Effects of Bleach on a Septic System

Because the key to a functioning septic system is the bacteria that lives in your septic tank, an overload of harsh chemicals, such as bleach, could potentially kill off the bacteria in your tank and cause problems in your overall system. The bacteria in the tank provides an anaerobic (meaning that oxygen is not required) breakdown of solids in the tank.     

According to a recent research study (Gross), bacteria in a septic tank can be killed if there is an overabundance of toxic substances. Research showed that 1.85 gallons of liquid bleach, 5 gallons of a liquid cleaner or 11.3g of a drain cleaner in a standard 1,000-gallon septic tank can cause a bacteria “die-off.” The study noted other substances that were harmful to the tank bacteria including anti-bacterial soaps and cleaners.

A short-term use of household cleaners should not cause a permanent die-off of septic tank bacteria, but long-term use resulting in a bacteria die-off could result in greases, oils and solids being pushed out of the tank into the drain field. If these elements get into the drain field, it can result in blockages and ultimately a failed drain field system. Symptoms of a failed drain field include slow drainage and flushing of drains and toilets in the house, as well as standing water on the grass or soil over the drain field. A completely blocked drain field will cause a backup into the house.

Discontinuing the use of harsh cleaners and chemicals is the first step. Over time, bacteria will naturally begin to reproduce in the tank, and a live colony should become established. Although many over-the-counter additives are sold, these substances can actually lead to septic tank problems as the solids and “scum layer” in the tank are often broken down and then flushed into the drainage system, causing blockages.