Decrease In Initial pH Research Articles

Removal of Reactive Black 5 by zero-valent iron modified with various surfactants

Zero-valent iron (ZVI) particles were synthesized by the aqueous phase borohydride reduction method, and the synthesized ZVI particles were used for the reductive degradation of Reactive Black 5 (RB5) dye in aqueous solution. The sizes of the synthesized ZVI particles were in the microscale range, with an average diameter of 13.57 μm. To study the efficiency of surfactant-treated ZVI particles for the decolorization of RB5 solution, three different surfactants, triton X-100 (TX100, non-ionic surfactant), cetyl trimethyl ammonium bromide (CTAB, cationic surfactant), and sodium dodecyl sulfate (SDS, anionic surfactant) were selected for the treatment of ZVI. The normalized residual concentration after decolorization of 500 mg/l RB5 by ZVI for 3 h was 0.236, while ZVI particles treated with TX100 (0.5 g/l), CTAB (1.0 g/l), and SDS (2.5 g/l) exhibited normalized residual concentration of 0.172, 0.154, and 0.393, respectively, after 3 h. The color removal efficiency was found to be increased with decrease in initial pH of dye solution, and ZVI exhibited good color removal efficiency at acidic pH. Decolorization kinetics by pseudo-first-order rate equation showed that removal rate was increased after treatment with TX100 as well as CTAB, while that was reduced after SDS treatment.

Coagulation/flocculation process for dye removal using sludge from water treatment plant: Optimization through response surface methodology

In this study, performance of a waterworks sludge (FCS: ferric chloride sludge) for the removal of acid red 119 (AR119) dye from aqueous solutions were investigated. For this purpose, response surface methodology (RSM) was applied to optimize three operating variables of coagulation/flocculation process including initial pH, coagulant dosage and initial dye concentration. The results showed that the decrease of initial pH was always beneficial for enhancing dye removal and no re-stabilization phenomenon was occurred even at the used maximum FCS dosage. It seems that iron hydroxides of the FCS could neutralize the negative charges on dye molecules or cause to the trapping of the dye ones. Therefore, the sweep flocculation and/or the charge neutralization might play key roles in the enhancement of dye removal. The optimum initial pH, FCS dosage and initial dye concentration were found to be 3.5, 236.68 mg dried FCS/L and 65.91 mg/L, respectively. Dye removal of 96.53% is observed which confirms close to RSM results. Therefore, it can be concluded that reusing the FCS as a low-cost material into the coagulation/flocculation process in wastewater treatment plants can offer some advantages such as high efficiency for AR119 dye removal and economic savings on overall treatment plant operation costs.

Removal of As(V) from aqueous system using steel-making by-product

For As(V) removal aqueous system, 3 types slag which is a waste product from steel making process was used. Arsenic was mainly removed by Ca-As precipitation such as form Ca3(AsO4)2. The removal efficiency of arsenic on slag was affected by iron oxide contents because arsenic was removed by adsorption on iron oxide. The experimental results were well fitted by pseudo-second-order and Langmuir isotherm model compared to other models. Arsenic was completely removed by Slag Y and Slag J within 12 h, 0.5 g and 0.7 g of Slag Y and Slag J are sufficient to remove arsenic of 20 mg/l arsenic. The removal efficiency increases with the decrease of initial pH and the decrease of initial arsenic concentration. The calcium that is a major component comes from dissolution of the lime (CaO). The calcium concentration increased at low initial pH because the solubility of the lime (CaO) increases at acidic condition. The equilibrium pH sharply increase after reaction because of creation of hydroxide ion.

Complexing agent and heavy metal removals from metal plating effluent by electrocoagulation with stainless steel electrodes

In the present study, the treatability of a metal plating wastewater containing complexed metals originating from the nickel and zinc plating process by electrocoagulation using stainless steel electrodes was experimentally investigated. The study focused on the effect of important operation parameters on electrocoagulation process performance in terms of organic complex former, nickel and zinc removals as well as sludge production and specific energy consumption. The results indicated that increasing the applied current density from 2.25 to 9.0 mA/cm 2 appreciably enhanced TOC removal efficiency from 20% to 66%, but a further increase in the applied current density to 56.25 mA/cm 2 did not accelerate TOC removal rates. Electrolyte concentration did not affect the process performance significantly and the highest TOC reduction (66%) accompanied with complete heavy metal removals were achieved at the original chloride content (≈1500 mg Cl/L) of the wastewater sample. Nickel removal performance was adversely affected by the decrease of initial pH from its original value of 6. Optimum working conditions for electrocoagulation of metal plating effluent were established as follows: an applied current density of 9 mA/cm 2, the effluent's original electrolyte concentration and pH of the composite sample. TOC removal rates obtained for all electrocoagulation runs fitted pseudo-first-order kinetics very well ( R 2 > 92–99).

Agronomic Implications of the Application of Lime plus Gypsum By‐products to a Hyperdistric Acrisol from Western Spain

: A laboratory experiment involving the use of leaching columns reproducing the topmost portion of a Hyperdystric Acrisol (FAO 1998) or plinthic Palexerult (Soil Survey Staff 2003) treated in its Ap horizon with sugar foam wastes and phosphogypsum was conducted. The amendments increased the contents in exchangeable calcium (Ca) of the Ap horizon and, to a lesser extent, also that of the AB horizon. However, the contents in exchangeable magnesium (Mg) and sodium (Na) decreased as much in Ap as they did in AB; by contrast, the potassium (K) content exhibited a less marked decrease. The potassium chloride (KCl)–extractable aluminium (Al) of the Ap horizon was dramatically decreased much more than that of the AB horizon by the amendments. In the soil solution from Ap, the amendments raised the pH and decreased the Al concentration; in that from AB, however, they caused an initial pH decrease, a tendency that reversed as the gypsum was leached and eventually led to the pH exceeding that in the soil solution from control. The first few water extractions exhibited increased Mg concentration. This trend was reversed in the second leaching cycle, where the concentrations of Mg in the amended columns were lower than those in the controls. In the soil solution, the variation of the Ca and sulphate (SO4 2–) concentrations was influenced by the salt‐sorption effect. The total Al content in soil solution from AB increased during the first leaching cycle and then decreased during the second. The amendments decreased the activities of Al3+, AlOH+2, and Al(OH)2 + in the Ap horizon and increased those of Al3+, AlSO4 +, Al(SO4)2 −, and AlF+2 in the first leaching cycle in the AB horizon. The productivity of the Ap horizon after the treatments was assessed using a wheat crop (T. aestivum, var. ‘Jabato’) in a greenhouse.

SOIL SOLUTION DYNAMICS INTO PALEXERULT AMENDED WITH GYPSUM AND LIME BY-PRODUCTS

A laboratory experiment involving the use of leaching columns reproducing the topmost part of a clayey-skeletal kaolinitic acid thermic plinthic Palexerult amended with lime and gypsum by-products was used to study changes in soil solution composition during two leaching cycles. The lime amendment mainly affected the composition of the soil solution of the Ap horizon, where it increased pH and Ca and decreased the F and Al concentrations. Gypsum by-products caused an initial pH decrease in the soil solution; however, as the gypsum was leached, the pH rose and eventually exceeded that of both Ap and AB in the controls. After the gypsum by-product application, Mg and Na strongly increased, but afterward decreased to levels lower than those in the controls; Al contents increased in the first water extracts from Ap and AB horizons and that of F in all extracts from Ap and most from AB. The variation of the Ca and SO42− concentrations in the AB horizon was influenced by surface sorption and precipitation.

Effect of excipients on PLGA film degradation and the stability of an incorporated peptide

The effect of pH modifying excipients on the chemical stability of a model peptide (VYPNGA) and the degradation of poly(dl-lactide-co-glycolide)(PLGA) was studied in PLGA films under accelerated storage conditions. pH modifiers included a basic amine (proton sponge), a basic salt (magnesium hydroxide) and two pH buffers (ammonium acetate and magnesium acetate). Changes in film pH were monitored using 13C NMR, peptide degradation products were quantified by LC/MS/MS and PLGA degradation was analyzed by TGA, DSC and SEC. Inclusion of pH modifiers had little impact on PLGA degradation. The proton sponge affected an initial decrease in pH but reduced peptide deamidation and chain cleavage relative to an unbuffered control. Magnesium hydroxide produced an initial increase in pH but also showed increased peptide deamidation. Ammonium acetate decreased pH and increased peptide chain cleavage, presumably due to increased PLGA hydrolysis. Magnesium acetate buffer increased the initial pH but resulted in increased peptide loss. The extent of peptide acylation increased in all formulations, most notably in the proton sponge modified films. The effectiveness of pH modifiers in PLGA formulations under storage conditions is dependant on both the mechanism of pH alteration and the peptide degradation reaction of interest.

Solubilization of heavy metals from a fluvial AMD generating tailings sediment by heterotrophic microorganisms: Part I: Influence of pH and solid content

The study demonstrates that a heterotrophic mixed culture is able to mobilize considerable amounts of heavy metals (Fe, Zn, Mn, Pb, Cu, Cd, Cr) from a sulfidic AMD generating fluvial tailings material even under moderately acidic conditions as they exist at real sites. The experiments were carried out in shaking flasks by inoculation with a mixed culture of heterotrophic bacteria. The solid content and a decrease in initial pH of the suspensions were investigated as important factors of the viability of the heterotrophic microorganisms. With the mixed culture, up to 17% Pb, 27% Cd, 100% Cr, 25% Fe, 35% Cu, 79% Mn, and 28% Zn were mobilized in one batch run. Compared to the autotrophic processes, especially Pb seems to be mobilized by heterotrophic microbial action. Even under increasingly unfavorable conditions (increase in solid content, decrease in initial pH) the mixed culture demonstrated a high diversity and a good viability. As a result, it was clearly shown that heterotrophic processes also play an important role in the mobilization of metals in such acid-generating materials. Heterotrophic microorganisms improve the solubility of metals primarily released by biooxidation, and enhance the transport of these environmentally relevant metals by excretion of complexing agents. The synergistic action of both autotrophic and heterotrophic bioleaching processes generates at such sites a long-range contamination of ground- and surface-water.

Treatment of a Textile Dye Wastewater by an Electrochemical Process

This study explored the effectiveness of an electrochemical process to treat a sulfur dye wastewater from a textile industry. The treatment system included a 4.0 L reactor equipped with five steel electrode plates, and a separate sedimentation tank of equal liquid volume. The experimental part involved two distinct, sequential stages. In the first stage, the effect of initial pH and electrical charge (i.e., current times reaction time) on the treatment process was explored. Experiments were conducted in a factorial mode, involving three initial pH values (3, 4 and 5), and six electrical charges (ranging from 150 to 1,350 coulomb), respectively. Results indicated that chemical oxygen demand (COD), total suspended solids (TSS), and color removal efficiency improved with a decrease in initial pH and an increase in electrical charge. Overall, high percent removal values were observed ranging from 63% to 80% for COD, 81% to 96% for TSS, and 93% to 99% for color. During the second stage, the electrode corrosion pattern was investigated for a period of 45 days. Under stable operating conditions, electrode consumption was found to conform to Faraday's law. Moreover, process performance regarding COD, TSS, and color reduction was comparable to that obtained in the first stage of the study.

Laboratory investigation of aluminum solubility and solid-phase properties following alum treatment of lake waters

Water samples from two southern California lakes adversely affected by internal nutrient loading were treated with a 20 mg/L dose of Al 3+ in laboratory studies to examine Al solubility and solid-phase speciation over time. Alum [Al 2(SO 4) 3·18 H 2O] applications to water samples from Big Bear Lake and Lake Elsinore resulted in a rapid initial decrease in pH and alkalinity followed by a gradual recovery in pH over several weeks. Dissolved Al concentrations increased following treatment, reaching a maximum of 2.54 mg/L after 17 days in Lake Elsinore water and 0.91 mg/L after 48 days in Big Bear Lake water; concentrations in both waters then decreased to <0.25 mg/L after 150 days. The solid phase was periodically collected and analyzed using X-ray diffraction (XRD), differential scanning calorimetry-thermogravimetric analysis (DSC-TGA), scanning electron microscopy (SEM), and surface area analyses to investigate the nature of the reaction products and crystallinity development over time. Poorly ordered, X-ray amorphous solid phases transformed over time to relatively well-ordered gibbsite, with strong diffraction peaks at 4.8 and 4.3 Å. XRD also indicated the formation of a second (possibly aluminosilicate) crystalline phase after 150 days in Lake Elsinore water. Surface areas also decreased over time as crystals reordered to form gibbsite/microcrystalline gibbsite species. DSC-TGA results suggested that the initially formed amorphous Al(OH) 3 underwent transformation to >45% gibbsite. These results were supported by geochemical modeling using Visual MINTEQ, with Al solubility putatively controlled by amorphous Al(OH) 3 shortly after treatment and approaching that of microcrystalline gibbsite after about 150 days. These findings indicate that Al(OH) 3 formed after alum treatment undergoes significant chemical and mineralogical changes that may alter its effectiveness as a reactive barrier to phosphorus release from lake sediments.

Bioreactor operation parameters as tools for metabolic regulations in fermentation processes: influence of pH conditions

The influence of controlled- and uncontrolled-pH conditions together with the initial pH on the product and by-product distributions and oxygen transfer characteristics, whereupon the process rate limitations in relation to the intracellular reaction rates were investigated in serine alkaline protease (SAP) fermentation process by recombinant Bacillus licheniformis carrying pHV1431 ::subC on a defined medium with the sole carbon source glucose in the pH range of 6.80–7.25 in batch bioreactors. Although the same amount of cell was produced at all the conditions in each type of operation, with the increase of initial pH the cell formation rates increased; moreover, uncontrolled-pH operation was favourable for the cell formation. The SAP synthesis rates and concentrations were higher at uncontrolled-pH operations. Among the fermentations, pH 0=7.10 uncontrolled-pH operation produced maximum SAP activity that was ca. 900 U cm −3 at t=21 h . According to the biomass and SAP production profiles, bioprocess was divided into two periods; Period I (0<t⩽10 h) covers the cell growth phase and Period II (10<t⩽24 h) covers the SAP production phase. In Period I in both operations, while the oxygen uptake rate (OUR) increased with the increase in initial pH the oxygen transfer rate (OTR) decreased. In Period II, among uncontrolled-pH operations OUR was the lowest at pH=7.10 while OTR decreased with the increase in initial pH. At the oxygen transfer condition applied, the bioprocess is biochemical reaction limited at all the conditions; nevertheless, with the decrease in initial pH, Damköhler number that is the oxygen transfer limitation decreases. Further, the perturbation effects of initial pH and the operation conditions on the intracellular reaction rates were calculated for Periods I and II by using the experimental data obtained and, the diversions in the pathways and certain metabolic reactions and potential strategies for improving SAP production are also discussed.

Photosynthesis and calcification in the calcifying algae Halimeda discoidea studied with microsensors

AbstractWith microsensors, we measured the steady‐state microprofiles of O2, pH and Ca2+ on the topside of young segments of Halimeda discoidea, as well as the surface dynamics upon light–dark shifts. The effect of several inhibitors was studied. The steady‐state measurements showed that under high light intensity, calcium and protons were taken up, while O2 was produced. In the dark, O2 was consumed, the pH decreased to below seawater level and Ca2+ uptake was reduced to 50%. At low light intensity (12 mmol photons m‐2 s‐1), Ca2+ efflux was observed. Upon light–dark shifts, a complicated pattern of both the pH and calcium surface dynamics was observed. Illumination caused an initial pH decrease, followed by a gradual pH increase: this indicated that the surface pH of H. discoidea is determined by more than one light‐induced process. When photosynthesis was inhibited by dichlorophenyl dimethyl urea (DCMU), a strong acidification was observed upon illumination. The nature and physiological function of this putative pump is not known. The calcium dynamics followed all pH dynamics closely, both in the presence and absence of DCMU. The Ca‐channel blockers verapamil and nifedipine had no effect on the Ca2+ dynamics and steady‐state profiles. Thus, in H. discoidea, calcification is not regulated by the alga, but is a consequence of pH increase during photosynthesis. Acetazolamide had no effect on photosynthesis, whereas ethoxyzolamide inhibited photosynthesis at higher light intensities. Therefore, all carbonic anhydrase activity is intracellular. Carbonic anhydrase is required to alleviate the CO2 limitation. Calcification cannot supply sufficient protons and CO2 to sustain photosynthesis.

Acidification of Urine is not a Feasible Method for Preventing Encrustation of Indwelling Urinary Catheters

Encrusting deposits form on urinary catheters as a result of infection by bacteria which produce urease. Urease catalyses the hydrolysis of urea to produce ammonia, with the result that the pH of the urine increases and the deposits are precipitated. It has been suggested that acidification of urine may prevent this rise in pH and so prevent encrustation. Experiments were performed in vitro to determine whether acidification could be used to prevent the rise in pH when urease is present in urine. It was found that, in the presence of urease, the initial decrease in pH resulting from acidification was countered by further urea being converted into ammonia. Thus, although acidic washout solutions may dissolve encrusting deposits, acidification of urine is not a feasible method for preventing catheter encrustation.

A 31P-nuclear magnetic resonance study of skeletal muscle metabolism in rats depleted of creatine with the analogue β-guanidinopropionic acid

Rats were fed a diet containing 1% β-guanidinopropionic acid (GPA) for 6–10 weeks to deplete their skeletal muscle of creatine. 31P-NMR was used to monitor metabolic changes in the gastrocnemius muscle at rest, during stimulated steady-state isometric contraction at 4 Hz and during recovery from stimulation. In resting muscles, the [creatine phosphate] was reduced to 10% (2.8 μmol·g−1) and the [ATP] to 50% (3.3 μmol·g−1) of those found in rats fed a control diet. The concentration of the phosphorylated form of the analogue (PGPA) was 23 μmol·g−1. There was no significant difference in muscle performance or in the relative changes in the [ATP] during stimulation. Intracellular pH decreased rapidly on stimulation and recovered during the stimulation period to near resting values in both groups. In control rats, the initial decrease in pH was greater and the time to recovery was longer than in GPA-fed rats. The rate at which PGPA supplied energy to the contracting muscle (0.027 mM·s−1) was insignificant relative to the minimum estimated rate of ATP turnover (1 mM·s−1). The rate of PGPA resynthesis during recovery (0.018 mM·s−1) is enzyme-limited and provides an independent estimate of creatine kinase flux during this period (18.9 mM·s−1). The creatine kinase flux (creatine phosphate → ATP) in the resting muscle of GPA-fed rats was 12-fold less than in control animals, 1.3 vs. 15.7 mM·s−1. These results demonstrate that neither the [creatine phosphate] nor the activity of creatine kinase is critical for aerobic metabolism. Skeletal muscle appears to adapt to a diminished creatine pool by enhancing its aerobic capacity.

Recording pH Method of Characterizing Composition and Monitoring Dissolution Profile of an Anhydride–Acid Copolymer and Its Salt Derivatives

A sensitive potentiometric monitoring method was developed that permits the continuous measurement of the dissolution profiles of methyl vinyl ether-maleic anhydride-acid copolymers and salt derivatives. Three distinct rate periods were observed in the dissolution of the anhydride copolymer. The relative dissolution rate of the anhydride copolymer, expressed as percent anhydride dissolved, was independent of sample weight over the weight range studied. The acid form of the copolymer showed only one dissolution rate period, with dissolution being very rapid. The rapid initial pH decrease observed during the first stage of dissolution for a series of anhydride-acid copolymer powder samples correlated closely with the anhydride-acid ratio, permitting chemical characterization of the copolymer functionality simultaneously with the analysis of dissolution profiles. Similarly, the extent of copolymer alkaline salt conversion was inversely proportional to the initial maximum pH increase observed during the first stage of dissolution of these salts. Mechanisms of dissolution of copolymer powder materials are discussed and compared to the dissolution of compressed disks and films reported previously.