Wadtewater treatment Lagoons come in all different sizes and shapes. Many different types of industries and municipalities have once through lagoon systems. Some pulp and papermills have wastewater treatment lagoons that are over 36 acres! Some papermills have 40 million gallons a day flowing through their wastewater plant! Aerated lagoons or stabilization ponds often times have problems with BOD removal efficiency in the fall and winter due to their size and surface area.

For every 10 degree F◦ temperature change, there is one logs growth difference in biological activity.  As temperatures drop, it is harder for the bacteria in the lagoons to keep up with the BOD. Again, that time and numbers game comes into play. Since you cannot change the time, and you do not have a RAS to play with, the only thing many plants with lagoon systems can do is supplement with bacteria products. Bioaugmentation is actually a cheap solution to BOD and TSS problems if applied correctly. See Papermill Case History

Equalization pond, but isn't that just supposed to equalize the flow and influent components?

These EQ ponds are not sterile. There is plenty of food present for the bacteria.  There are many bacteria present. Just make sure the "Critical 5" are present: pH, N, P, temperature and D.O. are in the correct range, and you can easily get quite a bit of degradation in your EQ tanks or ponds depending upon your holding time. Many times these are considered a wide spot in the pipe, when in reality they can also be a good place to jump start your biological activity. Most of the bacteria present have a 20 minute to 2 hour life span, so there usually is quite a bit of holding time as far as bacteria are concerned.

Many plants overlook the importance of the EQ, allow solids to build up in there, do not pay attention to D.O. and let them turn septic.  They basically shoot themselves in the foot by creating a septic influent that make it harder for the bacteria to work on in the aeration basin. Do not overlook this critical piece of equipment in a system.

The larger the wastewater pond, the more time you are giving the bacteria to work on the incoming food. But, the problem is, that the more surface area you have, and the further away you are from the incoming influent, the more the temperature can drop in the winter months. Cold weather can easily impact your "Critical 5".

Although oxygen transfer efficiency increases in cooler temperatures, biological activity slows down. This slowdown in activity can be a serious problem for some plants. Surface aerators also throw the water up many times 1-2 feet into the air, again allowing the water to significantly cool down. While this is a good thing in the summer months, when it can get very hot, it can be a detriment in the winter when the biological activity has already slowed down.