Potential of Bacterial Strains Isolated from Coastal Water for Wastewater Treatment and as Aqua-Feed Additives.

Bacteria have various and sustained effects on humans in various fields: molecular biology, biomedical science, environmental/food industry, etc. This study was conducted to evaluate the wastewater treatment capacity and feed-additive fish-growth effect of four strains of bacteria: Pseudoalteromonas mariniglutinosa, Psychrobacter celer, Bacillus albus, and Bacillus safensis. In a wastewater degradation experiment, (i) nitrate-N and nitrite-N were removed within 1 h in all of the 4 bacterial strains; (ii) the removal rates of TAN and TN were higher in all of the strains relative to the B. subtilis. In a feed-additive experiment (5% Kg-1), (i) the growth of fish was higher in all of the 4 bacterial strains with the B. subtilis relative to the commercial feed; (ii) there was no significant growth difference for B. albus and B. safensis relative to the B. subtilis, but growth was higher in P. mariniglutinosa and P. celer. The results indicated that the 4 bacterial strains can be effectively utilized for biological wastewater treatment processes and as aqua-feed.

Evaluation of floc-harvesting technologies in biofloc technology (BFT) system for aquaculture.

This study was conducted to examine floc-harvesting performance by three separation technologies, namely sedimentation, centrifugation, and membrane filtration, for biofloc generated from a BFT system in aquaculture. According to the experimental results, sedimentation demonstrated the poorest harvesting performance with the lowest energy consumption; centrifugation showed the highest harvesting performance with the highest energy burden; membrane filtration achieved better harvesting performance than sedimentation and better energy efficiency than centrifugation. In terms of large-scale floc recovery, a two-step harvesting process utilizing centrifugation with membrane filtration was found to be a reliable way to overcome the limitation of sedimentation and obtain moderate energy-efficiency. Overall, the energy-consuming aspects of the floc-recovery process on an industrial scale should be concerned, even though the use of biofloc as an aquaculture feed would be a positive in terms of an environment-friendly approach to recycling of aquaculture wastewater.

Biological wastewater treatment: Comparison of heterotrophs (BFT) with autotrophs (ABFT) in aquaculture systems.

The present study was conducted to compare wastewater purification capacities between heterotrophs (BFT) and autotrophs (ABFT) and to evaluate the effects on the growth of fish (Nile tilapia, Oreochromis niloticus) in aquaculture systems. The wastewater treatment capacity of heterotrophs is far superior to that of autotrophs, but the BFT system requires more energy for aquaculture than does the ABFT system. Regardless, both systems effected positive influences on fish growth performance, showing excellent water-purification capacities compared with the control group (CON). No significant differences were found between CON and ABFT or between ABFT and BFT, but there were significant differences between CON and BFT. Both systems BFT and ABFT were revealed to be cost effective in relation to CON, having reduced water replacement by 82%. Therefore, the BFT and ABFT systems could be economical aquaculture systems if due advantage is taken of what both have to offer.

Tuna byproducts as a fish-meal in tilapia aquaculture.

Potentiality of the use of tuna byproducts as a fish-meal replacement on Nile tilapia (Oreochromis niloticus) was examined for 84 weeks by tracking the concentrations of cadmium and mercury in the internal organs, muscles and fish whole body through generation including their immature eggs and their larvae. The results confirmed that the tuna byproducts can be used as a fish-meal substitute in tilapia aquaculture, because their acceptable ranges for cadmium and mercury consequently did not exceed the food safety values (both < 0.5 mg kg-1), despite their proportional increases in the fish body. The use of tuna byproducts as a protein source is expected to reduce the cost of feed with other fishmeal substitutes in tilapia aquaculture. However, fish (flounder) indiscriminately consuming tuna byproduct feed were prohibited and recalls of sales were issued by the government (July 2018, Republic of Korea), as the threshold for mercury in the fish bodies had been exceeded (0.6-0.8 mg kg-1). Further study of the use of tuna byproducts as fishmeal replacements for other species in aquaculture is needed, as concentration ratios can vary depending on the species.

Dynamic filtration with a perforated disk for dewatering of Tetraselmis suecica.

Dynamic filtration equipped with a perforated disk was adopted for the first time to dewater and concentrate Tetraselmis suecica, from a typical solution of 2-100 g/L of dense biomass suited for the downstream process. An ultrafiltration membrane, polyethersulfone 150 kDa, was found to best perform in terms of high biomass retention and filtration rate. At 1600 rpm, the highest rotation speed of the disk we tested, plateau permeate flux increased up to 20.2 times higher than those with no rotation; this improvement was attributed to fouling reduction (up to 98%) via distinctively high-shear stress on the membrane surface. Even at a high biomass concentration (100 g/L) where fouling formation was very serious, the heightened shear stress caused high flux to be maintained and fouling resistance to be reduced in an effective way. When trans-membrane pressure was increased in a stepwise manner, flux continuously rose at high rotation speed; at low speed, on the other hand, the limiting flux was observed. The dynamic filtration with the perforated disk, which was an effective high-shear stress generator, was proven to be a promising dewatering means of T. suecica, and especially so for the production of highly concentrated biomass.

Evaluation of various harvesting methods for high-density microalgae, Aurantiochytrium sp. KRS101.

Five technologies, coagulation, electro-flotation (EF), electro-coagulation-flotation (ECF), centrifugation, and membrane filtration, were systematically assessed for their adequacy of harvesting Aurantiochytrium sp. KRS101, a heterotrophic microalgal species that has much higher biomass concentration than photoautotrophic species. Coagulation, EF, and ECF were found to have limited efficiency. Centrifugation was overly powerful to susceptible cells like Aurantiochytrium sp. KRS101, inducing cell rupture and consequently biomass loss of over 13%. Membrane filtration, in particular equipped with an anti-fouling turbulence generator, turned out to be best suited: nearly 100% of harvesting efficiency and low water content in harvested biomass were achieved. With rotation rate increased, high permeate fluxes could be attained even with extremely concentrated biomass: e.g., 219.0 and 135.0 L/m(2)/h at 150.0 and 203.0 g/L, respectively. Dynamic filtration appears to be indeed a suitable means especially to obtain highly concentrated biomass that have no need of dewatering and can be directly processed.

Use of extracts from oyster shell and soil for cultivation of Spirulina maxima.

Calcium ion and trace metals play important roles in various metabolisms of photosynthetic organisms. In this study, simple methods were developed to extract calcium ion and micronutrients from oyster shell and common soil, and the prepared extracts were tested as a replacement of the corresponding chemicals that are essential for growth of microalgae. The oyster shell and soil were treated with 0.1 M sodium hydroxide or with 10 % hydrogen peroxide, respectively. The potential application of these natural sources to cultivation was investigated with Spirulina maxima. When compared to standard Zarrouk medium, the Spirulina maxima cultivated in a modified Zarrouk media with elements from oyster shell and soil extract exhibited increases in biomass, chlorophyll, and phycocyanin by 17, 16, and 64 %, respectively. These results indicate that the extracts of oyster shell and soil provide sufficient amounts of calcium and trace metals for successful cultivation of Spirulina maxima.

Effects of molten-salt/ionic-liquid mixture on extraction of docosahexaenoic acid (DHA)-rich lipids from Aurantiochytrium sp. KRS101.

In this study, lipid extraction from Aurantiochytrium sp. was performed using a molten-salt/ionic-liquid mixture. The total fatty acid content of Aurantiochytrium sp. was 478.8 mg/g cell, from which 145 mg/g cell (30.3% of total fatty acids) of docosahexaenoic acid (DHA) was obtained. FeCl3·6H2O showed a high lipid extraction yield (207.9 mg/g cell), when compared with that of [Emim]OAc, which was only 118.1 mg/g cell; notably however, when FeCl3·6H2O was mixed with [Emim]OAc (5:1, w/w), the yield was increased to 478.6 mg/g cell. When lipid was extracted by the FeCl3·6H2O/[Emim]OAc mixture at a 5:1 (w/w) blending ratio under 90 °C, 30 min reaction conditions, the fatty acid content of the extracted lipid was a high purity 997.7 mg/g lipid, with most of the DHA having been extracted (30.2% of total fatty acids). Overall, lipid extraction from Aurantiochytrium sp. was enhanced by the synergistic effects of the molten-salt/ionic-liquid mixture with different ions.

Acid-catalyzed hot-water extraction of docosahexaenoic acid (DHA)-rich lipids from Aurantiochytrium sp. KRS101.

In this study, acid-catalyzed hot-water extraction of docosahexaenoic acid (DHA)-rich lipids from Aurantiochytrium sp. was performed, and its yield-enhancing effects were investigated. The total fatty acid content of the Aurantiochytrium sp. was 482.5mg/g cell, of which 141.7mg/g cell (29.4% of total fatty acids) was DHA. The lipid-extraction yield by acid-catalyzed hot-water treatment was compared with those by organic solvents. Among the various acid-catalyzed hot-water treatment conditions, the most optimal were 1.00% H2SO4 concentration, 100°C, 30min, under which the lipid-extraction yield was 472.4mg/g cell, and most of the DHA was extracted (29.2% of total fatty acids). Acid-catalyzed hot-water extraction treatment markedly improved the lipid-extraction yield of Aurantiochytrium sp.

Methods of downstream processing for the production of biodiesel from microalgae.

Despite receiving increasing attention during the last few decades, the production of microalgal biofuels is not yet sufficiently cost-effective to compete with that of petroleum-based conventional fuels. Among the steps required for the production of microalgal biofuels, the harvest of the microalgal biomass and the extraction of lipids from microalgae are two of the most expensive. In this review article, we surveyed a substantial amount of previous work in microalgal harvesting and lipid extraction to highlight recent progress in these areas. We also discuss new developments in the biodiesel conversion technology due to the importance of the connectivity of this step with the lipid extraction process. Furthermore, we propose possible future directions for technological or process improvements that will directly affect the final production costs of microalgal biomass-based biofuels.

Use of organic waste from the brewery industry for high-density cultivation of the docosahexaenoic acid-rich microalga, Aurantiochytrium sp. KRS101.

In the present study, spent yeast from a brewery was used as the growth substrate for the docosahexaenoic acid (DHA)-rich microalga, Aurantiochytrium sp. KRS101. A significant biomass yield (6.69 g/l/d) was obtained using only spent yeast as the growth substrate, with simple stirring as pretreatment. Maximization of nutrient utilization through the use of stepwise cultivation increased the yield to 31.8 g/l of biomass. DHA constituted 38.2% (w/w) of the total fatty acids, and the highest DHA productivity was observed when the C/N ratio was 20:1 (w/w). Spent yeast thus served as a good growth substrate for the production of DHA. Economic assessment revealed that stepwise cultivation using spent yeast as either the sole growth substrate or as a nutrient source could substantially reduce the production cost of microalgal DHA.

A novel fed-batch process based on the biology of Aurantiochytrium sp. KRS101 for the production of biodiesel and docosahexaenoic acid.

The biology of Aurantiochytrium sp. KRS101 was thoroughly investigated to enhance its production of biodiesel and docosahexaenoic acid (DHA). Nutrients and salinity were optimized to prevent biomass loss due to cell rupture. Calculation of yield coefficients showed that nitrogen was mostly responsible for the early stage of cell growth or division, whereas carbon was necessary for the entire process of cell development, particularly cell enlargement during late stages. Using these distinctive yield coefficients, a modified fed-batch cultivation method was designed, resulting in increases in palmitic acid (PA) and DHA production of up to 137% and 29%, respectively. This modified fed-batch cultivation method, using appropriate supplies of nitrogen and carbon, may improve the yields of PA and DHA, thus expanding the biotechnological applications of Aurantiochytrium sp. KRS101.

High-cell-density cultivation of oleaginous yeast Cryptococcus curvatus for biodiesel production using organic waste from the brewery industry.

Waste spent yeast from brewery industry was used as a sole growth substrate to grow an oleaginous yeast Cryptococcus curvatus for the purpose of biodiesel production. Approximately 7 g/l/d of biomass productivity was obtained using only spent yeast (30 g/l) without additional nutrients and pretreatment of any kind. To make best use of available nutrients in the spent yeast, stepwise cultivation was carried out in a batch culture mode and the highest biomass and lipid content, which were 50.4 g/l and 37.7%, respectively, were obtained at 35:1 of C/N ratio. Lipid from C. curvatus was found to be a quality-sufficient source of oil as a transportation fuel in terms of cetane, iodine values, and oxidation stability, although the values of cold filter plugging point were less desirable. Economic evaluation revealed that the use of the spent yeast could significantly reduce the unit cost of yeast-based biodiesel production.

Continuous microalgae recovery using electrolysis: effect of different electrode pairs and timing of polarity exchange.

Microalgae have great potential as a feedstock for biofuel production. Continuous operation is an important benefit of the continuous electrolytic microalgae (CEM) harvest system, but it is necessary to optimize cultivability and recovery efficiency in order to improve overall performance. Two pairs of best-candidate electrodes for polarity exchange (PE) were examined to improve these two key factors: (i) aluminum and dimensionally stable anode (Al-DSA), and (ii) Al-platinum (Al-Pt). Al-DSA was better than Al-Pt because it led to less cell damage and was less expensive. Moreover, cell viability and recovery were improved by optimizing the timing of PE. A P1:P2 ratio of 1:1.5 at 5min and 1:1.2 at 10min yielded the best results, with greatly reduced electricity consumption and enhanced cell viability and recovery. The CEM harvest system appears to be a well-suited option for the harvest of microalgae for biofuel production.