The Septic Problem
Septage is the material produced in a septic tank after treating many thousands of gallons of sewage from a house. It has a biological oxygen demand (BOD) of 3000-6000 mg/l and a total solids (TS) of 11,000-40,000 mg/l or 1.1-4 % solids. This compares to a BOD of 100-400 mg/l and a TS of 400-1200 mg/l for municipal sewer, the untreated material from homes that enters treatment plants.
Depending on your geographic location, septage is disposed of via land spread, private lagoons, private dewatering facilities or municipal treatment plants. When this material is deposited at municipal treatment plants the high BOD of septage depletes much of the oxygen in the treatment process, effectively killing the treatment process. This is root of most of the treatment plant difficulties although there are additional problems associated with sludge concentration and flow.
The land spreading of raw septage has been banned in most geographic areas due to the negative effects on the environment and the associated negative public perception.