22 AUSTRALIAN WATER MANAGEMENT REVIEW SYDNEY WATER AND OXYZONE COLLABORATE TO DEVELOP AN INNOVATIVE OZONE TRAILER FOR DISINFECTION OF WATER MAINS
Water authorities, under the Water Supply Code of Australia, are required to disinfect new water mains before putting them into service to protect public health. Sydney Water s traditional practice is to disinfect new mains using super chlorinated water for 24 hours. The super chlorinated water is then flushed out into the environment. The super chlorinated water has the potential to damage the environment so it must be dechlorinated prior to discharge. Mains disinfection using chlorine has a small but real risk of supplying highly chlorinated water to customers. During the recent prolonged drought, water restrictions were introduced by the NSW Government. Sydney Water led a successful customer behavioural change program on water efficiency, however there was public concern in relation to water wastage in the mains chlorination process. Equally legitimate concerns were raised by the property development industry when delays were experienced connecting water mains to new developments. Ozone is a very strong oxidant with the added advantage of breaking down rapidly into harmless Oxygen. These two properties make ozone attractive for the water mains disinfection process - Ozone provides a high level of confidence in regards to bacterial inactivation while being able to break down as the job is being completed. This reduces the risk in relation to chemicals coming into contact with operators (in terms of health and safety) and eliminates the risk of causing environmental harm. In the case of chlorination, operators need to neutralise the chlorine using another chemical as it is being discharged into the environment. This leads to greater exposure risks. To find an alternative to chlorine disinfection Sydney Water worked with a predecessor of Oxyzone Pty Ltd to conduct a pilot plant study at West Ryde by fabricating a pipe test rig and using ozone as the disinfectant. The study demonstrated that water main disinfection by ozonation offered excellent disinfection in a very short contact timeframe, had no negative impact on water quality, and was potentially a very cost effective alternative. In the pilot study, ozone was found to be faster in terms of achieving bacterial inactivation, more effective, cheaper, better for the environment and safer than chlorine. Sydney Water was conscious of the fact that engineering issues would arise when trying to develop a mobile ozone disinfection system capable of disinfecting water mains in the field. However, the benefits of overcoming these issues were quickly recognised. In light of the encouraging pilot plant findings, it was decided to buy or build a trailer mounted ozone generator and dosing system to trial disinfection of water mains under field conditions. A commercially available local system was found. Sydney Water purchased a unit but found that it did not provide a consistent ozone residual within the water phase. In order to overcome these shortcomings Sydney Water worked in collaboration with Oxyzone Pty Ltd (experts in the design of ozone generator systems) to design and build a prototype ozone trailer which: was able to effectively dissolve ozone in the water phase could maintain an effective ozone residual throughout the length of main to be disinfected was effective in achieving bacterial inactivation had no other detrimental effects on water quality was environmentally friendly was safe to operate could be automated as much as possible for ease of operation would be efficient and cost effective Oxyzone constructed a new prototype incorporating a corona discharge ozone generator with mixer, degas unit, injector and compatible pump. Operational staff members from Sydney Water s Civil Delivery business formed part of the developmental team from the onset to provide an operator s perspective on how to make the trailer easier to use. After successful trials of the prototype ozone trailer, permanent modifications were carried out to build a new ozone trailer. Based on the experience generated over the trial, Oxyzone and Sydney Water incorporated additional features to minimise operator intervention (automation) and to meet occupational health and safety requirements during operation. Design Process The broad design objectives were that the unit had to be mobile, self-contained, and simple to operate with minimal operator intervention as well as being effective in achieving its purpose. The enhanced automation reduced operational complexities in the final version when compared to the prototype version. The innovative use of devices such as a pressure reducing valve (PRV), Maric flow control valves, pressure transducers, a variable speed drive (VSD) and atmospheric ozone detector (with automatic shutdown if excess ozone is detected) achieved minimal operator intervention. An integrated automatic online measurement device, the ozone monitoring cabinet (OMC), was developed separately as a quality assurance hold point, to take real time measurements, alert operators as to the completion of the job and to minimise the potential of human errors. The OMC also automatically emails results back to nominated recipients thus eliminating any need for paper based records. The ozone trailer design was based on a 10ft x 5ft galvanised frame aluminium plate floor custom manufactured dual axle box trailer with override brakes which was able to accommodate the disinfection system. The total weight of the unit is between 1,550kg and 1,800kg depending on the options fitted. 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Figure 1: Custom made design of galvanised frame box tandem trailer Figure 2: Front view showing tool box, diesel pump, Maric flow valves and stainless steel pipe work Figure 3: Rear view showing inlet/outlet of pipe, diesel generator, oxygen gas supply system Figure 4: Side view showing oxygen gas supply system, PRV, stainless steel pipe work Figure 5: Side view showing ozone generation cabinet, electrical panel and diesel generator 24 Australian water management review
A venturi injector followed by a static mixer is used to introduce the ozone gas into the water flow to allow maximum dissolution of ozone gas. This is followed by a degas/contact chamber, the primary function of which is to separate undissolved gases through a vortex in the column of water. The undissolved ozone escapes to the top of the column to be released into a water trap using a specialised relief valve. The ozone destruction unit converts ozone into oxygen through a catalyst which in turn is regenerated using an electric heater. Generation of ozone gas is carried out by a purpose designed and built air cooled corona discharge ozone generator capable of producing 120 g of ozone per hour. Built using only high quality Australian manufactured components, the ozone generator has been designed for mobility, serviceability and dependability. The generator is also designed with an IP55 rating to operate in all weather conditions including rain. Fragile ozone cell components are housed securely in heavy gauge stainless steel cabinets to prevent corrosion and to withstand movement on rough road conditions. The ozone generator has a number of inbuilt safeguards designed to cease its operation if the water supply, oxygen feed or the operating environment becomes unsafe. A solar panel has been fitted on the top of ozone generation unit to provide a trickle charge to the battery when the system is not in use. Occupational health and safety considerations In addition to the inbuilt safeguards and low voltage fitting, the design incorporated additional safeguards to address potential health and safety issues. An external atmospheric ozone monitor is installed in the vicinity of the area that is prone to ozone release. The monitor will trigger an automatic shutdown of the ozone generator if it detects ozone concentration above 0.1 ppm and alert the operator of a possible problem by way of a flashing light. The ozone generator is designed to automatically shut down in case of water pressure loss and insufficient oxygen gas supply. Unlike chlorination, ozone is manufactured onsite which eliminates the transportation of dangerous chemicals and reduces the potential risk of exposure to chemicals. Operation & Maintenance of the Ozone Trailer Operation The trailer has been designed for curb side operation reducing the risk to potential traffic exposure. Once the operational timing sequence is finished then the disinfection of the new main is deemed complete. The OMC signals the operator that the job is complete and will then automatically transmit the results to predetermined recipients eliminating any need for paper based records. A typical time from start to the completion of the job is about 1 hour (includes preparation and packing up time) after which the new main can be put into service. Maintenance Oxyzone Pty Ltd designed and manufactured the ozone generator modules, control system and performed the fabrication work for the ozone trailer at their premises in Somersby on the NSW Central Coast. The tandem axle trailer was custom designed and built by a local manufacturer to meet the ozone trailer specifications. Spare parts for maintenance are available from stock. Scheduled maintenance requiring the full servicing of the ozone generator modules and a complete system check and adjustment is required annually with only a functional check at six monthly intervals. Trials Small lengths of isolated 100mm mains were trialled first in different geographical locations of Sydney, until it was verified that the design of the ozone trailer had optimised ozone dissolution within the water phase. After successful trials of 100mm mains the same process was successfully duplicated on 150mm, 200mm, 250mm and 300mm mains. Development of the Ozone Monitoring Cabinet To minimise operational complexities related to use of the ozone disinfection process, Sydney Water has developed a real time continuous turbidity and Oxidation Reduction Potential monitoring system for use in the field. These measurements will be used as a hold point to either pass or fail a water main ozonation job at the same time the main is being disinfected. Figure 6: OMC showing traffic light system and trolley to reduce operational complexity This monitoring system allows operators with minimal technical skill to operate the ozone disinfection trailer. Operational data is collected electronically and transferred to a nominated e-mail account. The system alerts the operator if/when the pass criteria has been met for the ozone disinfection process. This system eliminates all paper work, manual intervention and judgement calls made by operators. THE AUSTRALIAN WATER MANAGEMENT REVIEW 25
Benefits of the Ozone Trailer Overall assessment found that the ozone trailer disinfection process was vastly superior to the superchlorination process: the capital cost of a new trailer is expected to be recouped by operational savings within a matter of months. the implementation of the new ozone process within Sydney Water will lead to an annual saving of approximately $1.4 million and deliver an approximate 40% saving for the disinfection of new mains. mains can be placed into service on the same day they are ozonated. The chlorine process could take up to 3 separate days to complete a job. field trials comparing the disinfection performance of chlorination versus ozonation showed that the ozone trailer reduced the job disinfection failure rate from between 21-29% to only 3%. the traditional chlorination process used to disinfect new mains uses 20 mg/l of chlorine. When this highly chlorinated water is discharged from the main into the environment, the chlorine needs to be neutralised to ensure no environmental harm. One of the main advantages of ozone is its ability to break down into Oxygen in a relatively short period. the new process will use less water by reducing the amount of flushing required to complete jobs and will largely eliminate repeating jobs that have failed due to potential sample contamination issues. the ozone trailer functions optimally over the various water pressures that can be found throughout Sydney Water s area of operations. the trailer is mobile, durable, reliable and able to operate across a variety of field conditions the process is highly automated ozonation offers significantly improved health & safety aspects for employees The Future Sydney Water now a has total of three trailers in use and Oxyzone are actively commercialising the trailer as the PPDS (Portable Pipeline Disinfection System). The trailer is protected by an Australian Innovation Patent and there has been a high level of interest shown by the Australian water industry and at least one international water utility. Other practical applications utilising the ozone trailer are also now becoming apparent including: Disinfection of high risk broken mains Cleaning pumps Washing down reservoirs Mining sector use, and Disinfection of air conditioning cooling towers or where other mobile disinfection/treatment applications are required. Award The Ozone Trailer Portable Pipeline Disinfection System has been entered into the Sydney Engineering Excellence Awards 2014 where it has progressed to the finals. The award winners will be announced in mid September 2014. 26 AUSTRALIAN WATER MANAGEMENT REVIEW