5.3.2 Septic System

Categories: 5.3 Wastewater Treatment Process Design
Time of issue: 2022-04-28 18:37:34
Views: 0

Description:

Information

Description of the system

A septic system consists of a septic tank and a subsurface wastewater infiltration system (SWIS, leach field) to treat wastewater from individual houses or a cluster of houses. The effluent is not discharged into surface water body.

Septic system is typically applicable to remote or isolated house(s) which are not viable to connect to the public sewers, nor economically to build a connection pipe. It is widely applicable for less environmental sensitive zones. The system needs a piece of land with unsaturated soil for building the dispersal system which size depends upon the soil permeating characteristics and the household populations. The system can be used in almost every temperature.

(Source: NSFC, 2000)

Figure 5.4 Flow chart of conventional septic system process

There is not effluent discharge standard, as the effluent from the septic tank will be treated by microorganisms growing along the dispersal trenches and finally flow mixed with the groundwater. As far as the septic system is built in compliance with the design codes, it should not cause contamination of groundwater for drinking wells or other applications. Of course, the septic system is not an advanced treatment system which applications shall be permitted by the local authority.

B. Design Consideration

Site survey. Selection of the most appropriate system depends on several site-specific factors. A thoroughly site survey shall be conducted by qualified engineers or professionals to investigate the type and condition of the soils (including permeability and stability), depth to groundwater and bedrock, slope and stability of the land, natural drainage characteristic, water course location, tendency to flood, area available for land application, vegetation and planting, and presence or proximity of any potential geologic hazards (primarily landslides), etc.

Design of a septic tank or SWIS refers to Section 4.2.1 and Section 4.3.5, respectively.

C. Construction and Commissioning/testing

Construction and installation of a watertight system is critical to the performance of both the treatment stage and land disposal stage. All tanks must be completely watertight to prevent groundwater infiltration and effluent exfiltration. In addition, all risers and lids must be watertight along with all sewer pipes, sewer pipe joints, and tank inlet and outlet pipe connections.
The sites for dispersal system must be protected from vehicular traffic before, during and after installation to minimize damage to the soil. To protect soil treatment capacity, installation shall be taken place when soil moisture conditions are neither too wet nor too dry.
The trench media, and where used, treatment system sand shall be put in place using methods that minimize compaction of the soil and prevent smearing or glazing of soil in the trench.
Once the trench is constructed, the berm shall immediately have a suitable grass seed applied in order to establish a sod layer as soon as possible.
Use clean water to test the trenches before backfilling to ensure even distribution.
For a pressure distribution system, check the time to fully pressurize the system. Adjust dose time if needed.

D. Operation management

Detailed requirements on operation and maintenance of a septic system are discussed in Section 4.2.1 and Section 4.3.5. Keeping regular inspections and using properly, most of system problems may be avoided or identified timely. Once the following issues are observed, please contact professionals for assistance:

Strong odors in the leach field.
Plumbing or septic tank backup.
Slow draining fixtures.
Gurgling sounds in the plumbing system.
Muddy soil or water ponding around or in the leach field even during dry season.