In the last newsletter, we talked about the importance of TKN, or Total Kjeldahl Nitrogen, in a wastewater treatment plant. This time, let’s talk specifically about what TKN does in a lagoon system, because when it is not addressed before it gets there, it can create problems across the entire treatment process.

Those problems do not always show up all at once, and that is part of what makes them so costly. They build slowly, spread across the lagoon, and eventually show up in the form of algae blooms, high suspended solids, elevated oxygen demand, poor effluent quality, and a lagoon that becomes harder and harder to manage.

Any operator who has worked with lagoons for any length of time knows algae is one of the biggest headaches, especially once the weather turns warm. In the northern part of the country, operators may fight that battle six or seven months out of the year. In the South, it can stretch eight, nine, or even ten months depending on the climate. By the time summer is fully underway, many lagoons start turning that familiar pea-green color, and people often accept it as just part of lagoon treatment. But that is a mistake. While some seasonal algae is common, excessive algae growth is usually telling you something. It is often a visible symptom of an upstream loading problem, and TKN is frequently part of that story.

It is also worth clearing up a common misunderstanding. Most municipal lagoons are not too small. In many cases, they are too large for the actual loading they receive. That may sound backwards, but it matters. When wastewater is spread out across a large lagoon surface area, it becomes diluted, and that dilution can slow the breakdown of more complex organic materials. Instead of being concentrated enough for efficient biological activity in a controlled environment, those compounds are dispersed over a broad area and processed slowly. That creates the perfect setting for long, drawn-out conversions that feed nuisance conditions instead of stable treatment.

That is where TKN becomes a real problem.

TKN is made up of organic nitrogen and ammonia nitrogen. In a lagoon system, that nitrogen does not simply vanish once it enters the water. It has to be biologically broken down over time. The organic fraction begins converting, and as it does, it contributes to the formation of ammonium. In the lagoon environment, that ammonium becomes part of a slow-moving cycle. As conditions allow, it moves through nitrification and is converted toward nitrate. The problem is that this transformation is not happening in a tight, controlled reactor. It is happening over a broad, open body of water exposed to sunlight, temperature swings, wind, varying detention times, and seasonal changes in biological activity.  That matters because nitrogen, especially in available forms, is fertilizer.

And when you fertilize a warm lagoon with plenty of sunlight, algae is going to respond.

So when operators see a bright green lagoon in the heat of the year, they should not just think, “That is algae.” They should also be asking, “What is feeding it?” Many times, the answer is excess nutrient loading, including TKN that was not sufficiently addressed before it entered the lagoon. The lagoon is not just reacting to sunlight. It is reacting to food. And if you keep feeding it nitrogen and organics day after day, you should not be surprised when the algae takes over.

That bright pea-green color some people have learned to tolerate is not just an aesthetic issue. It is a warning sign. It is the system telling you that too much nutrient conversion is happening in the wrong place and in the wrong way. Once algae growth gets heavy, the lagoon becomes more unstable. Oxygen levels can swing widely from day to night. Solids increase. Settling worsens. Water clarity drops. The system becomes more difficult to predict and more difficult to operate with confidence.

And that warning sign usually comes with real consequences.

One of the first places operators feel it is in TSS. As algae populations grow, they contribute directly to suspended solids in the lagoon effluent. That means even when the lagoon appears to be functioning on the surface, the discharge quality may be headed in the wrong direction. Along with that, cBOD can appear artificially elevated because the algae itself contributes oxygen demand. In other words, the system may look like it has a BOD problem when in reality part of what you are seeing is biological material created inside the lagoon as a result of excess nutrient availability. That distinction matters, because if you misread the problem, you may spend money treating the symptom instead of solving the cause.

This is where many lagoon systems get trapped. Operators focus on the algae because the algae is what they can see. They talk about the color, the surface condition, the clarity, or the solids in the final discharge. But algae is often only the last chapter of the story. The story usually started upstream with too much organic loading, too much nutrient carryover, poor lift station conditions, excess septicity, or inadequate pre-treatment of the wastewater before it ever reached the lagoon.

That is why the smartest place to deal with TKN is before it gets there.

If you can reduce the TKN and associated organics upstream, you give the lagoon a much better chance to function the way it was intended to function. The lagoon becomes less reactive, more stable, and easier to operate. The water quality improves. The algae pressure drops. Solids become easier to manage. The risk of elevated cBOD decreases. And the entire system becomes less expensive to live with over time.

That upstream work is not glamorous, but it matters.

A strong lift station maintenance program matters. If lift stations are allowed to accumulate grease, rags, sludge, and septic organic material, then the wastewater arriving at the lagoon is already in bad shape. By the time it gets there, you are no longer dealing with a clean influent stream. You are dealing with a partially degraded, nutrient-rich load that is ready to create trouble. Routine maintenance, cleaning, and proactive management of those collection points can make a major difference in what ultimately reaches the lagoon.

The right bacteria and enzyme program can matter too. When properly applied, these programs can help reduce organic buildup, improve degradation ahead of the lagoon, and take pressure off the downstream treatment process. They are not magic, and they are not a substitute for good operation and maintenance, but they can be useful tools when they are part of a broader strategy. The goal is simple: reduce the amount of problematic material entering the lagoon so the lagoon does not have to spend months converting it under less-than-ideal conditions.

That is really the larger point. Lagoons tend to magnify what comes into them. If the incoming load is reasonably stable and manageable, the lagoon can often do its job very well. But if the lagoon is being fed too much TKN, too much organic matter, and too many nutrients for too long, it will eventually show you the result. It may show you in algae. It may show you in TSS. It may show you in cBOD. It may show you in odor, color, poor clarity, or inconsistent performance. But one way or another, it will show you.

Too many operators spend their time chasing symptoms in the lagoon while the real problem keeps flowing in every single day. They focus on what is visible at the end of the pipe instead of what is entering the system at the front end. That approach usually leads to frustration, higher operating costs, and a lagoon that never quite seems to improve for long. If you want a better lagoon, start by fixing what is feeding it.

When you get control of TKN before it enters the lagoon, you are not just solving one parameter. You are improving the overall biological health of the system. You are reducing the nutrient fuel that drives nuisance algae. You are improving the odds of better solids control. You are protecting effluent quality. And you are making life easier for the operator responsible for keeping the whole thing in compliance.

A clean, stable lagoon is usually not the result of luck. It is the result of upstream discipline.

In the next article, we will talk about another major lagoon issue: the hidden downside of dredging large sludge buildups.