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A Novel Approach To Seawater Desalination Using Dual-staged Nanofiltration
As the quantity and quality of inland water sources decline, more coastal municipalities are looking at seawater desalination as a potential source of drinking water. The Long Beach Water Department (LBWD) developed an alternative technology to desalt seawater by using dual-staged nanofiltration (NF2). This novel NF system treats the first-stage permeate through a second stage in order to produce finished water with salinity levels that meet drinking water standards.
Three commercially-available NF membranes were selected for this study based upon their designation as NF membranes by the manufacturers and their salt rejection characteristics. Results from the bench-scale evaluation were integrated in a performance-predicting model, which was subsequently calibrated against the results obtained with an 8-gpm pilot unit. The pilot-test plan considered the impact of temperature, pressure, and array configuration on permeate water quantity and quality. The percentage of desalinated water that could be blended into LBWD's distribution system was determined by taking into account the issues of disinfection by-product (DBP) formation, disinfectant residual, and corrosivity. Finally, viral challenge tests were considered to verify the inherent redundancy of the system and the impact that recycling streams would have on virus accumulation.
Optimizing Filtration And Disinfection Systems With A Risk-based Approach
Treated wastewater effluents contain high concentrations of particles; many of these particles are large (with diameters greater than 100 m) and consist of densely-packed bacterial cells. Microorganisms occluded in wastewater particles can be difficult to inactivate in chlorine disinfection systems, as the chlorine must first diffuse through the macro- and microscopic pore spaces prior to inactivating the occluded microorganisms. The impact of microorganisms occluded in particles is evident in disinfection, where reduced inactivation rates occur even with increasing doses of the disinfectant. Reduction of occluded microorganisms in plant effluents can be accomplished using filtration to remove the total number of particles, and disinfection to ensure that intra-particle chlorine concentrations are sufficient to inactivate the occluded microorganisms.
In addition to addressing inactivation of dispersed microorganisms, treatment systems design and operation should include consideration of the removal of microorganisms in wastewater particles that may pose a health risk in post-treated waters. In this project, a systematic approach was developed to co-optimize filtration and chemical disinfection systems to collectively reduce the concentration of occluded viable microorganisms in treated effluents to acceptable levels. The optimization process was successfully applied to wastewater samples collected from seven facilities, each with different treatment trains. A range of operating conditions was identified that resulted in acceptable treatment based on particle guidelines developed using the existent regulatory framework for indicator organisms. Extension of the current approach to a pathogen basis was considered, but current data are insufficient to adopt such a procedure although preliminary results suggest that intra-particle chlorine concentrations that are sufficient to inactivate indicator organisms may not be adequate to sufficiently reduce concentrations of occluded pathogens.
Exploring the success factors that combine to deliver this performance. Finding ways to get more from your processes, with examples, case studies and scenarios.
Solid-Liquid Filtration is a crucial step in the production of virtually everything in our daily lives, from metals, plastics and pigments through to foods (and crockery) and medicines. Using a practical and applied approach, Trevor Sparks has created a guide that chemical and process engineers can use to help them:
- Understand how filtration processes affect production processes, production costs, product quality, environmental impact and productivity
- Optimise process development and project execution, with real examples and supporting software forms and tools.
- Develop reporting tools to monitor processes, and find ways to get more from processes
This book's focus is helping process engineers understand their filtration processes better. Its accessible approach and style make it a valuable resource for anyone working in this sector, regardless of prior knowledge or experience.
About the author
Trevor Sparks PhD., founder of Filter-Ability Ltd, Ireland, is a consultant within the filtration industry, working for end-users and technology-providers. He has worked in the process industries for 20 years and has focussed on filtration for the last 15 of these. He has previously worked for BHR Group Limited, Larox Oyj (now a part of Outotec), Finland, and as a Marie-Curie Research Fellow at UC RUSAL in Ireland. He is a Member of the Council of the Filtration Society.
- Several examples and scenarios are provided throughout the book in order to help engineers understand the importance of filtration and the effect that it has on the bottom-line.
- Covers methods for optimizing processes, include process variable, plus laboratory testing, modeling and process troubleshooting
- Accompanied by optimization software that enables readers to model and plan optimal filtration processes and set ups for their particular circumstance.
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