As denitrification is very efficient in the reactor floculation of sludge is also high. It disturbs the settle/decant and refill phase of the reactor. Please suggest some way which will help to maintain the optimum SVI without affecting the reactor performance.
The best thing you can do is to insert a pre -DN phase during feeding of approx 20 minutes without any aeration and a post-DN Phase of 10 - 20 minutes just before you start settling. If you have an agitator this should be running in these phases. Other wise you must let you aeration run on the lowest possible speed or just give an air pulse of 1 minutes very 5 minutes during these phases.
You need to apply anaerobic or anoxic conditions to your reactor because anaerobic condition enhance sludge aggregation so that will give SVI less than 70 mL/gram , may be you can do that by cutoff the aeration in the last 20% of aeration period and keep mixing only without aeration
It is obvious that in a SBR system performing simultaneous N and P removal , the initial volume, that keeps the sludge should be as minimal as possible so that the fill volume to initial volume ratio, which is the equivalent of internal recirculation in continuous systems, be maintained at the highest level.
SVI is a direct index for lowering the sludge volume and hence, the initial SBR volume.
The best way to maintain SVI below 100 ml/l is chemical intervention/conditioning, i.e. addition of a minimal dose of a selected coagulant. Synthetic coagulants and/or polyelectrolytes may be tested for this purpose, or a well known coagulant such as FeSO4 may be used at 10-20 mg/L for the same purpose.
Biological configuration additions may increase the complexity of the already complex SBR operation for this purpose, and they should be tried if chemical conditioning does not work.
Thank you. Dear Orhon sir..Does the coagulant have any+ve/-Ve effect on the microbial consortia present in the the SBR? As you pointed this may increase the complexity. The how can I use this to my benifit. Please do suggest.
Hello Jyotsna,
is bulking your problem? or are you having rising problems due to uncontrolled denitrification?
Dear Sir
For instance bulking is my problem . Denitrification rate is also very high. Colud it be the reason behind bulking of sludge?
Which is you SVI? Do you really have bulking? Or uncontrolled denitrification during the settling phase? If you have good denitrification rate it could indicate that your BOD is high and that the typical low F/M ratio that can produce high risk of bulking is not the case. In addition, in SBR configuration the typical bulking problem is reduced because of the high COD during part of the cycle.
Which is the COD/N/P ratio of your wastewater? Another possible bulking risk is low N or P concentration.
When you are measuring SVI with out stirring will you get a two phase system with some of the sludge on the top ? If this is the case Denitrification during settling is most likely your problem and my earlier answer is valid.
If it is more general a bulking problem you should verify that oxygen will get up towards the end of you cycle. It is also advisable to work with a non stirred feeding phase at the start of the cycle to adsorb the incoming COD onto the sludge flock.
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