Higher Initial pH Values Research Articles

Machine learning-assisted optimization of food-grade spirulina cultivation in seawater-based media: From laboratory to large-scale production

The shortage of food and freshwater sources threatens human health and environmental sustainability. Spirulina grown in seawater-based media as a healthy food is promising and environmentally friendly. This study used three machine learning techniques to identify important cultivation parameters and their hidden interrelationships and optimize the biomass yield of Spirulina grown in seawater-based media. Through optimization of hyperparameters and features, eXtreme Gradient Boosting, along with the recursive feature elimination (RFE) model demonstrated optimal performance and identified 28 important features. Among them, illumination intensity and initial pH value were critical determinants of biomass, which impacted other features. Specifically, high initial pH values (>9.0) mainly increased biomass but also increased nutrient sedimentation and ammonia (NH3) losses. Both batch and continuous additions could decrease nutrient losses by increasing their availability in the seawater-based media. When illumination intensity exceeded 200 μmol photons/m2/s, it amplified the growth of Spirulina by mitigating the light attenuation caused by a high initial inoculum level and counteracted the negative effect of low temperature (<25 °C). In large-scale cultivation, production efficiency would be reduced if illumination was not maintained at a high level. High salinity and sodium bicarbonate (NaHCO3) addition promoted carbohydrate accumulation, but suitable dilution could keep the required protein content in Spirulina with relatively low media and production costs. These findings reveal the interactive influence of cultivation parameters on biomass yield and help us determine the optimal cultivation conditions for large-scale cultivation of Spirulina-based seawater system based on a developed graphical user interface website.

Multi-antibiotics removal under UV-A light using sol-gel prepared TiO2: Central composite design, effect of persulfate addition and degradation pathway study

The removal of three antibiotics i.e., metronidazole (MNZ), ciprofloxacin (CIP) and tetracycline (TET), from aqueous system via TiO2 photocatalysis under UV-A light was investigated. Photocatalyst(s) were prepared using sol-gel method under different calcination temperatures (400–800 °C) and water-alcohol ratio. The spherical shaped catalyst (mean particle size ∼ 61 nm) was characterized via FTIR, XRD, BET, SEM, Raman, XPS, UV-DRS, and Fluorometry, and point of zero charge was also determined (pHPZC ∼ 6.6). Batch photo-catalytic degradation studies have shown complete degradation of MNZ, CIP and TET after 50, 75 and 20 min with a TOC removal of 37%, 44% and 31%, respectively. The activity of sol-gel prepared TiO2 was comparatively higher than commercially available pure anatase TiO2 nanoparticles due to lesser mean particle size. The ratio of water to alcohol in the preparation of TiO2 catalyst was found to have significant effect on antibiotic removal. Moreover, persulfate (PS) addition of 0.1 g/L amplified the pseudo-first-order removal-rate constant by 2.75, 3.3 and 1.6 times for MNZ, CIP and TET, respectively. The higher initial pH values (8 and 10) have shown the best removal efficiency for all antibiotics. Subsequently, central composite design (CCD) experiments were conducted under multi-antibiotic conditions. Near complete removal of all antibiotics were observed within 120 min. Scavenging studies revealed that hydroxyl and superoxide radicals play major roles in photo-catalytic degradation of MNZ, CIP and TET. During photocatalysis, MNZ degradation was initiated by hydroxylation reaction, CIP by piperazine ring opening by hydroxyl attack and TET by multiple hydroxylation process. Overall, TiO2 showed good efficiency at degrading multiple antibiotics and has the potential for practical application on a larger scale.

Potential Use of Agricultural Waste—Carob Kibbles (Ceratonia siliqua L.) as a Biosorbent for Removing Boron from Wastewater

The release of boron (B) into the environment as a result of anthropogenic activity modifies sustainable natural conditions, thus affecting ecosystems. To meet water quality regulations, commercial and natural boron adsorbents are available to reduce its concentrations in industrial effluents, with the former being not only more expensive but also less sustainable. In the publication, the biosorption parameters of carob kibbles (Ceratonia siliqua L.) were optimized in order to remove boron from aqueous solutions using batch experiments. The biosorbent used in the present research was agro-waste biomass provided by the local locust-beam gum industry. Boron removal by carob kibbles was favored at high initial pH values, and this capacity was found to be a function of boron initial concentration, biosorbent content in the solution, and particle size. The change in temperature did not affect the potential of biomass to remove boron. The highest boron removal efficiency (55.1%) was achieved under the following optimal conditions: 50 g/L biosorbent dose (Cs), with particle size range 0.025–0.106 mm, for the initial concentration (C0) of boron in the solution of 100 mg/L, at an initial pH of 11.5, for 5 h at 25 °C. This investigation suggests that carob kibble agro-waste can be valorized as a biosorbent to remove boron from wastewater, and the boron-loaded residue may eventually be explored as a new boron-fertilizer.

Treatment of catalyst wastewater through an environmentally friendly electrodeposition-precipitation-electrooxidation coupling process: Recovery of copper and silicate, and removal of COD

An environmentally friendly coupling process of electrodeposition—chemical precipitation—electrooxidation was explored to recover copper and silicate, and remove COD, showing a promising effect in treating catalyst wastewater. The feasibility and the key influencing factors of the process were investigated. The results showed that more than 99.8% of copper and 89.7% of silicate were recovered through the electrodeposition process and precipitation process, and 96.4% of COD was removed in the electrooxidation process. The purification of recovered copper was higher than 99.12% and the residual COD was lower than 500 mg/L. A higher initial pH value (>12.9) or the addition of a certain amount of NaCl is essential in avoiding the fouling of the anode in the electrodeposition process. In the chemical precipitation process, CaCl2 was selected as the precipitator, and the dosage of Ca: Si molar ratios of 1:1 was feasible for silicate removal. After processing, the content of copper and COD met the discharge standard.

Metabolic activity of Hordeum vulgare, Brassica napus and Vicia faba in Worm and Root type Biopore Sheaths

AimsBiopores offer favorable chemical, biological and physical properties for root growth in untilled soil layers. There they are considered as nutrient “hotspots” with preferential root growth. However, the literature lacks a quantification of metabolic activity due to nutrient acquisition of main crops while growing in the biopore sheath.MethodsA pot experiment was performed to map the metabolic activity of roots, as indicated by pH change. The roots of spring barley (Hordeum vulgare L.), spring oilseed rape (Brassica napus L.) and faba bean (Vicia faba L.) were growing through the biopore sheath influenced by an earthworm (Lumbricus terrestris L.) or a taproot (Cichorium intybus L.), in comparison to subsoil without a pore (bulk soil). pH sensitive planar optodes were applied in order to image a planar section of the sheath, while preserving an intact biopore sheath during the experiment.Results Roots were first found in the field of view in worm biopore then root biopore and bulk soil. At time of the first measurement the pH value was highest in worm biopore sheath (LS-Mean±SEM: 7.16a±0.11), followed by root biopore sheath (6.99ab±0.12) and bulk soil (6.61b±0.12). In spring oilseed rape a significant alkalization (+0.80 Δ pH) was found over time in bulk soil. Faba bean significantly acidified the root biopore sheath (-0.73 Δ pH). Spring barley showed no significant pH changes.ConclusionsThe results of the current study reveal a trend of faster root growth through biopores and a higher initial pH value in the biopore sheaths compared to the bulk soil. Biopores serve not only as an elongation path for roots, but their sheaths also provide an environment for root activity in the subsoil.

Plant growth promoting endophytic Pseudomonas aeruginosa RD10 isolated from water hyacinth for phenol degradation

A total of twelve endophytic bacteria were isolated from the root of E. crassipes. All these bacterial strains were analyzed for phenol degradation potential. Twelve endophytic bacteria were subjected to polyphenol resistance analysis and all showed phenol tolerance up to 300 ppm. Among the twelve bacterial strains, the strain RD10 was resistant up to 800 ppm, and reduced growth were observed at higher concentrations. The plant growth-promoting properties of endophytic bacterial strains were analyzed. Among the isolated bacterial strain, only five strains produced ACC deaminase. IAA production was detected in seven bacterial isolates, while siderophore production was determined from only five bacterial strains. Among the isolated endophytes, the strain RD10 exhibited ACC deaminase, IAA, and siderophore activity in submerged fermentation. ACC deaminase production of 125.2 ± 4.8 m/ml was shown by strain RD10 and IAA production was 89.7 ± 5.1 μg/ml. Moreover, maximum siderophore production was observed (53.9 ± 4.9% siderophore units) in strain RD3. Catechol 2,3-dioxygenase activity of the bacterial strains was analyzed. Catechol 2,3 dioxygenase activity ranges from 0.03 ± 0.01 U/mg to 35.2 ± 1.1 U/mg. Phenol degradation by the isolated endophytes was studied and the initial phenol concentration was 500 ppm. The strain RD1 degraded 1.2 ± 0.2% phenol and more than 50% phenol degradation was observed in strains RD3, RD4, RD6, RD7, RD9, RD10, and RD11, respectively. The endophytic bacterial strain was Gram-negative, rodshaped and motile. It was non-spore-forming bacteria, capsulated and, showed a positive reaction to oxidase and catalase. In MacConkey agar medium, strain RD10 forms smooth and flat colonies, and the diameter of the colonies ranged from 2 to 3 mm. The colonies have an alligator skin-like appearance on top view and have regular margins. The strain RD10 was streaked on blood agar medium and the strain RD10 produced strong pigmentation on blood agar. Antibiotic sensitivity of strain RD10 against various antibiotics in terms of zone of inhibition was analyzed. The endophytic strain RD10 was sensitive to all selected antibiotics. Based on biochemical characters, pigment analysis and, molecular characterization, the strain was confirmed as P. aeruginosa RD10. In this study, P. aeruginosa RD10 was cultured at 400, 500 and, 600 mg/l phenol concentration for 96 h. Optimum growth was achieved at 500 mg/l concentration and an inhibitory effect was observed at 600 mg/l phenol concentration. The results confirmed that the selected strain can withstand and grow well at 500 mg/l phenol concentration. The strain RD10 was cultured at various incubation temperatures with 500 mg/l phenol concentration. Optimization of environmental factors can lead to maximum degradation of phenol. The results revealed that phenol degradation was influenced by temperature. The highest phenol degradation was achieved at 30 °C in Erlenmeyer flask culture and decreased at high temperatures. P. aeruginosa RD10 could degrade phenol at pH 5.5 (10.2 ± 0.5% removal), at pH 6.0, 15.4 ± 1.1% of the phenol was degraded after incubation for 72 h at 30 °C. Phenol removal (%) declined to 70.4 ± 2.9% at higher initial pH value (9.0).

Degradation of ranitidine and changes in N-nitrosodimethylamine formation potential by advanced oxidation processes: Role of oxidant speciation and water matrix

This study investigated the effects of thirteen (photo/electro) chemical oxidation processes on the formation potential (FP) of N-nitrosodimethylamine (NDMA) during the chloramination of ranitidine in reverse osmosis (RO) permeate and brine. The NDMA-FP varied significantly depending on the pretreatment process, initial pH, and water matrix types. At higher initial pH values (> 7.0), most pretreatments did not reduce the NDMA-FP, presumably because few radical species and more chloramine-reactive byproducts were generated. At pH < 7.0, however, electrochemical oxidation assisted by chloride and Fe2+/H2O2, catalytic wet peroxide oxidation and peroxydisulfate-induced pretreatments removed up to 85% of NDMA-FP in the RO brine. Ultraviolet (UV) irradiation or prechlorination alone did not reduce the NDMA-FP effectively, but combined UV/chlorine treatment effectively reduced the NDMA-FP. In contrast, after UV irradiation (2.1 mW cm−2 for 0.5 h) in the presence of H2O2 and chloramine, NDMA formation increased substantially (up to 26%) during the post-chloramination of the RO permeate. Mass spectrometric analysis and structural elucidation of the oxidation byproducts indicated that compared with the reactive nitrogen species generated by UV/NH2Cl, sulfate radicals and (photo/electro)chemically generated reactive chlorine species were more promising for minimizing NDMA-FP. Unlike, the hemolytic •OH driven by UV/H2O2, the •OH from Fe(IV)-assisted pretreatments showed a significant synergistic effect on NDMA-FP reduction. Overall, the results suggest the need for a careful assessment of the type of radical species to be used for treating an RO water system containing amine-functionalized compounds.

Accumulation of Ectoines By Halophilic Bacteria Isolated from Fermented Shrimp Paste: An Adaptation Mechanism to Salinity, Temperature, and pH Stress.

Shrimp paste is a traditional fermented food produced by many Asian countries. Bacteria play important roles in the shrimp paste fermentation process. In order to survive under the low water activity (Aw) conditions caused by the high salt concentration, the bacteria need to employ a special adaptation strategy. This study found that most halophilic bacteria isolated from shrimp paste accumulated ectoines (ectoine and hydroxyectoine) as protective osmotic agents. Five isolated bacteria, including three high ectoine producers and two high hydroxyectoine producers, were selected for further study. Based on their morphological and biochemical characteristics and 16S rRNA gene sequences, the five strains were classified into three genera: Salinivibrio (strains M7 and M316), Salimicrobium (strains M31 and M69), and Vibrio (strain M92). The accumulation of ectoines by Salimicrobium species is reported here for the first time. The effects of salinity, incubation temperature, and initial pH on the growth rate and accumulation of ectoines by the five strains were investigated. The results revealed that the bacterial growth rate was inhibited while the accumulation of ectoines by the five selected strains was triggered by an increase in the external salinity, incubation temperature, or initial pH. In addition, a high concentration of ectoine only (21.2 wt%) was produced by strain M316 at the optimum salinity and temperature, and under pressure of a high initial pH value. To the best of our knowledge, this is the first report demonstrating that the production of ectoines by bacterial strains can be enhanced by increasing the pH of the culture medium to induce pH stress. This finding suggests a new ectoine producer and fermentation strategy that may help to improve the production of ectoines in the future.

Hygrothermal performance of six insulation systems for internal retrofitting solid masonry walls

The study investigated the hygrothermal performance and risk of fungal growth in a phenolic foam system with a closed cell structure and a diffusion-open and capillary active lime-cork based insulating plaster, for internal retrofitting purposes. The setup comprised two 40-feet (12.2 m) insulated reefer container with controlled indoor climate, reconfigured with 24 holes (1 × 2 m each) containing solid masonry walls with embedded wooden elements on the interior side. Focus was on the conditions in the masonry/insulation interface and embedded wooden elements, and the performance of the two systems were compared to three diffusion-open insulation systems and one diffusion-tight. The effect of exterior hydrophobisation was also investigated. Relative humidity and temperature were measured in several locations in the test walls over 2½ years, and the risk of fungal growth was evaluated by on-site measurements and the VTT mould-growth model. The findings indicate that internally insulated walls with bare brick exterior surfaces performed poorly with high risk of fungal growth. The effect of exterior hydrophobisation was found to vary with the orientation and the installed insulation system, with a generally positive effect on walls facing south-west but limited effect for north-east. Furthermore, the more diffusion-tight insulation systems were found to perform better in combination with exterior hydrophobisation than the highly diffusion-open systems. The lime-cork insulating plaster showed high relative humidity and risk of moisture-induced problems. The on-site fungal tests showed no growth in the masonry/insulation interface inside the two insulation systems, probably due to high initial pH-value.

Utilization of Carbide Slag by Wet Grinding as an Accelerator in Calcium Sulfoaluminate Cement.

In this study, wet-ground carbide slag (i.e., WGCS) was utilized as an accelerator in calcium sulfoaluminate cement (CSA) for obtaining considerably faster setting processes for some special engineering processes such as plugging projects and rapid repair engineering. The WGCS–CSA system was designed, in which the replacement ratio of CSA by carbide slag was chosen as 4%, 8% and 12%. The setting time and compressive strength were measured, and the mechanism of the system hydration was studied in detail by means of calorimetry, XRD, thermogravimetry (TG) and SEM. The results showed that WGCS shortened the setting time of cement and significantly augmented the early strength. The addition of 8% of WGCS contributed to increasing the 2-h compressive strength from 4.2 MPa to 32.9 MPa. The decrease in the setting time and the increase in the initial strength were mainly attributed to the high initial pH value of the liquid phase and the high content of calcium ions in WGCS. Both these factors contributed to the ettringite formation and, at the same time, to the transformation of the morphology at a later time. Such results testify that WGCS can be used as an accelerator in the CSA system and also that it provides a novel approach to the reutilization of carbide slag.

Influence of initial pH on the production of volatile fatty acids and hydrogen during dark fermentation of kitchen waste

ABSTRACT The purpose of this work was to determine the effect of initial pH on the production of volatile fatty acids (VFA) and hydrogen (H2) in the dark fermentation processes of kitchen waste. The study was conducted in batch bioreactors of working volume 1 L for different initial pH in the range from 5.5 to 9.0. The dark fermentation processes were carried out for 4 days at 37°C. Initial organic load of the kitchen waste in all bioreactors amounted to 25.5 gVS/L. Buffering of pH during the fermentation process was carried out with the use of ammonia contained mainly in digested sludge. The optimal conditions for the production of VFA and H2 were achieved at the initial pH of 8. Production of VFA and H2 in these conditions was, respectively, 13.9 g/L and 72.4 mL/gVS. The main produced components of VFA were acetic and butyric acids. The production of ethanol and lactic acid was at very low levels due to the high ratio of the volatile fatty acids to total organic content of 0.86. With the optimal initial pH of 8 the yield of CO2 production was 0.30 gC/gC. High initial pH value (above 8) extended the lag phase duration in the course of H2 production. The dominant groups of micro-organisms at the most favourable initial pH of 8 for the production of VFA and H2 were Bacteroidetes, Firmicutes, Spirochaetes and Waste Water of Evry 1 (WWE1) at the phylum level.

Degradation of sulfamethoxazole by heat-activated persulfate oxidation: Elucidation of the degradation mechanism and influence of process parameters

In this article, heat-activated persulfate oxidation was investigated as a promising technique for the removal of sulfamethoxazole from an aqueous environment. It was found that the degradation efficiency of sulfamethoxazole increases with increasing persulfate concentration due to the increased SO4− production. As suggested by the Arrhenius equation, the sulfamethoxazole degradation rate constant increased with increasing temperature. An activation energy of 103 kJ/mol was determined. Furthermore, the initial pH of the reaction mixture had a large influence on the degradation of sulfamethoxazole. At higher initial pH values, the degradation of sulfamethoxazole increased. The main cause for this increase is a difference in sulfamethoxazole distribution: at higher pH, the deprotonated form of sulfamethoxazole is present and found to be more susceptible to degradation. A second reason was found to be the formation of OH at higher initial pH values, although this contribution was smaller. To elucidate the degradation process, six intermediates were identified, and the difference in formation of these compounds at different initial pH values was revealed. Through ECOSAR modeling, some degradation products were found to be of main interest when monitoring the toxicity of the degradation mixture.

Adsorption of U(VI) from eutrophic aquesous solutions in a U(VI)-P-CO3 system with hydrous titanium dioxide supported by polyacrylonitrile fiber

Hydrous titanium dioxide supported by commercially available polyacrylonitrile fiber (c-PANF/TiO2·xH2O) was synthesized via a simple blending method to first investigate its U(VI) adsorption behavior from eutrophic aqueous solution in a U(VI)-P-CO3 system. TG-DSC and XRD analysis demonstrated that the material had good structural stability during the adsorption process. The theoretical maximum U(VI) adsorption capacity (qe) of c-PANF/TiO2·xH2O calculated from the Langmuir isotherm was ~256 mg/g. However, high initial solution pH values, total dissolved carbonate concentration and ionic strength could inhibit U(VI) chemisorption. In particular, qe and sorption efficiency (S%) values were maintained at ~100 mg/g and > 80% for the [P] range of 0 to 150 μmol/L, and then they rapidly decreased once [P] exceeded 150 μmol/L due to the competitive adsorption between HPO42-/H2PO4- and uranium anionic complexes such as UO2(CO3)34−, UO2(CO3)22− and UO2PO4-. XPS analysis suggested that Ti3+ defects and OH groups on the composite surface could be the U(VI) adsorption sites. Moreover, a 0.1 mol/L H2SO4 solution was found to be the most effective desorption agent. The findings reported in this study are significant in regards to the extraction of uranium from eutrophic seawater and for the understanding of uranium adsorption behaviors in multi-carbonate systems.

In situ and short-time anaerobic digestion coupled with alkalization and mechanical stirring to enhance sludge disintegration for phosphate recovery

In situ and short-time anaerobic digestion coupled with alkalization and mechanical stirring was studied to enhance sludge (especially high-inorganic sludge) disintegration for phosphate recovery. Anaerobic digestion batch experiments with varying conditions were carried out. It was observed that high initial pH values (e.g. 9, 10, 12 and 13) in conjunction with mechanical stirring resulted in effective sludge disintegration. Results showed that mechanical stirring mainly worked as the role of uniform mixing for better material exchange and bacteria contact, but without the function of vortex shear force for cell wall breaking. Bacterial effects contributed less and less to phosphate recovery from sludge as alkalization increased, indicating that chemical effects have a more significant role during operation. Meanwhile, almost all insoluble non-apatite inorganic phosphorus was dissolved back into the supernatant with alkalization and mechanical stirring. Therefore, compared with other sludge disintegration methods, in situ and short-time anaerobic digestion coupled with alkalization and mechanical stirring is economical and practical, requiring only 7 days for sludge disintegration, especially with optimum alkalinity (pH 9 & 10).

Influence of initial anolyte pH and temperature on hydrogen production through simultaneous saccharification and fermentation of lignocellulose in microbial electrolysis cell

An investigation on the performance of hydrogen production by simultaneous saccharification and fermentation (SSF) in a dual-chamber microbial electrolysis cell (MEC) was carried out to consider different anolyte pH levels and culture temperatures, and the influences of anolyte pH value and culture temperature on changes of current, organic acid and pH value were also evaluated. The maximal hydrogen production rate (HPR) of 2.46 mmol/L/D (hydrogen energy recovery 219.02%) was obtained at the initial anolyte pH of 6.5. Within the range of the tested operation temperatures (30–50 °C), the optimal temperature for hydrogen production by SSF in the MEC systems was 35 °C. Moreover, the contents of organic acids and reducing sugar significantly changed with varying in initial anolyte pH and temperature levels. The result indicates that a low initial anolyte pH value and high culture temperature was beneficial to hydrolysis of cellulose, and a high initial anolyte pH value and a moderate culture temperature to hydrogen production.

Effects of pH and substrate concentrations on dark fermentative biohydrogen production from xylose by extreme thermophilic mixed culture.

Biohydrogen is considered as one of the most promising energy alternatives considering the climate and energy crisis. The dark fermentative hydrogen production from xylose at extreme thermophilic condition (70°C) using mixed culture was conducted in this study. The effects of initial pH values (ranged from 5.0 to 10.0) and substrate concentrations (ranged from 2.5 to 15.0g/L) on the hydrogen production, substrate degradation and metabolite distributions were investigated using batch-mode operations. Results showed that initial substrate pH values in the neutral region (6.0-7.0) were beneficial for hydrogen production. The fermentation at initial pH 7.0 and 7.5g/L xylose reached an optimal hydrogen yield of 1.29mol-H2/mol-xyloseconsumed. Ethanol, butyrate, and propionate were the major liquid metabolites. The xylose biodegradation efficiency of the mixed culture decreased sharply at high initial culture pH values. The increase of xylose concentration resulted in the accumulation of propionate and an obvious decrease in the final pH value, as well as a low hydrogen yield. Polymerase chain reaction-denaturing gradient gel electrophoresis analysis indicated that hydrogen producing bacteria were enriched by repeated culture under extreme thermophilic conditions. Also, the mixed culture was dominated with bacterial species related to Clostridium and Thermoanaerobacterium.

Changes in heavy metal extractability from contaminated soils remediated with organic waste or biochar

The effect of the addition of organic waste or biochar on the extractability of heavy metals (Cd, Cu, Ni, Pb and Zn) was assessed in five heavy metal-contaminated soils. The amendments studied were: municipal organic waste compost (MOW), green waste (GW), biochar derived from tree bark (BF) and biochar derived from vine shoots (BS). The amendments were added to the soil at 10% dose. A pHstat leaching test was applied to the soils and soil+amendment mixtures to assess the effects of the amendments on the extractable metal concentration at the initial pH and in the 2–12pH range. MOW increased the DOC content in the mixtures for most soils, whereas the rest of amendments only increased the DOC content for the soil with the lowest DOC value. Moreover, in the mixtures obtained from soils with a low buffering capacity, the amendments increased pH (up to 3units) and the acid neutralization capacity, thus decreasing the extractability of heavy metals at the initial pH of the mixtures. In a few cases, the amendments further decreased the concentrations of extractable metal due to an increase in the sorption capacity of the mixture, even though the soil had high initial pH and ANC values. MOW and GW generally led to larger decreases in metal extractability in the resulting mixtures than biochar, due to their higher sorption and acid neutralization capacities.

Characteristics of pyridine biodegradation by a novel bacterial strain, Rhizobium sp. NJUST18

Pyridine is one of the most widespread heterocyclic industrial contaminants. Due to rather tough safe level, thorough purification of wastewater containing this eco-toxicant is required. In this study, a novel pyridine-degrading bacterium, strain NJUST18, was isolated from the soil contaminated by pyridine and identified as a member of genus Rhizobium. The biodegradation assays suggested that strain NJUST18 could utilize pyridine as the sole source of carbon and nitrogen, at initial concentration as high as 2600 mg l−1. Pyridine depletion, biomass increase, TOC reduction, pH increase, and NH4+ release during pyridine biodegradation indicated that pyridine could be mineralized by strain NJUST18. Pyridine degradation at high initial concentrations or high initial pH values demonstrated that this biodegradation process was both pH and NH4+ dependent. Release of NH4+ into the alkaline medium led to the formation of free ammonia (NH3) accompanied by the delayed pyridine degradation. High concentration of NH3 generated weakened pyridine biodegradation. A neutral to slightly alkaline pH was crucial for high strength pyridine degradation by NJUST18. Rhizobium sp. NJUST18 could degrade relatively high concentration of pyridine, offering bright prospects for bioremediation of pyridine contaminated environment.

Effects of process parameters on the physical properties of poly (urea–formaldehyde) microcapsules prepared by a one-step method

The physical properties of microcapsules are strongly influenced by the synthetic conditions used for their preparation. To prepare microcapsules possessing a smooth surface morphology, high mechanical strength, and reduced permeability of the core material, in situ polymerization in an oil-in-water emulsion was performed using poly (urea–formaldehyde) and tetrachloroethylene as the shell and core materials, respectively. The influence of the synthetic conditions, including the initial pH value, concentration of wall material, concentration of NaCl, and heating rate, on the properties of the resulting microcapsules was investigated systematically by an orthogonal factorial design. The physical properties of the microcapsules were characterized using scanning electron microscopy and optical-photographic microscopy. The results showed that the concentration of shell material has a substantial effect on the mechanical strength of the microcapsules. Additionally, a slow heating rate and high initial pH value enhance the preparation of well-defined spherical microcapsules having excellent barrier properties. Finally, a moderate concentration of sodium chloride can remarkably improve the compactness of the capsule wall. The optimum conditions, determined on the basis of utilization of wall material, are as follows: initial pH value: 3.5; concentration of shell material: 3.6 × 10−2 g/mL; heating rate: 0.5 °C/min; and concentration of sodium chloride: 5.0 × 10−2 g/mL.

Numerical prediction of CO2 capture process by a single droplet in alkaline spray

Carbon dioxide captured by single droplets in sprays plays a fundamental role in reducing greenhouse gas emissions. This study focuses on CO2 capture processes in single droplets in alkaline sprays using a numerical method. Three different initial pH values of 10, 11, and 12 in the droplet are considered. The capture behavior in the absence of chemical dissociation is also investigated for comparison. The predictions suggest that the chemical dissociation in the droplet substantially elongates the CO2 capture process and the mass diffusion is the controlling mechanism of CO2 capture process. For the chemical absorption, the final CO2 capture amount by the droplet is mainly determined by HCO3- which is significantly influenced by the initial pH value. An increase in initial pH value raises the carbon capture amount by the droplet. The mean concentration of CO32- is highly related to the variation of mean pH value, but its concentration is by far lower than those of H2O⋅CO2 and HCO3-. Corresponding to the initial pH values of 10, 11, and 12, the times required for turning the basic droplet to the acidic one are in the orders of 10, 100, and 1000ms. On account of larger carbon capture amount and shorter absorption period at a higher initial pH value, the carbon capture rate is lifted as the initial pH value rises, and CO2 capture by droplets at the initial pH value of 12 is better than those at 10 and 11.