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

There are several different types of anaerobic wastewater treatment technologies, but some commonly used include lagoons; anaerobic digestors like UASBs (upflow anaerobic sludge blankets) and EGSBs (expanded granular sludge beds); and packed bed anaerobic filters. They tend to exhibit the same common anaerobic bacteria-managing issues.
Below, we break down what these issues are including ways to avoid them so your anaerobic wastewater treatment can continue to work optimally for your industrial facility.
Oxygen exposure
The problem
Anaerobic wastewater treatment systems typically have several different groups of bacteria working together synergistically, and two of the groups are what we call facultative (they can grow anaerobically, or they can grow aerobically). Oxygen doesn’t kill these facultative types, but other bacteria necessary in these anaerobic digestion systems are called methanogens. They make biogas in the form of methane and are very strict anaerobes—so they are killed immediately by oxygen. If the methanogenic population is lost, the entire system is, too. Furthermore, since they are slow growers, it’s difficult to get their population back up again.
The solution
Because the startup of the systems can take months, it’s extremely important to protect the systems from oxygen. This is one of the fundamental differences with anaerobic wastewater treatment systems compared to the normal aerobic system—you have to keep oxygen out to protect the methanogenic population. To accomplish this, you need to invest in well-trained, educated professionals to operate these systems and incentivize them to continue with ongoing education and training. We recommend your plan for continuing education includes conferences and memberships with professional organizations that have deliberate training workshops for this type of operation. It’s also a good idea to keep a good rapport with your system supplier in case you need future new-hire employees to step up and be trained to run these highly volatile systems. Whatever your facility can do to keep on top of their training and know-how is worth the health of your anaerobic wastewater treatment system in the long run.
Equalization issues
The problem
Anaerobic wastewater treatment systems can be unstable. They don’t handle variation well in general, and they tend to get overloaded which can wash out the bacteria and force to you start the system from scratch again, which, as mentioned prior, can take months. In short, you don’t want to upset these systems . . . you want to keep them stable and consistent. For example, if your facility’s production rates vary periodically, it puts the methanogenic population at risk.
The solution
You need to adjust for the daily variations, and in order to do this well, you need a large enough equalization measure being taken in front of these digesters. For example, a holding pond, lagoon, or million-gallon tanks where you can normalize and balance out the daily fluctuations. This helps create a normalized, steady, continuous flow to the anaerobic system. If there is trouble with overloading or setting up the system, this might indicate the need to expand the system’s equalization measures or adjust manufacturing schedules.
Temperature
The problem
Anaerobic systems are not always ideal for colder regions. Since the bacteria have long growth rates of methanogens that symbiotically intermix with different bacteria populations, they just don’t do well where it’s cold. It can be a difficult situation because the bacteria take so long to proliferate to begin with. Then, when it’s cold, they take even longer—but when you take into consideration that every 1°F you lose, 10% of your anaerobic bacteria will go along with it, you can see why maintaining these temperatures are so important.
The solution
Anaerobes really like warm water, so the ideal temperature range would be 95°F to 100°F. Ambient water temperatures at industrial facilities typically range from 60°F to 85°F, so many need to heat these systems, and when you’re dealing with a half million or millions gallons of water a day, that can take up a lot of energy. If your facility is located in a colder climate, for example New York as opposed to California, your options are to heat the water all winter or shut down until spring.
Some facilities will take the biogas naturally released by the anaerobes and burn it in a boiler, creating steam. This steam then passes through to a heat exchanger that has the wastewater coming through one side and the steam coming in the other side and it heats the water efficiently to 95°F. This does add a level of complication to the overall system. Capturing and burning the biogas and ensuring you have the equipment to effectively maintain the required temperature all take skilled, professional maintenance.
pH
The problem
Another important operational parameter to maintain is pH. Bacteria can generally handle between 6.0 and 8.0 pH, but ideally you want to keep the system between 6.3 and 7.8. If the pH gets up to 8.5, ammonia, which is always present when you have a lot of manure and urine in a municipal plant or solids from a rendering or meat packing facility or slaughterhouse, will accumulate. When the pH gets above 8.0, and especially above 8.5, that ammonia becomes very toxic to the methanogens and they’ll be wiped out quickly.
The solution
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A possible solution could be just recycling your treated effluent to dilute the effluent coming in and mix it up a little bit more thoroughly. This might help the pH drop down and stay in the 6.3 to 7.8 range and prevent that ammonia toxicity. If recycling your treated effluent doesn’t solve the problem, then you need to install a pH control loop that can pump in acid. Just keep in mind you don’t ever want to use sulfate in anaerobic systems. A better option is usually phosphoric, hydrochloric acid, or even CO2.
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Hydrogen sulfide
The problem
As prior mentioned, you never want to add sulfate into anaerobic systems because along with the methanogens who make the methane, there is a different anaerobic population that reduce sulfate to hydrogen sulfide—and if you have methanogens producing methane and sulfate-reducing bacteria (called SRBs) creating sulfide, now you have sulfide in the gas along with your methane. This creates a very odorous, toxic, and corrosive hydrogen sulfide, which is that rotten egg odor. If your facility begins producing hydrogen sulfide en mass, this can be a big issue.
The solution
This needs to be prevented by eliminating sulfate in the wastewater going in, or, if this isn’t possible, then you need to capture the gas and control it so it can be treated and removed appropriately. It’s yet another issue that needs maintenance—and it will cost you—yet, if the issue is ignored, it will cause greater problems. This is ideally addressed during the design stage of the system it can be implemented on an operational level.

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