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

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

Session #2 Summary

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• 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

MBR Operations

Session #3 Agenda

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• 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

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 Mode Offline Intermittent / Filter MBR Mode Offline Membrane Clean Diffuser Clean Intermittent Filter Offline Membrane Clean Diffuser Clean No Flow Intermittent Pulse Low Flow / Medium Flow / High Flow Permeate Production Mode Level Based Control Permeate Header State Offline No Flow Low Flow / Medium Flow / High Flow / Membrane Relax / 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

• perator 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

• f 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

• perating 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
• r 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

Recycle Pumps

• Anoxic basin equipped submersible pumps
• standby pump can either be installed or a shelf spare
• Each pump feeds a separate process train
• The Duty RAS pump will run continuously unless all downstream MBRs are
• ffline or a low level condition is detected in the anoxic basin.
• Duty and standby assignments rotate between the pumps upon detection
• f one of the following conditions:
• Lead motor failure
• Initiation of manual control
• Expiration of a user defined period of continuous automatic
• peration, typically 24 hours
• Each automatic motor restart request
• Each pump driven by variable frequency drives (VFDs) and are equipped

with internal temperature and moisture sensors. A magnetic flow meter with local display indicates pump discharge flow rate

Pre‐Aeration Basins

Dissolved Oxygen probe monitors the temperature and oxygen concentration of the mixed liquor in each pre‐aeration basin

• If the mixed liquor temperature or dissolved oxygen

concentration fall below operator adjustable limits, an alarm is posted

• Mixed liquor temperature and dissolved oxygen

concentration are monitored and recorded at all times.

• Dissolved oxygen concentration is used as the input to a

PID control loop which modulates the speed of the Pre‐ Aeration Blower to maintain the operator entered DO setpoint

MBR Basins

• Each membrane basin is equipped with an automated diffuser

cleaning valve (DCV)

• Diffuser cleanings are initiated sequentially between all online

MBRs to minimize the interruption of permeate production

• Each basin equipped with two float switches to detect liquid

level

• Low level ‐ alarm is posted and the basin will be placed into

Intermittent Mode

• High level ‐ alarm is posted, the MBR permeate header is

placed into high flow, and diffuser cleaning is inhibited until the condition clears

Membrane Air Scour Blowers

Typically positive displacement blowers

• Driven by variable frequency drives (VFDs)
• Each membrane basin has a dedicated aeration header to

supply scour air – measured by a thermal‐dispersion mass flow meter The MBR air flow control system uses a calculated total air flow demand to control blower speed using the VFD Air scour is continuous during operation in Filter Mode In Intermittent Mode air is pulsed into the basin at an operator adjustable frequency and duration

Permeate Collection

Each MBR tank is equipped with at least one permeate header. Flow rate is controlled using a variable frequency drive on all permeate pumps in conjunction with a modulating flow control valve

Wasting

• The HMI provides the ability to schedule multiple wasting

events per day

• A flowmeter on the WAS piping allows the control system to

calculate total volume wasted per event

• The user may enable and disable each event schedule and

designate a start time, volume to waste for each

• When a scheduled WAS event is initiated either automatically
• r manually, by using the WAS transfer start button, the WAS

valve will open and remain open until the calculated WAS volume equals the target volume for that event, based on the measured WAS flow total through the flowmeter.

Membrane Clean In Place System

CIP system consists of an actuated water supply valve, a pressure regulating valve, an eductor, and a flow transmitter. CIP control is based on menu‐driven instructions from the HMI. There is a dependency on the operator to perform a series of related manual tasks

Critical Interlocks

There are six common interlocks that will reduce permeate production and/or place the MBRs into Intermittent mode. These critical interlocks are as follows:

• Permeability control failure
• Permeate pump failure
• Low MBR water level
• High TMP
• Diffuser Cleaning Valve Fail to Close
• No MBR Blowers available

Control System Architecture

• PC and PLC networked via

Ethernet

• Remote access gained

through dial‐up modem or VPN

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The Plant’s Brain

The Brain is Dead

Think logically about how flow enters the plant Concentrate on the absolute basics

• Screens
• Recycle
• Air scour
• Permeate flow
• Achieve a good balance

Manual Operation (Becoming the Brain)

Problem Definition

Biological

• Effluent BOD
• Effluent Nutrients

Membrane

• Low Permeability/High TMP
• TSS/Turbidity/Pathogens

System

• Odors
• Foam

Troubleshooting

Biological

• Collect analytical data (Usual Suspects)
• BOD(COD)/Nitrogen/Phosphorus
• Collect operational data
• MLSS/VSS/Temp/pH/DO/RR

Membrane

• Collect flow versus TMP (pressure data)
• Sample permeate from each SMU

See Warranty Statement/IOM

Biological Problems

The Usual Suspects

• Dissolved Oxygen out of range
• Integration and Control
• MLSS out of range
• Slug feed/shock load

Remedies

• Tune PID loops
• Adjust MBR/PA aeration setpoints
• Adjust MLSS in 10% increments
• Ensure adequate basin mixing
• Adjust recycle rate

High TMP

The Usual Suspects

• Organic fouling
• Inorganic fouling (hardness/Fe)
• Air locking
• Poor controls

Remedies

• Improve sludge quality
• Increase air scour rate
• Increase relax duration
• Change permeate flow setpoints (low and slow is best)
• Perform CIP

Troubleshooting High TMP

Check baseline clean water data

• Look at same flow values

Perform bleach CIP  acid CIP or vice versa Evaluate fouling rate

• Rate of increase should be about 0.07‐0.14psi/mo.
• Rapid fouling indicative of:
• Operation above critical flux
• Air locking (mainly suction systems)

Test Sludge Quality

• MLSS in MBRs? Equal?
• Filterability <10ml/5min?

Extract cartridge for testing

Membrane Integrity

Notes

• Generally one breach/1 MGD will register as

turbidity/TSS/fecal count spike

• Small holes/tears are self repairing

Troubleshooting

• Isolate source to MBR, SMU, cartridge

Remedies

• Repair damaged cartridge
• Replace damaged cartridge

Session #3 Summary

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• 1. In order to operate an MBR properly there are a few

critical things to check; air scour, mixed liquor and screens

• 2. Do not allow bypasses, provide at least the minimum air

scour, keep fluxes at or below design, keep a static sidewater in the MBR, clean membranes at least every 6 months

• 3. MBR controls are based around different modes for trains

and basins and states for equipment systems

• 4. Basins should be designed and equipment operated to

provide the greatest amount of flexibility and reliability

• 5. Troubleshooting issues with an MBR depends on defining

the problem, reviewing data and then taking the proper corrective action.