Floating solids on a secondary clarifier are usually a byproduct of influent composition or biological processes that have drifted from ideal operations. While some floating solids are not a big problem, heavy solids conentrations can increase effluent TSS resulting in uninteded biological solids wasting. Here are the  most common casues of floating secondary clarifier solids:

• Excess EPS
  While EPS in normal concentrations is needed for floc formation, at times we have excess EPS that creates non-filamentous or Zoogleal type bulking. Non-filamentous bulking sludge is less dense and can trap bubbles of air & nitrogen that acts to float the sludge. 
• Fats, Oil, & Grease (FOG)
  FOG compounds are adsorbed by the floc acting as a sponge. The FOG being less dense than water can disrupt gravity separation and if you have too much FOG acts to float the sludge.
• Denitrification
  If you have a system with nitrification, soilds can use nitrite/nitrate in resiration while in the anoxic clarifier bed. Denitrification appears as small bubbles released when you disturb the floating solids. Water spray and increaseing recycle pump rate usually solves this problem.
• Nocardia & M. parvicella filament foams
  Both Nocardia and M. parvicella produce thick foam on the aeration basin. This foam can continue into the secondary clarifiers and create high effluent TSS. 

Once you know the cause of the floating solids, you can select among various control options. Key is to identify the source of the floating solids, use a quick control strategy to maintain effluent compliance, and then take longer term steps to reduce likelihood of more floating sludge events.

The microscope can give you great information on a wastewater system's biomass  health. While expensive phase-contrast, high magnification/resolution microscopes are great, a simple low-cost microscope can provide much of the same information. Let's review what can be done with a microscope similar to the one pictured above.

• Floc size & density - simply look at floc shape, size, and density. You are looking for changes and relating what you see under the microscope to effluent quality. To see changes, you need to look at the biomass often!
  
  
• Indicator organisms - bacteria are usually too small to see under a low cost microscope, and aside from general shapes and motility, you don't see much. So, we look at indicator organisms which are much larger and more active than bacteria. As with the floc, you are looking for changes in indicator protozoa and metazoa (if present). Don't worry too much about exact ID for the protozoa. Look for general location methods, size, and relate what is there to your own system's operations. I have attached a "bug poster" for easy use in classifying common wastewater protozoa. Insteand of photos, I use drawings which makes you focus on the locomotion and main characteristics rather than exactly matching photos. By looking at the MLSS frequently, you learn what should be in your system when it is in good shape.

The big step up in microscopes comes when you add phase contrast capabilities to your microscope. This requires phase contrast objectives and diaphragm condenser. Phase contrast allows you to see more detail - it is very valuable in performing filament ID, evaluation of EPS, and looking at individual bacterial cells. These tests also require a bit more experience for the microscope operation and take more time. While phase contrast will make daily exam slightly better - it is overkill for most coursory exams. 

So just dust off the old microscope and start using it daily. A quick 5 minute look under the microscope using 10x and 40x objectives will give you good information and help improve your monitoring program.

If you don't have a bug poster near your microscope, I have included one that we made for Aster Bio here. 
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Your aerobic treatment system has high D.O., good floc formation, and is discharging great quality water. All of sudden, you start to notice small flying insects above the water which are soon followed by small red worms in the MLSS. The flying insects are midge, a native insect that lays eggs on decaying organic matter. It just happens that wastewater MLSS with high D.O. is a perfect environment for laying eggs and incubating larvae. Soon after seeing the midge flies, the worms "blossom".

Problems happen when the larvae consum the MLSS - which can cause loss of slower growing organisms such as Ammonia Oxidizing Bacteria (AOB). They can also create effluent TSS if they wash over the clarifier weir.

To control midge larvae, the EPA approves the use of Bacillus thuringensis (Bt) spore solutions (kill larvae by damanging their digestive tract) or Strike which is an insect growth regulator (similar to that used in pet flea/tick control).

Here is a bit more that I wrote on the midge problem in a previous post:
​ https://www.biologicalwasteexpert.com/blog/whats-eating-my-biomass-red-worms-blood-worms-midge-fly-larvae

Another post on ammonia and nitrite removal by microbes! Often grouped as nitrifiers, AOB & NOB cultures must be present if you require significant biological ammonia and nitrite oxidation. Both groups are obligate aerobes and are slower growing than most other wastewater bacteria. This makes AOB & NOB the most common bottleneck in wastewater treatment. 

As discussed in my last post, the organisms responsible for ammonia and nitrite removal are a diverse group. Instead of just Nitrosomonas and Nitrobacter, we have a variety of organisms that thrive under slightly different conditions. As they are all key microbes and slow growing, Paul Campbell - Aster Bio's molecular diagnostics guru - has developed a qPCR battery to monitor nitrifiers. qPCR works by fast quantificagtion of specific segments of genetic material. It can be customized to fit the actual poplations in the system. However, you need to make sure the qPCR is a good fit for you biomass which means off-the-shelf type kits are not always the right test.

What we now call a qPCR  nitrifier pannel can quantify levels of the following:

• Nitrosomonas amoA
• Nitrospira 16s (total Nitrospira)
• Nitrospira nxrB (measure of NOB)
• Multiple Nitrospira COMAMMOX - most common groups in WW as found by testing
• Nitrobacter nxrB
• Nitrosospira 16s
• AOA amoA - ammonia oxidizing archaea

We are working on development of qPCR for key ANAMMOX cultures. If anyone operates a system with ANAMMOX, we would like to obtain samples to calibrate the tests. Just contact me by email.

When talking about ammonia and nitrite treatment in wastewater, we often mention Nitrosomonas (ammonia oxidizing bacteria) and Nitrobacter (nitrite oxidizing bacteria). With the arrival of more advanced testing such as Microbial Community Analysis (MCA or a 16s DNA census) and customized qPCR for specific 16s segments or metabolic pathways, we have the ability evaluate the real organisms removing ammonia and nitrite in working wastewater treatment systems.

After testing industrial, municipal, and even Aster Bio's own "nitrifier" culture reactor, we have noticed that removing ammonia and nitrite from wastewater is a complex process that can involve many different microbes working as part of the microbial community. The most common "types" of nitrifiers are summarized below:

• Ammonia Oxidizing Bacteria (AOB) - the type organism here is Nitrosomonas. This group convert ammonia into nitrite. This has often been called the rate limiting step in nitrification. In pratice, the AOB cultures were lower than expected in testing of working systems. Meanwhile, a commercial nitrifier producition tank had 80 - 90% Nitrosomonas as given by 16s sequencing.
  
  
• Nitrite Oxidizing Bacteria (NOB) - the most common referenced organism is Nitrobacter. However outside the nitrifier reactor, the primary NOB is Nitrospira. Why the difference between a reactor and wastewater treatment units? It appears to be related to the mixed cultures and how nitrite concentrations are concurrently produced and oxidized which leads to lower nitrite concentrations than is seen in a lab reactor.
  
  
• Complete Ammonia Oxidation (COMAMMOX) - during MCA tests, Aster Bio has found Nitrospira reads at much higher levels than Nitrosomonas (often 5 - 10x higher concentrations). This fact led us to evaluate Nitrospira's metabolism. In addition to nitrite oxidation, a subset of Nitrospira can also oxidize ammonia into nitrite. These Nitrospira are the COMAMMOX bacteria, and appear to be very common in wastewater treatment.
  
  
• Ammonia Oxidizing Archaea (AOA) - archaea are a different kingdom than bacteria and are most often seen as methanogens in anaerobic digesters. In systems with lower pH resulting in more ammonium (NH4+), AOA which utilize NH4+ rather than NH3 become more important for ammonia oxidation. We are still exploring the role of AOA in wastewater and how vital they are for ammonia oxidation.
  
  
• Anaerobic Ammonia Oxidation (ANAMMOX) - relies on a novel biochemical pathway where organisms shunt nitrite and ammonia directly to nitrogen gas. This avoids the energy use oxidizing nitrite to nitrate while also accomplishing denitrification. ANAMMOX cultures have a slow rate of growth and much research is being done on how to optimize wastewater treatment systems to take advantage of this metabolic pathway. So far, it appears many of the ANAMMOX cultures are in the Planctomycete phylum.
  
  
• Heterotrophic nitrification - bacteria including some Pseudomonas, Paracoccus, and Alcaligines have the ability to obtain energy from ammonia oxidiation. However, the rate of ammonia oxidation is lower than that seen in obligate chemotrophic organisms.

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