Flat Plate Membrane Bioreactor (MBR) System Training Session #3 - PowerPoint PPT Presentation

Flat Plate Membrane Bioreactor (MBR) System Training Session #3

Session #2 Summary 1. An MBR system is made up of several subsystems 2. Operational challenges are rarely caused by the membranes themselves, it’s usually one of the subsystems 3. The basics to managing the membranes themselves are TMP, air scour, permeate flow, diffuser cleans, MLSS and filterability 4. All membranes have a biofilm, managing is key to successful operation. 5. Ways to control biofilm include air scour, relaxation, sludge quality, TMP control and maintenance cleans 6. Maintenance cleans can either remove organic or inorganic fouling 7. Flow balancing is important for proper operation 91

MBR Operations

Session #3 Agenda 1. A look at the critical items for MBR operations 2. Different modes of an MBR system 3. System components and process basins 4. Controls 5. Troubleshooting 93

What To Look For Aeration is critical • Equal air diffuser roll patterns above SMU • Air scour flowrate at or above minimum required at all times MLSS in MBRs is critical • Qualitatively make comparisons several times a day • Measure TSS in each MBR as often as possible (1X/day) • Watch for unequal thickening or thinning in different zones • Avoid inadvertent or excessive wasting • Quantitatively compare recycle flows Screening bypass (improper installation)

Operating Guidelines System headworks must operate properly • Cannot be bypassed at any time • Should have 100% redundancy • Can lead to membrane damage • Accumulation of debris can inhibit air scour Always maintain minimum MBR side water depth Always supply minimum cleaning air required Always filter wastewater at or below design flowrate Clean membranes every six months, or when: • TMP increases by 1.0 psig or Permeability decreases to 10 gfd/psi, at average design flow

Modes and States Plant Mode Offline Online Process Train Offline Intermittent / Filter Mode Membrane Diffuser MBR Mode Offline Intermittent Filter Clean Clean Membrane Diffuser Intermittent Low Flow / Medium Flow / High Offline No Flow Clean Clean Pulse Flow Permeate Production Level Based Control Mode Low Flow / Medium Flow / High Permeate Offline No Flow Flow / Membrane Relax / Header State Permeability Control

Plant Modes Offline Mode – Offline is a condition in which the PLC has been instructed (via the HMI) to halt all process operations. No automatic control of the system will occur when the plant is placed Offline. Online Mode – Online indicates that the PLC is controlling the system operations based on the measured conditions and process set points. The transition between Online and Offline is accomplished through the Startup and Shutdown procedures initiated at the HMI.

Process Train Modes Offline – Offline is a condition in which the PLC has been instructed (via the HMI) to halt all process operations. No automatic control will occur when the process train is placed Offline. Intermittent – The MBR process is in Intermittent Mode when the incoming flow or the level in the controlling basin is below the level necessary for permeate production. Filter – The process train is in Filter Mode when the incoming flow or the level in the controlling basin is high enough to begin permeate production. The actual modes and states of the zones within the MBR process will be dictated by the various set points and commands from the operator interface.

MBR Modes Offline Mode – Offline is a condition in which all equipment supporting an MBR is off (in the case of a motor) or closed (in the case of a valve). A membrane basin may be placed offline via a button at the operator Interface. Membrane Clean – Membrane Clean refers to a state unique to the MBR basins in which the basin has been taken Offline and the clean ‐ in ‐ place (CIP) process has been initiated at the operator interface. Diffuser Clean – Diffuser Clean refers to a state in which the coarse bubble diffusers at the base of the MBR SMUs are cleaned of accumulated debris. During this process, permeate production is paused and process air to the MBR basin is initiated. Diffuser cleaning occurs a minimum of once per day. Intermittent Mode – In Intermittent, permeate production has stopped. The term intermittent stems from the periodic operation of the process air blowers to pulse air into the MBR basins. Filter Mode – In Filter Mode, the system is producing permeate. The rate at which permeate is produced is dictated by the permeate production mode.

MBR Modes (cont.) No flow/Intermittent Pulse – In No flow the membrane air scour blowers are on but have a flow setpoint of 0 while in Intermittent Pulse they will send a pulse of air to the membranes for a maximum of 5 minutes based on the air flow setpoint in the system. Low flow/Medium flow/High flow – When the permeate pumps are in Filter Mode the air scour blowers are in either Low, Medium or High flow modes based on the flow condition that the MBRs are seeing.

Permeate Production Mode • Based on either a controlling level or a measured influent flow. In either mode, anoxic basin levels are monitored and used to detect low and high level water conditions, both of which impact permeate production. Both modes share common level and flow set points • Low Level Alarm – This set point is active in both Level and Influent Flow Based Control. While in Influent Based Control, if either anoxic basin falls below the low alarm level, this will engage Intermittent Mode for all MBRs irrespective of influent flow. • Low Flow Level – This set point is active in both Level and Influent Flow Based Control. • While in Influent Based Control: • If one anoxic basin falls below the low flow level setting, this will engage Intermittent mode for the supporting MBR. • If average anoxic basin levels fall below the low flow level setting, this will engage Intermittent Mode for all MBRs irrespective of influent flow. • High Flow Level – This set point is active in both Level and Influent Flow Based Control. While in Influent Based Control, if either anoxic basin reaches high flow level, this will engage High Permeate Flow irrespective of influent flow. • High Level Alarm – This set point is active in both Level and Influent Flow Based Control. While in Influent Based Control, if either anoxic basin reaches high alarm level, this will engage High Permeate Flow irrespective of influent flow. • Low Flow – This set point is active in both Level and Influent Flow Based Control. This is the minimum flow setting for any permeate header. • Medium Flow – This set point is active in both Level and Influent Flow Based Control. This is the medium flow set point in Level Based Control. In Influent Flow Based Control, this point is used to determine the number of MBRs, and thus permeate headers, required to process incoming flows. • High Flow – This set point is active in both Level and Influent Flow Based Control. This is the maximum flow setting for any permeate header.

Permeate Header States The MBR permeate header will alternate between six states based on the mode in which the MBRs are operating and the operator selected permeate production mode • Offline Mode – The permeate header is Offline when the basin(s) that is supports is Offline or in Membrane Clean. • No Flow – The permeate header is in No Flow when the basin(s) that is supports is in Intermittent or Diffuser Clean. • Low Flow – Low Flow is one of three states under the Level Based Control. A header in Low Flow produces permeate at a rate usually equal to half of the average rated throughput of that header. • Medium Flow – Medium Flow is one of three states under the Level Based Control. A header in Medium Flow produces permeate at a rate usually equal to the average rated throughput of that header. • High Flow ‐ High Flow is one of three states under the Level Based Control as well as a state under Influent Flow Based Control. A header in High Flow produces permeate at a rate usually equal to the maximum rated throughput of that header. • Relax –During Relax, permeate production temporarily stops while scour air continues to flow across the membrane surface. During permeate production the surfaces of the cartridges are pulled slightly inward due to the differential pressure across them. By stopping the permeate flow, the membranes relax (return to a flat profile) and allow the scour air to more effectively remove any accumulated material.

Fine Screens The headworks subsystem typically consists of: • two automated fine screens • rotary screw conveyor • solenoid actuated valve Screens remove solids greater than 2 mm in diameter Solids are discharged from the screens into a rotary screw conveyor Influent flow is measured upstream of the feed channel common to both screens Common feed channel is equipped with low and high level float switches • The high level float will initiate operation of the screens which will run continuously until the low level condition is detected • The fine screens will continue to run for an operator adjustable period • If the high level switch remains active greater than an operator adjustable time period a high level alarm will be generated

Anoxic Basins Each anoxic basin is equipped with a submerged differential pressure level transmitter Low and high analog alarm level set points are operator adjustable at the HMI low level ‐ alarm posted and all rotating equipment shuts down high level ‐ alarm is posted Measured liquid level is monitored and recorded at all times