December 5, 2013 by Heather Wiatrowski
Did you know that 22% of households in the USA use septic systems, also known as Onsite Wastewater Treatment Systems (OWTS), to handle their wastewater? And did you know we know almost nothing about the microbial ecology of these critical systems?
Shocking and shameful, really.
Why is understanding OWTS microbial ecology so important? First, OWTS represent a significant source of greenhouse gas emissions in the US. Secondly, microbial processes in OWTS protect our groundwater from contamination. When OWTSs fail, drinking water can be compromised, and the contaminants can end up in lakes and estuaries, which can hurt the fish.
Watch Mike Rowe from Dirty Jobs work with a Septic Tank Technician! http://dsc.discovery.com/tv-shows/dirty-jobs/videos/septic-tank-technician.htm
Most people think of the septic tank as the main part of the OWTS, but the part I’m most interested is the leach field. See those dark green stripes in the grass, on the picture on the right? Those are above perforated pipes buried in the soil, and liquids flow out of the tank through those pipes.
That’s where the microbes are working their magic. One of the most important processes that occurs in the leach field is nitrification. That’s the conversion of ammonia, which is highly toxic, into nitrate, which is much less toxic. There’s several types of microbes that can perform nitrification, and they are all incredibly fascinating, but we don’t know which ones are active in leach fields! There is some evidence that, in some of these systems, a process called anammox is occurring. That’s conversion of ammonia not to the less toxic nitrate, but directly to nitrogen gas. In wastewater treatment plants, anammox releases fewer greenhouse gases than nitrification, so it would be fantastic if we could manipulate septic systems to favor anammox as well.
That’s why I went to visit the Massachusetts Alternative Septic System Testing Center out on Cape Cod. Sure, the classic microbiologist Cape Cod field trip is Sippewissett Marsh, but MASSTC is way more interesting.
This is George Heufelder who runs MASSTC. MASSTC is one of a few facilities in the world that is equipped to test experimental septic systems. He works with the National Sanitation Foundation and private contractors that manufacture and market septic systems.
MASSTC receives sewage from the Massachusetts Military Reservation, and George Heufelder and Keith Mroczka can use the sewage to test up to 20 different systems at once.
They can also climb down these lysimeters to sample the water that is coming out of the leach field, which would presumably mimic the liquids that would end up in the groundwater.
I went out to MASSTC to get samples from the leach field, the tank, and the effluent, and I’m hoping to be able to get metagenomic data. With metagenomic data, I should be able to make some educated guesses on which microorganisms are responsible for nitrification.