Suctoria 

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Suctoria

When trying to determine species, stick to the basics, and focus on the causes and controls of the higher life forms present. The main point of any wastewater biomass identification is not to get a PhD, but to fix your plant!

Identification

Suctoria are a type of Stalked ciliate. Suctoria are a type of protozoa that can be branched or unbranched. Suctoria are "inverted bell-shaped bodies mounted on a stalk which is attached to a substratum." A key differentiating feature from Suctoria vs. Stalked ciliates is instead of the presence of cilia (minute hair-like projections) on the oral region of the organism the cilia have turned into tube like projectiles. Suctoria can be solitary or colonial. They can be branched also.  OK, these are the guys to shoot for in most activated sludge plants.  They almost always indicate an extremely healthy system and usually the BOD in the final effluent is very low, the TSS is low and things are running smoothly. If you have these in your plant, you are probably running very good and should congratulate yourselves! Although they look very pretty, watch out, well only if you are a microscopic higher life form. They are deadly! They stab unsuspecting higher life forms that swim by and suck their guts out. They have a rigid set of tentacles extending from the cell body which are hollow. They use these to spear their prey such as free swimming ciliates and flagellates. Usually sessile.

Additional Information:

They are members of the class Ciliophora. Many different genera and species exist. Some genera commonly seen in wastewater are Podophrya  and Tokophrya . Sheathed suctoria secrete a lorica, an outer membrane that protects the ciliate. Suctoria consume food via  oral tubules that wind completely around the top of the cell. Suctoria attach themselves to the base of something, usually floc structures. 

Suctoria: Similar to stalked ciliates only instead of hairs they have tubules or hollow tentacles.

Environment

They are one of the higher life forms found in waste water treatment processes. Suctoria are usually an indication of a very stable activated sludge operation. The species of suctoria found can be used to indicate approximate MCRT. The colonial forms of suctoria usually occur at higher MCRTs. Usually Suctoria mean you have an extremely low BOD in the final effluent. This does not correlate though unfortunately to filamentous bacteria vs. floc formers, since both can remove BOD.

Suctoria are found in large numbers when the bacterial population and dissolved oxygen concentration of the treatment process are high, the wastewater environment is stable and a mature floc structure has developed. Suctoria usually indicate a stable wastewater environment and a healthy biomass. Heavy attached growth on the stalks usually indicate the stalks have been around quite a while in the system and things have been pretty stable. 

Stalked ciliates are also capable of swimming freely. This may occur during low dissolved oxygen levels within the treatment process.

If the biomass is really old and rotifers and nematodes are usually present, and all of a sudden large numbers of stalked ciliates show up, check to see if a sudden spike of BOD has occurred.  Adjustments to RAS and wasting may need to be made in order to handle the sudden increase in BOD. Addition of biological products can also help overcome sudden spikes in BOD to help recover quicker and reduce changes or BOD or TSS permit violations.

How to find them:

Microscopic examination of a wet mount. Some of the larger suctoria can be seen at 40-100x and 200x. Blow them up to 400x and 1000x though to see more details.

What does it mean when I see an increase in Stalked Ciliates in my system?

It depends upon what the rest of the biomass looks like. Typically the presence of Stalked ciliates indicates a medium to low loading of food vs. the amount of biomass available to eat the organics. Stalked ciliates indicate a relatively healthy system, no toxicity, progressing along in a sludge age towards a medium to stable age. If mixed in with the right amount of stalked ciliates, a few free swimming ciliates and a rotifer or two, you are probably doing very well. If Suctoria are present, you probably have crystal clear water!

Stalked ciliates usually anchor themselves to a stable floc formation and create a vortex by swirling the water around to filter in single celled bacteria. Usually, this means that the sludge is a bit older than if only amoebae and flagellates are present and TSS is clearer and more floc structures are developing.
Stalk  ciliates reproduce by budding!  Technically they can reproduce asexually by binary fission or sexually by conjugation.
 
It may mean the sludge is young if the floc is clear, dispersed and weak, or if you have had rotifers in the past and were old, it may mean a recent higher loading of BOD that is forcing the sludge age to a younger age.  Usually you can expect a few solids in the effluent and slightly lower BOD levels than if free swimming ciliates are present in significant numbers. If you have once through lagoons, you may only get flagellates and free swimming ciliates. Lagoons differ from activated sludge and the types of higher life forms may vary depending upon the holding time of the lagoon and if a very large lagoon, different sections will have different stages of higher life forms. Stalked ciliates in lagoons are usually smaller and sometimes are more motile. 
 
Daily microscopic analyses is helpful in documenting where you are today, where you have changed since the previous day and how to react to changes proactively as opposed to when they have become critical!

What should I do if there is a significant change in my higher life forms and all of a sudden there is an increase in stalked ciliates?
First check to see why they have increased? Is there a change in loading that might impact other areas? Check your nutrients in this case if applicable to your plant. The biggest mistake people make when a high loading comes through or a spill, especially at industrial plants is not to increase nutrient levels when high loading occurs.

You might want to adjust your wasting or RAS levels. Some plants add bioaugmentation products in cases of higher loadings. You might need to slightly increase the dosage of product. If using micronutrients, adjust these levels also if the loading is significant.
 
You might need to check the Bed levels in your clarifier. Check your TSS off your clarifiers.  You will have nowhere near the level of single celled bacteria that you see with amoebae or flagellates, but there still might be some. Usually stalked ciliates are getting to the Goldilocks sludge age with nice floc, medium age and everything is just right!  Check the floc and correlate all the parameters, but you are probably doing ok!   If all you have are stalked ciliates, then you are progressing to an even higher sludge age. Stalked ciliates and suctoria indicate a medium age healthy sludge! Good work!

If you have extremely heavy attached growth on the stalks, that means they have been in the system a very long time. They are very stable and content. You probably have had very few BOD swings and a pretty stable sludge age.

More to come soon! 

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