Those of us working with industrial wastewater treatment often complain about textbooks and training courses focusing on municipal wastewater. Rick Marshall & Steve Leach - both highly experienced wastewater professionals - are offering a petrochemical focused wastewater course in December 2020. This course will be online using Zoom but have the same content as in-person training. I highly recommend this course for those of you working in petrochemical or refining wastewater treatment.
Microbial metabolism generates energy by moving electrons along metabolic pathways to a terminal electron acceptor. If this sounds complex or brings back images of the biology class electron transport chains, I apologize but it is good to know the general metabolic options in wastewater and not get bogged down by the individual biochemistry steps.
We often use the term aerobic, facultative anaerobe, or anaerobe when talking about wastewater bacteria. These terms are great, but the lines are not as clean as you may think. Let's start with the general options.
It all starts with where the electron ends
Going back to the electron tower (pictured above), microbes generate energy for growth by moving the electron to the highest energy acceptor. If the terminal electron acceptor is oxygen, you have an extremely high energy yield. As you move to other electron acceptors, less energy is produced.
Terms that we use in wastewater
Foam can tell you a lot about the biological state of your aeration basin. Some foams including the normal white foam and the greasy thick stable foams are produced from the byproducts of microbial growth. Here are the most common foams that you see on aeration basins:
Normal Biological Foam
As bacteria grow and divide, they produce extracellular materials including polysaccharides, proteins (enzymes), and even DNA/RNA. Also important for biofilm or floc adhesion, these materials trap air bubbles in a light color foam that is easily broken by waters spray if it even builds up more than 1 - 2" on the water surface. When the system is in log phase growth, you may notice both a lighter color and more foam than when the system is mature in decline phase growth.
Nocardia/Microthrix Parvicella (filaments)
Nocardia (often actually a Gordonia sp) is promoted by long chain fatty acids (FOG) and Microthrix is triggered often by low F/M, long chain fatty acids and lower temperatures. Both genera can exist in wastewater and not cause foaming, but under appropriate conditions, they start to produce hydrophobic extracellular materials. The hydrophobic biological polymers trap air and create the thick, stable, greasy foam. The best way to prevent foaming is to reduce grease and keep appropriate MCRT or F/M ratios in the system.
Surfactants are used in many products not just cleaning agents. Firefighting foams, food product emulsion stabilizers, even many personal care products contain surfactant chemistries. Under normal concentrations, bacteria readily remove surfactants or they are diluted beyond their ability to reduce surface tension (creating foam). Periodically, you may see higher loadings hit the aeration basin. With surfactants the foam is usually stable and has a light color. While their presence is temporary and foam levels should drop, you can use commercial antifoam products to prevent excess foam during peak events.
Plant soaps, Starches, & Proteins
The above chemicals are natural polymers found in wastewater. Foaming occurrs when normal biological foam beomes stabilized by the natural polymers. In this case, antifoams and water sprays are often effective. We have also effectively used pretreatment with enzymes to pre-digest the polymers prior to the aeration basin - this can be very valuable in food processing wastewater treatment.
Some Nitrosomonas species exhibit significant anaerobic growth - we have even found them in anaerobic digesters
For years, I have always been told that Nitrosomonas sp are obligate aerobic bacteria. We all accepted that Nitrosomonas used oxygen to convert ammonia into nitrite. That was the extent of their metabolic capabilities. However, Nitrosomonas have now been found to have a few other metabolic tricks available to survive in anoxic and anaerobic environments. How well does Nitrosomonas grow under D.O. limited environments, surprisingly well. In fact, Aster Bio's MCA tests on multiple anaerobic digesters has found significant Nitrosomonas populations. Here is what Nitrosomonas does in aerobic, anoxic, and anaerobic environments:
Much of our animal based foods come from CAFO systems where animals are housed at high density. WIth the high density comes problems with manure and urine. The number and size of these operations means that CAFO can be the largest source of wastewater in many areas. The waste is high in BOD5 and ammonia which is often treated in lagoon based systems with land application via irrigation systems. Odors and treatment inefficiencies in ponds can cause problems with operations, so there was room for improving biological treatment processes.
As this is an ongoing R&D project, I thought this would be a way to introduce you to how biological products are developed for new applications. We started with a manure degrading formulation developed in the 1990s but knew that advances in our technologies could improve the results. Working with several groups on introducing biological pretreatment in the animal houses, we are using extensive analytical testing in both pilot scale and working houses. Testing includes standard water chemistry tests and DNA based testing for changes in the biomass composition. The goals for adding biological products being:
In many areas, wastewater and stormwater go through facultative or moderately aerated lagoon systems prior to discharge. These lagoons remove residual oragnics, nutrients, and solids that can pass through the upstream treatment. In the case of stormwater, the lagoons remove nutrients from fertilizer runoff and hydrocarbons from parking lots/roads. Unlike modern wastewater treatment sytems, the lagoons have low levels of biomass (MLSS) that can range from 30 - 100 mg/L volatile solids. The solids component consists of:
The reason for ammonia appearing and AOB growing during summer months is a phenomenon related to sludge degradation on the pond bottom. While the sludge layer degrades all year, the rate of anaerobic lysis increases with summer temperatures. The pond bottom remains anaerobic/anoxic producing organic acids, methane, and nutrients (N, P). The upper layers have oxygen present from algae photosynthesis, natural diffusion from the surface, and action of mixers/aerators if present. In ponds with more sludge, the problems related to ammonia release and algae blooms tend to cause more problems. So what can be done to control this other than a big mechanical dredging project?
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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