Performance Of Photobioreactor Research Articles

Evaluation of the feasibility of photosynthetic biogas upgrading: Simulation of a large-scale system

The use of microalgae cultures has been proposed as an innovative method to remove CO2 from biogas. However, the design of a large-scale installations requires the identification of key operational parameters and the determination of the maximum treatment capacity of the system. The aim of this work is to advance in that direction, using mathematical modelling. A model was developed, considering a system composed of a bubble column connected with an open photobioreactor. Simulations were carried out to evaluate the operation of a potential large-scale system. Results show that biogas upgrading would be feasible at large scales. At a biogas treatment capacity of 0.12 m3 d−1 per m3 reactor, an upgraded biogas with less than 3 and 1% of CO2 and O2, respectively, could be obtained. Under such condition, more that 80% of the inorganic carbon from the biogas would be transformed into biomass. Considering the low volumetric capacity of the system, its feasibility is expected to be determined by the biomass economic value.

DESIGN AND EVALUATION OF A HELICAL-TUBULAR PHOTOBIOREACTOR FOR MICROALGAE PRODUCTION

Photosynthetic microalgae are important bioresource for producing desired and environmentally safe products including biodiesel production as third generation biofuels. Photobioreactor play important role in this process. Designing and manufacture the bioreactor for photocatalysis is still challenging at present time due to the important factors that must be closely considered with regard to light requirements. The aim of the present study was to design and evaluate a helical-tubular photobioreactor for algae production. The design considerations included light intensity controller circuit, surface-to-volume ratio, power required of both air pump and mixing pump to reach up the optimum operating parameters. Experiments were conducted to optimize light intensity and light/dark duration cycle. The photobioreactor performance was evaluated in terms of biomass productivity, lipid productivity, carbon capture efficiency and energy balance of algae production system. The experimental results reveal that the helical-tubular photobioreactor is recommended to be used under light intensity of 8 kLux and light/dark duration cycle of 18:6 h to obtain the highest biomass productivity of 1.80 kg.day-1 and lipid productivity 432 g.day-1 with carbon capture efficiency 87%. The manufactured photobioreactor is capable of produce 4.74 kWday which is equivalent to 4.39 kWday of net energy output.

Photo-bioreactors: Harnessing Solar Energy in Biological Way

Development of photo-bioreactors (PBRs) has been accelerated owing to their potential application in the production of algal biofuel. But the application of PBRs should be looked beyond fuel and towards feed items/wastewater treatment solutions it can provide. The PBRs discussed in the review are broadly divided into two major categories, that is, open and closed type. The open PBRs are simple open pond systems while closed ones include vertical, flat plate, tubular, foil and recently developed porous substrate bioreactor. The efficiency of all PBRs depends on the surface-to-volume illumination ratio apart from mixing. The recently developed porous substrate bioreactor is technologically superior to its predecessors in terms of water usage and does not require biomass separation. The authors emphasize on the development of PBRs with the hope that their success would match as that of solar energy panels for power generation which have come a long way from the laboratory to real-world applications.

Photobioreactors based on microalgae-bacteria and purple phototrophic bacteria consortia: A promising technology to reduce the load of veterinary drugs from piggery wastewater

Traditional swine manure treatments are not fully effective in the removal of veterinary drugs. Moreover, they are costly and entail a significant carbon footprint in many cases. Innovative biological approaches based on phototrophic microorganisms have recently emerged as promising alternatives to overcome those limitations. This work evaluated the removal of 19 veterinary drugs (i.e., 16 antibiotics, 1 analgesic, 1 anti-parasitic and 1 hormone) from piggery wastewater (PWW) in two open photobioreactors (PBR) operated with a consortium of microalgae-bacteria (AB-PBR) and purple photosynthetic bacteria (PPB-PBR). Multiple hydraulic retention times (HRT), in particular 11, 8 and 4 days, were tested during stage I, II and III, respectively. Ten out of 19 target compounds were detected with inlet drug concentrations ranging from 'non-detected' (n.d.) to almost 23,000 ng L-1 for the antibiotic oxytetracycline. Moreover, three of the antibiotics (i.e., enrofloxacin, sulfadiazine and oxytetracycline) were found at concentrations above the analytical linearity range in some or all of the samples under study. AB-PBR supported higher removal efficiencies (REs) than PPB-PBR, except for danofloxacin. Overall, REs progressively decreased when decreasing the HRT. The highest REs (>90%) were observed for doxycycline (95 ± 3%) and oxytetracycline (93 ± 3%) in AB-PBR during stage I. The other drugs, except sulfadimidine that was the most recalcitrant, showed REs above 70% during stage I in the same photobioreactor. In contrast, no removal was observed for danofloxacin in AB-PBR during stage III, sulfadimidine in PPB-PBR during stage III or marbofloxacin in PPB-PBR during the entire experiment.

Synergy between flow and light fields and its applications to the design of mixers in microalgal photobioreactors

BackgroundMixers are usually inserted into microalgal photobioreactors to generate vortices that can enhance light/dark cycles of algal cells and consequently enhance biomass productivity. However, existing mixer designs are usually developed using a trial-and-error approach that is largely based on the designer’s experience. This approach is not knowledge-based, and thus little or no understanding of the underlying mechanisms of mixer design for mixing performance of photobioreactors is attained. Moreover, a large pumping cost usually accompanies mixer introduction, and this cost is not favorable for practical applications. This study aims to improve this situation.ResultsIn addition to the individual effects of flow and light fields, improving the synergy (coordination) between these fields may markedly enhance the L/D cycle frequency with a lower increase in pumping costs. Thus, the idea of synergy between flow and light fields is introduced to mixer design. Better synergy can be obtained if (a) the vortex core and L/D boundary are closer to each other and (b) the vortex whose core is too far from the L/D boundary is removed. The synergy idea has two types of applications. First, it can facilitate a better understanding of known numerical and experimental results about mixer addition. Second, and more importantly, the idea can help to develop new rules for mixer design. A helical mixer design is provided as a case study to demonstrate the importance and feasibility of the synergy idea. An effective method, i.e., decreasing the radial height of the helical mixer from the inner side, was found, by which the L/D cycle frequency was enhanced by 10.8% while the pumping cost was reduced by 23.8%.ConclusionsThe synergy idea may be stated as follows: the enhancement of L/D cycle frequency depends not only on the flow and light fields individually but also on their synergy. This idea can be used to enhance our understanding of some known phenomena that emerge by mixer addition. The idea also provides useful rules to design and optimize a mixer for a higher L/D cycle frequency with a lower increase in pumping costs, and these rules will find widespread applications in PBR design.

Effect of dissolved oxygen concentration on microalgal culture in photobioreactors

High concentrations of dissolved oxygen can inhibit the growth of photosynthetic microorganisms in microalgal culture systems. Not taking into account this parameter can also affect the reliability of mathematical models predicting biomass productivity. This study investigates the impact of high dissolved oxygen concentrations (CO₂) on biomass productivity. The eukaryotic microalgae Chlorella vulgaris was cultivated in a torus-shaped photobioreactor in chemostat mode at constant light and for different CO₂. Results showed a loss of biomass productivity at CO₂ ≥ 31 g·m−3. By recalculating the specific rate of cofactor regeneration on the respiratory chain (JNADH2), the kinetic growth model was able to predict the impact of CO₂. This improved model was then used to explain the discrepancy in performances between two photobioreactor geometries, highlighting the utility of regulating gas-liquid mass transfer via aeration for better optimization of photobioreactor performances.

Performance and kinetics of algal-bacterial photobioreactor (AB-PBR) treating septic tank effluent.

Septic tank effluent contains high organic and nutrient contents. This study aimed to evaluate treatment performance of an algal-bacterial photobioreactor (AB-PBR) treating the septic tank effluent. The experimental unit employed a transparent plastic medium made from recycled drinking water bottles for attached-growth biofilm. Red LED lamp (light intensity ∼100 μmol/m2/s) was applied as an energy source for the growth of algal-bacterial biofilm in the AB-PBR. The experimental results showed that AB-PBR operated at the hydraulic retention time (HRT) of 3 days gave the highest chemical oxygen demand (COD), total nitrogen (TN) and total phosphorus (TP) removal efficiencies of 64, 45 and 35%, respectively, by which the effluent COD concentrations could meet the effluent standards of Thailand, but the effluent TN and TP concentrations needed to be further removed. The Stover-Kincannon model was applied to determine the kinetic values of COD and TN removals with R2 values greater than 0.8. Microbiological examinations indicated Chlorella sp. is the predominant algal species growing in the AB-PBR, while the amplicon sequencing information analytical results revealed the bacterial phylum of Proteobacteria to be the predominant bacterial group.

Biomass estimation of an industrial raceway photobioreactor using an extended Kalman filter and a dynamic model for microalgae production

Production of microalgae is one of the emerging biotechnological processes due to its potential applications to produce high value-added compounds. In photobioreactors for microalgae production, the biomass concentration is a desirable variable to be measured on-line to optimize the yield of the systems. However, biomass concentration can hardly be monitored in real time. There are few expensive commercial sensors that in fact provide uncertain measurements. State estimators, also known as software sensors, are algorithms designed to estimate unmeasured (or non-easily measurable) variables of a process. In this work, a state estimator using the extended Kalman filter algorithm is developed to estimate biomass concentration for an outdoor industrial raceway photobioreactor. The state estimator is based on a dynamic model for microalgae production specifically designed for this type of photobioreactor. Results demonstrate that, despite the complex non-linear dynamics that characterise this kind of bioprocess, a state estimator can provide a relatively accurate estimation of the biomass concentration. Furthermore, a state estimator could be used to optimize the operation of industrial photobioreactors by utilizing the estimated biomass concentration for automatic control of the process.

Performance of a novel photobioreactor for nutrient removal from piggery biogas slurry: Operation parameters, microbial diversity and nutrient recovery potential

Photobioreactor is deemed to be one of limiting factors for the commercial application of wastewater treatment based on microalgae cultivation. In this study, a novel Flat-Plate Continuous Open Photobioreactor (FPCO-PBR) was developed to treat piggery biogas slurry. The operation parameters, microbial stability and nutrient recovery potential of FPCO-PBR were investigated. Results showed that the appropriate influent mode for FPCO-PBR was multi-point or spraying mode. The optimal hydraulic retention time and interval time for biomass harvesting of FPCO-PBR were both 2 d. Nitrogen and phosphorus recovery rate were 30 mg L−1 d−1 and 7 mg L−1 d−1 respectively under optimal operating parameters. Microbial diversity remained relatively stable in FPCO-PBR. Biomass production rate of FPCO-PBR was 0.47 g L−1 d−1 under optimal operating parameters. The revenue generated from biomass was estimated to be 15.06 $ kg−1, which means that treating one ton of wastewater can generate $ 7.08 in revenue.

Advanced treatment of the low concentration petrochemical wastewater by Tribonema sp. microalgae grown in the open photobioreactors coupled with the traditional Anaerobic/Oxic process

In this paper, the filamentous microalgae Tribonema sp. grown in the open photobioreactors (PBRs) was directly integrated with the traditional Anaerobic/Oxic (A/O) process for the advanced treatment of low concentration petrochemical wastewater. The COD removal rate was only 71.7% after direct treatment of wastewater effluent from the primary clarifier in the open PBRs, while in-depth purification could be achieved in the secondary clarifier with COD removal rates reached to 97.8% in the open PBRs. The NH3-N and P of the two effluents were almost completely removed after 5–7 days in the open PBRs. The biomass concentration, productivity and the oil content in the open PBRs with the secondary clarifier effluent were all higher than those in the primary clarifier group. The filamentous microalgae Tribonema sp. as a post-treatment step for the A/O process can achieve deep removal of the pollutants and accumulate higher biomass concentration and oil content.

Simulation of algal photobioreactors: recent developments and challenges.

Widespread cultivation of phototrophic microalgae for sustainable production of a variety of renewable products, for wastewater treatment, and for atmospheric carbon mitigation requires not only improved microorganisms but also significant improvements to process design and scaleup. The development of simulation tools capable of providing quantitative predictions for photobioreactor performance could contribute to improved reactor designs and it could also support process scaleup, as it has in the traditional petro-chemical industries. However, the complicated dependence of cell function on conditions in the microenvironment, such as light availability, temperature, nutrient concentration, and shear strain rate render simulation of photobioreactors much more difficult than chemical reactors. Although photobioreactor models with sufficient predictive ability suitable for reactor design and scaleup do not currently exist, progress towards this goal has occurred in recent years. The current status of algal photobioreactor simulations is reviewed here, with an emphasis on the integration of and interplay between sub-models describing hydrodynamics, radiation transport, and microalgal growth kinetics. Some limitations of widely used models and computational methods are identified, as well as current challenges and opportunities for the advancement of algal photobioreactor simulation.

Theory of turbid microalgae cultures

Microalgae can be cultivated in closed or open photobioreactors (PBR). In these systems, light rapidly decreases as it passes through the culture due to the turbidity of the medium. Thus, microalgae experiment different light intensities depending on their position in the medium. In this paper, we study theoretically how the growth rate of microalgae is affected by different factors; incident light intensity, form of the PBR, microalgae population density, turbidity of non-microalgae components, and light path-length of the reactor. We show that for different types of PBR the average growth rate is completely determined by the incident light intensity and the optical depth. In the case of vertical cylindrical PBRs illuminated from above (e.g. race-way or panel-type reactors), we described (and we prove under general assumptions) in details the dependence of the AGR on the aforementioned factors. Finally, we discuss some implications of our analysis; the occurrence of the Allee effect, if light ostensibly limits or inhibits the growth rate in outdoor cultures, and how the geometry of the PBR affects microalgae growth rate and productivity.

Assessment of membrane photobioreactor (MPBR) performance parameters and operating conditions

Membrane photobioreactor (MPBR) technology is an emerging algae-based wastewater treatment system. Given the limitations due to the general use of conventional analytical approaches in previous research, this study aims to provide a more comprehensive assessment of MPBR performance through advanced characterisation techniques. New performance parameters are also proposed, encompassing five important aspects of MPBR system efficiency (i.e. biomass concentration, composition, production, nutrient uptake and harvesting potential). Under initial standard operating conditions, performance parameters, such as cell count/MLSS ratio, cell viability, proportion of bacteria and biomass yield coefficient, were found to offer new insights into the operation of MPBR. These parameters were then used, for the first time, to systematically investigate MPBRs operated under different hydraulic retention times (HRTs) and solids retention times (SRTs). Applying shorter HRT and SRT was observed to increase cell viability and productivity (up to 0.25 × 107 cells/mL·d), as anticipated due to the higher nutrient loading. It was noted that the faster growing algal cells featured lower requirement for nutrients. On the other hand, extending HRT and SRT resulted in a more heterogeneous culture (lower cell count/MLSS ratio and higher proportion of bacteria), achieving a higher degree of autoflocculation and greater NO3-N and PO4-P removals of up to 79% and 78% respectively. The results demonstrate the trade-off between applying different HRTs and SRTs and the importance of fully characterising system performance to critically assess the advantages and limitations of chosen operating conditions.

Hybrid operation of photobioreactor and wastewater-fed open raceway ponds enhances the dominance of target algal species and algal biomass production

Successful cultivation of algal biomass in outdoor open systems depends on maintaining the growth of desirable species against algal invaders that diminish biomass production potential by posing competitive pressure on target algal species. This study demonstrates a photobioreactor (PBR)-open raceway pond (ORP) hybrid system that enables the operation of PBR as a continuous source of the inoculum of desirable algal species to sustain the growth of target algal species in small-scale open raceway ponds (sORPs). A 47-day long operation of PBR-ORP hybrid system indicated that hybrid operation allowed sORPs to maintain the predominant growth of Parachlorella sp. JD076, a target microalga, whereas the sORP operated in conventional semi-continuous mode completely lost the desirable algal species. Moreover, the sORP assigned to PBR-ORP hybrid operation exhibited 40% and 62% increased algal biomass and lipid productivities compared to the sORP operated in conventional semi-continuous mode. The hybrid system produced significantly more biomass and lipids than the conventional semi-continuous system with CO2 amendment, and the hybrid system with CO2 amendment was also more productive than the same system with only aeration. These results thus align well with previous studies that suggested the operation of PBR-ORP hybrid system as a promising crop maintenance strategy to improve the growth and yield of target species at industrial algal cultivation.

Microalgae community shifts during the biogas upgrading in an alkaline open photobioreactor.

To achieve the functional specialization of a microalgae community through operational tuning of an open photobioreactor used for biogas upgrading under alkaline conditions. An open photobioreactor was inoculated with an indigenous microalgae sample from the Texcoco Soda Lake. A microalgae community was adapted to fix CO2 from synthetic biogas through different culture conditions reaching a maximum of 220mg CO2 l-1 per day. Picochlorum sp. and Scenedesmus sp. were identified as the prominent microalgae genera by molecular fingerprinting (partial sequencing of 16S rRNA and 18S rRNA genes) but only the first was detected by microscopy screening. Changes in the microalgae community profile were monitored by a range-weighted richness index, reaching the lowest value when biogas was upgraded. A robust microalgae community in the open photobioreactor was obtained after different culture conditions. The specialization of microalgae community for CO2 fixation under H2 S presence was driven by biogas upgrading conditions. The alkaline conditions enhance the CO2 absorption from biogas and could optimize specialized microalgae communities in the open photobioreactor. Denaturing gradient gel electrophoresis fingerprinting and richness index comparison are useful methods for the evaluation of microalgae community shifts and photosynthetic activity performance, particularly in systems intended for CO2 removal from biogas where the CO2 assimilation potential can be related to the microbial richness.

Evaluation of closed photobioreactor types and operation variables for enhancing lipid productivity of Nannochloropsis sp. KMMCC 290 for biodiesel production

Previously, we have successfully produced biodiesel using the marine microalga Nannochloropsis sp. KMMCC 290 cultivated in a raceway open pond. Here, we investigated the effects of closed photobioreactors and operating variables on cell concentration and lipid content of the microalga to increase its lipid productivity. The flatplate photobioreactor (FPP) showed higher performance than bubble column and air-lift photobioreactors. Among the variables evaluated, light intensity, aeration rate, and carbon dioxide feeding significantly influenced cell concentration, whereas a simultaneous increase in light intensity and aeration rate, as well as carbon dioxide feeding noticeably increased the lipid content. The lipid productivity in the FPP was 26.7 × 10-3 g/L/day, which was 16.6 times higher than that produced by the microalga cultivated in the raceway pond, 4.8 times higher than that from the simple flask-grown control culture, and 2.1 times higher than that from the FPP under initial conditions.

Microalgal cultivation and hydrodynamic characterization using a novel tubular photobioreactor with helical blade rotors.

Industrial-scale microalgal cultivation for food, feedstocks and biofuel production is limited by several engineering factors, such as cultivation systems. As a closed microalgal growth system, tubular photobioreactors are the most preferred ones in the mass algae production. In this work, microalgal cultivation and hydrodynamic characterization using a novel tubular photobioreactor equipped with helical blade rotors (HBRs) were investigated, with the aid of computational fluid dynamics and cultivation experiments to evaluate the effect of HBRs on the performance of tubular photobioreactor and growth of the Chlorella sp. The results showed that the use of HBRs in tubular photobioreactors would result in swirl flow and increase of radial velocity and circumferential velocity; it also indicated that the HBRs would enable microalgal cells to move forward helically and to be shuttled alternatively between the light zone and the dark zone. This has led to the faster growth rate of Chlorella sp. and no attachment on the tube surface in the tubular photobioreactor during the whole cultivation cycle. In conclusion, the HBRs could improve the performance of tubular photobioreactors and thus impact positively on the cultivation of microalgae cells for biotechnological industry.

Evaluation of the dynamics of microalgae population structure and process performance during piggery wastewater treatment in algal-bacterial photobioreactors

The dynamics of microalgae population during piggery wastewater (PWW) treatment in four open photobioreactors operated at 27days of hydraulic retention time, and inoculated with Chlorella sp. (R1), Acutodesmus obliquus (R2), Oscillatoria sp. (R3) and in the absence of inoculum (R4), were evaluated for 6months. In addition, the algal-bacterial biomass concentration, removal of organic matter, nutrients and heavy metals were also assessed. The results revealed a high diversity and rapid variations in the structure of microalgae populations, Chlorella sp. being dominant in R4 throughout most of the operational period. Steady state average biomass concentration ranged from 2445–2610mg/L in R1–R3 to 3265mg/L in R4. No significant differences were recorded in the removal efficiencies (REs) of total organic carbon (86–87%), inorganic carbon (62–71%), total nitrogen (82–85%) and total phosphorous (90–92%). Finally, Zn-REs accounted for 26% in R3, 37% in R2, and 49% in R1 and R4.

Light and Duty Cycle Optimization of a Photo-bioreactor in Batch Mode

Abstract This paper is focused on optimizing the amount of light duty cycle of a photo-bioreactor operating in batch mode. The mathematical model used is confined to one dissolved substrate, one biomass (algae), one internal cell quota, and the irradiance for photo-acclimated culture. The model has been previously published and validated with experimental data. The following optimization problem is studied: minimize the effluent substrate concentration subject to: maximum and minimum amount of light to be used, the time of the light/dark illumination and the total time of the batch experiment. Analytical solution for this optimization problem seems difficult to obtain. However, numerical results obtained from simulations show that it is possible to find solutions which satisfy the problem requirements.

A comparative study of photosynthetic unit models for algal growth rate and fluorescence prediction under light/dark cycles

Accurate description of light-limited algal growth, especially under short light/dark (L/D) cycles, is crucial for prediction of photobioreactor performance and for optimization of operating conditions. Here, a variety of widely used photosynthetic unit (PSU)-based models are evaluated to determine their ability to predict algal specific growth rate and photochemical efficiency under a range of light/dark cycle conditions. Six models were fit to previously published experimental data for algal specific growth rate and photochemical efficiency. Subsequently the weighted sum of squared error (SSE) values, normalized sensitivities to parameter change, and corrected Akaike Information Criterion (AICc) scores were compared. The quality of the fits and the model sensitivities were used to evaluate the assumptions and relative merits of the models considered. For the available data under light/dark cycling conditions, the Bernardi Model scored significantly better on the AICc measure and shows good potential for future use in predicting algal behavior under L/D cycles.