Maintaining Wastewater Treatment Plant Operating Efficiency During Shutdowns and Startups

Wastewater Treatment PlantUnder the current economic climate, many mills are experiencing more frequent and/or longer production outages. But the wastewater treatment system is a living “organism,” requiring a constant food source to remain viable. During extended down times, the mill sends little or no “food” to the microbiological population (bugs) resulting in a gradual depletion of the population. When the plant starts back up, there is sudden and often higher than normal loading, sent down to the wastewater treatment system with a diminished population. The result may be that the secondary system just cannot reduce the Biochemical Oxygen Demand (BOD) loading to acceptable levels prior to effluent discharge. This in turn impacts monthly numerical averages utilized for permit uses.

The amount of biomass loss will depend on how long the system is deprived of food. For outages of less than one week, our experience has shown that the system capabilities will not suffer and the system should be able to return to normal operation assuming proper steps are taken as production resumes. For outages of one to three or four weeks, additional steps may be necessary, such as supplemental bacteria addition and/or occasional food addition from stored wastewater. For extended outages, the scenario approaches a system start up, where significant food addition and bacterial seeding may be required. In these instances, it is critical that the population be re-established prior to production resuming in order to avoid a major overloading of the system.

To start, remember the eight microbiological growth pressures: BOD (amount and type of food); temperature; toxic or inhibitory compounds; retention time; pH; DO (aeration); nutrients (N & P); and health of the bacteria. Listed below are a few comments regarding maintaining and adjusting these growth pressures during shutdown and start up periods.

  • BOD or Food. Usually systems operate with an abundance of food, but during prolonged outages with low loading the bacteria may not have enough food to sustain the population. For extended outages, using wastewater stored in diversion tanks or basins may be necessary to sustain the population. In extreme cases, molasses or other available and relatively inexpensive food sources may be required.
  • Dissolved oxygen or Aeration. Aerators may go down during an outage, but it is important to have them fully operational before adding stresses to the system. An outage is an ideal time to check to ensure they are spaced correctly and operating properly.
  • Health of the Bacteria. With low loading conditions, loading swings, or toxic compounds, the health of the bacterial mass may suffer. Supplemental bacteria addition is a low cost strategy to help maintain a viable population during outages and upon startup. The EBS Bacteria Acceleration Chamber (BAC Unit) provides “grow up” of bacteria on site to maximize cost effectiveness. For more information see the article at
  • Nutrients (N & P). Nitrogen and Phosphorus are the critical building blocks to bacterial growth. While always important, during startup or upset conditions they can be the difference between success and failure.
  • Temperature. While it is often beyond our control, don’t forget that water temperatures will be much lower when the mill is down. This may make the system slower to respond when production resumes.

Environmental Business Specialists has been involved in numerous situations as mills slow down production rates, take machines up and down, or shut the plant down completely for a short period of time due to the economy. Our team has become quite adept at helping maintain system compliance during these situations because even if the plant or a machine shuts down for a short period of time, the Waste Water Treatment Plant keeps on running. If you are having problems, please call us for support.

Learn about the microorganisms in your wastewater treatment system.