Sewage treatment plants offer another alternative for septage treatment. Because septage is approximately 50 times as concentrated as domestic sewage, it must be blended with sewage before entering the plant to avoid upsetting the treatment process. The plant must have a method for feeding septage into the system at a controlled rate and have adequate capacity to handle the septage.
Septage may be added to either the liquid stream or solids stream of a wastewater treatment plant. When added to the liquid stream the septage is considered a high-strength wastewater. It should be diluted with the incoming sewage as it enters the treatment plant. The septage may also be combined with sewage sludge as a part of the solids stream. The septage should first be screened and slowly incorporated with the sludge for stabilization and dewatering.
The benefits and concerns of adding septage to a treatment plant must be considered. The treatment plant, septage hauler, and community can all benefit from handling septage. These benefits include:
The concerns of accepting septage into a treatment plant must also be considered and addressed. The daily volume of septage may need to be managed to avoid plant overload. Restricting the hours of septage receiving, or limiting the number of loads per day may be necessary to control the plant loading rate. The source of the material is always a concern. The plant may not be prepared to handle industrial wastes, grease-trap wastes, or other unusual materials. The treatment plant should have a contract with all approved haulers. In that contract, the type of waste accepted at the plant can be restricted. For added protection, the treatment plant may collect a small sample from each load and store it for one to two weeks. In this way, if the treatment system is upset, the samples can be analyzed to reveal the hauler who contributed the "bad" load.
Two approaches for adding septage to a treatment plant have proven successful. One approach is to provide a bar screen and receiving tank at the plant. The septage haulers screen the septage as it is discharged to the receiving tank. The tank then discharges the septage at a slow, constant rate into the treatment plant. Another approach is for the treatment plant to designate and approve septage discharge to a distant access port (sometimes referred to as a manhole). As the septage moves through the sewer system to the plant, it is blended with the incoming sewage.
Spills, odors, and debris are always a concern in a septage receiving area. Provide a water supply with a hose and a covered dumpster for debris to allow each pumper to clean the unloading area after each visit. A contract can be written in such a way, that if a hauler is negligent, they lose access to the plant.