Hyphomicrobium sp. form stalks with budding daughter cells during reproduction. It is the stalk extending from the biofilm that makes the Hyphomicrobium easy to see under a microscope. The daughter cells have flagella allowing for the Hyphomicrobium cells to swarm and colonize new areas. Hyphomicrobium in wastewater are associated with denitrification and are especially common in systems with methanol or other short chain alcohols.

So why do we commonly see Hyphomicrobium in systems without methanol in their influent? Stepping back and looking at the microbial community can give us the answer. Influent wastewater contains a big mix of organic and inorganic compounds. No one organism grows on all these compounds. Instead, we have an interaction among thousands of microbial forms. For example, a Pseudomonas may convert an insoluble fatty acid (grease) into soluble short-chain fatty acids which is a byproduct of their metabolism. Instead of short-chain fatty acids building up, bacteria such as Hyphomicrobium and Paracoccus begin to grow on this Pseudomonas waste product. This is an example of syntrophy among various organisms. Syntrohphy is also a reason why we cannot identify all microbes in wastewater MLSS using plate counts.

Here are some facts about Hyphomicrobium sp.:

• Aerobic and capable of using nitrate/nitrite as an alternative electron acceptor
• Uses methanol and other short-chain alcohols as a carbon source
• Under anoxic conditions Hyphomicrobium is a high rate denitrifier
• Biphasic life cycle – flagellated swarm then sessile where we see the stalk
• Studies have found the following pathways in various Hyphomicrobium isolates
  • Degrade PAH
  • Dichloromethane
  • Formaldehyde
  • Dimethyl sulfide & methanethiol oxidizing sulfide portion
  • Amines (MEA, DEA, TEA)

NITROSPIRA SP
Bergey’s Manual
Nitrospira make up the key nitrite-oxidizing bacteria in most wastewater treatment systems. While a lot of the literature highlights Nitrobacter, Nitrospira generally grow best on (very) low levels of nitrite found in WWTPs. Nitrobacter, on the other hand, likes higher nitrite concentrations and is easier to grow in the lab.

• Gram-negative
• Aerobic
• Some strains can use nitrate as a terminal electron acceptor

And, surprisingly, some strains of Nitrospira are Complete AMMonia OXidizers (COMAMMOX) capable of both ammonia and nitrite oxidation. In some WWTPs with significant ammonia nitrogen loadings, we have seen high levels of Nitrospira and extremely low levels of Nitrosomonas or other known ammonia-oxidizing bacteria. Using polymerase chain reaction assays (PCR), we can identify COMAMMOX strains present in some MLSS samples.

Short post continuing concepts with MLSS that does not compact in settling tests or in the secondary clarifier.

Poor settling and compacting sludge results in high SV30 and SVI. When sluddge does not settle or compact, the secondary clarifier bed depth increases. This results in less solids conentration in the RAS & WAS lines. What does this mean?

• Return line has less MLSS than is desirable. To maintain F/M ratio, you would have to return more flow via the RAS line.
• Hydraulics can become a problem if you increase return flows to maintain the F/M ratio.
• Waste sudge going for disposal has more water. Making dewatering more difficult or creating digester capacity issues.

While using our Microbial Community Analysis testing system on wastewater treatment system samples, Aster Bio has found that Nitrobacter (NOB) are not nearly as common as thought. Instead, the predominant NOB culture has been Nitrospira. Here is a bit more about Nitrospira (and forgive the filament photo - it was great for the blog header but is not Nitrospira)

Bergey’s Manual
Nitrospira make up the key nitrite-oxidizing bacteria in most wastewater treatment systems. While a lot of the literature highlights Nitrobacter, Nitrospira generally grow best on (very) low levels of nitrite found in WWTPs. Nitrobacter, on the other hand, likes higher nitrite concentrations and is easier to grow in the lab.

• Gram-negative
• Aerobic
• Some strains can use nitrate as a terminal electron acceptor

And, surprisingly, some strains of Nitrospira are Complete AMMonia OXidizers (COMAMMOX) capable of both ammonia and nitrite oxidation. In some WWTPs with significant ammonia nitrogen loadings, we have seen high levels of Nitrospira and extremely low levels of Nitrosomonas or other known ammonia-oxidizing bacteria. Using polymerase chain reaction assays (PCR), we can identify COMAMMOX strains present in some MLSS samples.

We have more on MCA identfied interesting microbes at https://blog.environmentalgenomics.com/

SV30 is among the simplest and most common of wastewater tests that we run. The SV30 reports the settled sludge (MLSS) volume after settling 30 minutes in a wide mouth graduated cylinder or dedicated settlometer.  The SVI calculation was designed to standardize the SV30 for different MLSS concentrations. For review:

SVI (ml/g) = SV30 (ml/L)                       
                     MLSS (g/L)                         
General SVI Guidelines

• ​< 80 - fast settling sludge, if supernatant is turbid low SVI indicates "old" sludge
• 100 - 200 - the range most activated sludge systems operate. Remember your secondary clarifier determines the upper limit for SVI.
• >250 - indicates severe bulking caused by filaments, non-filamentous bulking, or being extremely early on the growth curve.

So what ist he right SV30 & SVI for your system? Run the test at least daily. At the same time track effluent TSS, Return Sludge (RAS) concentration, and clarifier bed depths When all three tests/readings are in target range, you have your ideal SVI or SV30 (for a constant MLSS concentration).

Remember - the above ranges are just guidelines. Always refer to how well your secondary clarifier functions to get your system's true range for best SVI.

Every waste treatment system has some bottleneck that limits treatment capacity. Many systems can operate in the short term above design capacity. However, eventually you will encounter problems controlling operations. At this point, you can supply additional oxygen, use polymers to increase floc density & settling rates, and even use activated carbon or chemical oxidation to adsorb excess organics. In today's post, I want to focus on the most common bottlenecks in biological wastewater treatment systems. Make sure you know where you have bottlenecks to prioritize capital upgrades, or develop operational plans that minimize the bottleneck impact. Here are the most common bottlenecks:

• Secondary clarifiers
  Hydraulic overloading is an obvious problem. But,  you should also note that solids flux rates are also a limiting factor. If solids do not settle and compact, the bed depth control may be lost and clarifier fails to work properly. This is why we often do maintenance evaluations on pumps, rakes, and weirs.
• Aeration (dissolved oxygen)
  Oxygen transfer is also a common problem. As fine bubble diffusers become less efficient as they foul, oxygen transfer efficiency can be insufficient for maintaining oxygen residuals in the floc. 
  
• Mixing 
  This is more of a problem in lagoon based systems, but mixing is another possible bottleneck. Improper mixing can result in short-circuiting and failure to keep MLSS suspended in the water column.
• Waste solids handling
  Wasting can be limited by digester capacity, press or centrifuge functioning, or some other solids handling issue. When the bottleneck is wasting, the system often has "old slduge" and the associated fines/turbidity seen as deflocculation occurs.
  
• Primary treatment
  Here we can have insufficient primary clarifiers, oil water separators, DAF units, and even EQ tanks in need of sludge removal. In all cases,  you have a potential for solids, oils, or high COD waste to enter the biological unit.