INTEGRATED MEMBRANE SYSTEMS FOR WASTEWATER REUSE
Abstract:Several studies have been conducted on application of Membrane Bioreactors for wastewater reclamation (Adham et al, 1998; Adham et al, 2000). In these studies it has also been demonstrated that MBR effluent has excellent water quality for RO treatment. The application of an integrated membrane system incorporating the MBR and RO treatment processes provide utilities flexibility with regard to the ultimate quality of reclaimed wastewater. This reclaimed water can be “tailored” to various reuse applications improving its marketability. Incorporation of a UV disinfection process into these integrated systems can complete the loop with regard to the reuse alternatives that can be accommodated using this treatment train. This study provides information on pilot operation of RO membranes in this context and presents cost data on integrated membrane systems for wastewater reclamation.
Earlier studies on RO treatment of MBR effluent have been limited to testing one type of RO membrane at a fixed recovery. The pilot testing part of this study focussed on assessing the performance of several types of commercially available and newly developed desalting membranes (i.e. NF/RO) for desalting MBR effluent. Desalting membranes provided by three manufacturers including Saehan, Hydranautics and Osmonics were operated at the pilot scale for a period of over 12 months. During the first stage of testing four different membranes were operated at 10 gfd and 50% recovery for a target period of 1000 hours. Testing was performed using a pilot skid consisting of two membrane skids arranged in parallel. Throughout the testing period, operational and water quality parameters were monitored to assess the performance of each desalting membrane being tested. This data was used to determine the best performing membrane for this stage. This membrane was further tested at a higher flux (12 gfd) and recovery (75%) for approximately 3000 hours in the second phase of pilot testing. The long term performance of this membrane was assessed during this period and the cleaning frequency and efficacy of different cleaning procedures established.
Operational results from the first stage of pilot testing show that each desalting membrane tested operated on MBR effluent with minimal fouling while operating at 10 gfd and 50% recovery. The observed salt rejection varied between 96% and 98%. Data from the second phase of testing indicate that the membrane selected from phase one operated reliably on MBR effluent at 75% and 12 gfd flux. Different cleaning strategies were employed and low pH cleaning proved the most effective in this case. A cleaning frequency of more than 1000 hours was observed and it is expected that under optimized operating conditions the period between cleanings could be longer.
A cost analysis is being as a part of this study to determine the capital and O&M costs associated with a Reclaimed Water Integrated Membrane System incorporating a MBR system, UV disinfection and desalting by RO membranes. Blending scenarios associated with producing water with different TDS levels will be discussed and costs developed for each scenario. These costs will be compared to a conventional treatment train providing a commentary on the cost competitiveness of this approach.
As a result of this study the feasibility and costs of an integrated membrane system utilizing MBR and RO systems will be analyzed and its applicability to meeting current reuse criteria discussed.
Document Type: Research Article
Publication date: January 1, 2004
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