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Filamentous Identification

"the Easy Way"

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Ok, Everyone says I must look under the microscope at my Biomass and floc structures. What exactly am I looking for?

Here is a little basic information. A wastewater treatment plant is basically a bug factory. You are growing bacteria to clean the water. 90% of all the work that goes on in the secondary portion- i.e. the biological stage is the growth of a biomass to degrade organics and remove pollution. The bacteria are really what you want to look at. The higher life forms are nice, they indicate the age and health of the biomass, but the bacteria are the actual workhorses of the system.

Bacteria can be single celled, floc forming or filamentous. All three types will degrade organics. Which type is the best for my system?

Single celled bacteria also provide a food source for higher life forms. Single celled bacteria can cause TSS problems though and will not settle out very well. They can increase polymer consumption.

Filamentous Bacteria are bacteria that grow in long thread-like strands or colonies. Some of the positive attributes of filaments are that they are very good BOD removers. They add a backbone or rigid support network to the floc structure. They help the floc structure to filter out fine particulate matter that will improve clarifier efficiency. They help the floc to settle if in small amounts. They can reduce the amount of "pin" floc.

Some of the negative aspects are that they can interfere with separation and compaction of activated sludge and cause bulking when predominant. They can affect the sludge volume index (SVI) and they can cause poor settling if dominant.

Floc forming bacteria are usually desired. Floc is a collection of smaller particles agglomerating into larger particles containing particulate matter, debris, bacteria and Bio-polymers. Some of the positive aspects of floc forming bacteria is that they settle out easily as solids, reduce the need for polymers in clarifiers and reduce consumption in dewatering applications. If the right type of biomass is developed, a reduction in solids handling can also be found. Some of the negative aspects are they can be hard to dewater if they have a high polysaccharide coating. They also can form very small pin floc if older or straggler floc if young which can contribute to TSS problems.

How can I monitor my bacteria? One way is to use the microscope. Some of the things typically checked for visually and monitored by qualitative and quantitative observations: Floc size, floc color, and clarity of water among floc, floc structure, and filamentous presence.

Recommended microscopic analysis consists of visual inspection and photomicrographs using a compound microscope at various magnifications and illuminations. Typical magnifications are 40x, 100x and 200x. The illuminations are Bright Field, Dark Field, and Phase Contrast. See training sheet on microscopic analyses, details, how to take good photomicrographs.

Because every wastewater plant has a different bacterial population composing its biomass, a different type of influent, different pieces of equipment and different climates, the MLSS may have different floc structures. What may be considered good floc structures in one system may be poor floc structures in another wastewater treatment plant.

Nonetheless, some characteristics can be examined to determine relative floc condition. Generally, the more firm and compact a floc is, the better it will settle. The more lacy and dispersed a floc is, the less likely it will be to settle. The presence or absence of pin or straggler floc, which can be responsible for high-suspended solids (TSS) in wastewater, is also an important observation when examining floc structure. The presence of many filamentous bacteria is also examined to determine if filamentous bulking is responsible for poor settling.

First off, check to see if there are filaments present. Are they internal or external? What is the quantity? Ask for additional training sheet on filaments, what they mean and how to control them.

Is the Floc firm or compact? What does that mean? Is the floc going to stay together or will it shear easily due to flow, pumping or turbulence? Firm, well rounded, compact floc with clear water between particles? Are there lots of single celled bacteria or little floc structures that can cause TSS problems?

This floc to the left is relatively firm, compact rounded, golden brown floc, although there are a bit of filaments present

This floc to the right is small, weak, diffuse and will cause lots of TSS problems

Is it lacy, open, diffuse or irregular? What do these terms look like and what do they indicate? Obviously lacy and open will resemble a doily similar to what your grandma used to have. The more open the floc is, the harder it will be to settle or dewater.

These samples are weak, open and lacy due to filaments

Floc Color is important also.

 It indicates the age of the biomass. Clear indicates a very young biomass. Golden brown indicated a healthy floc. Black indicates the floc is turning anaerobic and running out of air or is older. Sometimes floc can be colored if the influent contains dyes. Usually this does not impact anything unless there are heavy metals or toxic compounds that will not pass a leach test when disposing of the solids.