Constant pH Conditions Research Articles

Biohydrogen Production by Anaerobic Fermentation of Sewage Sludge - Effect of Initial pH

The aim of this study is to investigate the usability of sewage sludge, a waste from waste water treatment facility, at constant temperature and different pH conditions in the hydrogen production by dark fermentation. It was understood from the results that hydrogen production varies according to the characterization of activated sludge. In the experiments performed at different pH values (pH 4-8) at 35℃, maximum hydrogen production was achieved within the first 24 hours. Except for one performed at pH 8, hydrogen gas release was observed at other pH values within 2 hours. However, according to the results obtained at the 24th hour, maximum hydrogen production (2489 mL/m3H2) was observed at pH 8.

Rates of Fe(II)-Oxidation and Solubility of Bacteriogenic Iron Oxides

ABSTRACTThe oxidation of Fe(II) at circumneutral pH by natural bacterial consortia capable of oxidizing Fe(II) in flocculent mats of bacteriogenic iron oxides (BIOS) was investigated in a series of microcosm experiments under constant pH and pO2 conditions. The oxidation of Fe(II) was faster in the presence BIOS compared to chemical oxidation in solution with pseudo–first-order rate constants ranging from 0.036 to 0.248 min−1 for BIOS compared to 0.004 min−1 for the chemical control. The Fe(II)-oxidation rates exhibited a kinetic dependency on BIOS concentrations, measured in terms of a pseudo–second-order rate constant at 0.066 Lg−1min−1. From the asymptotic decline in Fe(total) in the microcosms, apparent rate constants for HFO dissolution (zero-order values 0.001 to 0.046 mgL−1min−1) and precipitation (second-order values 0.007 to .297 min−1) were obtained from the BIOS and control microcosms, which yield an apparent equilibrium BIOS solubility of 0.157 mgL−1 (i.e., 2.8 μM). These results reflect the complex interplay of Fe(II) oxidation reactions associated with BIOS including homogenous chemical oxidation in solution, chemical oxidation on HFO surfaces, and bacterially mediated oxidation. Furthermore, BIOS precipitated in response to Fe(II) oxidation exhibit a greater apparent solubility than more stable varieties of HFO. The implication is that the competitive advantage of Fe(II)-oxidizing bacteria over autocatalytic surface chemical Fe(II) oxidation on HFO might be enhanced by a reduction in the total amount of BIOS that is precipitated.

Evolution of calcite growth morphology in the presence of magnesium: Implications for the dolomite problem

The effect of magnesium on calcite growth morphology was known to occur as step rounding in some cases and surface segmentation in others. What remains unknown are the conditions for and the relations between the different effects, suggesting a lack of comprehensive understanding of the fundamental cause. Here we investigated the evolution of spiral hillock morphology on calcite cleavage surfaces in solutions with increasing Ca to Mg ratios and supersaturation levels using in situ atomic force microscopy. We isolated the effects of Mg and saturation by conducting experiments under conditions of constant pH, ionic strength, and Ca2+/CO32−. Our results revealed three types of morphological variations, ranging from step rounding in one direction (type I), to all directions (type II), and finally to a mosaic-like surface segmentation associated with monolayer buckling and step bunching (type III). These results suggest that the effect of magnesium on calcite growth depends upon multiple parameters including the concentration of Mg in solution, the step speed, as well as the extensiveness of Mg for Ca substitution in calcite lattice. We propose that the morphological variation may be understood by a model taken into consideration of (1) the lifespan and flux size of Mg ions at kinks in comparison to step kinetics, and (2) the diffusion and alignment of point defects created by the substitution of Mg for Ca in the crystal lattice. Stress calculations show that the maximum amount of Mg which calcite lattice can sustain before plastic deformation is ∼40%, suggesting that lattice stress due to the mismatch between MgCO3 and CaCO3 is likely the ultimate cause for the difficulty of ambient condition dolomite crystallization.

Carbon dioxide sensitivity and its role in multifunctional neurons in the mollusk Onchidium

Intrinsically photoresponsive neurons in the abdominal ganglion of the amphibious mollusk Onchidium named Ip-1 and Ip-2 (Ip-1/2) react to several different stimuli. These neurons respond to light with slow hyperpolarization and to CO2 stimulation with slow depolarization. In this study, increasing the concentration of CO2 in the air caused hyperventilation and enlargement of the pneumostome in the intact animal. In a semi-intact preparation, pouring artificial seawater (ASW) with dissolved CO2 onto the central ganglia caused the previously closed pneumostome to open. In an ASW environment, Ip-1/2 neurons depolarized even under conditions of constant pH (alkaline ASW) and after dissolution of CO2. This depolarization prolonged the firing of action potentials in Ip-1/2 neurons. Adding protons (H+) to ASW caused Ip-1/2 depolarization only when the neurons' membranes were depolarized to a potential above the resting potential. Furthermore, in the presence of the carbonic anhydrase inhibitor acetazolamide (AZ), CO2-induced excitation in Ip-1/2 neurons was increased in both normal and alkaline ASW. These results suggest that when dissolved in ASW, CO2 directly induced the depolarizing response in Ip-1/2 neurons. Since Ip-1/2 neurons participate in pneumostome opening, these results suggest that increased CO2 levels in ASW directly stimulate CO2-sensitive central neurons, promoting ventilation.

Adsorption of Pb<sup>2+</sup>, Cu<sup>2+</sup> and Cr<sup>3+</sup> on Yongnian Bentonite

The Bentonite from Yongnian is Ca-Bentonite, Montmorillonite Content 52%, Colloidal Value 57ml/15g, Eca2+/CEC 53.60%. the Adsorption Characteristics of Pb2+, Cu2+ and Cr3+ onto Bentonite under Conditions of Constant Temperature and Ph have been Studied. the Results Show that the Adsorption Capacities of Heavy Metal Ions onto Bentonite from Yongnian Follow the Order of Pb2+> Cu2+> Cr3+. it is Found that the Adsorption Process of Bentonite Accords with the Langmuir Isotherm Model. the Maximum Adsorption of 3 Kinds of Metal Ions onto Bentonite is in Order of Cr3+>Cu2+>Pb2+.

Effects of Surface Properties of Organic Matters on Cation Adsorption in Solution Phase

Organic substances have been commonly added to mine tailings to improve physical and chemical conditions and facilitate plant establishment. Apart from their nutritional benefits, aggregation and physical improvements may be resulted from organo-mineral interactions between their functional groups and cations of variable charges on mineral surfaces. Organic matters (OM), e.g., woodchips (WC) and sugarcane residue (SR), were initially evaluated for their affinities for Cu2+, Ca2+, and Fe3+ in relation to their surface properties at constant or different pH conditions in aqueous phase, before examining the formation of organo-mineral association in solid phase. Results indicated that WC and SR had different adsorption kinetics for these cations. Their surface negative charges indicated by zeta potentials were positively related to the adsorption capacities. 13C NMR analysis of the OM before and after adsorption revealed that carboxylic and phenolic groups were the major contributors to cation adsorption in solution. SR was found to have more carboxylic groups and thus had higher cation exchange capacity than WC. Therefore, organic materials with high density of functional anion groups on the surfaces may be advantageous when stimulating organo-mineral interactions in mine tailings which are rich in primary and secondary minerals with positively charged surfaces. The organo-mineral association between the OM and base metal mine tailings will be examined in the solid phase in a follow-up experiment.

Partial nitritation for subsequent Anammox to treat high-ammonium leachate

Nitrogen removal via autotrophic denitrification, an anaerobic ammonium oxidation (Anammox) process, requires an appropriate NO2-N/NH4-N ratio to provide nitrite as an intermediate. In this study, a laboratory-scale Hybrid Sequencing Batch Reactor (HSBR) was implemented for treating high-ammonium raw leachate to yield an appropriate NO2-N/NH4-N mixture as a pretreatment for subsequent Anammox. The optimal operating conditions were examined through the long-term operation of the HSBR. The experimental results showed that the prerequisite ratio of NO2-N/NH4-N was found with an initial ammonium concentration of 1200 mg/L, dissolved oxygen (DO) of 0.5–1.0 mg/L, sludge retention time (SRT) of 3 days and temperature of 31°C, which is essential for the subsequent Anammox process. Moreover, the inhibition of free ammonia (FA) and free nitrous acid (FNA) were also examined under a constant pH condition, and it was found that AOB (ammonium oxidation bacteria) had a great ability to adapt to a broad FA and FNA concentration, whereas NOB (nitrite-oxidizing bacteria) were inhibited by either FA or FNA concentration to a certain extent. It appears that partial nitritation could be implemented by facilitating FA and/or suppressing FNA concentration.

Removal of Perchlorate Using Reverse Osmosis and Nanofiltration Membranes

Rejection characteristics of perchlorate (ClO4 ) were examined for commercially available reverse osmosis (RO) and nanofiltration (NF) membranes. A bench-scale dead-end stirred-cell filtration system was employed to determine the toxic ion rejection and the membrane flux. Model water solutions were used to prepare ClO 4 solutions (approximately, 1,000 µg/L) in the presence of background salts (NaCl, Na2SO4, and CaCl2) at various pH values (3.5, 7, and 9.5) and solution ionic strengths (0.001, 0.01, and 0.01 M NaCl) in the presence of natural organic matter (NOM). Rejection by the membranes increased with increasing solution pH owing to increasingly negative membrane charge. In addition, the rejection of the target ion by the membranes increased with increasing solution ionic strength. The rejection of ClO4 was consistently higher for the RO membrane than for the NF membrane and ClO4 rejection followed the order CaCl2 < NaCl < Na2SO4 at conditions of constant pH and ionic strength for both the RO and NF membranes. The possible influence of NOM on ClO4 rejection by the membranes was also explored.

Kinetic modeling of enzymatic hydrolysis of pretreated kitchen wastes for enhancing bioethanol production

It is well known that use of low cost and abundant waste materials in microbial fermentations can reduce product costs. Kitchen wastes disposed of in large amounts from cafeterias, restaurants, dining halls, food processing plants, and household kitchens contain high amounts of carbohydrate components such as glucose, starch, and cellulose. Efficient utilization of these sugars is another opportunity to reduce ethanol costs. In this study, the effect of pretreatment methods (hot water, acid solutions, and a control) on enzymatic hydrolysis of kitchen wastes was evaluated using a kinetic modeling approach. Fermentation experiments conducted with and without traditional fermentation nutrients were assessed at constant conditions of pH 4.5 and temperature of 30°C for 48h using commercial dry baker’s yeast, Saccharomyces cerevisiae. The control, which involved no treatment, and hot water treated samples gave close glucose concentrations after 6h. The highest and lowest rates of glucose production were found as 0.644 and 0.128 (h−1) for the control (or no-pretreated (NPT)) and 1% acid solutions, respectively. The fermentation results indicated that final ethanol concentrations are not significantly improved by adding nutrients (17.2–23.3g/L). Thus, it was concluded that product cost can be lowered to a large extent if (1) kitchen wastes are used as a substrate, (2) no fermentation nutrient is used, and (3) hydrolysis time is applied for about 6h. Further optimization study is needed to increase the yield to higher levels.

Impact of free ammonia on anammox rates (anoxic ammonium oxidation) in a moving bed biofilm reactor

Using a bench scale moving bed bioreactor (MBBR), the effect of free ammonia (FA, NH3, the un-ionized form of ammonium NH4+) concentration on anoxic ammonium oxidation (anammox) was evaluated based on the volumetric nitrogen removal rate (NRR). Although, a detailed microbial analysis was not conducted, the major NRR observed was assumed to be by anammox, based on the nitrogen conversion ratios of nitrite to ammonium and nitrate to ammonium. Since the concentration of free ammonia as a proportion of the total ammonia concentration is pH-dependent, the impact of changing the operating pH from 6.9 to 8.2, was investigated under constant nitrogen loading conditions during continuous reactor operation. Furthermore, the effect of sudden nitrogen load changes was investigated under constant pH conditions. Batch tests were conducted to determine the immediate response of the anammox consortium to shifts in pH and FA concentrations. It was found that FA was inhibiting NRR at concentrations exceeding 2mgNL−1. In the pH range 7–8, the decrease in anammox activity was independent of pH and related only to the concentration of FA. Nitrite concentrations of up to 120mgNL−1 did not negatively affect NRR for up to 3.5h. It was concluded that a stable NRR in a moving bed biofilm reactor depended on maintaining FA concentrations below 2mgNL−1 when the pH was maintained between 7 and 8.

Effect of pH on the Degradation of Aqueous Organophosphate (methylparathion) in Wastewater by Ozonation

Degradation of O,O-dimethyl -O-4-nitrophenylphosphorothioate (methylparathion) by ozonation in aqueous solution was studied in a batch reactor under constant ozone dosage and variable pH conditions. The effectiveness of the process was estimated based on the degree of COD (chemical oxygen demand) reduction and conversion of methylparathion. It was observed that ozonation is more effective at alkaline reaction of medium than other conditions. The degree of methylparathion conversion achieved after 120 minutes of the process at pH 9 was 98% compared to 81% and 60% at pH 7 and 3, respectively. Another parameter used to quantify the methylparathion during ozonation was the pseudo first order rate constant k (1/min). Results showed that the rate constant of the process was approximately much higher at pH 9 compared to pH 7 and 3. A significant improvement in chemical oxygen demand removal was observed at pH above 7. At pH 9, the reduction in chemical oxygen demand at the end of the process reached 93%. The methylparathion degradation intermediate products were analyzed by gas chromatography–mass spectrometry (GC–MS). The main intermediate product was p-nitrophenol. The result of the study concludes that ozonation is an effective process for the treatment of organophosphate (methylparathion) contaminated wastewater.

Mannitol production by heterofermentative Lactobacillus reuteri CRL 1101 and Lactobacillus fermentum CRL 573 in free and controlled pH batch fermentations

Certain lactic acid bacteria, especially heterofermentative strains, are capable to produce mannitol under adequate culture conditions. In this study, mannitol production by Lactobacillus reuteri CRL 1101 and Lactobacillus fermentum CRL 573 in modified MRS medium containing a mixture of fructose and glucose in a 6.5:1.0 ratio was investigated during batch fermentations with free pH and constant pH 6.0 and 5.0. Mannitol production and yields were higher under constant pH conditions compared with fermentations with free pH, the increase being more pronounced in the case of the L. fermentum strain. Maximum mannitol production and yields from fructose for L. reuteri CRL 1101 (122 mM and 75.7 mol%, respectively) and L. fermentum CRL 573 (312 mM and 93.5 mol%, respectively) were found at pH 5.0. Interestingly, depending on the pH conditions, fructose was used only as an alternative external electron acceptor or as both electron acceptor and energy source in the case of the L. reuteri strain. In contrast, L. fermentum CRL 573 used fructose both as electron acceptor and carbon source simultaneously, independently of the pH value, which strongly affected mannitol production by this strain. Studies on the metabolism of these relevant mannitol-producing lactobacilli provide important knowledge to either produce mannitol to be used as food additive or to produce it in situ during fermented food production.

Heterogeneous formation of ferric oxide nanoparticles on chlorite surfaces studied by x-ray absorption spectromicroscopy (STXM)

The homogeneous and heterogeneous formation of ferric iron oxides from acidic solution (pH 2.06–2.50) has been studied in the presence of chlorite under constant pH conditions using titration experiments. Significantly shorter induction times for the ferrihydrite formation have been macroscopically observed in the presence of chlorite particles, thus indicating heterogeneous nucleation as a major precipitation mechanism. A combination of Scanning Electron Microscopy (SEM) and Scanning Transmission X-Ray microscopy (STXM) on the O K-edge and Fe L-edge was used to clearly distinguish ferric iron precipitates from chlorite and to obtain the spatial distribution of iron precipitates on the chlorite surface under conditions of homogenous and heterogeneous formation.Oxygen K-edge results show the precipitation of a highly hydrolyzed chlorite surface associated ferric iron phase under heterogeneous conditions. Precipitates with different oxygen K-edge features are observed on the chlorite basal faces compared to the edge surfaces which can be attributed to cluster size effects and differences in the O/OH ratio. The results obtained from iron L-edge XANES corroborate the observations of the oxygen K-edge, indicating a thin surface layer of ferric iron precipitates and preferential precipitation at the chlorite edge surfaces. Under conditions where homogeneous ferrihydrite formation dominates, beside surface coatings separate iron colloids/nanoparticles are observed. Iron L-edge analysis and the pre-edge splitting on the oxygen K-edge indicate a higher long-range order/lower hydration comparable to ferrihydrite reference spectra. The results show that the Fe(III) secondary phase formation as surface coating or nanoparticles and their spatial distribution depends on the degree of supersaturation. These observations may have direct consequences for the retention and mobility of various contaminants in aquifer systems and potential remediation strategies.

A proton NMR study on the specific sorption of yttrium(III) and europium(III) on gamma-alumina [γ-Al2O3

The specific sorption of Eu(III) and Y(III) on γ-alumina was investigated with solid-state 1H NMR. Solution pH was shown to influence the recorded 1H NMR spectra of γ-alumina, and thus, metal ion-containing samples were prepared under constant pH conditions, 8.00±0.05. The metal ion concentration in the samples was varied between 6.58×10−7 M–3.95×10−4 M in case of Y3+ and 6.58×10−8 M–1.32×10−4 M in case of Eu3+. The mineral concentration was kept constant at 4g/l. After separation of the liquid phase, the samples were dried under vacuum to remove physisorbed water from the mineral surface. However, even after 48h of drying at 150°C and 20 mTorr, water was still detected in the proton spectra as two distinct peaks with chemical shifts at 1.3 and 0.9ppm. The europium addition to the γ-alumina samples induced significant spectral changes in comparison with yttrium-containing samples. These changes were attributed to the paramagnetism of europium rather than to complexation reactions occurring on the mineral surface. Proton spectra obtained for yttrium samples were therefore used to detect the spectral changes induced by the sorption reaction itself. The results revealed a large distribution of protons being removed from the mineral surface upon yttrium complexation. Removed protons were assigned to both bridging surface hydroxyls such as (AlVI)2–OH as well as to terminal hydroxyls, e.g., of type AlVI–OH. Acidic protons belonging to (AlVI)3–OH groups were not observed to participate in the surface reaction.

Effect of organic and inorganic matters on the oxidation of Fe(II) in raw water from Ömerli Dam

In Turkey, particularly in Istanbul, almost all of the surface and underground water sources contain ferrous iron [Fe(II)] at high concentration levels, which generate serious problems in use of water for industrial processes and at drinking water treatment plants. Ferric iron [Fe(III)] on the other hand precipitates as Fe(OH)3 and blocks the filters installed at water treatment plants, decreasing efficiency. Also, the period for re-wash of fi lters shortens which increases the cost. In natural waters, high iron concentrations are found together with natural organic and inorganic substances. Humic substances found in underground water sources prevent the oxidation of Fe(II). It was shown in recent studies that oxidation of Fe(II) was decreased dramatically by organic compounds found in humic substances. Although atmospheric oxidation of Fe(II) is a well known method in practice over decades, effects of organic and inorganic substances on the oxidation rate have only recently been investigated. Literature review showed that the research in the area of effect of organic and inorganic substances over the oxidation of Fe(II) was not satisfactory. Since high concentrations of Fe(II) exist in the surface and underground water and it is critically important for the purpose of drinking and industrial use, it will lead to research and development regarding the methods for treatment of Fe(II). An experimental study was carried out by aeration at constant pH, temperature, alkalinity, and mixing conditions in a laboratory scale batch reactor system, which was fed with raw water obtained from entrance of Ömerli Dam Treatment Plant and deionized water. Oxidation was performed for different concentrations of Fe(II). Effects of additional organic and inorganic materials on the oxidation mechanism of Fe(II) were investigated. Potassium hydrogen phthalate (KHP) as organic material and Mn(II), Zn(II), and Ni(II) as inorganic materials were used.

Solubility of aceclofenac in polyamidoamine dendrimer solutions

In the present study we investigated the effect of polyamidoamine (PAMAM) dendrimers on the aqueous solubility of aceclofenac. The aqueous solubility of aceclofenac was measured in the presence of dendrimers in distilled water. The effect of variables, such as pH condition, concentration, temperature and generation (molecule size) of dendrimer, has been investigated. Results showed that the solubility of aceclofenac in the dendrimer solutions was proportional to dendrimer concentration. The order in which the dendrimers increased the solubility at a constant pH condition was G3 > G0. The influence of dendrimer solution pH on the solubility enhancement of aceclofenac suggests that it involves an electrostatic interaction between the carboxyl group of the aceclofenac molecule and the amine groups of the dendrimer molecule. The solubility of aceclofenac was inversely proportional to the temperature of dendrimer solution.Different generation (G0 and G3) PAMAM dendrimers have the potential to significantly enhance the solubility of poor water-soluble drugs.

Intrinsic Dissolution as a Tool for Evaluating Drug Solubility in Accordance with the Biopharmaceutics Classification System

The Biopharmaceutics Classification System (BCS) is a tool that was cr eated to categorize drugs into different groups according to their solubility and permeability characteristics. Through a combination of these factors and physiological parameters, it is possible to understand the absorption behavior of a drug in the gastrointestinal tract, thus contributing to cost and time reductions in drug development, as well as reducing exposure of human subjects during in vivo trials. Solubility is attained by determining the equilibrium under conditions of physiological pH, while different methods may be employed for evaluating permeability. On the other hand, the intrinsic dissolution rate (IDR), which is defined as the rate of dissolution of a pure substance under constant temperature, pH, and surface area conditions, among others, may present greater correlation to the in vivo dissolution dynamic than the solubility test. The purpose of this work is to discuss the intrinsic dissolution test as a tool for determining the solubility of drugs within the scope of the Biopharmaceutics Classification System (BCS).

Effects of biosurfactants on surface properties of hematite

Application of microorganisms as surface modifiers has focused our attention in recent times. The adsorption of biosurfactants can be a way for the solid surface modification. In the present investigation rhamnolipids produced by Pseudomonas aerugiosa were used to make the hematite surface modification. Experiments were carried out with pure mineral hematite. In this paper, the influence of biosurfactant addition on both the stability and the flotability of hematite suspensions has been studied in detail. The stability experiments were conducted using Turbiscan LAb apparatus, at constant pH conditions and mineral amount. The flotation experiments were carried out using Hallimond tube. The adsorption isotherms of biosurfactant onto the hematite particles were also determined. The experiments were carried out with broth and pure rhamnolipid. The results of those experiments were compared and discussed.

Comparison of recovery methods for the enumeration of injured Listeria innocua cells under isothermal and non-isothermal treatments

This study compares the feature of different media with the combination of selective with non-selective media in a TAL method for recovery of Listeria innocua cells exposed to thermal treatments. Experiments were conducted in broth at constant temperature (52.5 and 65.0 °C) and pH (4.5 and 7.5) conditions, using NaCl or glycerol to adjust water activity to 0.95. Four different media were used in bacterial cell enumeration: (i) a non-selective medium – TSAYE, (ii) two selective media – TSAYE + 5%NaCl and Palcam Agar and (iii) TAL medium (consisting of a layer of Palcam Agar overlaid with one of TSAYE). Two food products were used as case studies aiming at comparison of results obtained on selective and TAL media enumeration. Parsley samples were inoculated with L. innocua and subjected to posterior thermal treatments both under isothermal (52.5, 60.0 and 65.0 °C) and non-isothermal (heating rate of 1.8 °C/min from 20.0 to 65.0 °C) conditions. The recovery capability of TAL method was also studied when a pre-cooked frozen food (i.e. meat pockets) was fried (oil temperature of ∼180 °C). TAL method proved to be better than Palcam Agar in terms of capability to recover injured cells and was effective in L. innocua enumeration when non-sterile samples were analysed.

Degradation of trace aqueous 4-chloro-2-nitrophenol occurring in pharmaceutical industrial wastewater by ozone

Degradation of 4-chloro-2-nitro phenol by ozonation in aqueous solution was studied in a semi batch reactor under constant ozone dosage and variable pH conditions. The effectiveness of the process was estimated based on the degree of conversion of 4-chloro-2-nitro phenol. It was observed that ozonation is more effective at alkaline reaction of medium than other conditions. The degree of conversion achieved (at the first 5 minutes of the process)at pH 9 was 99.64% compared to 99.03% and 77.35% at pH 7 and 3, respectively. Another parameter used to quantify the 4- chloro-2-nitrophenol during ozonation was the pseudo first order rate constant k (min -1 ). Results showed that the rate constant of the process was approximately much higher at the alkaline pH compared to acidic ones. A considerable improvement in chemical oxygen demand removal was observed at pH above 7. At pH 9, the reduction in chemical oxygen demand at the end of the process reached 56.9 %. The degree of organically bounded nitrogen conversion to nitrate was higher at pH 3. Of the total organic carbon reduction, 15.89 % was observed at pH 9. The 4-chloro-2-nitro phenol degradation intermediate products were analyzed by mass- spectrometry. The main intermediate product was chlorophenol.