Introduction

Percolation areas are used to distribute discharge from a septic tank. It is an integral part of a septic tank facility as it provides the majority of the wastewater treatment. Polishing filters are used to distribute wastewater from the secondary treatment facility. It also reduces micro-organisms and phosphorus in otherwise high quality wastewater discharge. While both percolation areas and polishing filters have different design criteria and components, the construction and installation factors for both are the same. To ensure you install a percolation area/polishing filter which is designed and constructed adequately we recommend a visit to our training and demonstration facility.

The objective of all percolation areas/polishing filters is to distribute wastewater as evenly as possible over the infiltration area, minimising the possibility of the ground becoming over-saturated. In general there are two main types of percolation systems, namely, raised bed and trench systems.

• Trench systems are installed where there is a minimum depth of 0.9m between the trench invertand the bedrock/water table for a secondary treatment system's effluent. This depth is increased to 1.2m for septic tank effluent.
• Raised bed systems are installed where the depths described above are not attainable.

Wastewater distribution can be achieved using a pressurised system or a gravity system, Molloy Precast design, manufacture and supplyboth types:

Gravity systems consist of 4" perforated pipes connected to a single distribution box. This box receives wastewater from the treatment tank by gravity or via a pump and distributes it evenly over the required number of pipes. it is critical that the level of the trench floor and pipe network are exact. This system is susceptible to failure sue to subsidance and poor workmanship.

A pressurised system distributes wastewater over the infiltration area via a network of 32mm dia. perforated pipes connected to a 50mm dia. manifold. This system is less susceptible to failure due to subsidence and poor workmanship ensuring an even distribution of wastewater over the infiltration area.