To add or not to add? This is one of the big questions for anyone, like us, who lives in a home with a septic tank.
For many of the eighteen years we've lived in rural Oregon, we've dutifully added enzymes to aid the tank's digestion of our waste. Whenever we've had our tank pumped or a line unclogged, the workmen have pushed an enzymatic additive, saying it'll help keep our septic system healthy.
But is this true? After some Google research today, my conclusion is…No.
Save your money and let nature do its thing. Mag Ruffman, the Tool Girl, says:
There are 1200 products on the market for use in septic tanks; some contain biological agents like bacteria, some contain enzymes, and others use chemicals as their active ingredients. Extravagant claims have been made for many of them. The truth is, there are more helpful bacteria in a single poo than you'll find in most biological septic preparations. Enzymes have not been proven effective in controlled tests.
What I found was that those selling septic enzymes are enthusiastic about them. But people without a financial ax to grind mostly said they aren't necessary, and can even be harmful (see here, here, here, and here).
In 1993, the Washington State Legislature found that " most additives do not have a positive effect on the operation of on-site systems, and can contaminate groundwater aquifers, render septic drainfields dysfunctional, and result in costly repairs to homeowners. It is therefore the intent of the legislature to ban the use, sale, and distribution of additives within the state unless an additive has been specifically approved by the Department of Health."
In 1994, the legislature added, "Chemical additives do, and other types may, contribute to septic system failure and groundwater contamination. In order to determine which ingredients of non-chemically based additive products have adverse effects on public health or the environment, it is necessary to submit such products to a review procedure."
Approved products merely are certified to not be harmful. There's no evidence they're effective. Apparently septic tank additives might be useful only in some special circumstances:
The beneficial effects of biological additives on the septic system are still being debated, but two benefits may ultimately be identified. Based on available literature, enzymatic products might have the ability to reduce the amount of oil and grease in the septic tank. Second, under septic tank bacterial "die-off" conditions, slight reductions in the amount of effluent solids have been achieved by using additives.
On the downside, this article says that additives can clog your drain field by pushing solids up to the surface of the tank and then out into the soil.
Bottom line: almost always, septic systems don't need additional enzymes or other additives. We're going to stop using them.