I often get this question. If you believe that a microbe is a microbe - then it should work perfectly. You could truck in sludge from a municipal plant and it would work perfectly for building biomass in a refinery. Of course we all know it is not that simple. To answer the title question, adding sludge can help but it all depends on  your expectations and treatment needs.

​To more fully answer the question, we need to look at wastewater microbiology and the nature of Mixed Liquor Suspended Solids (MLSS). As I like bullet points, here it is:

• ​The microbial composition depends upon the influent makeup including organics present, waste concentration, inorganics including TDS/chlorides, toxic and quasi toxic compounds.
• Another factor in microbial makeup is the system's environment - pH, macronutrient (N,P) concentrations, temperature, dissolved oxygen, and sludge age.
• MLSS contains a mixture of active bacteria, dead cells, extracellular polymeric substances (EPS), and adsorbed particles. In most systems the active bacteria portion is less than 15% with longer sludge ages having a lower active fraction.

​Now, when you add sludge from a plant without the same influent or operating conditions the MLSS experiences a shock which can kill many of the active microbes. This die off is seen with increased turbidity and floating solids often seen when adding off-site MLSS to a system. While some of the surviving bacteria will grow and potentially flourish, the most common benefit from adding sludge is the increase in adsorptive capacity (in effect adding a sponge). If the system can handle the solids even requiring adding polymer, the added mass can give you time for a sufficient microbial population to develop. This is where bioaugmentation can prove valuable.

​Bioaugmentation includes adding cultures screened for growth in the system. The resulting product is highly concentrated with respect to active microbial fraction. How we use it with adding MLSS from nearby plants is based on evaluation and experience. Here are the situations:

• If a similar wastewater facility is nearby - trucking in sludge can be highly beneficial using MLSS alone.
• Long distance transport can add substantial cost and long storage time can result in septic sludge being added with associated problems.
• If a system is experiencing moderate upset and has sufficient MLSS but low microbial activity, the best option is often adding bioaugmentation product as it can restore the active portion quickly without adding inert solids.
• In cases where the MLSS is depleted (lost) - adding sludge for mass purposes along with active bioaugmentation cultures is the most rapid option to restore full treatment efficiency.

National Geographic has recently run an article on intersex fish being found in wildlife refuge waters. While this can occur sporadically in nature, a trend for higher numbers of intersexed fish, amphibians, and reptiles has been identified over the past 30 years. While we may have anticipated this happening in highly polluted streams near industrialized areas, it is now being found in agricultural and non-industrialized areas.

​What are hormone mimics? In general a number of compounds including some naturally-occurring chemicals have the ability to mimic natural hormones in animals & humans. Most of the research has been on estrogen mimics causing males to become hermaphrodites. Early indicator species include small mouth bass - but early research also found a huge impact in alligators in Florida in the 1990s.

​What is important is the concentration of hormone mimics in waters causing disruption in indicator species. We do not know the long run impact on higher trophic level organisms including humans. So, the next generation of wastewater permits will start to also include reduction of hormone mimics and pharmaceuticals that are currently passing through conventional wastewater treatment systems. The issue is how to remove these compounds without excessive costs or other environmental impacts.

​I am including a link the National Geographic story. A online search will also give further references on hormone mimics and regulators efforts to remove problematic chemicals from waters.

Extracellular polymeric substances (EPS) is literally the glue that hold bacteria in a biofilm or floc. This glue also allows the floc to act like a sponge - adsorbing organic and inorganic insoluble compounds and forming the matrix that we call biofilm or floc (depending upon your system).

​What exactly is the EPS composition? Well it has been found to be:

• ​Polysaccharides
• Proteins
• DNA
  
• Lipids

​The exact ratio and composition of the materials determines the nature of the EPS and how strong a floc is formed. To fully understand the EPS and its role in floc formation, we need to define the types of EPS that we see in wastewater:

• Crude - seen in early growth phases, is not developed and often in free solution
• Capsular - attached tightly to the bacterial cell which forms the eventual floc
  
• Loosely bound - the EPS is weak, not forming tight bonds with bacterial cells. This is a function of charge density and EPS molecular weight.
  
• Tightly bound - EPS forms tight bonds with cells. In this case charges are a match between bacterial cells and EPS forming a dense floc.
  
• Slime - EPS has significant quantities of entrained water, grease, or fatty acids. This is the non-filamentous bulking condition.
  ​
  

​What factors change the EPS formation?

• Dissolved Oxygen
  
• pH
  
• Temperature
  
• Oil & Grease - encapsulates and reduces floc density
  
• Toxic shocks - floc structure breaks down under severe shocks
  
• Nutrients - N, P - chronic low N & P can favor filaments, slime and loosely bound EPS
  
• Micro-nutrients - Fe, Ca, Mg, etc - sever lack of micronutrients can create loosely bound EPS
  

A recent study on houses in Peru and Brazil led by Maria Gloria Dominguez-Bello of New York University, examined microbial communities on walls in houses from remote areas of Peru (both totally rural and in small villages) and compared the diversity and type of microbes to those found in urban Brazil housing.

We may not realize it, but our immediate environment is full of microbial communities. And, our houses have differences in microbes found on walls in various rooms. In this study, they found you could identify room use by the microbes on walls.

Another finding, was the more we seal off our houses with walls, windows, and insulation - the less microbial diversity on the walls (especially soil microbes). Instead, our walls tend to keep our human associated bacteria (E. coli, Steptococcus mutans, and on) in higher concentrations than found in rural, more open air houses.

So what does this mean? Well right now we just know there are differences in the microbial communities in urban versus rural houses. The next phase of research needs to look at how this impacts our personal microbiome on our skin and digestive tract. We may find that the urban environment has an impact on our digestive tract health.

At Aster Bio we have been bench testing several new organisms with the goal of converting sulfides and H2S into harmless oxidized forms at non-acidic pH. While many Thiobacillus cultures exist that oxidize reduced sulfur, they tend to thrive at pH levels below 5 which is outside the range of many other organisms. So, we started looking for other sulfur oxidizing cultures that worked at higher pH.

After screening a number of candidates, we found some unique microbes with excellent applicability to waste treatment. The first is a Paracoccus denitrificans. This unusual bacterium has a number of key metabolic pathways that are useful in control of both sulfides and malodorous short-chain volatile fatty acids. An additional benefit, is the P. denitrificans can utilize nitrate/nitrate when growing on the short-chain volatile fatty acids. So what does all this mean for waste treatment?

• Help remove H2S & sulfides in collection systems & wastewater at neutral pH
  
  
• Odors from short-chain volatile fatty acids (acetic, propionic, butyric) can be controlled under aerobic and anoxic conditions
  
  
• Nitrate/nitrite reduction – even under aerobic conditions the organisms utilize nitrate for respiration. The P. denitrificans is among the most active denitrifying microbes we have screened
  
  

So what Aster Bio going to do with the P. denitrificans? Our current work is on optimizing industrial scale growth of the microbe in aseptic reactors with downstream stabilization. Once we finish that task – it is not easy – we will work to develop techniques to introduce the P. denitrificans into working systems so that the organisms can work to exploit its ecological niche and improve wastewater quality without odor masking chemicals or oxidants. I will keep you posted on field trial results.

We all like quick and easy tests to screen for potential problems in the biological treatment unit. The problem is that many of these tests require specialized equipment, reagents, or are just expensive.

​Today, I want to talk about using the oxygen uptake test done daily in most facilities as a way to estimate influent toxicity. Does it work in all places, all the time..... no. But, It can prove useful in many systems that have periodic "suspicious" influent conditions.

​The spiked DOUR simply consists of a set amount of MLSS from the aeration tank to which you add a set amount of influent or waste stream to be tested. You can allow to react with the biomass for 2 - 4 hours using an aquarium air stone or you can do the test immediately. Then, you saturate the sample with oxygen as in a typical DOUR by shaking.  Once saturated with oxygen, you use a BOD bottle & DO probe to record oxygen uptake by the biomass + sample. Once the DO is depleted to <1.0 mg/L, you convert the uptake rate to mg O2/L/hour.

​An increase in DOUR in the spiked versus the normal MLSS and is expected. The red flag here is if the spiked DOUR pulls down the O2 extremely fast - due to chemical oxygen demand. Or, if the respiration is reduced significantly which indicates toxicity.

​Key to the spiked DOUR being an effective operational tool is running the test frequently to get a correlation between the spiked DOUR to system operational numbers. Another important issue is whether to allow the sample to aerate for a time period before running the DOUR tests.

​I have used spiked DOUR to test equalized waste streams in industrial pretreatment and pulp & paper wastewater. With frequently tested samples, it proved useful in predicting high strength or toxic influent which allowed for operators to slow the influent flow and prevent system wide upset.