Higher Initial pH Research Articles

Role of RIM101 for Sporulation at Alkaline pH in Ashbya gossypii.

Microorganisms need to sense and adapt to fluctuations in the environmental pH. In fungal species, this response is mediated by the conserved pacC/RIM101 pathway. In Aspergillus nidulans, PacC activates alkaline-expressed genes and represses acid-controlled genes in response to alkaline pH and has important functions in regulating growth and conidia formation. In Saccharomyces cerevisiae, the PacC homolog Rim101 is required for adaptation to extracellular pH and to regulate transcription of IME1, the Initiator of MEiosis. S. cerevisiae rim101 mutants are defective in sporulation. In Ashbya gossypii, a filamentous fungus belonging to the family of Saccharomycetaceae, little is known about the role of pH in regulating growth and sporulation. Here, we deleted the AgRIM101 homolog (AFR190C). Our analyses show that Rim101 is important for growth and essential for sporulation at alkaline pH in A. gossypii. Acidic liquid sporulation media were alkalinized by sporulating strains, while the high pH of alkaline media (starting pH = 8.6) was reduced to a pH ~ 7.5 by these strains. However, Agrim101 mutants were unable to sporulate in alkaline media and failed to reduce the initial high pH, while they were capable of sporulation in acidic liquid media in which they increased the pH like the wild type.

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.

Ammonia recovery from simulated anaerobic digestate using a two-stage direct contact membrane distillation process.

Ammonia is a key inorganic contaminant in wastewater and an important nutrient element for agriculture. Herein, a two-stage direct contact membrane distillation (DCMD) system was developed and investigated for ammonia recovery from a synthetic anaerobic digestate. In the 1st stage DCMD (DCMD-1), both ammonia and water moved across MD membrane to realize ammonia separation, while in the 2nd stage (DCMD-2), only water migrated and as a result ammonia was concentrated. It was found that increasing the initial feed solution pH could enhance ammonia removal in the DCMD-1 from 16.0±2.0% (no pH adjustment) to 84.2±1.9% (pH 12). A higher feed solution temperature increased both ammonia flux and water flux. The optimal condition was determined as an initial feed pH of 12, a feed temperature of 60°C, and the 0.6M H2 SO4 adsorption solution. With the addition of the DCMD-2, the ammonia concentration was improved from 3gL-1 to 7.8±0.2gL-1 , which was further enhanced to 26.3±3.0gL-1 after five batches of operation. These results have demonstrated the feasibility of a two-stage DCMD system for ammonia recovery from anaerobic digestate and warrant further investigation of several key issues that may advance this technology. PRACTITIONER POINTS: A two-stage membrane distillation system is developed to remove and recover ammonia from anaerobic digester effluents. The system uses ammonia/ammonium equilibrium to separate ammonia in the 1st stage and then concentrate it in the 2nd stage. A high initial pH of the feed solution plays a key role in achieving high ammonia removal. Minimizing the volume of permeate solution can increase the ammonia concentration.

Ca(OH)2 induced a controlled-release catalytic system for the efficient conversion of high-concentration glucose to lactic acid

The catalytic conversion of carbohydrate to platform chemicals, e.g. lactic acid (LA), is the key to unlock the potential of biomass. In this study, we report that the combination of Ba(OH)2 and Ca(OH)2 can efficiently catalyse high-concentration (> 0.5 M) of glucose to relatively high yield of LA (> 40 %) under mild conditions (60 °C). Both glucose conversion and LA yield were sensitive to the pH of the catalytic system. A high loading of Ba(OH)2 led to a high initial pH of the reaction solution, resulting in serious side reactions. While, a low loading of Ba(OH)2 led to a quike decrease of OH− and Ba2+ both of which were continuously consumpted by the formed LA. The combination of Ca(OH)2 with Ba(OH)2 could significantly improve LA yield, since Ca(OH)2, with limited solubility, could act as a controlled-release catalyst for the real-time supply of OH− and Ca2+. OH− was indispensable for glucose isomerization to fructose as well as for fructose retro-aldol reaction to C3 intermediates. Ca2+ could combine with LA to form stable calcium lactate, liberating Ba2+ to catalyse the conversion of C3 intermediates to LA. Under the preliminary optimized reaction conditions, the yield of LA could be reached to 42.55 % and 38.32 % from 0.5 M and 1 M glucose, respectively. This catalytic system has advantages of mild reaction condition, short reaction time, and capable of conversion of high-concentration substrates, enabling it with a great potential for practical applications.

The association of pH values during the first 24 h with neurological status at hospital discharge and futility among patients with out-of-hospital cardiac arrest

Study objectivePost-resuscitation prognostic biomarkers for out-of-hospital cardiac arrest (OHCA) outcomes have not been fully elucidated. We examined the association of acid-base blood values (pH) with patient outcomes and calculated the pH test performance to predict prognosis. MethodsThis was a post-hoc analysis of data from the continuous chest compression trial, which enrolled non-traumatic adult emergency medical system-treated OHCA in Canada and the United States. We examined cases who survived a minimum of 24 h post hospital arrival. The independent variables of interest were initial pH, final pH, and the change in pH (δpH). The primary outcome was neurological status at hospital discharge, with favorable status defined as modified Rankin Scale (mRS) ≤ 3. We reported adjusted odds ratios for favorable neurological outcome using multivariable logistic regression models. We calculated the test performance of increasing pH thresholds in 0.1 increments to predict unfavorable neurological status (defined as mRS >3) at hospital discharge. ResultsWe included 4189 patients. 32% survived to hospital discharge with favorable neurological status. In the adjusted analysis, higher initial pH (OR 6.82; 95% CI 3.71–12.52) and higher final pH (OR 7.99; 95% CI 3.26−19.62) were associated with higher odds of favorable neurological status. pH thresholds with highest positive predictive values were initial pH < 6.8 (92.5%; 95% CI 86.2 %–98.8%) and final pH < 7.0 (100%; 95% CI 95.2 %–100%). ConclusionIn patients with OHCA, pH values were associated with patients’ subsequent neurological status at hospital discharge. Final pH may be clinically useful to predict unfavorable neurological status at hospital discharge.

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.

Hydrothermal carbon dioxide fixation in magnesium hydroxide and serpentine: Effects of temperature and pH

This study investigated hydrothermal fixation of CO2 in serpentine or magnesium hydroxide as one of the compounds containing Mg at an initial CO2 pressure of 7.1 MPa. The carbonation of magnesium hydroxide gave primarily magnesite and the yield increased with increasing initial pH and increasing temperature, reaching 97.9 % at 473 K. Carbonation of serpentine also gave magnesite, and the yield initially increased and then slightly decreased with increasing temperature. Both low and high initial pH enhanced serpentine carbonation at 573 K and the yield of magnesite reached 12.7 % at an initial pH of 1.0. Estimation of chemical species indicated that both the dissolution of serpentine via the action of H+ and the formation of magnesite from MgHCO3+ and Mg2+ via the release of H+ were important reactions. Hydrothermal serpentine carbonation is a promising CO2 fixation method for naturally abundant mineral rocks without expensive additives.

The pH of Cement-based Materials: A Review

Cement-based materials (CBMs), such as paste, mortar and concrete, are highly alkaline with an initial high pH of approximately 12.0 to 13.8. CBMs have a high pH due to the existing oxide mineral portlandite and alkali metal contents in Portland cement. The high pH of concrete provides excellent protection and reinforces the steel bars against corrosion. The pH of concrete does not remain constant due to ageing and other defect-causing factors, such as chloride ingress, alkali leaching, carbonation, corrosion, acid attack, moisture and biodegradation process. Reducing the concrete pH has negative impact on the strength, durability and service life of concrete buildings. However, the high pH of concrete may also cause concrete structure deterioration, such as alkali silica reaction, porosity and moisture related damages in concrete structures. The pH of CBMs can be influenced by high temperatures. For instance, the extremely high volume (85%–100%) of slag-blended cement pastes shows considerable pH reduction from 12.80 to 11.34 at 800 °C. As many concrete structure deterioration are related to concrete pH, using an accurate and reliable method to measure pH and analyse the durability of reinforced concrete structure based on pH values is extremely important. This study is a comprehensive review of the pH of CBM in terms of measurement, limitations and varying values for different CBM types.

Catalytic ozonation of refractory O-isopropyl-N-ethylthionocarbamate collector with coexisted kaolinite in sulfide flotation wastewaters

Clay minerals, acting as effective ozonation catalysts, are always coexisted with detrimental flotation reagents in sulfide flotation wastewaters. In this study, the catalytic ozonation of refractory O-isopropyl-N-ethylthionocarbamate (IPETC) collector was investigated with coexisted kaolinite (Kaol). The removal of IPETC, mineralization and the decrease of electrical energy consumption were enhanced by catalytic ozonation with Kaol relative to sole ozonation. The IPETC removal increased at higher initial pH and larger Kaol dosage, suggesting a beneficial role of coexisted Kaol in the IPETC removal in alkaline medium. The hydroxyl radicals (•OH) scavenging experiments confirmed •OHs as the main reactive species responsible for IPETC removal by catalytic ozonation. The Rct characterization revealed the yields of more •OH radicals at larger Kaol dosage. The presence of Kaol reduced equilibrium ozone concentrations in pure water, showing the positive roles of Kaol in the catalytic ozone decomposition and ozone mass transfer. The changes of byproducts adsorbed on Kaol indicated that surface oxidation reactions by active species might also contribute to IPETC removal and its mineralization. The mechanisms of IPETC removal were proposed by catalytic ozonation with Kaol.

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.

Removal of arsenic(III) from aqueous solution by concrete‐based adsorbents

The present paper investigates the adsorption of arsenic(III) (As(III)) onto 2 concrete‐based low‐cost materials, i.e., Aerocrete and Vermiculite impregnated by ferric oxyhydroxide. Adsorption experiments were performed to study the effect of initial pH, initial concentration of As(III), contact time, and ions usually present in water. No significant effect of the initial pH on the adsorption of As(III) by Aerocrete and Vermiculite was observed at the pH range of 4–8. The As(III) removal efficiency decreased at a high initial pH (i.e., 10). The Langmuir isotherm showed that the maximum As(III) adsorption capacity of Aerocrete and Vermiculite is 15.15 and 13.51 mg/g, respectively, which is higher than that observed using titanium dioxide (i.e., 3.52 mg/g), at pH 7 and 24 ±1 °C. A pseudo‐second order kinetic model fitted well the experimentally obtained kinetic data. This suggests that chemisorption most probably controls the adsorption of As(III) on Aeroctere and Vermiculite. Significantly, As(III) (1 mg/L) could be removed almost completely by both Aeroctere and Vermiculite (1 g/L) in 30 and 60 min, respectively at pH 7 and 24 ±1 °C. Importantly, Ca2+, Mg2+, Na+, HCO3−, SO42−, and Cl− ions had no significant effect on the adsorption of As(III) on Aeroctere and Vermiculite. The results showed that the proposed concrete‐based adsorbents have the potential to remove As(III) from water.

Adsorption of Cu(II) ion by a novel hordein electrospun nanofiber modified by β-cyclodextrin

In this study, hordein and hordein/N,N′-methylene bisacrylamide (MBA) nanofiber membranes were prepared by electrospinning technique. Then the fabricated membranes were modified with β-cyclodextrin (β-CD) to remove heavy metal ions from aqueous solution. The prepared nanofiber membranes were characterized by ATR-FTIR, SEM and XRD. The diameters of the nanofibers were determined to be around 600–910 nm and β-CD was successfully attached to the nanofiber membrane, which was confirmed by ATR-FTIR and XRD analysis. Cu(II) was selected as the model ion to investigate the heavy metal adsorption properties of the membranes. Adsorption capacities of the membranes increased with a higher initial pH, adsorption temperature and a longer adsorption time before reaching the saturation point. The adsorption isotherm results were described with the Langmuir model. It was found that additions of MBA and β-CD at proper concentrations could significantly improve the adsorption capacities and the maximum adsorption of hordein, hordein/MBA, and hordein/MBA/β-CD nanofiber membranes were 64.94, 81.97, and 88.50 mg/g, respectively. Furthermore, regeneration study showed that these hordein nanofiber membranes possessed reasonably good reusability. The novel functionalized hordein/MBA/β-CD nanofiber membranes have great potential in the application of water treatment.

Assessment of conservative dietary management as a method for normalization of 24-h urine pH in stone formers.

Low urine pH is a metabolic risk factor for stone formation. While medical therapy is typically prescribed (as urinary alkalinization), patients typically prefer dietary modifications. We aimed to assess capacity to alter urine pH with dietary management alone. We analyzed a retrospective cohort of stone formers seen between 2000 and 2015 with multiple 24-h urine collections (24hUC). Patients ≥ 18years old with low urine pH (< 6.0) were included; those prescribed alkalinizing agents or thiazides were excluded. Demographic data, 24hUC parameters, and medications were abstracted. 24hUC was utilized to calculate gastrointestinal alkali absorption (GIAA). The primary outcome was urine pH ≥ 6.0 on second 24hUC. Predictors were selected utilizing multivariable logistic regression. The database consisted of 2197 stone formers; 224 of these met inclusion criteria. On second 24hUC, 124 (55.4%) achieved a favorable pH ≥ 6.0. On univariable analysis, a second pH ≥ 6.0 was associated with high initial pH, low initial sulfate, younger age, increase in citrate/GIAA/urine volume, and decrease in ammonium (P < 0.02). On multivariable analysis, high initial pH (OR = 23.64, P < 0.001), high initial GIAA (OR = 1.03, P = 0.001), lower initial sulfate (OR = 0.95, P < 0.001), increase in urine volume (OR = 2.19, P = 0.001), increase in GIAA (OR = 8.6, P < 0.001), increase in citrate (OR = 2.7, P = 0.014), decrease in ammonium (OR = 0.18, P < 0.001), and younger age (OR = 0.97, P = 0.025) were associated with a second pH ≥ 6.0. The analysis demonstrated a corrected AUC of 0.853. These data suggest that certain dietary recommendations (increases in urine volume, citrate, GIAA, and decreased acid load) may normalize urine pH in a select group of patients. This may allow urologists to counsel patients with low urine pH on possibility of success with dietary modification alone.

Activation of persulfate by CoO nanoparticles loaded on 3D mesoporous carbon nitride (CoO@meso-CN) for the degradation of methylene blue (MB)

A simple and facile synthesis method is developed for the fabrication of CoO loaded ordered mesoporous carbon nitride (CoO@meso-CN) composites, at various CoO loadings, and used, for the first time, to activate persulfate (PS) for methylene blue (MB) degradation. The interfacial interaction between the ultrafine CoO nanoparticles, immobilized by high surface area, regular mesopores, and graphitic nature of the meso-CN support can further enhance the catalytic activation of PS for methylene blue (MB) degradation. Among all catalysts studied, the 5-wt% CoO@meso-CN exhibits the best catalytic performance with a kobs of 0.264 min−1. High initial pH, especially at pH-11, is more beneficial for PS activation. Furthermore, the CoO@meso-CN nanocatalyst is highly stable with a consistently high degree of MB degradation and negligible cobalt leaching for at least 5 consecutive catalytic cycles. Both SO4− and OH are the major reactive species based on results of EPR and quenching experiments. The degradation intermediates of MB are also identified by HPLC/MS/MS and the possible degradation pathway is proposed. Results clearly demonstrate that CoO@meso-CN is a promising green catalyst with enormous potential for the remediation of hazardous chemicals using PS.

Efficient degradation of carbamazepine by organo-montmorillonite supported nCoFe2O4-activated peroxymonosulfate process

Carbamazepine (CBZ) is one of most frequently detected pharmaceutical contaminants in water ecosystem, which cannot be removed efficiently by traditional techniques. Degradation of CBZ by peroxymonosulfate (PMS) activated with organo-montmorillonite supported nCoFe2O4 (nCoFe2O4/OMt) was investigated in this study. The degradation efficiency of CBZ (5 mg L−1) was 93% within 60 min in the presence of 0.4 g L−1 nCoFe2O4/OMt and 0.5 mM PMS at pH 6.8 and 25 °C, following a pseudo-first order kinetics. High PMS concentration and low initial pH could enhance CBZ degradation. The presence of Cl−, NO3− and HCO3− showed marked enhancement, slight suppression and obvious inhibition of CBZ degradation, respectively. High concentration of humic acid could decrease the CBZ degradation. X-ray photoelectron spectroscopy of nCoFe2O4/OMt before and after reaction revealed that both Co2+/Co3+ and Fe2+/Fe3+ were involved in PMS activation during the CBZ degradation. Electron paramagnetic resonance and radical scavenger experiments confirmed that both OH and SO4− played a predominant role on the CBZ degradation. The degradation products were identified by LC–MS/MS to understand the possible pathways.

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.

Determination of Critical Soil Silicon Levels for Rice Production in Louisiana Using Different Extraction Procedures

ABSTRACTWhile silicon (Si) fertilization is widely practiced in rice production, establishing critical soil Si levels has remained understudied. Field trials were established at 12 sites across Louisiana from 2013 to 2015 to determine critical soil Si for rice cultivation. Five silica slag (14% Si) rates at 0, 1, 2, 4, 6, and 8 Mg ha−1 and two lime rates (2 and 4 Mg ha−1) were arranged in randomized complete block design with four replications. Post harvest soil samples were analyzed for Si using seven extraction procedures. The critical soil Si levels established by the linear plateau model using 0.5 M acetic acid-1 hr (OAc-1) extraction procedure were 36, 41 and 50 mg kg−1 for plant Si uptake, grain yield, and relative yield as response variables, respectively. Generally, soils having high initial Si and pH had minimal responses to Si fertilization, whereas Si content of soils with low initial Si was significantly increased.

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).

Effective degradation of primary color direct azo dyes using Fe0 aggregates-activated persulfate process

The present study examined the oxidation power of a Fe0 aggregates/persulfate (PS/Fe0) system for the degradation of the wastewater containing mixed primary direct dyes (i.e., Sirius® Gelb S-2G, Sirius® Red F3B, and Sirius® Turkis GL01). Results indicated that decolorization efficiency was determined by operating parameters of the PS/Fe0 system and the structural complexity of dye molecules. System efficiency increased with increasing persulfate and Fe0 dosages. Faster decolorization was observed in experiments conducted at pH < 10. The process obeyed a first-order kinetics. Slow heterogeneous reactions were observed at high initial pH (>10.5) and low PS concentration (<2 × 10−3 M). Inhibitory effect occurred in systems containing salts Na2SO4, NaCl, Na2CO3, and Na2HPO4 at 1 × 10−2 M. The effect was suppressed when reaction temperature was raised to 55 °C. Heat enhanced not only decolorization efficiency, but also COD removal. Complete decolorization of a mixed dye containing ADMI (the American Dye Manufacture Institute) 15105 was achieved within10 min in the PS/Fe0/55 °C system with an initial pH of 6.0 and dosages of 5 × 10−3 M Na2S2O8 and 0.5 g/L Fe0. Low molecular weight intermediates including organic acids were identified. Due to a relatively low activation energy (4.68 kcaL/mol), the PS/Fe0 system exhibited higher efficiency at higher temperature. This study demonstrated that Fe0-activated PS is a promising process for the treatment of textile wastewaters containing mixed azo direct dyes.

Electrochemical Induced Calcium Phosphate Precipitation: Importance of Local pH.

Phosphorus (P) is an essential nutrient for living organisms and cannot be replaced or substituted. In this paper, we present a simple yet efficient membrane free electrochemical system for P removal and recovery as calcium phosphate (CaP). This method relies on in situ formation of hydroxide ions by electro mediated water reduction at a titanium cathode surface. The in situ raised pH at the cathode provides a local environment where CaP will become highly supersaturated. Therefore, homogeneous and heterogeneous nucleation of CaP occurs near and at the cathode surface. Because of the local high pH, the P removal behavior is not sensitive to bulk solution pH and therefore, efficient P removal was observed in three studied bulk solutions with pH of 4.0 (56.1%), 8.2 (57.4%), and 10.0 (48.4%) after 24 h of reaction time. While P removal efficiencies are not generally affected by bulk solution pH, the chemical-physical properties of CaP solids collected on the cathode are still related to bulk solution pH, as confirmed by structure characterizations. High initial solution pH promotes the formation of more crystalline products with relatively high Ca/P molar ratio. The Ca/P molar ratio increases from 1.30 (pH 4.0) to 1.38 (pH 8.2) and further increases to 1.55 (pH 10.0). The formation of CaP precipitates was a typical crystallization process, with an amorphous phase formed at the initial stage which then transforms to the most stable crystal phase, hydroxyapatite, which is inferred from the increased Ca/P molar ratio from 1.38 (day 1) to the theoretical 1.76 (day 11) and by the formation of needle-like crystals. Finally, we demonstrated the efficiency of this system for real wastewater. This, together with the fact that the electrochemical method can work at low bulk pH, without dosing chemicals and a need for a separation process, highlights the potential application of the electrochemical method for P removal and recovery.