Many of us in industrial wastewater have experienced a toxic shock event. In most cases, toxic shock is noted by loss of nitrification and deflocculation (turbidity/floating solids). Today, I will work thorough my process for identifying what caused or is causing the upset.
I like it when a facility looks under the microscope daily. Even if you do not have a high dollar phase contrast microscope, you can make valuable observations with they standard light microscope that is common to many high school classrooms. But what are you looking at when you observe samples at 100x, 400x, and even 1000x magnification? Today, I'll cover what you see when using a microscope.
First, the "bugs" we note using the microscope are mostly single celled protozoa and a few multicellular lifeforms. The bacteria - or the actual workers - can be seen as part of the floc or as very, very small particles in the water. Some bacteria can become filamentous in form or are large enough to be seen with microscope, but most even at 1000x appear as small rods or spheres.
We rely on the protozoa and higher life forms as indicator organisms for the underlying bacteria populations. For example, stalk ciliates are only present and active when there is sufficient dissolved oxygen and low levels of inhibitory or toxic compounds. This just happens to be where we are in decline phase growth or target F/M for most wastewater treatment plants. Multicellular forms such as rotifers, worms, or tardigrades appear even further along the F/M curve and can indicate old sludge or too low an F/M where you are carrying too much dead or inactive biomass.
I recommend looking under the microscope daily for the following:
While I use the microscopic exam daily, I also like to run newer molecular testing that looks directly into the floc's microbial community. With high throughput sequencing, we look at DNA in the system and find our which microbes are present and at what % of total biomass reads (identifying DNA segments). This is a total microbial census of the MLSS and is good to run when establishing a baseline population database, making operational changes or on a quarterly basis for tracking long term changes. Following Microbial Community Analysis (MCA), we identify key microbes that are most important for good treatment. We can then use qPCR technology to track these specific microbes. qPCR is faster, highly quantitative, and cheaper than the full microbial census (MCA).
Microbes consume dissolved oxygen (DO) when growing on wastewater pollutants. The rate at which the microbes consumer oxygen is the respiration rate. During periods of high loadings the respiration rates increases as the microbes become more active and cellular division rates increase.
OUR rates increase in response to higher soluble organic loadings (BOD5), faster microbial division (low F/M), and following upset conditions when microbes are moving back towards stable population - this is log phase growth.
Another facet of OUR testing includes a potential for a drop in respiration rates due to acute toxicity where previously respiring microbes are inactivated (killed). I have seen this with phenol, cyanide, and tall oil releases in industrial wastewater.
So any large change in OUR rates should be investigated. If you are changing MLSS concentrations, you should standardize the OUR by using the SOUR calculation (divide OUR by MLSS or MLVSS in grams).
Here is a link to the OUR test protocol that I have used for the past 25 years.
Being both deadly in enclosed spaces and a nuisance at even low levels, hydrogen sulfide is among the most problematic of compounds in wastewater treatment. Instead of covering the whole geochemical sulfur cycle, I want to look into the wastewater specific cycle that converts benign sulfates and sulfur into the problematic reduced sulfide species. Instead of graphics, I want to detail each form of sulfur found in wastewater.
Activated sludge systems operate by moving a suspended biomass (MLSS) through an aerated basin and then separating solids for recycle back to the aeration basin. This process was invented in the early 20th century for treating wastewater and many variations on the process exist including contact stabilization, extended aeration, batch reactors, oxidation ditches, and pure oxygen systems. A key operating parameter has been the Food to Microorganisms (F/M) ratio. F/M is traditionally calculated using MLSS or MLVSS as the M and BOD5 as the F. Key is to be consistent and always know what you are using to calculate F/M and identify the best F/M ratio for operations.
Now we move to biofilm type systems versus suspended growth. Here we have tricking filters (old but still good), MBBR, and fixed film media. All relay on a biofilm which is actually just floc grown in attached form. Calculated F/M in this system is difficult since the biomass is attached to media. So we operate any biofilm based system on loading per unit of surface area - this can be BOD5/square meter or Ammonia/square meter. Again just be consistent in calculating.
The key benefit of a biofilm vs suspended growth system is the ability to hold more biomass than comparable activated sludge units which rely totally on solids separation to keep biomass in the aeration tank. Of course this advantage is not present for all influents. For example, systems with significant influent oil & grease can foul (coat) the media which can be a big problem.
Nitrosomonas species also known as Ammonia Oxidizing Bacteria (AOB) have always been discussed as obligate aerobic chemoautotrophs. Under aerobic conditions, the Nitrosomonas convert ammonia to nitrite while using carbon dioxide and carbonate as a carbon source.
I have recently read multiple peer reviewed papers that document the ability of Nitrosomonas to utilize various organic compounds as an energy source with nitrite as an alternative electron acceptor - producing N2 gas as a final product. This ability to use their waste product from aerobic reactions as an electron acceptor reveals how Nitrosomonas can survive in systems with substantial anoxic periods.
Here is a link to a 2009 paper with more details:
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.
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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