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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