Thomas Arnot

Cross-flow and dead-end microfiltration of oily-water emulsion. Part I: Experimental study and analysis of flux decline

Microfiltration for the separation of oil-in-water emulsions has been investigated and a method of identifying fouling mechanisms applicable to microfiltration in general has been developed. For a variety of membranes, simultaneous experiments in both dead-end and cross-flow modes have been performed at various pressures, and in the latter case at different cross-flow velocities. The oil phase comprised dodecane at 1000 ppm. Initial fouling rates were very significant with the two polymeric membranes used but distinctly less severe with the Ceramesh membrane, possibly due to its tight pore size distribution. Good performance was achieved with this membrane under turbulent flow conditions. Flux decline and rates of permeate flow resistance change have been analysed using a new formulation of the equations illustrating a method of resistance mechanism recognition.

Separation of concentrated organic/inorganic salt mixtures by nanofiltration

This paper considers nanofiltration (NF) of concentrated organic/inorganic mixtures using the FILMTEC™ NF-200B membrane. Mixtures of salt (up to 17% (w/v)) and lactic acid (2% (w/v)) were used as model solutions. The work centres on the effects of salt concentration, pH and temperature on the flux and rejection of lactate. For all solutions under study, the rejection of salt was low, while the rejection of lactate was maximal at neutral pH, and decreased with salt concentration and temperature. The flux was found to decrease with salt concentration and increase with temperature, the activation energy being higher for low fluxes. The flux for pure water and 2% (w/v) lactic acid was at a maximum at neutral pH, but for salt-containing solutions, it increased with pH in the whole range analysed (pH 3–10). The observed flux and rejection patterns suggest that the effects of skin shrinkage in concentrated salt solutions, and sorption of lactate by the membrane, affect behaviour in addition to the conventional effects of charge, solute size and osmotic difference between the retentate and permeate streams.

Controlling fouling in membrane bioreactors operated with a variable throughput

Membrane bioreactors (MBRs) have been used increasingly for municipal wastewater treatment. The current wastewater treatment plants are designed to treat three times the average flow in dry weather (DWF) which covers the expected range of incoming flow rates. If throughput in MBRs can be changed readily by changing the energy input into the system, a smaller plant can be designed. Under varying throughput operation, a high aeration rate is required to generate a high crossflow velocity to minimize fouling. At low flow rates, a low aeration rate is used to minimize energy consumption. The aim of this work is to explore the feasibility of designing smaller membrane plants by varying the throughput. This requires the control of membrane fouling, so that chemical cleaning is not compromised. Fouling is controlled by limiting the membrane flux and also by flushing the surface of the membranes with large air bubbles. Variations of the permeate flux and the aeration rate were varied in this study and their effect on controlling fouling noted. Intermittent permeation while retaining aeration was found to be an effective technique for long-term sustainability of high fluxes.

The influence of surfactant on water flux through microfiltration membranes

Abstract The influence of different types of surfactants on two types of microfiltration membranes was investigated for different pore sizes and membrane usage. The surfactants were an anionic (sodium lauryl sulphate) surfactant and two non-ionic surfactants of which one [poly(ethylene glycol)2025] has an inverted cloud point. The other was polyoxyethylene sorbitan monooleate (Tween 80). The chosen microfiltration membranes are commercially available Ceramesh and PVDF [poly(vinylidene fluoride)]. The flux reductions were found to be more pronounced with the latter which is hydrophobic. Below the cloud point the minimum reduction was 20% for the hydrophobic membrane. New and cleaned membranes were studied, the reductions being greater in the former case. Overall the flux reductions were as significant as those found previously for hydrophobic ultrafiltration membranes.

Combined Use of Bacteriophage K and a Novel Bacteriophage To Reduce Staphylococcus aureus Biofilm Formation

ABSTRACT Biofilms are major causes of impairment of wound healing and patient morbidity. One of the most common and aggressive wound pathogens is Staphylococcus aureus, displaying a large repertoire of virulence factors and commonly reduced susceptibility to antibiotics, such as the spread of methicillin-resistant S. aureus (MRSA). Bacteriophages are obligate parasites of bacteria. They multiply intracellularly and lyse their bacterial host, releasing their progeny. We isolated a novel phage, DRA88, which has a broad host range among S. aureus bacteria. Morphologically, the phage belongs to the Myoviridae family and comprises a large double-stranded DNA (dsDNA) genome of 141,907 bp. DRA88 was mixed with phage K to produce a high-titer mixture that showed strong lytic activity against a wide range of S. aureus isolates, including representatives of the major international MRSA clones and coagulase-negative Staphylococcus. Its efficacy was assessed both in planktonic cultures and when treating established biofilms produced by three different biofilm-producing S. aureus isolates. A significant reduction of biofilm biomass over 48 h of treatment was recorded in all cases. The phage mixture may form the basis of an effective treatment for infections caused by S. aureus biofilms.

Membrane Bioreactors for Treating Waste Streams

Abstract: Membrane bioreactors (MBRs) have a number of advantages for treating wastewater containing large quantities of BOD. This paper reviews the inherent advantages of an MBR, which include high potential biomass loadings, lower sludge yields, and retention of specialized organisms that may not settle well in clarifiers. A major problem in effluent treatment occurs when mixed inorganic and organic wastes occur with high concentrations of pollutants. Inorganics that might cause extremes of pH and/or salinity will inhibit microbial growth and only specialized organisms can survive under these conditions. Refractory organics are only biodegraded with difficulty by specialized organisms, which usually do not resist the extreme inorganic environments. The use of membrane bioreactors to help separate the micro‐organisms from the inorganic compounds, yet permit the organics to permeate, has been developed in two different designs that are outlined in this paper. The use of membrane contactors in a multimembrane stripping system to treat acidic chlorinated wastes is proposed and discussed.

Enhancement of the antimicrobial properties of bacteriophage-K via stabilization using oil-in-water nano-emulsions

Bacteriophage therapy is a promising new treatment that may help overcome the threat posed by antibiotic‐resistant pathogenic bacteria, which are increasingly identified in hospitalized patients. The development of biocompatible and sustainable vehicles for incorporation of viable bacterial viruses into a wound dressing is a promising alternative. This article evaluates the antimicrobial efficacy of Bacteriophage K against Staphylococcus aureus over time, when stabilized and delivered via an oil‐in‐water nano‐emulsion. Nano‐emulsions were formulated via thermal phase inversion emulsification, and then bacterial growth was challenged with either native emulsion, or emulsion combined with Bacteriophage K. Bacteriophage infectivity, and the influence of storage time of the preparation, were assessed by turbidity measurements of bacterial samples. Newly prepared Bacteriophage K/nano‐emulsion formulations have greater antimicrobial activity than freely suspended bacteriophage. The phage‐loaded emulsions caused rapid and complete bacterial death of three different strains of S. aureus. The same effect was observed for preparations that were either stored at room temperature (18–20°C), or chilled at 4°C, for up to 10 days of storage. A response surface design of experiments was used to gain insight on the relative effects of the emulsion formulation on bacterial growth and phage lytic activity. More diluted emulsions had a less significant effect on bacterial growth, and diluted bacteriophage‐emulsion preparations yielded greater antibacterial activity. The enhancement of bacteriophage activity when delivered via nano‐emulsions is yet to be reported. This prompts further investigation into the use of these formulations for the development of novel anti‐microbial wound management strategies.

A novel bacteriophage cocktail reduces and disperses Pseudomonas aeruginosa biofilms under static and flow conditions.

Pseudomonas aeruginosa is an opportunistic human pathogen that forms highly stable communities – biofilms, which contribute to the establishment and maintenance of infections. The biofilm state and intrinsic/acquired bacterial resistance mechanisms contribute to resistance/tolerance to antibiotics that is frequently observed in P. aeruginosa isolates. Here we describe the isolation and characterization of six novel lytic bacteriophages: viruses that infect bacteria, which together efficiently infect and kill a wide range of P. aeruginosa clinical isolates. The phages were used to formulate a cocktail with the potential to eliminate P. aeruginosa PAO1 planktonic cultures. Two biofilm models were studied, one static and one dynamic, and the phage cocktail was assessed for its ability to reduce and disperse the biofilm biomass. For the static model, after 4 h of contact with the phage suspension (MOI 10) more than 95% of biofilm biomass was eliminated. In the flow biofilm model, a slower rate of activity by the phage was observed, but 48 h after addition of the phage cocktail the biofilm was dispersed, with most cells eliminated (> 4 logs) comparing with the control. This cocktail has the potential for development as a therapeutic to control P. aeruginosa infections, which are predominantly biofilm centred.

Controlled flux behaviour of membrane processes

Controlling ultrafiltration (UF) and microfiltration (MF) membrane fluxes at or around a region where fouling is minimal can provide an interesting and economic operating regime. Selectivity may be enhanced and cleaning may be easier. For a given flux it is sometimes possible to filter a product suspension at the same trans-membrane pressure (TMP) as for pure water (PWP), but this can require a lot of energy input to maintain cross-flow or high shear in other ways if high fluxes are required. The critical flux is the flux above which one starts to observe fouling. By operating at lower cross-flow velocities and just above the critical flux, and thus, with lower TMPs, periodic cleaning can be effected by temporarily stopping permeation. A change in feed rate demands a change in flux which is obtained by temporarily increasing energy inputs. Controlled flux improves macromolecular fractionation. As flux increases the rejection of high molecular weight materials decreases whilst that of lower molecular weight materials decreases. This paper discusses the causes of fouling and the use controlled flux operation to mitigate its effects.

Enhanced system kLa and permeate flux with a ceramic membrane bioreactor

A cross-flow ceramic membrane was coupled to a bioreactor to fulfil the alternate functions of process stream clarifier and primary aerator. At the same air supply rate (delivered as a back-flush), ceramic membranes provided up to 72% greater aeration than a ring-sparger located in the bioreactor. In Biol.ogical treatment of dairy food process waste, the air backflush had the additional benefit of inhibiting membrane fouling, thereby maintaining higher (by about 100%) permeate fluxes.