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

Biological wastewater treatment systems can be a big investment for your facility. When implemented correctly, these systems will provide your process with a long list of benefits, but there can be some challenges with purchasing these systems, too.

If your facility is considering biological wastewater treatment, you might be wondering if there are common problems with these systems and the best ways to avoid them.

In general, when engineering, designing, installing, and running a biological 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.

Common engineering and design issues

Most problems with biological wastewater treatment systems occur at the engineering and design stages. When studies aren’t completed for long enough periods of time over vast-enough amounts of data, it’s common for a system to fall short in some way. Here are some of the engineering and design stage issues we see the most.

Choosing inappropriate treatment technologies

Sometimes chemical solutions might be a better selection for the application rather than biological. We see this a lot when harmful components of the wastewater intoxicate the bacteria or if there is a very low degradable but high nonbiodegradable organic content. In these cases, chemical oxidation is usually the preferred treatment option versus biological.

It’s important for your water treatment specialists to look at the ratio of BOD to COD to ensure the waste is, in fact, biodegradable and there is not much toxicity. Dairy products, cheese, and whey, etc., produce highly biodegradable waste, in which biological treatment technologies are a good fit. But when BOD to COD ratios are low, this indicates there are a lot of organics present that aren’t biodegradable and that physical/chemical technologies might be a better choice.

Gathering inaccurate waste stream data

True of any treatment system design, it’s important to gather as much information about your waste stream as possible at the very beginning of the engineering process. Do you have the right flow rates? How are you sure they’re accurate? Flow rates in food processing and dairy facilities, among others, go up and down from day to day and change over time. Often, we see these facilities spend two or three days keeping track of their wastewater data when they might need a thorough, two-week study instead. This ensures the system designers and engineers not only know the average rates but are certain of the maximums and minimums over time.

What about the chemistry and chemical makeup of the water? Is there a good level of data about your normal average concentration of BOD, COD, sugar, fats, oils, solids, pH, temperature, and salinity? Is there a strong understanding of the chemistry of the water?

This is the essential information that will be factored into your system’s design, and with biological wastewater treatment, you don’t just need a good design basis, but you’ll also need to know the necessary pretreatment measures for the water. Pretreatment could be as simple as equalization or solids removal, but you’ll often need pH and temperature control capabilities, too.

If these steps aren’t designed correctly according to your facility’s true parameters, you will likely see an increase of operational problems with your plant after implementing the new system.   

Improper aeration capabilities

When designing an effective biological water treatment system, it’s important to not over or under aerate the water. For example, if the system is anaerobic or anoxic (where no oxygen is used), the design must enable your facility to create that anoxic, oxygen-free environment or the anaerobic reducing environment for the proper bacteria to grow.

When the system is under aerated, itruns out of oxygen, and the first thing you’re going to notice is foul odors. If you over aerate the system, it won’t create any operational issues, per se, but you’ll be running rotary aeration equipment unnecessarily, which will consume more electricity than you need and inflate costs. For a facility that processes a million gallons of waste per day, it would be easy to accrue hundreds of thousands of dollars in excess operating cost per year because the aeration is overdesigned.

Getting the correct pH

If the pH component of your system isn’t designed correctly, bacteria stop growing, which means they won’t remove the necessary pollutants quickly enough and you’ll have those pollutants breaking through the system and going out in the effluent. This means you won’t meet your effluent limits and could encounter surcharges or fines. You may even have your plant shut down if you’re discharging to a creek or a river, and you have excess pollutants in your effluent because you’re not controlling the pH.

How to avoid these common engineering and design issues

These issues can have a big impact on your biological wastewater treatment system, so how do you avoid them?

We recommend these three steps:

1. Wastewater characterization study: By pulling samples and sending them to the laboratory, you’re making sure the proper parameters are analyzed that are necessary for developing the design. To do this, repeatedly measure flow throughout the day along all the major shifts of the plant—and do that for several days to cover all the variations. Then pull a report together, and from that data, your water treatment experts will form the basis of the system’s technology and configuration choices.

2. Laboratory study: A proper laboratory or wastewater treatability study can take anywhere from three to five weeks, but this step is extremely important. It will illustrate whether there is toxicity; how much of the BOD will need to be taken out; if bacteria can be used to treat the water all the way to the discharge limits or, if it can’t be treated all the way, what steps are needed afterward (posttreatment technologies) to get to the discharge limits. These studies are extremely helpful for avoiding design problems when you grow biological organisms in the wastewater. It will help your facility design the pH, understand the source of any odors, know if there’s a need for extra nutrients and chemical dosing of nitrogen or phosphorous, and everything else about bacterial growth on the wastewater pollutants.

3. Pilot study: If, after the wastewater characterization and laboratory studies are complete and it’s decided you’re working with an extremely complex waste with lots of variation, you may need to run a pilot plant study at the facility for anywhere from two to five months. This will put the biological technology, pretreatment, posttreatment, aeration, pH control, temperature control, nutrient dosing, etc., into practice. By running a slipstream into a small pilot at the flows and loading rates that duplicate the full-scale commercial design, all the variation from day to day can be properly analyzed. This step not only demonstrates how the technology will work, it also generates engineering data, which will help your water treatment engineers design the optimal system for the biological water treatment. With a successful pilot plant study, your system-design engineers should be able to guarantee the full-scale commercial system that will be the best fit for your waste stream.

Common plant operations issues

Although most problems with biological wastewater treatment systems typically occur in the design and engineering phases, some also occur during the operation of the system.

Let’s say the design, construction, and installation of the system is complete. It’s built and ready to be started up. In order to facilitate a successful implementation at the plant, there needs to be a dedicated team of operators available for training. The engineers who designed the system should provide an operation manual, and some will even include very specific, detailed SOPs which are written so the operators how to make up the nutrient solution. They should have some type of skills to operate the engineered system as they will need to learn about growing and maintaining living organisms, and if the necessary life support chemistry isn’t followed, the bacteria will die.

The systems can’t be overloaded and exceed the capacity with either the volume of water or the load of BOD/COD of the pollutant that the system is designed to remove without having problems with the effluent. So it’s important to have operational procedures with contingencies in place to always keep your wastewater treatment plant up and running at specification within limits in order to discharge.

They’ll also need to maintain the biological system by collecting daily, weekly, and monthly samples and doing the analytical work and maintaining them in a spreadsheet database so loss of performance can be detected.

It’s also important to maintain a relationship with your water treatment specialists and system manufacturer because they designed your system and will be the best consultant for solving problems before they occur.  

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.