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The hydration of graphene oxide (GO) membranes is the key to understand their remarkable selectivity in permeation of water molecules and humidity-dependent gas separation. We investigated the hydration of single GO layers as a function of humidity using scanning force microscopy, and we determined the single interlayer distance from the step height of a single GO layer on top of one or two GO layers. This interlayer distance grows gradually by approximately 1 Å upon a relative humidity (RH) increase in the range of 2 to ∼80%, and the immersion into liquid water increases the interlayer distance further by another 3 Å. The gradual expansion of the single interlayer distance is in good agreement with the averaged distance measured by X-ray diffraction on multilayered graphite oxides, which is commonly explained with an interstratification model. However, our experimental design excludes effects connected to interstratification. Instead we determine directly if insertion of water into GO occurs strictly by monolayers or the thickness of GO layers changes gradually. We find that hydration with up to 80% RH is a continuous process of incorporation of water molecules into single GO layers, while liquid water inserts as monolayers. The similarity of hydration for our bilayer and previously reported multilayered materials implies GO few and even bilayers to be suitable for selective water transport.

The feasibility of a bench-scale system for removal and recovery of phosphorus (P) as struvite from CO2-rich wastewater was tested. A continuous 12 L reactor system combining a fluidized seedbed and aeration for pH increase was developed and tested using synthetic feed. For a 100 mL min−1 influent rate, an aeration and recycle rate combination of 7 L min−1 and 700 mL min−1 was sufficient for increasing and maintaining the reactor pH from 6.7 to between 7.6 and 8.0. Significant P removal was achieved in 6 h runs without a seedbed (91–92%), while neither the struvite nor sand seedbeds improved P removal (91–96%). Struvite was recovered in all runs, with additional calcium (Ca) precipitation in the seedbed runs. Reactor operation was possible for an extended period of time, up to 46 h without any major adjustment during long-term run. The average P removal was 88%, and precipitate collected after 24 h was found to be mainly struvite, while the final precipitate had a Ca: total phosphorus molar ratio of 0.56 and also contained calcite. This study has demonstrated the technical feasibility of an aerated crystallization reactor system for chemical-free struvite removal and recovery from CO2-rich wastewater such as stored livestock manure.

The aim of this study was to achieve aerobic granulation utilizing fermented municipal wastewater under low pH, and alkalinity conditions. Stable granulation was achieved after a 166-day start-up period. Due to low influent strength, supplemental carbon addition, in the form of sucrose, was added to the feed storage tank on the 82nd day of start-up to facilitate granulation. This increased the system's organic loading rate from 1.43 ± 0.14 to 2.53 ± 0.18 kg COD/m(3)/d, and reduced the influent pH due to fermentation of the added sucrose. Although granulation was successful, the nutrient removal was limited. Removal rates at an influent pH of 6.23 ± 0.06 were 54.4% ± 8.3% for phosphorus, 21.9% ± 4.1% for ammonium, and 84.0% ± 3.0% for total chemical oxygen demand (COD). During the second phase of experimentation, increased amounts of sucrose were added to the feed, which resulted in increased volatile fatty acid concentrations and pH reduction to 5.62 ± 0.12 due to fermentation. Under further reduced pH conditions, phosphorus, ammonium, and total COD removal were found to be 58.9% ± 4.7%, 37.9% ± 4.7%, and 87.1% ± 0.9%, respectively. Settling volume indexes, SVI10 and SVI30, were found to be 148.8 ± 28.9 mL/g, for the influent pH of 6.23 ± 0.06, and 157.5 ± 40.6 mL/g, for the influent pH of 5.62 ± 0.12. This high SVI is indicative of the formation of lower-density granules in comparison to high-ash-content granules. The absence of denitrification-induced chemical phosphorus precipitation within the granule was likely a contributing factor to the low granule density observed in the system.

A hydrogenotrophic denitrification system, which consisted of a sequencing batch membrane bioreactor, was evaluated for removal of nitrate from a synthetic groundwater feed. A hollow fiber microporous membrane diffuser was used for bubble-less diffusion of hydrogen into the bioreactor, and a membrane filter was used for separating the biomass from treated water. The nitrate loading of 0.328 kg N m−3 d−1 was completely denitrified to below detectable levels; however, inorganic fouling of both membrane filter and diffuser occurred. The increase in pH during denitrification caused inorganic precipitation and clogging of the membranes. The foulant material was quantified as beta three calcium phosphate βCa3 (PO4)2.

A hydrogenotrophic denitrification system, comprising a suspended growth membrane bioreactor (MBR) with membrane hydrogen gas diffusion, was developed to remove nitrate from groundwater. A hollow fiber gas permeable membrane module was designed for hydrogen delivery and a commercially available hollow fiber membrane module was used for solid/liquid separation. The MBR was operated at an SRT of 20 days and at room temperature. Four nitrate loading rates of 24, 48, 96 and 192 NO3−-N mg l−1 d−1 were applied to the system. As the nitrate loading was raised, pH increased due to increased denitrification and release of OH− ions. The oxidation reduction potential (ORP) remained fairly stable when full denitrification was achieved, but increased when nitrate loading rates reached 192 NO3−-N mg l−1 d−1 and residual nitrate was present in the reactor. Nitrate removal was complete (100%) in the first three nitrate loadings and 72% in the system with 192 NO3−-N mg l−1 d−1. Nitrate utilization rates of 30.6, 23.4, and 37.7 g NO3−-N m−3 d−1 were achieved in the first three loadings. Average effluent dissolved organic carbon (DOC) concentration of approximately 8 mg l−1 was observed in all four nitrate loading regimes, possibly owing to the generation and release of soluble microbial bi-products (SMP).

A novel hydrogenotrophic denitrification system, which consisted of a sequencing batch membrane bioreactor, was evaluated for simultaneous removal of nitrate and soluble microbial products (SMP) from a synthetic groundwater feed. A hollow fiber membrane diffuser was used for bubble-less diffusion of hydrogen into the bioreactor under anoxic condition followed by aerobic SMP removal and biomass filtration. During the anoxic period, the nitrate loading of 0.328 kg N m−3 d−1 was completely denitrified to below detectable levels. A denitrification rate of 0.8 kg N m−3 d−1 was obtained at steady state biomass concentrations of 1,162 mg l−1. During the aerobic period when biomass filtration was performed, 81% of SMP produced within the anoxic phase was retained by the membrane, 9% was biologically removed, 5% was passed through the membrane and 5% was discharged during the wasting of mixed liquor. The aerobic cycle was instrumental as it allowed for effective biomass filtration via membrane scouring and assisted in further reduction of effluent organic matter.

Removal of phosphorus (P) from pig manure can be accomplished by struvite (MgNH 4 PO 4 ) precipitation but the use of liquid pig manure in most reactors is hindered by manure total solids (TS), low soluble P concentration and interfering ions such as calcium (Ca). In addition, the cost of typical alkali and magnesium (Mg) additions adds significantly to reactor operational costs. Anaerobic fermentation can increase acidity of liquid manures by increasing both VFA and carbonic acid content. This pre-treatment increases soluble P by dissolving P solids in the acid environment and also enables pH increase by air stripping CO 2 and carbonic acid. Manure solids separation technologies such as a centrifuge or rotary press produce a liquid stream with TS of Aeration rates were varied for different trials which affected pH increase and TP removal which averaged 32% PO 4 and 31% TP removal for 3 trials of 24 hrs each. Air stripping did not increase pH as much as expected, with an average increase of 0.25 pH units (range of 0.07 to 0.94 pH units). This was attributed to the buffering effect of manure alkalinity of 6 g/L and a VFA concentration of 8 g/L. This data is significant due to the significant TP reduction from a relatively small pH increase at low reactor pH conditions. Comparison of influent and effluent nutrient concentrations indicated a 1:1 molar reduction in Mg and P-PO 4 and the dried precipitate consisted of 85% pure struvite. Precipitate impurities were organic solids and not Ca, due to the precipitation point being low. Struvite crystals harvested from the reactor were up to 200 µm in size and no increase was found from longer reactor runs. Although TP removal was moderate, this system could be used as a second stage reduction of TP before land application. It is also apparent that struvite can form even though the manure influent is high in Ca due to the precipitation point being at a low pH. Small operational modifications such as settling tanks and dry precipitate screening would improve recovery and struvite purity.

This paper presents the operational strategy for nitrogen removal in a two-stage, partial nitrification (PN) process coupled with anaerobic ammonium oxidation (Anammox) process. The process was used to remove ammonium from centrate obtained from a full-scale, wastewater treatment plant in British Columbia, Canada. The PN, which was carried out in a sequencing batch reactor (SBR), successfully converted approximately 49.5 +/- 1.0% of ammonium to nitrite. The operation of SBR under higher dissolved oxygen in combination with slow feeding resulted in significant reduced HRT without nitrate accumulation. Partially nitrified centrate was further treated in Anammox reactors, where the mixture of ammonium and nitrite was converted mainly to nitrogen gas. Anammox treatment was carried out in two different types of Anammox reactors: a moving bed hybrid reactor and an up-flow fixed-bed biofilm reactor. The hybrid Anammox reactor removed an average of 55.8% of NH4-N, versus the 48.3% NH4-N removed in the up-flow fixed-bed reactor. Nitrite removal in the hybrid and up-flow fixed-bed Anammox reactors averaged 80.8% and 62.5%, respectively. This study also illustrated that in both Anammox reactors, better ammonium removal was achieved when the nitrite to ammonium ratio is between 1.35 and 1.45. As such, alkalinity was found to neither control nor limit the Anammox reaction.

Molecular adlayers on mica have been visualized previously by coating the sample with graphene and imaging it by scanning force microscopy. While it had been argued that this shows that ambient water on mica exhibits ice-like structures, recent apparently similar experiments indicate different behaviors. Here, we demonstrate that adhesive tapes, which are often used to mechanically exfoliate graphenes onto solid substrates, can lead to water-containing adlayers, which differ substantially from pure water layers. We exfoliated graphenes with the aid of different adhesive tapes and demonstrate that the results depend on the particular tape. Our results imply that structure and properties of confined water adlayers can be controlled by minor amounts of additives.

An anaerobic submerged membrane bioreactor was coupled with a novel hydrogen delivery system for hydrogenotrophic denitrification of municipal final effluent containing nitrate. The biological treatment unit and hydrogen delivery unit were proven successful in removing nitrate and delivering hydrogen, respectively. Complete hydrogen transfer resulted in reducing nitrate below detectable levels at a loading of 0.14 kg N m−3 d−1. The produced water met all drinking water guidelines except for color and organic carbon. However, the organic carbon was removed by 72% mostly by membrane rejection. To reduce the organic carbon and color of the effluent, post treatment of the produced water is required.

A general method for measurement of active biomass and decay coefficient and Extracellular polymeric substances (EPS) concentration in steady-state biomass was developed. The model was applied to the process of hydrogenotrophic denitrification in order to measure biomass constituents and decay and yield coefficients. It was found that steady-state biomass obtained after operation at 20 day solids retention time (SRT) was composed of 41% active biomass, 25.6% cell debris and 33.4% extracellular polymeric substance. The value of 0.041 d(-1), and 0.27 mg active biomass per mg NO3-N were obtained for decay coefficient and true yield, respectively.

Hydrogen-dependent denitrification has gained significant attention due to its potential economic advantage over heterotrophic denitrification. However, effective hydrogen delivery and biomass retention under anaerobic conditions are significant challenges to implementation of this process. An innovative hydrogenotrophic denitrification system, that addresses these challenges, consisting of an anaerobic submerged membrane bioreactor (MBR) and a novel hydrogen delivery unit, was evaluated for removal of nitrate from a synthetic groundwater feed. The hydrogen delivery unit was designed to release hydrogen-supersaturated water to the reactor and was efficient in hydrogen delivery, providing complete mass transfer. The anaerobic submerged MBR was successful in both reducing nitrate from 25 mg NO(3)-Nl(-1) to below detection and separating biomass from treated water to produce effluent free of suspended solids. Nitrogen gas produced during denitrification was internally recycled to effectively achieve membrane scouring and reactor mixing. The total organic carbon was similar to that of the incoming feed water, averaging approximately 6 mgl(-1).

It is important to determine the effect of changing environmental conditions on the microbial kinetics for design and modeling of biological treatment processes. In this research, the kinetics of nitrate and nitrite reduction by autotrophic hydrogen-dependent denitrifying bacteria and the possible role of acetogens were studied in two sequencing batch reactors (SBR) under varying pH and temperature conditions. A zero order kinetic model was proposed for nitrate and nitrite reduction and kinetic coefficients were obtained at two temperatures (25 +/- 1 and 12 +/- 1 degrees C), and pH ranging from 7 to 9.5. Nitrate and nitrite reduction was inhibited at pH of 7 at both temperatures of 12 +/- 1 and 25 +/- 1 degrees C. The optimum pH conditions for nitrate and nitrite reduction were 9.5 at 25 +/- 1 degrees C and 8.5 at 12 +/- 1 degrees C. Nitrate and nitrite reduction rates were compared, when they were used separately as the sole electron acceptor. It was shown that nitrite reduction rates consistently exceeded nitrate reduction rates, regardless of temperature and pH. The observed transitional accumulation of nitrite, when nitrate was used as an electron acceptor, indicated that nitrite reduction was slowed down by the presence of nitrate. No activity of acetogenic bacteria was observed in the hydrogenotrophic biomass and no residual acetate was detected, verifying that the kinetic parameters obtained were not influenced by heterotrophic denitrification and accurately represented autotrophic activity.

A novel hydrogenotrophic denitrification system, which consisted of a sequencing batch membrane bioreactor, was evaluated for simultaneous removal of nitrate and soluble microbial products (SMP) from a synthetic groundwater feed. A hollow fiber membrane diffuser was used for bubble-less diffusion of hydrogen into the bioreactor under anoxic condition followed by aerobic SMP removal and biomass filtration. During the anoxic period, the nitrate loading of 0.328 kg N m(-3) d(-1) was completely denitrified to below detectable levels. A denitrification rate of 0.8 kg N m(-3) d(-1) was obtained at steady state biomass concentrations of 1,162 mg I(-1). During the aerobic period when biomass filtration was performed, 81% of SMP produced within the anoxic phase was retained by the membrane, 9% was biologically removed, 5% was passed through the membrane and 5% was discharged during the wasting of mixed liquor. The aerobic cycle was instrumental as it allowed for effective biomass filtration via membrane scouring and assisted in further reduction of effluent organic matter.

Removal of phosphorus (P) from hog manure can be accomplished by struvite (MgNH4PO4) precipitation but the use of liquid hog manure in most reactors is hindered by manure total solids (TS), low soluble P concentration and interfering ions such as calcium (Ca). In addition, the cost of typical alkali and magnesium (Mg) additions adds significantly to reactor operational costs. Anaerobic fermentation can increase acidity of liquid manures by increasing both VFA and carbonic acid content. This pre-treatment increases soluble P by dissolving P solids in the acid environment and also enables pH increase by air stripping CO2 and carbonic acid. Manure solids separation technologies such as a centrifuge or rotary press produce a liquid stream with TS of