Lagoons are a cost-effective and popular way to treat water. Many people utilize the advantages of covered lagoons for wastewater, using them to treat large communities or homes. You can find lagoons on farms to treat the endless amounts of waste that cows and pigs produce, or you could see one in someone's backyard, acting as a private source of water treatment that can be siphoned back to water plants in an irrigation system. Even cities build lagoons to help them efficiently treat wastewater from citizens.
Whatever your reason for building and maintaining a covered lagoon, it's a complex system requiring adequate knowledge. It's essential to understand all the different aspects of lagoons, from the chemical decomposition process to their general uses and maintenance.
Covered lagoons are incredibly effective and work uniquely, breaking down bacteria and suspended solids in an anaerobic process. Here's everything you need to know about them.
Lagoon systems are deep, pond-like basins that can treat wastewater. A lagoon uses time as its primary factor in decomposition. The waste in the lagoon undergoes a series of biological and chemical processes, effectively treating the water through natural methods.
This is a broad definition of lagoon systems. In a real-life situation, you'll have to tailor your lagoon to fit your location's specific needs. To build and construct a lagoon, you'll first have to prep the area and determine the various factors that go into maintaining one.
A few things you should keep in mind if you're determining whether to build a lagoon:
A lagoon is a more general term used to label a wastewater treatment strategy. The definition of a deep body of water using natural processes to break down waste generally applies to all lagoons. Still, specific types of lagoons also fit under this umbrella definition.
You should match your lagoon type to the environment surrounding it and the goal it should accomplish. The two main lagoon categories are aerobic and anaerobic. Aerobic simply refers to the involvement of oxygen, whereas anaerobic denotes the absence of oxygen.
Aerobic lagoons require oxygen in the wastewater treatment process. Aerobic lagoons are commonly used in one of two ways:
Naturally aerobic lagoons use natural processes to cleanse the water. To achieve this breakdown, these lagoons are usually much shallower than others. Sunlight penetrates the lagoon's depths along with oxygen carried in from the wind and surrounding air, combining to create an effective cleansing process.
Because of the need for adequate sunlight and warmer water, naturally aerobic lagoons are better suited for hotter climates. If the water freezes, the natural treatment process ceases to exist, so it's vital to find a suitable climate to keep the water at the correct temperature.
Treatment ranges for these lagoons are typically shorter — adequate cleaning can be completed in anywhere from three to 50 days. Shallowness can cause problems in these types of lagoons, resulting in weeds sprouting on the bottom. To counter this growth, naturally aerobic lagoons should be paved or lined. However, algae and aerobic bacteria are positive growths in these lagoons, aiding in the treatment process.
Whereas naturally aerobic lagoons use sunlight and naturally occurring oxygen to treat water, aerated lagoons use aeration systems to add oxygen to the water. These lagoons often require significant amounts of energy to power this aeration, resulting in more costs. However, these costs are offset by the efficiency and quickness with which the water is treated — aerated lagoons are often smaller and require less time for treatment.
Aerated lagoons are also usually less expensive to run than mechanical water treatment processes, and if the lagoon uses wind-driven energy, this can lower costs significantly. Because of their small sizes and short detention times, aerated lagoons serve well in many small communities.
Anaerobic lagoons act as a counter-strategy to aerobic ones, eliminating oxygen from the treatment process — anaerobic literally means "without oxygen." Anaerobic lagoons institute a unique but effective technique for breaking down and treating waste. They split between two more types — covered and uncovered.
Uncovered anaerobic lagoons are just as they sound — lagoons without a cover, using the absence of oxygen as the main driver for treatment. However, uncovered lagoons can often pose problems as they rely on a thin crust forming on the surface to keep odors and gases in. If this crust breaks, it could emit greenhouse gases and expose an unpleasant smell.
A covered anaerobic lagoon is generally considered the better option between the two. Covered lagoons use a manmade cover to keep gases in. These lagoons are in widespread use and are great at effectively treating wastewater.
A covered lagoon is one of the best lagoon types for various reasons. Like other lagoons, this type is a large, earthen basin that treats wastewater. Covered lagoons use the absence of oxygen to break raw sewage down into other compounds that you can siphon out of the lagoon as effluent. The lagoon is covered with a strong material such as high-density polyethylene (HDPE) to trap gases and odors.
To ensure a lack of dissolved oxygen, covered lagoons are usually deeper than most, generally ranging between 8 and 15 feet. They also typically take longer to work than other lagoons, as the process involves a slow breaking down of organic compounds. Treatment generally takes around 20 to 150 days. They aren't heated, and they need to stay relatively cool without freezing for optimum efficiency. Like with other lagoons, the treatment process ceases to work if the water freezes.
A complex microbial process is involved in treating water in a covered lagoon. In a basic overview, raw wastewater, or influent, enters the lagoon near the bottom. With the lack of dissolved oxygen, the waste breaks up into two sections — a thick bottom layer and a liquid layer. The bottom layer is slowly processed and broken down into two main compounds, which are methane and carbon dioxide.
At the deep depths of a covered lagoon, anaerobic conditions remain stable and work against volatile organic compounds. The top layer usually consists of scum, grease and other materials floating in the water. The layer at the bottom of your lagoon will eventually accumulate and have to be cleaned out.
From a microbial perspective, the treatment process operates at two different levels — acid formation and methane production. During the acid phase, bacteria convert complex organic compounds into simple organic compounds. Simply, bacteria in covered lagoons transform carbs, fats and proteins into organic acids.
The methane stage involves two steps. In the first step, known as acetogenesis, bacteria transform organic acids to acetate, hydrogen gas and carbon dioxide. Then, methanogenic organisms known as "methane formers" convert the acetate, hydrogen gas and carbon dioxide into methane gas.
The methane step relies mainly on the lagoon's external factors — primarily temperature. If the temperature isn't ideal, this could slow or inhibit the process, creating issues with treatment. This is why it's so essential to pick the correct climate and type of lagoon for your location. Something as simple as the temperature can dictate a complex microbial process in the dark depths of your lagoon.
The ideal temperature for a covered lagoon digester ranges between 77 to 104 degrees Fahrenheit (25 to 40 degrees Celsius), with a pH level between 6.6 to 7.6 and alkalinity ranging from 1,000 to 5,000 mg/L. Water that gets too cold or drops below freezing will make the treatment process suffer, and a pH level that falls below 6.2 will stop the methane production process altogether.
Once the water is treated, it is siphoned off as effluent for other uses, whether that be into other treatment systems or a recycled water system that transfers to irrigation.
Because of their large size and slow treatment process, covered lagoons are popular choices for cattle owners and those who run farms. The vast landscapes and lack of residential homes offer an ideal space for a covered lagoon. Covered lagoons are also cheaper and less expensive to build and maintain, making them ideal for individuals looking to cut costs but retain effectiveness.
Because covered lagoons produce methane, you can also use them to heat buildings, power engines and generate electricity. Methane production improves covered lagoons' overall value, as they can treat water and power buildings.
Covered lagoons are often involved in a series of treatment systems. One lagoon may bridge into several others, cleansing the water at each step to ensure safe, effectively treated effluent.
A great example of an effective covered lagoon system is at Royal Farms in Tulare, California. In this system, cattle manure is flushed from the pens into a three-cell covered lagoon system where this influent is treated. The covered lagoons successfully reduce odor and provide a natural way to break down raw wastewater.
Royal Farms recovers heat from the engine generators to warm nursery barns, and they use the final irrigation effluent as barn flush water and irrigation water for crops. The generated electricity covers energy costs, and any remaining is sold.
Royal Farms is an excellent display of the value in building a covered lagoon, as it can be a versatile tool to treat your water and power your facility.
Anaerobic covered lagoons offer various advantages and disadvantages. Depending on your situation, location and climate, you'll want to determine which benefits are most rewarding and which disadvantages would be most detrimental.
Some anaerobic lagoon advantages include:
Covered lagoons can also bring several disadvantages, such as:
At Bristola, we provide an innovative submersible robotic cleaning system that offers solutions to all of your covered lagoon cleaning needs. Our process eliminates common cleaning disadvantages like system downtime and human exposure hours. Instead, we increase water quality, carbon reduction and facility efficiencies, all with zero-human entry for a safer and quicker process. You can keep your system running while we clean out your lagoon. Contact us today to get more information on our solution!