Optical Detection of Fe3+ Ions in Aqueous Solution with High Selectivity and Sensitivity by Using Sulfasalazine Functionalized Microgels

A highly selective and sensitive optical sensor was developed to colorimetric detect trace Fe3+ ions in aqueous solution. The sensor was the sulfasalazine (SSZ) functionalized microgels (SSZ-MGs), which were fabricated via in-situ quaternization reaction. The obtained SSZ-MGs had hydrodynamic radius of about 259 ± 24 nm with uniform size distribution at 25 °C. The SSZ-MG aqueous suspensions can selectively and sensitively response to Fe3+ ions in aqueous solution at 25 °C and pH of 5.6, which can be quantified by UV-visible spectroscopy and also easily distinguished by the naked eye. Job’s plot indicated that the molar binding ratio of SSZ moiety in SSZ-MGs to Fe3+ was close to 1:1 with an apparent association constant of 1.72 × 104 M−1. A linear range of 0–12 μM with the detection limit of 0.110 μM (0.006 mg/L) was found. The obtained detection limit was much lower than the maximum allowance level of Fe3+ ions in drinking water (0.3 mg/L) regulated by the Environmental Protection Agency (EPA) of the United States. The existence of 19 other species of metal ions, namely, Ag+, Li+, Na+, K+, Ca2+, Ba2+, Cu2+, Ni2+, Mn2+, Pb2+, Zn2+, Cd2+, Co2+, Cr3+, Yb3+, La3+, Gd3+, Ce3+, and Bi3+, did not interfere with the detection of Fe3+ ions

Screening of freshwater oleaginous microalgae from South China and its cultivation characteristics in energy grass digestate

Microalgae biodiesel attracts considerable attention from energy organizations around the world. Lack of high oil-producing oleaginous microalgae is considered as one of the main bottlenecks for large-scale production of microalgae biodiesel. To address this issue, a nitrogen limitation-based method for screening oleaginous microalgae using 24-well plates was developed in the present study. Thirty microalgae strains collected from a subtropical freshwater system of South China were selected and cultivated in bubbling column photobioreactors, with lipid yields as the endpoints. The dry weight (DW) of seven strains exceeded 6.0 g L-1 and total lipid contents of 10 strains were over 40% DW. Coelastrella sp. GN12 was further evaluated as it had the highest lipid yield (4.94 g L-1) and abundant triacylglycerol (95% total lipid). This strain was cultured in various digestates from mono-digested energy grass diluted with BG-11. A ratio of 25% energy grass digestate: BG-11 (v: v) (designated as EG25) and a pure unsterilized energy grass digestate (designated as EG100U) were the most effective at growth and oil accumulation (with total lipid content > 50% DW). Total nitrogen removal rates of EG25 and EG100U were 73% and 57%, respectively, and the strain was even more effective at removing total phosphorus (96% and 94%, respectively). Therefore, energy grass digestate can be used as a substitute medium for GN12, transforming waste into valuable energy sources and achieving the benefits of resource recycling and clean energy production. (C) 2020 Elsevier Ltd. All rights reserved

Advancements in the application of surfactants in microalgal production, harvesting and processing: A review

While the possibility of a microalgae industry is exciting, commercial practice has been hampered by the high operational costs. Surfactants-assisted microalgae industrial innovations, which are primarily based on the unique structure of surfactants with hydrophobic and hydrophilic groups, have garnered significant interest in recent years. However, lack of systematic overview of coupling of surfactant and microalgae industry so far. Here, we begin with an overview of main direction of surfactant coupled with microalgae industry, followed by a summary of the background, advantages, and research status of each main direction in the order of microalgae growth, harvesting, and processing. Additionally, we addressed the mechanisms involved in certain key directions. Final concluding remarks on the future potential for expanding surfactant applications in the microalgae industry are also suggested

Treatment of Synthetic Ammonium Sulfate Wastewater by Mixed Culture of Chlorella pyrenoidosa and Enriched Nitrobacteria

Ammonium sulfate wastewater can cause eutrophication and black odor of water body. Although ammonia nitrogen can be used as nutrient of microalgae, high ammonia nitrogen levels could inhibit the growth of microalgae. Nitrobacteria can transform ammonia nitrogen into nitrate nitrogen. In this study, mono Chlorella pyrenoidosa culture (mono-C.py), synchronous mixed culture (mixed-a), and asynchronous mixed culture (mixed-b) systems were examined for their ability to treat ammonium sulfate wastewater. Nitrogen removal rate of mixed-b at the end of culture (52.96%) was higher than that of the mono-C.py (46.37%) and the mixed-a (39.11%). Higher total suspended solid concentration (2.40 g/L), crude protein yield (0.76 g/L), and heating value yield (35.73 kJ/L) were obtained in mixed-b, meanwhile with excellent settlement performance (91.43 +/- 0.51%). Mechanism analysis of settlement showed that the relative abundance of floc-forming-related bacteria Sphingopyxis and Acidovorax were increased generally, while nitrification/denitrifying members were decreased in mixed-b along with the culture proceeding

The joint effect of ammonium and pH on the growth of Chlorella vulgaris and ammonium removal in artificial liquid digestate

Although ammonium containing digestate is an ideal alternative medium for microalgae cultivation, high ammonium or unfavorable pH may inhibit microalgal growth. In this study, the joint effect of ammonium and pH on the growth of C. vulgaris and nutrient removal in artificial digestate was investigated. Our results show that ammonium and pH both affected algal growth, but free ammonia (FA) was the main actual inhibitory factor. Algal specific growth rate presented a negative correlation with FA and their relationship was well fitted by a linear regression model. Microalgal growth was little affected below 36.8 mg L-1 FA, while the obvious inhibition occurred at 184 mg L-1 FA (EC50), indicating a high tolerance to FA. Ammonium removal was well described by a first-order kinetics model. FA stress stimulated the production of extracellular organic matters (EOMs), which was good for micmalgae adaptation but adverse to pollutant removal

Lipid Biosynthesis and Metabolic Regulation in Microalgae

With the increasingly severe energy and environmental problems, biodiesel from microalgae has become a hot topic. Compared with traditional oil crops, microalgae have advantages of rapid growth, high lipid content, non-occupation of arable land, etc., which have been considered as a highly potential feedstock of biofuels. Although neutral lipids, especially triacylglycerols (TAG) which are the main feedstock of biodiesel production, can be accumulated in many algal cells under stress conditions, little is known about microalgal lipid synthesis and metabolic regulation so far. In order to better understand and manipulate microalgal lipid metabolism for improvement of lipid production, we present an overview of advances of lipid biosynthesis and metabolic regulation in microalgae, including TAG biosynthesis pathway, biochemical regulation and genetic engineering strategies. Effects of nutrition on lipid production are represented. Five genetic engineering strategies are summarized including enhancement of fatty acids synthesis pathway, enhancement of Kennedy pathway, regulation of alternative pathway of TAG, inhibition of competing pathway of lipid biosynthesis and lipid catabolism. The prospects of research on microalgal lipid metabolism are also discussed

Metabolic changes of starch and lipid triggered by nitrogen starvation in the microalga Chlorella zofingiensis

The aim of this research was to study the metabolic changes of starch and lipid biosynthesis in the microalga Chlorella zofingiensis under nitrogen starvation in comparison to nitrogen abundant condition. C. zonfingiensis showed a rapid growth and kept stable chlorophyll content when grown in nitrogen-replete medium, while a severe inhibition of cell growth and a sharp degradation of chlorophyll occurred under nitrogen depletion. Nitrogen-replete C. zonfingiensis cells possessed basal levels of starch and lipid. Upon nitrogen starvation, both starch and lipid increased greatly within cells, but starch synthesis preceded lipid accumulation. After 2 days of stress condition, starch was partially degraded, possibly to support lipid synthesis. It was speculated that starch accumulation acted as a quick response to environmental stress, whereas lipid served as long-term energy storage. Additionally, C. zonfingiensis tends to lower the degree of unsaturation in response to nitrogen starvation which is desirable for biodiesel production. (C) 2013 Elsevier Ltd. All rights reserved

Seasonal variation in the growth, lipid accumulation, and fatty acid composition of Chlorella sp. GN1 cultured in flat plate photobioreactors outdoors

To evaluate the feasibility of producing biodiesel feedstock from Chlorella sp. GN1, the growth, lipid, and fatty acid profile in long-term outdoor cultivation during four seasons were studied. The alga grew well in the four seasons, and the dry weight (2.73 g/L) and specific growth rate (0.652 day(-1)) reached their highest values in the autumn. Nitrogen deficiency induced all the lipid contents to exceed 40% of the dry weight in the four seasons, and higher lipid contents (> 50% of the dry cell weight) were achieved in autumn and summer. The highest lipid content (52.8%) was acquired in autumn. Additionally, in the four seasons, C16 and C18 were primary fatty acids (> 90%) in the alga, which were ideal fatty acid components for biodiesel. Moreover, more saturated fatty acids were synthesized in cells during summer and autumn, while the proportion of polyunsaturated fatty acids reached the highest level in the winter. The study indicated that the alga has great prospects for biodiesel feedstock preparation

Characterization of lipid and fatty acids composition of Chlorella zofingiensis in response to nitrogen starvation

Cellular biochemical composition of the microalga Chlorella zofingiensis was studied under favorable and nitrogen starvation conditions, with special emphasis on lipid classes and fatty acids distribution. When algal cells were grown in nitrogen-free medium (N stress), the increase in the contents of lipid and carbohydrate while a decrease in protein content was detected. Glycolipids were the major lipid fraction (50.7% of total lipids) under control condition, while neutral lipids increased to be predominant (86.7% of total lipids) under N stress condition. Triacylglycerol (TAG) content in N stressed cells was 27.3% dw, which was over three times higher than that obtained under control condition. Within neutral lipids fraction, monounsaturated fatty acids (MUFA) were the main group (40.6%) upon N stress, in which oleic acid was the most representative fatty acids (34.5%). Contrarily, glycolipids and phospholipids showed a higher percentage of polyunsaturated fatty acids (PUFA). Lipid quality assessment indicated the potential of this alga as a biodiesel feedstock when its neutral lipids were a principal lipid fraction. The results demonstrate that the neutral lipids content is key to determine the suitability of the microalga for biodiesel, and the stress cultivation is essential for lipid quality. (C) 2015, The Society for Biotechnology, Japan. All rights reserved