Effect of temperature on the conversion ratio of glucose to Chlorella pyrenoidosa cells: Reducing the cost of cultivation

Heterotrophic Selenium Incorporation into Chlorella vulgaris K-01: Selenium Tolerance, Assimilation, and Removal through Microalgal Cells

Chlorella has been applied in the production of selenium (Se) enriched organic biomass. However, limited information exists regarding heterotrophic selenium tolerance and its incorporation into Chlorella. This study aimed to investigate the potential of using Chlorella vulgaris K-01 for selenium biotransformation. To assess the dose-response effect of Se stress on the strain, time-series growth curves were recorded, growth productivity parameters were calculated, and Gaussian process (GP) regression analysis was performed. The strain's carbon and energy metabolism were evaluated by measuring residual glucose in the medium. Characterization of different forms of intracellular Se and residual Se in the medium was conducted using inductively coupled plasma-mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometer (ICP-OES). The EC50 value for the strain in response to Se stress was 38.08 mg/L. The maximum biomass productivity was 0.26 g/L/d. GP regression analysis revealed that low-level Se treatment could increase the biomass accumulation and the carrying capacity of Chlorella vulgaris K-01 in a heterotrophic culture. The maximum organic Se in biomass was 154.00 μg/g DW. These findings lay the groundwork for understanding heterotrophic microalgal production of Se-containing nutraceuticals, offering valuable insights into Se tolerance, growth dynamics, and metabolic responses in Chlorella vulgaris K-01.

Effective bioremediation of tobacco wastewater by microalgae at acidic pH for synergistic biomass and lipid accumulation

Tobacco wastewater is too difficult to decontaminate which poses a significant environmental problem due to the harmful and toxic components. Chlorella pyrenoidosa is a typical microalgal species with potential in removal of organic/inorganic pollutants and proves to be an ideal algal-based system for wastewater treatment. However, the strategy of tobacco related wastewater treatment using microalgae is in urgent need of development. In this study, C. pyrenoidosa was used to evaluate the removal efficiency of artificial tobacco wastewater. Under various solid-to-liquid (g/L) ratios, 1:1 ratio and acidic pH 5.0 were optimal for C. pyrenoidosa to grow with high performance of removal capacity to toxic pollutants (such as COD, NH3-N, nicotine, nitrosamines and heavy metals) with the alleviation of oxidative damage. Algal biomass could reach up to 540.24 mg/L. Furthermore, carbon flux of C. pyrenoidosa was reallocated from carbohydrate and protein biosynthesis to lipogenesis with a high lipid content of 268.60 mg/L at pH 5.0. Overall, this study demonstrates an efficient and sustainable strategy for tobacco wastewater treatment at acidic pH with the production of valuable microalgal products, which provides a promising biorefinery strategy for microalgal-based wastewater bioremediation.

The filtration and fouling performance of membranes with different pore sizes in algae harvesting

In this study, ultrafiltration membranes with three different pore sizes were applied for algae harvesting to investigate filtration performance. The critical fluxes (J_C) increased as the pore size increased, and the J_C of 0.03-, 0.05- and 0.1-μm membranes were 20.0, 25.0 and 42.0Lm^-2h^-1, respectively. During continuous filtration, 0.7J_C was selected as the operation flux and the 0.1-μm membrane had the highest initial flux and final flux. It also had the highest flux decline rate, and therefore, the 0.1-μm membrane was more appropriate for algae separation compared to the 0.03- and 0.05-μm membrane. The mechanism by which pore size influenced filtration performance and membrane fouling was presented from the viewpoint of permeate drag force (F_D). A lower F_D retarded the velocity of algae cells towards the membrane, which could decelerate the deposition of particles on the membrane and thus reduce the membrane fouling rate. As the pore size increased, the membrane hydraulic resistance (R_m) decreased, which led to a decrease of F_D.

Cultivation of Chlorella pyrenoidosa in outdoor open raceway pond using domestic wastewater as medium in arid desert region

Chlorella pyrenoidosa was cultivated in secondary wastewater effluent to assess its nutrient removal capabilities. Wastewaters were obtained from a wastewater treatment plant located in Ouargla, Algeria. The experiments were conducted in winter under natural sunlight in an outdoor open raceway pond situated in the desert area. The highest biomass of the microalgae was found to be 1.71±0.04g/L. Temperatures ranged between 18 and 31°C. The average annual insolation was no less than 3500h with an annual solar irradiance of more than 2000kWh/m(2). Analyses of different parameters including COD, NH4(+)-N and TP were conducted throughout the cultivation period. Their average removal efficiencies were 78%, 95% and 81% respectively. The results demonstrated the potential of nutrient removal by microalgae grown on secondary wastewater in arid areas.

Heterotrophic cultivation of Chlorella pyrenoidosa using sucrose as the sole carbon source by co-culture with Rhodotorula glutinis

Heterotrophic cultivation of microalgae is a feasible alternative strategy to avoid the light limitation of photoautotrophic culture, but the heterotrophic utilization of disaccharides is difficult for microalgae. Aimed at this problem, a co-culture system was developed by mix culture of C. pyrenoidosa and R. glutinis using sucrose as the sole carbon source. In this system, C. pyrenoidosa could utilize glucose and fructose which were hydrolyzed from sucrose by R. glutinis. The highest specific growth rate and final cell number proportion of algae was 1.02day(-1) and 45%, respectively, when cultured at the initial algal cell number proportion of 95.24% and the final algal cell density was 111.48×10(6)cells/mL. In addition, the lipid content was also promoted due to the synergistic effects in mix culture. This study provides a novel approach using sucrose-riched wastes for the heterotrophic culture of microalgae and may effectively decrease the cost of carbon source.

Construction and application of the Synechocystis sp. PCC6803-ftnA in microbial contamination control in a coupled cultivation and wastewater treatment

Inspired by iron fertilization experiments in HNLC (high-nitrate, low-chlorophyll) sea areas, we proposed the use of iron-rich engineered microalgae for microbial contaminant control in iron-free culture media. Based on the genome sequence and natural transformation system of Synechocystis sp. PCC6803, ftnA (encoding ferritin) was selected as our target gene and was cloned into wild-type Synechocystis sp. PCC6803. Tests at the molecular level confirmed the successful construction of the engineered Synechocystis sp. PCC6803-ftnA. After Fe(3+)-EDTA pulsing, the intracellular iron content of Synechocystis sp. PCC6803-ftnA was significantly enhanced, and the algae was used in the microbial contamination control system. In the coupled Synechocystis sp. PCC6803-ftnA production and municipal wastewater (MW, including Scenedesmus obliquus and Bacillus) treatment, Synechocystis sp. PCC6803-ftnA accounted for all of the microbial activity and significantly increased from 70% of the microbial community to 95%. These results revealed that while the stored iron in the Synechocystis sp. PCC6803-ftnA cells was used for growth and reproduction of this microalga in the MW, the growth of other microbes was inhibited because of the iron limitation, and these results provide a new method for microbial contamination control during a coupling process.

Comparison of axial vibration membrane and submerged aeration membrane in microalgae harvesting

The submerged aeration membrane (SAM) system and axial vibration membrane (AVM) system can mitigate membrane fouling. In this study, both systems were investigated to compare the performance of filtration and the membrane fouling in algae filtration. In 5-h filtration, the transmembrane pressure (TMP) of SAM reached to 70.0 kPa, while there was almost no increase in TMP for AVM. After continuous filtration, it could be found that there was hardly any algae cells on the membrane of AVM (0.11 g/m(2)), which was about 32.4 times less than that of SAM (3.56 g/m(2)). Compared with the SAM system, AVM had a lesser membrane fouling, regardless of the reversible fouling or irreversible fouling. By SEM, FTIR and EEM, it could be found there was less irreversible extracellular organic matter (EOM) on the membrane of AVM. By MW distribution, it could be observed that less EOM with high-MW adhered to membrane of AVM.