Feeding Package Treatment Plants

As an inspector, I had the privilege of inspecting about 25 small, extended aeration package treatment plants in three counties in the Commonwealth. I learned many things about wastewater treatment from the plants and operators. One of the most important things I learned is that package treatment plants are difficult to operate in the best of times, but at reduced organic loadings and low flows, operational control can be even more difficult.

Operators have no control over the amount of biochemical oxygen demand (BOD), organic load or overall flow that comes into the treatment plant. Operators must simply deal with what comes at them.

Identifying reduced organic loading is fairly easy. Reduced organic loading causes a reduced mixed liquor suspended solids (MLSS) concentration, as well as a reduced microorganism population. The MLSS looks like thin chocolate milk instead of the expected “deep, rich chocolaty color.”

I have been asked many times by operators, “How do I deal with low BOD and low flow and still meet my permit limits?” I normally respond with, “You have to feed the bugs (bacteria), but first you have to get some bugs.”

Then the question becomes, “Where can I find bacteria for a wastewater treatment plant?” Because waste from horses has just about the same bacteria we use to treat wastewater, horse manure is a good source of bacteria. For a small package treatment plant, two or three five-gallon buckets of manure (without straw – it clogs things up) should be a good start. Just add it to the aeration basin. Another method of reseeding your plant is to have a load of MLSS from the nearest wastewater treatment plant hauled to your facility and added to the basin.

Now that you have bugs, you must feed them so that they multiply enough to remove the pollutants from the wastewater. In a low-BOD loading situation, the feeding of dried sorghum is an effective solution. However, once you start feeding them you have to continue until the BOD load increases.

This feeding method is good for use at schools, during vacations and at campgrounds during slow times, such as midweek. It is also used as a way to keep the organisms alive in a treatment plant that has issues due to overdesign or the facility being too large for the amount of influent BOD and flow.

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