Development of a floating photobioreactor with internal partitions for efficient utilization of ocean wave into improved mass transfer and algal culture mixing

Culturing microalgae in the ocean has potentials that may reduce the production cost and provide an option for an economic biofuel production from microalgae. The ocean holds great potentials for mass microalgal cultivation with its high specific heat, mixing energy from waves, and large cultivable area. Suitable photobioreactors (PBRs) that are capable of integrating marine energy into the culture systems need to be developed for the successful ocean cultivation. In this study, prototype floating PBRs were designed and constructed using transparent low-density polyethylene film for microalgal culture in the ocean. To improve the mixing efficiency, various types of internal partitions were introduced within PBRs. Three different types of internal partitions were evaluated for their effects on the mixing efficiency in terms of mass transfer (k _L a) and mixing time in the PBRs. The partition type with the best mixing efficiency was selected, and the number of partitions was varied from one to three for investigation of its effect on mixing efficiency. When the number of partitions is increased, mass transfer increased in proportion to the number of partitions. However, mixing time was not directly related to the number of partitions. When a green microalga, Tetraselmis sp. was cultivated using PBRs with the selected partition under semi-continuous mode in the ocean, biomass and fatty acid productivities in the PBRs were increased by up to 50 % and 44 % at high initial cell density, respectively, compared to non-partitioned ones. The results of internally partitioned PBRs demonstrated potentials for culturing microalgae by efficiently utilizing ocean wave energy into culture mixing in the ocean.     

Effect of photobioreactor inclination on the biomass productivity of an outdoor algal culture

The profiles of photon flux density incidented on a tubularloop photobioreactor in the day could be altered by inclining the bioreactor at an angle with the horizontal. The photon flux density at noon decreased with increasing angle of inclination, whereas the photon flux density in the early morning and late afternoon increased with increasing angle of inclination. The overall photosynthetic radiance received by the bioreactor inclined at 0, 25, 45, and 80 degrees was 1:0.89:0.77:0.62. Regardless of the angle of bioreactor inclination, the overall biomass output rate of a fed-batch culture over an 8-h/day period was comparable (26-36 g-biomass m(-2) bioreactor surface area day(-1)). As a bioreactor inclined at an angle occupied smaller land area, and daily biomass output rate per land area of a bioreactor inclined at 80 degrees (130 g-biomass m(-2) land) was about six times of that obtainable at horizontal position (21-g biomass m(-2) land). The bioenergetics growth yield from the absorbed photosynthetic radiance was not a constant but an inverse function of the photon flux density. The quasi-steady state chlorophyll content of the Chlorella cells varied between 36 and 63 mg g(-1) cells. Photoinhibition of the maximum photosynthetic capacity was not observed in this study.     

Marine algal carbohydrates as carbon sources for the production of biochemicals and biomaterials

The high content of lipids in microalgae (>60% w/w in some species) and of carbohydrates in seaweed (up to 75%) have promoted intensive research towards valorisation of algal components for the production of biofuels. However, the exploitation of the carbohydrate fraction to produce a range of chemicals and chemical intermediates with established markets is still limited. These include organic acids (e.g. succinic and lactic acid), alcohols other than bioethanol (e.g. butanol), and biomaterials (e.g. polyhydroxyalkanoates). This review highlights current and potential applications of the marine algal carbohydrate fractions as major C-source for microbial production of biomaterials and building blocks.     

Perspectives on cultivation strategies and photobioreactor designs for photo-fermentative hydrogen production

Photosynthetic bacteria have considerable biotechnological potential for biological hydrogen production due to higher substrate conversion efficiency and hydrogen yield. Phototrophic fermentation using photosynthetic bacteria has a major advantage of being able to further convert the byproducts originating from dark fermentation (e.g., volatile fatty acids) to hydrogen. Through the combination of dark and photo-fermentation processes, organic feedstock is fully converted into gaseous product (H₂) at the highest possible H₂ yield, with significant reduction of chemical oxygen demand (COD). The performance of photo-fermentation is highly dependent on the medium composition, culture conditions, and photobioreactor design. Therefore, this article provides a critical review of the effects of key factors affecting the photo-hydrogen production efficiency of photosynthetic bacteria, and also summarizes the strategies being applied in promoting the performance of photo-fermentation.     

Influence of fluorescent coating at rear and front side of a flat panel photobioreactor on algal growth

The focus of this study is the enhancement of microalgae growth rate using spectral conversion of green light. For this purpose, three reactors were considered and fluorescent pigment Rhodamine 6G was dissolved in a thermoplastic acrylic resin, the mixture was then applied on the front side of the first reactor, and on a mirror located at the rear side of the second one. Comparing their maximum specific growth rate (μ _max) of Chlorella sp. to that in the third (uncoated) reactor, the former resulted in an increase up to 15% while the latter in decrease to at least 30%. Also, the rear side coated reactor showed up to 50% increase in biomass productivity rate (P) in early 4 days of experiment. However, this value decreased over time and the uncoated reactor in 12 days exhibited higher biomass productivity rate.     

Optimized aeration by carbon dioxide gas for microalgal production and mass transfer characterization in a vertical flat-plate photobioreactor

To optimize the aeration conditions for microalgal biomass production in a vertical flat-plate photobioreactor (VFPP), the effect of the aeration rate on biomass productivity was investigated under given conditions. Air enriched with 5% or 10% (v/v) CO(2) was supplied for the investigation at rates of 0.025-1 vvm. The CO(2) utilization efficiency, change of pH in the medium, and the optimum aeration rate were determined by evaluating biomass productivity. To investigate the VFPP mass transfer characteristics, the overall volumetric mass transfer coefficient, k(L)a, was evaluated for several different flat-plate sizes. Increasing the height of the VFPP could improve both the mass transfer of CO(2) and the illumination conditions, so this appeared to be a good method for scaling up. Based on a comparison of the k(L)a value at the optimum aeration rate with previously reported results, it was confirmed that the range of CO(2) concentration used in the experiments was cost-effective for mass culture.     

Investigation of biomass and lipids production with Neochloris oleoabundans in photobioreactor

The fresh water microalga Neochloris oleoabundans was investigated for its ability to accumulate lipids and especially triacylglycerols (TAG). A systematic study was conducted, from the determination of the growth medium to its characterization in an airlift photobioreactor. Without nutrient limitation, a maximal biomass areal productivity of 16.5 g m⁻² day⁻¹ was found. Effects of nitrogen starvation to induce lipids accumulation was next investigated. Due to initial N. oleoabundans total lipids high content (23% of dry weight), highest productivity was obtained without mineral limitation with a maximal total lipids productivity of 3.8 g m⁻² day⁻¹. Regarding TAG, an almost similar productivity was found whatever the protocol was: continuous production without mineral limitation (0.5 g m⁻² day⁻¹) or batch production with either sudden or progressive nitrogen deprivation (0.7 g m⁻² day⁻¹). The decrease in growth rate reduces the benefit of the important lipids and TAG accumulation as obtained in nitrogen starvation (37% and 18% of dry weight, respectively).     

Effects of algal and terrestrial carbon on methane production rates and methanogen community structure in a temperate lake sediment

1. Sources of atmospheric CH₄ are both naturally occurring and anthropogenic. In fact, some anthropogenic activities may influence the production of CH₄ from natural sources, such as lakes. 2. Ongoing changes in the catchment of lakes, including eutrophication and increased terrestrial organic carbon export, may affect CH₄ production rates as well as shape methanogen abundance and community structure. Therefore, inputs from catchments to lakes should be examined for their effects on CH₄ production. 3. We added algal and terrestrial carbon separately to lake sediment cores and measured CH₄ production. We also used quantitative polymerase chain reaction and terminal restriction fragment length polymorphism to determine the effects of these carbon additions on methanogen abundance and community composition. 4. Our results indicate that CH₄ production rates were significantly elevated following the addition of algal biomass. Terrestrial carbon addition also appeared to increase methanogenesis rates; however, the observed increase was not statistically significant. 5. Interestingly, increased CH₄ production rates resulted from increases in per‐cell activity rather than an increase in methanogen abundance or community compositional shifts, as indicated by our molecular analyses. 6. Overall, anthropogenic impacts on aquatic ecosystems can influence methanogenesis rates and should be considered in models of global methane cycling and climate.     

Effect of CO2 enhancement in an outdoor algal production system usingTetraselmis

One of the objectives of microalgal culture is to provide reliable production technology for important live aquaculture feed organisms. Presented here are the results of experiments designed to provide a better understanding of the relationship between inorganic carbon availability and algal production.Our results suggest that through additions of CO₂ gas we were able to maintain sufficient dissolved carbon to stabilize outdoor algal cultures. Increases in the rate of addition of CO₂ increased levels of dissolved CO₂, total dissolved inorganic carbon (CO₂), and decreased pH in the growth medium. This translated into improved buffering capacity of the culture medium and higher growth rate. A minimum of 2.4 mM CO₂ was found necessary to maintain a maximal growth rate of 0.7 doublings/day. We also found that the increased productivity more than offsets the cost of adding the CO₂.     

A simple algal production system designed to utilize the flashing light effect

Arrays of foils similar in design to airplane wings have been placed in an algal culture flume to create systematic mixing. Vortices are produced in the culture due to the pressure differential created as water flows over and under the foils. In a flume having a flow rate of 30 cm/s, the foil arrays produced vortices with rotation rates of ca. 0.5-1.0 Hz. This rotation rate is satisfactory to take advantage of the flashing light effect if the culture is sufficiently dense. Solar energy conversion efficiencies in an experimental culture of P. tricornutum increased 2.2-2.4 fold with the foil arrays in place versus controls with no foil arrays and solar energy conversion efficiencies averaged 3.7% over a three-month period. Five-day running means of solar energy conversion efficiencies reached as high as 10% during the three-month period. The use of foil arrays appears to be an effective and inexpensive way to utilize the flashing light effect in a dense algal culture system.     

Coupling microbial fuel cells with a membrane photobioreactor for wastewater treatment and bioenergy production

Microbial fuel cells (MFCs) and membrane photobioreactors are two emerging technologies for simultaneous wastewater treatment and bioenergy production. In this study, those two technologies were coupled to form an integrated treatment system, whose performance was examined under different operating conditions. The coupled system could achieve 92–97 % removal of soluble chemical oxygen demand (SCOD) and nearly 100 % removal of ammonia. Extending the hydraulic retention time (HRT) of the membrane photobioreactor to 3.0 days improved the production of algal biomass from 44.4 ± 23.8 to 133.7 ± 12.9 mg L^?1 (based on the volume of the treated water). When the MFCs were operated in a loop mode, their effluent (which was the influent to the algal reactor) contained nitrate and had a high pH, leading to the decreased algal production in the membrane photobioreactor. Energy analysis showed that the energy consumption was mainly due to the recirculation of the anolyte and the catholyte in the MFCs and that decreasing the recirculation rates could significantly reduce energy consumption. The energy production was dominated by indirect electricity generation from algal biomass. The highest energy production of 0.205 kWh m^?3 was obtained with the highest algal biomass production, resulting in a theoretically positive energy balance of 0.033 kWh m^?3. Those results have demonstrated that the coupled system could be an alternative approach for energy-efficient wastewater treatment and using wastewater effluent for algal production.     

Perspectives on an ocean management system

Abstract

Over the past ten years, federal management authorities for ocean uses and resources have become excessively compartmentalized and complex. In the interest of evaluating the need for a better articulated and organized national ocean program, this article examines the concept of ocean management. It attempts to portray an analytical review approach for assessing current ocean uses and management strategies. It explores the implications of ocean management as they impinge on the federal government's role in an organization for the marine environment. The concept of ocean management is reviewed from three perspectives: (1) an analysis of current conflicts among uses competing for scarce ocean resources; (2) an evaluation of existing programs which are designed to integrate other marine authorities; and (3) a survey of existing legal and administrative authorities that pertain to the marine environment. In light of these perspectives, the authors examine approaches that have been suggested for revising our ocean management system and offer recommendations toward this end.     

Continuous marennin production by agar-entrapped Haslea ostrearia using a tubular photobioreactor with internal illumination

The marine diatom Haslea ostrearia was immobilized in a tubular agar gel layer introduced into a photobioreactor of original design with internal illumination for the continuous synthesis of marennin, a blue-green pigment of biotechnological interest. Marennin was produced for a long-term period (27–43 days) and the volumetric productivity was maximum (18.7 mg day⁻¹ l⁻¹ gel) at the highest dilution rate (0.25 day⁻¹) and lowest agar layer thickness (3 mm). Heterogeneous cell distribution in the agar layer revealed diffusional limitation of light and nutrients. However, the 3 mm gel thickness led to a more homogeneous cell distribution during incubation and to an increase of the whole biomass in the agar gel layer. Received: 22 October 1999 / Received revision: 14 February 2000 / Accepted: 18 February 2000     

Effect of process variables on photosynthetic algal hydrogen production

Chlamydomonas reinhardtii is a green alga that can use the sun's energy to split water into O(2) and H(2). This is accomplished by means of a two-phase cycle, an aerobic growth phase followed by an anaerobic hydrogen production phase. The effects of process variables on hydrogen production are examined here. These variables include cell concentration, light intensity, and reactor design parameters that affect light transport and mixing. An optimum cell concentration and light intensity are identified, and two reactor designs are compared. The maximum hydrogen production observed in this study was 0.29 mL of hydrogen per milliliter of suspension. This was measured at atmospheric pressure during a 96 h production cycle. This corresponds to an average hydrogen production rate of 0.12 mmol/mL.h.     

Process development and evaluation for algal glycerol production

This article and develops a process for large-scale production of glycerol by means of a hemophilic algae. The process is shown to be economically and technically feasible. Although the proposed process is extremely capital intensive, the total production cost is competitive with existing glycerol process. In addition, the overall energy requirement is much lower than that of the petrochemical process. This proposed process provides an alternative route for glycerol production that is minimally dependent on fossil fuels and is therefore, less sensitive to crude oil availability and price. The primary raw material carbon dioxide from stack gas, is an inexpensive and renewable resource. Maximal Utilization of solar energy is made not only in the glycerol synthesis steps but also in the product recovery system. Significant improvement in the process economics can be realized through further development of large-scale cultivation technology, and biomass distribution and collection machinery. Due to the labor intensive nature of the proposed algal process, it is particularly suitable for less developed nations with limited fossil fuel resources and lower labor costs.     

Monoseptic cultivation of phototrophic microorganisms--development and scale-up of a photobioreactor system with thermal sterilization

The use of phototrophic microorganisms as sources of biological active substances in photoautotrophic and mixotrophic cultivation modes requires an adequate cultivation system with thermal sterilization. A corresponding photobioreactor system in the 10, 25 and 100 l scales was developed. This "Medusa"-photobioreactor system represents a concept based on the air-lift loop principle, whose working volume is irradiated by external light sources. The incident irradiation can be varied by a light control system. An effective CO(2)/O(2) gas exchange is enabled due to the efficient supply with process gas by several gas supply nozzles within the system and a large degassing surface. Using a model to describe the growth characteristics of the organisms, the volumetric irradiation coefficient I(DX) was defined as scale-up parameter. On this basis the scale-up from 1 l bubble columns to the 10 and 100 l scales was realized. The scale-up was performed successfully with Chlorella salina as model organism. A maximum biomass concentration of 7.89 g (dry weight) l(-1) at a maximum specific growth rate of 0.058 h(-1) and a yield of 35 mg l(-1) h(-1) was obtained in a batch cultivation in the 100 l scale under photoautotrophic conditions with an initial biomass concentration of approx. 0.03 g l(-1).     

Immobilization of Anabaena azollae from Azolla filiculoides in polyvinyl foam for ammonia production in a photobioreactor system

Anabaena azollae (AS-DS), isolated from Azolla filiculoides and grown in nitrogen-free medium, was immobilized in 5-mm-cube polyvinyl foam pieces and incorporated into a photobioreactor system for the production of NH₃. NH₃ was produced continuously and in significant amounts. Benlate (methyl-1-butyl-carbamoyl)-2-benzimidazole carbamate at 5 ppm and l-methionine-d,l-sulphoximine at 50 m stimulated NH₃ production continuously for a period of 1 week.S. Kannaiyan is with the Biotechnology Unit, Department of Agricultural Microbiology, Tamilnadu Agricultural University, Coimbatore-641003, Tamilnadu, India; K.K. Rao and D.O. Hall are with the Division of Life Sciences, King's College London, Campden Hill Road, London W8 7AH, UK.     

Estimatingin situ algal production rates with the help of light measurements and experimentally measured production rates

Summary A method is described with which algal production can be estimated if irradiance above and under water are known and the relationship is determined between production rate and irradiance. Large numbers of water samples can be quickly and efficiently processed. Some of the equipment developed and in use is also described. The reliability and precision of the method presented is shown to be reasonable if certain conditions are met.