As temperatures drop microbial growth rates slow and system conditions favor organisms such as the foam producing filament, Microthrix parvicella. With slower growth rates, vital slower growing organisms such as Ammonia Oxidizing Bacteria (AOB) and Nitrite Oxidizing Bacteria (NOB) also become more susceptible to washout - hence the common strategy of increasing MCRT during colder months. The challenge is maintaining the MCRT balance needed to protect AOB/NOB (Nitrifiers) while also keeping long MCRT filaments such as M. parvicella and Nocardiaforms below critical levels.

Why you should monitor M. parvicella populations

• Sludge Bulking: It leads to poor settling characteristics, resulting in high sludge volume index (SVI) values.
• Foaming: Creates stable foams that can overflow tanks, causing operational difficulties.
• Process Disruption: Affects the overall performance of the activated sludge process, leading to compliance issues.

Current control strategies

• FOG Control: Keeping FOG down disfavors the foam producing filaments, especially important in winter.
• Adjust MCRT: Shorter MCRT results keeps slower growing filaments from over taking desirable floc forming organisms.
  
• Disinfection: Use of hypochlorite or other oxidant chemistry can be used to damage filaments. Not an easy fix but can be used in times of critical performance issues.
  
• Bioaugmentation: Adding low temperature organisms with the ability to degrade FOG under winter conditions can help in systems with elevated influent FOG or extensive histories with cold weather foaming.
  

Embracing a more holistic approach for winter operations
Maintaining nitrifier populations while keeping winter's problematic filaments under control requires maintaining a delicate ecological balance. There is no single fix or program that replaces understanding and monitoring the complex ecosystem inside the MLSS. Using molecular tools gives vital details on even slight changes in populations and guides operators in adjusting wasting rates and other control options. It is best to monitor and catch problems before they result in increased chemical use or compromise treatment efficiency.

If you have any questions about molecular testing or foaming control options, you can contact us at [email protected] or visit our website at www.asterbio.com.

Much larger than bacteria, protozoa (single cell eukaryotes) and metazoan (multiple cell organisms) are easily seen with light microscopy at 10x and 40x objectives. Both are usually very active and easily spotted as they feed and move about the sludge. Meanwhile, individual bacteria cells look like tiny specs that bounce with water flow on the slide.

Floc, often referred to as "bugs" is composed of:

• Living and dead bacteria
• Extracellular biopolymers (EPS) functioning as glue creating a biofilm that serves to trap stored insoluble organics being acted on by extracellular enzymes and protecting cells from surrounding environment.
• Inorganics - EPS also contains grit and other inorganics trapped in the matrix

Both protozoa and metazoan prey on either free bacteria or graze on the floc. This grazing and filter feeding helps improve wastewater operation.

• Filter feeders remove free bacteria cells from solution and encourage floc formation by consuming cells not in the biofilm (floc). You can watch stalk ciliates actively filtering free floating cells while attached to floc. In the case of "young sludge" - high F/M - you will see flagellates and amoeba moving along consuming free cells.
• Grazing feeders move along developing floc and consume outer layers of the biofilm. Grazing feeders include free crawling ciliates, rotifers, water bears, and other metazoan. By grazing on the outer layers, these organisms reduce excess EPS and help keep the biomass active and aerobic. All are good for improving floc density and settling.
  
  

Can protozoa and metazoan "eat" key organisms in the system?
While it is possible, a healthy ecosystem contains both primary producers and predators. This relationship between predator and prey ensures no overgrowth of any single organism and a more diverse biomass. So, just note the indicator organisms present and relate activity to where the system is on the growth curve. Don't worry about protozoa or metazoan eating all the biomass.

Poster with indicator organisms and how they relate to the growth curve is available for download here
https://asterbio.com/bug-poster/