One of Those Things Everyone Should Know- II

A reprint from Penn State Extension.
Faith Kibuye, Extension Program Specialist, Water Resources: https://extension.psu.edu/septic-system-basics
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How the septic tank treats wastewater
Once wastewater flows into the first chamber of the septic tank, the treatment process begins. Solids separate and settle to the bottom of the tank while the oils and greases float to the top. There is no oxygen in septic tanks; therefore, naturally occurring bacteria that function without oxygen (or anaerobic bacteria) break down the solids. This breakdown process is known as anaerobic digestion. Over time, the solids form a layer of sludge at the bottom, the oils and greases form a layer of scum at the top, and partially treated wastewater stays in the middle.

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As more wastewater flows into the first tank from the home or building, the partially treated wastewater in the middle of the tank is displaced and flows out of the first chamber into the second chamber of the tank.  While in the second chamber, additional separation of solids and floatation of scum happens, thus improving the quality of the wastewater. Eventually, treated wastewater, known as septic effluent, leaves the second chamber through a baffled outlet and towards the drain field. Double-compartment tanks provide better treatment because of the additional settling of solids in the second compartment before wastewater exits the tank. Depending on the tank size and overall wastewater flow from a household, wastewater in the tank can have at least 24 hours of settling and treatment before moving into the drain field.

The tank must have a baffle at both the tank inlet and outlet to prevent the wastewater from short-circuiting across the liquid surface and to keep the scum layer and suspended particles from flowing with the wastewater into the drain field (See Figure 2). The exit baffle or tank outlet should also be fitted with an exit filter to capture any solids or particulates in the tank effluent. This prevents solids and particulate matter from exiting and clogging the drain field.

Over time, the sludge at the bottom of the tank accumulates and requires pumping by a licensed professional. It is recommended that septic tanks be pumped every 3 to 5 years or when a system inspection indicates that the tank is more than one-third filled with solids. Pumping frequencies can vary depending on the tank size and the number of people in the household. Local regulations may require septic system inspection and/or pumping on a certain schedule (often every 3 years). Regular pumping is beneficial because it:  

• Ensures that there is sufficient space within the septic tank to hold wastewater and allow for solids to settle
• Prevents solids or sludge from accumulating up to levels that back up into the home
• Prevents sludge and solids from flowing from the tank and causing clogs in the drain field

2. Distribution box
The distribution box is also called the D-box. It is a small round or rectangular watertight containment made of concrete or plastic. The D-box is underground between the septic tank and the drain field piping. It is connected to the outlet pipe on the septic tank on one end and the series of pipes leading to the drain field on the other end.

The purpose of the distribution box is to receive septic tank effluent and evenly distribute it into the pipes that disperse wastewater in the drain field. Uniformly distributed wastewater in the drain field ensures that the drain field operates effectively and prevents one area from being overloaded with septic effluent.
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The Bradford County Conservation District is committed to helping people manage resources wisely.  You can visit the Bradford County Conservation District at 200 Lake Rd in Wysox across from the Wysox Fire Hall. Contact us at (570) 485-3144 or visit our web page at www.bccdpa.com.