Totally Different Condition of Diffusers in SBR1 and SBR2 of the Same WWTP

This week I had a job of supervising the process of cleaning a WWTP, namely one aerated Equalization basin and two SBRs. The WWTP is for wastewater from a company that manufactures pharmaceuticals. The wastewater is not aggressive whatsoever.
When the basins were emptied we discovered that the membrane plate diffusers in Equalization tank and SBR2 were in great condition: no ruptures, no cloggings, membranes were soft, etc. On the other hand, diffusers in SBR1 were in a very bad condition: 6 out of 40 had ruptured membrane, and all the rest had some kind of hardened material underneath the membrane, and when I put pressure with my hand it crumbles. Another strange thing is that it looks as if the aeration in SBR1 is just fine. There is no significant increase of backpressure to the blowers and the target DO of 2 mg/l is being easily achieved.

Do you have any idea how is this possible? Just to make it clear, same wastewater goes alternately from equalization basin through SBR1 or SBR2, depending on the cycle.

The operator said that he did not put any additives to the SBR1, but the fact is that he is not to be trusted, because there are rumors that in the past he tried to sabotage the biological process.

There are couple of pictures attached, for your reference.

Thank you in advance for your answers.

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Taxonomy

• Pharmaceuticals Waste
• Membrane Bioreactor Systems
• Wastewater Treatment
• Bioreactors & Processes
• Water & Wastewater
• Semiconductors
• Sequencing Batch Reactor (SBR)

7 Answers

1. Hello @Mirko.
   We have seen such issues in the past usually caused by membrane breaking or popping up. The grid loses pressure, bubble pattern goes uneven. At first anaerobic cycle (and SBR has them) , the system depressurises and water + active sludge enter the grid. This happens in one group, usually associated with one dropper. At next start, sludge clogs the whole grid from inside and makes that layer you mentioned. Backpressure may be ok as the membranes popped out. Aeration still happens with bad pattern and coarser bubbles. All 40 diffusers on same dropping pipe? 

   I fully agree with Mr. @Martins and Mr @Qiao. 

   Hardened membranes usually happen when softeners in EPDM get lost. This is ageing or exposure to the UV radiation (sometimes in summer tank was drained, no water on top of diffusers for some weeks... only for that tank). Check the logs of the plant.

   Replacing all membranes and backwashing the grids might be a solution. Condensate removal to be implemented.

    

2. Pharacutical factories have a coating material for their pills that by our experiance can clloge membrane diffusers and as bill cathcart said the equalization size could cause diffrent waste streams to each SBR

3. The design of an air diffusion system should include an air bleeding pipe to remove any dirt inside periodically. The dirt could be inside of the diffusion system during the installation period or through failed blower filter or condensate.   

    

   Once the diffuser blocked, the back pressure could increase and be ruptured ​the diffuser’s membrane. Once the diffuser raptured, the air flow pattern changed during the aeration and result in some anaerobic area part of the SBR. Due to the aeration system designed too conservative or unevenly aerated, the DO might be still achieved the setpoint in some spots depends the DO probe’s position installed.  

    

   Replace the whole diffusers in the SBR1 and install an air bleeding pipe to allow the dirt get out of the aeration system.

4. Because the SBR operates under aerobic followed by anaerobic conditions, without full aeration produced by fine bubble aeration, oxygen will not be transferred effectively.  This will cause permanent anaerobic conditions in part of the tank. It appears that iron bacteria have also grown locally in the areas around the diffusers and these would form crystallised material.  The other issue I would expect would be foaming from such a plant due to the stress reaction of aerobic bacteria.  It does stress the importance of inspecting submerged aeration membranes on a regular basis.  These damage is most likely to be natural events caused by the aeration system rather than deliberate sabotage.

5. I think the suggestions already given should be checked, especially the on by Ken Martins.  Another thing to look into is the capacity of the equalization basin and the schedule of the processes taking place in the manufacturing operation.  Do they do something different the same time every day that could possibly effect the chemical properties of the effluent - flushing, cleaning, certain process, etc? Depending on the size of the equalization, and the sequencing of the SBR's, the effluent from a certain process more to one SBR than the other.

6. Mirko,

   Is it possible that SBR1 has leaks in the piping and when the system is not pressurized it allows wastewater to leak into the aeration piping.  That would lead to solids build up behind the membrane.  Another possibility is that one of the blowers for SBR has a faulty air filter that is allowing dirt and dust in that would eventually build up behind the membrane. 

   Also, since these are SBRs, you should also consider that they could possibly be programmed differently.  I would verify that these are programmed to operate in the same batch sequence.

   1 Comment

   1. It can be piping leaks or if a membrane has collapsed, sludge can enter the piping from the damaged diffuser during non aeration phase. If it is the case, it is very easy to confirm it visually. During normal operation you can also verufy it if you have drainage valves => you open it frequently to remove condensates anf if sludge is resent in piping, ypu will observe brown water coming out from the piping drainage system.

7. This is something you are not going to get to the bottom of.  Even if the op was doing something untoward to get something in a well mixed system to attack one set of diffusers and leave the other unscathed is difficult.  For all you know it was down to a manufacturing fault in a single batch which were fitted in this one tank.  Replace them, get the process back up and running and move on.