mbr sub systems

Knowledge Base - MBR Subsystems

Air Supply Systems

� How is airflow measured?

� My blower is tripping offline or not providing the same airflow rate that it used to.

What should I do?

� My Hach DO probe is not accurate. Do I need to calibrate it?

� SCFM - definition

� Troubleshooting MBR airflow readings.

� What is Air Scouring?

� What is coarse bubble aeration in an MBR?

� What is my DO setpoint?

� What is proportional airflow?

� When I try to manually operate a valve actuator it returns to its previous position as soon as I release the manual override knob. How can I get the valve to hold its

position?

Anerobic Zone

� Activated Sludge - definition

� Anaerobic (An) - definition

� What is DeNitrification and where in the process does it happen?

Anoxic (Pre & Post)

� Anoxic (Ax) - definition


Chemical Cleaning

� Backpulsing - definition

� Backwash - definition

� Chemically enhanced backwash (CEB) - definition

� Clean In Place (CIP) - definition

� Do I need to prepare for Winter?

� How does the Membrane Chemcial Dosing System (CDS) Work?

� Is silt a problem in MBRs?

� Maintenance Cleaning - definition

� Recovery Cleaning - definition

� What causes a Trans Membrane Pressure (TMP) Alarm?

� What chemical (and concentration) should be used to perform a maintenance

clean?

� What is Biofilm?

� What is the impact of wax on membrane performance?

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� What is the MAP to MBR Success?

� When is it appropriate to use Acid for a membrane cleaning?

Chemical Dosing

� Do I need to prepare for Winter?


� What is the impact of wax on membrane performance?

Disinfection

� What is Turbidity?

Equalization

Headworks


Internal Recycle


� Does my magnetic flowtube flowmeter require regular maintenance?

� Mixed Liquor (ML) - definition

� What MLSS should we being running in the MBR.

� Why do we recycle sludge and what is the appropriate flow rate?

MBR Zone


� Biohydraulics - definition

� Cassette - definition

� How are the Flat Plate Membranes installed in a treatment basin?

� How do I know if the diffuser clean cycle has been performed?

� How do I take a train offline for long term storage?

� How does static pressure figure into my TMP calculation?


� Is Flux the same as Flow?

� Is TMP the same as suction pressure?

� Mixed Liquor (ML) - definition


What should I do?

� My permeate pumps do not maintain a prime. Is this a problem?

� My turbidity transmitter is not working. Do I need to calibrate it?



� Relaxation - definition

� Seeded - definition

� Troubleshooting MBR airflow readings.

� What are the components of a Flat Panel Membrane?


� What is Air Scouring?

� What is Biofilm?

� What is coarse bubble aeration in an MBR?

� What is Localized Dewatering?

� What is Permeability Control (PC)?

� What is proportional airflow?

� What is Q for my Plant?

� What is sludge filterability?

� What is Turbidity?

� What MLSS should we being running in the MBR.


position?

� Why do I sometimes experience a failure to permeate after a diffuser cleaning Cycle.


Permeate Control


� How does static pressure figure into my TMP calculation?

� Is Flux the same as Flow?

� Is TMP the same as suction pressure?

� My permeate pumps do not maintain a prime. Is this a problem?

� My turbidity transmitter is not working. Do I need to calibrate it?



� What is Q for my Plant?


position?

pH Adjustment

Pre-Aeration (PA) Zone




What should I do?

� My Hach DO probe is not accurate. Do I need to calibrate it?




� What is my DO setpoint?

� What is Symbio?

Sludge Wasting


� How much sludge should I waste, and how often?


Supplemental Carbon Supply

Systems Integration


� How do I take a train offline for long term storage?

� If my HMI fails will the MBR continue to operate?

� My plant shut down due to an equipment alarm. How do I restart it?

� What are Critical Alarms?



� What is SCADA?

� Why do I sometimes experience a failure to permeate after a diffuser cleaning Cycle.

Activated Sludge - definition

Activated Sludge process is a process in sewage treatment in which air or oxygen is forced into sewage to develop a biological floc which reduces the organic content of the sewage. The biological floc and the treated effluent is then separated by gravity settling or a membrane in the case of an MBR.

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Anaerobic (An) - definition

(1) A condition in which free and dissolved oxygen is unavailable.

(2) Requiring or not destroyed by the absence of air or free oxygen.

(3) Absence of oxygen, as opposed to aerobic. In wastewater treatment the absence of oxygen is indicated as anoxic; and anaerobic is used to indicate the absence of any electron acceptor (nitrate, sulfate or oxygen).

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Anoxic (Ax) - definition

(1) Condition in which oxygen is available in the combined form only; there is no free oxygen. Anoxic sections in an activated sludge plant may be used for denitrification.

(2) Absence of oxygen. Other electron acceptors are present in an anoxic environment (nitrate, sulfate, etc).



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Backpulsing - definition

The reversal of permeate flow through the membranes to flush trapped particles from the membrane pores and cavities. This process is not required with Kubota flat platemembranes. « Return to top

Backwash - definition

The reversal of flow through a filtration medium. Often used as a cleaning operation that involves periodic reverse flow to remove foulants accumulated at the membrane surface. This process is not necessary with Kubota flat plate membranes. « Return to top

Biohydraulics - definition

Term given to the process optimization of a membrane bioreactor system by integrating biological treatment processes for maximum nutrient removal and the metabolism of carbonaceous material with reactor hydraulics.

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Cassette - definition

An assembly of membranes intended to be removed from an immersed system as a unit. (Also referred to as a membrane unit or rack)

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Chemically enhanced backwash (CEB) - definition

A technique to clean the membrane where the fibers are soaked in chemical solution by stopping the backwash pumps for a fixed period, then the entire system is back flushed before resuming normal operation. An expensive process step required with somecompetitors membranes. This is another process step that is eliminated with Kubota membranes. « Return to top

Clean In Place (CIP) - definition

A system or process for cleaning membranes while preventing physical damage to them by allowing them to remain in the basin that they are located in.

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Do I need to prepare for Winter?

Assuming by winter you are referring to Christmas in Ohio, not a January morning on the beach in Hawaii - Yes.

Points of consideration as we head into the cooler months are:

� I&I as a result of rain or snow melt.

� Decreased water temperatures which result in decrease flux rates.

� Potential impact on communications.

� Environmental impacts on equipment (freezing pipes, sticking actuators, freezing blower guards, slippery decks, etc).

� Critical spare parts inventory.

� Chemical inventory (MPE50, additional cleaning chemicals if silt is an issue).

� Addressing maintenance issues prior to the onset of harsh weather.



Your EQuipTech Customer Support Representative can provide you with additional ideas and help in developing your spare parts and chemical inventories. Contact them via the EQuipTech Hotline at 512-652-5848 or at [email protected].

Weather Check

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Does my magnetic flowtube flowmeter require regular maintenance?

Of course our first answer is - refer to the manufacturer's documentation. But we'll go on to explain - Magnetic flowtube style flowmeters are very accurate and high reliable. When installed on the clean water systems (permeate, plant reuse water) of an MBR facility, they are virtually maintenance free. Meters installed on the dirty systems (RAS, WAS, influent) can, over time, suffer from accumulated build up inside the tube. Because they can ultimately produce a restriction in the line, the first indication of their failure is often a reduction in flow values, that can't be explained by pump performance.

Resolution to this issue is often very simple. Following the manufacturers recommendations remove and service the tube.

It is important to remember that on some systems the failure of a flowmeter can result in plant shutdowns. If the PLC does not see the expected flow from a pump / valve during a permeate cycle its alarm reaction may be to shutdown that pump / valve. An evaluation of your system will help determine if adding flowmeters to your critical spares inventory is prudent for your facility.

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How are the Flat Plate Membranes installed in a treatment basin?

Multiple cartridges (between 25-400) are inserted into cassettes and the cassettes, in turn, stacked on top of integral air diffusers. The nozzle of each cartridge is connected to a permeate manifold that is connected to header located outside of the MBR. The entire assembly consisting of cassettes and an air diffuser is referred to as a submerged membrane unit or SMU.

The engineered configuration of a Kubota SMU, and specifically the fixed vertical orientation of the cartridges, allow the diffused air to uniformly scour each membrane sheet. In normal operation, an equilibrium is established within seconds between the material being brought to the membrane surface through filtration and the material that is scoured away by the crossflow of mixed liquor. The result of this equilibrium is commonly referred to as a biofilm.

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How do I know if the diffuser clean cycle has been performed?

The diffuser clean cycle is a critical function for the MBR and confirmation of its execution is important. Try to schedule the diffuser clean cycle(s) so that the process can be viewed by plant personnel. Otherwise, use SCADA trending analysis to verify that permeation was suspended at the same time as the diffuser clean cycle was scheduled and that an airflow reading was present. While this will not provide hard proof that the cycle is happening, it is indicative of the systems attempt to conduct the cleaning.

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How do I take a train offline for long term storage?



Whether for the purposes of maintenance, equipment rotation or as a response to changes in process demand, the procedure for preparing a basin for long term storage is the same. Most of the requirements are obvious:

� Take the equipment offline in the control system.

� Thoroughly clean the basins and membranes. Caution must be taken when cleaning the membranes/cassettes to avoid contact with high pressure water which can damage the equipment.

� Properly mothball support equipment (pumps, blowers, and instrumentation) per the manufacturer's recommendations.

� Protect membrane equipment from UV, weather, falling object damage, animal damage, etc.

A less obvious, and very important requirement, is the treatment of membranes with an appropriate surfactant. Flat plate membranes that have become wet (in clean water or sludge) and are then allowed to dry run a risk of becoming hydrophobic. A simple application of the surfactant to the membrane material will prevent permeability related problems upon re-starting of the equipment which otherwise could prove very problematic.

Your EQuipTech Customer Service Representative can assist with procedures and purchasing of the appropriate chemicals. Contact them via the EQuipTech Hotline at 512-652-5848 or at [email protected].

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How does static pressure figure into my TMP calculation?

For systems where the control elements (valve or pump) are below the water level in the MBR, a level signal can be used to determine PS. However, most systems do not have a level transmitter in the MBR and it is typical for pumped systems to have the centerline of the pump above the measured water level. Therefore, the PLC must record the last static pressure measured during a relax period of no flow and set that equal to PS. This means that PS is constantly being updated. If the system is in Intermittent Mode for any length of time, the PLC use the static pressure recorded during the last relax state for calculating TMP.

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How does the Membrane Chemcial Dosing System (CDS) Work?

1.1 Membrane Chemical Dosing System (CDS) The Chemical Dosing System (CDS) primarily consists of a Mazzei eductor, an actuated valve to control makeup or dilution water and a pressure regulator. The clean-in-place (CIP) procedure is fairly straight forward but can require some initial field adjustments to optimize fill time.

Before performing a cleaning, refer to the Operation and Maintenance Manual for the KUBOTA Submerged Membrane Unit. See Section 6.0 for chemical handling recommendations and membrane cleaning protocol.

To perform a cleaning, an operator must put the system in the CHEMICAL CLEANING MODE. After the operator has performed this action, that train's Permeate and Air Scour are stopped. The operator must also stop recycle flow to the affected train by shutting the appropriate slide gates. At this point, the selected MBR is totally isolated



with nothing coming into or leaving the system.

In the CHEMICAL CLEANING MODE, each of the units in the MBR to be cleaned must be prepared to receive the cleaning chemical by closing the isolation valve leading from the permeate collection header to the permeate flow control valve. Next, the valve on the chemical feed line leading to the permeate collection header in the MBR to be cleaned must be opened. After all valves at the MBR are correctly positioned, the cleaning solution can be transferred to the membranes.

After soaking for about two hours, the membranes should be clean and are ready to be put back into service. To place an MBR back online, return all manual valves and gates to their original positions and acknowledge that the process is complete at the HMI. Air scouring will resume at the appropriate intensity and after a short time delay permeate flow will resume.

Operating Note: Chlorine content of spent solution may be high following a cleaning. In addition, turbidity may be high until cleaning solution is removed. Rinsing (backfilling) the clean membrane units can mitigate these effects. There is no limit to how much rinse water is used. However, it is still important not to exceed maximum backpressure.

The target fill time for cleaning solution is 10-20 minutes. Therefore, if one bank of membranes is being filled, the feed flow rate should be between 220-440 gpm.

Referencing Figure 4-2 below, to adjust the flowrate, there are three options. First, adjust the flow using the pressure regulator (Callout 2) just upstream of the Mazzei eductor (Callout 4). Second adjust the valve (Callout 5) just downstream of the eductor using the performance table found in the IOM. For fine tuning of stock chemical federate, the small throttling valves (no callout) upstream of the rotameter can also be adjusted.



In summary, to clean all of the membranes in a given train, perform the following tasks:

1. Refer to Section 6.1.2 of the SMU IOM to calculate the amount of bleach required to perform the cleaning. Verify that this amount of chemical is contained in the feed tank. a. Generally, all the top or bottom cassettes in one bank (11) will be cleaned at a time. b. Assuming 12.5% stock bleach solution roughly 88 gal is required per cleaning. c. All of the upper or lower cassettes in one MBR must be cleaned at the same time. Therefore, assume at least 200 gal of stock bleach per cleaning.

2. Connect tote containing sufficient chemical. 3. Put the reactor to be cleaned in the CHEMICAL CLEANING MODE at the HMI. 4. Close the influent gate to the basin being cleaned. 5. Turn the permeate isolation valve in the pipe chase to the cleaning position. 6. Open the chemical feed valve to the MBR to be cleaned. 7. Acknowledge manual actions have been performed and initiate transfer of the calculated amount of cleaning solution via the HMI. 8. Confirm the request at the prompt. 9. Wait approximately two hours. A timer can be set at the HMI. a. To avoid high chlorine in plant effluent, rinse the cleaned membranes to remove spent solution. b. Rinsing with twice the amount of solution added should be sufficient. For example, if all the upper cassettes in one MBR are cleaned, flush each bank (left and right) with approximately 4,000 gal of water before placing the reactor back in service. c. Another method of reducing chlorine concentration in the effluent is to make



sure sufficient permeate dilution water is available. As a default, make sure the permeate to rinse ratio is greater than 3:1 before discharging spent chemical. 10. Return the permeate and chemical valves and slide gates to their original positions.

Caution: Read MSDS before attempting a cleaning. Make sure to wear appropriate PPE and be aware of bleach off-gas.

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How is airflow measured?

Accurate airflow measurement is critical in the MBR system. Set-points for MBR airflow are based on a calculation that considers membrane model and quantity. Advances in MBR technology have resulted in newer systems having multiple airflow setpoints and utilizing an energy saving strategy know as Proportional Air Scour. Customer airflow set-points are accessible via the SCADA system. Airflow balance is closely monitored by the control system and deviations from expected values can result in the generation of Critical Alarms and train shutdown.

The Enviroquip standard for airflow measurement is the Sierra Instruments Model 620 Mass Flow meter. The manual for this instrument will explain the theory of operation, installation guidelines and troubleshooting techniques.

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How much sludge should I waste, and how often?

In a healthy treatment system microorganisms consume the organic pollutants in the wastewater and use that energy to grow new cells. Left unchecked these populations can grow to the point where they become unhealthy and starve for food. Unhealthy sludge is typically malodorous, contributes to foaming and negatively impacts the biological process. To prevent this from happening sludge is periodically wasted from the process.

Wasting in bulk should be avoided if possible. Instead it is recommended that smaller volumes be wasted multiple times per day. Enviroquip's current automated wasting strategy offers five selectable wasting times per day, with totalized flow tracking.

Regardless of the strategy employed at your facility it is never recommended to waste in excess of 10% of the MBR system volume in one day.

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If my HMI fails will the MBR continue to operate?

A failure of the Human Machine Interface (HMI) normally has no immediate impact on the operation of your facility. A malfunction of the HMI leaves the operator without visual confirmation of the plants functionality but it is the Programmable Logic Controller (PLC) that truly controls the treatment systems. Indications of an HMI failure are a blank screen that doesn't recover on rebooting, seemingly normal graphics displays without data in the appropriate boxes, inability to change setpoints on systems (make sure you're properly logged in). PLC failures are usually easy to identify because



major systems generally cease to function.

It is critical that each facility maintain a backup copy of all installed software applications. This should include:

Remember - You are responsible for maintaining your system backups!

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Is Flux the same as Flow?

No, but it's related.

The filtration rate per area of membrane is referred to as flux. It is expressed in Gallon Feet / Day (gfd). Calculate membrane flux for each header using the equation below. Note that flow is the only measured parameter and that 1,440 min/day is a conversion factor. All other parameters are fixed values located in the Warranty Table. The area per cartridge is 8.61 for the Model 510 and ____ for the Model 515.

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Is silt a problem in MBRs?

Many types of fouling can occur and the most overlooked is Silt fouling. The most common times that silt fouling happens are after heavy rains or snow melt. There are also other contributing factors to silt in the influent construction, pipe repairs and storm water / sewer crossed pipes. A fair indicator that Silt fouling has occurred is a temporary recovery after bleach and acid cleaning are completed. For example, after you bleach clean, your flow and pressure only return to normal for 1-30 minutes. You then perform an acid cleaning only to see the same results.

As Silt will not stay in suspension in the sludge, the membranes foul as soon as the system begins to permeate. Another way to see this is run a clean in place using only clean water; this will push the silt off the membrane surface. When the system begins to permeate, again you will see a short-lived recovery.

The sludge thickener MPE50 is excellent for controlling free silt in the MBR basins. Continuous dosing may be required until the rain stops or cross-contamination corrected. You will have to monitor your MLSS closely during dosing periods in order to maintain the recommended 15,000 ml/g MLSS.

PC Operating System with licensing information

HMI / SCADA Applications with licensing information

Alarm Dialer Software with licensing information

Communications Software Backup (RSLinx) with licensing information



Cold weather brings cold influent, that in turn affects membrane permeability. Do not mistake a fouling problem with temperature related issues. Ensure you try all cleaning options before adding MPE50 and if possible ask your Lab manager if testing can be done to determine if Silt fouling is present.

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Is TMP the same as suction pressure?

It's not quite that easy.

(1) In strict terms, the pressure difference between the high and low pressure side of a membrane is referred to as transmembrane pressure or TMP. This generally includes the pressure across a biofilm.

(2) The calculation of Pressure (TMP) requires a correlation between flow, piping losses and additional logic to estimate static pressure. Generally speaking it is the actual pressure required to move water through the membranes, after taking all the other variables into consideration. Two reversible calculations for your reference are:

or

Where, PP = Piping system losses (no membranes) PG = Gauge pressure reading during filtration PS = Static pressure or gauge pressure reading at zero filtration or no flow

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Maintenance Cleaning - definition

An in-situ chemical cleaning lasting between 1hr and 4hr. During a Maintenance Cleaning the Membrane Zone shall not be drained or rendered incapable of returning to service within 15 min. Spent solution shall be rinsed into the mixed liquor using permeate or potable water. The rinse volume shall be greater than or equal to the amount of dilute chemical added. No additional chemicals are required for neutralization of spent solution.



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Mixed Liquor (ML) - definition

Mixed Liquor in its various forms can be described as:

(1) Mixed Liquor - A mixture of activated sludge and water containing organic matter undergoing activated sludge treatment.

(2) Mixed Liquor Suspended Solids - The mass concentration of the solid portion of Mixed Liquor. The solids are comprised of biomass, and inert inorganic total suspended solids.

(3) Mixed Liquor Volatile Solids - The portion of the MLSS that is vaporized when the dry solids are put in a 500C oven for 10 minutes. The MLVSS is measured as a percentage of MLSS and is usually around 60-80% of MLSS.

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My blower is tripping offline or not providing the same airflow rate that it used to. What should I do?

Enviroquip almost always specifies Positive Displacement blowers for our MBR applications. These blowers will move a very predictable amount of air at a given speed set-point. If this flow-rate drops unexpectedly there are several things to check:

� Confirm that the blower inlet filter is clean. A clogged filter will cause overloading, overheating, and a decreased rate of discharge.

� Confirm VFD speed is at its normal set-point.

� Verify that belt slippage is not an issue.

� Confirm internal cooling fans are operational.

� Confirm atmospheric temperatures are not in excess of design.

It is very important to remember that most newer MBR facilities have several permeate interlocks related to airflow. If your system lacks redundancy and/or the only available blower(s) is not able to satisfy your MBR Scour Air Setpoint it is very likely the affected train will shutdown. Some of your options in this case are:

Adjusting airflow setpoints outside of normal recommended limits is risky. You should first contact your Enviroquip Customer Service Representative before taking such action.

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My Hach DO probe is not accurate. Do I need to calibrate it?

Lower the permeate flow setpoint to reduce flux rates and then lower the MBR Scour Air Setpoint to a level the blowers can accomodate.

Lower the permeate flow setpoint to reduce flux rates and then increase your Allowable Airflow Deviation %, thus allowing the system to deviate further from the original setpoint.

Taking basins offline to free up airflow into another basin.



The LDO probe does not require field calibration. In most cases, accuracy can be restored by wiping the probe tip with a clean, soft cloth. The link below will take you to the Hach Technical Manual Website.

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My permeate pumps do not maintain a prime. Is this a problem?

YES!

The failure to maintain prime is an indication of air leaks into the permeate system. Air accumulation in the suction side of an MBR header can contribute to the following issues:

� Unbalanced suction to the membranes, resulting in increased flux rates through some units and reduced flux rates through others. This variance in load can impact the cleaning requirements of individual cassettes resulting in a system imbalance and contributing to potential for a localized dewatering event.

� Delays in establishing permeate flow upon exit of Relax mode thereby reducing the plants net flux.

� Possible equipment damage resulting from running pumps dry.

� Inaccurate interpretation of the suction pressure due to instabilities introduced via the compression of entrained air. This can prove very problematic in the calculation of TMP and Permeability resulting in a general decrease in system performance.

� Magnetic flow tubes are design to operate with pipes full of liquid. The presence of air can result in unstable readings.

� Entrained air can contribute to water hammer situations and ultimately piping/equipment failure.

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My plant shut down due to an equipment alarm. How do I restart it?

Some alarms are 'latching', meaning that they remain in place after the alarm condition is corrected. Pressing the 'alarm reset' button on the HMI will unlatch the alarm and allow the plant to restart. It is important to remember that once the alarm is reset the system will probably go into a mode transition scenario. This means there will be a time delay after resetting the alarm, before things will return to their normal online status. These mode transitions can take as long as ten minutes. Do Not Panic! If the offending alarm clears, without re-alarming, and the system is selected to be "Online" then allow the process to happen.



If alarms persist and impact the system's ability to come online - address the alarms as they arise.

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My turbidity transmitter is not working. Do I need to calibrate it?

The Hach turbidity transmitter should be calibrated on a regular schedule. The frequency of this maintenance requirement will vary depending on site conditions. However in many cases problems can be corrected by confirming that the lamp in the sample chamber is not burned out and that the lamp, sample body and detector are clean. The equipment manual can be found in your Enviroquip IOM or at the Hach website.

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Recovery Cleaning - definition

An in-situ chemical cleaning lasting between 4hr and 24hr. During a Recovery Cleaning the Membrane Zone shall be drained and refilled with dilute cleaning solution or the membranes to be cleaned moved to a dedicated tank. The spent solution shall be chemically neutralized and combined with plant influent for treatment.

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Relaxation - definition

Temporary suspension of flow while continuing to apply coarse air scouring. For warranty flux calculations, the assumed relaxation period is 1 minute out of every 10 minutes of permeate operation.

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SCFM - definition

Standard Cubic Feet per Minute (SCFM) is a volumetric flow rate corrected to standard conditions of gas density, thus representing a precise mass flowrate. SCFM is volumetric flowrate at a "standardized" pressure, temperature, and relative humidity. However great care must be taken, as the "standard" conditions vary between definitions, and should therefore always be checked.

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Seeded - definition

Active biomass (>70% volatile fraction) at a TSS concentration >3,000 mg/l has been charged to the MBR

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Troubleshooting MBR airflow readings.

Please note that this response assumes your system utilizes a thermal mass sensing element like the Sierra 620 which is typically installed on Enviroquip MBRs.

If your situation is this - Airflow indication on HMI (or on the local readout of the sensor) is near maximum, branch airflow valve is not opening as expected and/or blower is off or at minimum speed, bubble patterns in the MBR are weak or non-existent (visual flow indications apply to preair basins also) then read on.

Air delivery piping is often installed in situations that can allow condensation to accumulate inside the pipe. In small quantities it usually goes unnoticed. However if sufficient condensation develops, and the tip of the thermal mass sensing element gets wet, your airflow reading will spike high. This false reading will be transmitted to the PLC which will begin to recalculate blower speed (going lower) and/or valve position (closing), as it tries to meet its given setpoint. Since the false high signal will not usually be affected by these changes, the PLC will continue to adjust its outputs lower and slower until it can go no further. The most serious part of this failure is that systems which are not programmed to recognize this failure mode can continue to permeate water in violation of the golden rule for successful MBR operations which is "NEVER ALLOW PERMEATION WITHOUT PROPER AERATION".


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What are Critical Alarms?

By definition Critical Alarms identify situations within the MBR system that directly impact the ability of the facility to treat water. Critical Alarms should always be considered "call outs".

Enviroquip's current Control Specifications identify eleven critical alarms.

1. High TMP

2. Low Permeability

3. Permeate Pump or FCV Failure/Fault

4. MBR Low Level (switch or analog)

5. No Blowers Available or Too Few Blowers Available

6. High Level ("Imminent Overflow", any Basin, switch or analog)

7. MBR Low Air Flow (Low Air Scour)

8. Recycle Pump Failure/Fault

9. Diffuser Cleaning Valve Failure

10. PLC - HMI communication failure

11. PLC not in run mode

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What are the components of a Flat Panel Membrane?



The Kubota Corporation manufactures flat sheet, thin-film composite membranes exclusively for use in wastewater treatment applications. Each sheet of membrane material is made by dipping a non-woven mat of polyethylene terapthalate (PET) into a solution of chlorinated polyethylene and subsequently allowing the wetted mat to dry. During the drying process, a thin membrane skin (about 1 micron thick) forms over the mat with a nominal pore size of 0.4 microns.

Finished sheets of membrane material are cut to size and ultrasonically welded to Acrylonitrile Butadiene Styrene (ABS) panels for mechanical support. Inserted between the membrane and the panel is a polyester spacer material that serves as a plenum to evenly distribute permeate flow to channels cut into the panel. Each of the channels, or grooves, terminates at a nozzle on top of the panel. The finished product is referred to as a membrane cartridge.

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What causes a Trans Membrane Pressure (TMP) Alarm?

High TMP readings can be an indication of the need for Chemical Cleaning. Specifically the TMP reading is an indication of the pressure required to pull clean water through the membrane material. A steady increase in TMP (over time) is expected. This is a result of normal organic or inorganic deposits accumulating on the membranes during the treatment process. Standard maintenance cleanings will normally restore the TMP to its original value. Tracking TMP daily is an important part of maintaining your MBR as the TMP reading is used to calculate system Permeability. Permeability is your best indication of membrane performance. An inaccurate TMP value will result in a incorrect Permeability reading.

Rapid increases (over hours or days as opposed to weeks or months) in TMP can indicate problems. Possibilities include:

� Membrane blinding as the result of influent slugs.

� Air entrapment in permeate piping.

� Low mixed liquor quality.

� Instrumentation problems (Confirm pressure transducer and gauge reading match).

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What chemical (and concentration) should be used to perform a maintenance clean?

Chemicals and concentrations can vary by site. Bleach is the chemical most commonly used for maintenance cleanings as it is highly effective in treating organic deposits. Inorganic deposits are traditionally treated with Citric and/or Hydrochloric acids. Other more caustic chemicals have proven beneficial under extreme circumstances.

Identifying the appropriate chemical and dose for the application is easily achieved by following a standard test procedure available from your EQuipTech Support Representative. The procedure is designed to test individual membranes, thereby



reducing chemical use/costs expended when performing large scale tests.

This testing can help establish "normal" cleaning requirements for your facility and define baselines for historical comparison. Please refer to your plant’s O&M for general cleaning requirements and contact your EQuipTech Support Representative for additional details.

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What is Air Scouring?

Mechanical removal of accumulated biological solids from the surface of the submerged membrane units using rising air/mixed liquor flows between the membrane plates. The air/mixed liquor flow is the generated from compressed air delivered through course air diffusers at the base of the submerged membrane.

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What is Biofilm?

Biofilm is a mixture of extracellar material that forms on the surface of a membrane and provides a porous surface for microorganisms to metabolize the contaminants.

If one were to take a cartridge out of service for examination, a typical biofilm would appear as a clear thin slime layer covering the membrane surface and having a thickness on the order of a few microns. Unlike other membrane applications (e.g. tertiary filtration) any membrane in a mixed liquor environment will be covered with this type biofilm or cake layer. Moreover, it is the biofilm itself that does most of the filtering, making the membrane a secondary boundary between the mixed liquor and filtered effluent (permeate). Capitalizing on the enhanced filtration provided by biofilm formation, the Kubota membrane cartridge is able to produce reuse quality water while sustaining high permeability. A direct result of high permeability is the ability of the Kubota SMU to be gravity operated. Nearly half of the over 2,000 Kubota installations worldwide operate in what is called a gravity mode. In gravity mode, roughly two feet of water head above an SMU can drive design flow (Q) and less than four feet can drive peak flow (2Q) through a plant.

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What is coarse bubble aeration in an MBR?

(1) Mechanical removal of accumulated biological solids from the surface of the submerged membrane units using rising air/mixed liquor flows between the membrane plates. The air/mixed liquor flow is the generated from compressed air delivered through coarse air diffusers at the base of the submerged membrane.

(2) The Enviroquip MBR utilizes a centipede type diffuser to deliver coarse bubble air to the membrane plates. While this does add oxygen for use by the biological process, and design credits are taken for its contribution, its primary function is to scour the flat plate membranes; removing excess bio-film and helping to ensure stable flux rates. This "scour air" is absolutely critical in all MBR designs. Standards for the flowrates vary by system, but it is always a requirement. Because blower operation costs (energy) are a large part of a facility’s electrical bill, much engineering effort is committed to their efficient use. Enviroquip’s Control Standard includes a Proportional Airflow Control Strategy which modifies airflow setpoints based on influent flowrates. Lower flux demands will result in lower airflow requirements. The golden rule for successful MBR



operations is "NEVER ALLOW PERMEATION WITHOUT PROPER AERATION".

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What is DeNitrification and where in the process does it happen?

DeNitrification is the biological process whereby nitrates are converted to nitrogen gas. Certain bacterial species use nitrate as an oxygen source and produce nitrogen gas as a biproduct through a process called denitrification. Denitrification occurs in an anoxic environment where these microbes, nitrates, and BOD are present.

Because nitrates can negatively impact local water supplies and environments their levels in wastewater effluent are often regulated by licensing authorities. DeNitrification is the biological process by which nitrates are removed from wastewater. It is the result of certain microorganisms converting existing nitrate (NO3) to nitrogen (N2) and oxygen (O2) gas. This conversion requires an environment that is very low in or totally free of oxygen. For our purposes this low oxygen environment in which nitrates are present is referred to as Anoxic. A separate basin is usually provided for this process. It is fed from the nitrate rich MBR recycle and raw influent wastewater. Any oxygen remaining in the MBR recycle flow is quickly depleted as the microorganisms consume the organic material in the raw wastewater, leaving the contents of the basin anoxic and thus a suitable environment for the nitrate to nitrogen conversion.

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What is Localized Dewatering?

Simply stated Localized Dewatering is the accumulation of concentrated solids between membrane plates. The phenomenon occurs in all MBR technologies (flat plate, & hollow fiber) and is normally the result of mis-operation related to insufficient airflow or RAS rates. The impact on system performance is the same regardless of membrane type: reduced flux rates & increased TMP.

Enviroquip is the World's Only MBR equipment provider that has successfully deployed a system designed to assist in the remediation of Localized Dewatering events. The Membrane Treatment System (MTS V3) is easily transportable, highly efficient, and simple to operate. Advances in the design of this system have resulted in a product that can restore 1 million gallons per day of treatment capacity, per machine.

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What is my DO setpoint?

A standard answer to that question is 2.0 mg/L. This set-point usually allows for complete nitrification without over aerating which ultimately is a waste of energy. Additionally this setpoint is sufficient to support process health without usually risking carry over into the denitrification zones. DO set-point calculations are unique to each facility and the optimization of DO can have significant positive impacts on energy consumption.

Systems designed to operate with a simultaneous Nit/DeNit strategy will have two setpoints. A low (normally 0.2) and a high (normally 0.8). The system's PLC will monitor and control blowers and valves to cycle between these setpoints and dwell at each for an operator determined period.

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What is Permeability Control (PC)?

Systems that have a built-in Permeability Control Set-Point should be aware of this control scheme. Permeability control is a PLC process that adjusts the permeate flow in an attempt to recover permeability during a periods of reduced treatment capacity. Instead of shutting the system down in response to this reduced capacity - special algorithms are employed to keep the system treating water, without risking damage to the membranes.

There are two different permeability control strategies currently utilized.

1. Upon satisfaction of the PC set-point the PLC will decrease the permeate flow set-point in predefined steps. The PLC will adjust valve position or pump speed in an effort to satisfy the adjusted set-point. The logic will constantly monitor for opportunities to improve the set-point with an ultimate target of returning to normal flows. Typically MBR airflow set-points will be increased to maximum values during PC in a effort to improve flux rates.

2. The second strategy is different from the first in that instead of using a stepped approach, the controls are adjusted proportionally.

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What is proportional airflow?

Proportional airflow is a new energy saving control strategy applied to the scour air delivery system of the Enviroquip MBR. Aeration demand is calculated by the PLC based on the number of membrane cartridges in service and three global airflow setpoints. Air header setpoints are assigned according to the control water level or influent flow rate. The PLC calculates the air-flow setpoint for each header using this equation.

Example of Proportional Airflow Settings




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What is Q for my Plant?

Q is an indication of your facility's design flow set-point. It is a calculated value based on the number of membranes, the square footage of treatment area, and the Flux Rate defined for your plant.

Use the following equation to determine the plant design permeate flow:

Total #SMUs x #Cartridges per SMU x Flux x 8.61/1440 x (1.1 or 1.2 or 1.3 to account for relax time in minutes) = Plant Q

If your plant has 3 flow set-points they are probably set to:

See your Enviroquip Warranty Sheet for plant specifics

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What is SCADA?

SCADA is the acronym for Supervisory Control And Data Acquisition. The term refers to a large-scale, distributed measurement (and control) system. SCADA systems are used to monitor or to control chemical or transport processes, in municipal water supply systems, to control electric power generation, transmission and distribution, gas and oil pipelines, and other distributed processes.

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What is sludge filterability?

Low Flow .5 Q

Normal Q

Peak 2Q



Filterability is a measurement of sludge quality. It is a good indicator of your sludge's potential impact on membrane performance and cleaning requirements. Testing procedures are simple flow/time. There is a special filter paper requirement needed for this test. Weekly testing is highly recommended for MBR facilities and is typically considered a requirement for Enviroquip MBR System Warranties.

The current test procedure and a supply of paper can be obtained through your EQuipTech Support Representative. They can be contacted via the EQuipTech hotline at 512-652-5848 or at [email protected].

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What is Symbio?

For applications within the United States, we have coupled our proprietary SymBio® technology for simultaneous nitrification and denitrification (SNdN) with the MBR technology. This combination is proposed for plants designed to meet stringent nutrient removal requirements such as 3-5 ppm TN. Low total nitrogen levels are achieved by using a simultaneous nitrification and denitrification concept in conjunction with the conventional concept of recyle to a pre-anoxic basin from the MBR. Use of SymBio® process results in lower aeration energy consumption for the MBR process and also lowers the internal recycle requirement for denitrification to the anoxic zones. More info

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What is the impact of wax on membrane performance?

Excessive wax, like fats, oils and greases (FOG) can foul membrane material temporarily, or permanently, reducing membrane capacity. Enviroquip's recommendations are that the influent concentration of FOG (wax) should not exceed 20% of measured biochemical oxygen demand (BOD). However, we do have experience with school applications where wax concentrations can be very high during summer maintenance work and procedures have been developed to minimize wax impact.

Should wax concentrations exceed the calculated maximum value, additional bleach cleaning and or addition MPE50 may be required. In some cases it may be advisable to haul wax laden influent to a conventional plant to avoid additional cleaning and or a reduction in membrane capacity.

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What is the MAP to MBR Success?

The Enviroquip MAP to MBR Success is a simple tool for remembering the necessary steps for ensuring long term successful operations of your flat plate MBR system.



MAP To MBR Success

Monitor and Trend

Monitoring and reviewing trend data for the following items will provide insight to a systems health and performance. • Permeability • TMP • Air Scour Rate • MLSS • Filterability • Diffuser Clean Cycles • MLSS • Filterability • Diffuser Clean Cycles

Act

• Perform a membrane Maintenance Cleaning if TMP increases by 1.0 psi at a given flow (pick one) or permeability drops below 10gfd/psi. Remember the maximum TMP is 3.0 psig. • Never allow filtration without aeration. No exceptions. Low air at low flux is okay at high permeability. • Immediately and properly respond to Critical Alarms. • Keep MBR MLSS concentration at or below 15, 000 mg/L unless otherwise instructed. • Keep diffusers clean at all times by extending cleaning time or cleaning more frequently, if necessary. Clean for 10 min/day as a minimum.

Prepare

Post a detailed plan listing Critical Alarms and how to respond to each alarm. • High TMP • Low Permeability • Permeate Pump or FCV Failure/Fault • MBR Low Level • No Blowers Available (or too few blowers available) • High High Level (Imminent Overflow) • MBR Low Air Flow • Recycle Pump Failure • Diffuser Clean Valve Failure • HMI/PLC Communications Failure

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What is Turbidity?

Turbidity is a measure of the cloudiness of water- the cloudier the water, the greater the turbidity. Turbidity in water is caused by suspended matter such as clay, silt, and organic matter and by plankton and other microscopic organisms that interfere with the passage of light through the water (American Public Health Association, 1998). Turbidity is closely related to total suspended solids (TSS).



Nephelometric turbidity unit (NTU) is a measure of the clarity of water. Turbidity in excess of 5 NTU is just noticeable to the average person. MBR effluent is around .04 to .08 NTU.

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What MLSS should we being running in the MBR.

MBRs operate at substantially higher MLSS concentrations than conventional wastewater treatment facilities. Normal operation is typically greater than 8,000mg/L and lower than 15,000mg/L. It is important to remember that increasing the MLSS above your plant's design set-point has carry over effects on different systems. DO, SRT, Flux Rates and Wasting Schedules are some of the factors effected by deviations in MLSS. Finding the "Sweet Spot" for your facility is important to ensuring long term trouble free operations.

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When I try to manually operate a valve actuator it returns to its previous position as soon as I release the manual override knob. How can I get the valve to hold its position?

It is very likely that your PLC still wants to control the valve position. If you need to operate in manual, and cannot keep the override knob from releasing, it will be necessary to disconnect the valve power supply. Often this can be accomplished by opening the fused terminal block (in the control panel) supplying the valve. Please remember that only Authorized and Qualified personnel should perform electrical tasks.

Important - please note that using a cheater bar to move your actuator/valve will likely result in costly damage to the equipment.

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When is it appropriate to use Acid for a membrane cleaning?

If normal Maintenance Cleans using bleach, which targets organic deposits, do not fully recover membrane performance, then other options can be considered. Iron and calcium deposits are common in many parts of the country and over time can contribute to reduced flux rates. Hydrochloric and Citric acid cleanings can be excellent tools for the restoration of flux rates when such inorganic fouling is suspected. Your Enviroquip Customer Service Representative can provide a procedure for testing individual membranes for response to different cleaning chemicals and concentrations. The test is simple and can save time and money by optimizing your cleaning efforts.

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Why do I sometimes experience a failure to permeate after a diffuser cleaning Cycle.

Positive confirmation of coarse airflow to the MBR is critical to its operation. Various permissives are monitored in the PLC program to ensure that there is never an opportunity for the MBR to permeate without airflow to the cassettes. One of these permissives is "Diffuser Clean Valve (DCV) Closed". This input to the PLC comes from a limit switch in the DCV actuator. If, after performing the cleaning operation, the DCV does not indicate fully closed, the system will not be allowed to return to an online status. There is typically an alarm "Diffuser Clean Valve Failed to Close" indicating this condition. A visual inspection of the valve position is recommended. Often the actuator is closed, but not quite enough to generate the switched signal. Manually closing the valve slightly can resolve the issue.



This is a very important alarm / subsystem. Do not ignore it.

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Why do we recycle sludge and what is the appropriate flow rate?

Constant recirculation of MLSS, and its subsequent mixing with new influent flow, is critical to sludge health and treatment process success. Recycle flow carries Mixed Liquor through each treatment phase ensuring opportunities for Nit/DeNit, Bio-P, food distribution, and ultimately treatment in the MBR.

Generally, the recycle rate should be 3 to 6 times Q. However, the specific value may be determined by the original plant design or may be operator optimized to satisfy the plant’s operating environment.

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