Vibratory Shear Enhanced Membrane Processing for enhanced water recovery in ground water treatment

2017-03-16T03:27:38Z (GMT) by Jack Leong
As the worldwide population grows, the demand for drinkable water rises accordingly. Recently desalination technology has provided the means of converting seawater into potable water. Although effective, desalination technologies also produce unwanted concentrates that have ill effects on the environment when disposed of incorrectly and also the procedures involved with the disposal of such wastes take up a large proportion of industrial operational costs. Technologies that reduce the volume of discharged concentrate are also known as volume reduction processes.
   Magnetic Ion Exchange (MIEX) is the current method of water treatment used at Wanneroo Groundwater Treatment Plant in Western Australia. Vibratory Shear Enhanced Process (VSEP) was installed at a facility to deal with the large volumes of concentrated waste generated by the MIEX process. The incorporation of VSEP to treat MIEX wastes is the first of its kind. Compared to previous use of VSEP in literature, VSEP will be used as a primary treatment method for the highly organic MIEX waste. VSEP was selected as an adequate inland waste treatment option on the basis of its low energy requirements, ability to prevent fouling and the benefits of re-using permeate streams onsite. Additionally, the highly organic nature of MIEX waste is much greater than concentrates previously explored using VSEP in literature and provides an insight into the interactions of high concentration waste streams and membrane surface. Initial results based on the installation of VSEP alone have reduced the amount of concentrate by up to 76% with further improvement a possibility. Furthermore, over 97% of dissolved organic carbon in the MIEX waste was removed in the process. Organic characterisation of the process streams indicated that the average molecular weight observed in the permeate stream was 1000 Da, smaller than that seen in the feed stream (1400 Da). Exploration of performance with regards to sequential batches between chemical cleans showed that significant deterioration of flux and extended batch times would occur in later batches. Increasing the frequency of cleaning would improve the overall performance and maintenance of the VSEP system.
   A techno-economic analysis was performed on the installation of VSEP into an existing groundwater treatment plant. Whilst operating at 80% volumetric capacity, savings in terms of salt consumption, waste disposal and transport costs have been observed. Within the first year of operation, there has been a reduction of 42% of salt consumption costs and 23.9% reduction in waste disposal costs. Further optimisation and increasing the volumetric capacity could result in further economic improvements. Cumulative cash flow predictions based upon the initial two years of operation showed the project would reach a payback period in 6 years and 8 months and achieve a positive net present value of $170,998AUD in the suggested project life cycle of 10 years.
   While VSEP is effective at removing the majority of dissolved organics and divalent solutes, the remaining organics has the potential to influence the performance of MIEX due to the build-up of low molecular organics. In an effort to address this, other concentrate management options such as carbon adsorption and natural evaporation were considered and evaluated.
   A lab scale test using activated carbon to treat VSEP permeate was conducted to determine if post-treatment of VSEP permeate was a feasible option to improve MIEX resin regeneration upstream. Results showed the best carbon sorbent (Darco Mesh) was able to reduce the dissolved organic carbon content in VSEP permeate over 5 fold. Adsorption isotherm were utilised to predict that 110 kg of activated carbon was required to treat 1 kL of VSEP permeate. The excessive amount of activated carbon required, challenges associated with regenerating it due to likely emission of halogenated species and the extensive equilibrium time make the implementation of carbon sorbents onsite unreasonable.
   A Wind Aided Intensified Evaporation (WAIV) unit was also installed at Wanneroo as an additional opportunity to further treat the permeate generated from the VSEP. A WAIV system utilising natural energy sources such as wind and solar radiation was capable of removing the water content from the VSEP permeate. Extensive operation resulted in levels close to zero liquid discharge (ZLD), hence limiting the concentrate wastes to be disposed over the dual system to minimal.
   The results obtained from this thesis demonstrate that there are numerous cost effective concentrate management procedures available for industries that produce waste concentrate that is high in organic content. The final waste produced by the introduction of the technologies is comparatively cleaner than current management options. The incorporation of VSEP should not be limited to the treatment of MIEX waste. Any industries that deal with high volumes of concentrate wastes could reap benefits from the incorporation of VSEP. However the benefits lie heavily on the ability to re-use either permeate or the waste streams of VSEP. Further exploration of VSEP in conjunction with other technologies such as WAIV can result in zero-liquid discharge, which would almost eliminate all costs associated waste disposal and significantly reduce the environmental impact of its disposal.