On-Site (septic) Wastewater Treatment Systems
Many houses have on-site wastewater treatment plants, commonly referred to as septic systems. Most septic systems are buried underground and operate much like full-scale wastewater treatment plants. Anaerobic bacteria in the septic tank degrade wastes and produce a liquid effluent and sludge. The sludge stays in the tank until the home owner has it pumped out (this should be done routinely).
One of the biggest differences is that the effluent or liquid portion of the waste is allowed to seep into the ground. Underground pipes with small holes in them distribute the effluent and the liquid slowly seeps into the ground. The soil around these holes is rich in bacteria and other organisms that help to degrade the compounds in the effluent.
While it is difficult to study these systems at people's homes, P&G scientists have developed a laboratory scale model of a septic system and conduct studies to make sure P&G products are safe for septic systems.