WEF Discussion Forums : Operation and Maintenance : very low SVIs!!

We operate a conventional activated sludge plant and must nitrify to remove ammonia. For no reason that can be found our SVI's began to drop and have not stopped since 11/01! Here is some data:

SVI's <50

Mixed Liquor 2800 mg/L

RAS 10,000 mg/L

MCRT/SRT 7.0 Days

Little or no blankets in secondaries

DO's 2-3 ppm

SOURS' good 15 mg/g/hr

Few filaments- dispersed flock-mostly free swimmers

We halted wasting to build up inventory.

Historically our SVI's do drop this time of year (we begin to build up inventory to nitrify)

but they level off, not the case here. HELP

Need more info?


]]> Wed, 17 Nov 2010 15:55:14 GMT I should add that microscopically there few filaments and as many stalked ciliates as free swimmers. DEB


]]> Wed, 17 Nov 2010 23:41:01 GMT I'm not sure what your problem is. What are you experiencing that is negative? Low SVI is generally a good thing. It means you are settling well. Stopping wasting is pretty drastic. Is your MLSS too low?


]]> Wed, 24 Nov 2010 23:41:33 GMT I wish my plant ran those S.V.I. numbers.


]]> Sun, 28 Nov 2010 19:18:12 GMT SVI's too low can be a bad thing .When the mixed liquor settles much too quickly the effluent quality suffers-too many solids are left behind. The irony is that it is usually high Safes we must control.


]]> Mon, 29 Nov 2010 15:15:29 GMT

Deb,

I agree very fast settling can be a problem. By the amount of stalks and free swimmers, it appears you have a younger sludge. So increasing the MLSS might be helpful. As temps drop you will also need more bugs to do the same amount of work. I would increase the MLSS incrementally instead of halting wasting completely. Let the process ease into the change. It's more fun to put the pedal to the medal for quick results, but risky. Easy to overshoot your goal and potentially create new problems. The numbers you posted look good, and you are probably headed in the right direction. It's hard to give advice without knowing more about your plant.


]]> Mon, 29 Nov 2010 23:55:03 GMT