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Filamentous Identification

"the Easy Way"

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How Important are Nutrient Supplements to Wastewater Treatment Operations?

Within a biological (Secondary) wastewater treatment system, heterotrophic bacteria (bacteria which utilize/degrade carbon molecules as a food substrate, i.e.; BOD) require a number of nutrients in their diet to maintain growth and reproduction.

Obviously, Nitrogen and Phosphorus are extremely important to the bacteria. Nitrogen composes up to 10.8% of the total dry weight and Phosphorus is 2.15% of the inorganic content. While many municipal plants and refineries have an abundance of nitrogen in the influent water, many plants are deficient in nutrients.

Did you know that nutrients could contribute to as much as 17% to the budget of a wastewater treatment plant? Ok, that seems very large, so how do you go about optimizing something that is going to cost you a significant amount to your plant. In the second case, why not just skip it and do with less?

Major problems can occur at a wastewater treatment plant that is deficient in nutrients. Filamentous bacteria can grow, BOD removal can be limited, Solids handling can increase, TSS can increase or zoogleal bulking and sliming can occur. Lets look at the impact at each of these types of conditions.

Filamentous bacteria can grow when nutrient conditions exist. While filaments are very good BOD removers, and TSS will probably be the lowest the plant has ever had due to the filtering effects created by the net of filaments, sludge volume will significantly increase. Filaments can take up as much as 3-5 times as much space as the normal floc forming bacteria. Think in terms of sludge dewatering and hauling. What does that mean to your budget? Solids handling can be up to 50% of your budget costs, this may include polymers, solids handling fees, landfill or land-farming charges for solids generated. Now, increase what you are spending right now by 3-5 times, and all of a sudden, the 17% cost does not seem quite so high!!

Here is a system with filamentous bulking, and after treatment with sodium hypochlorite. You can physically see the difference in solids.

What happens if you are nutrient deficient to BOD? Floc formers need nutrients in order to grow and multiply. They consume the BOD as a food source. If they are sluggish and not growing as well, BOD removal is slowed down. If you are on a tight permit and have strict BOD limits, you cannot afford to violate on a permit. One violation can sometimes be anywhere from $10-20,000 per day or more! Now, all of a sudden that 17% yearly cost does not seem quite so high.

TSS- how can low nutrient levels cause TSS problems? Many lagoon systems or some activated sludge systems, especially in papermills can grow Tetrads. These form very small clusters of 2-4 cells that do not settle and can cause serious TSS problems. We have seen one papermill spend $750,000.00 on polymers in one lagoon for one incident to settle the TSS generated, when in fact, the low cost of just adding nitrogen would have alleviated the problems. Thinking twice now about how important nutrients are?

Zoogleal bulking or sliming- how can that be such a big deal? When simple sugars or carbon compounds come through a system, such as a food plant and there are limited nutrients, zoolgeal bacteria will thrive. They can take over an entire system and cause serious sliming. We had one juice plant that spent a fortune on vac trucks to come in and suck out the slime. When we heard about the problem, we recommended to the plant to significantly add nitrogen to the system. They were discharging to a POTW anyhow, so if they slightly overdosed, it would not be that big of a problem. He cleared up the slime in the clarifiers and sludge tanks in less than a day! The cost of nutrients vs. sliming problems was insignificant!

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 organic acids are present or high instant BOD swings come through, but add the stress of nutrient deficiency and/or septicity 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.

Nutrients levels and BOD Loading needs to be closely monitored to optimize and control any system. Nutrient deficiency can cause excessive growth of filaments. It also can cause development of poor floc structures that either generate high levels of slime that are hard to dewater and increase polymer consumption but also can cause small, poor floc development and increase the level of TSS. High polysaccharide coating produced by the bacteria, zoogleal growth and filaments can cause sliming in the process side if allowed to carry through into the plant.

Some plants tend to slug feed nutrients or to set their feed point at one level. Although the books recommend that if you have 1-2 ppm levels in the final effluent, your plant still can be nutrient deficient if you tend to get high swings of BOD loading. Imagine if I gave you 5 hamburgers for breakfast and nothing the rest of the day. You would be hungry by nighttime. Think about this, most of the bacteria in your system have a life span of 20 minutes to 2 hours. What good is it to them if the food comes in at one time, and the nutrients at a different time. They still are short when they need them. Adjusting your nutrients is critical if you tend to have serious swings in BOD loading to your plant daily. What is serious? To bacteria, any time to make a change of more than 10% it is serious!!!!!

This plant did not have too many problems running, but the SVI's were a bit high and they did spend a bit on polymer to dewater sludge. Solids handling were limited during the winter, due to the fact that land application of the sludge was required.

We walked through the plant, made suggestions on solids levels in the clarifiers. We looked under the microscope. They had a ton of filaments, Type 021N. We looked at their plant data. They did not add sufficient Nitrogen to the plant. They would get slugs of high BOD influent periodically. We recommended that they increase daily supplements of Nitrogen and when spills came through, "spill some nutrients also"!! The biggest problem people have with nutrients is dosing and trying to be conservative.

This plant did what we recommended though. The biggest benefit was the settling to the clarifier in the cold months. The 1/2 hour SVI had over a 62% reduction from 740 ml in the settleometer down to 280! This made a difference in solids handling also! What a simple fix, just add nutrients

Nutrient Overdosing

Wastewater Biomass Analyses

Copyright ©2003 Environmental Leverage Inc. All rights reserved.
Revised: May 02, 2006.

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