Common Problems with Aerobic Wastewater Treatment Systems and How to Avoid Them


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When engineering, designing, installing, and running an aerobic wastewater treatment system for your industrial facility, issues most commonly arise during the engineer/design and operational phases. We break down some of the more frequently occurring mishaps during these two parts of the process below.

BOD- and COD-overloaded system

The problem

When aerobic wastewater treatment systems are designed, they’re set up to manage a limited amount of BOD and COD. When these limitations are exceeded, especially over prolonged periods of time, problems ensue—and this is one of the most common issues we see with these systems.

For example, let’s say you have an aerobic wastewater treatment system that is designed to process 1,000 kilograms of BOD per day, but this limit is consistently exceeded. You’ll have BOD breaking through into the facility’s effluent, which could create a situation in which the facility is noncompliant with its discharge and sewer permits. It will reduce the dissolved oxygen in the system and create an anoxic atmosphere, which can cause odors and an overflow of biosolids.

How to avoid it

The main way to avoid this issue is to ensure the water treatment plant operators and managers thoroughly understand the design capacity and the limitations of the system. For example, if the plant is expanding and adding new production lines, it’s more than likely there will be additional volumes of wastewater created and extra pollutants in that waste. When an aerobic wastewater treatment plant has a fixed limit on its capacity and the design hasn’t been adapted for growth, the facility might need to reduce the amount of wastewater and pollutants by implementing resource recovery and reuse programs.

In short, you should always have contingency plans for the wastewater management side of a facility’s growth and expansion, otherwise the facility will have to expand the wastewater treatment plant itself—and that means either retrofitting the existing plant or upgrading it with additional capacity by adding aeration equipment. You could also ship out the excess water and dispose of it by other means, but this option can be on the pricier end. For this reason, it’s always best to consult with your wastewater treatment expertsprior to the expansion, and possibly at the design stages, to ensure the wastewater treatment system can handle the changes.

Operator error

The problem

Another issue with aerobic wastewater treatment systems we often see is operator error. This can happen when there aren’t enough resources for operators and management of the water treatment plant, or maybe there are but the facility is experiencing frequent turnover at the operational level, and the newer, younger operators haven’t been trained by the system providers directly—the ones who designed and know how to operate the system in and out. They need to understand how to measure COD, nitrogen, phosphorous, dissolved oxygen, etc. Are they capturing the correct flow rates? pH? TSS? Are they gathering the necessary data, and do they know what to do with it? Are they covering all the system trends? Is the facility in compliance or trending towards an out-of-compliance scenario? If the operators are not in control of the system, they need to understand how to collect the relevant samples and do the analytical work necessary to regain this control.

How to avoid it

It’s important to work closely with your system providers and designers to ensure they can consult your operators and assist in any initial and ongoing wastewater treatment operation training. For example, daily operational procedures and statistical process control, which will allow the operators to make sure your facility is getting the most out of its wastewater treatment plant.

Poor sludge management

The problem

With any aerobic wastewater treatment, proper sludge management is key when it comes to avoiding unnecessary costs and pricey noncompliance fees. All these systems will produce sludge and some sort of biomass. When bacteria clean pollutants from your industrial waste, they grow and degrade and remove the pollutants while producing this biomass or sludge. If there is too much sludge being formed and not enough being removed, it builds up in the system, which means you’ll have excess solids going in your effluent, creating foul odors and septic conditions and putting your effluent out of compliance, unless you routinely waste, dewater, and discharge it.

How to avoid it

The key to properly managing your sludge waste is to understand your sludge balance and always have a well-conceived procedure for managing your sludge. This will help you put in place effective procedures for wasting and clarifying it, and operators will know how to implement these procedures as they track and dispose of it cost-effectively. In a well-balanced system, the solids will settle by gravity and be separated out at the bottom of the clarifier, and the clean, clarified effluent water goes out the top of the clarifier. If you have too many solids being generated and they’re going everywhere, you could consider upgrading that activated sludge plant with MBBR media where the bacteria colonize onto the surface of the media and it’s being retained in the aeration basin. In this case, much less sludge is produced. You can also add a membrane and make your aerobic suspended growth system into a membrane bioreactor, and that would be much easier to separate the solids than clarification and you can recycle those solids or you can waste those solids in a much more controlled way.

Aeration system design outgrows itself over time

The problem

Say your aeration system is designed, constructed, and is operating for five to 10 years without any maintenance or service. You might have minor maintenance along the way, like changing the oil in your car, but over time, problems can occur in your aerobic wastewater treatment plant if your system is not generating the same amount of air. Your dissolved oxygen levels might be dropping lower and lower, this indicates your blower output might not be where it needs to be. Are you getting the cubic feet per minute of air that you’re supposed to? Is the pressure too high in the pipes or manifolds in the distribution arms of that aerations system? Is the pressure building up and getting higher and higher so that the blower output is getting lower and lower? Are there leaks in the pipes or manifolds? Maybe it’s a big leak, maybe a valve is open or there is a crack in the line somewhere. If your aeration system isn’t getting enough oxygen into the water, you need to go through the diagnostic process to understand how to fix it.

How to avoid it

A simple inspection by the maintenance personnel or management team could be enough to fix and avoid the issue, but the facility might need to hire an engineering firm to do an audit and evaluate a more thorough engineered solution to the problem. The facility might need a system upgrade or additional equipment. Also keep in mind that when the system is designed, the engineers should provide a set of manuals and standard operational procedures. There is a lot that goes into equipping the facility to operate and maintain an aerobic wastewater treatment system, and the engineering and design providers should do their best to prepare and educate the client to operate the system according to design.

Can SAMCO help?

SAMCO has over 40 years’ experience custom-designing and manufacturing biological wastewater treatment systems, so please feel free to reach out to us with your questions.

Our biological treatment solutions—including FBBR, MBR, MBBR, and activated sludge solutions, among others—can help your facility:

  • decrease its footprint, chemical use, and energy consumption 
  • produce high-quality effluent
  • recycle organically contaminated water
  • manage high levels of BOD and difficult-to-treat wastewaters

For more information or to get in touch, contact us here. You can also visit our website to set up a call with an engineer or request a quote. We can walk you through the steps for developing the proper solution and realistic cost for your biological wastewater treatment system needs.

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