Septage consists of the mat of grease and scum on the surface of septic tanks, the accumulated sludge at the bottom of those tanks and the sewage removed at the time of pumping. Organic solids and nutrient concentration are a function of the relative proportion of sludge and supernatant. The fraction of each component is determined by the interval between pumping and the quantity and characteristics of the waste discharged. Septage solids and organic concentrations can vary over three orders of magnitude. Assuming a septage generation rate of approximately 100 gallons per person per year and approximately one million people served by septic tanks in Virginia, the volume of septage which must be disposed of within the Commonwealth could be estimated at nearly 100 million gallons per year. However, as limited requirements exist for removing septage at specified intervals, the volume of septage handled annually is somewhat difficult to predict.
Improper disposal of unstabilized septage poses potential hazards to water quality and public health due to the presence of pathogenic organisms and possibly toxic substances in this material. The organic characteristics of septage may be 20 to 50 times as concentrated as those of domestic sewage.
Although heavy metal levels in septage are normally lower than corresponding values for domestic sewage sludges, a wide variation in concentration levels is often observed. A variety of potentially pathogenic organisms may be present in septage. Septage should be stabilized by a method of pretreatment prior to further management to prevent development of odor problems and possible public health problems as a result of public exposure. Septage stabilization would generally involve additional treatment by acceptable methods such as:
1.) Direct discharge to sewage treatment facilities.
2.) Direct discharge to sludge digestion facilities.
3.) Lime stabilization (ph 11 or higher).
4.) Chlorine oxidation (ph 3 or lower).
5.) Long term storage of 90 days or more in open lagoons.
Subsequent dewatering of treated septage may be used to reduce the volume of material which must be handled. Air drying could result in additional stabilization. Design standards for long term storage lagoons have been incorporated in the 1989 Sewage Handling and Disposal Regulations administered through the VDH Office of Environmental Health Services. Separately treated septage would have to be tested for microbiological indicators in order to verify compliance with the Class B pathogen control requirements imposed by State and Federal Regulations. The Federal Standards specify application limitations based on the crop or vegetation nitrogen requirements (Agronomic Rate). The State Regulations limit the applied depth for each application.