Niranjali Jayasuriya

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.

Pollutant load removal efficiency of pervious pavements: is clogging an issue?

Pervious pavements in car parks and driveways reduce the peak runoff rate and the quantity of runoff discharged into urban drains as well as improve the stormwater quality by trapping the sediments in the infiltrated water. The paper focuses on presenting results from the laboratory tests carried out to evaluate water quality improvements and effects of long-term decrease in infiltration rates with time due to sediments trapping (clogging) within the pavement pores. Clogging was not found to be a major factor affecting pervious pavement performance after simulating 17 years of stormwater quality samples.

Catchment process affecting drinking water quality, including the significance of rainfall events, using factor analysis and event mean concentrations

To ensure the protection of drinking water an understanding of the catchment processes which can affect water quality is important as it enables targeted catchment management actions to be implemented. In this study factor analysis (FA) and comparing event mean concentrations (EMCs) with baseline values were techniques used to asses the relationships between water quality parameters and linking those parameters to processes within an agricultural drinking water catchment. FA found that 55% of the variance in the water quality data could be explained by the first factor, which was dominated by parameters usually associated with erosion. Inclusion of pathogenic indicators in an additional FA showed that Enterococcus and Clostridium perfringens (C. perfringens) were also related to the erosion factor. Analysis of the EMCs found that most parameters were significantly higher during periods of rainfall runoff. This study shows that the most dominant processes in an agricultural catchment are surface runoff and erosion. It also shows that it is these processes which mobilise pathogenic indicators and are therefore most likely to influence the transport of pathogens. Catchment management efforts need to focus on reducing the effect of these processes on water quality.

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.

Adsorption Study on Moringa Oleifera Seeds and Musa Cavendish as Natural Water Purification Agents for Removal of Lead, Nickel and Cadmium from Drinking Water

The effectiveness of plant based materials Moringa oleifera (Moringa) seeds and Musa cavendish (banana peel) for removing heavy metals namely lead (Pb), nickel (Ni) and cadmium (Cd) from contaminated groundwater was studied. Tests were carried out with individual and combined biomass at neutral pH condition on synthetic groundwater samples. The optimum biomass doses were determined as 200 mg/L for single biomass and 400 mg/L (in the ratio of 200 mg/L: 200 mg/L) for combined biomasses and used for adsorption isotherm studies with contact time of 30 minutes. Results showed that combined biomasses was able to met the Pb, Ni and Cd WHO standards from higher Pb, Ni and Cd initial concentrations which were up to 40 µg/L, 50 µg/L 9 µg/L, respectively compared to individual biomass of Moringa seed and banana peel. Moringa seeds exhibited the highest removal of Pb (81%) while the combined biomasses was most effective in removing Ni (74%) and Cd (97%) over wider their initial concentration ranges. The experimental data were linearized with Langmuir and Freundlich adsorption isotherm models. Freundlich model described the Pb adsorption better than the Langmuir model for all the tested biomasses. However, the Langmuir model fit better with the experimental data of Ni adsorption by Moringa seeds. Both models showed negligible differences in the coefficient of determination (R2) when applied for Ni and Cd adsorption on banana peel and combined biomasses, suggesting that there were multiple layers on the biomass interacting with the metals. Chemisorption is suggested to be involved in Pb adsorption for all tested biomasses as the value of nF calculated was lower than one. This type of adsorption could explain the phenomenon of different behavior of Pb removal and the higher Pb adsorption capacity (represented by KF values) compared to Ni and Cd. The study demonstrates that Moringa seeds, banana peel and their combination have the potential to be used as a natural alternative to the other water treatment agents for removing the Pb, Ni and Cd from drinking water.

A Simple Time Series Approach to Modelling Urban Water Demand

Abstract An urban water demand model at a water supply distribution zone level is developed. The model is based on a previous proposition that water use is made up of base use determined from winter consumption and as a function of day of the week, rainfall and temperature and of seasonal use assumed to be composed of the potential use that is dependent on temperature in the absence of rainfall, and of the short effects of climatic factors. Daily data at East Doncaster zone from April 1991 to December 1999 are used in the regression model and is evaluated based on R2 and standard error. The model is tested independently using data collected from 2000–2001.

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.

Use of regionalisation approach to develop fire frequency curves for Victoria, Australia

It is important to perform fire frequency analysis to obtain fire frequency curves (FFC) based on fire intensity at different parts of Victoria. In this paper fire frequency curves (FFCs) were derived based on forest fire danger index (FFDI). FFDI is a measure related to fire initiation, spreading speed and containment difficulty. The mean temperature (T), relative humidity (RH) and areal extent of open water (LC2) during summer months (Dec–Feb) were identified as the most important parameters for assessing the risk of occurrence of bushfire. Based on these parameters, Andrews’ curve equation was applied to 40 selected meteorological stations to identify homogenous stations to form unique clusters. A methodology using peak FFDI from cluster averaged FFDIs was developed by applying Log Pearson Type III (LPIII) distribution to generate FFCs. A total of nine homogeneous clusters across Victoria were identified, and subsequently their FFC’s were developed in order to estimate the regionalised fire occurrence characteristics.

Assessment of fire danger vulnerability using McArthur’s forest and grass fire danger indices

McArthur’s fire danger index (FDI) is an integrated measure of the risk of fire occurrence, spreading speed and containment difficulty. The climatic parameter-dependent McArthur forest and grass fire danger indices were used to categorize fire danger severity. This paper explored the characteristics of four different climatic stations in Victoria, Australia, to determine their spatial and temporal variations impacting FDIs and the risk of fire occurrence. Sensitivity analysis was performed to develop nomograms to relate the variation of FDIs with key climatic parameters. These nomograms combine temperature, relative humidity and wind speed to determine fire risk categories in assisting field-based emergency and fire management authorities to identify danger and response plans to mitigate risks by mobilizing human and mechanical resources.