David Phipps

Residence time distribution of a model hydrodynamic vortex separator

Abstract This study investigates the macromixing within a hydrodynamic vortex separator (HDVS). The device is a scale model of a prototype unit and is operated with zero baseflow. The device under investigation is typically used for the removal of settleable and colloidal solids. The macromixing is investigated by conducting tracer experiments from which the residence time distribution (RTD) is obtained and interpreted to characterise the mixing regime within the HDVS. The method of moments and non-linear regression are used to obtain various RTD functions and flow-model parameters to aid in the characterisation of the devices mixing regime and the degree of any non-ideal flow behaviour. The axial dispersion model (ADM) and tanks-in-series model (TISM) are used in this study. The RTD imperfectly approximates a plug-flow distribution but, the device has some amount of dispersion and is equal to approximately 2–3 perfectly stirred tanks in series. The ADM seems to give a closer representation of the experimental curves compared to the TISM. The sludge hopper appears to be acting as a stagnant zone.

Development of an optical fibre sensor system for online monitoring of microwave plasma UV and ozone generation system

An optical fibre sensor system is being developed to monitor the outputs of a microwave-generated plasma UV lamp, capable of producing germicidal UV and ozone gas simultaneously, for use in food treatment. Optical fibres offer the advantage of allowing for remote monitoring of the measurement site. The fibres are not affected by high electromagnetic fields and the control electronics can be kept away from such a harsh environment, making them an ideal choice for the monitoring of the microwave radiation device. The sensor system monitors UV intensity at 254 nm and also ozone gas concentrations, based on the Beer-Lambert Law for absorption spectroscopy.

Experimental investigations of microwave plasma UV lamp for food applications.

The food industry is keen to have new techniques that improve the safety and/or shelf life of food products without the use of preservatives. There is considerable interest in developing UVlight and ozone (O3) treatments to enhance shelf life. A microwave radiation device that is a novel source of germicidal UV and O3 suitable for the food industry has been developed, which offers speed, cost and energy benefits over existing sources. With this system comes the need to monitor a number of conditions, primarily UV intensity and ozone gas concentrations. The effectiveness of intense UV exposure for short periods of time was assessed on different microorganisms. Culture plates were exposed to a range of doses of UV-C light, and the reduction in numbers of surviving microorganisms was recorded. The results on the biocidal capacity of the microwave generated UV light are presented.

Residence time distribution and the investigation of bed movement in a continuously operated upflow filter (COUF) for tertiary wastewater treatment.

This paper describes an investigation to define the liquid phase flow regime in a continuously operated upflow filter (COUF) together with an assessment of the relative motion of the solid (filter media) phase. The importance of such measurements in the development of a model for these systems, including aerated biological filtration versions is discussed. Initial work was carried out on a model-scale demonstrator unit using Rhodamine WT fluorescent dye tracing for liquid phase studies. Initial outputs show that the liquid phase residence time distribution (RTD) is well approximated by a plug flow assumption. The pattern in which individual particles of the bed move during the operation of the COUF was also investigated on the demonstrator using colored beads as a tracer. The gross movement of the bed and the internal mixing regime described can be regarded as analogous to RTD. Techniques were developed whereby bed movement in the cleaning process could be measured and assessed over time, leading to the generation of 3D bed movement visualisation plots. This work could potentially lead to developments of technologies that could better clean the media and lead to a more even bed movement allowing the filter to operate more efficiently.

Water and Energy Efficient Showers

The performance of showers was studied in a laboratory, in the homes of volunteers and with focus groups, with a view to identifying key factors which would encourage the reduction of both water and energy consumption. Focus groups defined their principal requirement for a “good shower experience” to be adequate water flow to enjoy the experience of showering (enough volume at the right temperature in order to keep warm and to wash satisfactorily). Laboratory work investigated pressure:flow-rate correlation, spray pattern, temperature and “skin pressure”. The pressure:flow-rate relationship followed a simple square-root relationship for most showerheads. Suggestions are made for the use of a Head Factor in design. Showers in homes were modified by temporary insertion of flow restrictors or by replacing conventional shower heads with aerating heads. Flow restrictors proved to be generally unacceptable, while aerating heads were popular. The study has shown a financial payback within a few months for a mixer or pumped shower operating at over 8 l/min by installing a water saving showerhead.

Monitoring and control system for tuneable high frequency microwave assisted chemistry

Microwave chemistry is an established technique in the synthesis of organic compounds at a frequency of 2.45 GHz. This is considered to be a result of the development of microwave ovens, rather than an objective solution, which maximises efficiency through careful selection of the operating frequency. To obtain a frequency for a dielectric, the complex permittivity should be determined as a function of frequency. If the correct heating frequency is found, superheating can occur when a liquid solvent reaches its boiling point and exceeds it. This paper presents sensor diodes and temperature sensors used in a mono-mode reactor, with computer control of an E-H tuner, frequency and incident power to control temperature and power, experimental results showing heating and reactions using ethanol are reported.

A demonstration of athermal effects of continuous microwave irradiation on the growth and antibiotic sensitivity of Pseudomonas aeruginosa PAO1.

Stress, caused by exposure to microwaves (2.45 GHz) at constant temperature (37 ± 0.5°C), alters the growth profile of Pseudomonas aeruginosa PAO1. In the absence of microwave treatment a simple, highly reproducible growth curve was observed over 24 h or more. Microwave treatment caused no reduction in growth during the first 6 h, but at a later stage (>12 h) the growth was markedly different to the controls. Secondary growth, typical of the presence of persisters clearly became apparent, as judged by both the dissolved oxygen and the cell density profiles. These treated cells showed distinct morphological changes, but on regrowth these cells reverted to normal. The microwave induced persisters were subject to antibiotic challenge (tobramycin) and showed increased sensitivity when compared to the unstressed planktonic cells. This is in marked contrast to antibiotic induced persisters which show increased resistance. This provides evidence for both a nonthermal effect of microwaves and a previously undescribed route to a novel form of antibiotic susceptible persister cells.

Water Saving in Domestic Car Washing

There is considerable interest in promoting domestic water efficiency. A wide range of studies have focused on water saving within the house, both by technical means (low flush WCs, reduced flow in showers, etc.) and by changing user habits. However, rather less attention has been paid to water use outside the house. One of the activities that uses water outside the house is car washing. Much is known about water use in commercial car washes but relatively little about domestic car washing. The aim of this study was to gather information about the water used for this activity. Key questions were whether the wash is done in a commercial carwash or at home, and, if the latter, what is the volume used per wash and the frequency of washing? As part of this trial the use of water on different types of cars using different washing regimes was measured. From the study conclusions are drawn about the likely water use for domestic car washing.

Nitrifying continuous upflow filters: Understanding large scale plant from laboratory and pilot scale experiments.

Continuous up-flow filters (CoUFs) are principally designed to be used in tertiary wastewater treatment for the removal of particulate solids, prior to final effluent discharge. However, good designs are adaptable and with the addition of aeration this type of plant can also act as effective nitrifying filters (ACoUFS). Given the difficulties of evaluating operational plant in situ, relatively few studies have been made at full scale. Instead, in order to understand and improve the performance of such plant, laboratory and pilot scale studies are more usually undertaken though there is always an element of uncertainty in how such results will transfer to full-scale operation. Here, based on a series of previous studies, a logical route from small scale laboratory work, via pilot plant studies to operation at full scale is presented. The process starts with a laboratory scale screen involving critical selection of media, followed by the evaluation of the media for both bulk hydrodynamic properties, principally pressure drop, and then for biofilm support and basic nitrifying capability. This is then extended at pilot scale into the macroscopic behaviour of the moving bed, hydrodynamic studies and to the nitrification itself. The transfer of the results to full scale plant is then discussed.

Storm Water Best Management Practices into the Existing Urban Landscape - Systems for Controlling Sediments

The operation of an ‘advanced’ hydrodynamic vortex separator (AVS) designed for stormwater sediment interception has been examined using particle capture and retention efficiency testing and dye tracer testing. For retention efficiency in particular (referring to the efficiency with which a chamber retains pollutants following capture) the results are compared with those for other configurations, including simple vortex and gravity separation devices. The results show how the collection and retention efficiencies of the AVS are enhanced through the presence of a quiescent zone in the base where solids are stored. A simple model of system operation is considered, based on the surface loading rate of the active region and the particle sedimentation velocity. It is concluded that a comprehensive model of system performance needs to take into account a variety of factors, including the detailed characteristics of the sediment material and the hydrodynamic characteristics of the specific separation device in question.