Previously, we looked at where drip distribution should be applied and a general look at the parts of a drip system. Here we will take a look at some of the choices that need to be made when designing a drip distribution system. Filtration is very important and there are basically three choices. Proprietary products may have made this choice for you by specifying what needs to be used in conjunction with the pretreatment choice (septic tank or aerobic treatment).

The three types of filters are: sand, disc, and spin or screen. All will function adequately with the proper pretreatment, so the designer needs to weigh the pros and cons of each.

Sand filters are like swimming pool filters; they are relatively inexpensive and easy to maintain. However, if the sand escapes it can wear out pumps or be passed downstream where it can plug the emitters in the tubing.

Probably the most common filter now is a disc filter that was developed in the 1990s. They use serrated plastic discs as the medium. In addition, filter maintenance and cleaning can be completely automated with pressure gauges and control panels. They require only periodic cleaning and replacement.

The third type has a stainless steel screen that filters the effluent by forcing the water through a directional plate, creating a centrifugal action that rotates debris down the screen wall to a debris holding basin that periodically needs to be emptied.

The distribution system includes components that carry the wastewater from the pump to the soil treatment area. One end of the tubing is connected to the pump through a supply manifold. Along its length, tiny holes (orifices, emitters) allow the wastewater to drip into the soil. Spacing of the emitters ranges from every 12 inches to 24 inches depending on the area to cover and the type of soil.

The tubing itself is generally 1/2 inch in diameter with the emitters placed in the tubing wall. Operating pressures can vary from 15 to 65 psi in tubing. The other end of the dripline is connected to a return manifold that connects back to the tank for either manual or automatic flushing.

Each brand of tubing is unique, so the designer needs to know what each one and how they operate. Probably the best choice is to use tubing with pressure-compensating emitters because it will automatically increase flow if an emitter starts to plug. It can also be used on sloping or uneven sites where equal distribution is provided without any additional design requirements.

About the Author
Jim Anderson is connected with the University of Minnesota onsite wastewater treatment education program and is an emeritus professor in the university’s Department of Soil Water and Climate. Send him questions about septic system maintenance and operation by email to kim.peterson@colepublishing.com. 

This article is part of a series on drip distribution:

• Is Drip Distribution Right for Your Site?
• Choosing a Filter for a Drip Distribution System
• Sizing a Drip Distribution System
• Tips for Drip System Design
• Site Prepping for Drip Distribution Installation
• Tips for Drip System O&M
• Controlling the Flow: Drip System O&M