Membrane bioreactors need some extra care, so follow these steps for top-notch operation and maintenance service
Currently, there are two small-flow membrane bioreactors actively marketed for U.S. residential septic system applications: Bio-Microbics BioBarrier and the BUSSE GT system. These membrane bioreactors require yearly maintenance, and the operation and maintenance (O&M) is unique for each.
First, we will discuss the O&M of the BioBarrier membrane bioreactor. The BioBarrier was the first system for black water and graywater that was certified for water reuse (NSF/ANSI Standard 350, Class R, and also EN 12566-3). This membrane bioreactor is pre-engineered to fit into both new and existing tank configurations.
The flat sheet membranes and processes used in this advanced system act as an impenetrable physical barrier for pollutants found in wastewater. The BioBarrier uses ultrafiltration with microsized-pore sheets for separation of solids and contaminants from the wastewater.
The system’s operation sequence doesn't require complicated backwash functionality and is automated. The purpose of the membrane O&M is to clean the membranes and maintain their filtration rate.
Bio-Microbics recommends two types of cleanings.
Under normal operational conditions for residential applications, CIP is performed once a year; for commercial applications, it's performed once every six months. The following is the typical procedure with the membrane models remaining in the aeration tank.
- Stop operation of the membranes.
- Pour a chemical solution (a mixture of water and Clorox, at 500 ppm chlorine) into the membrane modules.
- Wait a minimum of four hours for the chemical solution to react with the membranes.
- Restart operation of the membranes.
After two or more years of CIP cleaning, the intensive cleaning is recommended in which the membrane modules are removed from the aeration tank.
- If needed, wash the membrane sheets with semipressured clean water to hose off any large buildup of sludge.
- Soak the membrane module in chlorinated (700 ppm of chlorine) bath water for a minimum of four hours.
- If needed, the chemically cleaned membranes should be soaked in acidic bath water for a minimum of four hours with the pH of the solution between 2 to 2.5.
- Reinstall the membrane module in the aeration tank, and resume operation.
The O&M of the BUSSE GT system is a little different. European Standard EN 12566-3 certifies the BUSSE GT for water reuse. The flat sheet membranes and processes used in this advanced system act as an impenetrable physical barrier for pollutants found in wastewater. The BUSSE GT uses microfiltration with microsized-pore sheets for separation of solids and contaminants from the wastewater.
For residential applications, the membranes are typically cleaned annually. With commercial applications, more frequently cleaning may be needed.
- Prior to cleaning, insert a John Guest hose (12 mm diameter and 0.6 meter length) into the filtrate collector of the membrane to avoid any sludge or dirt getting into the filtrate collector and inside of the single membranes in the process. Make sure that the end of the hose is always over the waterline during the initial cleaning process in the cleaning box.
- Clean the soiled membrane and the space between the membrane plates with a water hose using bubbles and a low-pressure water jet. Don't use a pressure washer or mechanical tools since this can damage the surface of the membrane.
- After the precleaning, put the membrane in the washing box. Put a capful of laundry detergent (Tide or equivalent) in the box. Don't let the detergent get into the John Guest hose. Fill the washing box with water (if possible, warm water around 100 degrees F) until the water covers the top of the membrane. Let the membrane sit in the detergent for about 30 minutes.
- Chemical clean:
- Drain the washing box.
- Remove the John Guest hose because the chemical cleaning solution must also get inside the membranes through the filtrate collector.
- Fill the washing box with clear water until the water covers the top of the membrane.
- Add the chlorine bleaching solution (sodium hypochlorite solution/household bleach), 1 gallon per membrane. Soak the membrane in the chemical cleaning solution for two to three hours.
- After the chemical cleaning, the membrane has to be rinsed three times and neutralized.
- First rinse: Fill with clear water until the top of the membrane is covered with it. Leave the membrane in the rinse for 30 minutes. After rinsing for 30 minutes, drain the washing box.
- Second rinse: Refill the washing box with clear water until the top of the membrane is covered. Leave the membrane in the rinse for 30 minutes. After rinsing for 30 minutes, drain the washing box.
- Third rinse: Add rinsing agent (what is used in dishwashers — for example, Jet-Dry) to the clear water and fill the washing box with the mixture until the top of the membrane is covered. Leave the membrane in the rinse for 30 minutes. After rinsing for 30 minutes, drain the washing box. The rinsing agent is added to make the pores of the membranes stay open during the drying process. NOTE: If you are going to reinstall the membrane immediately after washing, you do not need to do this step.
- After the last rinsing process, dry the membrane outdoors under a roof or in a vented room with good circulation. Do not leave it in direct sunlight during the drying process. The membrane shouldn't be stored below freezing or outdoors for long periods.
About the author
Sara Heger, Ph.D., is an engineer, researcher and instructor in the Onsite Sewage Treatment Program in the Water Resources Center at the University of Minnesota. She presents at many local and national training events regarding the design, installation and management of septic systems and related research. Heger is education chair of the Minnesota Onsite Wastewater Association and the National Onsite Wastewater Recycling Association, and she serves on the NSF International Committee on Wastewater Treatment Systems. Ask Heger questions about septic system maintenance and operation by sending an email to email@example.com.