Performance Of Photobioreactor Research Articles

Investigation of light/dark cycles effects on the photosynthetic growth of Chlamydomonas reinhardtii in conditions representative of photobioreactor cultivation

In microalgae cultivation, the combination of light attenuation and culture mixing exposes the microalgae to fluctuating light regimes, which is a factor that can interact with cell metabolism and affect photosynthetic conversion. Here we investigate the effect of light/dark cycles (L/D cycles) on the growth of microalga Chlamydomonas reinhardtii using a photobioreactor equipped with a light-emitting diode (LED) panel to simulate L/D cycles. The L/D cycles applied were engineered to mimic L/D cycles obtained in photobioreactor operating conditions, i.e. L/D cycle frequencies and light attenuation conditions applied during the light period. Long-term experiments were run in continuous mode to investigate whether cells adapt to applied L/D cycles.For cycles of duration higher than 40s, microalgal response was close to the response assuming no L/D cycle effect (no light integration). Biomass growth rate showed responses at durations below 12s, which points to partial light integration resulting in an increase of measured biomass growth rate. This increase is known as the “L/D cycle effect”, where L/D cycle frequencies are found to generate positive effects for photosynthetic conversion. To investigate whether the growth increase was explained by L/D cycle effects, results were compared against the predictions of a kinetic model assuming no light integration but time-solved for light regimes corresponding to L/D cycles applied experimentally. The model was found to very accurately represent any of the light regimes applied, including those leading to an increase in biomass growth rate. It was then concluded that expected primary coupling between L/D cycles and photosynthetic conversion was negligible. The main influence was on pigment adaptation, which when integrated into the kinetic model assuming no L/D cycle effects was found to very accurately predict culture growth under all light regimes.

Hydrodynamic and Heat Transfer Effects of Varying Sparger Spacing Within a Column Photobioreactor Using Computational Fluid Dynamics

This research investigates the placement of spargers on thermofluid effects within a column photobioreactor (PBR) using computational fluid dynamics (CFD). This study compares two configurations, each with three rows of spargers spaced at different widths: one with spargers spaced 7.62 cm apart and the other spaced 10.16 cm apart. These spargers are modeled in a PBR with overall dimensions of 34.29 cm in length, 15.25 cm in width, and 34.28 cm in height. The objective of this research is to predict the performance of PBRs using CFD, which can be used to improve the design of PBRs used to grow microalgae for biofuels and bioproducts.

Improving performance of flat-plate photobioreactors by installation of novel internal mixers optimized with computational fluid dynamics

A novel mixer was developed to improve the performance of flat-plate photobioreactors (PBRs). The effects of mixer were theoretically evaluated using computational fluid dynamics (CFD) according to radial velocity of fluid and light/dark cycles within reactors. The structure parameters, including the riser width, top clearance, clearance between the baffles and walls, and number of the chambers were further optimized. The microalgae culture test aiming at validating the simulated results was conducted indoor. The results showed the maximum biomass concentrations in the optimized and archetype reactors were 32.8% (0.89gL−1) and 19.4% (0.80gL−1) higher than that in the control reactor (0.67gL−1). Therefore, the novel mixer can significantly increase the fluid velocity along the light attenuation and light/dark cycles, thus further increased the maximum biomass concentration. The PBRs with novel mixers are greatly applicable for high-efficiency cultivation of microalgae.

Cultivation of Microalgae <i>Monoraphidium</i> sp., in the Plant Pilot the Grand Valle Bio Energy, for Biodiesel Production

At present, Brazil imports approximately 11 billion liters/year of diesel. With the interruption of the works in the new Petrobras refineries, the projection is that by 2025 this volume will increase to 24.2 billion liters of diesel/year. In this sense, the biodiesel factory Grand Valle Bio Energy Ltda., located in the state of Rio de Janeiro, in conjunction with the FAPERJ makes some investments in technology development for the cultivation and use of microalgae as an alternative raw material in the production of biodiesel. Based on arguments previously said, this work presents the results of the microalgae cultivation Monoraphidium sp. in photobioreactors the pilot plant of the company. The installation with an area of 120 m2 is included with 2 open photobioreactors of type falling film (20 m × 1 m), with a cascade of 18mm and capacity of 4000 L. The lineage cultivated is selected from previous ecophysiological studies that are identified as promising for biodiesel production by having a high potential for the production of lipids. This lineage is maintained at collection of the stock of cultures Laboratory of Green Technologies of the School of Chemistry/ UFRJ. The cultivation was performed in means ASM-1 (Gorham et al., 1964), initial pH 8.0, with aeration and circulation average of 8 hours a day during 19 days. The culture was started with an inoculum of 1 × 107 cel/ml. The lipid production was determined in two phases of growth: on day 4 (exponential phase) and 15 day (stationary phase). For the determination and quantification of lipid content, two different methods were assessed for a sample of biomass, submitted to the same processes the separation and drying. The results showed the methodology of Bligh & Dyer with modifications as the most efficient in extracting lipids. The total lipid content of the biomass Monoraphidium sp. was 30.58%. The growth rate varied between 0.74 ± 0.01 and 0.68 ± 0.02.

Growth of an Indigenous Algal Consortium on Anaerobically Digested Municipal Sludge Centrate: Photobioreactor Performance and Modeling

Centrate from dewatering anaerobically digested municipal sludge is a particular concern in wastewater treatment, as it contains high ammonia concentrations and is often recycled to the head of the plant, reducing efficiency. Algae have the potential to remove ammonia from this wastewater, while producing biomass that can be used as an energy feedstock. In this research, an indigenous algal consortium was cultivated on municipal sludge centrate in a semi-continuous photobioreactor under natural light conditions. The goals of this research were to (1) enrich an algal consortium capable of growth on sludge centrate; (2) determine the main species of the consortium;(3) measure biomass, lipid production, and nutrient removal rates; and (4) develop a simple model to describe the system. The results suggested that Chlorella sp. was the dominant species (95 %) in the consortium. Mean biomass productivity was 5.2 g m−2 day−1, which was relatively high compared with other studies carried out with high ammonia strength wastewaters. Lipid production was low, comprising only 10 % of total biomass. The algal consortium effectively removed nutrients from the centrate, with observed mean removal efficiencies for total nitrogen, total phosphorus, and chemical oxygen demand of 65, 72, and 8 %, respectively. A simple irradiance-based model was developed from the fundamental Michaelis-Menten photosynthesis-irradiance (PI) response for photosynthetic organisms. A good fit to the experimental data was obtained with the irradiance-based model (R2 = 0.96), indicating that the system was light limited. The results show that biomass production can be predicted based on irradiance only.

Concentrated microalgae cultivation in treated sewage by membrane photobioreactor operated in batch flow mode

This study investigated the microalgae biomass production and nutrients removal efficiency from treated sewage by newly developed membrane photobioreactor in which Chlorella vulgaris was cultured in batch flow mode. Its performance was compared with conventional photobioreactor. The results show that the volumetric microalgae productivity was 39.93 and 10.36mgL−1d−1 in membrane photobioreactor and conventional photobioreactor, respectively. The nutrients removal rate in membrane photobioreactor was 4.13mgNL−1d−1 and 0.43mgPL−1d−1, which was obviously higher than that in conventional photobioreactor (0.59mgNL−1d−1 and 0.08mgPL−1d−1). The better performance of membrane photobioreactor was due to the submerged membrane module in the reactor which acted as a solid–liquid separator and thereby enabled the reactor to operate with higher supply flow rate of cultivation medium. Moreover, in the outflow stage of the membrane photobioreactor, the microalgae culture liquor in the reactor could be further concentrated.

Enclosed tubular and open algal–bacterial biofilm photobioreactors for carbon and nutrient removal from domestic wastewater

The mechanisms underlying carbon and nutrient removal from domestic wastewater in an enclosed tubular and an open biofilm photobioreactors were comparatively evaluated at hydraulic retention times (HRTs) of 10, 7 and 5d, and internal recirculation rates of 4.2 and 9Lm−2min−1. Similar organic carbon removal efficiencies were recorded in both photobioreactors (63–97%) regardless of the operational conditions, while a superior inorganic carbon removal was always achieved in the open biofilm photobioreactor (≈100%). Nitrogen and phosphorous removal decreased in both photobioreactors when decreasing the HRT to 7 and 5d, phosphorus being only efficiently removed in the open photobioreactor. Maximum organic carbon, nitrogen and phosphorus removals of 89±2%, 92±5% and 96±2%, respectively, were achieved in the open biofilm photobioreactor at a HRT of 10d. Assimilation into algal–bacterial biomass accounted for most nitrogen and phosphorous removal in both photobioreactors and for carbon removal in the tubular photobioreactor, while stripping (as a result of the low pHs mediated by an intense NH4+ nitrification) was responsible for most inorganic carbon removal in the open system. No significant differences in the carbon, nitrogen and phosphorus content of the harvested biomass were recorded regardless of the photobioreactor configuration and nutrient loading rates. Finally, the monitoring of the dynamics of microalgae population revealed that open biofilm photobioreactors can support a higher microalgae diversity than their enclosed counterparts.

Exploring the high lipid production potential of a thermotolerant microalga using statistical optimization and semi-continuous cultivation.

A recently isolated thermotolerant microalga Desmodesmus sp. F2 has the traits of becoming potential biodiesel feedstock, such as high growth rate, high lipid content, and quick precipitation. Its overall lipid productivity was 113 mg/L/d when grown under non-optimal conditions using batch cultivation. A two-step response surface methodology was adopted to optimize its cultivation conditions. The overall lipid productivity was increased to 263 mg/L/d when the cells were grown under the optimized conditions of 6.6mM initial nitrogen level and 6 days nitrogen depletion treatment in 700 μmol/m(2)/s light intensity at 35°C using batch cultivation. Fed-batch and semi-continuous cultivations were employed to further increase its lipid productivity to 213 and 302 mg/L/d, respectively. The 302 mg/L/d is the highest overall lipid productivity of microalgae ever reported in the literature. This study provides the information required for the design and operation of photobioreactors for large scale outdoor cultivation of this species.

Time-dependent radiation characteristics of Nannochloropsis oculata during batch culture

This paper reports the temporal evolution of the scattering and absorbing cross-sections of marine eustigmatophycease Nannochloropsis oculata grown in a flat-plate photobioreactor (PBR). The PBR was operated in batch mode under constant irradiance of 7500 or 10,000lux provided by red LEDs emitting at 630nm. The radiation characteristics between 400 and 750nm and pigment concentrations of N. oculata were measured systematically every 24h for up to 18days. They were found to vary significantly with time in response to changes in light and nutrients availability. The results were interpreted in terms of up- and down-regulations of pigments and other intracellular components. Finally, this study demonstrates that the light transfer in the PBR could be predicted using constant radiation characteristics measured during the exponential growth phase with reasonable accuracy provided that the cultures were not nitrogen limited. During nitrogen starvation, pigment concentrations decreased and radiation characteristics evolved rapidly. These results will be useful in the design and operation of PBRs for biofuel production at both small and large scales.

Numerical and experimental study on the performance of flat-plate photobioreactors with different inner structures for microalgae cultivation

Three types of 15-L flat-plate photobioreactors (PBRs), namely, bubble reactor, split flat-plate airlift reactor, and central flat-plate airlift reactor, were investigated for their performance based on numerical and experimental methods. The computational fluid dynamics (CFD) method was used to calculate mixing and light regime characteristics parameters of PBRs. The performance of flat-plate PBRs was preliminarily evaluated according to the light–dark cycle of algal cells and fluid mixing along the light attenuation direction. The analysis showed that the optimal PBR was the split airlift type, whereas the bubble PBR was the poorest. The photoautotrophic cultivation of Chlorella pyrenoidosa was conducted to confirm the actual performance of PBRs. The result of microalgae culture experiment showed the biomass productivity in split airlift reactor was 0.018 g L−1 h−1 which was 50 and 12.5 % higher than those in bubble and central airlift PBRs, respectively. The maximum biomass concentration and specific growth rate of algal cell in split flat-plate airlift reactor were greatest, and those in bubble reactor were lowest. Therefore, the experiment results are completely consistent with those obtained through the computational approach, suggesting the numerical model combining fluid hydrodynamics with irradiation transfer as well as statistical treatment developed in this study can be applied to optimize and evaluate the performance of PBRs efficiently.

Predicting Hydrodynamic and Heat Transfer Effects of Sparger Geometry and Placement Within a Column Photobioreactor Using Computational Fluid Dynamics

This research investigates the effects of the sparger on flow patterns and heat transfer within a column photobioreactor (PBR) using computational fluid dynamics (CFD). This study compares two types of spargers: a porous membrane, which occupies the entire floor of the reactor, and a single sparger, which is located along the centerline of the PBR floor. The PBR is modeled using the Lagrangian–Eulerian approach. The objective of this research is to predict the performance of PBRs using CFD models, which can be used to improve the design of PBRs used to grow microalgae that are used to produce biofuels and bioproducts.

Removal of nitrogen and phosphorus from municipal wastewater effluent using Chlorella vulgaris and its growth kinetics

Chlorella vulgaris was used for the removal of residual ammonia/ammonium ion (NH3/) and orthophosphate ion () from secondary wastewater effluent collected from a municipal wastewater treatment plant. The uptake rates for nitrogen and phosphorus were studied with different initial algal cell densities and the addition of CO2 gas for pH control and supply of inorganic carbon. Our result showed that typical NH3/ and concentrations could be readily removed within 48 h. It was found that the culture with an initial algal cell density of ∼350 mg/L and CO2 gas supply could significantly enhance both the rates of cell growth and nutrient uptake. The Monod equation well described the algal cell growth under substrate-limiting conditions, and could be used for the design and operation of photobioreactors for potential tertiary wastewater treatment.

Energetic Performance of Photobioreactors for Algal Cultivation

Microalgae are currently being investigated as a potential fuel crop. For algae to be an energy-efficient fuel crop, cultivation systems and operating conditions that have been optimized for biomass productivity have to be refocused toward energy production. In this work, data from the literature on a variety of algal photobioreactors (PBRs) were compiled to reassess them in terms of biomass productivity per unit energy input to the cultivation process. This assessment showed that PBRs that have been optimized for biomass productivity without considering the energy input did not necessarily perform well in terms of energy efficiency. This review recommends that selection of algal PBRs for energy production should consider optimal geometry for efficient utilization of incident light, and their operation should be based on the optimal sparging rate for efficient mixing to maximize energy efficiency.

Physiological response of Nannochloropsis sp. to saline stress in laboratory batch cultures

In the present paper, we investigated the physiological response of the marine microalga Nannochloropsis sp. to salt stress (13, 27, 54, and 81 g L−1 NaCl). Increasing the sodium chloride concentration caused up to a 70 % decrease in the chlorophyll a concentration, cell growth, and net photosynthesis rate. The chlorophyll a fluorescence measurements indicated a strong reduction in the effective quantum yield of photosystem II (−60 %) and an increase in nonphotochemical quenching when the cells were exposed to NaCl concentrations greater than 27 g L−1 (control). In contrast, the specific lipid content increased up to 80 % when the sodium chloride concentration was increased from 27 to 54–81 g L−1. These results are relevant for the outdoor cultivation of this microalga using open photobioreactors, in which microalgae are subjected to strong changes in salinity concentration caused by water evaporation.

Photobioreactor operation condition optimization for high-energy cyanobacterial biomass synthesis to produce third-generation biofuels

The distinctive features of cultivation of two strains of thermophilic cyanobacteria, Mastigocladus laminosus and Anabaena variabilis, in a pouring-off-filling-up type of photobioreactor are investigated. The dependence of the biomass growth rate and concentration doubling time on the carbon dioxide content in the injected air is studied and the culture medium composition is optimized. It is shown that tap water added with macro- and microelements, instead of analogous distilled water based nutrient medium, facilitates faster biomass growth. The minimum biomass doubling time is 0.9 day for Mastigocladus laminosus and 1.1 days for Anabaena variabilis when the carbon dioxide content in the injected air is 4 vol. %.

Photo-oxygenation to support nitrification in an algal–bacterial consortium treating artificial wastewater

Oxygenation by photosynthesis in a mixed culture of algae and nitrifiers was investigated for its potential to support nitrification. An open photo-bioreactor (1L fermentor; 30°C) was inoculated with an enriched culture of nitrifiers obtained from activated sludge and a pure culture of Scenedesmus sp. The reactor was illuminated (60μmol/m2s) and operated as a sequencing batch reactor with 50% discharge per cycle and sludge retention time of 15 or 30days. Full nitrification of synthetic wastewater (50mgNH4+-N/L) without mechanical aeration was achieved after less than 14 cycles (18.5h React per 24h cycle) and the biomass steadily increased until a concentration of 1.9g VSS/L with 29mg chl-a/L. The maximum observed nitrification rate was 7.7mgNH4+-N/Lh. A mass balance showed that ammonium removal was primarily by nitrification (81–85%) rather than by ammonium uptake by algae.

Long term outdoor operation of a tubular airlift pilot photobioreactor and a high rate algal pond as tertiary treatment of urban wastewater

530L high rate alga pond (HRAP) and 380L airlift tubular photobioreactor (TPBR) were operated and compared in a urban wastewater treatment plant (WWTP), with the main purpose of removing nitrogen and phosphorous from the effluent of the WWTP while generating a valuable biomass. The photosynthetic activity in TPBR was during entire experiment higher than HRAP. The maximum areal productivity reached was 8.26±1.43 and 21.76±0.3gSSm−2d−1 for HRAP and TPBR respectively. Total nitrogen (TN) removal averaged 89.68±3.12 and 65.12±2.87% for TPBR and HRAP respectively, while for total phosphorus (TP) TPBR and HRAP averaged 86.71±0.61 and 58.78±1.17% respectively. The lipid content showed no significant differences (p<0.05) between HRAP and TPBR averaging 20.80±0.22wt%. The main operating disadvantage of TPBR versus HRAP was the sever biofouling which forced to stop the experiment. Under the same conditions of operation TPBR was more limited at low temperatures than HRAP, and HRAP was more light limited than TPBR.

Global Future Prospects and Problems of Microbial Biofuel: Algal Biodiesel

Human population explosion, progressive industrialization, automobiles and world energy requirements, particularly for the fossil fuel is likely to deplete limited natural resources over short period of time. Therefore, search for an alternative fuel resource is the only way to overcome the upcoming energy crisis. Biofuel, in this context seems to be a sustainable option. Biomasses so far used for biodiesel production include animal fats, vegetable oils like soybean, rapeseed, Jatropha, mahua, mustard, flax, sunflower, palm, hemp, field pennycress, Pongamia pinnata etc. which require agricultural land for their growth. In the present context, population explosion does not permit the use agricultural land for the cultivation of petro crops and therefore the scientists have to find an energy feedstock which does not require fertile land use. Keeping it in view, emphasis has been given to the autotrophic tiny organisms of algae for biodiesel production, the world over. Certain algal species contains oil producing substrate and are rapidly growing under normal conditions. This algal fat can be processed into biodiesel by trans esterification. Biodiesel production from algae involves identification of high fatty acid storing algal species, their cultivation in open or hybrid photobioreactors, harvesting, oil extraction and process standardization. Biodiesel production from algae had been emphasized by Bhatnagar et al. (2011) which need proper initiative to become energy sustainable.

Process and reactor design for biophotolytic hydrogen production

The green alga Chlamydomonas reinhardtii has the ability to produce molecular hydrogen (H2), a clean and renewable fuel, through the biophotolysis of water under sulphur-deprived anaerobic conditions. The aim of this study was to advance the development of a practical and scalable biophotolytic H2 production process. Experiments were carried out using a purpose-built flat-plate photobioreactor, designed to facilitate green algal H2 production at the laboratory scale and equipped with a membrane-inlet mass spectrometry system to accurately measure H2 production rates in real time. The nutrient control method of sulphur deprivation was used to achieve spontaneous H2 production following algal growth. Sulphur dilution and sulphur feed techniques were used to extend algal lifetime in order to increase the duration of H2 production. The sulphur dilution technique proved effective at encouraging cyclic H2 production, resulting in alternating Chlamydomonas reinhardtii recovery and H2 production stages. The sulphur feed technique enabled photobioreactor operation in chemostat mode, resulting in a small improvement in H2 production duration. A conceptual design for a large-scale photobioreactor was proposed based on these experimental results. This photobioreactor has the capacity to enable continuous and economical H2 and biomass production using green algae. The success of these complementary approaches demonstrate that engineering advances can lead to improvements in the scalability and affordability of biophotolytic H2 production, giving increased confidence that H2 can fulfil its potential as a sustainable fuel of the future.

Responses of Synechocystis sp. PCC 6803 to total dissolved solids in long-term continuous operation of a photobioreactor

This study evaluated how Synechocystis sp. PCC 6803 responds to high total dissolved solids (TDS) associated with eliminating nutrient limitation during long-term operation of a photobioreactor. The unique feature is that the TDS were not dominated by Na+ and Cl−, as in seawater, but by HCO3− and NO3− from nutrient delivery. The TDS-stress threshold was about 10g/L. Whereas inorganic N and P limitations slowed the rate of inorganic C (Ci) uptake in the light, TDS stress was manifested most strongly as a substantial increase of endogenous respiration rate at night. Relief from TDS stress was incomplete when lowered pH led to a HCO3− increase (560mgC/L as a threshold). Impaired photosynthesis led to a cascade of reduced Ci-uptake, pH decrease, HCO3− accumulation, and HCO3−-associated stress. Thus, long-term photobioreactor operation requires balancing the delivery rates of CO2, N, P, and other TDS components to avoid general and Ci-associated TDS stresses.