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Understanding Pig Lagoons: Everything You Need to Know

There are three key things to understand about lagoons: (1) How they are designed, (2) the anaerobic process that takes place inside lagoons, and (3) the benefits they offer to farmers. Let’s look at these separately:


Most lagoons are constructed as an earthen basin. They are earth-walled structures that use basin liners to prevent groundwater contamination. Lagoons must have a liner, which is typically made of clay or geosynthetic plastics.

Lagoons must meet specific design criteria. Everything from size to dike construction are carefully engineered to meet state regulations. It is far more complicated than just digging a hole in the ground. Just like a building must meet certain codes and regulations, so does a hog lagoon.

Where Can Lagoons be Built?

Another major aspect of lagoon design is the location. In North Carolina, there are many rules that say hog lagoons may only be built certain distance away from wells, only in certain soil types, etc. Along with placement of lagoons, the fields where waste water can be applied must be carefully placed (more on that later).One thing that many people don’t realize is that no new hog lagoons have been built in North Carolina for more than twenty years. The state legislature passed a moratorium on construction of new hog farms in 1997 and those restrictions remain in place today.


Lagoons may not seem very complicated, but there is actually a lot going on in that earthen basin. From anaerobic bacteria to pink water, lagoons require a closer look.

Anaerobic Process

The anaerobic process is where the magic happens in the lagoon. It is the process that occurs when anaerobic bacteria grow in an oxygen free environment (the treatment zone of a lagoon) and decomposes organic matter (waste). The result of this process creates something very valuable to the farmer — fertilizer! Those anaerobic bacteria do a great job of treating the waste and turning waste into useful nutrients that can be used as fertilizer.



Managing Lagoon Levels

Farmers must maintain a buffer of at least 19” between the top of the lagoon and the liquid storage. This space – called a freeboard – is designed to prevent the lagoon from overflowing.The lagoon system is built to effectively manage significant rainfall events. Maintaining a minimum freeboard level is specifically designed to handle 24 hours of rain during a 25-year storm – the largest storm that can be expected during a 25-year period based on historical record. If the freeboard level falls below 19 inches, the farm must immediately notify the NC Department of Environmental Quality (DEQ) and submit an action plan to return to normal levels within 30 days.

Pink Lagoons?

Color is a good indicator of proper lagoon function. The pink tint often seen on hog lagoons means it is working as intended. Purple sulfur bacteria reduce the concentration hydrogen sulfide, a significant source of odor. In other words, pink reduces stink.


Anaerobic lagoons produce nitrogen which is a valuable fertilizer for farmers. Farmers must follow a detailed process to properly manage their lagoons. Here’s how it works:

The farmer samples the surface water of the lagoon and sends it off for analysis every 90 days.  The results from that analysis tell the farmer how much plant available nitrogen is contained in the lagoon’s temporary storage depth. The farmer then applies the nitrogen to crops based on guidelines set by the DEQ. State regulations also require farmers to keep detailed records of the nutrients applied.

To simplify, the process looks like this:

the cycle

the cycle

Ultimately, it is a sustainable cycle that allows pigs to fertilize crops like corn which then gets fed back to pigs in their feed ration.

Busting Myths About Pig Lagoons

A group of agriculture students from University of Mount Olive recently visited a farm in Duplin County to learn more about hog farm lagoons and how they work. It was interesting to hear from the students and get a better sense of what they knew — and didn’t know — about how our farmers manage waste responsibly.

We want to spread that understanding to everyone in North Carolina and have put together the following information to educate people about how these waste management systems work.Let’s start by correcting a few common misconceptions about lagoons:

Hog farmers developed the lagoon system. Wrong. The idea of using storage ponds to treat waste has been around for decades. Today, there are dozens of municipalities in North Carolina, as well as several business operations, that use holding ponds to store waste.

Lagoons are an antiquated system and should be replaced with new technologies. Wrong. The system most commonly used by North Carolina hog farmers was perfected by scientists and researchers from N.C. State University — and is still widely considered to be the most efficient way to manage animal waste on our farms.

Farmers are constantly spraying waste on surrounding fields. Wrong. Every hog farmer in North Carolina must implement a comprehensive nutrient management plan set forth by the NC Department of Environmental Quality that is customized for their farm. The plan helps determine how many animals a farm can raise, where they can apply nutrients, and how often they can apply. Most farmers apply only a few times a month, for a few hours a day, on a variety of different fields. The notion that farmers can apply wherever they want, whenever they want is completely untrue.

Lagoons are full of nothing but animal waste. Wrong. While lagoons are used to store animal waste, the vast majority of the liquid in lagoons is water — and the waste in the lagoon is treated with naturally-occurring bacteria that breaks down the waste. You’ll often see turtles or geese swimming in lagoons.

Lagoons are nothing more than cesspools of toxic waste. Wrong. Lagoons, as just mentioned, are filled with mostly water. Farmers often get the waste on their clothes and body. Some have even fallen in (oops!). It isn't toxic. It is simply organic materials that farmers use as fertilizer to help their crops grow, and the lagoon safely contains the material. Contents of the lagoon are also tested to make sure their nutrient levels are just right!

Lagoons always flood during big storms and hurricanes. Wrong. When Hurricane Matthew dumped more than 8 trillion gallons of water on North Carolina in 72 hours — the biggest rainfall event our state has ever seen — more than 98 percent of the lagoons operated as intended. There are 3,300 active hog lagoons in North Carolina; six farms had structural damage to the lagoons and 28 farms filled to the point that some amount of liquid spilled out.

We'll be covering how lagoons work in another blog post. Stay tuned to learn why lagoons are pink and how they help farmers!