Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/86284
RESEARCH layer, responsible for the salt rejection, generally supported by poly(ether)sulfone and non-woven polyester webbing materials (40 and 120 µm thick respectively) 2 Within all these components, the polyamide active layer of RO membranes remains the most fragile and prone to various types of fouling and damage 3-5 . with slow degradation over time necessitating replacement every 3-8 years, depending on the application. At present, only landfill disposal options , RO modules into microporous membranes, whereby different chemical treatments (ie, chlorine- and permanganate-based compounds) have been tested to remove the polyamide active layer present on the membrane surface 7-9 are available to membrane users in Australia. Because of the large variety of substances present within the RO element, landfill disposal is not a sustainable approach for the management of membrane waste. obviously affects the environmental sustainability of current RO desalination process. The lack of potential alternatives NCEDA-FUNDED PROJECT In a project recently funded by the National Centre of Excellence in Desalination Australia (NCEDA), a range of potential alternative options for the fate of old RO membranes is being assessed. This study aims to evaluate and develop the technological readiness, environmental impact and financial assessment for the various strategies to be proposed to membrane users. Those strategies are grouped within two categories: reuse and alternative disposal options. DIRECT REUSE There is a strong potential for directly reusing spent RO membranes with little treatment (ie, cleaning), or, ideally, with no treatment at all for lower-intensity applications. This study will consider the technical feasibility and validity of this option via pilot-testing of real disposed membranes from desalination plants in partnership with Dow, marketability and financial assessment. The concept of direct membrane reuse has only been considered in a couple of recent studies 2,6 characterisation of the aged RO membrane, and the relative high rejection of salts still demonstrated during autopsy analysis, the repurposing of the membranes for applications including selective demineralisation of brackish-water and seawater pretreatment can be considered as a suitable reuse strategy for old RO membranes. Another reuse option is the conversion of . Based on advanced the dense layer, treated modules have the potential to be reused as ultrafiltration (UF) membranes if the integrity of the supporting layers and the overall stability of the module elements are not significantly challenged. The polymer material removed from the RO modules (dissolved in a solution from the conversion process) could be captured and treated to recover the valuable polymer material 10 . Once stripped from the University of New South Wales has revealed the potential to use sodium hypochlorite (optimum exposure is a solution of 6.25 g/L NaOCl for 48 hours, equivalent to 300,000 ppm.h) in order to oxidise and remove the active polyamide layer. When this process was applied to Dow Filmtec BW30FR membranes, the permeability increased from 4 to above 170 L m-2 . Initial work conducted at transmission greater than 96%. Rejection characterisation, using model solutions of dextran, proteins and humic acid, allows the estimation of the resulting molecular weight cut-off of the converted membrane to between 10 to 100 kDa. In order to account for the wide variety h-1 bar-1 with NaCl been previously recycled as geotextiles in residential gardens under a layer of gravel, in order to maintain rock position and eliminate weed growth 6 Potential agricultural applications for the spacers, including bird netting, wind- breakers or for nets used as lawn protection have also been proposed 2 . the resulting RO material could be also utilised as a filler material or aggregate in concrete. Finally, low-temperature gasification of the polymeric wastes to produce syngas has demonstrated promising results for mixed municipal plastic waste, and will be considered for membrane modules 13,14 . Once ground, . of performances and conditions of used membranes, this process was applied to a number of virgin and old membranes from various applications, which resulted in similar hydraulic and rejection performances. Potential applications for the converted RO membranes include use in pretreatment filtration in desalination plants or within advanced treatment of wastewater. In both cases, it is expected that converted RO modules could remove all suspended solids, large organics species and a significant fraction of pathogens from feed streams. NEW DISPOSAL OPTIONS New methods for disposal of RO modules at the end of their lifetime, such as the recovery of their embodied energy during combustion in electric arc furnace steel-making to substitute for coke, is being conducted 11,12 Current efforts have focused mainly on the combustion and energy recovery from the polymeric materials. However a number of other strategies can be considered in the future and will be assessed within a life-cycle assessment study. For example, sheets and spacers have . | 40 | Desalination & Water Reuse | May-June 2012 STAKEHOLDER COALITION This research project will also contribute to the formation of a coalition of key stakeholders, establishing a policy advisory group to initiate, encourage and direct legislation for a systematic approach towards membrane management in the water and wastewater industry. Through the development of sustainable lifecycle strategies for both low- and high-pressure membranes, the advisory group will advocate a product stewardship scheme (similar to those already implemented in Europe, US and Canada for electronic wastes) to be developed and applied to membrane modules. This initiative, named MemRegen, will be officially launched during a pre-conference workshop organised during the upcoming Singapore International Water Week, in July 2012 (www.siww.com.sg). The event, titled Clean, green and sustainable: Lower-energy desalination and used membrane regeneration for the water global industry is co-organized by UNSW; King Abdullah University of Science & Technology, Saudi Arabia; and Nanyang Technological University and PUB, Singapore. The workshop will describe the vision and inspiration for this advisory group. It will also address key sustainability issues in membrane technology, including energy utilisation and material regeneration/ reuse. ACKNOWLEDGEMENTS The authors acknowledge the financial support of the NCEDA, which is funded by the Australian Government through the Water for the Future initiative. The in-kind support from the SkyJuice Foundation, Dow Chemical, Sydney Water, Water Corporation and South Australia Water is also gratefully acknowledged.