Ultrafiltration at St Marys Water Recycling Plant

Summary

The ultra filtration system at St. Mary's employs hollow membrane fibers with microscopic pores to filter out suspended solids, bacteria, and viruses from tertiary treated wastewater. The system, consisting of 48 membrane modules in 16 stacks, operates efficiently, producing 58 million liters of filtrate daily. It includes a cleaning mechanism with backwashing and chemical cycles to maintain optimal performance. The filtrate is then sent for further treatment, while used cleaning solutions are treated and recycled.

Takeaways

• 💧 The ultra filtration system at St. Mary's uses hollow membrane fibers to purify tertiary treated wastewater.
• 🌌 Each membrane fiber contains millions of microscopic pores, each about 0.02 microns in diameter, significantly smaller than a human hair at 75 microns.
• 🚰 The filtration process involves drawing water through the pores, leaving behind suspended solids, bacteria, viruses, and pathogens.
• 🔨 Membrane fibers are arranged in modules, each holding 30,000 fibers, and are secured by resin at both ends.
• 🔩 Modules are connected to a common header for filtrate collection, and are protected by plastic shrouds that facilitate upward water flow.
• 🏗️ Three membrane modules form a stack, with 16 stacks making up one cassette, for a total of 48 membrane modules per cassette.
• 🔄 The system is designed for high filtration efficiency, with 6 ultrafiltration cells in total.
• 🌡️ Treated wastewater from the feed water balance tank is first strained to remove larger solids before entering the ultrafiltration system.
• 🚰 The system produces 58 million liters of filtrate daily, which is then sent to a reverse osmosis system for further treatment.
• 🧼 Over time, fibers can become blocked, necessitating cleaning through backwashing and chemical cleaning cycles to maintain flow.
• 🔄 Backwashing is performed every 20 to 30 minutes in one cell at a time, while chemical cleaning occurs every 24 hours, also in a staggered manner.
• ♻️ Used cleaning solutions and removed contaminants are treated and returned to the wastewater treatment process.

Q & A

What is the purpose of the ultrafiltration system at St. Mary's?

The ultrafiltration system at St. Mary's uses hollow membrane fibers to remove suspended solids, bacteria, and viruses from tertiary treated wastewater.

How small are the pores in the membrane fibers used in the ultrafiltration system?

Each pore in the membrane fibers is about 0.02 microns in diameter.

How does the size of the membrane pores compare to the diameter of a human hair?

The pores are approximately 0.02 microns in diameter, while a human hair is about 75 microns in diameter.

What is the function of the membrane fibers in the ultrafiltration system?

The membrane fibers act as a physical barrier that allows only filtrate to pass through while leaving behind suspended solids, bacteria, viruses, and pathogens.

How are the membrane fibers arranged within the ultrafiltration system?

The membrane fibers are arranged horizontally into modules, with each module containing 30,000 fibers held by resin at each end.

What role do the plastic shrouds play in the ultrafiltration modules?

The plastic shrouds encase the sides of the modules, protect the fibers, and draw the feed water upward through the modules.

How many membrane modules are loaded into one cassette in the ultrafiltration system?

Each cassette contains 48 membrane modules, arranged into 16 stacks of three modules each.

What happens to the filtrate after it passes through the ultrafiltration system?

The filtrate is sent to the reverse osmosis system for further treatment.

How are the membrane fibers cleaned when they become blocked?

The fibers are cleaned through cycles of backwashing and chemical cleaning. Backwashing pushes filtrate through the membrane pores to dislodge particles, while chemical cleaning removes any remaining material stuck to the membranes.

What is the frequency of the backwash and chemical cleaning cycles in the ultrafiltration system?

Backwashing occurs every 20 to 30 minutes, while chemical cleaning cycles occur every 24 hours, each in one cell at a time.