Easily seen using a phase contrast microscope, filamentous bacteria provide the structural support on which floc forming organisms grow. Without filaments, floc tends to shrink in size and be more susceptible to sheer. Problems arise when filaments become overabundant and extend from the floc. Once extended from floc and reducing floc density, filaments begin inhibiting settling rates. So like many things, filaments are good in moderation but bad when overabundant. What conditions promote filamentous growth?
Some of the above problems can be fixed which reduces growth conditions favorable for filaments. Consider corrective measures such as:
I am posting an article from Paul Campbell that was published on Aster Bio's Environmental Genomics Blog - www.environmentalgenomics.com.
One of the fun things about wastewater microbial community analysis (MCA) is that we can often tell what type of influent the plant is seeing without any prior knowledge. We can even identify some operational challenges facing operators. As an example, we recently received a sample from a refinery located on the Texas Gulf Coast, no information about the current operating conditions, just a request for MCA. The results were really quite interesting (see graph, below).
While the chart generally presents microorganisms present at greater than 0.1% of the sequencing reads, I’ve intentionally removed some genera. Three microorganisms (Thiobacillus, Thauera and Methyloversatilis) each accounted for more than 3% of the sequencing reads. Thiobacillus accounted for almost 5%!
But, the interesting organism in the chart is Marichromatium. This is a genus of purple sulfur bacteria. While these microorganisms can photosynthesize when necessary, in the MLSS they can live off of organic acids. But, the really interesting part is that Marichromatiumrequires a reduced sulfur compound (sulfides) for growth.
So, the MCA strongly suggests that the facility is refining a high-sulfur crude. Furthermore, the sulfides are getting into the influent water, where they impact operations. The ammonia-oxidizing and nitrite-oxidizing bacteria (Nitrosomonas and Nitrospira, respectively) barely make up 0.5% of the sequencing reads – a typical refinery would have 1.5 to 3%. Sulfides are known to inhibit the growth of these two fragile organisms.
This is a great example of how the microbial community analysis both identifies a problem with the biomass (a low nitrifier population) and the cause (chronic toxicity due to sulfide exposure).
We sure love to use acronyms in environmental science and wastewater treatment. I have had full discussions with people mistaking "the nitrifiers" for "denitrifiers" when speaking - think about how close the words sound in normal speech. So, I thought a list of terms would help get everyone on the same page.
MBR systems use membrane separation instead of a DAF or clarifier to remove biological solids from effluent wastewater. MBR systems are becoming more common as membrane technology has improved and overall costs are lower when compared with larger foot print activated sludge systems. When compared with extended aeration activated sludge units, MBR systems typically have the following differences:
Pores in the membrane allow for water to pass with solids being retained. As pores become clogged with solids - both biological & particulate - the system goes into a backwash cycle to clear the pores and restore membrane function. The problem is that backwashing is not perfect, overtime pores deteriorate with accumulated solids. Even with cleaning technologies that include oxidants, acids, or enzymes - the pores will eventually become plugged.
A leading cause of plugged pores in biological waste treatment units is the accumulation of high molecular weight and "sticky" biological polymers. Organisms that thrive in the low F/M conditions found in MBR systems also tend to excrete copious amounts of extracellular polymeric substances (EPS). While some EPS is good and improves separation potential, the wrong EPS and overabundance of EPS can both create blinding conditions in membrane pores.
The easiest ways to monitor EPS in a biological treatment unit is to run SV30, SVI, and microscopic exam on at least a daily basis. Additional monitoring with molecular testing is equally important - including both Microbial Community Analysis (MCA) and qPCR for specific problem or good organisms which gives earlier warnings for EPS blinding potential. When you have a buildup of problematic EPS, do not just assume that it cannot be corrected. Multiple control methods exist, it is just best to address the EPS problem before membrane issues start to compromise unit performance.
Environmental Genomics testing and the research bottleneck - a great post by Paul Campbell, head of Aster Bio's molecular testing lab
Also check out Aster Bio's new Environmental Genomics website for more information: www.environmentalgenomics.com
Our ability to discover new microorganisms far exceeds our ability to understand and confirm the roles that they may play in different environmental niches.
You can extract DNA from almost any random environmental sample, subject it to next-generation sequencing to identify the metagenomes in the sample, and generate a fairly complete genome of a never-seen-before, never-cultured microbial strain. Then, wham, you run into the research bottleneck: how do you discover the role that your new, favorite microbe plays in the world?
Hard work and time. Bioinformatic analysis of the genome can provide insights into the potential metabolic activities your microbe may have (and, by extension, some of the roles it may play). Tracking co-occurrence and co-exclusion patterns with samples taken under different conditions helps, too. But, eventually, you just have to isolate the strain and start running tests.
This is highly relevant to wastewater microbial community analysis. For example, we occasionally find the genus Ferruginobacter to be the dominant strain in some wastewater plants, but completely absent from others. So, what's it doing?
The genus Ferruginobacter was first reported in 2009 (Lim et al., DOI 10.1099/ijs.0.009480-0). It's an obligate aerobe that doesn't denitrify (it won't reduce either nitrate or nitrite). Members of the genus are heterotrophs, although there are differences in the carboon sources they can grown on. So, what makes it so common in the biomass of one wastewater treatment plant and absent in another?
This is not an uncommon phenomenon. Scientists continue to discover new bacteria and archaea all the time, so for the foreseeable future, "I don't know" will be a common reply to "Why is this microorganism in my wastewater?" The good news? Generally speaking, a significant portion of the abundant genera have been studied, in some cases for over a century (Clowes, 1900. DOI 10.1038/062128b0), because they were abundant and easy to isolate. These key taxa do provide a lot of insight into how a particular wastewater treatment plant operates.
When compared to BOD/COD removing microbes, we spend an inordinate amount of time monitoring or worrying about ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) populations. What makes these bacteria so difficult to maintain in a wastewater treatment unit? Here are a few reasons:
In my last post, I covered the differences between acute and chronic toxicity. While acute toxicity rapidly kills or harms your biomass, chronic toxicity tends to be a longer term loss of activity. Instead of an instant kill, chronic toxicity works by growth inhibition. As organism reproduction slows, the desired microbes can start to decrease as a percentage of total biomass. For example, ammonia oxidizing bacteria (AOB) have a very slow growth rate compared to most heterotrophic microbes. If we inhibit this slower growth rate, the AOB population drops resulting in eventual ammonia breakthrough into the effluent.
Since it does not happen instantly, chronic toxicity can sneak up on operators. There has been little way to detect chronic toxicity problems until you had significant microorganism loss or inhibition. However, this post is not all gloom & doom - a new way to monitoring exists that detects chronic toxicity before treatment efficiency falls. The new monitoring technology - Aster Bio's Environmental Genomics - DNA based monitoring.
DNA is present in all organisms and we can use this DNA to identify which organisms are present. Using Environmental Genomics testing, Aster Bio can do a complete microbial census of everything present in MLSS - full sequencing of all DNA present. For routine chronic toxicity testing, we can monitor population of target organisms such as AOB/NOB, sulfur reducing organisms (SRB), and bulking/foaming filaments among other organisms. In fact, we can customize our rapid qPCR tests for any target organism in a wastewater plant.
The advantages of using qPCR testing include:
Often you hear about chronic and acute toxicity when discussing effluent bioassay (biomonitoring) with test organisms. Both concepts are important for biological units that are having issues with ammonia oxidation, deflocculation, and COD/BOD removal. Over the next few posts, I am going to go into acute vs chronic toxicity with specific examples. In this post, I am going to make sure we all agree what is acute vs chronic toxicity.
Acute Toxicity - something that damages organisms immediately upon exposure. Focus on the fast kill part! Acute toxicity is often seen with pH swings, phenol, cyanides, or solvents. In bioassay tests, this is the die off of test organisms. With wastewater bacteria, acute toxicity usually comes with an immediate loss of nitrification and deflocculation. As soon as the acute toxic compound washes out or the biomass adapts, the system starts to recover.
Chronic Toxicity - a slower, accumulating toxic effect. Often we see metals that buildup in biomass as a source of chronic toxicity. You will not see the sharp change in biomass with chronic toxicity. Instead, a loss of treatment efficiency will take hold over time. In bioassay tests, chronic toxicity manifests itself as low reproduction or failure to see weight gain.
Recording color and foam changes is a great, simple way to monitor wastewater treatment systems. While you cannot use color and foam alone - you need to do the standard battery of tests including SV30, D.O., OUR, microscopic exam, MLSS - it is a quick, painless way to see changes in biomass.
Look at both the water and MLSS color. In systems with dye and highly colored influent, color observations are less accurate, but changes should still be monitored. A healthy MLSS is brown in color. The brown color results from bacteria cells, biological polymers, and particulate materials. Lighter brown usually indicates an immature biomass - where biopolymers are not at optimal levels. Dark colors - trending towards gray/black indicate older sludge, septicity, and if accompanied by odors, a problem with aeration/mixing. Colors are subjective and depend upon ambient light, so try to monitor changes and record observations. In summmary:
Foam originates from influent surfactants, biological polymers, and even microbial produce surfactants. For observation purposes: record depth, color, and foam stability. As foam is directly related to biological activity (again high surfactants in the influent can confound this observation) - it gives you great information on microbial activity. Here is how I interpret foam observations:
Remember, noting color and foam are just observational tests. They should be done in conjunction with normal physical and laboratory tests. An observant operator can see if something has changed by looking at color or foam in a few seconds - unlike lab tests that can take several hours or days. So, start recording observations and it will help you maintain good biological waste treatment.
Summer time collection system and wastewater treatment plant odors. Is hydrogen sulfide the only thing you should monitor?
With oxygen being less soluble in warmer water and higher temperatures triggering microbial growth, summer months can bring an explosion in biological activity in both collection systems and wastewater treatment plants. While microbial growth is good for reducing pollutants, it also has unwanted side effects including:
The different electron acceptors and different "levels" of anaerobic conditions are why I always ask for pH and redox information when doing odor control projects. As pH increases, sulfides and volatile organic acids remain more soluble and stay in the water column. This is why some odor control methods include adding caustic or other base solutions. ORP or Redox Potential gives us information on what electron acceptor is being used by microbes. At a pH of 7, when we are above -150 mV ORP - you will be using non-sulfate electron acceptors and odors will be minimal. Control strategies with ORP include adding peroxide, nitrate, or other electron accepting alternative.
With all the options, I like to pick a solution that best fits the system and problem. Do a system survey to see where problem originate and then think of various options. I have written on system using lift-station aeration systems (blowers), pure oxygen injection with nano-bubbles, nitrate solutions, and even targeted hydrogen peroxide additions. All have merits and ways to improve their effectiveness. The key is to not pick a solution until you do the survey.
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.
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