Septic Tank Alternatives: Lagoons and Constructed Wetlands

Septic tanks and a subterranean discharge is the single largest way people rural communities treat waste water. That is, in places where the soil, topography and hydrology allow for underground discharge.
The other limitation of septic systems is the capacity, if you expect large volumes of water then you need a large tank/multiple tanks and that can be very expensive.

Constructed Wetland at the Edmonton International Airport source: watercanada.net

I have already written a fair amount about septic systems, and in this article I am going to explore some of the other options for onsite watsewater treatment. Then next two most common options are Lagoons and constructed wetlands. A sewage lagoon is a water-tight earthen berm including the bottom. The construction is not complex, but it can become land intensive depending on the size. Constructed wetlands are identical to lagoons but they are allowed to grow over with vegetation forming a complete wetland ecosystem.

Sewage Lagoon Site Plan source: elkhorn.unl.edu

Lagoons are sometimes referred to as stabilization ponds. In a basic level, they reduce organic contamination in domestic sewage down to levels suitable for release back into the environment with minimal impact. If they are operated correctly, they can have a positive effect on the receiving water way. The lagoons I operated have lower phosphate, ammonia and nitrogen levels than the river they discharge into.

Constructed Wetland Diagram source: www.civil.columbia.edu

Constructed Wetland Diagram source: http://www.civil.columbia.edu

Lagoons are best constructed with a bulldozer or front end loader because it will be easier to create even depth impermeable layers of soil. The impermeable layers are constructed by compacting clay based soils into a water tight layer. If the available soil is impractical for compaction, a layer of sand topped with a plastic/rubber liner at least 30mm thick. There are professional installers and commercial DIY options available.  Below is a table from University of Missouri outlining the size and space a lagoon requires.

NUMBER OF BEDROOMS

MINIMUM SEPTIC TANK LIQUID CAPACITY1(GALLONS)

LAGOON WATER SURFACE AREA2(SQUARE FEET)

SQUARE LAGOONS(FEET SQUARE)

ROUND LAGOONS (FEET DIAMETER)

ESTIMATED AREA NEEDED FOR ENTIRE LAGOON (SQUARE FEET)

1 TO 2

1,000

9003

30 FEET

34 FEET

5,800

3

1,000

1,320

37 FEET

41 FEET

7,050

4

1,250

1,760

42 FEET

47 FEET

7,750

5

1,500

2,200

47 FEET

53 FEET

9,200

1FOR HOMES WITH MORE THAN FIVE BEDROOMS, TANK VOLUME IN GALLONS = (1.5 X DAILY SEWAGE FLOW) + 500.
2ADD 440 SQUARE FEET OF WATER SURFACE AREA FOR EACH ADDITIONAL BEDROOM.
3MINIMUM LAGOON WATER SURFACE AREA IS 900 SQUARE FEET AT THE 3-FOOT OPERATING LEVEL.

You may be wondering how a lagoon/wetland system can handle larger volumes than a septic system. The answer is oxygen. Septic systems operate under anaerobic conditions meaning they are oxygen deprived. Lagoons and wetlands are facultative. Facultative environments are partially aerobic, and partially anaerobic. In a lagoon the surface is aerobic as oxygen from the atmosphere is added to the water and the deeper you go the more anaerobic conditions become. Aerobic conditions allow a much more efficient bacteria to break down the waste. These more efficient bacteria are surprisingly named aerobic bacteria.

Aerobic and Anaerobic Processes in a Sewage Lagoon source: elkhorn.unl.edu

If a lagoon or wetland is operating properly, there will be a musty smell.  This is the same smell produced by natural wetlands, if you have ever been to a swamp you know the smell I am referring to.  If the oxygen balance is disrupted, for any reason, either overloading or ice cover or chemical contamination the process will turn septic/anaerobic.  Then the lagoon will produce a wide bouquet of odors, most notably a rotten egg smell caused by the formation of hydrogen sulfide.  If you have ever opened a septic tank and caught a whiff, that is the smell I am referring to.  If you decide to treat your onsite waste this way, maintenance of the oxygen balance is critical to avoid the inferior treatment and smells of anaerobic conditions.  Simple things like keeping trees at least 50 feet away from the lagoon will add more oxygen to the water by allowing for more sunlinght (photosysthisis produces oxygen) and wind contact (physically transfers oxygen to the water).  In extreme cases pumping water so it circulates to the surface will also add a lot of oxygen, as will pumping air directly into the water via an air compressor and diffuser will almost guarantee you never see anaerobic conditions.

Constructed Wetlands in Series source: http://www.mda.state.mn.us

Sometimes waste systems are combined and there is a septic tank that feeds into a lagoon or wetland and then into a receiving water system.  This arrangement can improve all around wastewater treatment and extend the life of the entire system.  If your local regulations and soil conditions allow for these types of waste water treatment they are definitely worth considering.  Properly maintained and properly designed they can become an attractive and functional feature to any property.

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5 thoughts on “Septic Tank Alternatives: Lagoons and Constructed Wetlands

  1. An interesting thing my septic tank guy just told me a week ago after needing one pumped out was Not to use rdex in septic tanks cause it just breaks waste down small enough to settle to the bottom of the tank and collect, but in a lagoon situation I am thinking the opposite would be true.

    • One of the primary treatments done to assist lagoons is to add chemicals designed to make things settle down to the bottom. And smaller pieces are easier for bacteria to consume.

  2. Terrific article! This is the kind of info that are supposed to be shared around the internet.
    Shame on Google for now not positioning this post higher!

    Come on over and talk over with my site . Thank you =)

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