Industry publications and journals focus on newer technologies such as MBR, Granular Activated Sludge, and other advanced systems. However, much of our wastewater is still treated in lagoon systems and these systems still have an important part in treating wastewater. What most people don't realize is that lagoons can also be upgraded to meet higher loadings and more stringent effluent permits.

Some examples of lagoon upgrades include:

• Adding advanced aeration & mixing which reduces short circuiting, anoxic zones, and maximizes biological activity. I am especially interested in new microbubble/nanobubble technologies that improve oxygen transfer with less utility costs.
  
  
• Opportunity to enhance performance by adding MBBR into lagoons. The MBBR media develops biofilm that remains suspended in the lagoon and treating pollutants. If you see this as lowering the F/M or increasing MCRT for microbes in the system, you are correct.
  
  
• Installation of smaller advanced treatment modules to remove ammonia or phosphorus while using the lagoon for primary BOD/COD reduction.

A subset of industrial wastewaters including pulp & paper have lower than optimal C:N:P ratios. To ensure proper bacterial growth, these facilities often add various nutrient blends to supplement both N & P. What happens when they do not supplement macronutrients at optimal levels or even add not nutrients at all?

We have long known that deficient macronutrients often impacts floc formation and the filament/floc forming organism balance. But what happens with the actual microbial makeup in the biomass. Molecular testing allows for conducting a total microbial census and we can compare similar systems with and without added macronutrients.

Diazatrophs are microbial organisms that use N2 gas - present at approximately 80% of our atmosphere - to provide nitrogen needed for cell growth. This reaction is most described in agriculture with legume crops where the microbes grow in root nodules. In wastewater, diazotrophs include a diverse mix of organisms including Rhizobia, Rhodopseudomonas, Frankia, Klebsiella, Azotobacter, Paenibacillus, and many cyanobacteria genera. Some of these organisms are floc forming and desirable in wastewater but others like cyanobacteria can create water quality issues.

In systems adding macronutrients, operators want to add sufficient N & P to keep a healthy, floc forming microbial population but not overdose nutrients. In the past, nutrient dose was based on finding N & P residuals in the effluent and maintaining these at target residuals. With molecular testing, we are now able to monitor for the presence of AOB/NOB (feeding too much nitrogen) and diazotroph populations (if in excess, you have insufficient nitrogen).

Aster Bio has been testing an increasing number of BNR plants with excellent phosphorous removal efficiencies. Our testing - Environmental Genomics™ MCA - is a total microbial census of MLSS with relative % of each genera. Using this molecular sequencing technology, you can see key differences among microbial populations based on system design and operation. 

Data from MCA Test
We use high-throughput sequencing of the 16s region to conduct the microbial census. The sequencing produces over 100 MB of data per run, so making it useful also means summarizing the data in a convenient table. Below are two different runs from a healthy BNR system with biological phosphorus removal and a conventional activated sludge system. The table presentation gives % of total reads for common functional groups - of course there is a lot of data behind this summary that is also interesting.

Key Differences
The Non-BNR systems of course have fewer PAO/GAO populations. The "Bulking" column is composed of Zooglea/Thauera genera. These genera are common bacteria that can form good floc, denitrify, and degrade a wide range of organic compounds. Under certain influent conditions, the bulking group can produce excess EPS that causes non-filamentous bulking.

BNR system testing reveals that the PAO/GAO cultures are inversely related to the Bulking genera. I have also noted that the BNR systems also tend to have more known filamentous bacteria genera present. 

With a complex community of inter-related microbes, anaerobic require balanced populations of fermentative bacteria and methanogenic archaea. Most textbooks breakdown the microbial communities into three groups:

• ​Hydrolyzing & Acidogenic bacteria are bacteria with anoxic and fermentative biological pathways. These organisms degrade complex organics into forms used by other anaerobic organisms. These microbes utilize any remaining alternative electron acceptors and eventually use organic compounds as the terminal electron acceptor.  This stage can also product nuisance H2S gas
• Acetogenic bacteria are anaerobic cultures that continue the fermentation process and produce the acetate/acetic acids that are the preferred feedstock for developing methanogenic archaeal populations. In both the Hydrolyzing and Acetogenic processes, H2 and CO2 gases are produced.
• Methanogenic archaea - note this is a separate kingdom from bacteria with unique enzyme cofactor micronutrients - are obligate anaerobic cultures responsible for producing valuable methane gas (CH4). Two varieties of methanogens exist based on substrates utilized:
  Acetic Acid Cleavage - CH3COOH --> CH4 + CO2
  Carbon Dioxide Reduction - CO2 + 4H2 --> CH4 + 2H2O
  
  

Traditional Monitoring

• Methane and CO2 percentages in produced gas
• pH, Temperature, ORP
• Alkalinity
• Organic acids
• H2S
• Trace micronutrients used by methanogens that may not be present in the influent
  
  

Adding Environmental Genomic testing to monitoring
Aster Bio uses Microbial Community Analysis (MCA) as a part of our Environmental Genomics testing suite.  The MCA test is a full microbial census for both bacteria and archaeal populations using high throughput sequencing technology. The resulting census gives relative % of the genera present. For monitoring, this shows drifts and changes in populations in response any operational change. MCA also proves useful in discovering problem sources in digesters not achieving desired methane conversion. While not a daily test, routine monitoring with MCA supplements traditional monitoring and an help improve anaerobic digester performance while reducing operating costs.

I had a recent question on why a system was with a history of stable operations was seeing an increase in non-volatile solids which we view as a decrease in the "bug" portion of MLSS.  Effluent quality remains excellent, but the local engineers wanted to think about what was driving this change. To understand MLSS to MLVSS ratio changes, it helps to think about what is happening in the system.

MLSS is total dried solids and includes “everything” after removing the water. This includes living microorganisms, dead microorganisms, extracellular materials including biopolymers, adsorbed organics, organic particulates, inorganic particulates.

MLVSS is the portion of MLSS that is removed during a high heat (550 Deg C) muffle furnace step. The residual contains non-volatile solids - Often benchmarked at 75% of solids being volatile in domestic WW.
How much of the volatile portion is living microbes? Usually less than 15% - longer sludge ages with lower F/M drop the % downward even further.

If you see an increase in the non-volatile fraction – this can mean

• More influent non-volatiles!
• Insufficient wasting leading to buildup of non-biodegradable or inorganic solids. As sludge becomes “old”, you enter endogenous respiration where active living biomass as a % falls
• Influent biodegradable organics drops so a lower microbial population is supported
  ​

What does this MLSS/MLVSS ratio change mean for operations:

• Don’t use the ratio in a vacuum – use settling tests, turbidity, microscopic exam, respiration rates and other available tests to determine operations.
• Monitor & measure
• Look upstream to see if anything has changed