Lagoon Systems Can Provide Low-Cost Wastewater Treatment
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Spring 1997 Vol. 8, No. 2 L SMALL A F N L O O I W T A S N C L E E S A U Pipeline R I N G H O Small Community Wastewater Issues Explained to the Public Lagoon Systems Can Provide Low-Cost Wastewater Treatment t is no wonder that one of the for homes on large lots in areas where other treatment more efficient, so that less land most popular methods for onsite systems or sewers are too costly or area is necessary, and aerators can be used to I wastewater treatment around the otherwise impractical. Lagoons also work upgrade some existing systems to treat more world is also one of the simplest well for many seasonal rental properties and wastewater. and least expensive. Lagoon systems use recreational areas, because they are able to Every lagoon system must be individually natural and energy-efficient processes to handle intermittent periods of both light and designed to fit its specific site and use. provide low-cost wastewater treatment. heavy use. Designs are based on such factors as the They are one of the most cost-effective type of soil, the amount of land area wastewater treatment options for many What are lagoon systems? available, the climate, and the amount of homes and communities. There are several different types and sunlight and wind in an area. In the U.S., most wastewater treatment names for lagoons and many possible Other important design considerations for lagoons are found in small and rural system designs. Lagoon systems include lagoon systems include the amount and type communities. Lagoons are especially well- one or more pond-like bodies of water or of wastewater to be treated and the level of suited to small communities because they basins designed to receive, hold, and treat treatment required by state and local can cost less to construct, operate, and wastewater for a predetermined period of regulations. Depending on local standards maintain than other systems. They time. Lagoons are constructed and lined and the final method of disposal chosen, also require more land than other with material, such as clay or an wastewater leaving lagoon systems often wastewater treatment methods, and artificial liner, that will prevent leaks requires additional treatment, or “polishing,” land is more likely to be available and to the groundwater below. to remove disease-causing organisms or inexpensive in rural areas. While in the lagoon, wastewa- nutrients from the wastewater before it can Lagoons can also be designed to ter receives treatment through a be returned to the environment. serve individual households. They combination of physical, This issue of Pipeline includes a brief sometimes are a good option biological, and chemical pro- overview of some of the different types of cesses. Much of the treatment wastewater treatment lagoons, how they occurs naturally, but some work, their operation and maintenance, and systems are designed to also use some of their advantages and disadvantages. aeration devices that increase the Only a few of the many possible classifica- amount of oxygen in the tions and designs for lagoon systems are wastewater. Aeration makes mentioned here. Readers are encouraged to reprint Pipeline articles in local newspapers or include them in flyers, newsletters, and presentations. Please include the name and phone number of the National Small Flows Clearinghouse (NSFC) on the reprinted information and send us a copy for our files. If you have questions about reprinting articles or about any of the topics discussed in this issue, contact the NSFC at (800) 624- 8301 or (304) 293-4191. 1 PIPELINE - Spring 1997; Vol. 8, No. 2 National Small Flows Clearinghouse 1-800-624-8301 LAGOON SYSTEMS There Are Many Designs, Names for Lagoons agoons are not all the same. Aerobic Lagoons treat wastewater naturally, using both aerobic Some employ different Dissolved oxygen is present throughout and anaerobic processes. Because they are L biological, chemical, and much of the depth of aerobic lagoons. They used so often by small communities, physical processes to treat the tend to be much shallower than other lagoons, facultative lagoons are described in detail wastewater, while others may play a so sunlight and oxygen from air and wind beginning with the article on page 4. different role in overall treatment. Some can better penetrate the wastewater. In lagoon designs provide adequate treatment general, they are better suited for warm, *Exact detention times for wastewater in for certain methods of discharge, while sunny climates, where they are less likely to lagoons are based on factors such as the others should be used in combination with freeze. Wastewater usually must remain in particular design, the amount of wastewater to other lagoons or with additional treatment. aerobic lagoons from 3 to 50 days to receive be treated, and the level of treatment desired. Complicating matters further, there can be adequate treatment.* several different names for the same type of Wastewater treatment takes place naturally lagoon. For example, the terms lagoon and in aerobic lagoons with the aid of aerobic Discharge Design pond are often used interchangeably, and bacteria and algae. Because they are so shal- names, such as polishing, stabilization, and low, their bottoms need to be either paved or A design feature that can maturation, can refer to a lagoon’s particular lined with materials that will prevent weeds distinguish lagoons is how they role in treatment. This can be very confusing from growing in them. discharge wastewater. for community leaders and homeowners Sometimes, the wastewater in aerobic trying to evaluate lagoon systems. lagoons needs to be mixed to allow sunlight Continuous Discharge Lagoons. These The following is a brief overview of some to reach all of the algae and to keep it from lagoons release wastewater continuously, of the more common types of lagoons and forming a layer that blocks out the air and so the rate of output roughly equals the some of the terms used for them. sun completely. rate of input. The hydraulic flow pattern Anaerobic Lagoons in the lagoon is designed so the waste- Aerated Lagoons water remains in the lagoon long enough The word anaerobic means without Aerated lagoons are very common in small to receive treatment before it reaches the oxygen, which describes the conditions communities. These systems use aerators to outlet. inside this type of lagoon. Anaerobic mix the contents of the pond and add oxygen lagoons are most often used to treat animal to the wastewater. They are sometimes re- Controlled Discharge Lagoons. In these wastes from dairies and pig farms, ferred to as partial-mix or complete-mix lagoons, wastewater is discharged in commercial or industrial wastes, or as the lagoons depending on the extent of aeration. controlled amounts, usually once or twice first treatment step in systems using two or Partial-mix aerated lagoons are sometimes per year. This method is common in cold more lagoons in a series. facultative lagoons that have been adapted climates where discharges typically occur Typically, anaerobic lagoons are designed and upgraded to receive more wastewater. after spring thaw and again in fall. to hold and treat wastewater from 20 to 50 With the exception of wind-driven designs, days.* They are relatively deep (usually 8 most aerators require energy to operate. Hydrograph Controlled Release to 15 feet) and work much like septic tanks. However, energy costs are almost always Lagoons. This design can be used for Inside an anaerobic lagoon, solids in the considerably less than those for other mechan- lagoons that discharge directly to surface wastewater separate and settle into layers. ical community treatment systems. Aeration water. It includes devices that measure The top layer consists of grease, scum, and makes treatment more efficient, which the level and quality of the wastewater other floating materials. This layer keeps offsets energy costs in some cases. Aerated and receiving water and the velocity of oxygen out, allowing bacteria and other lagoons require less land area and shorter the receiving water to determine when organisms that thrive in anaerobic condi- detention times for wastewater than other conditions are most favorable for tions to work to treat the wastewater. lagoons. More information about partial-mix discharge. This method can sometimes As with septic tanks and most other aerated lagoons is included in the articles on eliminate the need for further treatment. lagoon designs, the layer of sludge that pages 5 and 6. settles at the bottom of an anaerobic lagoon Complete Retention Lagoons. These eventually accumulates and must be Facultative Lagoons lagoons are only practical in very dry removed periodically. Also similar to a septic Both aerobic and anaerobic conditions climates where evaporation rates exceed tank, the wastewater that leaves an anaerobic exist in facultative lagoons, which also are rainfall amounts. Wastewater is never lagoon always requires further treatment. called stabilization ponds, oxidation ponds, released from this type of lagoon. Instead Odor can be a problem with anaerobic photosynthetic ponds, and aerobic-anaerobic it is allowed to evaporate and, when soil lagoons. However, in many cases odor can ponds. They are the most common type of conditions are favorable, to slowly be managed through a variety of methods, wastewater treatment lagoon used by small percolate through the soil at the bottom such as adding sodium nitrate, communities and individual households. of the lagoon. recirculating pond effluent, and Facultative lagoons can be adapted for use 22 through regular maintenance. in most climates, require no machinery, and PIPELINE - Spring 1997; Vol. 8, No. 2 National Small Flows Clearinghouse 1-800-624-8301 LAGOON SYSTEMS Advantages and Disadvantages of Lagoon Systems http://www.nsfc.wvu.edu • Lagoon systems can be cost-effective to • Lagoon systems require more land than Pipeline Is Now design and construct in areas where land other treatment methods.