Short chain organic acids are readily biodegradable and relatively non-toxic, so why should wastewater operators be interested in simple organic acids?
Many wastewater unit operators find Nocardia or M. parvicella foams the most challenging problem facing their wastewater treatment plant. As filamentous organisms develop in an existing ecological niche and are hard to bring under control.
The foaming is caused by extracellular materials produced by the microbes. Unlike many extracellular polymers, the nocardia EPS has a hydrophobic component. When aerated, the hydrophobic polymers create a foam containing EPS, Nocardia organisms, water, and insoluble fatty acids/grease/oils. Nocardia forms are actually interesting bacteria with excellent metabolic capabilities with respect to grease degradation. Unfortunately their tendency to foams makes them unsuitable for aerated basins. As it is not normal surfactant or biological foam, anti-foams have limited effect on the Nocardia foam. Control is most often done using hypochlorite/water spray directly on the foam. Some operators have reported using flocculant & antifoam have helped reduce the scum problem.
Back in the 1990s, a few companies studied filament control using specialized surfactants & enzymes to disrupt the filament EPS and sheath. It was effective on several common filament types, but remained in limited use due to the low cost and widespread availability of hypochlorite as the primary control option.
Instead of trying to make a product that covers all filaments, I have begun studying the potential of an enzyme blend with appropriate dispersants to directly "attack" the Nocardia EPS. Using the enzyme blend with existing sprayers, the stable foam will be disrupted and normal secondary clarifier wasting will help bring the excessive Nocardia population under control.
I'd like to test the various enzyme blends on the widest range of Nocardia foams. So if any of your have an ongoing problem with Nocardia foam, I'd like a sample. Just contact me an we can make arrangements for the Aster Bio lab to study and run the samples. Any help you can give here is much appreciated and will possibly turn into a new cost effective way to quickly bring Nocardia foam under control.
I often get questions regarding aeration basin foam that tends to carryover into secondary clarifiers. Below is a quick guide for determining foam cause by appearance.
With many waterways experiencing problems with algae blooms - including toxin producing cyanobacteria -more wastewater treatment plants have received more stringent nutrient discharge permits. While nitrogen in the form of ammonia and nitrite have long been regulated, facilities are now being required in many areas to bring effluent phosphate below 1 mg/L.
Effluent phosphorus comes in two main forms, soluble and particulate. The particulate form is bound in the MLSS and can be removed by improving solids separation. Improving solids removal should be the first strategy in meeting effluent phosphorus permits. Often we also have to remove a soluble phosphorus from the effluent which is more difficult.
Biological Phosphorus Removal
In biological phosphorus removal, conditions promoting the growth of phosphorus-accumulating organisms (PAO) must be maintained. The PAOs are facultative anaerobic bacteria that store energy in the form of polyphosphate granules (inside cells). The stored energy powers uptake of volatile fatty acids (VFA) - usually acetic, propionic, & butyric under anaerobic conditions. The uptake of VFAs ends up releasing phosphate into the surrounding water. Once in an aerobic environment, the PAO organisms use the stored VFAs for energy and uptake the free phosphorus in the water and store it as polyphosphate inside the cells.
PAO organisms do not develop unless their ecological niche exists in the system. So a normal aerobic system will not have an abundance of PAO in the biomass - since conditions exploited by their unique metabolism are not present. What are the required conditions to favor PAO growth:
Using alum, ferric salts, or even lime for chemical precipitation is the oldest method for reducing soluble phosphorus in effluents. Today we usually use alum or ferric salts since they function better at the near neutral pH seen in wastewater treatment units. Coagulants can be added at any stage in the waste treatment unit to bind with phosphorus. However, the most common area is to use the coagulants in the secondary or tertiary clarifiers. This avoids removing the phosphorus needed for biological treatment in the biological unit. It also reduces coagulant dosage when compared to dosing at the primary clarifier where other competing materials bind with the coagulants.
The major downside to chemical precipitation is the increased volumes of sludge and metal salts in the sludge.
Another option for phosphorus removal, that most mimics natural processes, is to construct wetlands that act as a biofilter to remove trace organics, nutrients, and solids before final discharge. Constructed wetlands should be a first choice option in areas with large amounts of land as they have fewer energy, chemical or labor requirements demanded by either advance biological systems or chemical treatment. In many cases, the wetlands can be a natural area or park that benefits wildlife and local residents. Most of the phosphorus removal in constructed wetlands is accomplished through plant and uptake of the nutrients.
With new permits requiring the removal of more nitrate/nitrite and phosphorus, wastewater treatment systems are becoming more complex with anaerobic/ass erobic/anoxic zones that frequently require separate reactors. The footprint and operational challenges have become larger than seen with conventional activated sludge treatment of 30 years ago.
Among the new trends in advanced wastewater treatment, Aerobic Granule Sequencing Batch Reactors claim to simultaneously oxidize organics, oxidize ammonia, reduce nitrate/nitrite, and remove soluble phosphate. All while not requiring secondary clarifiers to settling biological solids. What is this new technology? What are its advantages? What are the disadvantages?
First the technology
In the southern US we have had a fairly mild winter with a lot of temperature fluctuation. Low temperatures have a big impact on biomass activity in lagoons, constructed wetlands, stormwater, and long retention time systems. This post is going to be about the temperatures that I have found to be "inflection" points where the biological makeup in wastewater seems to change markedly and during the switch, tends to appeach stressed (high turbidity, more bulking, lower COD removal).
As most wastewater systems run using mesophilic organisms - we have a normal temperature range from 10 - 40 deg C (according to the text books). However, we can further break this down into groups based on narrower temperature ranges. For example, Pseudomonas fluorescens - a very nice wastewater organism with excellent metabolic capabilities - thrives from 5 - 32 Deg C. So in colder weather, P. fluorescens and other lower temperature mesophiles increase as a percentage of the population. The same drift in populations is seen at higher temperatures as we see increased predominance of high temperature microbes as we go above 37 Deg C.
Knowing that mesophiles can be further divided into low, medium, and high temperature groups, we need to look at where temperature growth pressures do not clearly favor any group and tend to cause upsets as the biomass adjusts.
In lagoons we often see stress as we drop below somewhere between 15 - 20 Deg C. Even many activated sludge units experience high turbidity in this temperature range. As the cold temperature group of mesophiles increase in population, turbidity drops and the biomass reaches a new equilibrium. Below 5 - 10 Deg C, we experience another fluctuation as true psychrophiles start to establish in the biomass.
On the high end, as temperatures go above 37 - 42 Deg C we see another change in biomass dynamics favoring higher temperature mesophiles. Above 45 Deg C, the changes and stress become very apparent with many systems not functioning to needed efficiency and more thermophilic strains start to appear.
Again, my values are based on observation of municipal and industrial wastewater systems. Each system has its own range where the combination of setup, retention times, influent makeup, and operational parameters dictate the temperature fluctuation points.
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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