Water Journal : Water Journal September 2012-1
refereed paper membrane technology water SEPTEMBER 2012 73 After only six months of operation, the drum screens were found to be exhibiting signs of imminent mechanical failure, making loud noises while rotating. On further investigation it was found that the condition of the drive cog on the drum screen motor had deteriorated. The equipment supplier is currently repairing the unit and modifying the drum screen to prevent recurrence of this problem. Another MBR process (Branxton), commissioned three months after the Paxton upgrade, experienced similar problems with inlet drum screens. The drive cog was damaged at Branxton following failure of a drive bearing. The drum screens need regular inspection and maintenance in order to operate effectively, and it is important to ensure that these tasks can be performed safely. The screens also need to be tilted regularly to clean rag build- up and to prevent blockages. At the upgraded Paxton WWTP no safe method was provided for lifting and accessing the screens to allow inspection, maintenance and cleaning. A system including two davits has been proposed to remedy this deficiency. During the design process it is critical to make provision for safe and efficient removal of equipment for maintenance and servicing. The majority of the major process equipment, including recirculation and effluent pumps, and the air blowers for aeration and membrane scouring, are housed in a small building. There is currently no safe method for removing this equipment for maintenance. The installation of appropriate lifting devices to allow safe and efficient equipment removal is being investigated. Conclusions The upgrade of Paxton WWTP provided valuable lessons for the design, commissioning, operation and maintenance of an MBR process, including: • Increased challenges for nitrogen removal, particularly in under-loaded situations, and the need for careful design of air blower capacity and turndown capability; • Need for effective screening to prevent fouling of membranes and the need for excessive labour for operation and maintenance; • The critical importance of completing thorough pre-commissioning tests; • The need to provide safe and efficient capability to inspect, operate and maintain equipment. The final MBR process provided a robust and effective treatment barrier. Fostering operator input at all stages of the upgrade resulted in much better outcomes in terms of safety, performance and reliability. Commissioning of the MBR process also revealed significant opportunities for optimisation including: • Improving nitrogen removal by modifying the internal recirculation ratio; and • Options to minimise energy consumption. The upgrade process also highlighted strengths and limitations of the Alliance contract delivery method and how it was applied for this application. This paper was originally presented at Ozwater'12 in Sydney in May. The Authors Katie Jones (email: Katie.firstname.lastname@example.org. au) is a Chemical Engineer with six years' experience in the water industry. Katie started with Hunter Water Australia in 2006 as a Cadet Chemical Engineer. Her current role involves supervising the operation of four wastewater treatment plants in the NSW Hunter region. Katie has been involved in numerous plant upgrades providing operational input though the design, commissioning and optimisation stages. Darren Bailey (email: darren.bailey@ hwa.com.au) is a Chemical Engineer with over 25 years' experience in the water industry. His current role as Manager -- Treatment Operations for Hunter Water Australia involves managing operations and maintenance and providing operational support services for water and wastewater treatment plants in the Hunter region and for clients throughout Australia. Darren has also contributed to numerous research and upgrade projects in the water treatment field. Lisa Procter (email: lisa.procter@hwa. com.au) is a Chemical Engineer with over 20 years' water industry experience. Her current role as Manager -- Wastewater Treatment Operations for Hunter Water Australia involves managing operation and maintenance and providing operational support services for treatment plants in the NSW Hunter Region and for clients throughout Australia. Lisa has also contributed to numerous research and upgrade projects related to wastewater treatment. Figure 15. Blowers and recirculation pumps.
Water Journal November 2012-1
Water Journal August 2012