Water. desalination + reuse

Direct membrane filtration simplifies reuse process projects _________ Ronald van 't Oever Pentair X-Flow, Enschede, Netherlands, ___ Editor's Note: Recent trials have proven that direct membrane filtration of high solids (algae) and disinfection provides a simpler treatment process with substantial cost reduction. In Pillbara, Australia, two plants are being constructed to treat wastewater for recycling aiming for a 4-log removal of bacteria and viruses by filtering alone. Ultraviolet (UV) treatment provides the final requirement to reach the required 6-log removal rate. This article gives an overview of the application, and details on the technology and design used. TO REACH the required water quality for reuse, the treatment process for recycling usually contains many steps. In the Pillbara, 1,500 km north of Perth, Western Australia, two units using raw sewage-treatment plant effluent are being constructed based on a new design featuring Direct Membrane Filtration (DMF). This replaces the original plan that would have used flocculation, dissolved air flotation (DAF), media filtration, and ultrafiltration (UF). The original design used traditional hollow-fiber UF membranes (0.8 mm ID). The UF provides 4-log removal of bacteria and viruses, which is part of the Western Australian regulatory requirements for nonpotable uses of recycled water. A fresh look at available products and processes opened the route to apply hollow fiber tubular membranes (5.2 mm ID), which reduces the necessary processes and investment cost. HigH SOlidS Package The High Solids Package (HSP) with Pentair X-Flow's tubular Compact 33 V membranes is used for applications with high solids in the feedwater. In the early years, sand filter backwash water was part of the reclaim focus of drinking water facilities and this backwash water, which contains high iron hydroxide loads, was and is treated in this way. With dead-end filtration of high solids feedwater (up to 750 ppm), the effluent still meets drinking water standards. The water loss, by reusing this backwash water, is dramatically reduced by up to 95%-plus in many cases. The original plan for the Pillbara case is shown below: Figure 1. Water recycling plant process train as originally proposed. As can be seen, several process steps leads the effluent from the storage pond to the final storage tank, with the use of chemical adjustment and treatments throughout the process. The goal of this extensive treatment was to reach a 6.5-log removal to allow for a third pipe reticulation with indoor and outdoor use. The UF and UV steps are the primary technologies required to achieve such high log removal. Looking to the future, this level of log removal will open doors for other recycling applications. Raw wateR The starting point and challenge is the poor water quality combined with the harsh environment. The treated wastewater available after the sewage treatment is shown in Table 1. | 18 | Desalination & Water Reuse | August-September 2013

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