Onsite (or decentralized) private wastewater treatment systems are used to treat wastewater from a home or business and return treated wastewater back into the receiving environment. They are typically referred to as septic systems because most involve a septic tank for partial treatment.
Types of Septic Systems
There are a number of different types of septic systems depending on household size, soil type, site slope, lot size, and local regulations.
Conventional or Gravity System
In this system, the wastewater flows into the septic and through the inlet baffle. Heavy solids settle to form a sludge layer on the bottom of the tank. Lighter materials including oil and grease, float to the top forming a scum layer. The wastewater liquid in the middle flows through the outlet baffle to the drainfield. An effluent screen placed in the outlet of the septic tank is used to filter suspended solids out of the effluent.
Pressure Distribution System
Performing the same basic actions as the conventional septic systems, pressurized systems include a pump chamber that collects treated wastewater from the septic tank. They are used when there is only two to three feet of suitable soil beneath the drainfield. The pump chamber contains a pump, pump control floats, and a high-water alarm float.
Consisting of a series of connected chambers, the area around and above the chambers is filled with soil. Pipes carry wastewater from the septic tank to the chambers. In the chambers, the wastewater comes into contact with the soil. Microbes on or near the soil treat the effluent.
Drip Distribution System
A type of effluent dispersal that can be used in many types of drainfields, the main advantage of the drip distribution system is that no large mound of soil is needed as the drip laterals are inserted into the top six to 12 inches of soil. The disadvantage of the drip distribution system is that it requires a large dose tank after the septic tank to accommodate the timed dose delivery of wastewater to the drip absorption area.
Aerobic Treatment Unit (ATUs)
Using many of the same processes as a municipal sewage plant, but on a smaller scale, ATUs inject oxygen into the treatment tank. The additional oxygen increases natural bacterial activity within the system that then provides additional treatment for nutrients in the effluent. Some ATUs may also have a pretreatment tank and a final treatment tank including disinfection to further reduce pathogen levels. The benefits of this system are that it can be used in homes with smaller lots, inadequate soil conditions, in areas where the water table is too high, or for homes close to a surface water body sensitive to contamination by nutrients contained in wastewater effluent. Regular maintenance should be expected for ATUs.
An option in areas of shallow soil depth, high groundwater, or shallow bedrock, the constructed sand mound contains a drainfield trench. Effluent from the septic tank flows to a pump chamber where it is pumped to the mound in prescribed doses. Treatment of the effluent occurs as it discharges to the trench and filters through the sand, and then disperses into the native soil. While mound systems can be a good solution for certain soil conditions, they require a substantial amount of space and periodic maintenance.
Recirculating Sand Filter System
Able to be constructed above or below ground, effluent flows from the septic tank to a pump chamber. It is then pumped to the sand filter. The sand filter is often PVC-lined or a concrete box filled with a sand material. Pumped under low pressure through the pipes at the top of the filter, the effluent leaves the pipes and is treated as it filters through the sand. The treated wastewater is then discharged to the drainfield. Sand filters provide a high level of treatment for nutrients and are good for sites with high water tables or that are close to water bodies. However, they are typically more expensive than a conventional septic system.
Featuring unique drainfields, the base of the evapotranspiration system drainfield is lined with a watertight material. After the effluent enters the drainfield, it evaporates into the air. Unlike other septic system designs, the effluent never filters to the soil and never reaches groundwater. Evapotranspiration systems are only useful in specific environmental conditions. The climate must be arid and have adequate heat and sunlight. These systems work well in shallow soil; however, they are at risk of failure if it rains or snows too much.
Constructed Wetland System
Mimicking the treatment processes that occur in natural wetlands, wastewater flows from the septic tank and enters the wetland cell. The wastewater then passes through the media and is treated by microbes, plants, and other media that remove pathogens and nutrients. The wetland cell typically consists of an impermeable liner, gravel, and sand fill, along with the appropriate wetland plants, which must be able to survive in a perpetually saturated environment. A wetland system can work via either gravity flow or pressure distribution. As wastewater flows through the wetland, it may exit the wetland and flow into a drainfield for further wastewater treatment into the soil.
A decentralized wastewater treatment system under some form of common ownership that collects wastewater from two or more dwellings or buildings and conveys it to a treatment and dispersal system located on a suitable site near the dwellings or buildings. It is common to find cluster systems in places like rural subdivisions.
Effluent pumps are designed to pump liquids with solids up to 3/4-inches in diameter – and most commonly for a septic system. Sewage pumps can also be used for effluent pump applications and are capable of passing two-inch solids.
When selecting a pump for a septic system, you need to consider head pressure (TDH-total dynamic head), horsepower (HP), and flow rates.
TDH: How high vertically the pump needs to push the water, the length of the horizontal run, and friction loss due to the size pipe and fittings.
Horsepower: The greater the HP, typically the more liquid a pump can move in a shorter period of time. However, you do want to size the right HP for the application because short cycling could cause shorter life for the pump.
Gallons Per Minute (GPM)/Flow Rate: The pump’s design, combined with the HP and TDH, will determine the GPM provided. Again, it is important to size the pump correctly for each separate application. If not, you can shorten the life of the pump or it may not pump at all.
At JMI, our selection of stocked effluent pumps ranges from 1/3 to 2HP, and from 42 to 164GPM at 10’ TDH. Our sewage pumps range from 4/10 to 2 HP and from 50 to 190 GPM at the same TDH. Some effluent models have a shut off head up to 70’ TDH. We offer a variety of brands, including Barnes, Little Giant, Metropolitan Industries, and JMI. There are also a number of switches to choose from to operate the pumps.
A septic system installation should also include an alarm to alert the user of when the water level is higher or lower than it should be. The main causes of a high water level include:
- The effluent filter is clogged.
- The submersible pump has failed or the float that controls it failed.
- The outlet line is plugged.
A module can be used with any alarm to automatically call/text/email notifications alerting you of the situation. There are also specific controls that can monitor all of the pump or system attributes to maintain complete awareness and record of the performance of a system.
As with all our pump products and accessories, the JMI Pump Systems professional staff can help you determine the correct pump and controls for your septic system or other pump application. Your Partners in Pumping are available at 262-253-1353 or firstname.lastname@example.org to assist you.