WEF Discussion Forums
Laboratory Management and Technical Issues
A long time back I found that a frozen settled raw domestic sewage made a good seeding material. This was before seeding material was available commercially. We let the batch of fressh raw sewage settle, decanted to eliminate solids, mixed thourghly and despenced a constant volume into plastic bottles and then froze the containers. We thawed the bottles of seed in warm water and despenced the seed as needed. We checked the seed quality and amounts needed before using it for any real samples. The seeding material was utilized for a month and another batch was made and checked for the next month.
Freezing preserved the bacteria in a constant state and the nitrifiers were stopped. GGA standards were consistent. This would be an inexpensive way to make large volumes of seed material for large volume users. I hope Standard Methods will include this as an accepted practice in the future.
I have evaluated labs that successfully freeze seed material taken from their own waste stream. My take on the issue is that if Standard Methods doesn't say you CAN'T do it, then you CAN, and revision of the method would not be required. I would be a bit wary of using influent because it can be inconsistent, but if you happen to freeze the influent on a day when it made a good seed, you have a good seed for several tests. But of course, the opposite applies...freeze it on a bad day and you have a few months worth of bad seed. Other sampling sites in the plant might be more consistent (effluent from a clarifier or oxidation ditch, for example), contain a healthy population of hungry bacteria, and work just as well even if frozen.
Freezing seed material allows you to keep seed for a longer period of time. You now have time to thaw a portion of that seed and analyze GGA to determine that it will work properly. The large batch, despenced in smaller containers, allows for many analyses utilizing the same consistent seed material that has previously been check for good performance. If it a bad batch just discard that batch and prepare a new one. If you are an industry that does not have a good seed population in the raw waste, go to the local WWTP and borrow some of their influent to make your seed. Normal domestic influent contains a good mixture of organisms to decompose most organic matter in the sewage stream. If the industry discharges to that WWTP then those same organisms will be doing the treatment anyway.
The remaining bacterial population will very depending on treatment processes being used and different sludge ages for activated sludge systems. This is why I reccommend influent sewage for seed material.