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Indicator organisms seen in microscopic exams & how to make sense of what you observe

10/20/2019

 
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Microscopic exam should be done often by wastewater system operators. While a high end, phase contrast scope is great, a simple high school biology level microscope will allow you to see indicator organisms, floc size & density. Now that you are performing a microscopic exam, do you have to ID each protozoa, metazoa, and filament? The answer is NO! Operators have enough to do without performing a microscopic exam that involves ID of every organisms and in the case of filaments, often using staining. I like to use a simple daily exam sheet to record the following groups and their relative frequency.

Amoeba
Amoeba are slow moving single celled protozoa. With streaming cytoplasm, amoebae envelop free bacteria, organic particles, and other "food" sources. In wastewater, we often have "free" amoeba which are jusAt the streaming cytoplasm inside a cell envelope. There is also the testate form which has a shell. The free amoeba are most common during early phases of growth, but you can see testate amoeba even with low F/M, mature systems.

Flagellates
A large and diverse group of protozoa, flagellates are grouped by how they move. Propelled by whip like flagella, these protozoa tend to "bounce" and move in what seems a somewhat random manner. With large flagellates or when using a phase contrast microscope, you can often see the flagella propelling the organism. Flagellates are seen early on the growth curve and tend to decrease in relative frequency as you move along the growth curve. 

Free Swimming & Crawling Ciliates
Ciliates move faster and in a more purposeful manner than flagellates. They also tend to be larger and easier to observe with 10x and 40x objectives (100x and 400x magnification). When ciliates are the dominate protozoa, you will have floc forming, Dissolved Oxygen increasing, and a more mature biomass. In the exam, look for:
  • Diversity - free swimming vs crawling
  • How activate the ciliates are (how fast they are moving)
Stalk Ciliates & Suctorians​
Stalk ciliates and suctorians are the ideal indicator protozoa for most wastewater systems. Present only in systems with good D.O., low soluble organics, and good floc forming conditions; stalk forms do not move and are easy to observe. These protozoa anchor to the floc and are only mobile in early phases and after shock events. Stalks are highly susceptible to shock events - pH swing and toxic compounds. So, note any change in their frequency. Note the following:
  • Single stalk forms - most common
  • Colonial stalks - if seen, you have great quality water
  • Suctorians - similar to a stalk, but look like a pin cushion and stab/suck cytoplasm from passing flagellates and ciliates. These are very fun to watch if you have a few minutes.
Metazoa and higher forms
Everybody loves the rotifers and tardigrades (water bears). They are easy to see and interesting to watch. If they become the dominant indicators, you are probably tilting toward an old sludge. Also they are more resistant to shocks than stalk forms, so you can have some problems and still see rotifers. 

Floc Size & Density
It is also important to note the floc. How big are the floc particles (you don't have to get a precise measurement, just use relative size from day to day). Also not floc density and can you see filaments extending from the floc. Inside the floc, filaments are not bulking and function as a structure to improve floc strength. Also not if there are free bacteria and pin flocs in the sample.  Again, you need to note changes from day to day. And if you see something strange, look for a cause and definitely note the observation.

Old sludge - what high MCRT and  very low F/M can do to effluent quality

10/14/2019

 
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Nocardia, a slower growing organism, can become a problem with long sludge ages.
Lately, my most common recommendation in consulting with wastewater has been to increase wasting rates. We all know that wasting takes time, involves disposal costs, and there is the temptation to use the aeration tank as an aerobic digester to lower solids going to disposal. So why do we waste? Or what happens if we move along the growth curve to the far right (endogenous respiration)?

Here is what I often see:
  • Nocardia and other slow growing organisms that exploit a niche can become more of a problem
  • Effluent turbidity and fines/pin-floc passing into effluent increase
  • Beneficial EPS decreases - organisms store excess organics in EPS but as you enter endogenous respiration the bacteria begin to utilize EPS for cell maintenance/growth
  • Oxygen requirements - while individual cell respiration rates drop with a mature biomass, the overall oxygen consumed is higher when you add up all the biological solids
  • Filaments become more of a bulking agent with decreased floc former EPS

While you may not have permit issues related to running in endogenous respiration mode, it costs money as supplying oxygen and mixing for additional biomass takes energy. 

How bulking MLSS can impact MBR systems

10/2/2019

 
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From: Membrane Bioreactor (MBR) Technology for Wastewater Treatment and Reclamation: Membrane Fouling by Oliver Terna Iorhemen *, Rania Ahmed Hamza and Joo Hwa Tay https://www.mdpi.com/2077-0375/6/2/33/htm
If you operate an activated sluge sytem with secondary clarifiers, you are very familar with problems related to filamentous and non-filamentous bulking. Gravity solids separation requires biological solids to settle and compact within the clarifier's hydraulic residence time. Bulking is related to influent makeup, biological unit environmental conditions, and many factors that can create a biomass that dose not settle and/or compact.

Enter the membrane solids separation systems - the MBR utilizes a membrane that retains solids in the biological unit and allows water to pass through the membrane for effluent discharge. As pressure required to push water through the membrane increases, the system uses backflushing to clean the membrane. If backflushing does not improve pressure requirements, the membrane must be chemically cleaned and eventually will require replacement.

What causes permeability decline?
  • Influent 
    • Hydrophobic compounds - i.e. Fats, Oils & Grease
    • Colloids
    • Particulates - both organic & inorganic
  • Biological 
    • Extracellular polymer substances (EPS)
    • Soluble mirobial products - some can impact membrane pores

This brings us back to how filamentous and non-filamentous bulking organisms can impact the membrane. A non-ideal MLSS increases biological fouling potential. EPS in particular can foul the membrane by:
  • Cake formation - common and cleaned during backflush
  • Pore blocking - solids/eps impede water flow through pores
  • Biofilm growth - EPS allows for biofilm attachment to membrane thereby blocking pores

If your biomass drifts to increased EPS (non-filamentous bulking, foaming filaments) and filaments that can stregthen biofilms on the membrane, then the membrane maintenance will include more cleaning cycles and earlier replacement than a system with better conditioned MLSS. Therefore, it is important to monitor EPS and filaments even with an MBR system.

A great short reivew of MBR fouling - ​https://www.mdpi.com/2077-0375/6/2/33/htm

    Author

    Erik Rumbaugh has been involved in biological waste treatment for over 20 years. He has worked with industrial and municipal wastewater  facilities to ensure optimal performance of their treatment systems. He is a founder of Aster Bio (www.asterbio.com) specializing in biological waste treatment.

    View my profile on LinkedIn

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