest number of microalgae cells (2.1 × 106) was obtained at pH 7 and photoperiod of 18/6 h under sodium light, and 12/12 h under light-emitting diode. Based on the results, it can be concluded that the determination of the optimal parameters for the growth and development of microalgae determines the production of their biomass, and such research should be carried out before starting the large-scale production process. In quantifying the biomass during cultivation, it is advantageous to use direct measurement methods. [ABSTRACT FROM AUTHOR]

Batch growth and β‐carotene production of Dunaliella salina CCAP19/18 was investigated in flat‐plate gas‐lift photobioreactors with a light path of 2 cm, operated in physically simulated outdoor conditions. Dunaliella salina CCAP19/18 showed robust growth with respect to pH 8.0‐9.0 and 15–35°C at increasing salinity, simulating the evaporation of open photobioreactors. The highest β‐carotene concentration of 25 mg L‐1 (3 mg gCDW−1) was observed in batch processes at pH 8.5, 15–30°C and increasing salinity up to 110 g L‐1, simulating a typical Mediterranean summer climate. Intracellular β‐carotene accumulation of D. salina CCAP19/18 was shown to be independent of light availability, although nutrient limitation (K2HPO4, MgSO4, and/or ammonium ferric citrate) seems to enable stable β‐carotene content in the algal cells despite increasing cell densities in the photobioreactor. Fully controlled, lab‐scale photobioreactors simulating typical climate conditions of any region of interest are valuable tools for enabling a realistic characterization of microalgae on a laboratory scale, for production processes projected in open photobioreactor systems (e.g. thin‐layer cascade photobioreactors). [ABSTRACT FROM AUTHOR]

To prevent the formation of biofilm or to remove already formed biofilm on the transparent walls of the closed cultivation systems, it is important to ensure that there are sufficient wall shear stresses to disrupt the stability of the biofilm. A pilot-scale flat-panel photobioreactor and laboratory tubular system were used to determine the critical value of the wall shear stress. The formation of biofilm on transparent walls of the cultivation systems reduces light penetration into the cultivation medium, which can subsequently reduce the production of microalgae, since light radiation a key parameter influencing the growth of microalgae. To study the influence of hydrodynamic conditions on the prevention of biofilm formation, a numerical model of a flat-panel photobioreactor was validated based on the experimental data. Using the validated model, a critical value of wall shear stress that above which avoids the formation of biofilm was defined to be 0.2 Pa. To refine the values from the numerical model, and to investigate the influence of hydrodynamic conditions on the process of disruption of the formed and stabilized biofilm, a simple experimental tubular system with the one-dimensional flow was developed. For one-dimensional flow, it is easier to describe the hydrodynamic behaviour and more precisely define the parameters influencing biofilm formation. The experiments in this simplified tubular system were focused on removing already formed biofilm. The formed biofilm on the transparent wall was completely removed from the surface when the wall shear stress reached a value of 53 Pa. However, the stability of the biofilm was already disturbed at a value of 6 Pa. The resulting values of critical wall shear stress could be used to select the operating conditions of the cultivation systems or to adjust their geometry affecting the hydrodynamic conditions. According to the velocity distribution based on the measured values, the thickness of the biofilm was less than the thickness of the viscous sublayer. Thus, the prevention of formation, disruption, or even removal of biofilm can be ensured by shear forces in the viscous sublayer. • CFD model of hydrodynamic conditions was experimentally validated. • Critical value of wall shear stress which avoids formation of biofilm was defined. • Disruption of stability of formed biofilm was studied in the tubular system. • Wall shear stress which ensure the disruption of stability of biofilm was defined. • Hydrodynamic conditions can be used for treatment of transparent walls in PBRs. [ABSTRACT FROM AUTHOR]

Summary: Even though microalgae are able to produce various valuable metabolites, microalgal culture on an industrial scale still faces challenging difficulties. Open systems may be cheaper to construct, easier to operate and maintain, and possess greater surface area to volume ratio, but they are also easily contaminated, have high water loss due to evaporation, and suffer from unfavorable weather. On the other hand, closed photobioreactor systems possess higher biomass yields, better control over culture parameters, and lower contamination risks. However, photobioreactors are costlier to construct and maintain. Thus, a hybrid semi‐closed thin layer cascade photobioreactor was proposed to cultivate high‐density microalgal cultures for biodiesel production. Computational fluid dynamics analysis was carried out to observe fluid behavior in the hybrid photobioreactor design. The simulation results showed satisfactory performance in the improved design, making the photobioreactor a potential candidate for microalgal biodiesel production. [ABSTRACT FROM AUTHOR]

An increasing number of microalgae strains are used for commercial production of metabolites. When conducting research, the moment of the process scaling tends to be very difficult. One of the most complex issues is related to planning and designing an efficient system for propagation of appropriately high amounts of inoculum required for inoculating cultures on a semi-technical and industrial scale. The following paper aimed at designing an automated station for the preparation of microalgae inoculation material intended for inoculation of the system, comprising of six 90 dm3 volume photobioreactors. The system, comprised of eight airlift photobioreactors of 12 dm3 volume each, installed in mobile storage units connected to the control system in the form of a docking station. Each of the photobioreactors had a separate system used for monitoring temperature and pH, mixing, and LED lighting. The station constituted the last stage of preparing the inoculation material for inoculating technical-scale photobioreactors, used for conducting experiments with Haematococcus pluvialis microalgae. Achieved results, repeatability of the processes, and the ergonomics of the station increased the productivity and quality of the research and development processes. [ABSTRACT FROM AUTHOR]

Energy is becoming one of the most expensive production inputs nowadays. Energy reserves are starting to run out and their polluting nature has become undeniable. Therefore, there is an urgent necessity for renewable energies. One of these energy sources is algae, which are seen as promising for biofuel production. Algae can be cultured in non-agricultural land, high photosynthetic activity, harvested throughout the year high biomass production. High lipid from algae is possible by reducing some elements of growth conditions from the nutrient medium. In this study, Isochrysis affinis galbana species were cultured in two reactors; flat panel photobioreactors with different light paths (1, 3, 5, 7 and 10 cm) and tubular photobioreactors, with 50% nitrogen reduction and 20% inoculation densities. Biomass, lipid and protein ratios were determined. The highest lipid content of 33.13% was obtained from I. aff. galbana with 12.11% protein in flat panel photobioreactors with 50% nitrogen reduction and 10 cm light path, and a 0.991 g L-1 biomass rate was obtained. The highest optical density was found in the 10 cm light path flat panel photobioreactor with a 50% nitrogen reduction. [ABSTRACT FROM AUTHOR]

• Compact NMR spectroscopy as an online non-invasive microalgae in vivo lipid sensor. • The NMR signal is quantitative when calibrated with total lipid reference method. • The NMR performance is compatible with the bioprocess operating conditions. • Lipid productivities are measured in real-time for real-time optimization purposes. The production of lipids by microalgae is widely studied, especially to find the best bioprocess operating conditions and optimize the productivity of the targeted product. In this context, being able to monitor online the evolution of the lipid concentration is a great advantage regarding the control and/or the optimization of the production. Yet, most non-invasive analyses hit a brick wall on the interference of the lipid signal with the ubiquitous water of the culture medium. This article shows how a compact NMR spectrometer connected to a photobioreactor can circumvent this drawback and measure, in real-time and in a non-invasive manner, the total lipid concentration, and that directly on the entire cells grown in their culture medium. The water signal could be enough-selectively removed using the W5 version of the WATERGATE pulse sequence. The NMR signal nicely correlates (R² > 0.99) with the offline FAME (Fatty Acid Methyl Ester) total lipid analysis as performed by GC-FID (Gas Chromatography coupled to Flame Ionization Detector) within limits of detection and quantification of respectively 9 and 30 mg.L−1. The lipid specific signal appears also quite robust regarding the dissolved dioxygen, making the benchtop NMR spectroscopy an appropriate universal device for the online monitoring of lipids produced in bioprocesses. [ABSTRACT FROM AUTHOR]

Background: Biodiesel is expected to play a key role in the development of a sustainable, economical, and environmentally safe source of energy. The third generation of biodiesel is derived from microalgae and cyanobacteria that have sufficient amount of oil. The optimization of biomass and oil content in biodiesel production based on algal cultivation relies upon several factors. The present experimental work aims at optimizing some of the cultivation conditions to obtain maximum oil and biomass yield and create a prediction model that describe the effect of the initial inoculum concentration, and irradiance on the biomass yield and oil concentration were designed using Design Expert 6.0.8. Results: The results revealed that the optimum surface-to-volume ratio for the airlift bubble column photobioreactor was 0.9, and the most applicable model for describing Microcystis aeruginosa growth was the hyperbolic tangent model with a model constant value of 1.294 mg·L− 1·d− 1/μmol·m− 2·s− 1. The optimum cultivation conditions were 81 μmol·m− 2·s− 1 irradiance and 67 mg·L− 1 initial inoculum concentration, and these conditions achieved a biomass yield of 163 mg·L− 1·d− 1 and an oil concentration of 143 mg·L− 1. Conclusions: This work focused on the cultivation of microalgae in closed systems. Cyanobacteria as M. aeruginosa has high lipid content, and high lipid productivity makes it suitable as a lipid feed stock for biodiesel production. The response surface method was the most suitable route to study the simultaneous influence of irradiance and initial inoculum concentration through statistical methods as well as to establish a model for predicting the biomass yield and oil concentration of M. aeruginosa. [ABSTRACT FROM AUTHOR]

• A new tubular photobioreactor design following the Fibonacci equation has been proposed. • The proposed design allows up to a 1.4-times increase in intercepted solar radiation compared to horizontal surface. • The proposed design allows to achieve up to 8.6% solar efficiency at outdoor conditions. • The reliability of the reactor for the outdoor production of Spirulina has been demonstrated. In this work, a new tubular photobioreactor design based on the Fibonacci equation is proposed. A small 6 L unit was evaluated indoors and a larger 250 L unit was evaluated outdoors; both units maintained the same concept and the same aspect ratio. To test the new design, the Arthrospira (Spirulina) platensis strain was used. The results show that the proposed design allows the temperature, pH and dissolved oxygen to be maintained within the optimal ranges recommended for the selected strain. Consequently, overheating was avoided, even under outdoor conditions, and the dissolved oxygen concentration remained below the 200%Sat limit. Modelling of the growth in both reactors demonstrated that cell performance was optimal under indoor and outdoor conditions, with outdoor maximal specific growth rates reaching 0.8 1/day. Moreover, under outdoor conditions, photosynthetic efficiency reached 8.3%, thus confirming high light-utilization efficacy even at high irradiances when using this new photobioreactor design. Our work represents a first step in the development of this promising technology as an alternative to those presently used. Developing industrial-scale microalgae biotechnology requires more productive and effective photobioreactors capable of maximizing biomass productivity under high light conditions. [ABSTRACT FROM AUTHOR]

Marine macroalgae – next-generation renewable feedstock is a potential solution to the growing need for sustainable future resources, with seaweed protein to cater to the ever-increasing demand of feeding the fast-growing population. The conventional cultivation methods for marine macroalgae are impeded by low productivity, seasonal constraints, and climate change issues, necessitating improved cultivation strategies. The present study demonstrates the use of tank-based (T-PBR) and vertical (V-PBR) outdoor photobioreactors for free-floating substrate-independent land-based cultivation of filamentous green seaweed Enteromorpha prolifera. Optimization of the stocking density (SD) for seasonal variation was carried out to attain maximal biomass productivity. The study demonstrated biomass production with average annual productivity of 480 g fw m−2 d−1 in V-PBR and 413 g fw m−2 d−1 in T-PBR. The season-specific SD, carbon dioxide supplementation (5%), and nutrient supply management ensured a year-round consistent supply of E. prolifera biomass. In spite of seasonal variation in biomass quality and quantity, an annual average content of 24% protein and 51% carbohydrate was observed. The present work substantiates the advancement of land-based seaweed cultivation for sustainable vegan protein production. [Display omitted] • Year-round outdoor cultivation of macroalgae Enteromorpha prolifera biomass. • Tank and vertical photobioreactors for improved land-based cultivation. • Optimized stocking density and CO 2 supplementation improve biomass productivity. • Consistent biomass supply for the macroalgal biorefinery. • Demonstrates the potential for advancing vegan sea protein production. [ABSTRACT FROM AUTHOR]

In order to refine the treatment of microalgae consortium (MC) for municipal wastewater (MWW) during the winter, this study investigated the effectiveness of tubular and aeration column photobioreactors (TPBR and APBR) in wastewater treatment plant (WWTP) during winter by two start-up modes: microalgae/microalgae-activated sludge (AS). The operation results showed that under 5.7–13.1 °C, TPBR enhanced the assimilation of N and P pollutant by microalgal accumulation, meeting the Chinese discharge standard within 24 h (NH 4 +-N, TP, and COD ≤8.0, 0.5, and 50 mg·L−1). The microbial community profiles were identified and showed that inoculating AS under low-temperature still promoted bacterial interspecific association, but influenced by the inhibition of microbial diversity by the homogeneous circulation of TPBR, the nitrogen transfer function of MC was lower than that of APBR at low temperatures, except nitrogen fixation (K02588), nitrosification (K10944, K10945, and K10946), assimilatory nitrate reduction (K00366), and ammonification (K01915 and K05601). And the intermittent aeration in the APBR was still beneficial in increasing microbial diversity, which was more beneficial for reducing COD through microbial collaboration. In the treatment, the cryotolerant MGPM were Delftia , Romboutsia , Rhizobiales , and Bacillus , and the cold stress-related genes that were highly up-regulated were defense signaling molecules (K03671 and K00384), cold shock protein gene (K03704), and cellular protector (K01784) were present in both PBRs. This study provided a reference for the feasibility of the low temperature treatment of MC with the different types of PBR, which improved the application of wastewater treatment in more climatic environments. [Display omitted] • TPBR was beneficial for microalgal biomass accumulation at low-temperatures. • Homogeneous circulation of TPBR weaken the growth of microalgal symbiotic bacteria. • Diverse microenvironments formed by intermittent aeration enhancing treatment of MC. • Symbiotic bacteria highly up-regulated K03704, K00384 and K01784 under cold stress. [ABSTRACT FROM AUTHOR]

The present study investigated the effect of different culture conditions on the vegetative growth of a new species, Haematococcus alpinus (strain LCR‐CC‐261f) using airlift photobioreactors. The influence of culture medium, aeration rates, CO2 concentration in air‐gas mixture, temperature, light intensities, and wavelengths were investigated to achieve sustainable high cell density cultures. Growth parameters were determined by fitting the data to a form of the logistic equation that included a lag phase. The shear‐sensitive vegetative cells favored lower aeration rates in the photobioreactors. MLA medium increased to 40 mM nitrate produced high density cultures. Temperatures between 12°C and 18°C, 3% (v/v) CO2 concentration and a narrow photon flux density ranging between 37 and 48 μmol photons · m−2 · s−1 were best suited for growth. The wavelength of the light source also impacted growth and a high cell density of 9.6 × 105 cells · mL−1 was achieved using a mixture of red and blue compared to warm white, red, or blue LEDs. [ABSTRACT FROM AUTHOR]

The microalgae growth rate in photobioreactors responds with inertia to light stimuli. Here, light variations experienced by the algae are accessed through a coupling of an irradiance field calculation and a Lagrangian particle tracking. The response of algae to fluctuating light is then described by a relaxation model involving a single time constant, the value of which is identified from published data. The overall growth rate is calculated as the sum of individual growth rates of all particles. Instantaneous adaptation and full integration asymptotic behaviors are recovered whilst a finite time constant reveals that the overall growth rate is dependent both on mixing and light distribution. This methodology thus quantitatively relates the design parameters to the photobioreactor performance. [ABSTRACT FROM AUTHOR]

Biological hydrogen production is attractive since renewable resources are utilized for hydrogen production. In this study, a novel panel photobioreactor (1.4 L) was constructed from Plexiglas with a network of nylon fabric support for agar immobilized bacteria complex. Two strains of Rhodobacter capsulatus DSM 1710 wild-type strain and Rhodobacter capsulatus YO3 (hup−, uptake hydrogenase deleted mutant) with cell concentrations of 2.5 and 5.0 mg dcw/mL agar, respectively were entrapped by 4% (w/v) of agar. The system was operated for 72–82 days in a sequential batch mode utilizing acetate as substrate at 30 °C under continuous illumination. Immobilization increased the stability of the photobioreactors by reducing the fluctuations in pH. The pH remained between 6.7 and 8.0 during the process. Both hydrogen yield and productivity were higher in immobilized photobioreactors compared to suspended culture. The highest hydrogen productivities of 0.75 mmol H 2 /L/h and 1.3 mmol H 2 /L/h were obtained by R. capsulatus DSM1710 and R. capsulatus YO3 respectively. • Biological hydrogen from acetate by agar immobilized Rhodobacter capsulatus. • Long-term hydrogen production for 72–82 days in indoors. • The range of pH change was between 6.7 and 8.0 throughout the process. • The highest productivity of 1.3 mmol H 2 /L/h was obtained by R. capsulatus YO3. • The highest hydrogen yield was 3.53 mol H 2 /mol acetate by R. capsulatus YO3. [ABSTRACT FROM AUTHOR]

The present study reports the use of Citrus limetta (CL) residue for cultivating Chlorella sp. mixotrophically to augment production of biodiesel. The cultivation of Chlorella sp. using CL as media was carried out by employing a fed-batch technique in open tray (open tray+CL) and in software (BioXpert V2)–attached automated photobioreactor (PBR+CL) systems. Data showed the limit of nitrogen substituent and satisfactory organic source of carbon (OSC) in CL, causing > 2-fold higher lipid content in cells, cultivated in both the systems than in control. For the cells grown in both the systems, ≥ 3-fold enhancement in lipid productivity was observed than in control. The total fatty acid methyl ester (FAME) concentrations from lipids extracted from cells grew in PBR+CL and in open tray+CL techniques were calculated as 50.59% and 38.31%, respectively. The PBR+CL system showed improved outcomes for lipid content, lipid and biomass productivity, FAME characteristics and physical property parameters of biodiesel than those obtained from the open tray+CL system. The physical property parameters of biodiesel produced from algal cells grown in PBR+CL were comparable to existing fuel standards. The results have shown lower cold filter plugging point (− 6.57 °C), higher cetane number (58.04) and average oxidative stability (3.60 h). Collectively, this investigation unveils the novel deployment of CL as a cost-effective feedstock for commercialisation of biodiesel production. [ABSTRACT FROM AUTHOR]

Abstract Microalgae may be exploited in water or wastewater treatment facilities to reduce excess concentrations of nutrients and metals to comply with regulatory limits. In this study, we characterized the growth and phosphorus (P) removal capacity of an isolated strain of Tetradesmus obliquus VRUC280. Investigations were carried out from laboratory scale (50 mL) up to a 100 L outdoor photobioreactor (PBR). After 10 days, batch cultures removed up to 74% of the media P, while in the PBR, 95% removal was achieved within five days. The harvested biomass was then inactivated (freeze-dried) and used for metal adsorption tests, employing solutions containing 6.0 mg Cu L−1 or 4.8 mg Ni L−1. Metal removal rates were evaluated after 15, 30, 60 and 120 min by the analysis of liquid and biomass metal contents. For the latter, a specific biomass digestion method was developed. Cu removal ranged between 50% and 65%, while for Ni, removal varied between 30% and 50%. 300–400 mg Cu Kg DW−1 and 130–250 mg Ni Kg DW−1 were rapidly adsorbed on the cell surface of T. obliquus (ca. 15–30 min incubations). This study demonstrates the potential of microalgae, in this case T. obliquus , to remove sequentially P and metals from aqueous media. Highlights • When scaled up from 50 mL to 100 L, T. obliquus removed 95% of the P. • Inactivated biomass was then used for Cu and Ni adsorption test of 120 min. • Up to 65% of Cu and 50% of Ni was removed within 15–30 min. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the mitigation of greenhouse gasses generated in the anaerobic digestion process of physicochemical sludges by evaluating the effect of CO2 supply and light intensity requirements on the growth of microalga Chlorella spp. and measuring the consumption of CO2. The best conditions at a laboratory scale were performed in an airlift photobioreactor (PBR) at pilot-scale plant (26 L) during 60 days with a CO2 supply of 2% v v−1 from an electric generator coupled to an anaerobic digestion of physicochemical sludge process. The maximum %CO2 consumed was 91.92% which was reached in the seventh supply cycle and biomass production was 2.18 g L−1. The results obtained showed that airlift-type PBRs are a suitable complement for anaerobic digestion of physicochemical sludge technologies in order to reduce emissions of greenhouse gases produced during the combustion of biogas. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A mutant strain C. sorokiniana MB-1-M12 was cultivated outdoors for lutein production. • Lutein production is better with semi-continuous operation compared to fed-batch operation. • Simulated outdoor cultivation yielded a high lutein productivity of 3.34 mg/L/d. • Productivity was enhanced to 4.46 mg/L/d in outdoor cultivation with 60 L PBRs. • Strain MB-1-M12 is suitable for outdoor large-scale cultivation for lutein production. Abstract A lutein-enriched mutant, Chlorella sorokiniana MB-1-M12 was grown mixotrophically for lutein production. The lutein production efficiency of the strain was enhanced via optimizing the operating strategies. The results show that using semi-continuous cultivation with a medium replacement ratio of 75% resulted in a higher lutein productivity and lutein concentration of 6.24 mg/L/d and 50.6 mg/L, respectively, which were markedly higher than those obtained from batch and fed-batch cultivation. Cultivation under simulated outdoor cultivation conditions (i.e., temperature of 35 °C/25 °C for a 12 h/12 h light/dark cycle) could achieve the highest lutein productivity and lutein concentration of 3.34 mg/L/d and 30.8 mg/L, respectively. Lutein production via outdoor cultivation of MB-1-M12 strain with a 60-L tubular photobioreactor was performed using semi-continuous operation. With a medium replacement ratio of 75%, a good lutein productivity (4.46 mg/L/d) and concentration (27.4 mg/L) was obtained, indicating the feasibility of producing lutein under outdoor cultivation of the microalgal strain. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the problem of pH regulation in photobioreactors has been addressed by using a robust Proportional–Integral controller in combination with a linear active disturbance rejection approach. This formulation is based on the Generalized Proportional–Integral (GPI) observers design to estimate online external disturbances and non-modeled dynamics. The methodology uses a model reference optimization procedure with tracking and regulatory target closed-loop transfer functions for first-order plus dead-time models. The proposed controller is validated on a full-scale Raceway photobioreactor, whose results show a significant improvement in the accuracy of pH regulation and, consequently, a positive influence on biomass production. Moreover, a classical feedforward approach has been used for comparison purposes. The performance of the robust technique is evaluated with different indexes, whose results confirm the good performance of the proposed active disturbance rejection control scheme. Highlights • GPI observers can be used to estimate disturbances in microalgae production systems. • A GPI+2-DoF PI control scheme has better results than commonly used control schemes. • Parametric uncertainty can be reduced by means of disturbance observers. • Processes subject to disturbances require the use of active rejection techniques. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A SM-PBR was constructed for nutrients recovery from LL and lipids production. • The membrane module can protect microalgae cells from LL contamination. • Excess phosphate feeding increased lipid content but decreased biomass production. • N recovery and lipids production were boosted in the SM-PBR than traditional PBR. Abstract The aim of this work was to realize high-efficiency nutrients recovery from landfill leachate (LL) for microalgal lipids production. Negative effects of LL on microalgal lipid synthesis was revealed and a scalable membrane-based tubular photobioreactor (SM-PBR) was proposed to offset these negative effects. Microalgal biomass concentration was improved from 0 g/L in the traditional PBR to 2.13 g/L in the SM-PBR. Major operating conditions were optimized to enhance nutrients recovery and lipid productivity. The maximum N recovery efficiency of 74.31% and the maximum daily lipid production of 404.98 mg/d were obtained under the volume ratio of 5:3 (microalgae culture/LL stream) and phosphate feeding concentration of 50 mg/L. The obtained lipid was convinced to have a good combustion and anti-degradation property, with high cetane number (>52%) and low linolenic acid content (<12%). The SM-PBR provided a feasible approach for large-scale microalgal lipid production with LL. [ABSTRACT FROM AUTHOR]

Abstract Treatability of anaerobically digested distillery wastewater is challenging because of its high pollution load of COD up to 40,000 ppm. This research investigates the possibilities of retrofitting the effluent treatment plant (ETP) of a distillery with microalgae treatment step. For this, at first the photobioreactors of capacity 50 L and 500 L were customized for the cultivation of Spirulina sp. under xenon lamp and sunlight. The reactor supported the maximum specific growth rate up to 0.42 ± 0.03 d−1 in the 50 L reactor at laboratory and 0.10 ± 0.02 d−1 in the 500 L reactor at the outdoor for Spirulina sp. The treatability of wastewater of COD 30,000 ppm–40,000 ppm was carried out in those reactors with the Spirulina sp. of culture volume fraction 0.8 and 0.93 under xenon lamp and sunlight respectively. The chemical oxygen demand and total dissolved solids reduction were 60–70% in both the volume fractions of the culture. Ion chromatography analysis indicated the reduction of major inorganic pollutants in the wastewater by the Spirulina sp. The algae were sustainable when the culture volume fraction was increased from 0.8 to 0.93. Thus, the phycoremediation was shown the significant pollution reduction in the wastewater. The addition of this step is valuable and it benefits the distillery by not only improving the quality of wastewater but also through the generation of algae biomass that would be appropriate for animal feed or biofuel application. However, the detail biochemical study is needed for the best use of algae biomass and the treatment could be checked for the long run sustainability. Graphical abstract Image 1 Highlights • Customized photobioreactor system for the growth of algae and treatment. • COD and TDS reduction up to 60–70% with variable wastewater and culture ratio. • Inorganic pollutant uptake by Spirulina sp. and its analysis using ion chromatography. • Sustainability of algae at the culture volume ratio of 0.93 at the site of distillery. [ABSTRACT FROM AUTHOR]