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How to maintain an IC Anaerobic Tank?

by micheal•

How to Maintain an IC Anaerobic Tank: A Practical Guide from Someone Who’s Supplied Them for Decades

If you’re reading this, chances are you either have an IC anaerobic tank in your wastewater treatment system, you’re thinking about installing one, or you’re just curious about how these workhorses keep industrial effluents clean. I’ve been in the wastewater equipment game for 18 years, and for the last 12, I’ve specialized in supplying IC anaerobic tanks—those towering, two-stage anaerobic systems that handle high-strength organic waste better than almost any other tech out there. Let me tell you: selling a top-tier IC tank is only half the job. The other half is making sure it runs for 15, 20, even 25 years without breaking a sweat. I’ve seen too many clients install a $200k tank, skip proper maintenance, and have it die in three years. That’s not just a waste of money—it’s a hit to their operations, their compliance, and their peace of mind. Today, I’m walking you through exactly how to maintain your IC anaerobic tank like a pro. No overly technical jargon, just real-world tips I’ve picked up from working with brewers, food processors, chemical manufacturers, and every other type of industrial facility that relies on these systems. IC Anaerobic Tank

First, let’s start with the basics: what makes an IC anaerobic tank different from other anaerobic systems, because that’s key to maintaining it right. IC stands for Internal Circulation, and the whole design hinges on that internal loop—biogas produced in the lower zone lifts mixed liquor and sends it up to the upper zone, where it separates, and the treated liquid exits, while the sludge recirculates back down to the lower zone. That internal flow is non-negotiable. If that loop breaks, your tank stops treating waste efficiently, you get sludge buildup, and performance plummets. So any maintenance plan starts with protecting that internal circulation system.

Let’s break maintenance down into daily, weekly, monthly, and annual tasks. That way, you can build a routine that doesn’t feel overwhelming. I learned early on that the best maintenance schedules are the ones people actually stick to—too many facilities try to do everything once a quarter and forget half the steps.

Daily Checks: The Non-Negotiables You Can’t Skip

Daily checks are 15 minutes of work that prevent 10 hours of headaches later. I tell every new client to assign one operator—rotate them if you have to—to do these checks first thing in the morning, before the shift rush. The first thing to look at is the biogas meter. IC tanks produce methane-rich biogas, and that meter should be consistent. If you see a 10%+ drop in daily biogas production, that’s a red flag. Biogas is a byproduct of the microbes breaking down organic matter, so less gas means less waste being treated. I once had a brewery client who missed a daily check for three days and came back to a tank producing 40% less gas—turns out their influent pipe got clogged with spent grain, cutting off food to the microbes.

Next, check the pressure gauges on the IC tank’s top and bottom zones. The bottom zone (where the hottest, most active microbes live) should have a slightly higher pressure than the top zone—usually 2 to 5 psi higher. If the bottom gauge is reading too low, that means the internal circulation loop isn’t working. Maybe there’s a blockage in the downcomer pipe, or the biogas separator isn’t functioning right. If the pressure difference is too high, that’s a sign of excessive sludge buildup or a gas pocket that’s trapped, which can throw off the whole system. I also tell clients to listen to the tank’s sound—through the access ports, you should hear a gentle bubbling, not gurgling or silence. Silence means no circulation; gurgling means a blockage that needs attention today, not next week.

One more daily task: test the influent pH. Anaerobic microbes, especially methanogens, hate pH swings. They operate best between 6.5 and 7.5. If your influent pH drops below 6 or goes above 8, that’s toxic to the microbes—they’ll die off within days, and your tank’s performance will tank fast. I’ve seen chemical plants accidentally dump a batch of caustic waste and have their IC tank go from 90% COD removal to 10% in 48 hours. Daily pH checks catch that before it becomes a disaster.

Weekly Tasks: Dive Deeper Without the Overhaul

Once a week, you’re going to do a bit more hands-on work. First, pull sludge samples from three points: the bottom of the tank, the mid-point, and the top of the sludge bed. Take them in clean plastic bottles, label them clearly with the date and location, and send them off to a wastewater lab for testing. The key things to look for are: total solids (TS) and volatile solids (VS). Healthy IC tanks have a VS content of 70% to 80% in the bottom sludge—VS is the organic part, which is what your microbes eat. If VS drops below 60%, that means your microbes are stressed or dying. Also, look for any signs of filamentous bacteria—long, stringy growths that make sludge float or form clumps. Filaments are a sign of overloading or nutrient imbalance, and they can mess with the internal circulation by clogging pipes.

Weekly, you should also clean the influent and effluent screens. These are the little mesh screens that keep large debris (like fruit pulp, plastic bits, food scraps) from entering the IC tank. Over a week, those screens get caked with gunk, which restricts flow. I once had a winery client who skipped weekly screen cleaning, and the debris built up so much that flow to the tank dropped by 60%—they had to shut down parts of their production line to clear it out. A quick rinse with a high-pressure hose (no more than 50 PSI, or you’ll tear the mesh) takes 10 minutes and saves you from a shutdown.

Also weekly, check the temperature of the tank. Most IC tanks are operated in mesophilic range (20°C to 40°C, or 68°F to 104°F) for general use, or thermophilic (45°C to 55°C, or 113°F to 131°F) for higher-temperature waste. Fluctuations of more than 2°C a day stress microbes—they can only adjust so fast. If you’re heating the tank (many facilities use biogas to heat it, which is a bonus), check your heating system’s efficiency and make sure the temperature sensor is calibrated.

Monthly Maintenance: Address Hidden Issues

Monthly is when you tackle the parts that you can’t see on a daily basis. First, inspect the internal circulation pump (if your IC tank has a pump-aided loop, though many IC tanks rely on biogas lift, some larger ones have pumps). Check for leaks, listen for unusual noises, and test its flow rate. If flow is lower than the manufacturer’s specs, that’s a sign of impeller wear or pipe scaling. Scaling is common if your wastewater has high mineral content—calcium, magnesium, or iron can build up on pipes and reduce flow. I’ve had a meat processing plant with hard water that had ¼-inch of scale in their internal pipes after six months—monthly flushing with a mild acid solution (we recommend citric acid, it’s safe for microbes and equipment) clears that up without damaging the tank.

Monthly, you should also check the gas piping and valves. Biogas is flammable, so this is not a task to skip. Look for any rust, cracks, or loose connections in the pipes. Test the pressure relief valve on the tank’s top—this is a critical safety feature, and if it’s stuck, excess pressure can damage the tank’s structure. Also, check the flame arrestor if you use biogas for energy—this prevents flashbacks, and it should be cleaned monthly to keep it working.

Another monthly task: adjust organic loading if needed. IC tanks are designed for high loading (up to 10 kg COD per m³ per day), but if your production changes—like you add a new product line or run a promotion that increases waste—you need to adjust influent flow or add nutrients. Microbes need nitrogen, phosphorus, and trace metals (iron, nickel, cobalt) to survive. If your waste is high in carbon (like sugar or starch waste), it might be low in nitrogen, and adding a small amount of urea or ammonia (10 to 15 mg/L) will keep your microbes healthy. I tell clients to keep a nutrient log, and monthly testing of influent nutrient levels ensures you’re not under-feeding your microbes.

Annual Overhaul: Keep the Tank Running for Decades

Every year, you need to do a more thorough check, even if the tank is running great. This is when you pull the access ports and inspect the internal components. First, check the sludge bed depth. The ideal sludge bed in an IC tank is 3 to 5 meters thick—any thicker than that, and you get compaction, dead zones where microbes don’t get food. If the sludge bed is too thick, you’ll need to waste some sludge. Don’t worry, wasting sludge is a normal part of maintenance—you don’t have to replace all the sludge, just the excess that’s at the bottom of the bed.

Annual cleaning of the gas separators is also key. Over a year, biogas byproducts (like hydrogen sulfide and moisture) can build up in the separators, reducing their efficiency. If separators aren’t working, biogas gets trapped in the sludge bed, which breaks the internal circulation. I once had a dairy client who skipped annual separator cleaning, and their internal circulation dropped by 50%—it took three days of manual cleaning to get back to full flow.

Also annually, test the effluent quality more thoroughly than monthly. Check for COD, BOD, total suspended solids (TSS), and ammonia levels. This gives you a baseline for the tank’s performance, so you can spot trends before they become problems. If COD removal drops below 80% (for mesophilic tanks), that’s a sign you need to adjust your maintenance routine.

Common Mistakes to Avoid (I’ve Seen Them All)

Over 12 years, I’ve seen the same mistakes over and over, and they’re easy to fix. First, don’t overfeed the tank. Many facilities think “more waste = more gas = better,” but IC tanks can only handle so much. Overloading causes acidification—volatile fatty acids (VFAs) build up, lowering pH, and killing methanogens. If your VFA levels are over 500 mg/L, that’s a sign of overloading. I always tell clients to add 20% more waste per month, not 100%, to let the microbes adjust.

Second, don’t ignore small leaks. A tiny leak in the influent pipe might seem trivial, but over time, it can introduce room-temperature water to the heated sludge bed, causing temperature swings and stressing microbes. Fix leaks as soon as you see them.

Third, don’t skip microbe “resting” periods. If your production slows down (like seasonal businesses—brewers slow in summer, food processors have holiday shutdowns), don’t shut the tank off completely. Reduce flow to 10% of normal, keep the temperature steady, and add a small amount of nutrients. If you shut it down for a month, when you start back up, you’ll have to seed it with new microbes, which is costly and time-consuming.

Why Proper Maintenance Makes the Difference

Here’s the thing: an IC anaerobic tank is a long-term investment. A $200k tank that’s maintained properly will pay for itself in 2 to 3 years from lower energy and disposal costs. A tank that’s not maintained will need expensive repairs in 3 years, or have to be replaced in 5, which is a huge loss. I had a client last year who told me their previous tank lasted 6 years because they only did maintenance when something broke. The IC tank I supplied them in 2018 is still running at 95% efficiency, with monthly maintenance and annual overhauls. That’s the power of a good routine.

Chemical Dosing System If you have an IC anaerobic tank, or you’re looking to install one, you don’t have to figure this out alone. I’ve worked with operators of all skill levels, from small craft breweries to large chemical plants, and I can help you build a maintenance plan tailored to your specific waste stream. Whether you need help setting up daily checks, interpreting lab results, or troubleshooting a circulation issue, just reach out. My team and I know IC tanks inside and out—we don’t just sell them, we support them for their entire lifecycle.

References

  • Metcalf & Eddy, Inc. (2014). Wastewater Engineering: Treatment and Resource Recovery (5th ed.). McGraw-Hill Education.
  • Speece, R. E. (1996). Anaerobic Biotechnology for Industrial Wastewaters. Archae Press.
  • International Water Association (IWA). (2019). Upgrading and Retrofit of Anaerobic Sludge Reactors. IWA Publishing.

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