Greg Leslie

How do surface scientists, modellers, chemists and engineers located around Australia share data and access resources in a collaborative project designed to reduce the energy of seawater desalination by 40%? The solution is the Membrane Research Environment ( ...

ABSTRACT Membrane bioreactors (MBR) represent the state-of-the-art for treating municipal wastewater. The energy costs generally contribute to 50% of the total operating costs of MBRs. The energy is not only required for the biological process and membrane fouling control, but also required for achieving desired mixing conditions. However, the current MBRs design is mainly based on the biokinetics and membrane fouling considerations neglecting the effects of hydrodynamics. Current methods of design for a desired flow regime within the MBR are largely based on empirical techniques (e.g. specific mixing energy). In this study, a model was developed using computational fluid dynamics (CFD) to account for mixing of the whole MBR and biological nutrient removal. The modelling results were compared against experimental results of two full scale MBRs in Australia for the mixing regimes and against a modelling benchmark for the biological nutrient removal component of the model.

A study was conducted to examine the removal of methyl tert-butyl ether (MTBE) and 15 other organic compounds, as well as perchlorate ion, in waters of different quality. The 15 organic compounds consisted of halogenated solvents (chlorination), disinfection by-products, pesticides, and nitrosodimethylamine (NDMA). These studies were conducted using a pilot scale 20kW mobile electron beam system at Water Factory 21, Orange County, CA where wastewater is treated and re-injected into the ground as a barrier to salt water intrusion. Future applications for this treated water include water reuse. Ground water and treated wastewater, after having gone through a reverse osmosis-polishing step (RO permeate), were used to prepare mixtures of the compounds. Using fundamental radiation chemistry, it was possible to examine the factors effecting removal efficiency of all the compounds as well as MTBE destruction and reaction by-product formation and removal. All of the organic compounds were destroyed in the studies and we also observed the destruction of perchlorate ion in one of the waters.

ABSTRACT Flux decline in bench scale membrane bioreactors (MBRs) configured for chemical phosphorous removal using ferric chloride increased as the molar Fe to P ratio increased from 2 to 4 and was strongly dependent on the valence state of the low concentrations of filterable iron present in the supernatant. MBRs operating without pH control over the pH range 5.1–7.1 exhibited variable but generally higher concentrations of dissolved and colloidal (<0.8 μm filterable) iron in the supernatant of the anoxic zone (1.18–26.43 μM) than in the aerobic and membrane chambers (0.18–6.72 μM). At pH 5.1, 97% of the iron suspended in the anoxic chamber was present as Fe(II). In contrast, the concentration of iron was relatively uniform in the three chambers of the MBRs (3.2 ± 0.4 μM) when pH was controlled by caustic addition. Under pH-controlled conditions, 70–80% of the iron in the supernatant was in the form of soluble (<0.2 μm) Fe(II) rather than Fe(III). While dosing of the MBRs with a moderate concentration of ferric chloride (Fe/P molar ratio of 2) led to effective phosphorus removal and minimal enhancement in extent of fouling, a higher ferric chloride dose (Fe/P = 4) gave little improvement in P removal and led to severe membrane fouling. While Fe(III) dosing is an effective strategy for P removal provided sufficient Fe is added, the dangers of overdosing are severe with careful optimisation of dose clearly required in order to avoid debilitating membrane fouling.

The effect of continuously dosing membrane bioreactors (MBRs) with ferric chloride (Fe(III)) and ferrous sulphate (Fe(II)) on phosphorus (P) removal and membrane fouling is investigated here. Influent phosphorus concentrations of 10 mg/L were consistently reduced to effluent concentrations of less than 0.02 mg/L and 0.03-0.04 mg/L when an Fe(III)/P molar ratio of 4.0 and Fe/P molar ratio (for both Fe(II) and Fe(III)) of 2.0 were used, respectively. In comparison, effluent concentrations did not decrease below 1.35 mg/L in a control reactor to which iron was not added. The concentrations of supernatant organic compounds, particularly polysaccharides, were reduced significantly by iron addition. The sub-critical fouling time (tcrit) after which fouling becomes much more severe was substantially shorter with Fe(III) dosing (672 h) than with Fe(II) dosing (1200-1260 h) at Fe/P molar ratios of 2.0 while the control reactor (no iron dosing) exhibited a tcrit of 960 h. Not surprisingly, me...

ABSTRACT With continuing growth in the reverse osmosis water treatment industry and the finite lifespan of the membranes, the number of membrane modules requiring disposal is expected to drastically increase over time. This study aimed to provide a quantitative assessment of the environmental impact from membrane manufacturing and its impact on the desalination process, using the tool of life cycle assessment. The results showed no significant difference between the manufacturing of 16″ and 8″ elements, and that module fabrication contributed to less than 1% of the CO2-e emissions for the production of potable water from seawater. The study also looked at the environmental impact of a number of proposed end-of-life disposal options for membranes within the context of the Australian desalination industry. The results of the study show that membrane reuse over one year is more environmentally favourable to landfill disposal, regardless of the transportation distance required. However, in terms of direct reduction of waste to landfill, incineration provided the greatest benefit, at the expense of increased greenhouse gas emissions. Overall, this study provides detailed quantitative information for membrane users and manufacturers to enhance their decision making process when it comes to end-of-life membrane options.

Based on global research and local knowledge, this paper aims to discuss MBR design considerations from an Australian perspective. It includes discussion on how applicable (or otherwise) this technology may be for Australian conditions and it lists some of the local opportunities and local barriers that this technology may experience. Some of the existing Australian MBR examples are listed and

Unlike conventional wastewater treatment systems that have a single effluent discharge point, membrane bioreactors (MBR) may have multiple extraction points resulting from the location of the membrane element in the reactor. This leads to multiple residence time distributions for an MBR system. One method to characterise the mixing is based on the concept of residence time distribution (RTD). A set of RTDs were generated using the conservative tracer, lithium chloride, for pilot plant MBRs with capacity up to 300 m3/day. Flat sheet and hollow fibre pilot plant MBR systems were operated in parallel on primary effluent collected at the Bedok Water Reclamation Plant in the republic of Singapore. Analysis of the RTD profiles indicated that membrane geometry did not impact on the kinetic conversion associated with nitrification because both MBRs were in well mixed conditions. However, the energy required to achieve perfect mixing with a hollow fibre module MBR, as defined by the velocity gradient, was lower than that with a flat sheet module MBR. The implication is that energy input associated with reactor mixing will depend on the configuration of the membrane. The difference in energy requirements between flat sheets and hollow fibres is such that careful consideration should be given to membrane selection in larger municipal installations.

A pilot scale membrane bioreactor (3.7 m(3)/day capacity), configured for alternate point ferrous sulphate addition, was evaluated in a fourteen month trial to comply with an effluent discharge requirement of less than 0.15 mg-P/L at the 50(th) percentile and less than 0.30 mg-P/L at the 90th percentile. Ferrous sulphate was added at a molar ratio (Fe(II):PO4) of 2.99 in the filtration chamber for 85 days and 2.60 in the primary anoxic zone for 111 days. Addition of ferrous salts to the anoxic zone achieved a final effluent phosphorous concentration (mg-P/L) of <0.05 (29%), <0.15 (77%) and <0.30 (95%), while addition of ferrous salts in the filtration zone achieved <0.05 (18%), <0.15 (63%) and <0.30 (95%). Analysis of the concentration of iron(II) in the supernatant indicated that phosphorus was mainly removed via adsorption to amorphous iron oxyhydroxides particles in both dosing scenarios. However, analysis of residence time distribution (RTD) data of the reactor indicated that severe short-circuiting from the dosing point to the membrane outlet could occur when the ferrous salts were added to the membrane zone while the reactor behaved close to a completely mixed reactor when dosing to the primary anoxic zone, resulting in improved phosphorus removal. The addition of ferrous salt was also found to delay the onset of severe increase in trans-membrane pressure as a result of the removal of macro-molecules. However, detailed analysis of the form and concentration of iron species in the supernatant and permeate indicated that the presence of fine iron particles resulted in a higher fouling rate when Fe(II) was added to the membrane zone rather than the primary anoxic zone and could cause more severe irreversible fouling in long-term operation.

The interaction of organic micropollutants with dissolved organic carbon (DOC) can influence their transport, degradation and bioavailability. While this has been well established for natural organic carbon, very little is known regarding the influence of DOC on the fate of micropollutants during wastewater treatment and water recycling. Dissolved organic carbon-water partition coefficients (K(DOC)) for wastewater derived and reference DOC were measured for a range of micropollutants using a depletion method with polydimethylsiloxane disks. For micropollutants with an octanol-water partition coefficient (log K(OW)) greater than 4 there was a significant difference in K(DOC) between reference and wastewater derived DOC, with partitioning to wastewater derived DOC over 1000 times lower for the most hydrophobic micropollutants. The interaction of nonylphenol with wastewater derived DOC from different stages of a wastewater and advanced water treatment train was studied, but little difference in K(DOC) was observed. Organic carbon characterisation revealed that reference and wastewater derived DOC had very different properties due to their different origins. Consequently, the reduced sorption capacity of wastewater derived DOC may be related to their microbial origin which led to reduced aromaticity and lower molecular weight. This study suggests that for hydrophobic micropollutants (log K(OW) > 4) a higher concentration of freely dissolved and thus bioavailable micropollutants is expected in the presence of wastewater derived DOC than predicted using K(DOC) values quantified using reference DOC. The implication is that naturally derived DOC may not be an appropriate surrogate for wastewater derived DOC as a matrix for assessing the fate of micropollutants in engineered systems.

ABSTRACT Membrane bioreactor (MBR) processes for the treatment of municipal and industrial wastewater have been extensively investigated in the past years. For this purpose, synthetic model feeds containing dissolved macromolecules and/or suspended solids were used to allow for a stable and reproducible feed composition. Lab-scale setups equipped with single membrane filaments and pilot plants containing single-bundle configurations were applied. Despite the fact that numerous of the corresponding findings were successfully transferred to large-scale MBR processes, it is expected that the filterability of activated sludge differs significantly from that of common model substances. Moreover, phenomena linked to the highly complex multi-phase flow of liquid, suspended solids and dispersed air bubbles which physically interacts with the membrane filaments make downsizing difficult. Therefore, the overall objective of this study was to evaluate the transferability of lab-scale microfiltration results to large-scale MBR processes. Our investigations have shown that the rheology of a model feed containing silica particles is similar to that of activated sludge with MLSS ⩽ 3.5 g/L. A noticeable sub-critical fouling was observed, but was removable by an intensive chemical cleaning using sodium hypochlorite. Lower fouling rates when increasing the aeration frequency with the same net aeration rate were found for both single-fibre and single-bundle tests, but are more pronounced on the larger scale. A macroscopic circulation flow affects the filtration performance of full-scale MBRs, but is difficult to mimic on a smaller scale. Fibre motion enhances the filtration performance, but is insensitive to packing density variations for bundles of up to four filaments.

ABSTRACT The long-term decrease of hydraulic performances observed in membrane systems is generally explained by the gradual accumulation of irreversible foulants. Although the use of chemicals is primarily aimed to remove most of the foulants, few studies have reported their potential degradation impact on the membrane, consequently leading to the decrease in hydraulic performances. However, the impact of chemical ageing on the intrinsic membrane characteristics has not been studied in details, and the understanding of its relative role in the long-term filtration behaviour is, so far, limited. In this study, a polyvinylidene fluoride (PVDF) micro-porous membrane was aged through long-term fouling/cleaning cyclical experiments using model organic and 20,000 ppm sodium hypochlorite (NaOCl) solutions. The membranes were then thoroughly characterised, both physically and chemically, by various analytical techniques. The apparent pore size of the aged membrane was observed to enhance due to the combined effect of increased wetting and hydrophilicity of the membrane. Furthermore, NaOCl exposure led to early degradation of the PVDF membrane through cross linking and thus, slight loss of its mechanical properties. The impact of NaOCl on PVDF tensile properties was found to be less pronounced on fouled membranes, revealing the relative role of fouling during membrane ageing.

ABSTRACT Analytical solutions of the Nernst-Planck, Poisson and continuity equations for a membrane undergoing reverse osmosis in a cross-flow system reveal that the flow of alternating ionic charge induced in the membrane during impedance measurements is actively assisted by the flow of water. The actively driven current manifested "inductive" responses in impedance measurements of a Filmtec BW30 reverse osmosis membrane mounted in an Inphaze flat-bed cross-flow module after 16 hours of filtering a mineral salt solution seeded with CaCl2 and NaHCO3 at pressure of 900 kPa. Fitted transfer functions resolved conduction and capacitive properties of four membrane layers, diffusion/concentration phenomenon and a pseudo "inductor" shunted by a conductor. A 10-fold decrease in the shunt conductance correlated with smaller increases in the conductance values for the filtrate and membranous layers, and the onset of fouling diagnosed by a rapid increase in flux decline.