Spirochaetes (a.k.a. Spirochetes, both are correct) and Spirillum – Twisted sisters
The term Spirochaete came into use in the late 19th century: from spiro- ‘in a spiral’ + Greek khaitē ‘long hair’. That reflects these squiggling little guys pretty accurately. Sometimes they can be confused with another wavy looking organism, the Spirillum.
These two groups of organisms reflect the saying same, same, but different… really well!!
The spirochaetes tend to be a little bit skinnier, often they are longer than their Spirillum counterparts and it is fairly common to see one end of the “strand” cross-over “itself”. They are very like a writhing snake in the way they move. They can be almost impossible to see at 100x magnification, you will just see a sort of “shimmer”, particularly along the edges of flocs. They often are visible at 400X & 1000x, like in the two photos above. You may have to watch a “field of view” for a while without moving around the slide, and then all of a sudden you can see them!
Spirillum are more of a rigid spiral (rather than wriggly curves) and they may seem to shimmer, teeter or “vibrate” as they move around the flocs. You are more likely to see Spirillum appear to be trying to “drill in” to the edge of a floc cluster, than you would to see a spirochete show similar behaviour.
As a diagnostic tool for the operator, either of these organisms is useful as a signal of low dissolved oxygen or septic conditions.
A sudden appearance or increase in of spirochetes or Spirillum in your mixed liquor may be an indication of:
- Loss of aeration efficiency
- High organic load leading to low DO conditions
- RAS pump failure leaving solids in clarifier for extended periods
- Sewer pump failure or restriction, and/ or high temperatures, leading to sewage going septic in the collection system
- Low flow leaving biomass in anoxic or anaerobic zones of the process for longer than normal
- A dump of septage into the plant, (from a licensed wastage contractor or grey nomads)
Spirillum are defined as micro-aerophiles, which means they are favoured by low dissolved oxygen but must have some dissolved oxygen present to survive (typically 1 – 9 % DO preferred). They cannot survive without a little free oxygen (and cannot denitrify nitrate).
Spirochetes may be strictly anaerobic (conditions with no oxygen of any kind available) or facultatively anaerobic. They really like septic conditions.
Our experience has been as the population transitions from Spirillum to spirochetes, the DO is getting lower, the spirochetes are liking completely anaerobic conditions which the spirillum cannot handle. This makes it quite good if you are trying to get on top of an aeration issue, because if you can see the spirochete population being replaced by Spirillum, you know things are going back up in the right direction.