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.