Continuous microalgal culture module and method of culturing microalgae containing macular pigment.

This study established and investigated continuous macular pigment (MP) production with a lutein (L):zeaxanthin (Z) ratio of 4-5:1 by an MP-rich Chlorella sp. CN6 mutant strain in a continuous microalgal culture module. Chlorella sp. CN6 was cultured in a four-stage module for 10 days. The microalgal culture volume increased to 200 L in the first stage (6 days). Biomass productivity increased to 0.931 g/L/day with continuous indoor white light irradiation during the second stage (3 days). MP content effectively increased to 8.29 mg/g upon continuous, indoor white light and blue light-emitting diode irradiation in the third stage (1 day), and the microalgal biomass and MP concentrations were 8.88 g/L and 73.6 mg/L in the fourth stage, respectively. Using a two-step MP extraction process, 80 % of the MP was recovered with a high purity of 93 %, and its L:Z ratio was 4-5:1.

Fabrication and application of glutathione biosensing SPCE strips with gold nanoparticle modification.

Glutathione (GSH) is a major antioxidant in organisms. An alteration in GSH concentration has been implicated in a number of pathological conditions. Therefore, GSH sensing has become a critical issue. In this study, a disposable strip used for tyrosinase-modified electrochemical testing was fabricated for the detection of GSH levels in vivo. The system is based on tyrosinase as a biorecognition element and a screen-printed carbon electrode (SPCE) as an amperometric transducer. On the tyrosinase-SPCE strips, the oxidation reaction from catechol to o-quinone was catalyzed by tyrosinase. The tyrosinase-SPCE strips were modified with gold nanoparticles (AuNPs). In the presence of AuNPs of 25 nm diameter, the cathodic peak current of cyclic voltammetry (CV) was significantly enhanced by 5.2 fold. Under optimized conditions (250 µM catechol, 50 mM phosphate buffer, and pH 6.5), the linear response of the tyrosinase-SPCE strips ranged from 31.25 to 500 µM GSH, with a detection limit of approximately 35 µM (S/N > 3). The tyrosinase-SPCE strips have been used to detect real samples of plasma and tissue homogenates in a mouse experiment. The mice were orally administrated with N-acetylcysteine (NAC) 100 mg kg-1 once a day for 7 days; the plasma GSH significantly enhanced 2.8 fold as compared with saline-treated mice (1123 vs. 480 µM µg-1 protein). NAC administration also could alleviate the adverse effect of GSH reduction in the mice treated with doxorubicin.

A Low-Cost Fertilizer Medium Supplemented with Urea for the Lutein Production of Chlorella sp. and the Ability of the Lutein to Protect Cells against Blue Light Irradiation.

This study aimed to investigate the use of organic fertilizers instead of modified f/2 medium for Chlorella sp. cultivation, and the extracted lutein of the microalga to protect mammal cells against blue-light irradiation. The biomass productivity and lutein content of Chlorella sp. cultured in 20 g/L fertilizer medium for 6 days were 1.04 g/L/d and 4.41 mg/g, respectively. These values are approximately 1.3- and 1.4-fold higher than those achieved with the modified f/2 medium, respectively. The cost of medium per gram of microalgal biomass reduced by about 97%. The microalgal lutein content was further increased to 6.03 mg/g in 20 g/L fertilizer medium when supplemented with 20 mM urea, and the cost of medium per gram lutein reduced by about 96%. When doses of ≥1 µM microalgal lutein were used to protect mammal NIH/3T3 cells, there was a significant reduction in the levels of reactive oxygen species (ROS) produced by the cells in the following blue-light irradiation treatments. The results show that microalgal lutein produced by fertilizers with urea supplements has the potential to develop anti-blue-light oxidation products and reduce the economic challenges of microalgal biomass applied to carbon biofixation and biofuel production.

An efficient Photobioreactors/Raceway circulating system combined with alkaline-CO2 capturing medium for microalgal cultivation.

High efficiency of microalgal growth and CO2 fixation in a Photobioreactors (PBRs)/Raceway circulating (PsRC) system combined with alkaline-CO2 capturing medium and operation was established and investigated. Compared with a pH 6 medium, the average biomass productivity of Chlorella sp. AT1 cultured in a pH 11 medium at 2 L min-1 circulation rate for 7 days increased by about 2-fold to 0.346 g L-1 d-1. The maximum amount of CO2 fixation and CO2 utilization efficiency of Chlorella sp. AT1 could be obtained at a PBRs to Raceway ratio of 1:10 in an indoor-simulated PsRC system. A similar result was also shown in an outdoor PsRC system with a 10-ton scale for microalgal cultivation. Under the appropriate circulation rate, the stable growth performance of Chlorella sp. AT1 cultured by long-term semi-continuous operation in the 10-ton outdoor PsRC system was observed, and the total amount of CO2 fixation was approximately 1.2 kg d-1 with 50% CO2 utilization efficiency.

Ability of an alkali-tolerant mutant strain of the microalga Chlorella sp. AT1 to capture carbon dioxide for increasing carbon dioxide utilization efficiency.

An alkali-tolerant Chlorella sp. AT1 mutant strain was screened by NTG mutagenesis. The strain grew well in pH 6-11 media, and the optimal pH for growth was 10. The CO2 utilization efficiencies of Chlorella sp. AT1 cultured with intermittent 10% CO2 aeration for 10, 20 and 30min at 3-h intervals were approximately 80, 42 and 30%, respectively. In alkaline medium (pH=11) with intermittent 10% CO2 aeration for 30min at 3-, 6- and 12-h intervals, the medium pH gradually changed to 10, and the biomass productivities of Chlorella sp. AT1 were 0.987, 0.848 and 0.710gL-1d-1, respectively. When Chlorella sp. AT1 was aerated with 10% CO2 intermittently for 30min at 3-h intervals in semi-continuous cultivation for 21days, the biomass concentration and biomass productivity were 4.35gL-1 and 0.726gL-1d-1, respectively. Our results show that CO2 utilization efficiency can be markedly increased by intermittent CO2 aeration and alkaline media as a CO2-capturing strategy for alkali-tolerant microalga cultivation.

Simultaneous microalgal biomass production and CO2 fixation by cultivating Chlorella sp. GD with aquaculture wastewater and boiler flue gas.

A microalgal strain, Chlorella sp. GD, cultivated in aquaculture wastewater (AW) aerated with boiler flue gas, was investigated. When AW from a grouper fish farm was supplemented with additional nutrients, the microalgal biomass productivity after 7days of culture was 0.794gL-1d-1. CO2 fixation efficiencies of the microalgal strains aerated with 0.05, 0.1, 0.2, and 0.3vvm of boiler flue gas (containing approximately 8% CO2) were 53, 51, 38, and 30%, respectively. When the microalgal strain was cultured with boiler flue gas in nutrient-added AW, biomass productivity increased to 0.892gL-1d-1. In semi-continuous cultures, average biomass productivities of the microalgal strain in 2-day, 3-day, and 4-day replacement cultures were 1.296, 0.985, and 0.944gL-1d-1, respectively. These results demonstrate the potential of using Chlorella sp. GD cultivations in AW aerated with boiler flue gas for reusing water resources, reducing CO2 emission, and producing microalgal biomass.

Cultivation of Chlorella sp. GD using piggery wastewater for biomass and lipid production.

The development of a culture system for Chlorella sp. GD to efficiently produce biomass and oil for biodiesel production was investigated. Chlorella sp. GD was cultivated with 0%, 25%, 50%, 75% and 100% piggery wastewater (diluted by medium) at 300 µmol m(-2) s(-1), a 2% CO2 aeration rate of 0.2 vvm and 26±1°C; after a 10-day culture in batch cultures, the maximum specific growth rate and biomass productivity of the microalga obtained in 100% piggery wastewater were 0.839 d(-1) and 0.681 g L(-1) d(-1), respectively. The highest lipid content and lipid productivity were 29.3% and 0.155 g L(-1) d(-1) at 25% wastewater, respectively. In semi-continuous cultures, the biomass and lipid productivities with 25-75% wastewater ratios were greater than 0.852 and 0.128 g L(-1) d(-1), respectively. These results show that Chlorella sp. GD grows efficiently in piggery wastewater, and that a stable growth performance was achieved for long-term microalgal cultivation in a semi-continuous culture.

Cultivation of microalgal Chlorella for biomass and lipid production using wastewater as nutrient resource.

Using wastewater for microalgal cultures is beneficial for minimizing the use of freshwater, reducing the cost of nutrient addition, removing nitrogen and phosphorus from wastewater and producing microalgal biomass as bioresources for biofuel or high-value by-products. There are three main sources of wastewater, municipal (domestic), agricultural and industrial wastewater, which contain a variety of ingredients. Some components in the wastewater, such as nitrogen and phosphorus, are useful ingredients for microalgal cultures. In this review, the effects on the biomass and lipid production of microalgal Chlorella cultures using different kinds of wastewater were summarized. The use of the nutrients resource in wastewater for microalgal cultures was also reviewed. The effect of ammonium in wastewater on microalgal Chlorella growth was intensively discussed. In the end, limitations of wastewater-based of microalgal culture were commented in this review article.