Photon counting fibre optic distributed temperature sensing with a CMOS SPAD array.

Time-resolved fibre optic Raman distributed temperature sensing (DTS) measurements experience long measurement times due to a weak backscattered Raman signal inside optical fibres or limited detector count rates. Here, improvements to previous work based on individual detectors are demonstrated using a 512 pixel complementary-metal-oxide semiconductor (CMOS) single-photon avalanche diode (SPAD) line sensor array with integrated (on-chip) timing electronics. Multiplexed single photon counting increases count rate and decreases measurement time for practical applications. This allows temperature to be measured every 0.5 m with 0.7 °C accuracy and a 10 s measurement time using a 13.0 m optical fibre, performance over longer distance is also investigated.

Relating algal-derived extracellular and intracellular dissolved organic nitrogen with nitrogenous disinfection by-product formation.

The dissolved organic nitrogen (DON) pool from algal-derived extracellular and intracellular organic matter (EOM and IOM) comprises proteins, peptides, free amino acids and carbohydrates, of which, proteins can contribute up to 100% of the DON. Previous reports of algal-derived DON character have focused on bulk properties including concentration, molecular weight and hydrophobicity. However, these can be similar between algal species and between the EOM and IOM even when the inherent molecular structures vary. A focus on bulk character presents challenges to the research on algal-derived nitrogenous-disinfection by-product (N-DBP) formation as N-DBP formation is sensitive to the changes in molecular structure. Hence, the main aim of this study was to characterize algal EOM and IOM-derived DON, specifically proteinaceous-DON, using a combination of bulk and molecular characterization techniques to enable a more detailed exploration of the relationship between the character of algal-derived proteins and the N-DBP formation potential. DON from the EOM and IOM of four commonly found algae and cyanobacteria in natural waters were evaluated, namely Chlorella vulgaris, Microcystis aeruginosa, Dolichospermum circinale, and Cylindrospermopsis raciborskii. It was observed that 77-96% of total DON in all EOM and IOM samples was of proteinaceous origin. In the proteins, DON concentrations were highest in the high molecular weight fraction of IOM-derived bulk proteins (0.13-0.75 mg N L-1) and low to medium molecular weight fraction of EOM-derived bulk proteins (0.15-0.63 mg N L-1) in all species. Similar observations were also made via sodium dodecyl sulphate polyacrylamide gel electrophoresis and liquid chromatography-high resolution mass spectrometry. Solid-state 15N nuclear magnetic resonance (NMR) spectroscopy of the EOM and IOM revealed the existence of common aliphatic and heterocyclic N-groups in all samples, including a dominant 2° amide peak. Species dependent variability was also observed in the spectra, particularly in the EOM; e.g. nitro signals were found only in the Cylindrospermopsis raciborskii EOM. Dichloroacetonitrile (DCAN) and N-nitrosamine concentrations from the EOM of the species evaluated in this study were lower than the guideline limits set by regulatory agencies. It is proposed that the dominant 2° amide in all samples decreased N-DBP formation upon chlorination. For chloramination, the presence of nitro groups and aliphatic and heterocyclic N-DBP precursors could cause variable N-nitrosamine formation. Compared to non-algal impacted waters, algae-laden waters are characterised by low organic carbon: organic nitrogen ratios of ∼7-14 and elevated DON and protein concentrations. Hence, relying only on bulk characterization increases the perceived risk of N-DBP formation from algae-laden waters.

Microalgae harvesting using flocculation and dissolved air flotation: Selecting the right vessel for lab-scale experiments.

Flocculation combined with dissolved air flotation (DAF) is a promising technology for harvesting microalgae; therefore, optimisation of flocculant-DAF operating conditions are frequently explored in laboratory experiments. DAF systems have jars of differing volumes, height to diameter ratios, shapes and materials used to manufacture the jars; thus, the harvesting efficiency (η) may differ between these jars. The aim was to systematically compare η between different types of benchtop DAF jars. Evaluation of 30 different types of DAF jars revealed that η was not influenced by the volume of the jars, but was impacted by the height to diameter ratio, with optimal η at a ratio ranging between 1.6 and 2.05. There was no difference in η between cylindrical and cuboid jars, but jars made of hydrophobic (polypropylene) plastic resulted in a lower η. Overall, these results are useful to guide the design of lab-scale DAF microalgae harvesting experiments.

High resolution TCSPC imaging of diffuse light with a one-dimensional SPAD array scanning system.

We report a time-correlated single-photon counting (TCSPC) imaging system based on a line-scanning architecture. The system benefits from the high fill-factor, active area, and large dimension of an advanced CMOS single-photon avalanche diode (SPAD) array line-sensor. A two-dimensional image is constructed using a moving mirror to scan the line-sensor field-of-view (FOV) across the target, to enable the efficient acquisition of a two-dimensional 0.26 Mpixel TCSPC image. We demonstrate the capabilities of the system for TCSPC imaging and locating objects obscured in scattering media - specifically to locate a series of discrete point sources of light along an optical fibre submerged in a highly scattering solution. We demonstrate that by selectively imaging using early arriving photons which have undergone less scattering than later arriving photons, our TCSPC imaging system is able to locate the position of discrete point sources of light than a non-time-resolved imaging system.

Time-resolved spectral-domain optical coherence tomography with CMOS SPAD sensors.

We present a first spectral-domain optical coherence tomography (SD-OCT) system deploying a complementary metal-oxide-semiconductor (CMOS) single-photon avalanche diode (SPAD) based, time-resolved line sensor. The sensor with 1024 pixels achieves a sensitivity of 87 dB at an A-scan rate of 1 kHz using a supercontinuum laser source with a repetition rate of 20 MHz, 38 nm bandwidth, and 2 mW power at 850 nm centre wavelength. In the time-resolved mode of the sensor, the system combines low-coherence interferometry (LCI) and massively parallel time-resolved single-photon counting to control the detection of interference spectra on the single-photon level based on the time-of-arrival of photons. For proof of concept demonstration of the combined detection scheme we show the acquisition of time-resolved interference spectra and the reconstruction of OCT images from selected time bins. Then, we exemplify the temporal discrimination feature with 50 ps time resolution and 249 ps timing uncertainty by removing unwanted reflections from along the optical path at a 30 mm distance from the sample. The current limitations of the proposed technique in terms of sensor parameters are analysed and potential improvements are identified for advanced photonic applications.

Understanding variability in algal solid-liquid separation process outcomes by manipulating extracellular protein-carbohydrate interactions.

Coagulation-flocculation followed by sedimentation or dissolved air flotation (DAF) are processes routinely used for separating microalgae from water; however, during algae separation then can exhibit inconsistent separation, high coagulant demand, and high operating cost. To circumvent these problems, previous studies reported the development of a novel DAF process in which bubbles were modified instead of particles. While this process was shown to be sustainable and inexpensive, the problem of inconsistent algal separation across species remained. Recent research has suggested that this could be due to the varying concentration and character of algal-derived proteins and carbohydrates within the extracellular organic matter (EOM) and their associated interactions. This hypothesis is tested in the current study using the novel modified-bubble DAF process, which has been highly susceptible to EOM protein and carbohydrate concentrations and character. Biomolecular additives (commercially available proteins and carbohydrates, and algal-extracted proteins) of widely differing molecular weight (MW) and charge were dosed in varying proportions into samples containing either Chlorella vulgaris CS-42/7, Microcystis aeruginosa CS-564/01, or Microcystis aeruginosa CS-555/1 after removing the intrinsic EOM. These cell-rich suspensions were then subject to flotation using cationic bubbles modified with poly(diallyldimethylammonium chloride) (PDADMAC). When additives were dosed independently, separation increased from <5% to up to 62%. The maximum separation was obtained when the dose was double the respective biopolymer concentration measured in the intrinsic EOM for the equivalent species, and, in the case of protein additives, when MW and charge were >50 kDa, and >0.5 meq·g-1, respectively, irrespective of the species tested. When evaluating steric- and charge-based protein-carbohydrate interactions on cell separation by simultaneously dosing high MW and high charge protein- and carbohydrate-additives, enhanced separation of up to 79% was achieved. It is suggested that enhanced cell separation is achieved due to proteins and carbohydrates bridging with cells and forming protein-carbohydrate-cell suprastructures in the presence of a flocculant, e.g. PDADMAC, and this only occurs when the intrinsic EOM comprises proteins and carbohydrates that have high MW (>25 kDa) and charge (>0.2 meq·g-1), and interactions with each other and with the cell surface.

Formation of algal-derived nitrogenous disinfection by-products during chlorination and chloramination.

Algal cells and algal organic matter (AOM) are a source of high dissolved organic carbon (DOC) and nitrogen (DON) concentrations. This poses a possible health risk due to their potential to form disinfection by-products (DBPs), some of which may be of health concern, after disinfection. While several studies have focussed on the formation of carbonaceous DBPs from AOM, only a few studies have focussed on the formation of nitrogen containing N-DBPs from AOM. Hence, the main aim of this study was to thoroughly investigate the N-DBP formation potential of the AOM from a species of cyanobacteria commonly found in natural waters, Microcystis aeruginosa. Three haloacetonitriles, two halonitromethanes, two haloacetamides, and eight N-nitrosamines were analysed by gas chromatography-mass spectrometry after chlorination and chloramination of the extracted AOM. To provide further insight into the influence of changing DON character on N-DBP formation potential, the AOM from three other species, Chlorella vulgaris, Dolichospermum circinale and Cylindrospermopsis raciborskii, were also tested. Dichloroacetonitrile (DCAN) was the DBP formed in the highest concentrations for both chlorination and chloramination of bulk AOM from all the species. Furthermore, during chlorination and chloramination, the high molecular weight fraction (>1 kDa) of AOM from M. aeruginosa had a greater DCAN formation potential (normalised to DOC or DON) than the AOM in the low molecular weight fraction (<1 kDa) of M. aeruginosa, regardless of growth stage. N-Nitrosamine formation from the bulk AOM of all species occurred only after chloramination. The molar concentration of N-nitrosodimethylamine (NDMA) was lower than the other N-nitrosamines detected. However, NDMA formation increased with culture age for all four species, in contrast to most other N-nitrosamines whose formation remained consistent or decreased with culture age. Overall, algal growth could result in elevated concentrations of N-DBPs due to the increasing concentrations of high molecular weight algal DON in the AOM. It is suggested that the AOM comprises precursors containing long C-chain amine (R1-NH-R2) or cyclic N-containing amine structures. Comparisons to previously measured N-DBP concentrations in drinking water suggest that the AOM from the algae and cyanobacteria examined in this study are not likely to be a major source of precursors for either DCAN or NDMA in real waters. However, AOM may present a major precursor source for other N-nitrosamines.

Detailed algal extracellular carbohydrate-protein characterisation lends insight into algal solid-liquid separation process outcomes.

The effectiveness of algal solid-liquid separation processes has been impacted by the strong influence of algal extracellular organic matter (EOM), where the composition of proteins and carbohydrates and their associated interactions have been implicated. However, despite this, no studies have analysed the detailed protein and carbohydrate composition in EOM in relation to their impacts on separation. Hence, the aim of this study was to explore the relationship between the variety of carbohydrates and proteins present in the EOM of select algal and cyanobacterial samples and the associated separation performance to better understand the influence of specific biopolymers. The protein and carbohydrate composition of the EOM of three species - Microcystis aeruginosa CS-555/1, Chlorella vulgaris CS-42/7 and Microcystis aeruginosa CS-564/01, previously observed to result in variable treatment performance were investigated. The carbohydrates were analysed via high-performance anion-exchange chromatography (HPAEC) with pulsed amperometric detection (PAD) while the proteins were analysed using sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) combined with liquid chromatography-mass spectrometry (LC-MS). Ten unique monosaccharides were identified; of these, the greatest proportion of charged uronic acid carbohydrates were present in the EOM of M. aeruginosa CS-564/01. The protein profiling revealed that M. aeruginosa CS-564/01 had a greater proportion and concentration of proteins >75 kDa when compared to M. aeruginosa CS-555/1 or C. vulgaris CS-42/7. It was determined that three serine- and two threonine-based proteins, detected in greater concentrations in M. aeruginosa CS-564/01 than CS-555/1, could covalently interact with carbohydrates (OHenderson et al., 2010a, 2010b-linked glycosylation). These proteins have the ability to form numerous localised networks with carbohydrates and cells in the presence of coagulant molecules, thereby providing a good hypothesis to explain the excellent treatment performance observed for M. aeruginosa CS-564/01 previously. It is proposed that the uronic acids in M. aeruginosa CS-564/01 could interact with proteins via glycosylation, explaining why the coagulant demand for this strain remained low despite the high charged carbohydrate concentration. Overall, it is proposed that process performance could be impacted by: (a) physicochemical characteristics and (b) carbohydrate-protein interactions.

Direct integration of micro-LEDs and a SPAD detector on a silicon CMOS chip for data communications and time-of-flight ranging.

We present integration of singulated micron-sized light emitting diodes (micro-LEDs) directly onto a silicon CMOS drive chip using a transfer printing method. An 8x8 micro-LED device array with individual control over each pixel is demonstrated with modulation bandwidths up to 50 MHz, limited by the large modulation depth of the driver chip. The 2 kHz frame rate CMOS driver also incorporates a Single Photon Avalanche Diode device thus allowing detection and transmission functionality on a single integrated chip. Visible light communications at data rates up to 1 Mbps, and time-of-flight ranging with cm-scale resolution are demonstrated using this hybrid integrated system.

An evaluation of measurement techniques for algal-derived organic nitrogen.

Algal-derived organic matter (AOM) from algal blooms in water supply systems contains dissolved organic nitrogen (DON) and dissolved organic carbon (DOC) among other constituents. The DON and DOC are disinfection by-product (DBP) precursor compounds, and must be well characterised to facilitate effective removal, thus minimising DBP formation during disinfection. While DOC character has been studied extensively, DON analysis suffers from inaccuracies due to sample pre-treatment and instrument sensitivities. A liquid chromatography method that combines size exclusion chromatography with highly sensitive organic carbon and nitrogen detectors (LC-OCND) has been widely adopted for DOC analysis; however, its potential for application for DON charactersation has been suggested as a viable alternative to existing DON characterisation techniquesnot been assessed despite its potential. Hence, the aim was to compare the effectiveness of conventional total dissolved N-dissolved inorganic N (TN-DIN), and LC-OCND methods for analysing DON in AOM. A suite of N-containing model compounds representative of DON and AOM extracted from Chlorella vulgaris CS-42/7 and Microcystis aeruginosa CS-555/1 were used to evaluate the techniques. The DON of both model compounds and AOM was first analysed using the conventional method and, then, via LC-OCND. It was observed that LC-OCND had a better precision for DON when TN contained more DIN. LC-OCND provided direct quantitative measurements for bulk and fractionated DON and DIN, with little interference caused by DIN. Additionally, LC-OCND provided information on MW distribution and protein content of the AOM. For example, LC-OCND results showed that M. aeruginosa AOM contained more HMW material than C. vulgaris AOM. However, as LC-OCND uses UV oxidation, it could not completely oxidise complex aromatic structures, and thus had a lower recovery for HMW model compounds and algal DON in comparison to the conventional method that used high temperature catalytic oxidation. Overall, it is advised that a combination of LC-OCND and TN analysis be used to provide a more detailed characterisation of N-containing AOM and other similar HMW aquatic NOM samples.

The impact of cell morphology and algal organic matter on algal floc properties.

Physical floc properties were systematically investigated by analysing the structure of algal and cyanobacterial flocs produced by five species (green algae (Chlorella vulgaris) and cyanobacteria (Microcystis aeruginosa (strain CS-564), Microcystis aeruginosa (strain CS-555/01), Dolichospermum circinale and Cylindrospermopsis raciborskii) using aluminium sulphate (alum) at different doses and pH values. The properties of spherical, compact flocs were determined using a laser diffraction instrument and a new in situ image analysis technique was validated to analyse the structure of more complex flocs. The incorporation of algal-derived organic matter (AOM) into the flocs was inferred by evaluating the dissolved organic matter concentration character before and after flocculation using liquid chromatography with organic carbon detection (LC-OCD). D. circinale, C. raciborskii, and M. aeruginosa (CS-564) produced large flocs (2-9 mm), while M. aeruginosa (CS-555) and C. vulgaris produced smaller flocs (<2 mm). While differences in physical floc properties were observed to result from changes in coagulation mechanism, the cell morphology and the AOM composition were the most influential factors. Examination of floc properties can give a rapid insight at the plant for trouble shooting, particularly through the use of the in situ techniques and provide a mechanism by which floc properties can be tailored to downstream processes.

Enhanced real-time cyanobacterial fluorescence monitoring through chlorophyll-a interference compensation corrections.

In situ fluorometers can be used as a real-time cyanobacteria detection tool to maintain safe drinking and recreational water standards. However, previous studies into fluorometers have established issues arising mainly from measurement inaccuracies due to green algae interference. Therefore, this study focusses on developing correction factors from a systematic study on the impact of green algae as an interference source. This study brings a novel technique where the chlorophyll-a (Chl-a) and phycocyanin measurements are used to correct the fluorometer output for interference bias; four fluorometers were tested against three key cyanobacterial species and the relationship between phycocyanin output, green algae and cyanobacteria concentrations were investigated. Good correlation (R2 > 0.9, p-value < 0.05) was found between the fluorometer phycocyanin output and increasing green algae concentration. The optimal correction method was selected for each of the fluorometer and cyanobacteria species pairs by validating against data from the investigation of green algae as an interference source. The correction factors determined in this study reduced the measurement error for almost all the fluorometers and species tested by 21%-99% depending on the species and fluorometer, compared to previous published correction factors in which the measurement error was reduced by approximately 11%-81%. Field validation of the correction factors showed reduction in fluorometer measurement error at sites in which cyanobacterial blooms were dominated by a single species.

pH sensing through a single optical fibre using SERS and CMOS SPAD line arrays.

Full exploitation of fibre Raman probes has been limited by the obstruction of weak Raman signals by background fluorescence of the sample and the intrinsic Raman signal of the delivery fibre. Here we utilised functionalised gold nanoshells (NS) to take advantage of the surface-enhanced Raman spectroscopy (SERS) effect to enhance the pH responsive spectrum of 4-mercaptobenzoic acid (MBA). However, the fibre background is still dominant. Using the photon arrival time-resolving capability of a CMOS single-photon avalanche diode (SPAD) based line sensor, we recover the SERS spectrum without a fibre background in a 10 s measurement. In this manner, pH sensing through a multimode fibre at a low excitation power that is safe for future in vivo applications, with short acquisition times (10 or 60 s), is demonstrated. A measurement precision of ± 0.07 pH units is thus achieved.

Ballistic and snake photon imaging for locating optical endomicroscopy fibres.

We demonstrate determination of the location of the distal-end of a fibre-optic device deep in tissue through the imaging of ballistic and snake photons using a time resolved single-photon detector array. The fibre was imaged with centimetre resolution, within clinically relevant settings and models. This technique can overcome the limitations imposed by tissue scattering in optically determining the in vivo location of fibre-optic medical instruments.

Time-resolved spectroscopy at 19,000 lines per second using a CMOS SPAD line array enables advanced biophotonics applications.

A SPAD-based line sensor fabricated in 130 nm CMOS technology capable of acquiring time-resolved fluorescence spectra (TRFS) in 8.3 milliseconds is presented. To the best of our knowledge, this is the fastest time correlated single photon counting (TCSPC) TRFS acquisition reported to date. The line sensor is an upgrade to our prior work and incorporates: i) parallelized interface from sensor to surrounding circuitry enabling high line rate to the PC (19,000 lines/s) and ii) novel time-gating architecture where detected photons in the OFF region are rejected digitally after the output stage of the SPAD. The time-gating architecture was chosen to avoid electrical transients on the SPAD high voltage supplies when gating is achieved by excess bias modulation. The time-gate has an adjustable location and time window width allowing the user to focus on time-events of interest. On-chip integrated center-of-mass (CMM) calculations provide efficient acquisition of photon arrivals and direct lifetime estimation of fluorescence decays. Furthermore, any of the SPC, TCSPC and on-chip CMM modes can be used in conjunction with the time-gating. The higher readout rate and versatile architecture greatly empower the user and will allow widespread applications across many techniques and disciplines. Here we focused on 3 examples of TRFS and time-gated Raman spectroscopy: i) kinetics of chlorophyll A fluorescence from an intact leaf; ii) kinetics of a thrombin biosensor FRET probe from quenched to fluorescence states; iii) ex vivo mouse lung tissue autofluorescence TRFS; iv) time-gated Raman spectroscopy of toluene at 3056 cm-1 peak. To the best of our knowledge, we detect spectrally for the first time the fast rise in fluorescence lifetime of chlorophyll A in a measurement over single fluorescent transient.

Hydrophobically-associating cationic polymers as micro-bubble surface modifiers in dissolved air flotation for cyanobacteria cell separation.

Dissolved air flotation (DAF), an effective treatment method for clarifying algae/cyanobacteria-laden water, is highly dependent on coagulation-flocculation. Treatment of algae can be problematic due to unpredictable coagulant demand during blooms. To eliminate the need for coagulation-flocculation, the use of commercial polymers or surfactants to alter bubble charge in DAF has shown potential, termed the PosiDAF process. When using surfactants, poor removal was obtained but good bubble adherence was observed. Conversely, when using polymers, effective cell removal was obtained, attributed to polymer bridging, but polymers did not adhere well to the bubble surface, resulting in a cationic clarified effluent that was indicative of high polymer concentrations. In order to combine the attributes of both polymers (bridging ability) and surfactants (hydrophobicity), in this study, a commercially-available cationic polymer, poly(dimethylaminoethyl methacrylate) (polyDMAEMA), was functionalised with hydrophobic pendant groups of various carbon chain lengths to improve adherence of polymer to a bubble surface. Its performance in PosiDAF was contrasted against commercially-available poly(diallyl dimethyl ammonium chloride) (polyDADMAC). All synthesised polymers used for bubble surface modification were found to produce positively charged bubbles. When applying these cationic micro-bubbles in PosiDAF, in the absence of coagulation-flocculation, cell removals in excess of 90% were obtained, reaching a maximum of 99% cell removal and thus demonstrating process viability. Of the synthesised polymers, the polymer containing the largest hydrophobic functionality resulted in highly anionic treated effluent, suggesting stronger adherence of polymers to bubble surfaces and reduced residual polymer concentrations.

Examination of the physical properties of Microcystis aeruginosa flocs produced on coagulation with metal salts.

Coagulation-flocculation (C-F) is a key barrier to cyanobacterial and algal cell infiltration in water treatment plants during seasonal blooms. However, the resultant cell floc properties, in terms of size, strength and density, which dominate under different coagulation conditions and govern cell removal, are not well understood. This paper investigated the floc properties produced during C-F of the cyanobacterium, Microcystis aeruginosa, under low and high doses of aluminium sulphate and ferric chloride coagulants and at different pH values, so as to promote charge neutralisation (CN) and sweep flocculation (SF) dominant conditions (or a combination of these). It was demonstrated that application of ferric chloride produced larger flocs that resulted in higher cell removal during jar testing. These flocs were also larger than those observed for natural organic matter (NOM) and kaolin, suggesting a role of algogenic organic matter (AOM) as an inherent bioflocculant. Under SF conditions, stronger flocs were produced; however, these had lower capacity for size recovery after exposure to high shear. Analysis of particle size distribution demonstrated that large scale fragmentation followed by erosion dominated for CN while erosion dominated under SF conditions. Overall, marked differences were observed dependent on the coagulation regime imposed that have implications for improving robustness of cell removal by downstream separation processes. While the cyanobacterium, M. aeruginosa, appeared to share general floc characteristics commonly observed for NOM and kaolin flocs, there were distinct differences in terms of size and strength, which may be attributed to AOM.

Advanced fluorescence lifetime imaging algorithms for CMOS single-photon sensor based multi-focal multi-photon microscopy.

We have developed a fast hardware friendly bi-exponential fluorescence lifetime algorithm suitable for 2D CMOS single-photon avalanche diode (SPAD) arrays. The performance of the proposed algorithm against other techniques is demonstrated on the data from a plant specimen (Convallaria) by using 0.13µm CMOS SPAD arrays mounted on a multi-beam multi-photon microscopy system.

An implementation of a spike-response model with escape noise using an avalanche diode.

This paper introduces a novel probabilistic spike-response model through the combination of avalanche diode-generated Poisson distributed noise, and a standard exponential decay-based spike-response curve. The noise source, which is derived from a 0.35-µm single-photon avalanche diode (kept in the dark), was tested experimentally to verify its characteristics, before being combined with a field-programmable gate-array implementation of a spike-response model. This simple model was then analyzed, and shown to reproduce seven of eight behaviors recorded during an extensive study of the ventral medial hypothalamic (VMH) region of the brain. It is thought that many of the cell types found within the VMH are fed from a tonic noise synaptic input, where the patterns generated are a product of their spike response and not their interconnection. This paper shows how this tonic noise source can be modelled, and due to the independent nature of the noise sources, provides an avenue for the exploration of networks of noise-fueled neurons, which play a significant role in pattern generation within the brain.

Demonstrating ultra-filtration and reverse osmosis performance using size exclusion chromatography.

Advanced water treatment plants employing ultrafiltration (UF) and reverse osmosis (RO) membrane processes are frequently implemented for the production of high-quality recycled water. It is important that process performance is able to be quantified and assessed to ensure it is fit for purpose. This research utilizes size exclusion chromatography with organic carbon, organic nitrogen and UV(254) detection to determine the change in both DOC concentration and character through a UF/3 stage-RO pilot plant. It was determined that 97% of the influent DOC was removed on average to produce a water of less than 0.5 mg L(-1) as C. The UF process removed more than half of the biopolymer fraction, equating to 4.5% DOC removal, while the RO process generally removed all DOC except a small proportion of the low MW humics and acids and low MW neutral fraction. While not changing significantly in concentration, the Stage 3 RO permeate typically contained low concentrations of humic fraction, indicating a change in character and therefore a change in rejection mechanism. Overall, it was determined that while TOC monitoring is important in advanced water treatment systems, improved understanding of the character of the TOC present lends greater insight into the assessment of process performance.