Vasantha Aravinthan

Energy characterisation of ultrasonic systems for industrial processes

Obtaining accurate power characteristics of ultrasonic treatment systems is an important step towards their industrial scalability. Calorimetric measurements are most commonly used for quantifying the dissipated ultrasonic power. However, accuracy of these measurements is affected by various heat losses, especially when working at high power densities. In this work, electrical power measurements were conducted at all locations in the piezoelectric ultrasonic system equipped with ½″ and ¾″ probes. A set of heat transfer calculations were developed to estimate the convection heat losses from the reaction solution. Chemical dosimeters represented by the oxidation of potassium iodide, Fricke solution and 4-nitrophenol were used to chemically correlate the effect of various electrical amplitudes and treatment regimes. This allowed estimation of sonochemical-efficiency (SE) and energy conversion (XUS) of the ultrasonic system. Results of this study showed overall conversion efficiencies of 60-70%. This correlated well with the chemical dosimeter yield curves of both organic and inorganic aqueous solutions. All dosimeters showed bubble shielding and coalescence effects at higher ultrasonic power levels, less pronounced for the ½″ probe case. SE and XUS values in the range of 10(-10) mol/J and 10(-3) J/J respectively confirmed that conversion of ultrasonic power to chemical yield declined with amplitude.

Impact of pulsed ultrasound on bacteria reduction of natural waters

There is a limited work on the use of pulsed ultrasound for water disinfection particularly the case of natural water. Hence, pulsed ultrasound disinfection of natural water was thoroughly investigated in this study along with continuous ultrasound as a standard for comparison. Total coliform measurements were applied to evaluate treatment efficiency. Factorial design of 2(3) for the tested experimental factors such as power, treatment time and operational mode was applied. Two levels of power with 40% and 70% amplitudes, treatment time of 5 and 15 min and operational modes of continuous and pulsed with On to Off ratio (R) of 0.1:0.6 s were investigated. Results showed that increasing power and treatment time or both increases total coliform reduction, whereas switching from continuous to pulsed mode in combination with power and treatment time has negative effect on total coliform reduction. A regression model for predicting total coliform reduction under different operating conditions was developed and validated. Energy and cost analyses applying electrical and calorimetric powers were conducted to serve as selection guidelines for the choosing optimum parameters of ultrasound disinfection. The outcome of these analyses indicated that low power level, short treatment time, and high R ratios are the most effective operating parameters.

Investigating the feasibility and the optimal location of pulsed ultrasound in surface water treatment schemes

AbstractThe deterioration of surface water quality due to extreme weather events and increasing human activities has exacerbated the common problems in drinking water production such as filtration fouling and DPBs formation. This in turn has urged for exploring alternative methods for the traditional treatment methods that are able to improve the removal of contaminants with minimal impact on environment and human health. In this study, the application of pulsed and continuous ultrasound for improving the quality of natural water with fresh natural organic matter (NOM) mainly driven from vegetation has been evaluated. The evaluation was performed using cost-effective and quick measurements such as specific UV–vis absorbance, CODMn, alkalinity and conductivity. The changes in the characteristics of NOM induced by ultrasound were used to develop a framework for evaluating ultrasound performance in improving conventional surface water treatment processes and to identify the best fit of ultrasound within the ...

Coal seam gas water as a medium to grow Dunalliella tertiolecta microalgae for lipid extraction

AbstractThe coal seam gas (CSG) industry in Queensland, Australia is expected to produce about 300 GL of CSG water annually as a by-product of its methane extraction processes. Surat basin aquifers typically produce sodium bicarbonate/chloride type water, having high concentration of salts making it unfit for direct beneficial use. The objective of this bench-scale investigation is to assess the potential of using bicarbonate-rich CSG water as a medium for growing Dunalliella tertiolecta for biofuel production. The rates of microalgal growth and carbon sequestration were found to be 49.7 mg SS/L/d and 29 mg C/L/d, respectively, with an average total lipid content of 22% in CSG medium enriched with nutrients and amended for a salinity concentration of 10 gNaCl/L and 200 mg carbon/L in nonaerated batch reactor. In summary, the brine resulting from reverse osmosis treated CSG water could be trialed as an ideal medium to grow the microalgae D. tertiolecta.

Assessment on activated sludge models for acetate biodegradation under aerobic conditions

A comparison of four different established models along with parameter estimation was carried out in order to explain the aerobic biodegradation of acetate in an activated sludge system. These models were investigated using experimental OUR data from batch experiments of three different concentration studies. Model calibration reveals that ASM1 model is not suitable to explain the observed experimental OUR during the famine phase implying storage compounds could play an important role during that stage. Besides, the model corresponds to the accumulation concept and is not well fitted for all concentrations studies though it includes the storage phenomena. Both the ASM3 model and the model for simultaneous storage and growth on substrate can well describe the acetate biodegradation process, however the OUR data alone is not sufficient to justify the suitability of those models. Simulated profiles using the model outputs demonstrate that storage is overestimated while ammonia degradation is underestimated in ASM3 compared to simultaneous growth and storage model. The current study also gives reasonable outcomes related to parameter estimation as compared with previous study which is statistically interpreted in this paper.

Nutrient removal of nursery and municipal wastewater using Chlorella vulgaris microalgae for lipid extraction

AbstractMicroalgae grown in wastewater media can not only be exploited for the nutrient removal from the wastewater, but also for the production of biofuels. In this paper, we investigated the growth of Chlorella vulgaris in iceberg lettuce nursery and municipal wastewater in a batch reactor. We analyzed the microalgal growth rate, nutrient removal rate and lipid production along with real-time monitoring of pH and dissolved oxygen (DO) dynamics during the culture period, which is rarely reported. was found to be the preferred form of nitrogen among different species of nitrogen for the growth of microalgae, and total specific nitrogen depletion rates of 33.0 and 39.6 mg TN/gSS/d were observed for nursery and municipal wastewater, respectively. The specific phosphate removal rates were 3.4 and 10.8 mg  /gSS/d for nursery and municipal wastewater, respectively. The algal growth in nutrient-rich media resulted in increase in pH and DO concentration concurrently. The online measurements including pH and DO p...

Calibration of biokinetic model for acetate biodegradation using combined respirometric and titrimetric measurements

Simultaneous storage and growth model has recently gained increased acceptance among researchers that can better interpret the processes occurring in activated sludge processes during aerobic biodegradation of organic carbon. The model underwent further improvement and was successfully calibrated using respirometric measurements, acetate being a test substrate. However, model based interpretation of titrimetry needs to be verified for proper validation of this model since pH and dissolved oxygen dynamics occur simultaneously in a batch reactor. Hence, in this paper, it is aimed to modify the existing model by introducing stoichiometric parameters involved in titrimetry in each step of the growth and storage phases along with the consideration of non-linear carbon dioxide transfer rate in liquid phase. The model calibration was done for three different acetate concentrations using titrimetric, respirometric and combined respirometric-titrimetric measurements. The parameter estimation results from all three combinations were found to be very close that supports the validity of the model.

Assessing the application and downstream effects of pulsed mode ultrasound as a pre-treatment for alum coagulation.

The application of pulsed mode ultrasound (PMU) as a pre-treatment for alum coagulation was investigated at various alum dosages and pH levels. The effects of the treatments on turbidity and dissolved organic carbon (DOC) removal and residual Al were evaluated. Response surface methodology (RSM) was utilized to optimize the operating conditions of the applied treatments. The results showed that PMU pre-treatment increased turbidity and DOC removal percentages from maximum of 96.6% and 43% to 98.8% and 52%, respectively. It also helped decrease the minimum residual Al from 0.100 to 0.094 ppm. The multiple response optimization was carried out using the desirability function. A desirability value of >0.97 estimated respective turbidity removal, DOC removal and Al residual of 89.24%, 45.66% and ∼ 0.1 ppm for coagulation (control) and 90.61%, >55% and ∼ 0 for coagulation preceded by PMU. These figures were validated via confirmatory experiments. PMU pre-treatment increased total coliform removal from 80% to >98% and decreased trihalomethane formation potential (THMFP) from 250 to 200 ppb CH3Cl. Additionally, PMU application prior to coagulation improved the settleability of sludge due to the degassing effects. The results of this study confirms that PMU pre-treatment can significantly improve coagulation performance.

Insights into the scalability of magnetostrictive ultrasound technology for water treatment applications

To date, the successful application of large scale ultrasound in water treatment has been a challenge. Magnetostrictive ultrasound technologies for constructing a large-scale water treatment system are proposed in this study. Comprehensive energy evaluation of the proposed system was conducted. The effects of chosen waveform, scalability and reactor design on the performance of the system were explored using chemical dosimetry. Of the fundamental waveforms tested; sine, triangle and square, the highest chemical yield resulted from the square wave source. Scaling up from the 0.5L bench-scale system to the 15 L large-scale unit resulted in a gain of approximately 50% in sonochemical efficiency (SE) for the system. The use of a reactor tank with 45° inclined sides further increased SE of the system by 70%. The ability of the large scale system in removing contaminants from natural water samples was also investigated. The results revealed that the large-scale unit was capable of achieving a maximum removal of microbes and dissolved organic carbon (DOC) of 35% and 5.7% respectively at a power density approximately 3.9 W/L. The results of this study suggest that magnetostrictive ultrasound technology excited with square wave has the potential to be competitive in the water treatment industry.

Tracking ultrasonically structural changes of natural aquatic organic carbon: Chemical fractionation and spectroscopic approaches.

In this study, the structural alteration to DOC for a range of ultrasound treatments was investigated with chemical fractionation and UV-vis spectroscopic measurement. Ultrasound treatments were applied in continuous and pulsed modes at power levels of 48 and 84 W for effective treatment times of 5 and 15 min. Overall results show that the ultrasound treatments tended to degrade the hydrophobic aromatic fraction, while increasing the hydrophilic fraction to a lesser extent. The highest recorded reduction of hydrophobic DOC (17.8%) was achieved with pulse treatment of 84 W for15 min, while the highest increase in the hydrophilic DOC (10.5%) was obtained with continuous treatment at 84 W and 5 min. The optimal ultrasound treatment conditions were found to be pulse mode at high power and short treatment time, causing a minimal increase in the hydrophilic fraction of 1.3% with moderate removal of the hydrophobic fraction of 15.52%. The same treatment conditions, with longer treatment time, resulted in the highest removal of SUVA254 and SUVA280 of 17.09% and 16.93, respectively. These results indicate the potential for ultrasound treatments in DOC structural alteration. The hydrophobic fraction showed strong and significant correlations with UV absorbance at 254 and 280 nm. A254/A204 also exhibited strong and significant correlations with the hydrophobic/hydrophilic ratio. The other UV ratios (A250/A365 (E2/E3) and A254/A436) had weak and insignificant correlations with the hydrophobic/hydrophilic ratio. This confirms the applicability of UV indices as a suitable surrogate method for estimating the hydrophobic/hydrophilic structure.