MF/UF Flow Path Cleaning Comparison Study for Improved Foulant Removal in Wastewater Applications

MF/UF Flow Path Cleaning Comparison for Improved Foulant Removal in Wastewater Applications Jacob Hatt, Thursday March 7th 2: P.M. UF/MF Membrane Plant Configuration Submersed Membrane Design Pressurized Membrane Design Common material of construction: PVDF (Polyvinylidene fluoride) and PES (Polyethersulfone) 4 Pore Plugging Can occur when fine particles or organics get trapped in pores of fibers This type of fouling can be irreversible, requiring membrane replacement Chromatic Elemental Imaging (CEI, 150x) 6 MF/UF Foulant Found In Wastewater Applications Organics Metals Clay Sulfur 7 Common Cleaning Practices for Pressurized MF/UF Modules Air Scour Air Out Backwash In Pressurized air is applied to pre backwashed fibers to physically remove particulates Chemically Enhanced Backwash (CEB) Commodity chemicals such as chlorine, acid, caustic are backwashed into short segments (minutes) Clean-In-Place (CIP) MF/UF module taken off-line and cleaned with commodity or specialty cleaner. Cleaning duration 30 minutes-hours, sometimes Backwash Out overnight soak Air in 9 MF/UF Operation Process Example PROCESS STEP OBJECTIVE DURATION FREQUENCY Forward Flow Filtrate 15- Minutes Continuous Backwash Foulant Removal 30- Seconds Every 15- Minutes CEB Foulant Removal 1- Minutes 1 or Times/Day Chemically Enhanced backwash CIP Foulant Removal 2- Hours 1- Months Clean in Place RC Foulant Removal Varies As Needed Recovery Cleaning 10 Benefit of Cleaning from Interior to Exterior Fibers Multiple benefits to pulsing chemical from filtrate side of fibers to the feed side Push foulant out of pores Coats the membrane areas closest to the feed side of the fibers allowing cleaner to be more active (not as dilute) Removes any foulant inside of fibers CEI Exterior (150x) vs CEI Interior (150x) 13 Cleaning Study Candidate Background Wastewater facility Feedwater source: treated effluent Pretreatment: coagulant, clarifier, multimedia System performance: could not be recovered with simple acid/caustic cleanings any longer Plant was ready to replace membranes Decided to send one out for autopsy prior to replacement Current Cleaning Procedure: Cleaner introduced to the feed side of the fibers Circulated feed to reject for 30 minutes Soak for 20 minutes Circulation feed to reject for 30 minutes 14 UF Autopsy Results Fibers heavily fouled with iron from pretreatment (ferric chloride) Fiber Exterior Elements (Weight Percent, wt%) Carbon 45. Iron 30. Feed side of fiber Oxygen 22. Feed side of fiber Calcium 1. Fiber Interior Elements (Weight Percent, wt%) Carbon 57. Oxygen 23. Iron 17. Calcium 1. Filtrate side of fiber Stereoscope image (20x) shows foulant on fiber exterior, interior and walls 15.