This inter-disciplinary thesis is concerned with the production of polyunsaturated fatty acids (PUFAs) from newly isolated and identified alpine microalgae, and the optimization of the temperature, photon flux density (PFD), and carbon dioxide (CO2) concentration for their mass production in an airlift photobioreactor (AL-PBR). Thirteen strains of microalgae were isolated from the alpine zone in Canyon Creek, Canterbury, New Zealand. Ten species were characterized by traditional means, including ultrastructure, and subjected to phylogenetic analysis to determine their relationships with other strains. Because alpine algae are exposed to extreme conditions, and such as those that favor the production of secondary metabolites, it was hypothesized that alpine strains could be a productive source of PUFAs. Fatty acid (FA) profiles were generated from seven of the characterized strains and three of the uncharacterized strains. Some taxa from Canyon Creek were already identified from other alpine and polar zones, as well as non-alpine zones. The strains included relatives of species from deserts, one newly published taxon, and two probable new species that await formal naming. All ten distinct species identified were chlorophyte green algae, with three belonging to the class Trebouxiophyceae and seven to the class Chlorophyceae. Comparative study between the distribution of algae at Canyon Creek and Mount Philistine, another alpine region in New Zealand where algal distribution was studied in detail, revealed that algal distribution patterns in the New Zealand alpine zone are complex, with some taxa apparently widely distributed and others range restricted or rare (with the caveat that very few sites have been studied in detail). At least some of the differences between the two sites could be accounted for by geographic differences, resulting in contrasting environmental conditions such as rainfall. As hypothesized, alpine strains isolated from the Canyon Creek were rich in PUFAs. Eight among the ten strains have PUFA proportions higher than monounsaturated fatty acids and saturated FAs. In a comparison of FA profiles of Scenedesmaceae species from a hot environment (Algerian Sahara) with the Scenedesmaceae species from Canyon Creek, the latter revealed a much greater degree of unsaturation. In addition, the Canyon Creek strains contained some FAs (such as docosapentaenoic acid, DPA) that were absent from Saharan strains. Among the strains from Canyon Creek Lobochlamys segnis LCR-CC-5-1A was selected for optimization experiments on the basis of growth kinetics, temperature response and FA composition, of which 60% of total FAs were PUFAs. Of that 60%, the α-linolenic acid (ALA) content was 46%. Two identical 1.5 Liter AL-PBRs were used for culturing Lobochlamys segnis LCR-CC-5-1A to study the effect of CO2 concentration, PFD and temperature on specific growth velocity, production of PUFAs, omega-3 FAs and, specifically, the concentration of ALA. The concentrations of CO2 examined in this research were 1.5, 3.0 and 4.5% in air. Similarly, the reponses of the strain to seven different PFDs, namely 38, 77, 115, 178, 210, 236 and 253 µmol m-2 s-1 and six different temperatures, 5, 10, 15, 20, 25 and 30οC, were analyzed. The maximum specific growth velocities (µmax) of the cultures were calculated from the experimental data and the cell production rate was calculated from fitting logistic growth models to these data; the two were compared by converting the former to the latter. The significance of the tested parameters was assessed using ANOVA and Tukey tests. The optimum conditions assessed at lab scale for maximum production of biomass, PUFAs and ALA were found to be a CO2 concentration of 3.0%, temperature of 20°C, and PFD of 178 µmol m-2 s-1. Increasing biomass production has the effect of maximizing PUFA production because there was no significant increase in concentration of PUFAs, omega-3 FAs, or ALA under levels of CO2, temperature, and PFD differing from those under which maximum growth occurred.

Differences in biofilm formation between Scenedesmus obliquus and Chlorella vulgaris were examined, as well as the effects of substrate properties. Species selection and species control had significant effects. In non-sterile conditions, C. vulgaris shifted from planktonic (23.7% attachment) to sessile (79.8% attachment) growth, and formed films of higher average thickness (52 ± 19 µm) than in sterile conditions (7 ± 6 µm). By contrast, S. obliquus attained similar thicknesses (54 ± 31 µm and 53 ± 38 µm) in both sterile and non-sterile conditions. The effect of substrate properties was minimal. Both species grew films of similar thickness (~ 30 µm for S. obliquus, <10 µm for C. vulgaris) on materials ranging from hydrophilic (glass) to hydrophobic (polytetrafluoroethylene). Micropatterning the surface also had little effect on film formation. The results indicate that species selection and species control are more important that substrate properties in the development of microalgal biofilms.

Differences in biofilm formation between Scenedesmus obliquus and Chlorella vulgaris were examined, as well as the effects of substrate properties. Species selection and species control had significant effects. In non-sterile conditions, C. vulgaris shifted from planktonic (23.7% attachment) to sessile (79.8% attachment) growth, and formed films of higher average thickness (52 ± 19 µm) than in sterile conditions (7 ± 6 µm). By contrast, S. obliquus attained similar thicknesses (54 ± 31 µm and 53 ± 38 µm) in both sterile and non-sterile conditions. The effect of substrate properties was minimal. Both species grew films of similar thickness (~ 30 µm for S. obliquus, <10 µm for C. vulgaris) on materials ranging from hydrophilic (glass) to hydrophobic (polytetrafluoroethylene). Micropatterning the surface also had little effect on film formation. The results indicate that species selection and species control are more important that substrate properties in the development of microalgal biofilms.

The culture of coccolithophorid algae is an attractive option for sequestration or recycling of CO2 as they can fix carbon by photosynthesis as well as in calcium carbonate scales known as coccoliths. They also produce high amounts of lipids which have a potential application as a renewable fuel. Five species of coccolithophorids (Pleurochrysis carterae, CCMP647, Pleurochrysis sp. CCMP1211, Gephyrocapsa oceanica CS-335/2, Emiliania huxleyi CCMP371, and Emiliania huxleyi CS-369) were screened for their ability to grow at high temperature. All species grew up to 28oC except E. huxleyi CS-369. However, Pleurochrysis sp. CCMP 1211 which was found to clump and can therefore not be recommended for large-scale cultivation. The salinity tolerance of these species was also examined. Growth of P. carterae, G. oceanica, and E. huxleyi in laboratory scale closed photobioreactors (plate, carboy, airlift, and tubular photobioreactors) showed the plate photobioreactor to be the best closed cultivation system. The highest productivities were achieved by P. carterae in the plate photobioreactor and were 0.54 g.L-1.d-1, 0.12 g.L-1.d-1, 0.06 g.L-1.d-1 for total dry weight, lipid and CaCO3 respectively. The growth of P. carterae and E. huxleyi was also examined in an outdoor raceway pond. The E. huxleyi culture was easily contaminated resulting in the loss of the culture in less than three weeks, but P. carterae grew well over a period of 13 months. The overall total dry weight productivity of P. carterae was 0.19 g.L-1.d-1 with lipid and CaCO3 contents of up to 33% and 10% of dry weight respectively. There was little protozoan and bacterial contamination. Medium pH increased to pH 11 during the day and was found to be a reliable variable for maintaining the health of the culture. A maximum pH achieved during the day of less than pH 8.5 indicated the imminent collapse of the culture. Heavy rain and low temperature were the main reasons for culture loss in mid winter, whereas high temperature during summer favoured P. carterae growth. A comparison of the growth of P. carterae and Dunaliella salina MUR8 in the raceway ponds showed no significant differences between these two species with regard to areal total dry weight productivity and lipid content. The effects of several limiting factors were also examined. A reduction in medium pH resulting from CO2 addition inhibited the growth of E. huxleyi in the plate photobioreactor, whereas P. carterae growth and productivities increased in the pH range of pH 7.7 to 8.0 in the plate photobioreactor and pH 9.1 to 9.6 in the outdoor raceway pond. The best operational pond depth for outdoor raceway culture of P. carterae was between 16 cm and 21 cm. Early morning temperatures, especially during the winter, highly affected the growth of P. carterae in the raceway pond, whereas artificially increasing the medium temperature improved the health of the culture but resulted in little increase in productivity. Photosynthesis of P. carterae was found to be highly inhibited by high oxygen concentration in the medium irrespective of temperature or irradiance. An economic model of P. carterae in a 63 ha raceway plant resulted in a cost for the biomass of between 7.35 Aus$.Kg-1 and 14.17 Aus$.Kg-1 depending on the harvesting method used.

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Currently the three main algae strains that are manufactured commercially are Chlorella, Spirulina and Dunaliela salina, which are produced for biomass and bioproducts. Photobioreactors (PBR) allow the exploitation of over 50 000 known microalgae species with over 15 000 novel compounds having been chemically identified to date. Many of these algae could be sources of high-value products which are produced using a method that delivers them from renewable resources. Designing an optimal photobioreactor is a complex process because a large array of variables is included in the design, with several of the variables interacting with each other directly. The interactions of most of these variables have not been established. The initial information that is available is inadequate because most photobioreactors have been tested on a laboratory scale and the information given does not include the manufacturing materials, the size of tubing used and other design variables. Before designing a photobioreactor, it is important to understand the best conditions for the production of algae because these have a direct influence on the requirements. In order to produce algae biomass under the specific conditions, one has to investigate current photobioreactors that have been designed in order to establish whether they are capable of optimum production under the production conditions; determine possible factors that could influence the production negatively and how they could be prevented; and undertake a cost analysis to determine whether the production of algae is an economically viable process using the specific reactor. All of these criteria have to be met for a photobioreactor to be viable in the production of algae biomass. Currently a Bubble column reactor is considered to be the best design for a photobioreactor and also the most scalable. Due to the limited information available, testing was conducted to determine the effect of: 1) different manufacturing materials, 2) the gas dispersion unit, 3) the diameters of the tubing and 4) the density. Bubble column reactors were used to test the effects of the four variables and were considered to be the most important aspects in the design. For testing these variables and their interaction, Chlorella Vulgaris was used because it is one of the most popular algae species used for production currently. As temperature and the availability of light play a large role in the production of algae, all testing was done in a laboratory environment to ensure small temperature changes and the constant availability of light. The reactors that were tested were made of PVC couplings, with the clear tubing used being made of either PVC or acrylic tubing. Enriched air was supplied at a 5% volume per volume ratio of CO2, with a flow rate of 0.02 volume per volume per minute (vvm) for the 50 mm diameter reactors and 0.36 vvm for the 90 and 110 mm diameter reactors. Two gas dispersion units were used to determine whether they would have any effect on the production. The gas dispersion units create small bubbles to ensure a high surface area to volume ratio and thereby they allow for maximum CO2 and O2 mass transfer. A growth rate of 0.14 gram per litre per day was found to yield the best production of all the reactors and configurations that were tested. The 50 mm diameter reactors showed the best growth followed by the 110 mm diameter reactors. The 90 mm diameter reactors all had a negative growth rate which appeared to be due to an insufficient gas flow rate. The 50 mm reactors had the best growth rate of 0.14 and 0.10 grams per litre per day for the acrylic tubing, while 0.08 grams per litre per day was achieved with PVC tubing. The 110 mm reactors had a highest growth rate of 0.05 grams per litre per day with PVC tubing. It was found that the 50 mm and 90 mm reactors showed a better performance with acrylic tubing while the 110 mm reactors showed a better performance with PVC tubing. The gas dispersion unit is affected by the gas flow rate, the density, the diameter of the tubing and the material that is used. The gas dispersion units’ effect is dependent on the diameter of the reactor seeing that the 50 mm reactor shows better performance with the small unit, while the 110 mm reactor shows better performance with the large unit, due to the gas flow rate that is required in the reactors. Because the gas flow rate and gas dispersion unit directly affect the agitation, the optimal density is affected directly due to the availability of light and therefore the tubing material. The gas dispersion units should fit properly into the reactor and be capable of handling the gas flow rate that is required. The diameter of the tubing does not show any effect but could have an effect under different testing conditions and could not be conclusively eliminated. The density of algae does have an effect, although most reactors showed a better production rate at a higher culture density. The scale up of the bubble column reactor creates a dead zone when a module is constructed. The scale up of a bubble column reactor could range from increasing the vertical tubing length, increasing the diameter of the tubing to adding vertical tubing to a module. The dead zone is formed at the bottom of the reactor where the module interconnects the vertical growth tubes, because these fittings are not constructed from a clear material, due to cost of such a construction. The dead zone that is created causes a large portion of algae to form a sediment, which directly affects the production of the system because it is in a dark zone of the reactor. Improved results would be obtained if the algae were kept at a homogeneous density that would ensure maximum expose to light. The ratio of gas flow rate to reactor volume and diameter of the tubing was found to be crucial. It is suspected that the 90 mm tubing reactor had a negative growth rate as this ratio was not correct. The 50 mm reactors had to be run at a much lower reactor volume per volume gas flow rate which could consist of air, carbon dioxide enriched air or other gases as required. The inclusion of the tubing diameter in the ratio is of vital importance and should be studied further. A cost analysis shows that the bubble column reactors under the tested conditions are not financially viable. A large component of the cost is carbon dioxide and medium, which is a composition of nutrients. This could be removed if a free source were obtained, which would make the system financially viable. These sources could include waste water and flue gas from industrial processes. It is recommended that a gas dispersion tube be positioned at the bottom of the reactor to ensure that no sedimentation occurs and that there is a homogeneous culture, and to maximise the production capabilities of a bubble column reactor. It is also recommended that the gas flow rate inside the reactor be studied to obtain a ratio where the volume of the reactor, the height of the reactor and the diameter of the tubing are included to obtain a sufficient rate of flow. / AFRIKAANSE OPSOMMING: Tans is daar drie belangrike alg stamme wat kommersieel geproduseer word, Chlorella, Spirulina en Dunaliela salina. Fotobioreaktors het meegebring dat meer as 50 000 bekende alg spesies met meer as 15 000 komponente tot op datum chemies geïdentifiseer is. Baie van hierdie alge kan hoë waarde produkte wees, wat met behulp van hernubare metodes geproduseer kan word. Die ontwerp van 'n optimale fotobioreaktor is 'n komplekse proses aangesien 'n groot verskeidenheid veranderlikes ingesluit moet word wat ‘n invloed op mekaar kan hê. Die interaksie van meeste van hierdie veranderlikes is nog nie vasgestel nie. Die inligting oor hierdie onderwerp is beperk aangesien die meeste fotobioreaktors in 'n laboratorium getoets is en dus nie die vervaardigingsmateriale, die grootte van buise en ander ontwerp veranderlikes insluit nie. Voordat 'n fotobioreaktor ontwerp kan word, moet die ideale alg produksie toestande verstaan word, aangesien dit 'n direkte impak op die produksie vereistes kan hê. Om alg biomassa onder spesifieke omstandighede te produseer, moet die bestaande fotobioreaktor ontwerpe ondersoek word. Daar moet vasgestel word of die bepaalde ontwerp oor die kapasiteit beskik om optimale produksie te lewer; identifisering van faktore wat produksie negatief kan beïnvloed en hoe dit voorkom kan word; en 'n koste ontleding moet gedoen word om te bereken of die produksie van alge met die geidentifiseerde ontwerp 'n ekonomies lewensvatbare proses is. Daar moet aan al die vereistes voldoen word om te bepaal of 'n fotobioreaktor lewensvatbaar is vir die produksie van alg biomassa. 'n Borrel-kolom reaktor ontwerp word tans as die beste ontwerp vir 'n fotobioreaktor geag, asook die mees aanpasbare ontwerp. As gevolg van die beperkte inligting wat beskikbaar is, is navorsing gedoen om die invloed van verskillende faktore te bepaal, naamlik: vervaardigingsmateriaal, gasverspreidingseenheid, buisdeursnee en digtheid. Borrel-kolom reaktors is gebruik om die vier belangrikste veranderlikes in die ontwerp te toets. Om die veranderlikes en hul interaksie te toets, is Chlorella vulgaris gebruik, aangesien dit een van die gewildste alg spesies is vir die produksie van biomassa. As gevolg van die belangrike rol wat temperatuur en lig beskikbaarheid in die produksie van alge speel, is al die toetse in 'n laboratorium-omgewing gedoen om temperatuur wisseling te beperk en konstante lig beskikbaarheid te verseker. Die reaktors wat getoets is, is vervaardig uit PVC koppelstukke, met die deurskynende buise wat uit PVC of akriel vervaardig is. Verrykte lug is verskaf op 'n 5% volume per volume verhouding CO2, met 'n vloei tempo van 0,02 volume per volume per minuut (vvm) vir die 50 mm deursnee reaktors en 0,36 vvm vir die 90 mm en 110 mm reaktors. Twee gasverspreidingseenhede is gebruik om hulle invloed op die produksie te bepaal. Die gasverspreidingseenhede skep kleiner borrels, om 'n hoë oppervlak area tot volume verhouding te skep en daardeur 'n maksimum CO2 en O2 massa-oordrag te verseker. 'n Groeikoers van 0,14 gram per liter per dag is gevind as die beste produksie van al die reaktors en konfigurasies wat getoets is. Die 50 mm deursnee reaktors het die beste groei getoon, gevolg deur die 110 mm deursnee reaktors. Die 90 mm deursnee reaktors het 'n negatiewe groeikoers getoon, wat moontlik toegeskryf kan word aan onvoldoende gas vloei tempo. Die 50 mm reaktors het die beste groeikoers van 0,14 en 0,10 gram per liter per dag vir die akriel buise getoon, terwyl ‘n 0,08 gram per liter per dag behaal is met 'n PVC buis. Die 110 mm reaktors het die hoogste groeikoers aangedui van 0,05 gram per liter per dag met 'n PVC buis. Daar is bevind dat die 50 mm en 90mm reaktors 'n beter prestasie met akriel buise gehad het, terwyl die 110 mm reaktors 'n beter prestasie met 'n PVC buis gehad het. Die gasverspreidingseenheid word beinvloed deur die gas vloei tempo, digtheid, buisdeursnee en die vervaardigingsmateriaal wat gebruik word. Die gasverspreidingseenhede word verder beinvloed deur die reaktor se buisdeursnee aangesien die 50 mm reaktor ‘n beter prestasie getoon het met die kleiner gas eenheid, terwyl die 110 mm reaktor ‘n beter prestasie getoon het met die groter gas eenheid, as gevolg van die gas vloei tempo wat vereis is. Die gas vloei tempo en gasverspreidingseenheid het ‘n direkte invloed op die groei van die kultuur, dus is die optimale digtheid afhanklik van die lig beskikbaarheid en dus die vervaardigingsmateriaal van die buise. Die gasverspreidingseenhede moet stewig in die reaktor pas en in staat wees om die gas vloei tempo wat vereis word te kan hanteer. Hoewel die deursnee van die buise nie 'n invloed getoon nie, kan dit 'n invloed onder verskillende toets omstandighede toon en kon nie finaal uitgeskakel word. Die digtheid van die alge het wel 'n effek, hoewel die meeste reaktors ‘n beter produksie tempo op 'n hoër kultuur digtheid toon. Die groter skaal borrel-kolom reaktor ontwikkel 'n dooie sone indien ‘n module saamgestel word. Die groter skaal borrel-kolom reaktor kan insluit: die verhoging van die vertikale buis lengte, 'n toename in deursnee van die buise en toevoeging van vertikale buise in die module. Die dooie sone het gevorm aan die onderkant van die reaktor waar die module se vertikale groei buise met mekaar verbind is. Hierdie area is uit nie-deurskynende materiaal vervaardig as gevolg van die konstruksie koste. Die dooie sone het veroorsaak dat groot hoeveelhede van die alge ‘n sediment gevorm het en ‘n direkte invloed op die produksie van die stelsel gehad het aangesien dit 'n donker sone in die reaktor gevorm het. Beter resultate kan verwag word indien die alge op 'n homogeniese digtheid gehou kan word om maksimum lig blootstelling te verseker. Daar is bevind dat die verhouding van gas vloei tempo tot reaktor volume en buisdeursnee deurslaggewend is. Die negatiewe groeikoers in die 90 mm reaktor word toegeskryf daaraan dat hierdie verhouding nie korrek was nie. Die 50 mm reaktors het op 'n laer reaktor volume per volume gas vloei tempo gefunksioneer wat kan bestaan uit die lug, verrykte lug of ander gasse soos benodig. Dit dui daarop dat die insluiting van die buis deursnee in hierdie verhouding van kardinale belang is en verder bestudeer moet word. 'n Koste ontleding toon dat die borrel-kolom reaktors onder hierdie getoets omstandighede nie finansieel lewensvatbaar is nie. 'n Groot deel van die koste is die medium, wat 'n samestelling van voedingstowwe is, en koolstofdioksied koste. Om finansieel lewensvatbaar te raak, moet hierdie kostes deur 'n gratis bron vervang word. Die bronne kan bestaan uit afval water en oortolige CO2 uit industrie. Daar word aanbeveel dat 'n gasverspreidingsbuisie aan die onderkant van die reaktor geplaas word. Dit sal verseker dat geen sediment vorm nie en 'n homogeniese kultuur gehandhaaf kan word om maksimum produksie in 'n borrel-kolom reaktor te handhaaf. Verder word aanbeveel dat die gas vloei tempo binne die reaktor verder bestudeer word om 'n verhouding tussen die volume van die reaktor, die hoogte van die reaktor en die deursnee van die buise te bepaal deur sodoende 'n voldoende tempo van vloei te verkry.

The release of water effluents rich in nutrients such as nitrogen and phosphorus without adequate treatment represents environmental and human health concerns. Growing concerns about these impacts have resulted in increasingly stringent water quality regulations that encouraged the adoption of advanced treatment processes. Microalgae-based advanced wastewater treatment has gained momentum owing to its well-known advantages for advanced wastewater treatment, including the recovering of nutrients for the production of fertilizers, biofuels and fine chemical from microalgal biomass. Nevertheless, the progressive membrane fouling and permeate flux declining hamper the large-scale commercialization of membrane photobioreactors (MPBRs) in the wastewater sector. In order to get a further understanding of the fouling mechanisms and antifouling control strategies, this study investigated the effect of the hydraulic retention time on the fouling development, and the effect of different physical fouling control strategies in the fouling mitigation. A synthetic secondary effluent was continuously fed to three MPBRs operated at different HRTs (12, 24 and 36 hours). Different fouling behaviors were found as the HRT changed, which was confirmed by continuously monitoring the transmembrane pressure (TMP) and by measurements in the biomass and its algal organic matter (AOM) properties. Lowering the HRT resulted in higher fouling rates due to changes in the biomass and AOM properties. Higher HRTs led to lower fouling rates and to a lower organic rejection across the membrane. The retention of small-MW organics in SMPBR12h was found to exacerbate the fouling resistance, whereas the accumulation of large-MW biopolymers enhanced the rejection of organics, despite of not imparting significant resistance in SMPBR24h. In order to assess the impact of different physical fouling control strategies, namely relaxation, backwash and air scouring, OCT in-situ monitoring was employed in MPBR12h to provide real-time information of the fouling layer properties (thickness and relative roughness) and its interaction with the membrane surface. Different fouling mechanisms were observed under different fouling control strategies. MPBRRLX and MPBRBW presented similar fouling rates despite of the lower permeate productivities of the latter. The lowest fouling rates were observed in MPBRSC, where stronger interactions between the membrane and small-MW organics and particles was observed.

No description available.

Toxins produced by harmful algal blooms (HABs) are known to pose contamination risks to seafood products (e.g. fish and shellfish) consumed by human. In order to control contamination risks, monitoring regimes have to be performed rigorously. The effort to monitor the amount of toxins in consumable products has to rely on continuous supply to analytical standards. The current work presents the strategy in optimising the production of major diarrhetic shellfish poisoning (DSP) toxins, OA and DTX1, from Prorocentrum lima. The organism is also known to produce peridinin, a carotenoid pigment that has been found to have pharmaceutical potential. Results from this study showed that cultivation of P. lima CCAP 1136/11 was still, although not completely, reliant on supply of natural seawater. Characterisation of compounds produced by P. lima CCAP 1136/11 in batch culture identified three major bioactive compounds (OA, DTX1 and peridinin) and two minor OA-related compounds. Recovery of these major compounds was further optimised with two-stage extraction procedure. Several important considerations for the cultivation process include standardisation of inoculum age and initial cell density. These and several other growth parameters such as temperature, light and CO2 supplementation have been shown to affect the growth and production of DSP toxins and peridinin in the culture. One of the main highlights in this study revealed that providing culture with light and dark cycle at frequency of 0.5 hour benefit in the enhancement of OA, DTX1 and peridinin yield from P. lima CCAP 1136/11. As the last part of this study, a simple and scalable design of reactor has been proposed. Contrary to common observations for dinoflagellate culture, P. lima CCAP 1136/11 was found to be able to withstand increased sparging within the culture system, resulting in concomitant increased of growth and production of OA, DTX1 and peridinin. Future works have been suggested to focus on: (1) exploitation of different cultivation system, such as continuous or semicontinuous systems, and (2) exploration on genetic modification to enable commercial scale production of DSP toxins and peridinin.

Algae are a prolific source of biochemicals with economic importance, including nutraceuticals, biofuels, animal feed, etc. The general aim of this study was to establish how the hydrodynamic conditions generated within specific types or designs of photobioreactors determine their respective algae growth. The specific objectives of this study were: (1) To determine and compare key hydrodynamic parameters in the Air Accordion photobioreactor and the conventional bubble column, including Residence Time, Vessel Dispersion Number, Bodenstein Number, Mixing Time and oxygen liquid mass transfer coefficient (kla); and, (2) To test how differences in the hydrodynamic conditions would result in significant difference in growths of the green alga Scenedesmus obliquuus between the photobioreactors. The results of the study showed that: (1) The Residence Time of 566 s for the Air Accordion significantly exceeded by 28% that of 444 s for the bubble column, signifying greater liquid mixing in the Air Accordion; (2) The Vessel Dispersion Number for the Air Accordion of 0.168 significantly exceeded that for the bubble column of 0.166, indicating greater degree of mixing in the Air Accordion than in the bubble column; (3) The Mixing Time in both the Air Accordion and the bubble column declined as the air flow rate increased, indicating that the tracer ions in both photobioreactors mixed more quickly. For each of the flow rates tested, however, the mixing time for the bubble column significantly exceeded that for the Air Accordion, indicating that liquid mixing in the Air Accordion occured significantly quicker than in the bubble column. At 1.0 LPM, the bubble column's Mixing Time of 10 s exceeded by 25% that of the Air Accordion of 8 s; (4) The oxygen liquid mass transfer coefficients in both photobioreactors increased as the air flow rate increased, indicating that the transfer of oxygen from the air bubbles into the liquid within the photobioreactors gained efficiency. For each of the air flow rates tested, however, the oxygen liquid mass transfer coefficient for the Air Accordion significantly exceeded that for the bubble column, indicating a significantly more efficient oxygenation of the liquid in the Air Accordion occurring than in the bubble column. At 1.0 LPM, the Air Accordion's oxygen liquid mass transfer coefficient of 0.00138 s⁻¹ exceeded by 48% that of the bubble column of 0.000931 s⁻¹; and (5) The growth of Scenedesmus obliquus in the Air Accordion significantly exceeded that in the bubble column for both 0.1 LPM and 1.0 LPM. The final algae density of 0.25 g DW/L in the Air Accordion significantly exceeded by 31% that of 0.18 g DW/L in the bubble column at 0.1 LPM. Similarly, the final algae density of 0.37 g DW/L in the Air Accordion significantly exceeded by 19% that of 0.31 g DW/L in the bubble column at 1.0 LPM. Thus, the growth of Scenedesmus obliquus in the Air Accordion photobioreactor -- with significanlty more favorable hydrodynamic characteristics in terms of Residence Time, Vessel Dispersion Number, Mixing Time and oxygen liquid mass transfer coefficient -- significantly exceeded algae growth in the bubble column of the same volume and under the same environmetal conditons.

Aerobic activated sludge membrane bioreactors (AS-MBR) in municipal wastewater treatment are compact systems that can efficiently perform biological organic oxidation. However, aerobic processes require mechanical aeration accounting for over 40% of total expenditure of a wastewater facility. Additionally, a global urgency for nutrient (Nitrogen/Phosphorus) removal strategies due to surges of eutrophication events requires complex MBR configurations. An innovative and cost-effective process was developed with a dual income-stream: high-quality treated effluent and value-added microalgal biomass for several applications. The proposed process involved several integrated components; an ultrafiltration AS-MBR for organic oxidation followed by a microalgal membrane photobioreactor (MPBR) to remove nutrients (N/P) through assimilation while simultaneously photosynthetically generating dissolved oxygen effluent that was recirculated back into the AS-MBR, thereby reducing the need for mechanical aeration for oxidation. A lab-scale system was fed with a synthetic medium-strength municipal wastewater. The microalgal species C. vulgaris was initially tested in batch trials as a proof-of-concept study on its potential as a photosynthetic oxygenator for the AS-MBR and identify its nutrient utilization efficiencies. The MPBR and MBR were later constructed for continuous operation, with the aim to identify an optimal process configuration. The unit processes were subsequently isolated, where the AS-MBR was subjected to a modelled algal effluent to assesses the impact of varying influent characteristics and effluent recycle rates. A microbial community analysis was performed by high-throughput sequencing and a statistical data-driven modeling approach to assess treatment performances. The MPBR stage was then subjected to the effluent achieved by the AS-MBR stage under varying operating conditions to assess its treatment performance and the resulting algal biomass biochemical composition to identify its suitability for bioethanol, biodiesel, or animal feed production. The findings of this study ultimately confirmed the ability of C. vulgaris to support the AS-MBR for organic removal and fractional nutrient removal by supplying the oxygen demand, and further achieve an effluent polish stage for nutrient removal. The process configuration also demonstrated the ability to achieve a high microalgal biomass production with the potential of extracting valuable products as an added benefit of the wastewater treatment.