It’s a challenge for small clean-water plants to reduce nutrient discharges affordably, especially if they weren’t originally designed for that capability.

In 2012, the Montana Department of Environmental Quality began providing mechanical and lagoon treatment plants with no-charge training in nitrogen and phosphorus optimization and on-site assistance. The program gave operators a safe harbor to try various operational changes to reduce nutrient releases, with the understanding that while there could be short-term setbacks, the long-term payoffs would be worth the risk.

The initiative has been highly successful. The 34 participating mechanical plants included 14 that underwent facility upgrades to improve nutrient removal, and 20 that relied on process optimization alone. Eighteen of the 20 optimized plants saw significant reductions in nutrient discharges — a combined 127 tons per year of nitrogen and 19 tons per year of phosphorus.

Of particular interest, total nitrogen was reduced by 40% and total phosphorus by 25% at facilities not designed to remove nutrients, at a cost of less than $25,000 per plant. Achieving similar results through conventional upgrades typically would cost in the millions of dollars.

The optimizations at plants that were not upgraded reduced nitrogen and phosphorus at a cost of about 14 cents per pound, versus conventional costs of $4.19 for phosphorus and $1.85 for nitrogen. The initiative also showed that most plants designed for nutrient removal can do even better with low-cost process optimization. The program also provided optimization advice to 50 lagoon facilities.

DEQ staffers Josh Viall and Pete Boettcher, wastewater technical advisors, and Darryl Barton, section supervisor for compliance, training and technical assistance, talked about the optimization program in an interview with Treatment Plant Operator.

What was the motivation behind the optimization initiative?

Barton: The main concern was phosphorus discharges. In many cases phosphorus is the limiting nutrient for algae growth in surface waters. When you get excessive algae growth, eventually you get oxygen depletion, and that hurts trout survival in the streams.

Why were lagoon systems a significant part of the initiative?

Barton: Nutrient standards were becoming very difficult for lagoon systems to meet, especially for phosphorus. And we knew that many smaller communities wouldn’t be able to afford a mechanical treatment system. So the U.S. EPA and the Montana DEQ got together to develop a way to help lagoon systems do better with nutrient removal. 

How were the facilities chosen to be part of the optimization program?

Boettcher: We’re only working on lagoon systems that discharge with a permit. A number of lagoons are 100% retention or do land application. As of now we’re not working to optimize those systems. We also included all the mechanical plants that are publicly owned treatment works. We didn’t look at any private facilities.

What was the role of consultants in the optimization process?

Boettcher: We worked with Steve Harris from H&S Environmental on the lagoon systems and with Grant Weaver from Grant Tech Solutions on the mechanical plants. They worked with us on providing training for the operators and in visiting the treatment facilities. We sent them data on the plants so they knew what they were looking at before they got there. They provided reports on their findings and recommendations for each facility. The consultants were great to work with. They were willing to teach us what they knew so we could continue with the work after they were gone.

What was the range of flows for the mechanical lagoons facilities that were optimized?

Boettcher: Most of the mechanical systems we worked with were right around 1 mgd or less. Most of the lagoons were 100,000 gpd or less.

Was there federal, state or other funding for this optimization program?

Barton: The optimization program is funded through the State Revolving Fund. What’s great about that is we also have access to that fund to help them with their improvements.

What kinds of issues were found with the lagoon systems?

Boettcher: When you have high levels of solids in the bottom of a lagoon, you can get nutrient feedback. If they have over 16 to 18 inches of sludge, they should consider removing it because the nutrients it feeds back into the system will show up in the effluent. It also promotes algae growth. They can end up with algae in the final effluent, which will kick TSS way up.

Did the lagoon optimizations involve sludge removal?

Boettcher: Getting sludge out is pretty tough just for the cost, which can range from $250,000 to $1 million depending on how much they have, and then they have to figure out what to do with it when it does come out. Communities with lagoons typically don’t have much money. Just getting them to have the equipment they need to run for permit compliance is tough. 

In that case, what are some measures that can be taken to optimize lagoon systems?

Viall: One thing we recommend is a headworks so they can remove the rags and debris, which will build up the sludge layer much faster. Without a headworks they may only be able to operate for 15-20 years before they have to remove sludge. Some systems add enzymes and they’re having good luck.

Boettcher: We also work with operators on actually operating the lagoons instead of just turning them on and forgetting about it. We suggest they run DO analysis on each cell a couple of times a week. We’ve found that anything over 2 mg/L DO in the cell is really not needed. So they can dial the air down, or not run it at all during the day in summer, because the algae in the water will produce enough oxygen. They can turn the air on at eight or nine at night and turn it off at 8 in the morning, and that’s a huge cost savings on running the blowers. In winter they don’t have that option, but in spring, summer and fall they can save a lot of money that way.

What other kinds of steps can lagoon operators take?

Boettcher: Sometimes it’s a matter of sampling between the cells to see how each cell is doing. If they sample the influent and discharge from the first cell, they can see if that cell is actually removing BOD. If they do it between the second and third cell, they can see if the second cell is taking the ammonia out. Or instead of discharging out of cells 3 or 4, they can discharge out of Cell 2 if the water quality is better there. Or they can use a trash pump to send water from Cell 3 back to Cell 1, because it’s cheaper to pump aerated water back than to use a blower to push air into the system.

In general, how effective can lagoons be in removing nutrients?

Viall: We find that we can get ammonia knocked out, although that’s only during the warm weather. In facultative lagoons, it’s difficult to get total nitrogen low because the bacteria don’t have the proper mixing to come in contact efficiently with the nitrate. Lagoons don’t have the option of removing phosphorus unless they treat it chemically, and then they would also need some sort of clarification.

On the mechanical plant side, what basic measures did operators take to optimize nutrient removal?

Viall: We’ve found that mechanical plants are able to incorporate a variety of steps. With an oxidation ditch, or even just a conventional activated sludge process, a lot of it is just finding an area for denitrification, or an anaerobic zone for phosphorus release followed by uptake in an aerobic zone. If they just cycle the air off for an hour every two to three hours, that often will knock a lot of nitrate out. So for example, if they shut an aerator off and install a mixer for $40,000 or $50,000, that’s going to take some power to run but they’re going save in the long run because of how much energy the aeration costs, whether it’s powered by a rotor or a blower. They might not even have to add a mixer; they just have to shut the air off. Then they’re saving money immediately and at the same time getting better nutrient numbers.

In essence, what is the key to making optimization work in a plant not designed for nutrient removal?

Viall: Optimization only works if the operators are on board. A lot of times it takes a little bit of extra work. Maybe they’re nitrifying but there’s no way to denitrify with a lack of air. Then they need to rotate blowers, and often they’re not set up for that. They don’t have SCADA, and so they have to go out and manually shut a blower off for a few hours, and then turn it back on. A lot of it falls onto the operators’ shoulders. If they’re not willing to go the extra mile to make it work, then ultimately they end up getting a plant upgrade.

In general, how would you characterize the results of the optimizations in the mechanical plants?

Viall: As long as the operators would jump on board, it was pretty amazing. There were significant decreases in total nitrogen, and in some cases in phosphorus. This project shows the importance of operations, of actually paying attention. When operators care, you can see it in the numbers. We have some plants that are really run down and yet are putting out numbers where the engineers say, “I don’t know how they’re doing it.” They’re not running as designed, but the operators understand how the process works. They know where to test for ammonia or nitrate, and they can really dial it in and figure out where their air needs to be. 

What levels of nitrogen and phosphorus removal have the optimized mechanical plants been able to achieve?

Viall: If they had been running at 2 or 3 mg/L phosphorus going out, and they can stay consistently under 1 mg/L, that’s pretty good, especially if the plant was not designed for phosphorus removal. On total nitrogen, we like to shoot for 6 or 7 mg/L, but if we can keep them under 10, or right around 8, that’s acceptable, and it’s pretty doable for most plants.

What lessons can operators in other states take from this experience?

Boettcher: The big thing is that operators need to be engaged. They can’t be afraid to try something. Instead of saying, “Everything is running good, let’s not mess with anything,” we say, “Everything is running good, but you can make it run better.” Turn the air off for a length of time. Kick up the internal mixed liquor return. Change the mixed liquor concentration. And they need to run analysis. The more analysis they do, the better off they will be.

What has this program done for the relationships between plant operators and the regulatory agency in Montana?

Viall: It has helped the whole operator-to-government relationship. A lot of times operators picture the regulator saying, “You need to pay a lot of money and upgrade your facility because we’re telling you to.” Instead, we’re saying, “There are reasons for this; there are water quality issues going on, and we have staff who are here to help.” We’ll help diagnose their system. We’ll help them come up with ideas. We have extra heads to throw into the mix. So we’ve been able to build up a rapport with many of these operators.

Barton: When the DEQ was first enacting numerical discharge standards, there was a lot of desperation among small systems. They knew their lagoons probably couldn’t handle those limits. They just didn’t have the money. This program has served those small systems well. It’s a really useful tool that’s free of charge. If you look at the relationship between those systems and the state now, versus when the standards were being enacted, it’s like night and day.