SBR's are quite interesting ...

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SBR's are quite interesting and I'm afraid they are far from my favourite.  The normal pH for aerobic operation is 6.8-7.8.  When the plant goes into settlement stage, then frequently anaerobic bacteria grow with the resultant drop in pH and this in turn stresses the aerobic bacteria.  Frequently this results in foam and may result in poor settlement due to zoogleal growth.  How can you change things?  You can try the use of lime in short term to correct the pH, because there will be some live aerobic bacteria present.  There are freeze dried bacteria which you can add.  However, they want aerobic conditions and the correct pH to become established, so if you just add freeze-dried to your plant they will be wasted unless you have already corrected your plant.  So before I started, I would heavily de-sludge then run the aeration stage for longer than normal to kick start the plant.  After saying this, I am trying to advise you remotely.  I would normally want to look at the plant and examine it microscopically.  There are questions you need to ask such as How good is the aeration system?  If it is producing coarse air and reaching the surface without transferring oxygen to the water then you will return to the same conditions, which you have at present.  This can be overcome by supplementing the air by installing fine bubble aeration, which can be retro-fitted.  My e mail is don@lansonmicrobe.co.uk.  If you are interested then I can put you in touch with suppliers of Freeze-dried bacteria and fine bubble aerators.

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Thanks very much Don. You have given me some good information there. There was no form of pH control at this plant. The last 2 weeks I have been manually dosing hydrated lime for mainly alkalinity but also for pH , as well as NaOH. The SBR is set up like this : sewer enters a continuous aeration tank, from there it decant into the DAT ( decant aeration tank ). The DAT is where my stages happen. The manufacturer has set up the timings : aeration for 2 hrs, non aeration for 70min. There are 2 decant per day. My settled sludge volume 30min test shows 90%. We remove sludge from this plant via a truck, which connects to a single outlet 80 mm camlock fitting. Approx 10,000 is drawn from tank. Internal tank pipe work is unknown , potentially outlet is just that and no network of pipe at tank bottom to when withdrawing which will mean a small area of sludge is withdrawn  and mainly just fluid, this would make sense as I have withdrawn 20,000 Ltrs of "sludge" but have seen no shift in SSV. Settling characteristics of the sludge test = very poor flow formation, similar to soup consistency. The 10% supernatant from SSV is clear. The CAT tank SSV has very good settling characteristics/floc formation. Today's pH was - CAT=7.09 DAT=6.97. Not too sure if this brief description will give you a head start up but hope it does. 

Thanks again 

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