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Headloss, Velocity, & Fibrous Re-agglomeration Effects On Membrane Pre-Screening
Ovivo USA, United States of America;
Water and Wastewater Membranes need to be protected against fibrous & sharp debris that not only create excessive membrane cleaning cycles & labor intensity, but often abrade & damage membrane surfaces, as well as clog the aeration manifolds that scour the membranes. Fine & Ultra-fine Pre-Screening has become extremely important in protecting both membrane warrantees and membrane efficiency. This paper emphasizes the importance of fine screening with data showing how short fine cotton-wool fibers, hair & filamentous algae will pass through 3mm and 2mm aperture screens and “Agglomerate & "Recombine" downstream into stringy, rag type debris that increases the operating maintenance & membrane cleaning cycles.
This presentation with supporting pilot plant & field data focuses on why velocity and headloss are the two most important characteristics in understanding how screens are properly sized, maintained & operated. CFD (computational fluid Dynamics) analysis with screenings capture data reveals the direct relationship velocity & headloss have on a screen’s capture efficiency & performance. It emphasizes & disproves the myth as to why matting of solids onto screening surfaces will ultimately over time reduce the screenings capture efficiency rather than improve upon it as many believe. The presentation will also emphasize the aperture requirement for removing 2 dimensional versus 3 dimensional solids, as well as explain & document how small size debris that passes through 3mm, 2mm holes, slots or mesh is capable of re-agglomerating (re-combining) into large clumps & bundles of fibrous debris, commonly known as ragging, that foul downstream processes requiring higher maintenance & increased cleaning cycles. A screen’s effluent quality affects the life-span and operation & maintenance of downstream membranes & their aeration manifolds. The laboratory & field data provided in this presentation will demonstrate the importance of aperture selection, as well as the direct relationship headloss & velocity have on the performance & effluent quality exiting a screen. Membranes can be expensive investments; therefore it is imperative that one understand how we can best protect that investment, as well as maintain regulatory discharge compliance.
3:45pm - 4:30pm
A Survey of Operating Membrane Bioreactor Facilities in North America
Patrick Roe1, Gordon Culp2
1HDR Engineering, Inc., United States of America; 2Smith Culp Consulting;
Membrane bioreactors have been used to reclaim water in the United States and Canada for more than 20 years. However, some operating aspects, particularly variability in mixed liquor filterability and membrane flux limitations, have been challenging.
The authors have previously conducted separate assessments of ‘lessons learned’ in MBR design and operation: Membrane Bioreactors - Lessons Learned, Gordon Culp, Presented at the 2018 Nevada Water Environment Association Conference, and Fifteen Years of Progressive Membrane Bioreactor Experience in the Pacific Northwest, Patrick Roe, 2018 Water Environment Federation Technical Exhibition and Conference. These two assessments summarized the authors’ experience with several membrane bioreactors in the Pacific Northwest and presented case studies of operating successes and challenges.
To conduct a more comprehensive assessment, the authors have conducted a national survey of operating membrane bioreactor installations with significant design capacity (greater than 1 mgd). This presentation reports the survey results. The survey is focused on the following key areas:
Peak flow management and whether equalization is provided.
Membrane pretreatment processes, consisting of screening type and size, as well as whether primary treatment is included,
Use of chemicals to increase membrane flux rate
Membrane cleaning approach and chemicals used for cleaning,
Operations and maintenance staffing,
Membrane life and whether replacement with an alternate membrane type was considered,
Plant control systems, and
Membrane air scouring systems.
The survey results will be tabulated to present trends in MBR design, operation and maintenance. This guidance is intended for utilities modifying existing MBRs to improve performance and operability, as well as to provide guidance for design and operation of new membrane facilities.