Electrochemically-assisted ammonia recovery from wastewater using a floating electrode.

This work presents and explores a novel methodology for the removal and recovery of ammonia from wastewater based upon two mechanisms: electrochemical oxidation and a previously unreported electrochemically-assisted surface transfer mechanism. Recovery of ammonia is enabled by placing a porous cathodic electrode at the wastewater-air interface. In this configuration, the cathode creates local alkalinity and an electric field that draws ammonium ions towards the wastewater-air interface, resulting in near-linear reductions of dissolved ammonium irrespective of concentration. This approach leads to significant ammonia recovery without the need for ion-exchange membranes. In addition, anodic reactions that simultaneously occur at depth in the wastewater induce ammonia oxidation in accordance with proven mechanisms. The floating electrode approach offers improved ammonia removal efficiency in comparison to electrooxidation. Trials conducted on synthetic wastewater (900 mg NH4+-N l-1) and filtered anaerobic centrate (560 mg NH4+-N l-1) demonstrated ammonia concentration decreases up to 216 mg l-1 hr-1 and 110 mg l-1 hr-1, respectively, under the application of 5 mA cm-2 current density. The technology would be best used to treat municipal and industrial wastewaters possessing high ammonia concentration, including anaerobic digester centrate and urine, and offers potential to assist in removing ammonia from environmental waters.

Application of a novel sampling bailer device for the analysis of dissolved methane concentrations in municipal wastewater during and following anaerobic treatment.

Modern wastewater utilities need to be able to measure and quantify the amount of methane from their treatment facilities in order to understand the potential energy that can be produced and the amount of methane being lost. This paper describes the application of a novel sampling bailer designed for the collection of wastewater samples that minimises methane losses. Samples collected during and following anaerobic treatment from a wastewater treatment plant using a novel sampling bailer were analysed using a previously optimised analytical method. Analysis of wastewater and anaerobic pond samples using current industry approaches resulted in dissolved methane concentrations ranging from 0.01 to 14.33 mg L(-1). In comparison, the modified sampling protocol resulted in concentrations ranging from 0.08 to 18.73 mg L(-1). The relative standard deviations (RSD%) of low level spikes (5.0 mg L(-1) and 0.1 mg L(-1) methane; n = 5) were found to be 2.3 and 10.3, respectively. Statistical analysis of the dissolved methane concentrations using the two different approaches demonstrated a significant difference in the recovered dissolved methane concentrations, indicating there is a greater methane recovery potential in wastewater treatment plants than previously realised, when collected using the novel sampling bailer and analysed following the optimised analytical protocol.

Electron-beam-induced carbon contamination on silicon: characterization using Raman spectroscopy and atomic force microscopy.

Electron-beam-induced carbon film deposition has long been recognized as a side effect of scanning electron microscopy. To characterize the nature of this type of contamination, silicon wafers were subjected to prolonged exposure to 15 kV electron beam energy with a probe current of 300 pA. Using Raman spectroscopy, the deposited coating was identified as an amorphous carbon film with an estimated crystallite size of 125 A. Using atomic force microscopy, the cross-sectional profile of the coating was found to be raised and textured, indicative of the beam raster pattern. A map of the Raman intensity across the coating showed increased intensity along the edges and at the corner of the film. The intensity profile was in excess of that which could be explained by thickness alone. The enhancement was found to correspond with a modeled local field enhancement induced by the coating boundary and showed that the deposited carbon coating generated a localized disturbance in the opto-electrical properties of the substrate, which is compared and contrasted with Raman edge enhancement that is produced by surface structure in silicon.

Anaerobic digestion/co-digestion kinetic potentials of different agro-industrial wastes: A comparative batch study for C/N optimisation.

Anaerobic digestion (AD) of different agro-industrial wastes and their co-digestion potential has been exhaustively studied in this research. It explores variation of feedstock characteristics such as biodegradability and methane potential during AD and anaerobic co-digestion (ACoD) of chicken litter (CL) with yoghurt whey (YW), organic fraction of municipal solid waste (OFMSW), hay grass (HG) and wheat straw (WS) under mesophilic conditions. Comparative performance was made at different loading concentrations (2%, 3% and 4% VS) with 1:2g/g VS of substrate to inoculum and carrying C/N ratio. Among different kinetic models, the AD of single substrates showed better fit to the modified Gompertz model (R2: 0.93-0.997) indicating variation in lag phase and methane production rate depend on the substrate characteristics. During ACoD, the methane yield improved by 9-85% through the addition of two, three or four substrates due to the synergistic effect asa result of increased biodegradability and optimum conditions (such asC/N ratio). A surface (optimisation) model indicated that maximum methane production can be achieved by blending chicken litter (30-35%) and a (65-70%) mixture of yoghurt whey, hay and wheat straw with aC/N ratio of (26-27.5).

Semi-continuous anaerobic co-digestion of chicken litter with agricultural and food wastes: A case study on the effect of carbon/nitrogen ratio, substrates mixing ratio and organic loading.

In this study, four agro-industrial substrates, chicken litter (CL), food waste (FW), wheat straw (WS) and hay grass (HG) were assessed as feedstock for anaerobic digestion (AD) under semi-continuous conditions at organic loading rates (OLRs) of 2.0-3.0 g TS/L.d and hydraulic retention time (HRT) of 20 days. Six different substrate mixtures were prepared such that the C/N ratio of each was 20 or more. Using principal component analysis 68.1% of data variability was explained. Biogas production from CL, as a single substrate, was 181.3 ±â€¯9.8mLN biogas/g VSadded at OLR of 2.0gTS/L.d. The optimum substrates mixture was CL:FW:WS 60:20:20, where 73.0%, 167.2% and 116.9% increase in total biogas production at OLR of 2.0, 2.5, 3.0gTS/L.d, respectively, compared to that from CL, was obtained. Digestate sequential fractionation revealed carbohydrate degradation is an important factor that can explain the variation in performance and production of biogas for feedstocks of balanced C/N ratio.

Water adsorption kinetics and contact angles of pharmaceutical powders.

Water sorption kinetics and water contact angles have been characterized for a range of pharmaceutical powders: ambroxol hydrochloride, griseofulvin, N,n-octyl-D-gluconamide, paracetamol, sulfathiazole, and theophylline. The uptake of water by powder samples at saturated vapor pressure was modeled using a pseudo first-order kinetic relationship. Parameters from this model have been correlated with the concentration and reactivity of the active surface sites of the pharmaceutical powders and their contact angles. The study has shown that analysis of water adsorption kinetics can be a powerful technique for characterizing the surface chemistry and wettability of pharmaceutical powders, and is particularly sensitive to their surface modification through excipient adsorption: ethyl(hydroxyethyl)cellulose treatment of griseofulvin and butyryl chloride treatment of sulfathiazole are reported as case studies.

Face specific surface properties of pharmaceutical crystals.

A variety of surface specific techniques have been used to determine the face-specific structure, chemistry, and wettability of model pharmaceutical crystals, i.e., N,n-octyl-d-gluconamide and sulfathiazole (polymorphic forms I and III). The surface energetics of individual crystal faces were investigated by studying their wetting characteristics and interaction with chemically modified silica spheres using colloid probe atomic force microscopy (AFM). Contact angles (dynamic and static), interaction forces, and adhesion properties have been shown to correlate strongly with the face specific surface chemistry. This, in turn, is controlled by the molecular arrangement at the specific crystal face, which has been characterized by time-of-flight secondary-ion mass spectrometry (ToF SIMS) and inferred from molecular models. Of specific note, the magnitude of the adhesion force between a crystal face and a hydrophobic colloid probe is related linearly to the face-specific equilibrium contact angle. These studies further our understanding of the face-specific properties of pharmaceutical crystals and have implications when considering processing, formulation and delivery.

Dynamic contact angle measurement on materials with an unknown wet perimeter.

Whilst contact angle measurements obtained using the Wilhelmy balance technique are accurate and reproducible for planar surfaces, their use for characterizing particulate materials is highly dependent upon accurate knowledge of the wet perimeter. This communication suggests that the approach of Pepin et al. [Int. J. Pharm. 152 (1997) 1] for wet perimeter determination using non-polar liquids may lead to erroneous conclusions. Alternative approaches for wet perimeter determination are suggested.

Application of time-dependent sessile drop contact angles on compacts to characterise the surface energetics of sulfathiazole crystals.

The time-dependent wetting of sulfathiazole compacts with sessile water drops was evaluated using video microscopy. The influence of sulfathiazole crystalline form, particle size, pre-saturation with water, humidity and compaction pressure on the droplet spreading kinetics and contact angles are reported. The rate and extent of droplet spreading decreased for compact surfaces of high microscopic roughness; this was determined by atomic force microscopy (AFM). Pre-saturation of powder compacts with water (pre-saturated with sulfathiazole) enhanced droplet spreading and enabled pseudo-equilibrium contact angles to be determined for up to 10 min. Sessile-drop contact angles on both sulfathiazole powder compacts and single crystals are compared with particle contact angles determined by liquid penetration. This study has led to an improved understanding of the influence of physical heterogeneities and the face-specific surface chemistry of individual crystals on the wetting characteristics of pharmaceutical compacts.