Low Sulfate Concentrations Research Articles

Treatment of acidic sulfate-containing wastewater using revolving algae biofilm reactors: Sulfur removal performance and microbial community characterization

Industries such as mining operations are facing challenges of treating sulfur-containing wastewater such as acid mine drainage (AMD) generated in their plant. The aim of this work is to evaluate the use of a revolving algal biofilm (RAB) reactor to treat AMD with low pH (3.5–4) and high sulfate content (1–4 g/L). The RAB reactors resulted in sulfate removal efficiency up to 46% and removal rate up to 0.56 g/L-day, much higher than those obtained in suspension algal culture. The high-throughput sequencing revealed that the RAB reactor contained diverse cyanobacteria, green algae, diatoms, and acid reducing bacteria that contribute the sulfate removal through various mechanisms. The RAB reactors also showed a superior performance of COD, ammonia and phosphorus removal. Collectively, the study demonstrated that RAB-based process is an effective method to remove sulfate in wastewater with small footprint and can be potentially installed in municipal or industrial wastewater treatment facilities.

Studies on Antiviral and Immuno-Regulation Activity of Low Molecular Weight Fucoidan from Laminaria japonica

The antiviral activity in vitro and in vivo and the effect of the immune system of two fucoidan fractions with low molecular weight and different sulfate content from Laminaria japonica (LMW fucoidans) were investigated in order to examine the possible mechanism. In vitro, I-type influenza virus, adenovirus and Parainfluenza virus I were used to infect Hep-2, Hela and MDCK cells, respectively. And 50% tissue culture infective dose was calculated to detect the antiviral activity of two LMW fucoidans. The results indicated that compared with the control group, 2 kinds of LMW fucoidans had remarkable antiviral activity in vitro in middle and high doses, while at low doses, the antiviral activity of 2 kinds of LMW fucoidans was not statistically different from that in the blank control group. And there was no statistically difference between two LMW fucoidans in antiviral activity. In vivo, LMW fucoidans could prolong the survival time of virus-infected mice, and could improve the lung index of virus-infected mice significantly, which have statistical differences with the control group significantly (p 0.05). In this study, it was shown that both of two LMW fucoidans (LF1, LF2) could increase the thymus index, spleen index, phagocytic index, phagocytosis coefficient and half hemolysin value in middle and high doses, which suggested that LMW fucoidans could play an antiviral role by improving the quality of immune organs, improving immune cell phagocytosis and humoral immunity.

Hydration mechanisms of supersulfated cement

Considerable attention has been given to special cements, capable of reducing CO2 emissions, energy and limestone consumption. Supersulfated cements are made of blast furnace slag (GBFS), calcium sulfate (CS), and small quantities of activator, but achieving their optimal proportions is complex. In this paper, the effects of the both CS and alkali activator (KOH) contents were studied. The main results showed that the compressive strength, heat of hydration, and consumption of anhydrite phase were strongly influenced by the alkaline content, while low calcium sulfate or alkaline content increased the formation of CSH. The instability of ettringite was verified: with low CS, the probable hypothesis was its conversion into monosulfate due to the scarcity of sulfate; with high CS, it was associated with intense, rapid consumption of anhydrite with high KOH content, followed by the precipitation of ettringite on the surface of slag grains and its conversion into monosulfate.

Redox zonation and organic matter oxidation in palaeogroundwater of glacial origin from the Baltic Artesian Basin

Ordovician-Cambrian aquifer system (O-Cm) in the northern part of the Baltic Artesian Basin (BAB), Estonia, is part of a unique groundwater reservoir where groundwater originating from glacial meltwater recharge from the Scandinavian Ice Sheet is preserved. The distribution of redox zones in the anoxic O-Cm aquifer system is unusual. Strongly reducing conditions are found near the modern recharge area characterized by low concentrations of sulphate (<5 mg·L−1) and the presence of CH4 (up to 3.26 vol%). The concentrations of SO42− increase and concentrations of CH4 decrease farther down the groundwater flow path. Sulphate in fresh glacial palaeogroundwater originates probably from pyrite oxidation while brackish waters have gained their sulphate through mixing with relict saline formation waters residing in the deeper parts of the aquifer system. Stable isotopic composition of sulphate, especially relations between δ18OSO4-δ18Owater (∆18OSO4-H2O from +20.5 to +31.1‰) and δ34SSO4-δ34SH2S (∆34SSO4-H2S value of +47.9‰) support a widespread occurrence of bacterial sulphate reduction in fresh glacial palaeogroundwater. We propose, that the observed unusual redox zonation is a manifestation of two different flow systems in the O-Cm aquifer system: 1) the topographically driven flow system which drives the infiltration of waters through the overlying carbonate formation in the modern recharge area; 2) the relict flow system farther down the groundwater flow path which developed as a response to large hydraulic gradients imposed by the Scandinavian Ice Sheet in Pleistocene. Thus, the strongly reducing conditions surrounding the modern recharge area may show the extent to which post-glacial recharge has influenced the aquifer system. O-Cm aquifer system is an example of an aquifer that has not reached a near-equilibrium state with respect to present day flow conditions and still exhibits hydrogeochemical patterns established under the influence of a continental ice sheet in Pleistocene.

Stable sulfur isotope ratios and chemical compositions of fine aerosols (PM2.5) in Beijing, China

Pervasive particulate pollution has been observed over large areas of the North China Plain. The high level of sulfate, a major component in fine particles, is pronounced during heavy pollution periods. Being different from source apportionments by atmospheric chemistry-transport model and receptor modeling methods, here we utilize sulfur isotopes to discern the potential emission sources. Sixty-five daily PM2.5 samples were collected at an urban site in Beijing between September 2013 and July 2014. Inorganic ions, organic/elemental carbon and stable sulfur isotopes of sulfate were analyzed. The “fingerprint” characteristics of stable sulfur isotopic composition, together with trajectory clustering modeled by HYSPLIT-4 (HYbrid Single-Particle Lagrangian Integrated Trajectory) and FLEXPART (“FLEXible PARTicle dispersion model”), was employed to identify potential aerosol sources in Beijing. Results exhibited a distinctive seasonality with sulfate, nitrate, ammonium, organic matter, and element carbon being the dominant species of PM2.5. Elevated concentrations of chloride with high organic matter were found in autumn and winter as a result of enhanced fossil fuel (mainly coal) combustion. The δ34S values of the Beijing aerosols ranged from 2.8‰ to 9.9‰ with an average of 6.0 ± 1.8‰, further indicating that the major sulfur source was direct coal burning emission. Owing to the changing patterns between oxidation pathways of S(IV) in different seasons, δ34S values varied with a winter maximum (8.2 ± 1.1‰) and a summer minimum (4.9 ± 1.9‰). The results of trajectory clustering and FLEXPART demonstrated that higher concentrations of sulfate with lower sulfur isotope ratios (4.6 ± 0.8‰) were associated with air masses from the south or east, whereas lower sulfate concentrations with heavier sulfur isotope ratios (6.7 ± 1.6‰) were observed when the air masses were mainly from the north or northwest. These results suggested that the fine aerosol pollution in Beijing, especially sulfate pollution, was mainly due to coal combustion sources from regional and local regions.

Strategies for the stable performance and rapid inhibition recovery of a thermophilic digester treating coffee wastes and the synergistic effects of microbes

A 200-day experiment was conducted to evaluate strategies for the stable performance and rapid inhibition recovery of a thermophilic reactor treating coffee wastes, waste activated sludge, and milk waste under a high organic loading rate (OLR) and the synergistic effects of microbes. Excessive accumulation of propionate was determined to be the main reason for the deterioration of the reactor, which resulted from reduced methanogenic activity. Supplementation of inoculum sludge led to the complete inhibition recovery of the reactor in fewer than 35 d by enhancing propionate degradation. The microelement and low concentration of sulfate ensured the stable performance of the reactor at OLR of 4.6 g-TS/L/d. The efficiency of organic matters and propionate degradation was also improved. The microbial community was analyzed by high-throughput sequencing targeting 16S rRNA to determine the relationship between microbial composition and reactor performance. Propionate markedly inhibited Methanosarcina, which dominated the stable state; meanwhile, Methanobacterium and Methanothermobacter were more tolerant and comprised more than 75% of total archaea at the inhibitory stage. The deterioration of the reactor led to a shift in the CH4 generation pathway from acetoclastic to hydrogenotrophic. Clostridiales was responsible for organic degradation at stable stages; however, almost all of the genera of Clostridiales could not survive at stage II and were replaced by Thermoanaerobacterales and Lactobacillales.

Dissolved and particulate metal fluxes in an AMD-affected stream under different hydrological conditions: The Odiel River (SW Spain)

This study aims to characterize geochemically the acid mine drainage (AMD) sources causing deterioration of the water quality of a river reach with extreme hydrologic variability and to identify the patterns of dissolved and particulate contaminants along the reach. The hydrochemistry of the river reach is exposed to dramatic seasonal and spatial changes. The levels of sulfate and metals increase progressively along the reach due to the input of the first AMD discharges. However, the confluence with the Agrio River, which collects extremely acidic and metal-rich AMD from Riotinto mines, causes the total depletion of alkalinity and a dramatic decrease of pH values (down to 3.3), which strongly enhances the solubility of metals. A pH-controlled pattern of metal transport prevails in the river. Above pH 6, particulate Al and Fe is the predominant form of transport in the river; below pH 5, Al is chiefly transported in dissolved form, while the water velocity may control sedimentation of Fe precipitates. Particulate Cu, Zn, and Mn exhibit a similar pattern although with some differences. Above pH 6, Cu is generally transported by the particulate phase, while Zn and to a greater extent Mn, are mostly carried by the dissolved phase. Cobalt and Ni are mostly transported in dissolved form, even at circumneutral pH values, showing a more conservative behavior. Geochemical modeling results and analysis of high-energy X-ray diffraction patterns point to schwertmannite and ferrihydrite as the mineral phases responsible for the solubility control of Fe. Schwertmannite may precipitate close to mixing zones, where lower pH values and higher sulfate concentrations are found, while ferrihydrite probably precipitates farther from these zones, at higher pH values and lower sulfate concentrations. Metal and sulfate loadings are strongly linked to rainfall events. The highest dissolved loads were observed during floods in May 2016, when up to 48 t day−1 of Al, 16 t day−1of Fe, 8.4 t day−1of Zn, and so on, were transported by the river, values noticeably higher than those observed in other mining areas.

Impact of acidic, water and alkaline extraction on structural features, antioxidant activities of Laminaria japonica polysaccharides

This study comparatively evaluated the effects of different extraction methods on yield, structural features and antioxidant activities of Laminaria japonica (L. japonica) polysaccharides. Results showed that acid, water and alkaline extracted L. japonica polysaccharides (LJP-CA, LJP-W and LJP-A, respectively) differed significantly. Among three polysaccharides, LJP-W showed the highest viscosity with high uronic acid content and average molecular weight, whereas LJP-CA showed the lowest viscosity with low uronic acid and high sulfate content with moderate average molecular weight. LJP-CA was mainly composed of fucose, mannose and galactose, but the proportion of glucose was greatly increased in LJP-W and LJP-A. LJP-W had an even and smooth sheet-like appearance, while LJP-CA and LJP-A exhibited irregular and rough fragments or particles with stronger antioxidant activities. These results suggest that acid and alkali would propose an improved process for polysaccharide preparation from L. japonica and to exploit its potential application as a functional ingredient in food application.

Sulphate partitioning into calcite: Experimental verification of pH control and application to seasonality in speleothems

Carbonate-associated sulphate (CAS) is a useful carrier of palaeoenvironmental information throughout the geologic record, particularly through its stable isotope composition. However, a paucity of experimental data restricts quantitative understanding of sulphate incorporation into carbonates, and consequently CAS concentrations and their diagenetic modifications are rarely interpreted. However, in the case of calcite speleothems, the remarkably high-resolution CAS records which are obtainable via modern microanalytical techniques represent a potentially invaluable source of palaeoenvironmental information. Here, we describe the results of controlled experiments of sulphate co-precipitation with calcite in freshwater solutions where pH, saturation state, and sulphate concentration were varied independently of each other. Solution pH is confirmed as the principal control on sulphate incorporation into calcite. The relative efficiency of incorporation was calculated as a partition coefficient DSO4 = (mSO4/mCO3)solid/(mSO4/mCO3)solution. High crystal growth rates (driven by either pH or saturation state) encouraged higher values of DSO4 because of an increasing concentration of defect sites on crystal surfaces. At low growth rates, DSO4 was reduced due to an inferred competition between sulphate and bicarbonate at the calcite surface. These experimental results are applied to understand the incorporation of sulphate into speleothem calcite. The experimentally determined pH-dependence suggests that strong seasonal variations in cave air PCO2 could account for annual cycles in sulphate concentration observed in stalagmites. Our new experimentally determined values of DSO4 were compared with DSO4 values calculated from speleothem-drip water monitoring from two caves within the Austrian and Italian Alps. At Obir cave, Austria, DSO4 (×105) varies between 11.1 (winter) and 9.0 (summer) and the corresponding figures for Ernesto cave, Italy, are 15.4 (winter) and 14.9 (summer). These values approximate predicted DSO4 values based on our chamber experiments containing both low (2 ppm) and high (20 ppm) sulphate concentrations. Our experimental values of DSO4 obtained at crystal growth rates typical of stalagmites, closely match those observed in other cave sites from around the world. This validates the universality of the controls behind DSO4 and will enhance the use of speleothem CAS as a palaeoenvironmental proxy.

Hydration of calcium aluminate cement blended with anhydrite

Calcium aluminate cements (CACs) are used in combination with calcium sulfates as binders in self-levelling mortars. The influence of commercial CAC/anhydrite ratio on the solid phase assemblage and pore solution at water to binder (w/b) ratios of 0·40 and 0·72 was investigated between 1·5 h and 91 d of hydration using a multi-method approach including x-ray diffraction, thermogravimetric analysis and thermodynamic calculations. The reduction of the extent of hydration at the lower w/b ratio can be explained by a lack of water for complete hydration and lack of space. In the system with a CAC/anhydrite weight ratio of 1, ettringite and AH3were the main hydration products, whereas in the case of a CAC/anhydrite ratio of 2·3, in addition to ettringite and AH3, monosulfate was present along with strätlingite and at a later age. In contrast to the thermodynamic modelling results, anhydrite persisted even at low calcium sulfate contents as the precipitation of AH3around the anhydrite grains seemed to lead to a chemical blocking.

Methylmercury and methane production potentials in North Carolina Piedmont stream sediments

Methylated mercury (MeHg) can be produced by all microbes possessing the genes hgcA and hgcB, which can include sulfate-reducing bacteria (SRB), iron-reducing bacteria (FeRB), methane-producing archaea (MPA), and other anaerobic microbes. These microbial groups compete for substrates, including hydrogen and acetate. When sulfate is in excess, SRB can outcompete other anaerobic microbes. However, low concentrations of sulfate, which often occur in stream sediments, are thought to reduce the relative importance of SRB. Although SRB are regarded as the primary contributors of MeHg in many aquatic environments, their significance may not be universal, and stream sediments are poorly studied with respect to microbial Hg methylation. We evaluated suppression of methanogenesis by SRB and the potential contributions from SRB, MPA and other MeHg producing microbes (including FeRB) to the production of MeHg in stream sediments from the North Carolina Piedmont region. Lower methanogenesis rates were observed when SRB were not inhibited, however, application of a sulfate-reduction inhibitor stimulated methanogenesis. Greater MeHg production occurred when SRB were active. Other MeHg producing microbes (i.e., FeRB) contributed significantly less MeHg production than SRB. MPA produced MeHg in negligible amounts. Our results suggest that SRB are responsible for the majority of MeHg production and suppress methanogenesis in mid-order stream sediments, similar to other freshwater sediments. Further investigation is needed to evaluate the generality of these findings to streams in other regions, and to determine the mechanisms regulating sulfate and electron acceptor availability and other potential factors governing Hg methylation and methane production in stream sediments.

Investigation of kinetics and absorption isotherm models for hydroponic phytoremediation of waters contaminated with sulfate

Two common wetland plants, Pampas Grass (Cortaderia selloana) and Lucky Bamboo (Dracaena sanderiana), were used in hydroponic cultivation systems for the treatment of simulated high-sulfate wastewaters. Plants in initial experiments at pH 7.0 removed sulfate more efficiently compared to the same experimental conditions at pH 6.0. Results at sulfate concentrations of 50, 200, 300, 600, 900, 1200, 1500 and 3000 mg/L during three consecutive 7-day treatment periods with 1-day rest intervals, showed decreasing trends of both removal efficiencies and uptake rates with increasing sulfate concentrations from the first to the second to the third 7-day treatment periods. Removed sulfate masses per unit dry plant mass, calculated after 23 days, showed highest removal capacity at 600 mg/L sulfate for both plants. A Langmuir-type isotherm best described sulfate uptake capacity of both plants. Kinetic studies showed that compared to pseudo first-order kinetics, pseudo-second order kinetic models slightly better described sulfate uptake rates by both plants. The Elovich kinetic model showed faster rates of attaining equilibrium at low sulfate concentrations for both plants. The dimensionless Elovich model showed that about 80% of sulfate uptake occurred during the first four days' contact time. Application of three 4-day contact times with 2-day rest intervals at high sulfate concentrations resulted in slightly higher uptakes compared to three 7-day contact times with 1-day rest intervals, indicating that pilot-plant scale treatment systems could be sized with shorter contact times and longer rest-intervals.

Rotifer Diversity in the Acidic Pyrite Mine Pit Lakes in the Sudety Mountains (Poland)

The diversity of rotifers was studied in three artificial water bodies (Azure Lake, Yellow Lake, and Purple Lake), which were once pyrite mines. The physicochemical parameters and the zooplankton composition of the water were determined. Azure Lake had a pH of 3.4–6.9, conductivity values of 165–194 µS cm− 1, and low concentrations of sulphate, calcium, magnesium, copper, and iron, while the other lakes had a pH of 2.6–2.9, a conductivity of 1636–3400 µS cm− 1, and high concentrations of sulphate (up to 2863 mg dm− 3), Cu (up to 2650 µg dm− 3), and Fe (up to 178.3 mg dm− 3). The rotifer community in the lakes comprised 27 taxa (15 in Azure Lake, 13 in Purple Lake and 14 in Yellow Lake). We also found two species that are rarely observed in Poland (Aspelta cincinator and Elosa spinifera), and three species commonly found in acidic water (E. worallii, Cephalodella delicata, and C. hoodi). The types of rotifers in Azure Lake differed from those in the other two lakes. The Shannon–Weaver biodiversity index (H′) was the highest in Purple Lake (H′ = 1.255) and lowest in Azure Lake (H′ = 0.455). The effect of some of the physicochemical parameters on rotifer diversity is discussed.

Laser micro-ablation of fibrocartilage tissue: Effects of tissue processing on porosity modification and mechanics.

The temporomandibular joint disk (TMJd) is an extremely dense and avascular fibrocartilaginous extracellular matrix (ECM) resulting in a limited regenerative capacity. The use of decellularized TMJd as a biocompatible scaffold to guide tissue regeneration is restricted by innate subcellular porosity of the ECM that hinders cellular infiltration and regenerative events. Incorporation of an artificial microporosity through laser micro-ablation (LMA) can alleviate these cell and diffusion based limitations. In this study, LMA was performed either before or after decellularization to assess to effect of surfactant treatment on porosity modification as well as the resultant mechanical and physical scaffold properties. Under convective flow or agitation schemes, pristine and laser ablated disks were decellularized using either low (0.1% w/v) or high (1% w/v) concentrations of sodium dodecyl sulfate (SDS). Results show that lower concentrations of SDS minimized collagen degradation and tissue swelling while retaining its capacity to solubilize cellular content. Regardless of processing scheme, laser ablated channels incorporated after SDS treatment were relatively smaller and more uniform than those incorporated before SDS treatment, indicating an altered laser interaction with surfactant treated tissues. Smaller channels correlated with less disruption of native biomechanical properties indicating surfactant pre-treatment is an important consideration when using LMA to produce artificial porosity in ex vivo derived tissues. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1858-1868, 2018.

Geochemical behavior of Cu and sulfur isotopes in the tropical mining region of Taxco, Guerrero (southern Mexico)

This study was aimed to identify the main processes involved in the release of metals using sulfur isotopes and those acting on the fractionation of copper isotopes. We determined sulfur and copper isotopic ratios in rocks, tailings, precipitates and soils samples from the historical mining district of Taxco, Southern Mexico. Ratios of sulfur isotopes are reported in notation of δ per mil, and standardization was based on international standards OGS-1 and NBS123. Only copper ratio isotopes were studied in pyrite (Py), sphalerite (Sph) and galena. Results are reported as δ65Cu=((65Cu/63Cusample/65Cu/63CuNIST976standar)−1)∗1000. Error for all the analyzed samples was 0.01‰ and any mass bias was corrected trough bracketing method. The sulfur isotopic value of a sample from the Mexcala shale Formation was −7.7‰. The δ34S values in tailing ponds ranged from −2.6 to 1.2‰, in precipitates from −7.2 to −3.2‰, and in soils from −0.8 to 4.5‰. Isotopic δ34S values in rocks evidenced a magmatic influence of sulfides present in the Mexcala Formation. Oxidation of sulfides contained in tailings and precipitates was observed related with their low δ34S values close to zero, oxidation followed the order: sphalerite>pyrite>pyrite rich in copper>chalcopyrite>galena. In soils, oxidation is not the main process as supported by their positive δ34S values and low sulfate content. Results of δ65Cu values in rocks were −0.09 to 0.54‰; in sulfides values were δ65Cu=0.18‰ (Py) and δ65Cu=−0.20‰ (Sph), concentration of copper in galena was not enough to get a reliable isotopic value. In tailings δ65Cu ranged from −1.19 to 0.91‰ and in precipitates from −0.36 to 0.92‰; in soils values were between 0.26 and 1.72‰. Results in rocks indicate an igneous influence on copper provenance. The δ65Cu values in Py and Sph were within the range of terrestrial primary sulfides (from −1 to 1‰) confirming its igneous provenance. Processes related with fractionation of copper isotopes were oxidation of tailings and reprecipitation of 65Cu in tailings with a high content of Fe oxyhydroxides. Enrichment in 65Cu in precipitates and soils is favored by organic matter presence that retains 63Cu. Erosion of rocks and tailings is the main source of copper being rocks the initial and tailings the end members. The isotopic studies on environmental research provide a useful tool on: 1) The behavior of copper and sulfur isotopes in environments where both, natural and anthropogenic activities, are present. 2) Understanding surficial processes of dispersion of metals and identifying their source in mining areas surrounded by villages and agricultural soils.

Effects of alkali sulfates in clinker on hydration and hardening performance of Portland cement

In this study, two main alkali sulfates – aphthitalite and calcium langbeinite – fabricated in a laboratory are added to an industrial clinker with low alkali and sulfate content in order to adjust the contents of alkali sulfates in the clinker. Based on measuring the dissolution rate of the alkali sulfates and ion concentration in tricalcium aluminate (C3A)–alkali sulfate–water (H2O) systems compared with gypsum, and testing the heat flow, compressive strength, setting time and linear deformation of cement with different alkali sulfate contents, the differences between the alkali sulfates and gypsum are analysed. It is shown that aphthitalite could not act as a retarder, whereas calcium langbeinite can act to achieve almost the same retardation as gypsum. In view of the volume stability and strength development of cement, aphthitalite has a negative action when the equivalent sodium (Na2Oe) content induced is above 1·42%. The X-ray diffraction analysis patterns and scanning electron microscopy images show that aphthitalite restrains ettringite formation. It is suggested that more attention should be paid to the negative action of aphthitalite when alkali and sulfate contents in clinker appear to be high.

Effect of carrageenans alone and in combination with casein or lipopolysaccharide on human epithelial intestinal HT-29 cells.

The research described here was focused on the effect on human intestinal epithelial cell monolayers of sulfated red algal polysaccharides (κ-, λ-, and κ/β-carrageenans) alone and in combination with casein or lipopolysaccharide (LPS). HT-29 cells were investigated under normal and stress conditions; stress was induced by exposure to ethanol. Cell viability was monitored with a real-time system. The change in binding properties of negatively sulfated red algal polysaccharides assessed by the measurement of free carrageenans in mixtures with casein or McCoy's 5 A culture medium by means of toluidine blue O. Low sulfate content and the presence of 3,6-anhydogalactose are prerequisites for the recovery of ethanol-exposed HT-29 cells by carrageenans. Analysis of carrageenan binding ability confirmed that casein and LPS should affect carrageenan activity. Whether the combined action of the mucin-containing layer and carrageenans or the action of carrageenans alone was responsible for enhanced cell viability under stress conditions induced by ethanol is a subject for further research. © 2017 Wiley Periodicals Inc. J Biomed Mater Res Part A: 105A: 2843-2850, 2017.

Enhancement of extracellular polymeric substances (EPS) production in Spirulina (Arthrospira sp.) by two-step cultivation process and partial characterization of their polysaccharidic moiety

The interactive effects of light intensity and NaCl concentration were investigated for Spirulina two-step cultivation process using Full Factorial Design. In the experiment interval, light intensity had no effect while the NaCl concentration had significant effect on the enhancement of extracellular polymeric substances (EPS) production. Interestingly, results revealed a significant negative interaction between light and NaCl concentration indicating that high NaCl concentration (40gL−1) and low light intensity (10μmol photons m−2s−1) enhanced the EPS production. Under these conditions, EPS production reached a maximum of 1.02gg−1 of biomass (dry weight), which is 1.67-folds greater than EPS content under optimal growth conditions (10μmol photons m−2s−1, 1gL−1, 30°C). Desalting and deproteinezation steps of EPS were efficient to obtain polysaccharides (PS) with high carbohydrate (67.3±1.1%), low soluble proteins (5.14±0.32%), ash (5.85±0.71%) and sulfate (2.42±0.12%) contents. Rheological studies of PS at different concentrations (1%, 2.5% and 5%) revealed that the viscosity of the solution increased with the increase of PS concentration. In addition, PS exhibited a non Newtonian shear-thinning nature, a predominant gel-like behavior and a good resistance to consecutive heating-cooling cycles. The adopted process could be, then, a promising and economic strategy to enhance EPS production and extract polysaccharides with interesting rheological properties.

Twin‐screw reactive extrusion for phosphorylation of pea starch with a retained granular identity

The present work examines the ability to reactively modify a pea starch by phosphorylation in a twin‐screw extruder without the loss of its granular form, in order to produce a product for functional food uses. This reaction was studied by varying formulation variables of moisture content as well as reactant and sodium sulfate concentration at 95°C and 150 rpm. The modified starch was characterized for its phosphorus content, in vitro digestibility by the Englyst method, thermal gelatinization properties, and pasting behavior. Phosphorus contents of intact starch granules as high as 0.3% were found (close to the 0.4% limit for foods), produced continuously under extrusion conditions corresponding to a residence time of approximately one minute. Higher moisture content and low sodium sulfate concentration favored higher phosphorus content but increased the chances of amylose leaching and agglomerating of the exiting granules. In all cases, the pea starch experienced some change in its gelatinization transition consistent with simultaneous heat‐moisture treatment occurring along with the reaction inside the extruder. The current configuration of the process was not found suitable to major increases in resistant starch content though minor improvements in slowly digestible starch content were reported.

Effect of ferric sulfate on activity of moderately thermophilic acidophilic iron-oxidizing microorganisms

The effect of high ferric sulfate concentrations on the organisms predominating in biohydrometallurgical processes (bacteria of genus Sulfobaсillus and archaea of the genus Acidiplasma) was studied. Ability of the studied strains to grow and oxidize ferrous iron in the media with 125 to 500 mM ferric sulfate was determined. High concentrations of ferric sulfate significantly inhibited the oxidative activity and growth of the studied microorganisms. Bacteria of the genus Sulfobaсillus were found to be incapable of active iron oxidation in the presence of ferric iron sulfate at concentrations exceeding 250 mM. Archaea of the genus Acidiplasma oxidized ferrous iron completely in the presence of 500 mM Fe3+. Microbial growth was suppressed by relatively low ferric sulfate concentrations. Almost no growth occurred at ferric sulfate concentrations exceeding 199 mM, while lysis of the cells of all studied strains was observed at higher Fe3+ concentrations. Archaea (genus Acidiplasma, family Ferroplasmaceae) were shown to be more tolerant to high ferric sulfate concentrations than bacteria of the genus Sulfobaсillus. The results obtained may be used for improvement of biohydrometallurgical technologies and are also important for the understanding of the patterns of formation of microbial communities carrying out the technological processes.