After a cool, wet spring, the seasons are changing as the temperatures begin to climb. The time is here to think about what changes need to be made to the wastewater treatment plant during the warmer months of summer to keep the plant in compliance.
As the air temperature rises, so does the water temperature. This causes the bacteria in the plant to become more active because they, like all living things, have an optimum temperature in which they live and grow best.
As the temperature of the wastewater in the plant rises, the bacteria become more active and feed quicker. They still need the oxygen to do this, so as you reduce the concentration of the mixed liquor suspended solids (MLSS), you must also record the dissolved oxygen levels at different points and depths in the aeration section of the plant and adjust as necessary.
When making any process control change, you should collect and interpret all the data available to you to make the proper decisions concerning the operation of the plant.
In the change from cool operations to warm, you will have to waste more sludge than you have over the cooler months to get to the proper concentration for warm weather operations. This wasting of sludge should be planned so as not to lower the concentration of the MLSS by more than 20 percent a day. A plan also allows you to determine at what concentration you have decided to operate the plant during warmer months.
The planning is accomplished through the use of experience and data retention, looking it up in the monthly operating report records and trend charts of the plant for flow, water temperature, influent and effluent parameters, food-to-microorganism ratio (F/M) , sludge age and sludge volume index (SVI), as well as return activated sludge (RAS) and waste activated sludge (WAS) rates.
It is important to anticipate the changes in temperature brought on by the change in seasons and to make the appropriate changes to the treatment process to remain in compliance. Trend charts built with years of data are very helpful in determining when to anticipate these seasonal changes.