Correlating Buffering Agents' Premier pH with Interface Stability Toward Long-Term Zn Metal Anodes.

Aqueous solvents in Zn metal batteries inevitably induces hydrogen evolution reactions (HER) due to fluctuating pH levels in electrolytes, leading to severe side reactions and dendrite growth. To address these challenges, buffering agents have been recently proposed as a solution to maintain constant electrolyte pH values upon cycling. Nonetheless, the critical role of buffering additives' premier pH in determining interface stability is largely overlooked. Herein, two types of buffering agents, single amphoteric and conjugate acid-base pairs, are employed to correlate their initial pHs with the interface stability. Based on the observations, the lifetime of Zn metal anodes initially increases and then decreases as the initial pH level goes up from 2.0 to 5.0, with an optimal lifetime at pH 3.3 for both buffering agent categories. This phenomenon lies in ample H+ in low pH and rich OH- in high pH, leading to either severe HER or by-products passivation layer. The optimized pH allows cells to deliver a high average Coulombic efficiency of 99.61% over 1500 cycles at a large current density of 5 mA cm-2, which is significantly superior to 345 cycles achieved in the pristine electrolyte. Furthermore, this enhanced interface enables stable Zn/activated carbon full batteries over 15 000 cycles.

Effect of pH on the performance of hydrogen production by dark fermentation coupled denitrification.

High concentration nitrogen-containing organic wastewater is a potential substrate for hydrogen production by dark fermentation. In this study, the effect of initial pH on the performance of hydrogen production by dark fermentation coupled denitrification was investigated. The hydrogen production, liquid metabolites, nitrate, nitrite and microbial community were monitored under the condition of pH varying from 4 to 11. Results showed that the highest hydrogen production (70.94 ± 4.750 mL/g VSS), chemical oxygen demand (COD) removal rate (37.13 ± 1.86%) and nitrate reduction rate (1.57 ± 0.27 mg/L/h) were obtained at pH of 5. Under this condition, the nitrate was mainly reduced to N2 with hydrogen as the electron donor. When the initial pH was 6-11, nitrate mainly reduced to N2 through co-action with acetate. Microbial community analysis revealed that as the initial pH increased from 4 to 11, the main hydrogen-producing microorganisms were gradually converted from Clostridium sensu stricto 12 sp. into Clostridium sensu stricto 1 sp, which leaded to changes in the hydrogen production process.

Photocatalysis of aqueous PFOA by common catalysts of In2O3, Ga2O3, TiO2, CeO2 and CdS: influence factors and mechanistic insights.

Gallium oxide (Ga2O3), titanium dioxide (TiO2), cerium dioxide (CeO2), indium oxide (In2O3) and cadmium sulfide (CdS) were commonly used under UV light as photocatalysis system for the pollutants' degradation. In this study, these five catalysts were applied for the photodegradation of perfluorooctanoic acid (PFOA), a well-known perfluoroalkyl substance (PFAS). As a result, the PFOA photodegradation performance was sequenced as: Ga2O3 > TiO2 > CeO2 > In2O3 > CdS. To further explain the photocatalysis mechanism, the effects of initial pH, photon energy and band gap were evaluated. The initial pH of 3 ± 0.2 hinders the catalytic reaction of CdS, resulting in low degradation of PFOA, while it has no significant effect on Ga2O3, TiO2, CeO2 and In2O3. In addition, quantum yield was sequenced as TiO2 > CeO2 > Ga2O3 > In2O3, which may not be the main factor determining the degradation effect. Notably, the band gap energy from large to narrow was as: Ga2O3 > TiO2 > CeO2 > In2O3 > CdS, which exactly matched their degradation performance.

Lactic acid production with two types of feedstocks from food waste: Effect of inoculum, temperature, micro-oxygen, and initial pH.

Lactic acid (LA) is an important chemical with broad market applications. To optimize LA production, food waste has been explored as feedstock. Due to the wide variety of food waste types, most current research studies have obtained different conclusions. This study focuses on carbohydrate-rich fruit and vegetable waste (FVW) and lipid-rich kitchen waste (KW), and the effect of inoculum, temperature, micro-oxygen, and initial pH were compared. FVW has a greater potential for LA production than KW. As an inoculum, lactic acid bacteria (LAB) significantly increased the maximum LA concentration (27.6 g/L) by 50.8 % compared with anaerobic sludge (AS). FVW exhibited optimal LA production at 37 °C with micro-oxygen. Adjustment of initial pH from 4 to 8 alleviated the inhibitory effect of accumulated LA, resulting in a 46.2 % increase in maximum LA production in FVW. The expression of functional genes associated with metabolism, genetic information processing, and environmental information processing was higher at 37 °C compared to 50 °C.

Initial solution pH value for the construction of a 3D hydroxyapatite via the trisodium citrate-assisted hydrothermal route.

In this study, a trisodium citrate (TSC)-assisted hydrothermal method is utilized to prepare three-dimensional hydroxyapatite (3D HA). Understanding the role of TSC in the preparation of 3D HA crystals may provide valuable methods to design advanced biomaterials. As one of the indexes of solution supersaturation, the initial pH (ipH) value can not only directly affect the nucleation rate, but also affect the growth of HA crystals. In this work, the effect of the ipH on the microstructure, particle size distribution, and specific surface area of the 3D HA is explored. Results showed that the morphology of 3D HA transformed from a bundle to a dumbbell ball and then a dumbbell with an increase in the ipH. A corresponding mechanism of such a structural evolution was proposed, providing inspiration for the fabrication of innovative 3D HA structures with enhanced biological functionality and performance.

Response of rumen microorganisms to pH during anaerobic hydrolysis and acidogenesis of lignocellulose biomass.

Rumen microorganisms can efficiently degrade lignocellulosic wastes to produce volatile fatty acids (VFAs). pH is a key factor in controlling the type and yield of VFAs by affecting the microorganisms involved in rumen fermentation. However, the effects of different pH on rumen microbial diversity, communities, and mechanisms are unclear. In this study, the hydrolysis and acidogenesis of corn straw and diversity, communities, and mechanisms of rumen microorganisms were explored at different initial pHs. Results showed that the highest hemicellulose, cellulose, and lignin degradation efficiency of corn straw was 55.2 %, 38.3 %, and 7.01 %, respectively, and VFA concentration was 10.2 g/L at pH 7.0. Low pH decreased the bacterial diversity and increased the fungal diversity. Rumen bacteria and fungi had different responses to initial pHs, and the community structure of bacteria and fungi had obviously differences at the genus level. The core genera Succiniclasticum, Treponema, and Neocallimastix relative abundance at initial pH 7.0 samples were significantly higher than that at lower initial pHs, reaching 6.01 %, 1.61 %, and 5.35 %, respectively. The bacterial network was more complex than that of fungi. pH, acetic acid, and propionic acid were the main factors influencing the bacterial and fungal community structure. Low pH inhibited the expression of functional genes related to hydrolysis and acidogenesis, explaining the lower hydrolysis and acidogenesis efficiency. These findings will provide a better understanding for rumen fermentation to produce VFAs.

Ascorbic acid-mediated zero-valent iron enhanced hydrogen production potential of bean dregs and corn stover by photo fermentation.

Ascorbic acid was introduced to enhance the performance of zero-valent iron (Fe(0)) in hydrogen production by photo fermentation of bean dregs and corn stover. The highest hydrogen production of 664.0 ± 5.3 mL and hydrogen production rate of 34.6 ± 0.1 mL/h was achieved at 150 mg/L ascorbic acid, which was 10.1% and 11.5% higher than that of 400 mg/L Fe(0) alone. The supplement of ascorbic acid to Fe(0) system accelerated the formation of Fe(Ⅱ) in solution due to its reducing and chelating ability. Hydrogen production of Fe(0) and ascorbic acid-Fe(0) (AA-Fe(0)) systems at different initial pH (5, 6, 7, 8 and 9) was studied. Result showed that hydrogen produced from AA-Fe(0) system was improved by 2.7-27.5% compared with Fe(0) system. The maximum hydrogen production of 767.5 ± 2.8 mL was achieved with initial pH 9 in the AA-Fe(0) system. This study provided a strategy for enhancing biohydrogen production.

Lipid Production of Schizochytrium sp. HBW10 Isolated from Coastal Waters of Northern China Cultivated in Food Waste Hydrolysate.

Marine oleaginous thraustochytrids have attracted increasing attention for their great potential in producing high-value active metabolites using various industrial and agricultural waste. Food waste containing abundant nutrients is considered as an excellent feedstock for microbial fermentation. In this study, a thraustochytrid strain Schizochytrium sp. HBW10 was isolated from a water column in Bohai Bay in Northern China for the first time. Further lipid production characteristics of S. sp. HBW10 were investigated utilizing sulfuric acid hydrolysate of food waste (FWH) from two different restaurants (FWH1 and FWH2) with the initial pH value adjusted by NaOH or NaHCO3. Results showed that the highest concentration of total fatty acids (TFAs) was observed in FWH2 medium with the 50% content level on the fifth day, reaching up to 0.34 g/L. A higher initial pH promoted the growth and saturated fatty acid (SFA) accumulation of S. sp. HBW10, achieving nearly 100% of the sum of saturated and monounsaturated fatty acids (SMUFAs) in TFAs with initial pH7 and pH8 in FWH1 medium. This work demonstrates a possible way for lipid production by thraustochytrids using food waste hydrolysate with a higher initial pH (pH7~pH8) adjusted by NaHCO3.

Changes in solution turbidity and color during paracetamol removal in laboratory and pilot-scale semicontinuous ozonation reactors.

Injecting ozone by means of a venturi device causes an increase in the mass transfer coefficient with respect to gas dissolution through a microdiffuser. Moreover, it was observed that significant turbidity levels are not formed (<1 NTU) when using a microdiffuser, probably due to the relatively high stirring which avoids formation of intermolecular hydrogen bonds. On the contrary, employing a venturi injector led to the production of high turbidity levels in water (up to 20 NTU). This indicates that formation of supramolecular structures causing this turbidity requires the presence of certain facilitating species which are formed through ozone decomposition mechanisms. The maximum ozone transfer takes place when operating at pH0 9.0, that is, when this value is close to the pKa and employing a dose of R = 115 mol O3/mol Pa0. Under these conditions, the degradation of paracetamol generates color, which is attributed to the presence of condensation products from pyrogallol, catechol, resorcinol, acetamide, oxalic acid and 4-aminophenol. Once paracetamol is fully degraded and solution turns colorless, turbidity grows (>20 NTU). This is attributed to formation of high molecular weight structures from 4-aminophenol and oxamide. Operating with large ozone excess (R = 500 mol O3/mol Pa0), the maximum ozone transfer rate is achieved at pH0 = 12.0. Under these conditions, the pollutant is fully removed together with water aromaticity and oxalic acid (able to form linear structures through hydrogen bonding) is detected during color development. Then, turbidity is formed due to cyclic dimer formation from acetic acid.

New insights into Saccharomyces cerevisiae induced calcium carbonate precipitation.

Our previous study reported that Saccharomyces cerevisiae could induce calcium carbonate (CaCO3) precipitation, but the associated mechanism was unclear. In the present study, Saccharomyces cerevisiae was cultured under various conditions, including the presence of different organic acids and initial pH, and the yields of CaCO3 formation induced by the different organic acids were compared. The metabolism of organic acid by the metabolites of S. cerevisiae was also assessed in vitro. The SEM-EDS and XRD results showed that only acetate acid, pyruvic acid, and α-ketoglutaric acid could induce CaCO3 formation, and the weight order of the produced CaCO3 was pyruvic acid, acetate acid, α-ketoglutaric acid. In addition, the presence of only yeast metabolites and the initial neutral or alkaline environment also limited the CaCO3 formation. These results illustrated that organic acid oxidation intracellularly, especially the tricarboxylic acid cycle, was the major mechanism, and the CaCO3 yield was related to the amount of CO2 produced by the metabolism of organic acids. These findings will deepen the knowledge of the mineralization capacity of S. cerevisiae and provide a theoretical basis for the future application of yeast as an alternative microorganism in MICP.

Bio-hydrogen-producing Potential Evaluation and Capacity Enhancement from Tobacco Processing Leftovers by Photo-fermentation Under Diverse Initial pH.

The use of tobacco growing and processing residues for bio-hydrogen production is an effective exploration to broaden the source of bio-hydrogen production raw materials and realize waste recycling. In this study, bio-hydrogen-producing potential was evaluated and the effect of diverse initial pH on hydrogen production performance was investigated. The cumulative hydrogen yield (CHY) and the properties of fermentation liquid were monitored. The modified Gompertz model was adopted to analyze the kinetic characteristics of photo-fermentation bio-hydrogen production process. Results showed that CHY increased firstly and then decreased with the increase of initial pH. Highest CHY and hydrogen production rate of appeared at the initial pH of 8, which were 257.7 mL and 6.15 mL/h, respectively. The acidic initial pH was found to severely limit the bio-hydrogen production capacity. The correlation coefficients (R2) of hydrogen production kinetics parameters were all greater than 0.99, meaning that the fitting effect was good. The main metabolites of bacteria in the system were acetic acid, butyric acid, and ethanol, and the consumption of acetic acid was promoted with the increase of initial pH.

Development of chitosan-magnetic sawdust hydrochar for Pb and Zn immobilization process on various soil conditions.

A series of 60-day soil immobilized incubations were performed to explore the impacts of various factors (incubation time, chitosan modified magnetic sawdust hydrochar (CMSH) dosages, initial pH values, moisture contents, and humic acid (HA)) on CMSH immobilization of Pb and Zn. DTPA and BCR extraction techniques were undertaken to study the distribution of form transformations of Pb and Zn. CMSH showed significant immobilization ability for both DTPA-Pb and DTPA-Zn, and the highest removal rates were shown to be 57.40% and 90.00% for Pb and Zn respectively. After 60 days of incubation, the residual Pb was enhanced by 34-61% and residual Zn increased by 25-41%, which indicated that CMSH was effective in immobilizing Pb and Zn. Meanwhile, the immobilization efficiency improved with increasing incubation time, CMSH dosage, HA dosage, and initial solution pH. In particular, 5% HA application increased the soil TOC and accelerated the metal stabilization processes, with the residual forms of Pb and Zn eventually reaching a maximum of 73% and 71%, respectively. In addition, the alkaline initial solution promoted the ion exchange, surface complexation reaction, and cationic-π interaction, resulting in a better immobilization of Pb and Zn by CMSH. Finally, according to the orthogonal analysis of BCR results, HA dosage was the major factor affecting Pb and Zn immobilization by CMSH compared to soil pH and moisture content in this study.

Initial pH-driven production of volatile fatty acid from hybrid Pennisetum.

In this work, the impact of initial pH on the production of volatile fatty acids (VFAs) of hybrid Pennisetum was investigated. The batch experiments were conducted under six distinct beginning pH at a mesophilic temperature. Initial pH had an obvious effect on VFA yield and composition, and severe alkaline circumstances (pHin = 11.0) could boost VFA production and acetic acid selectivity. The highest VFAs yield and acetate proportion were obtained when the initial pH was 11.0, with 518 ± 29 mg g-1VS and 92%. Furthermore, microbial community analysis showed that alkaliphilic acetogenic anaerobe such as Amphibacillus, Tissierella, and Natronincola were the dominant species when the initial pH was 11.0. The Amphibacillus is the main hydrolysis bacterium under these conditions because of its high ability for xylan degradation at pH 9.0-10.0. Because of the increased VFA yield and superior acetic acid selectivity, the results suggest that adjusting the initial pH to 11.0 in batch mode would be possible for scaling-up purposes.

Experimental study on optimization of initial pH for photo-fermentation bio-hydrogen under different enzymatic hydrolysis of chlorella vulgaris.

In the paper, Use Chlorella as raw material, HAU-M1 Photosynthetic bacteria (PSB) as hydrogen-producing bacteria, the influence of initial pH on bio-hydrogen by photosynthetic organisms from Chlorella vulgaris with diverse enzyme addition was studied. The results showed that when using cellulase as hydrolase, the optimum initial pH was 7.0 and highest bio-hydrogen was 25.99 mL/g dry cell weight. Using neutral protease as hydrolase, the optimum initial pH was 8.0 and highest bio-hydrogen was 16.47 mL/g dry cell weight. Using mixed enzyme of cellulase and protease as hydrolase, the optimal initial pH was 7.0 and highest bio-hydrogen was 27.43 mL/g dry cell weight. The bio-hydrogen from Chlorella after mixed enzymatic hydrolysis is better than that of single enzymatic hydrolysis, we think the mixed enzymatic hydrolysis of cellulase and protease was superior to the single enzymatic hydrolysis of the two enzymes, which provides a scientific reference and low-cost bio-hydrogen technology by microalgae.

Effects of pH on the Properties of Membrane Vesicles Including Glucosyltransferase in Streptococcus mutans.

Streptococcus mutans releases membrane vesicles (MVs) and induces MV-dependent biofilm formation. Glucosyltransferases (Gtfs) are bound to MVs and contribute to the adhesion and glucans-dependent biofilm formation of early adherent bacteria on the tooth surface. The biofilm formation of S. mutans may be controlled depending on whether the initial pH tends to be acidic or alkaline. In this study, the characteristics and effects of MVs extracted from various conditions {(initial pH 6.0 and 8.0 media prepared with lactic acid (LA) and acetic acid (AA), and with NaOH (NO), respectively)} on the biofilm formation of S. mutans and early adherent bacteria were investigated. The quantitative changes in glucans between primary pH 6.0 and 8.0 conditions were observed, associated with different activities affecting MV-dependent biofilm formation. The decreased amount of Gtfs on MVs under the initial pH 6.0 conditions strongly guided low levels of MV-dependent biofilm formation. However, in the initial pH 6.0 and 8.0 solutions prepared with AA and NO, the MVs in the biofilm appeared to be formed by the expression of glucans and/or extracellular DNA. These results suggest that the environmental pH conditions established by acid and alkaline factors determine the differences in the local pathogenic activities of biofilm development in the oral cavity.

Effect of Organic Substances on Nutrients Recovery by Struvite Electrochemical Precipitation from Synthetic Anaerobically Treated Swine Wastewater.

Anaerobically treated swine wastewater contains large amounts of orthophosphate phosphorus, ammonium nitrogen and organic substances with potential nutrients recovery via struvite electrochemical precipitation post-treatment. Lab-scale batch experiments were systematically conducted in this study to investigate the effects of initial pH, current density, organic substances upon nutrients removal, and precipitates quality (characterized by X-ray diffraction, scanning electron microscopy and element analysis via acid dissolution method) during the struvite electrochemical precipitation process. The optimal conditions for the initial pH of 7.0 and current density of 4 mA/cm2 favoured nutrients removal and precipitates quality (struvite purity of up to 94.2%) in the absence of organic substances. By contrast, a more adverse effect on nutrients removal, morphology and purity of precipitates was found by humic acid than by sodium alginate and bovine albumin in the individual presence of organic substances. Low concentration combination of bovine albumin, sodium alginate, and humic acid showed antagonistic inhibition effects, whereas a high concentration combination showed the accelerating inhibition effects. Initial pH adjustment from 7 to 8 could effectively mitigate the adverse effects on struvite electrochemical precipitation under high concentration combined with organic substances (500 mg/L bovine albumin, 500 mg/L sodium alginate, and 1500 mg/L humic acid); this may help improve struvite electrochemical precipitation technology in practical application for nutrients recovery from anaerobically treated swine wastewater.

Enhancement of the biohydrogen production performance from mixed substrate by photo-fermentation: Effects of initial pH and inoculation volume ratio.

Co-digestion of substrates can improve hydrogen yield (HY) by adjusting carbon nitrogen ratio (C/N) of fermentation substrates. This study evaluated the enhancement of hydrogen production from co-digestion of duckweed and corn straw via photo-fermentation. The maximum HY of 78.0 mL/g Total solid (TS) was obtained from the mixed ratio of 5:1 (C/N of 13.2), which was 25.4% and 29.6% higher than those of single substrate of duckweed and corn straw, respectively. The effects of initial pH and inoculation volume ratio (IVR) on co-digestion photo-fermentative hydrogen production (CD-PFHP) from duckweed and corn straw were further studied. A maximum HY of 85.6 mL/g TS was achieved under the optimal condition (initial pH 8, IVR 20%, mix ratio of duckweed and corn straw of 5:1). Additionally, both mix ratio and initial pH showed statistical difference (p < 0.05). Acetic acid and butyric acid were found to be the main metabolic by-products during CD-PFHP.

Effects of different initial pH values on freeze-drying resistance of Lactiplantibacillus plantarum LIP-1 based on transcriptomics and proteomics.

The growth and the resistance to adverse environments of lactic acid bacteria would be affected by adjusting the initial pH of the medium. In order to explore the effect of changing the initial pH of culture medium on the freeze-drying survival rate of the Lactiplantibacillus plantarum LIP-1, the effect of initial pH on cell membrane fatty acid composition and key enzyme activity were mainly determined, and the internal mechanism was studied by transcriptomics and proteomics methods. We found that compared with initial pH 7.4 group, initial pH 6.8 group could improve the freeze-drying survival rate of the L. plantarum LIP-1. It was possibly due to the lactate dehydrogenase (LDH) was upregulated in the initial pH6.8 group, which led to a rapid decrease in culture pH. To reduce the inhibitory effect of long-term acid environment on growth, the strain upregulated the expression of fatty acid synthesis-related genes and proteins, promoted the relative content of cyclopropane and unsaturated fatty acids, improved integrity of the cell membranes. The adjustment of fatty acid composition maintained the integrity of the cell membrane in a freeze-drying environment to improve the freeze-drying survival rate of the initial pH6.8 group. In addition, the long-term acid environment stimulated a cross-stress tolerance mechanism that significantly upregulated the expression of a cold stress protein. The results indicated that the optimal initial pH of the medium could improve the ability of L. plantarum LIP-1 to resist freeze-drying.

Stepwise alkaline treatment coupled with ammonia stripping to enhance short-chain fatty acids production from waste activated sludge.

To recover resource from waste activated sludge (WAS) is of great significance. This study proposed a promising way, i.e., stepwise alkaline treatment coupled with ammonia stripping, to remarkably enhance short-chain fatty acids (SCFAs) production from WAS anaerobic digestion. The maximal production of SCFAs, with the value of 323 mg COD/g volatile suspended solid, was obtained with first initial pH = 10 adjustment followed by second initial pH = 10 adjustment on third day coupled with ammonia stripping. Mechanistic studies showed that solubilization of both extracellular polymeric substances and cells could be accelerated by stepwise initial pH = 10 adjustment. However, without ammonia stripping, the activities of either acidogens or methanogens could be inhibited by free ammonia formed under alkaline conditions; positively, anaerobes related to SCFAs production were enriched with ammonia stripping. Moreover, the proposed strategy can simultaneously achieve nitrogen and carbon recovery, providing some solutions for the carbon-neutral operation of wastewater treatment plants.

Enhancement of pH values stability and photo-fermentation biohydrogen production by phosphate buffer.

The main aim of this study was to investigate the effects of the initial pH values of the buffer on photo-fermentation biohydrogen production. Hydrogen production and the kinetics of it under different initial pH values were analyzed. Effects of initial pH values on reducing sugar consumption, hydrogen production rate, and byproduct production were evaluated at initial pH values of 5-7. The results showed that initial pH values of phosphate buffer had a significant effect on biohydrogen production via photo-fermentation. With the initial pH value of phosphate buffer at 6.0, the cumulative hydrogen production reached its maximum, 569.6 mL. The maximum hydrogen production rate was 23.96 mL/h at the initial pH value of 6.5. With the initial pH values at 5.0 and 7.5, the maximum hydrogen production rates were becoming lower, only 5.59 mL/h and 5.42 mL/h, respectively. And with the increase in pH values, the peak period of hydrogen production was gradually delayed, indicating that the alkaline environment had a negative effect on the ability of photosynthetic bacteria. This study revealed the influence of phosphate buffer initial pH values on the biohydrogen production via photo-fermentation and aimed to provide a scientific reference for further improving the theory and technology for biohydrogen production from biomass.