Muhammed Bhuiyan

An assessment of the dynamic stability of microorganisms on patterned surfaces in relation to biofouling control

Microstructure-based patterned surfaces with antifouling capabilities against a wide range of organisms are yet to be optimised. Several studies have shown that microtopographic features affect the settlement and the early stages of biofilm formation of microorganisms. It is speculated that the fluctuating stress–strain rates developed on patterned surfaces disrupt the stability of microorganisms. This study investigated the dynamic interactions of a motile bacterium (Escherichia coli) with microtopographies in relation to initial settlement. The trajectories of E. coli across a patterned surface of a microwell array within a microchannel-based flow cell system were assessed experimentally with a time-lapse imaging module. The microwell array was composed of 256 circular wells, each with diameter 10 μm, spacing 7 μm and depth 5 μm. The dynamics of E. coli over microwell-based patterned surfaces were compared with those over plain surfaces and an increased velocity of cell bodies was observed in the case of patterned surfaces. The experimental results were further verified and supported by computational fluid dynamic simulations. Finally, it was stated that the nature of solid boundaries and the associated microfluidic conditions play key roles in determining the dynamic stability of motile bacteria in the close vicinity over surfaces.

A novel approach to determine the efficacy of patterned surfaces for biofouling control in relation to its microfluidic environment

Biofouling, the unwanted growth of sessile microorganisms on submerged surfaces, presents a serious problem for underwater structures. While biofouling can be controlled to various degrees with different microstructure-based patterned surfaces, understanding of the underlying mechanism is still imprecise. Researchers have long speculated that microtopographies might influence near-surface microfluidic conditions, thus microhydrodynamically preventing the settlement of microorganisms. It is therefore very important to identify the microfluidic environment developed on patterned surfaces and its relation with the antifouling behaviour of those surfaces. This study considered the wall shear stress distribution pattern as a significant aspect of this microfluidic environment. In this study, patterned surfaces with microwell arrays were assessed experimentally with a real-time biofilm development monitoring system using a novel microchannel-based flow cell reactor. Finally, computational fluid dynamics simulations were carried out to show how the microfluidic conditions were affecting the initial settlement of microorganisms.

Application of Victorian brown coal for removal of ammonium and organics from wastewater

ABSTRACT Brown coal is a relatively abundant and low-cost material, which has been used as an effective ion-exchanger to remove ammonium from wastewater. In this study, the influences of pH, ammonium concentration and brown coal dose were investigated for removal of ammonium content from synthetic wastewater. Raw brown coal (RBC) treated with base solution has superior ammonium removal efficiency compared to RBC, which was due to chemical alterations and thus greater attachment of ammonium molecules to base-washed brown coal (BWBC), confirmed by Fourier transform infra-red spectroscopy. Scanning electron microscopy-electron diffraction scattering has identified the augmented sodium content in BWBC, which was subsequently replaced with nitrogen upon wastewater treatment. Crystallographic analysis showed a higher crystallinity formed in BWBC compared to RBC, which was likely due to formation of sodium salt crystals during NaOH treatment. Fitting batch experimental results to adsorption kinetic models suggested that the removal of ammonium was mainly governed by the reaction process rather than the physical diffusion mechanism. Both kinetic and isotherm studies confirmed higher adsorption capacity for BWBC compared to RBC. RBC in column mode was also experimented with to show organics removal from a secondary effluent. A comparatively lower removal of organics was obtained due to inability of charge neutralization as both brown coal and organics are positively charged.

Temporal Trends of Discrete Extreme Events - A Case Study

Investigating trends in discrete events is essential for the study of changing patterns of extreme events. Temporal trends in the inter-arrival times of occurrence of drought events were examined for 21 selected stations across Victoria, Australia. In the present study, the Standardize Precipitation Index (SPI) was applied for 12-month time scale to identify drought. A drought event here is defined as a period in which the SPI is continuously negative and reaching a value of -1.0 or less. Often, nonparametric tests are commonly used to test for trends including in discrete events. However, discrete events are not constant because of the presence of zero values or non-normality of data. The methodology applies to long-term records of event counts and is based on the stochastic concepts of Poisson process and standard linear regression. Overall, of the 21 stations, 15 showed statistically significant increasing frequency indicates those events are becoming more frequent. Only one station gave insignificant result. The remaining 5 stations showed the time between events was significantly increasing designates droughts are becoming less frequent.

Development of drought severity-duration-frequency curves in Victoria, Australia

Abstract One of the many ways in preparing for drought is to carry out a drought risk assessment by characterisation of the frequency, severity and duration of a drought. Therefore, the current study aimed at the development of severity-duration-frequency (SDF) curves to provide a comprehensive characterisation of the droughts for 10 selected stations in Victoria, Australia. The development of the frequency curves is based on the precipitation deficits which were computed based on the Standardised Precipitation Index (SPI). Instead of using SPI values, the precipitation thresholds were used to compute the severity of the droughts. This would be very helpful in delivering information that can be understood easily by ordinary users and decision-makers. The SDF curves were developed using the partial duration series (PDS) technique. Log Pearson Type III distribution was chosen and fitted well to the precipitation deficits for different durations of drought. Overall, SDF curves were successfully derived for 10 stations in Victoria and can provide useful information for medium/long term planning, such as in planning irrigation supply and developing drought relief policies.

Factors associated with Chronic Kidney Disease of unknown aetiology (CKDu) in North Central Province of Sri Lanka: a comparative analysis of drinking water samples

Chronic Kidney Disease of unknown aetiology (CKDu) is a major health concern in North Central Province (NCP) of Sri Lanka. Anuradhapura and Polonnaruwa are the two most affected districts in NCP. This research was designed to identify main suspected CKDu causative agents in drinking water in NCP. Drinking water samples were collected from shallow wells of CKDu patients and non-patients in Anuradhapura and Polonnaruwa districts. They were tested for chemical ions: chloride, fluoride, nitrate, phosphate, calcium, magnesium, sodium, cadmium and arsenic. An analytical framework was developed to analyse water quality data using statistical methods, namely univariate analysis of variance (ANOVA) and Dunnett’s T3 post hoc test, Kruskal–Wallis (KW) and Mann–Whitney’s post hoc test, discriminant analysis, factorial analysis followed by reliability tests. ANOVA, KW and their post hoc tests were applied to show the significant differences at p < 0.05 in mean and median values of chemical constituents between CKDu patient and non-patient samples. Discriminant analysis was applied to show the degree of accuracy in original sampling groups. Factorial analysis was applied to identify the ion combinations in each group. A secondary set of data obtained from drinking water samples of CKDu endemic and non-endemic areas were also analysed independently using the same analytical techniques to compare the results.

Design of drip irrigation system using microtubes

Abstract To obtain the best emission uniformity in drip irrigation the pressure regulators and pressure compensating emitters are in use since long back. In contrast, clogging has been the major obstacle, particularly in areas with brackish water where problems of precipitation of calcium-carbonate, organic materials and suspended sands are severe. Microtubes as small bore polyethylene tubes of approximately 2.0-4.0 mm internal diameters can be used to deliver equal discharges, by varying its length to adjust varying heads along a given lateral. These microtubes can be simpler than inside passages of those traditional drippers and thus will be less susceptible to clogging. The computed set of varying length microtubes that are emitting equal fl ows at the end-lateral can be copied to subsequent laterals of the manifold to work them as larger emitters with a characteristic pressuredischarge relationship. As such the variation of fl ow through these laterals is restricted by limiting their number to have emission uniformity EU ≥ 90%. For case studies on fl at-ground for a given set of lateral diameters (10-16 mm), the exponents in the pressure-discharge relationship varied narrowly: 0.60-0.69 for larger discharges and 0.78-0.84 for smaller discharges. Similarly on sloping terrain at S = 0.25% and 0.5%, the exponents varied relatively widely: 0.62-0.92 and 0.84-0.95 for larger and smaller discharges, and 0.65-0.97 and 0.85-0.99 for larger and smaller discharges, respectively. It can be reasoned that these laterals function as long path emitters. Variation of the corresponding microtube lengths can be around 0-85%, 0-460% and 0-810% longer than the given minimum length (1min = 1.25 m), respectively. When the required discharges and diameters of microtube, lateral and manifold and other ground conditions are given, the length of the microtubes, the pressure heads, emission uniformity and the best subunit dimensions can be obtained using the algorithm developed in this research.