Hello, Please Help;

We have had trouble with High SVI of above 300. In 30 mins sludge settles to only approx 980 out of 1000.

We got a lab identification done on the the activated sludge which states a frequent but not abundant amount of filaments largely outside the floc or extend from the floc into the bulk solution or bridge the various pieces of floc together. Sphaerotilus are the dominant type.

Process flow is 2100m3/day 5 days a week with a BOD of 300g/m3 Screened -> DAF -> 30/70 flow split to one SBR and continuous extended aeration.

Approx 10000kg biomass exist in both systems but with SBR getting 70% of the load we are getting the same symptoms in both systems.

Process changes were made late last year which were sending all WAS to our equalization tanks both of which are mixed and we run no lower than 50%. Could we be producing the filaments here? then flowing though the DAF and ending up in our ponds?

We are getting complete nitrification and our nitrates are low Phosphorus levels were approx 20g/m3

Many thanks

I would also be skeptical of having S. Natans in an extended aeration plant, not saying it can't happen though. If your SVI is 300 you have something going on-either he undervalued the amount of filaments or there's slime bulking.

I done a SVI and a DSVI

SVI = settled to 990ml in 30min MLSS @ 3000gm/3 SVI = 330

50% DSVI = settled to 940ml in 30min

is the DSVI equation for 50% water 50% MLSS;

940x2x1000/3000 ? if so DSVI = 626

Does this confirm filamentous bulking?

F/M is the amount of food (lbs) to the amount of biomass (lbs) within the plant. Causes for filament growth are low F/M, low DO (for the applied F/M), organic acids/ septicity, oil and grease, lack of nutrients, and low pH (for fungi). Ammonia is not a cause for their growth.

best regards,

Ryan

Hi Sludgefather,

So it is only really organotrophic FM that is being referenced in regards to fillaments?


Thanks,
argfin.

Thanks.

argfin.

Hi Alistair,

Thanks, yes we increased the DO and slowly increasing the MLSS in the SBR to around 4000g/m3.

We did lower our MLSS from 5000 to 3500 from September 11 till January 12 and stayed steady from January till just recently (Winter and Summer MLSS) so effectivly we increased our F:M but our F:M is quite low;

SBR = .056
Continuous Ponds = .03

Another thing to add is our supernatant in both systems is really clear.


Regards,
Brendon

Here are some guidelines that may be applied to a conventional activated sludge plant:
1. There must be sufficient aeration to maintain a dissolved oxygen concentration of at least two mg/L at all times throughout the aeration tanks.
2. Dissolved oxygen should be present at all times in the treated wastewater in the final settling tanks.
3. Activated sludge must be returned continuously from the final settling tanks to the aeration tanks.
4. Optimum rate of returning activated sludge will vary with each installation and with different load factors.  In general, it will range from 20 to 40 percent of the influent wastewater flow for diffused air and 10 to 40 percent for mechanical aeration units.
5. The optimum mix liquor suspended solids concentration in the aeration tanks may vary considerably, but usually is in the range of 600 to 3000 mg/L.  Optimum MLSS concentrations should be determined experimentally for each plant.
6. A sludge volume index of about 100 and a sludge age of three to fifteen days are normal for most plants.  When the optimum sludge volume index is established for a plant, it should be maintained within a reasonably narrow range.  A substantial increase in SVI is a warning of trouble ahead.
7. The suspended solids content in the aeration tanks may partially be controlled by the amount of sludge returned to them.  All sludge in excess of that needed in the aeration tanks must be removed from the system.  It should be removed in small amounts continuously or at frequent intervals rather than in large amounts at any one time.  Sludge held too long in the final settling tank will become septic, lose its activity and deplete the necessary dissolved oxygen content in the the tank.
8. Septic conditions in the primary sedimentation tanks will adversely affect the functioning of the activated sludge process.  Prechlorination or pre-aeration may be used to forestall septic conditions in the wastewater entering the aeration tanks. Septic primaries have been shown to cause filamentous bulking.
9. Periodic or sudden organic overloads that may result from large amounts of sludge digester overflow to the primary tanks or from doses of industrial wastes having an excessive BOD or containing toxic chemicals will usually cause operating difficulties.  Whenever possible, overloading should be minimized by controlling the discharge or by pretreatment of such deleterious wastes.