WEF Discussion Forums
Laboratory Management and Technical Issues
Continuous culture for BOD/CBOD seed?
I have consistency issues with the strength of the seed sources that we have tried. We have tried using commercial seed, mixed liquor (not strong enough), and are currently using primary clarifier effluent. For the purposes of staying on topic, lets assume that the variation in seed strength is a result of industrial dischargers, odor control chemicals and general waste water variability, not cleanliness or dilution water issues.
I've heard of the freezing technique but does anyone have any direct or indirect experience with maintaining a continuous culture of seed organisms? By this I mean a container of seed material that sits on the bench with continuous aeration. The source of the seed material could be clarifier or commercial, it doesn't matter.
Obviously you would have to periodically discard an aliquot of the culture and replace it with fresh material to avoid a buildup of wastes. I should think that eventually you could reach an equilibrium and have a consistent seed source.
Here are the variables that I would like to get input on:
1) How much and how often would you discard and replace?
2) What do you feed it and how much/often?
I think that I remember reading on this forum about someone who did something like this with mixed liquor and fed it glucose. That information has since disappeared.
Does anyone know how commercial seed producers culture their organisms? Do they batch culture from pure stock or maintain a continuous culture? What do they use as nutrient?
I used to run bench scale "treatment plants" at a lab I used to work in. Basically, we'd have a tub of aerated waste into which we would drip our food source (which varied). We'd use a peristaltic pump to do that. Glucose would work as should any simple carbon source. Then once a day or so, we'd turn off the air, let the contents settle, and decant our "effluent". I think we also used this waste as our BOD seed, but as i wasn't running BOD's at the time, i can't say for sure. Mainly, we ran these to provide design criteria for engineers designing full scale plants treating industrial wastes. Hope that helps...these systems are easy to set up and require no specialized equipment. They are also pretty easy to maintain. I suppose once you have determined that you've reached a steady state condition (by running BOD's on the influent, Mixed Liquor and effluent for a period of time), then try the ML out as seed.
I held off on replying, Brian, hoping that more people who had actually kept a bacteria culture going in the lab would reply. I have never tried to keep a seed going in the lab, but I have audited many labs that did. I'll mention one that did so with much success.
A commercial lab in Denver got their seed (primary effluent) from a regional wastewater treatment plant that had found the seed to work for them (taken fresh for each batch). The commercial lab kept the seed in their BOD incubator, aerated it, and fed it starch (only trial and error would let you know how much and how often starch or some other "food" would be required). The lab would get good results for several weeks, but then, invariably, the GGA results would fall below their lower limit (which they accepted as 168 mg/L) and they would have to disqualify the seeded bottles for that entire batch.
I used their last 60 GGA results to show them a trend downward after a couple weeks with the same well-fed seed, a trend that occurred at least three times in those 60 results. Before each "failure" below the lower limit, one could easily see the downward trend. I convinced them to use a control chart to plot their results and as soon as the downward trend wast noticed, go get a new seed from the WWTP. Three years thereafter, I again audited the lab and they had not been "out-of-control" once since they started control charting, which was much better than they, or I, could have hoped for.
If your precision is good (i.e., you get a low standard deviation on GGA results), by keeping a control chart you will be able to tell if you are giving the seed enough "food" to keep them healthy. If you aren't, the downward trend will start after only a few tests. That will take care of the "how much" and "how often" to feed the seed. To determine when to get a new seed, just watch the control chart. As soon as you notice a sustained downward trend (perhaps seven results in a row below the chart's mean value), get a new seed.
If you aren't using control charts already and don't have a software program to construct/use one, let me know (firstname.lastname@example.org) and I will send you a freebie Excel® program that does the trick.