Physiology and biotechnology of glycerol production using the green microalga Dunaliella.

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Comparison between Airlift Photobioreactor and Bubble Column for Skeletonema Costatum Cultivation

The cultivation of diatom Skeletonema costatum was achieved in airlift photobioreactor and the system performance was compared to that of bubble column. The standard F/2 medium (Guillard’s medium) for typical diatom cultivation could only yield the best growth character when the silicon concentration increased 4 times the normal value. In terms of cell growth, the airlift photobioreactor provided better performance than the bubble column where the maximum cell concentration, specific growth rate, and productivity in the airlift were 4.6 x 106 cell mL-1, 0.07 h-1, and 6.4 x 104 cell s-1 compared with 1.8 x 106 cell mL-1, 0.04 h-1, and 2.2 x 104 cell s-1 in the bubble column of the same size (3L) and operated at the same aeration rate (superficial velocity = 1.5 cm s-1) and light intensity (34 μmol photons m−2 s−1). This was because the airlift photobioreactor allowed circulatory flow in the system which helps prevent cell precipitation and enhance light utilization efficiency. The optimal operating conditions in the airlift system which was found most optimal to cell growth were: the ratio between downcomer and riser cross sectional area (Ad:Ar) of 3.27, superficial gas velocity 1.5 cm s−1 and the light intensity 34 μmol photons m−2 s−1. Preliminary economical assessment on the cultivation of S. costatum in airlift system compared with that in bubble column was carried out, whereas the analysis for nutritional values of the obtained biomass indicated relatively high protein content

Control of Inorganic Nitrogen and Suspended Solids Concentrations in a Land-Based Recirculating Aquaculture System

This study intended to evaluate the performance of land-based aquaculture system integrating solids separating units, nitrifying biofilters, and tubular denitrifying reactor during the closed-water tilapia cultivation for 98 days. Operation of both solids separating units was able to maintain suspended solids (SS) concentrations in the rearing tank below 35 mg SS/L. Simultaneous operation of nitrifying biofilters, ORP-controlled denitrifying reactor, and two solids separating units was capable of maintaining total ammonia nitrogen (TAN) and nitrite concentrations substantially below 1.0 mg N/L and nitrate concentrations less than 12.0 mg N/L despite nitrogen loading rate and tilapia weight density were as high as 21.6 mg N/L/day and 17.2 kg/m3, respectively. Without solids separating units, TAN and nitrite concentrations drastically increased above the acceptable limits of 1.0 mg N/L. Finally, the result of nitrogen balance analysis indicated that nitrification and denitrification were the primary treatment pathways in this recirculating system capable of removing 49.8% of total nitrogen input, whereas solids separating units removed 9.5% of total nitrogen input yet their presence was essential for sustaining the activity of nitrifying biofilters for an extended period

Nitrogen and Phosphorus Removal in the Recirculating Aquaculture System with Water Treatment Tank containing Baked Clay Beads and Chinese Cabbage

This research aims to describe the nitrogen and phosphorus removal in Recirculating Aquaculture System (RAS) by crop plants biomass production. The 3 experiment systems consisted of 1 treatment (fish tank + baked clay beads + Chinese cabbage) and 2 controls as control-1 (fish tank only) and control-2 (fish tank + baked clay beads), were performed. With all experimental RAS, Nile tilapia (Oreochromis niloticus) was cultured at 2 kg/m3 density. The baked clay beads (8-16 mm in diameter) were filled as a layer of 10 cm in the water treatment tank of control-2. While in the treatment tank, Chinese cabbage (Brassica pekinensis) was planted at 334 plants/m2 in baked clay beads layer. During 35 days of experiment, the average fish wet-weight in control-1, control-2 and treatment systems increased from 16.31±1.49, 15.18±1.28 and 11.31±1.49 g to 29.43±7.06, 28.65±3.12 and 27.20±6.56 g, respectively. It was found that the growth rate of 0.45±0.15 g-wet weight/day in a treatment tank was higher than in those 2 controls, which were rather similar at 0.37±0.16 and 0.38±0.05 g-wet weight/day, respectively. The fish survival rate of all experimental units was 100%. The average Chinese cabbage wet-weight in treatment system increased from 0.15±0.02 g to 1.00±0.38 g. For water quality, all parameters were within the acceptable range for aquaculture. The assimilation inorganic nitrogen in a treatment tank showed a slower rate and lower nitrite accumulation relative to those in control tanks. The nitrogen and phosphorus balance analysis illustrated that most of the nitrogen and phosphorus input in all systems was from feed (82-87% and 21-87%) while at the final day of experiments, nitrogen and phosphorus in tilapia culture revealed at 15-19% and 4-13%. The accumulation of nitrogen and phosphorus in the water, up to 56% and 70%, was found in control-1 while water in the tank with baked clay beads had substantial lower nitrogen and phosphorus concentration. The most important part was unaccounted nitrogen and phosphorus as high as 60% and 17% in treatment and 53% and 10% in control-2 systems. Nitrogen and phosphorus incorporated in plant (treatment) was only 1.31% and 0.11%, respectively. It can be implied from the results that the assimilation in plant was a minor process for nutrient removal in this RAS. On the other hand, the nitrification and denitrification occurred in the sediment layer of baked clay beads tank were the major treatment processes to maintain water quality in the recirculating system. Without baked clay bead, nitrogen waste was accumulated as nitrate in the water while in treatment tank with backed clay beads, nitrogen was significantly removed by denitrification process

Development of Aeration-Assisted Combined Nitrification and Solid Removal Unit for a Compact Recirculating Aquaculture System

This work focused on the development of water treatment unit, called aeration-assisted combined nitrification and solid removal (ACNS), for compact aquaculture system. Results of preliminary study indicated that aerated filtration could extend filtration time significantly and capture more solids as compared to non-aerated filtration. Operating parameters of ACNS, including screen pore size, influent flow rate, aeration rate and position of air diffuser, were determined at 130 µm, 750 L/h, 120 L/h and 1.0 cm below the base of screen, respectively. ACNS was subsequently evaluated for its performance in nitrogen and solid removal during the 60-days closed-water tilapia cultivation. Performance of aquaculture system with ACNS, as the only treatment unit, was comparable to the aquaculture system having both nitrifying biofilter and ACNS, as separated units. Specifically, ACNS could maintain suspended solids (28 ± 7.6 mg SS/L), ammonia (< 0.5 mg N/L) and nitrite (< 0.5 mg N/L) concentration below the recommended limits for extended period. ACNS also produced relatively high and constant effluent flux close to initial value despite increasing the filtration time in aerated compartment up to 7 days. This led to continuous filtration, without stopping the system to remove solids on screen, for 50 days

Manipulation of Biochemical Compositions of Chlorella sp.

This work aimed to study the effect of several environmental parameters (light intensity, temperature, and aeration rate) on the accumulation of nutritional components and lutein production in a green microalgae Chlorella sp. It was proven in this work that the biochemical composition of Chlorella sp. could be manipulated through the control of environmental conditions during the cultivation. A simple 2L bubble column photobioreactors installed in a well controlled culture chamber was employed as a model system where temperature, light intensity, and aeration rate (usg) could be controlled in the range from 30 - 40ºC, 10 - 30 kLux, and 0.5 - 1.5 cm/s, respectively. Lipid and protein productivity were the most abundant at 35°C, 10 kLux and 1 cm/s, whereas carbohydrate productivity was found to be maximized at 30°C, 30 kLux and 0.5 cm/s. In addition, Chlorella sp. could also generate strong antioxidizing agents like lutein which was found to be mostly produced at 35°C, 10 kLux and 1 cm/s

Performance evaluation of the compact aquaculture system integrating submerged fibrousnitrifying biofilters

This experiment assessed the performance of submerged fibrous nitrifying biofilters (SFNBs) to carry out the zerowaterexchange tilapia cultivation. Without biofilter cleaning, the SFNBs (21 m of biofilter length) were susceptible tohydrogen sulfide production when operating beyond the aquaculture density of 13.62 kg/m3. The SFNBs were able tomaintain total ammonia nitrogen (TAN) and nitrite below 1.0 mg N/L throughout the experiment and could handle inorganicnitrogen loading as high as 38.6 mg N/L/day when the solid removal from biofilters was performed biweekly. Ammoniumdegradation rate measured at the end of this study was 380±66 mg N/m2/day for biofilters subjected to cleaning. A significantlylower rate of 41.4±2.86 mg N/m2/day was associated with biofilters without any solid removal. Finally, the SFNBsshould be attractive for budget-limited farmers since they are simple to build and operate and can provide alternatives tocage-cultured systems

Culture system for Wolffia globosa L. (Lemnaceae) for hygiene human food

This study aimed to develop a suitable culture system for the mass production of Wolffia globosa for human consumption. W. globosa was grown in five different culture systems (static, vertical aeration, horizontal surface agitation, system with top water spraying and layer culturing system with top water spraying). Dry weight of W. globosa determined every 7 days indicated that a horizontal surface agitation provided the highest mass of 42.94±2.17 g/m2 and significantly difference with others in 28 days (p<0.05). Twenty one days-culture of W. globosa in the horizontal circulation produced the highest yield of 1.52±0.04 g dry weight/m2 /d and was significantly higher than yields in other systems. Frond size of W. globosa in 7 days culture was the biggest of all the culture systems; however, no significant difference was found among the culture systems. The biomass had 48.2% protein with complete essential amino acids, 9.6% fat and 14.5% crude fiber with low bacterial contamination

Comparison between Airlift Photobioreactor and Bubble Column for Skeletonema Costatum Cultivation

The cultivation of diatom Skeletonema costatum was achieved in airlift photobioreactor and the system performance was compared to that of bubble column. The standard F/2 medium (Guillard’s medium) for typical diatom cultivation could only yield the best growth character when the silicon concentration increased 4 times the normal value. In terms of cell growth, the airlift photobioreactor provided better performance than the bubble column where the maximum cell concentration, specific growth rate, and productivity in the airlift were 4.6 x 106 cell mL-1, 0.07 h-1, and 6.4 x 104 cell s-1 compared with 1.8 x 106 cell mL-1, 0.04 h-1, and 2.2 x 104 cell s-1 in the bubble column of the same size (3L) and operated at the same aeration rate (superficial velocity = 1.5 cm s-1) and light intensity (34 μmol photons m−2 s−1). This was because the airlift photobioreactor allowed circulatory flow in the system which helps prevent cell precipitation and enhance light utilization efficiency. The optimal operating conditions in the airlift system which was found most optimal to cell growth were: the ratio between downcomer and riser cross sectional area (Ad:Ar) of 3.27, superficial gas velocity 1.5 cm s−1 and the light intensity 34 μmol photons m−2 s−1. Preliminary economical assessment on the cultivation of S. costatum in airlift system compared with that in bubble column was carried out, whereas the analysis for nutritional values of the obtained biomass indicated relatively high protein content