Laurie

You should also observe the decants in both tanks, to determine if you have bulking sludge and carryover of fluffy sludge in the decant. This will also reduce the sludge age, so if your high ammonia tank displays low DO, this would cause sludge bulking, which may cause bulking and carryover and even reducing conditions for nitrification. Do a 30 sludge settling test for each tank and calculate the SVI = 30 min settl (mL/L) / MLSS (g/L). Your sludge age needs to be approx 20 days to obtain adequate nitrification moderate winters (basin temp 10 deg C). 

You also need to watch aeration times getting out of synch. If DO driven, then you need to check that the probes are calibrated and there is no slime film on them (eg the good tank). Add up the aeration hours per 24 hrs for both SBRs. If just timer related then  this should ensure even aeration.

Regards 

Grant H

I read through this a bit quickly and it does appear that forum members are keying in on DO as a problem in basin 2.  I would agree and add that depending on your mixed liquor conc a 2 to 3 to 4 ppm DO may not be adequate to effectively use all your nitrfiying organisms in the floc structure.  If your MLSS is in the 4,000 to 5000 ppm range then your DO is going to have to be I'd say 4.3 to 4.5 ppm minimum. I'd shoot for 2.5 if your MLSS is 2500-3000. As you start to go from 3000 to 4000 and upwards your DO is going to have to go up to into the mid to high 3s. The reason is if you think of the floc structure as a tennis ball, most of the nitrfyng organisms have incorportated themselves deep within the tennis ball. So, until carbon is consumed by the heterotrophic organisms and this DO demand subsides, its a tough nut to crack trying to get DO into the center of the tennis ball to make the nitrifiers happy. The heterotrophs are opportunists and they suck up the DO on the surface of the tennis ball and act almost as a DO barrier to the poor nitrifiers. So if you have 2 or 2.5 parts DO in the bulk liquid you may still have 1 ppm or less on a microscopic level deep within the floc structure (tennis ball).  The nitrifiers will be very discouraged.  Under these circumstances you may need a 4 or 5 ppm DO in the bulk liquid to achieve a high enough driving force to achieve the mass transfer of DO deep into nitrifier town in the center of the ball. In a past life I did a little work with pure culture nitrifiers and was able to observe ammonia reduction versus DO concentration over time. DO was cyclicly applied - little aerator "on" at DO = 1.5 ppm and DO off at DO = 5 ppm.  The sample of pure culture and ammonium chloride (and sodium bicarb and macro and micronutients) was mixed and ammonia conc was monitored via ammonia probe. It was interesting to note that ammonia reduction versus time was linear above 2.5 ppm in this particular sample of pure culture. At DO = 2.5 ppm the ammonia probe flatlined (no ammonia reduction) until the little aerator tripped back on at DO = 1.5 ppm and raised the DO. As soon as DO surpassed 2.5 ppm ammonia started to drop again linearly.  The point I am trying to make is that the heavier the organism concentration the more difficult it is to insure that adequate DO (and mixing impacts as well to a degree) is available for 100% of the organisms in the process - to drive DO into the deep recesses of the floc structure in a "heavy" mixed liquor one needs to increase the driving force and mass transfer rate by increasing the bulk liquid DO.  This why many times, particularly in the summertime, if ammonia starts to go up, wasting heavily will bring ammonia back down.  Yes, we are decreasing the bugs in the process including our nitrifier friends but nitrifier numbers is not the problem.  The problem is inadequate DO for the MLSS we have. Reducing the bug mass and in turn the endogenous demand allows the DO in the bulk fluid to come up, increase our driving force and mass transfer rate and greatly increases the mass of nitrfying organisms which have the DO they need to do their thing, even in consideration of the pounds we actually wasted from the process.  

As a side note - I guess you have a total N limit or desire to have a mix cycle in the beginning to drive nitrate down so you dont get popping in your settle cycle.  If your nitrate is very low in number 2 basin and ammonia is high you may want to temporarily elimiate your mix cycle and make it all react or aerate - ie, we dont need to mix to get rid of nitrate since we have none to begin with. Throw your time at aeration. You may only be doing a little bio-p action in the mix cycle.

I may have caught wind that your aeration system may be a jet system (big centrifugul pump with blower adding air in at the jet manifold in the basin).  Sounds like a jet-tech SBR system maybe? Anyway, your manifold jet nozzles may have some clogs. You might want to compare the running amps on the pumps between basins - it may or may not provide a clue depending on whether the piping is largely similar.

If you have air piping flexibility to use basin #1 blower on basin #2 it might exclude the blower being an issue. 

sounds like your alkalinity is OK. If you have 80 ppm going out the door you're good.  Sodium bicarbonate is an excellent source of alkalinity and you cant overdo it relative to pH - you're only going to go to 8.2 or so at most even if you mess up and overdo it.

Mark 

and the bug knows best

Here in the deep south this is how things work. For a given plant and a given load if i increase my MLSS theoretically i can get by nitrification wise with a lower DO. The total air required may go up a little because of greater endogenous respiration but the plant will work with a lower DO. The relationship is not linear but is proportional to some extent. Suprisingly enough the design equations for nitrification also support this relationship.

Last time i looked this was one of the principles behind oxidation ditches: Big tanks , lots of biomass (low F:M) but generally lower  DOs  which produces stable nitrogen removal performance.

Now with my given plant and my given biomass if i suddenly have a big hit of ammonia i require more air to increase the oxidisation of the ammonia and as the nitrifiers have to work harder i may have to raise the set point to achieve adequate oxygen transfer. (See comments in one of my previous posts about an overloaded plant requireing 4mg/l).

Many plants that are under aerated for whatever reason may show some improvement in nitrification capacity if the MLSS is reduced because the endogenous demand is reduced enough to increase the DO in the MLSS enough to get some oxygen transfer happening. Alternatively the aeration rate could be increased which would achieve the same thing.

At least i think thats how it works!!!

TerryF

Well, I believe the F:M and mixing energy provided will in fact impact the size of the floc particle. You know - quantity and characteristic of EPS bug glue on cell exteriors? Case in point - everyone "knows CBOD reduction has to be down in the range of 20-30 ppm before nitrfication really kicks in"... right? whys that? why doesnt separate stage nitrfication work real well and why do the nitrifiers have a tendency to wash out in such process configurations? It is because nitrifiers are really heterotrophic wannabees and live to incorporate themselves into the heterotrophic floc particle or onto the fixed film depending on the process? Ok, so we know where the nitrfiers like to hang out. How come nitrfication doesnt kick in (full steam) the first minute when the first drop of wastewater enters the aeration basin? Could it be that the bulk fluid DO is scavenged by the heterotrophs occupying the surface of the floc particle such that the DO on the interior of the floc structure is so low that only a minute fraction of the autotrophic organisms have adequate DO for nitrification? This is exactly what happens. Until the oxygen demand is reduced to close to the endogenous (carbon largely gone) demand the autotrophs are not hitting on all 8 cylinders - ok, 6 cylinders with a turbocharger. In cases where we have a very heavy mixed liquor and need to achieve the maximum nitrfication rate because the engineer didnt get the client to pay for a treatment tank way bigger than it really needs to be, then we are going to need to run a DO over 4 ppm to achieve this maximum rate,ie, using all the autotrophic organisms in the process as efficiently as God allows them to be. Again, mixing plays into this too from the perspective of insuring even distribution of DO and nutrient throughout the bulk fluid. Think of it this way - you have a crowd of a million people standing shoulder to shoulder versus a million people standing at arms length to each other. If you had to walk thru the crowd which would be easier? (possible?). I have a hard time diffusing oxygen into the tight crowd - cant get it in all those nooks and cranies unless I create greater force in a higher DO to drive it in there - chem E stuff you know - higher temp to lower temp - higher concentration to lower concentration drives the rate of the reaction so to speak. To get thru the tightly packed crowd you would have to have one heck of a big guy (high DO)  behind you pushing. And, I maintain, the same applies to DO, MLSS and the floc particle itself - the high DO pushes through the crowd of organisms in the bulk fluid and floc particle so when it finally reaches, Fred and Mary, nitrifiers of good repute, they have enough DO remaining such that they can do their thing at an optimal rate. Certain things in wastewater just arent taught in school - I believe I have a paper in work from some PHd type who somehow actually measured DO on the floc scale basis although that happened to be in very recent times.  In an SBR one doesnt have a lot of time to mess around - dilute your influent ammonia by 1/3 (say the batch volume) to say what - 18-22 ppm?? so we have to spend a half hour doing our CBOD reduction from say 80 to 10 in consideration of mix and then have the rest of the time allocated to nitrfication. We should get a pretty good specific rate and have this done in what - 4 -5 hrs maybe. 

There is no question nitrfication occurs at low DO; we run a small plant , domestic wastewater local to our office at about 0.45 ppm at MLSS = 3000. We completely nitrify and typically have a total N going out of less than 2 ppm; permit is 10ppm as it goes to the ground. Its an MLE plant, ie, no second anoxic. Did I mention there is about 2 days HRT? ie, nitrfication rate and denitrification rate are not optimal but there is boocoos of time in the process so no biggie - we get by with the slower rate and as a side bonus achieve a lower TN than we otherwise could with an MLE process.  Same approach as the symbio gizmo sans the messing around, and oh, pay no attention to that capacity issue. Play games with DO and nitrify and denitrify simultaneously but for a given MLSS concentration the sweet spot DO (DO at which we are nitrifying and denitrifying at a rate high enough to achieve our permit goal within the time in the process) will be higher the higher the MLSS. 

As we are aware, extended aeration and oxidation ditch (ie, extended air plants  with a psuedo 200Q internal recycle pump) processes are as big as they are and were developed not because the treatment time is actually needed to achieve permit if the reaction rates are not purposely (or by accident) limited ; they are as big as they are: 1. to minimize sludge production, 2. civil engineers (and I is one) are going to have a harder time screwing things up and not achieving permit if they design this process.  3. You know- 1-800-Vendor.    One can run ammonia on a normal domestic waste extended air plant about half way thru the process on supernatant from the 30 min settle test and read 0.1 ppm year round assuming DO and alkalinity are not limiting. Nitrification rate is nitrfication rate, ie, zero order, over the two-Ks value for ammonia, ie, run the ammonia up above 1 ppm, as high as you want - nitrification rate aint going any faster. Its first order relative to bugs, ie, the more you have, the faster you go at a given temp to the extent you have ammonia available in the process for them. You can raise the SRT as high as you want but it doesnt mean you are going to have more and more nitrfiers - that will be limited by the raw wastewater N and the contribution from heterotrophic decay.   If a system is overloaded with regard to ammonia such as one that might have a contributory school (because the engineer didnt know the "ammonia" was not 45 ppm and TKN was really 130 ppm ish) then running a 4000 MLSS with a lower D.O. isnt going to cut the mustard. Its not because the ammonia concentration is higher, its because we arent effectively using all the nitrifying organisms we have in the process to nitrify at the maximum rate they are able to if they have an unimpeded source of DO. We had terrible trouble at a plant in FL which we ran MLSS at 5000 to 5500 in the high season when all the snowbirds came down for the winter. The problem was we did not have isolated blower piping so we had to try to balance the air with butterfly valves - by the click you know. Inevitably backing off one basin one click and opening another basin one click wouldnt take the DO from 5.8 ppm (excellent nitrficiation) to 5.0 ppm in one basin and from 3.8 ppm (poor to little nitrfication) to 4.8 in the other basin - it would be like 5.8 to 3.5 and 3.8 to 5.5 so we'd really almost stop nitrfiying in the first and start in the second and round and round we'd go. Certain things in wastewater just arent taught in school - I believe I have a paper in work from some PHd type who somehow actually measured DO on the floc scale basis although that happened to be in very recent times. I maintain that you will effectively shut down nitrfication at a DO above 2 ppm in a heavy mixed liquor because I have seen it happen and can make it happen.

So if one gets "hit" with a slug of ammonia its true that more lbs of air are needed to achieve this total oxidation. What is really happening though is that the rate of nitrfication needs to be increased by allowing all of the nitrfiers to hit on all 6 cylinders since we have a higher concentration to treat within the same HRT in the process.  No, the "oxygen transfer" into the bulk fluid is not impeded by a higher ammonia concentration in the "slug". But to git-r-done within the HRT of the process we may need to jack up the DO so we are able to drive the DO throughout the MLSS to effectively maximise the rate of the nitrfication reaction. This is what I have observed in the field in FL, NC, VA, PA, DE, MD; IN;Il; other states could be different. 

...and the bug knows best.

and the bug knows best