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Blog —› July, 2012

Percolation Area: How it works, Installation Errors and Sizing

Posted on July 4, 2012 by Comments are off

How does a percolation area work?

A percolation system is now standard for all new septic tanks installed in Ireland today. These systems are engineered to treat the partially treated effluent from the septic tank and to distribute this treated liquid into the underlying ground water. If constructed correctly, and the site has the right conditions a standard percolation system will last trouble free for many years with little maintenance. A typical percolation system is composed of a series of trenches half a meter wide and 18m long. Each trench is made up of the following components as seen in the image below, 250mm of clean stone, a 4” distribution pipe, a second layer of clean stone to cover the pipe and a geotextile membrane covered with a layer of soil brought up to ground level. It is important that the trench is ventilated for an adequate oxygen supply. This is achieved by connecting the pipes at the end of each trench together and pointing a single pipe out of the ground for ventilation. This ventilation pipe can be brought up near a fence or boundary if desired. Effluent from the septic tank has to be fed into a distribution box. The purpose of this box is to ensure that each trench receives an equal volume of wastewater. Over dosing one trench will cause that trench to breakdown.

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Septic Tanks: How they work and tank sizing

Posted on July 4, 2012 by Comments are off

How does a septic tank work?

The purpose of a septic tank is to separate solids and fats, oils and greases (FOG) from the wastewater, emitting only a clarified liquid. As can be seen in the image below, solids settle to the bottom of tank creating the sludge layer while FOG rises to the top creating the scum layer. This leaves a clarified liquid in the centre which is discharged into the percolation area.  A septic tank should also have tees at the inlet and outlet, the purpose of the inlet tee is to prevent the influent flow from disturbing the scum layer, dissolving it back into the clarified zone. The purpose of the outlet tee is to prevent the scum layer being discharged into the percolation area. The contents of the septic tank is anaerobic, meaning there is no oxygen present. This results in the production of gases such as methane, hence, ventilation of the tank is required to release these gases. A septic tank should be designed to allow wastewater stay in the tank long enough to allow solids and FOGs separate from the clarified liquid. If this dwell time is insufficient, un-clarified effluent will be emitted from the septic tank which can cause the percolation area to break down.

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Domestic Wastewater Treatment: An Introduction

Posted on July 4, 2012 by Comments are off

Over 400,000 households in Ireland have on-site wastewater treatment systems. Typical wastewater treatment systems have two components, namely, a septic tank and a percolation area. Both components are essential to ensure adequate wastewater treatment. Inadequately treated wastewater can impact on the quality of ground water, drinking water and surface water which in turn can affect human health as well as the surrounding environment.

Domestic wastewater is made up of solids, biological pollutants as well as fats, oils and greases (FOGs). Removal of these materials is by a combined effort between the septic tank and percolation system. The purpose of a septic tank is to remove FOGs and solids from the wastewater, while the purpose of the percolation area is to biologically treat the wastewater, removing biological pollutants and to distribute treated wastewater into the groundwater network. It is vital that both components are installed and maintained properly to ensure a trouble free on-site wastewater treatment system.

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