High pH Buffering Capacity Research Articles

Porous geopolymer spheres as novel pH buffering materials

The production of biogas from anaerobic digestion is emerging as an alternative to fossil fuels due to its lower carbon footprint. However problems such as low methane yield and process instability arise when using low pH waste streams, hindering the technology widespread. In this study, porous metakaolin-based and biomass fly ash-based geopolymer spheres were produced using a simple and low cost technology. Afterwards, the pH buffer capacity of the produced spheres was evaluated. Results demonstrate that the geopolymers alkalis leaching can be controlled by the content of fly ash in the geopolymers, higher content promoting greater leaching. The fly ash-based spheres showed superior pH buffer capacity than their metakaolin-based counterparts, with a narrow pH fluctuation (1.6–1.9) over the 30 days measurements. The maximum leaching of hydroxyl ions from the geopolymer spheres (0.0317 mol/dm3 g) demonstrates the high pH buffer capacity of this innovative material, suggesting their use as pH regulator in anaerobic digestion.

Novel porous fly ash-containing geopolymers for pH buffering applications

In this work novel, porous biomass fly ash-containing geopolymers with high pH buffer capacity and tailored alkalis leaching were produced by using hydrogen peroxide as blowing agent. Results demonstrate that the geopolymers leaching rate can be controlled by the hydrogen peroxide content and by the solids-to-liquid ratio during geopolymers preparation. Total leaching of hydroxyl ions from the porous geopolymers ranged between 0.0104 and 0.0180 mol/(dm3 g). Higher solids-to-liquid ratios promoted a gentler alkalis leaching from the geopolymers, while higher porosities shifted the initial pH towards higher values without compromising their buffering ability.The excellent ability to control pH over time shown by these novel geopolymers demonstrates their potential as pH regulators in applications where high buffer capacity is required. Furthermore the reuse of biomass fly ash in these innovative materials reduces the environmental footprint associated with this waste disposal.

Evaluation of heavy metal leaching from coal ash-versus conventional concrete monoliths and debris

Application of coal ash in construction materials is constrained by the potential risk of heavy metal leaching. Limited information is available on the comparative heavy metal leaching from coal ash-versus conventional concrete. The current study compared total and leached heavy metal concentrations in unbound coal ash, cement and sand; and investigated the effect of initial leachant pH on heavy metal leaching from coal-ash versus conventional concrete monoliths and their debris. Total Pb, Mn and Zn in coal ash were lower than or similar to that of other materials, while Cu and Fe showed the opposite trend. Leached concentrations of Zn, Pb, Mn, Cu and Fe in unbound coal ash, its concrete and debris were comparable and in some cases even lower than that for conventional concrete. In all cases, leached concentrations accounted for just <1% of the total concentrations. Log–log plots of concentration and cumulative release of Fe versus time based on tank leaching data showed that leaching was dominated by diffusion. Overall, the risk of Zn, Pb, Mn, Cu and Fe leaching from coal ash and its concrete was minimal and comparable to that of conventional concrete, a finding in contrast to widely held public perceptions and earlier results reported in other regions such as India. In the current study the coal ash, and its concrete and debris had highly alkaline pH indicative of high acid neutralizing and pH buffering capacity, which account for the stabilization of Zn, Pb, Mn, Cu and Fe. Based on the low risk of Zn, Pb, Mn, Cu and Fe leaching from the coal ash imply that such coal ash can be incorporated in construction materials such as concrete without adverse impacts on public and environmental health from these constituents.

Biohydrogen Production by Co-Fermentation of Starch Wastewater and Sludge under Thermophilic Condition

In this paper, the possibility and potential of biohydrogen production by co-fermentation of starch wastewater (SW) and WAS under thermophilic temperature was studied in batch fermentation tests. WAS was first pretreated by thermophilic enzyme together with low intensity ultrasound (LIU) to improve the biochemical degradability. Then After 8 h pretreatment, all soluble substances were much higher than raw sludge without pretreatment. In addition, the SCOD, carbohydrate and protein of the tests which were accelerated by low-frequency ultrasound were 11.5% 18.4%, 17.8% higher than the control, respectively. Results from the co-fermentation further demonstrated that the sludge had high pH buffering capacity. A mixing ratio of 1:1 was found to be the best among of all co-fermentation tests. Moreover it was proved in this study that hydrogen production by co-fermentation of starch wastewater and sludge was a promising technology to recovery energy from the waste.

DEGRADABLE POLYETHYLENIMINE DERIVATIVES AS GENE CARRIERS

Gene therapy is a treatment for inborn and acquired diseases, although the development of safe and effective gene delivery system is a great challenge to make a gene therapy a success. Viral vectors have been used in a majority of clinics because of their high transfection efficiency in vitro and in vivo. However, their use has been limited because of several drawbacks, such as induction of immune response, recombination of wild-type viruses, limitation in the size of inserted gene, and difficulty in large-scale production. Nonviral vectors have been widely proposed safe alternatives to viral vectors because they have low immunogenicity, flexibility in the size of gene to be delivered, cell targetibility, and easy scalability of production, although they have low transfection efficiency compared to viral vectors. Among nonviral vectors, polyethylenimine (PEI) has been widely used as a standard gene carriers due to its high pH-buffering capacity for endosomal escape although high-molecular-weight PEI is too toxic owing to non-degradability. Recently, many types of degradable PEI have been studied due to high transfection efficiency with lower cytotoxicity. This review explains recent progress on the development of degradable PEIs as nonviral vectors. The present paper summarizes the transfection efficiency of DNA or silencing efficiency of small interfering RNA (siRNA) based on the kinds of degradable linkage between low PEI and crosslinkers. Degradable linkages, such as ester, disulfide, imines, carbamate, amide and ketal in the degradable PEIs are covered.

Pollutant release from a disturbed urban snowpack in northern Sweden

Water and pollutant release from a disturbed urban snowpack was studied in an experimental plot encompassing a road section and the adjacent grassed boulevard in the city of Luleå, in northern Sweden. Winter road maintenance in this area includes snow ploughing and applications of grit without any road salts. During the study period, 18 snowmelt events were observed. Compared to rural areas and urban areas with extensive use of chloride in winter road maintenance, in the former case, the observed snowmelt quality differed by relatively high and uniform pH (7.7–8.1) and, in the latter case, by low chloride event-mean-concentrations (EMCs) (5.7–123.4 mg/L) and conductivity (11.6–60.7 mS/m). Total suspended solids (TSS) EMCs greatly exceeded those reported for rural snowmelt and urban rainfall runoff and contributed to the high pH buffering capacity of deposited snow. Observed concentrations of total and dissolved heavy metals were compared to water quality guidelines that suggested a high likelihood of biological effects. Chloride was the only pollutant that indicated an early release and all other constituents showed a uniform release with snowmelt from the snowpack. The partitioning of heavy metals between total and dissolved phases indicated the highest dissolved fractions for Cu, followed by Cd, Ni and Zn, and the lowest values were observed for Pb. The urban snowmelt characteristics substantially differed from those reported for undisturbed sites with respect to higher pollutant loads, high pH buffering capacity and a general absence of early or delayed pollutant release from the snowpack.

Efficiency of Commercial Agricultural-Grade Limestone

The University of Georgia (GA) lime recommendation equation includes a multiplier of 1.5 to account for agricultural (ag) lime that is less reactive than reagent-grade calcium carbonate (CaCO3). Research has not been conducted with ag lime to arrive at this multiplier with GA soils typical of the coastal plain or with ag limes available in GA. These ag limes may differ in their reactivity from others tested previously. The efficiency of five dolomitic ag limes were compared to reagent-grade CaCO3 on two GA soils with different pH-buffering capacities. Reactions other than acid neutralization by lime affected pH, especially in the soil with low pH-buffering capacity. Results from the soil with high pH-buffering capacity yielded multipliers of 1.17, 1.16, 1.48, 1.34, and 1.73 for ag limes 1 through 5, respectively, with an average multiplier of 1.38. Based on these results, continued use of a multiplier of 1.5 is appropriate.

Biogeochemical processes in a clay formation in situ experiment: Part G – Key interpretations and conclusions. Implications for repository safety

Abstract The in situ porewater chemistry (PC) experiment carried out in the Opalinus Clay formation at the Mont Terri Rock Laboratory, Switzerland for a period of 5 a allowed the identification and quantification of the biogeochemical processes resulting from and affected by an anaerobic microbial disturbance. The unintentional release of degradable organic compounds (mainly glycerol) induced microbially-mediated SO4 reduction in the borehole with concomitant significant geochemical changes in the circulating water and the adjacent porewater. These changes included a decrease in SO 4 2 - concentration and pH and an increase in pCO2 and alkalinity relative to the non-affected formation water. However, the cation composition of the water and the mineralogy of the clay close to the borehole wall showed very little change. This is explained by (1) the strong chemical buffering processes in the clay and (2) by the diffusion-limited flux of solutes. With the aid of a reactive transport model with a minimum set of kinetic parameters for the hypothesised degradation reactions, the evolution of solutes in the borehole could be modelled adequately. The model was also applied to the prediction of restoration times upon depletion of the C source and results indicated restoration times to undisturbed conditions of about 15 a, but also highlighted the rather large uncertainties inherent in the geochemical model. Nevertheless, the simulations provided additional evidence of the high pH buffer capacity of the Opalinus Clay. The results from the microbiological investigations do not allow unambiguous identification of the origin of the microbial population in the borehole. Possible sources were the drilling procedure, the artificial porewater, and perhaps some revival of indigenous dormant strains. Regardless of the origin of the microbes, the results from the PC experiment underlined the importance of anaerobic microbial activity in the “disturbed” Opalinus Clay, facilitated by the introduction of space, water and organic material, in rapidly establishing very reducing conditions. The PC experiment also yielded valuable insight with regard to the safety of a high-level radioactive waste repository emplaced in Opalinus Clay. Anaerobic microbial perturbations in the clay host rock may occur from the construction and excavation procedures and emplaced organic by-products. The resulting effects on porewater chemistry, i.e., especially on pH and Eh, may affect the mobility of radionuclides eventually released from the waste. However, the overall results of the PC experiment suggest that such effects are temporary and spatially limited because of the large buffering capacity and diffusive properties of the clay formation. Nevertheless, the results also indicate that the amounts of organic materials in a high-level waste repository should be kept small in order to achieve background conditions within a short time period after repository closure. A further conclusion from the PC experiment is that commonly used equipment materials may not display commonly assumed inert behaviour. This particularly holds for the gel-type “robust” reference electrodes, which may release substantial amounts of glycerol.

Polymeric Micelles Comprising Stearic Acid-Grafted Polyethyleneimine as Nonviral Gene Carriers

Non-viral vectors composed of biodegradable polymers or lipids have been considered as a safer alternative for gene carriers over viral vectors. Among some of the cationic polymers, polyethyleneimine (PEI) possess high pH-buffering capacity that can provide protection to nucleotides from acidic degradation and promotes endosomal and lysosomal release. However, it has been reported that cytotoxicity of PEI depends on the molecular weight of the polymer. Hence modifications of PEI structure for clinical application have been developed in order to reduce the cytotoxicity, or improve the insufficient transfection efficiency of lower molecular weight PEI. In this study, 10 k PEI was modified by grafting stearic acid (SA) and formulated to polymer micelles with positive surface charge and evaluated for pDNA delivery. The amine group on PEI was crosslinked with the carboxylic group of stearic acid by 1-ethyl-3-(3-dimethylamino-propyl) carbodiimide (EDC) as linker. PEI-SA micelles were then prepared using oil in water (o/w) solvent evaporation method. The success of PEI-SA conjugation structure was confirmed with 1H NMR. The average diameter and zeta potential determined by photon correlation spectroscopy was 149.6 +/- 1.2 nm and 64.1 +/- 1.5 mV, respectively. These self-assemble positive charge micelles showed effective binding to pDNA for transfection. PEI-SA micelles exhibited lower cytotoxicity compared to that of PEI only, while flow cytometry analysis revealed PEI-SA/pEGFP complex provided 62% high EGFP expression. Luciferase activity also showed high transfection efficiency of PEI-SA micelles for weight ratio above 4.5 that was comparable to PEI only. These results demonstrated that stearic acid grafted PEI micelles can provide high transfection efficiency comparable to unmodified PEI, and exhibit low cytotoxicity. Stearic acid grafted PEI micelles can be promising polymer carriers in genetic therapy.

Secondary processes determining the pH of alkaline waters in crystalline rock systems

The understanding of the main hydrogeochemical processes controlling the features and behaviour of crystalline rock environments considered for the deep geological storage of spent nuclear fuel is a key issue for the improvement of our knowledge and management of these systems and for a more accurate prediction of their future evolution. In this paper, some of the most important irreversible processes (cooling, mixing and CO 2 exchange) are studied and their effects quantified by combining classical geochemical calculations and geochemical modelling. This methodology is applied to an alkaline thermal water system developed in crystalline rocks (the Caldas de Boí groundwater system, NE Spain) analogous to the deep geological environments expected for nuclear waste storage. One of the most remarkable results obtained in this study is related to the high pH-buffering capacity exhibited by these alkaline-thermal waters during the mixing processes, with colder and shallower waters, taking place during the uprising of the hot waters from the deep reservoir. Even for high mixing proportions of cold water (up to 60%), the final pH remains as alkaline as in the thermal and deep end member, although the rest of the physicochemical parameters (including temperature) change consistently with mixing. Another important secondary pH-determining process detected in this study is the conductive cooling of the thermal waters suffered during their rise to surface conditions, which is clearly responsible for a pH increase which enhances the typical alkaline character of these waters. Finally, the existence of external inputs of edaphic or biogenic CO 2 to the groundwater system, producing a pH decrease in some of the springs, has been proven to play a key role in their behaviour and evolution.

EDTA modified LDHs as Cu 2+ scavengers: Removal kinetics and sorbent stability

EDTA modified layered double hydroxides (LDHs) were investigated as potential sorbents to remediate heavy metals pollution. The polidentate ligand was introduced by an exchange method in a Zn–Al-LDH, which takes place with partial erosion of the layers, causing the intercalation of [Zn(EDTA)] 2− complex instead of the ligand. [Cu(H 2O) 6] 2+ cation was selected as a model cation to study the uptake mechanism, exploring the elimination kinetics from the first minutes up to the steady state. A flow injection analysis system coupled to an amperometric detector (FIA-AM) was applied to perform fast and reliable [Cu(H 2O) 6] 2+ determinations in monodisperse solid–aqueous solution systems. Furthermore, the sorbent stability was determined as a function of the pH and the nitrate concentration. The [Cu(H 2O) 6] 2+ elimination is produced by an exchange reaction with [Zn(EDTA)] 2− anions placed either in the solid interlayer or in the aqueous solution, this last being released from the sorbent. Additional [Cu(H 2O) 6] 2+ removal is produced by Cu(OH) 2 precipitation at high copper concentrations due to the LDHs high pH buffering capacity. The sorbent removes [Cu(H 2O) 6] 2+ with high affinity in a wide concentration range. The elimination process reaches equilibrium in less than 30 min and leaves metal cation concentrations lower than 0.05 ppm in the supernatants.

Enhanced anaerobic succinic acid production by Escherichia coli NZN111 aerobically grown on gluconeogenic carbon sources

Escherichia coli strain NZN111, a pflB and ldhA double mutant of E. coli W1485, is considered a candidate of succinic acid producer. However, it is reported that this strain fails to ferment glucose anaerobically. In this study, it was demonstrated that when a gluconeogenic carbon source was used to replace glucose in aerobic culture, the NZN111 cells restored the ability to ferment glucose in the subsequent anaerobic culture with succinic acid as the major product even though no further genetic manipulation had been carried out. Activities of enzymes including phosphoenolpyruvate (PEP) carboxykinase, PEP carboxylase, isocitrate lyase, malate dehydrogenase, malic enzyme, and pyruvate kinase in the NZN111 cells aerobically grown on different carbon sources were measured, and enhanced anaplerotic and oxaloacetate-reducing activities were revealed. Furthermore, supply of MgCO 3 or NaHCO 3 greatly improved succinate production by the malate-grown NZN111 cells. At the same time, pyruvic acid production was significantly reduced. When the malate-grown cells were anaerobically cultured in a salt medium with high pH buffering capacity, succinic acid was produced at a specific productivity of 308 mg/(g DCW h) with a molar yield of 1.31 mol succinic acid/mol glucose.

Sorption of selenium on Mg-Al and Mg-Al-Eu layered double hydroxides

Abstract Salt domes represent deep geological formations which are under consideration as final repositories for irradiated research reactor fuel elements. For long-term safety aspects the mobilisation of the radionuclides due to a water ingress is intensively investigated. At the Institute of Energy Research (IEF-6), leaching experiments were performed in a hot cell facility with UAl x -Al and U3Si2-Al dispersed research reactor fuel elements in repository-relevant MgCl2-rich salt brines under anaerobic conditions. The fuel plates corroded completely within one year and a Mg-Al-layered double hydroxide (LDH) with chloride as interlayer anion was identified as one crystalline phase component of the corrosion products (secondary phases). This Mg-Al-LDH was synthesized, characterized, and the ability to retard europium by an incorporation process was investigated. Europium, as a representative for lanthanides, was identified to be one of the radionuclides which were found in the corrosion products. We could show that europium was incorporated in the lattice structure. LDHs have high anion exchange capacities that enhance their potential to remove anionic contaminants from aqueous systems. In this work the sorption behaviour of selenium in the chemical form as selenite (SeO3 2−) on Mg-Al-LDH and on Mg-Al-Eu-LDH was investigated. Especially the influence of the larger europium-III ion was of interest. It represents in the Mg-Al-Eu-LDH about 10% of the molar aluminium amount. The sorption has been experimentally studied in a wide range of pH, ionic strength, radionuclide and sorbent concentration. Both LDHs with chloride as interlayer anion were synthesized by a coprecipitation method under controlled conditions, and their main physico-chemical properties were analyzed prior to the sorption experiments. The sorption kinetics of selenite on the LDHs in water and in MgCl2-rich brine were rapid using a LDH concentration of 10 g/L. Equilibrium, indicated by stable pH values, was obtained within 5 h for an initial selenite concentration of 4.28×10−13 mol/L. Selenite in water sorbed quantitatively on both LDHs. In MgCl2-rich brine a different behaviour to water was observed. The sorption was not quantitatively, due to the presence of high amounts of chloride anions. Chloride, as competing anion, affected the sorption behaviour of selenite. Using a LDH concentration of 0.1 g/L, the sorption of selenite was negligible. The effect of pH on selenite sorption was investigated, too. The sorption was relatively constant when the initial pH values were adjusted between 4 and 8, because both LDHs exhibit a high pH buffering capacity. For a selenite concentration range between 5.43×10−14 and 3.24×10−12 mol/L sorption isotherms were obtained and the data could be fitted to Freundlich and Dubinin–Radushkevich equations. The sorption capacities of the LDHs and the energies of sorption were determined. The sorption of selenite occurred via an ion exchange mechanism and the sorption behaviour was similar for both LDHs.

Geochemical assessment of metal transport in glacial till during electrokinetic remediation

This paper presents the chemical speciation and retention behavior of chromium (Cr), nickel (Ni), and cadmium (Cd) prior to and after the electrokinetic remediation in glacial till soil. The speciation of the metals was predicted using the chemical speciation program MINEQL(+). The simulations were performed for single-contaminant with only Cr(VI) or Ni, and multi-contaminants consisting of: (1) Cr(VI), Ni, and Cd; (2) Cr(III), Ni and Cd; (3) Cr(VI), Cr(III), Ni and Cd; (4) Cr(VI), Ni, and Cd with reducing agents; and (5) Cr(III), Ni, and Cd with oxidizing agent (Mn). The results showed that the speciation and distribution of cationic metals [Ni, Cd, and Cr(III)] in glacial till soil remain unaffected or slightly affected during electrokinetics. This is attributed to the high pH buffering capacity of the glacial till, leading the metals to precipitate in the soil prior to and after electrokinetics. This study showed that during electrokinetics, Cr(VI) existed as anionic complex and migrated towards the anode and the migration is maximum in case of a single-contaminant system. The study also showed that near the anode in the absence of any reducing and oxidizing agent, Cr(VI) mostly adsorbed, and some of Cr(VI) reduced to Cr(III) and migrated towards the cathode and finally precipitated due to high pH conditions. Ni and Cd remain adsorbed or precipitated due to the high pH conditions throughout the soil. Among the reducing agents, the sulfide had significant effect on the migration of metals compared to ferrous ions. While in the presence of oxidizing agent (Mn), no noticeable Cr(VI) was found in the soil sample indicating the reduction of Cr(VI) to Cr(III) and the predominance of reducing conditions due to the presence of naturally occurring iron in the glacial till soil. Overall, this study provides a reasonable explanation of the speciation and distribution of chromium, nickel and cadmium during the electrokinetic remediation of glacial till soil.

Effect of clay mineralogy on the feasibility of electrokinetic soil decontamination technology

To evaluate the effect of clay mineralogy on the feasibility of electrokinetic soil remediation technology, we contaminated six soils with Cu(II), Zn(II) and Pb(II) and performed electroremediation for 570 h. Cation exchange resin saturated with H + was placed between soil and cathode to prevent soil alkalinization and trap the migrated heavy metal cations. After the treatment, the heavy metal cations were sequentially extracted with water, 1 M MgCl 2 and hot 6 M HCl. In soils dominated by crystalline clay minerals, Cu(II) and Zn(II) significantly migrated from anode end and accumulated at the cathode end forming sparingly soluble hydroxides. Removal rates of Cu(II) and Zn(II) were highest in a soil dominated with kaolinite and crystalline hematite. In humic–allophanic and allophanic soils, the high pH-buffering capacity of allophane kept the soil pH above 5, even at the anode end, and Cu(II) and Zn(II) did not migrate significantly. In all soils, the migration of Pb(II) was infinitesimal due to the formation of insoluble PbSO 4 and very strong surface complexation at the mineral surfaces. These results show that the reactivity of component clay minerals to H + and heavy metal cations has a crucial effect on the efficiency of the electrokinetic remediation technology and it is not effective for remediation of allophanic soils. The results also indicate that allophanic soils may be useful as a barrier material in landfill sites.

Changes in pH and organic carbon were minimal in a long-term field study in the Western District of Victoria

Changes in soil pH from a long-term experiment at Hamilton, Vic., associated with time, fertiliser application, and stocking rate were assessed. The pH was measured in a 1 :5 suspension of soil in water (pHW) from 1980 onwards and in a 1:5 suspension of soil in 0.01 M CaCl2 (pHCa) from 1984 onwards. Topsoils (0–10 cm) were sampled regularly from 1980 to 1999, and the soil profile to a depth of 80 cm in 1994. The site was sown to perennial ryegrass, phalaris, and subterranean clover in 1977. Treatments fertilised with different amounts of superphosphate were grazed by sheep at stocking rates of 7–19 dry sheep equivalents (DSE)/ha. Average applications of phosphorus (P) ranged from 0.5 to 38.7 kg P/ha.year. The pHCa of the topsoil in 1984 was 4.9. It decreased at an average rate of 0.005 pHCa or 0.008 pHW units/year, with little variation due to fertiliser or stocking rate. Measurements in 1994 revealed subtle but statistically significant (P &lt; 0.01) trends in soil pHCa that were associated with grazing pressure, inputs of fertiliser, and whether or not areas sampled were used by the sheep for camping. The top 0–5 cm of soil was slightly less acidic (+0.07 pHCa units) in the camp areas compared with non-camp areas. Below 5 cm to a depth of 80 cm, camp areas were more acidic (–0.19 pHCa units). At the highest stocking rates, heavier applications of superphosphate were associated with greater subsoil acidity: –0.06 pHCa units per 100 kg phosphorus (P) applied. There was no relationship at medium stocking rates. At low stocking rates, higher P applications were associated with more alkaline subsoils. Net removal of product from 1979 to 1994 (wool and meat removed from plots and excreta transferred to camps) was estimated to be equivalent to 140–380 kg/ha of lime over this 15-year period. The organic carbon (OC) content of the topsoil did not change over 20 years of records from 1979, and was unaffected by inputs of P. In 1994, the OC content of the 0–5 cm layer of topsoil was greater than the 5–10 cm layer (mean values 5.5% and 3.8% respectively; P &lt; 0.001). The OC content of camp areas was higher than that of non-camp areas, this difference being more pronounced in the 0–5 cm layer (P &lt; 0.01). It was concluded that the rate of change of pH was slow because of the high pH buffering capacity of the soil, the small amount of alkalinity removed in product, and the generally high perennial grass content of the pastures. Soils shown to be at greatest risk of acidification from this study were those under camp areas, and where high fertiliser rates were applied to pastures with a low perennial grass content. Rotational grazing should diminish these problems by reducing the concentration of excreta in camp areas, and favouring perennials over annuals in both camp and non-camp areas. Inputs of lime may eventually be needed to compensate for the acidifying effect of product removal.

Determining the net flux of charge released by maize roots by directly measuring variations of the alkalinity in the nutrient solution

The net flux of charge released by maize, i.e. the strong ion exchange balance between the roots and their environment, was determined in acidic and alkaline solutions, i.e. solutions with a low and a high pH buffering capacity, respectively. The work was based on direct measurement of total alkalinity in culture solutions over a period of several days.

Distribution and change of microbial activity in combined UASB and AFB reactors for wastewater treatment

A thermophilic upflow anaerobic sludge blanket (UASB) reactor was combined with a mesophilic aerobic fluidized bed (AFB) reactor for treatment of a medium strength wastewater with 2,700 mg COD l−1. The COD removal efficiency reached 75% with a removal rate of 0.2 g COD l−1 h−1 at an overall hydraulic retention time 14 hours. The distribution of microbial activity and its change with hydraulic retention time in the two reactors were investigated by measuring ATP concentration in the reactors and specific ATP content of the biomass. In the UASB reactor, the difference in specific ATP was significant between the sludge bed and blanket solution (0.02 mg ATP g VS−1 versus 0.85 mg ATP g VS−1) even though the ATP concentrations in these two zones were similar. A great pH gradient up to 4 was developed along the UASB reactor. Since a high ATP or biological activity in the blanket solution could only be maintained in a narrow pH range from 6.5 to 7.5, the sludge granules showed a high pH tolerance and buffering capacity up to pH 11. The suspended biomass in AFB reactor had a higher specific ATP than the biomass fixed in polyurethane carriers (1.6 mg ATP g VS−1 versus 1.1 mg ATP g VS−1), which implies a starvation status of the immobilized cells due to mass transfer limitation. The aerobes had to work under starvation conditions in this polishing reactor. The anaerobic biomass brought into AFB reactor contributed to an increase in suspended solids, but not the COD removal because of its fast deactivation under aerobic conditions. A second order kinetic model was proposed for ATP decline of the anaerobes. The results on distribution of microbial activity in the two reactors as well as its change with hydraulic retention time lead to further performance improvement of the combined anaerobic/aerobic reactor system.

The high intracellular ph buffering of hagfish ( Eptatretus cirrhatus) dental plate retractor muscle cannot be attributed to the known histidine-related compounds present in other vertebrates

1. 1. Intracellular pH buffering capacity of hagfish ( Eplatretus cirrhatus) dental plate retractor muscles is among the highest reported for any vertebrate muscle. 2. 2. Over 80% of the pH buffering capacity of hagfish retractor and myotome muscle is due to components other than proteins and phosphate. 3. 3. The muscles have less than 0.5 μmol/g wet weight of l-histidine, and lack l-l-methyl histidine, l-3-methyl histidine and the histidine-containing dipeptides anserine, carnosine and ophidine. 4. 4. Instead, they contain an unidentified low molecular weight acid-soluble compound to which the high pH buffering capacity can be attributed.

Continuous Pre‐Anoxic and Aerobic Digestion of Waste Activated Sludge

Conventional aerobic sludge stabilization requires extensive energy input. Incorporation of endogenous nitrate respiration (ENR) into the aerobic‐digestion system offers the energy‐saving advantage. In the ENR system, nitrate instead of oxygen is utilized for the biomass destruction. In this study, continuous preanoxic and aerobic digestion of waste‐activated sludge is studied to evaluate its effectiveness for volatile suspended solids (VSS) destruction and nitrogen removal. The ENR occurs in the anoxic digester because of the recycling of nitrate from the aerobic digester. The anoxic effluent, in turn, provides a high pH and adequate buffer capacity for enhancing the subsequent aerobic decay and nitrification. Two experimental runs, differing in hydraulic‐detention time in anoxic and aerobic tanks, are conducted with the same recycle rate. The results indicate that total nitrogen removal is approximately 25%, with 40% VSS destruction. The denitrification/nitrification efficiencies and rates are also determined. A mathematical model developed from the mass balance of biomass, ammonium, and nitrate reasonably predicts transient responses of these parameters.