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Here is a scenario we come across occasionally in industrial facilities. Many industrial plants have to add N and P for the carbonaceous bacteria to consume as a nutrient source because there are insufficient levels in the process water. Some times plants overdose the nitrogen feed. They do not see residuals in the final effluent, so they continue to increase the ammonia levels. They keep adding more and more each day. They end up getting into a bad cycle and pretty soon, they can never see any in the final effluent and start to panic. Overdoses are often common in this scenario. Typical dosing of nitrogen many times for a rule of thumb has been suggested that dosing of nutrients is controlled so that there is a residual of 1-2 ppm in the final effluent. Part of the reason this rule of thumb guide is used is because final effluent residuals almost always have to be tested for permit levels. This saves on additional testing of influent parameters and the numbers are easily available.
Another thing we see quite often at papermills or chemical plants that indicates this type of condition exists is the presence of bristleworms. These little pink worms almost always indicate an overabundance of nitrates. Unless you have nitrates in your influent, you should not see these organisms growing in your plant. If you do, it means again, you are overdosing nitrogen, have purposely caused the development of a nitrification population and are wasting money. Cut back on your nitrogen dosing. How do you figure out if you are overdosing? One simple test to run is nitrates on the influent and effluent. If you do not have nitrates in the incoming process water, you should have no change in the effluent levels. If you have a large increase and it changes daily based upon your nitrogen feed, you are overdosing ammonia and have created unnecessary nitrification in your system.
You are then feeding the bacteria the correct amount of nutrients instead of overdosing them and wasting a ton of money. Another typical mistake plants make with nutrients is the time they dose. Some plants slug feed or use a continuous feed rate. You really need to feed nutrients based upon the influent loading. If you plant runs 24/7 and has continual consistent feed, a slow, continuous feed of nutrients is recommended. If, on the other hand, your plant runs only shifts, or tends to have batch dumps of high loadings, you need to slug feed your nutrients again based upon your feed loading. A typical loading of nutrients is 100-5-1 of Carbon, to nitrogen to phosphorus in order for optimal bacterial growth. During wide swing loads, nutrients should be increased. Nutrient deficiency can cause serious problems. It is already harder for the floc forming bacteria to work when high organic instant BOD swings come through, but add the stress of nutrient deficiency and this increases the problems. This creates a climate that is difficult for the floc forming biomass to grow in, but enables filamentous bacteria to take over.
Think of it this way, If I gave you 5 hamburgers for breakfast, but nothing for lunch or dinner, you would be hungry by nighttime. Why, you had tons of food? It is the same with the bacteria. Think of this, many of the bacteria in the wastewater treatment plant have a life span of 20 minutes to 2 hours. If they are in the late shift, they never saw the nutrients that were loaded earlier. Check your nutrients Base loading on influent Adjust feed rate based upon influent loading If necessary, test nitrates at back end a few times to get a baseline and determine if overdosing. Most importantly, make sure the bacteria are getting the right amount of nutrients at the right time. Too much and you are wasting money and running the plant inefficiently, too little and you can get zooglea or filamentous bacteria problems and create worse problems! But I am doing that and it still is a problem? Have you taken into the calculation your supernatant off your digestor, belt press or sludge dewatering unit? Many plants have digestors and sludge dewatering units. The supernatant off these units is returned to the front of the plant. This stream is almost always high in N and P. Run tests on this stream. Make a calculation on how many nutrients you are returning to the front of the system, and make sure to take that portion out of your math calculation when you are figuring out front loading dosing of nutrients. This is often a very important source of nutrients that is overlooked at many plants. Optimization of a plant's costs can be significant if this variable is considered.You can always do a Nitrogen balance across your system.
Contact Environmental Leverage if you need help with troubleshooting your plant. How Important are Nutrient Supplements to Wastewater Treatment Operations?
What if you do not have a lab or microscope onsite that is capable of performing an analyses of your system? Find out how Environmental Leverage's lab can perform an analyses of your biomass in your system and make recommendation on how to improve your system.
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The
problem with this scenario is that sometimes, plants overdose (by the way, it is
very rare, usually many plants are often under dosed) nutrients and create an
excess in the system. By having an excess in the system, a nitrification
population starts to develop. As the plant adds more and more ammonia, the
nitrifiers will continue to consume the excess nutrients. They grow, they thrive
and they multiply. A large amount of money is spent on unnecessary nitrogen.
Sometimes nutrients can cost up to 17% of the budget at a wastewater treatment
plant. This is not a situation you want to get into. If you do not have to
nitrify, don't. It is an expensive process.
How
do you solve this problem? Actually quite easy. You need to start
feeding based upon front loading of carbon. There are now quick easy way to test
TOC onsite in two hours. If you have testing equipment for COD, you can easily
run TOC instead. This is a better measure of the total carbons that bacteria
will see as a food source. Hach makes test N tube reagents that make it easy to
run an onsite test for TOC. When you get the results, do the math calculation on
N loading. As long as you do not have final effluent permits that are extremely
low, typical loadings are 100-5-1 of Carbon-nitrogen to phosphorus.
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