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Equalization tanks or holding, equalization lagoons come in all sizes and shapes. They may be small or very large. They can be above ground storage tanks, large lagoons, or covered sunken tanks. The can have slow mixing, large aerators or nothing at all. They can have covers, or be open to the air. What your equipment is like is not the main issue, the real issues are what
are you trying to accomplish with the Equalization and how well you are doing
it.
While Equalization is a good thing, sometimes too much is not better. Many plants figure out that if a little is good, more is better. If you have just created a wide spot in the pipe, and are letting solids build up in the bottom of the holding tank, you can cause more problems than help. Solids building up can cause septicity, growth of filaments, organic acids, gassing and sometimes even H2S generation. This can mean safety issues, excess electricity costs, excess polymer or chemical consumption and excess solids handling costs.
Visually inspect your tanks for gassing and ashing on the surface of the water.
Settling of solids and debris in Equalization tanks or ponds cause a significant impact on oxygen demand in the biological system, not to mention odor control problems onsite. Generation of septicity, organic acids create a higher demand when introduced into the aeration basins or lagoons.
Solids can build up in any tank where this in insufficient mixing to keep the particles suspended. When you finally take the tank down, you can see the solids that were resting on the bottom of the tank. These solids will go anaerobic, cause gassing and ashing or the growth of filaments.
Equalization tanks are not sterile. There will be some biological activity. If you are holding influent anywhere for more than one to two hours, you will get changes in consistency in the oxygen levels, septicity if there is no oxygen and in biological activity. This in turn can cause the growth of filaments, odor problems and oxygen scavenging problems on the aeration basin when septic influent is introduced into the basins.
No, this is not the hot springs at Old Faithful, but this Equalization tank was bubbling enough to simulate it, with sulfur gasses coming off. H2S gases are not only problems for odor control, but can become a safety issue also.
Gas bubbles are easy to see on the surface, and instantly tell you facultative or anaerobic activity is going on in the holding tank, lagoons or EQ basins. How much and how often will tell you the depth of activity. More activity will occur with warmer temperatures than colder ones, due to the activity of the bacteria slowing down with colder temperatures.
Floating solids and debris usually indicate the presence of activity also. Why does this matter? If you have designed your plant for X amount of BOD loading with 1.5X amount of lbs of O2 to handle the incoming BOD, you have just shortchanged your bacteria of oxygen. It may be 5-25% of your oxygen demand is due to septicity, depending upon your flow and just how septic you have loaded your plant.
Electricity for the extra oxygen needed is costly, filaments cause tons of problems cause increases in chemicals and solids dewatering, odor controls can cause serious problems with neighbors or even worse, safety issues. Municipalities as opposed to industrial facilities usually have Wetwells prior to their primaries. Again, same concept as Equalization tanks. We have seen some that are very large, and have a holding time of up to 24 hours. Grease and floating solids build up down there. Gassing occurs, septicity builds up and this can impact the primary clarifier as well as the aeration basins. How do you optimize these? Some plants just add a small mixer, some use bioaugmentation products in addition, and some have used venturi injectors in lines to add additional oxygen to EQ's or wetwells.
I do not have Sulfur compounds in my industrial influent so what is causing septicity? Septicity is the condition in which organic matter decomposes to form foul-smelling products associated with the absence of free oxygen. If severe, the wastewater turns black, gives off foul-odors, contains little or no dissolved oxygen and creates a heavy oxygen demand. Sulfides, sulfates, H2S, mercaptans, amines, indoles, skatoles, or organic acids that are formed during the breakdown of organics can all contribute to septicity. Hydrogen sulfide (H2S) is the most commonly known and prevalent odorerous gas associated with wastewater treatment systems. It is toxic and corrosive to metals and has a disagreeable rotten egg odor. For a 0.6-m ( 24-in) force main carrying wastewater with 300mgl BOD, if the velocity is 1 m/s and temperature is equal to 68° F, sulfides d up to 0.5 mg/l can be generate in only 2200 ft! Waste septicity can be treated by pre-aeration, by chemical oxidation (chlorine, hydrogen peroxide or potassium permanganate), by chemical precipitation (ferric chloride), or use of sodium nitrate in the collection system as an "alternate oxygen source".
Where do you find sulfur atoms:
Hydrogen sulfide can be oxidized to elemental sulfur: H2S + 1/2 O2 -----> So + H2O + energy Elemental sulfur in turn can be oxidized to sulfate: So + 1 1/2 O2 + H2O ---> SO42- + 2 H+ + energy Desulfuration of decaying organic material releases hydrogen sulfide Sulfate reducers can generate hydrogen sulfide; How does septicity impact the wastewater treatment plant?
Oxygen demand in wastewater treatment plants
DO in lagoon systems is impacted by even more variables
Now add temperature, depth, bubble size, pressure, alpha- factors, fouling, and you wonder why you have problems getting enough air into the water to satisfy all the demands. Numerous factors are related to how much actual oxygen transfer you are getting in your system The cheapest and most efficient aeration method is usually fine bubble aeration. BUT, there are lots of things that go into that. There are two big questions that must be answered first. The overall efficiency is based on a number of factors, bubble size, temp, pressure, etc. But it is these two other factors that really dictate results. First, there is the alpha-factor. This is the ratio of O2 transfer in dirty water compared to clean water. Most
transfer efficiencies for diffusers are typically given in clean water transfer
rates, but to really get the O2 into the water, it must go from the bubble into
the dirty water. The water has not only pollutants from the influent, but large
amounts of return activated sludge. In industrial wastewaters, the alpha varies
tremendously. It has been seen it as high as about 0.8 and as low as 0.2, the
lower being usually related to surfactants. The second factor is the fouling
factor. Since the dissolved oxygen membranes rest on the bottom of the tank
surrounded by mixed liquor, biological growth and chemical precipitants deposit
around the holes as the material ages. Therefore, the longer the material is in
the water, the smaller the holes get, and the higher Horsepower required to pump
the air through the holes. Maybe it is worth it to see how well the EQ tanks or wetwells are doing!! I need to get rid of Grease in my lift Station Solid Grease build-up in my lift stations
Bioaugmentation Solutions for Lift stations, Wet Wells and Collection Systems
BIOCUBEs-Solid
block biological products that are specifically formulated and packaged for use
in lift stations and large restaurant grease traps to remove grease build-up and
help increase degradation capabilities. Lift Station Formulation-MicroClear 207 bacterial formulation is used for softening and degrading food type fat, oils and grease in lift stations but can also be used in any high grease environment. Restaurant formulation-This biological product is a high strength formulation developed to degrade fats oils and grease quickly. It can be used in restaurants, grease traps and drain fields where food based grease is a problem. Sewer formulation-This product is an improved biological product, specifically formulated and packaged for use in sewers to help degrade grease build-up and stop blockage.
Information Request Form
For Direct Ordering Contact information: or call our office at 630-906-9791 P.O. 's can be faxed to our office 630-906-9792 Copyright ©2003 Environmental Leverage Inc. All rights reserved.
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Many
plants, especially industrial facilities have large swings in influent loading.
That may be either from BOD loading, pH or even toxicity. The purpose of an
equalization holding area is to try to even out those swings before sending the
wastewater on to the Biological portion of the system. Anytime you make more
than a 10% change to the bacteria, that technically is major to them and can
cause upsets, i.e, equalization is a good thing.
