by Bill Idarola
Many schools maintain their own wastewater treatment systems that exclusively serve their own populations. One unique aspect of these systems is the significant flow variations that they experience throughout the year. Along with the school population itself, the school’s wastewater discharge drops off significantly on weekends, holidays, and school vacations. These are minor though compared to the drastic changes that occur every year as the school year ends and summer vacation starts. The exact reverse happens when the new school year starts in the fall. Managing these fluctuations requires some proper planning and effective team communication.
Each year in June, the flow to a school’s wastewater treatment system can go from thousands of gallons per day to hundreds – a drop of over 90% in most cases. When the students return in the fall, this is reversed and the flow can increase tenfold within a day or two. For wastewater treatment systems that rely on a relatively constant level of biological activity to treat incoming wastes, these large fluctuations are not the easiest to accommodate.
The treatment process relies on maintaining certain parameters at a near steady state for best performance. Incoming wastes feed the bacterial/biomass in the plant and, in the absence of regular flow, the biomass begins to change. It’s the wastewater treatment plant operator’s job to anticipate this change and make adjustments to the plant to maintain good performance and good effluent quality.
In the summer, when the flow is low, the biomass begins to slowly digest itself and die off due to the loss of food supplied by the incoming wastewater. In the fall, when the students return, this same biomass, now reduced, will be expected to treat the same waste stream that was present prior to summer vacation. The treatment of the increase in waste load takes time, typically 2-3 weeks for the biomass to regrow and acclimate to the increase.
Other considerations to consider when it comes to seasonal variations in wastewater treatment processes are listed below.
- Maintenance activities – Summertime activities that can negatively affect the wastewater treatment system include floor stripping, tank cleaning/flushing, and discharge of spoiled waste. Some of these activities and the use of chemicals can cause treatment system failure when used in large volumes or during low flows.
- School activities – Summer school and other activities in the summer can sporadically make the flow change significantly from day to day.
- Temperature – Summer temperature increases can significantly change the nature of the biomass in the system, particularly in low flow periods.
- Communication – The wastewater treatment system operator needs to know the school’s schedule intimately. This allows him or her to plan accordingly and make the necessary adjustments to keep the system running effectively. The operator also needs to have a good rapport with school operations and management. Maintaining proper communication between all personnel will positively impact wastewater discharge and operation.
In summary, the significant seasonal flow variations in a school’s onsite wastewater treatment system at the start and end of each school year are far from insurmountable. From our viewpoint, good planning and effective communication between project partners have proven to be the keys to operations success.
Bill Idarola is the Connecticut regional manager for Weston & Sampson Services, Inc. in Rocky Hill.