Subdivision Septic System Design

Cluster Systems

A Cluster Supply Sewer System is a great option for Residential Neighborhoods and Rural areas. Many times in places such as residential and rural areas, commercial sewer lines are not accessible. When this is the case, a solution has to be created to properly dispose of the waste produced by each house. A Cluster System is the solution.

In some ways, the Cluster System acts like a commercial sewer system but on a much smaller scale. When a developer is planning a new neighborhood, each lot will have a separate septic tank. There will then be an underground piping system that leads from each of the separate septic tanks to one designated area in the neighborhood, known as the 'Green Space'.

While all solid material (sludge) stays inside of the individual septic tanks, the liquid (effluent) portion travels through the underground piping system to the green space. From the green space, the liquid can then be treated.

Below is a picture sequence of a cluster system installation.

There are many types of effluent treatment systems that perform secondary treatment of septic tank effluent. This information sheet describes technologies used for small volumes that are treated onsite. Many systems can be constructed using local materials and labor, which are less expensive and help support the local economy.

Technology Options

Common options for onsite effluent treatment include:

• Sand and gravel filters;

• Coco peat or sphagnum peat moss filters;

• Constructed wetlands;

• Alternative media filters, such as crushed glass, cinders, or other locally available materials; and

• Aerobic and anaerobic filter systems.

These treatment systems are generally used for smaller wastewater flows in rural or semi-rural areas, or for residential subdivisions, hospitals, public markets, resorts, or certain small-scale industries, where space is available. As flow volume increases, effluent filters become less cost-effective because they require very large land areas. Options for larger volumes can be found in the technology matrix and in other information sheets in this information kit.

How They Work

These systems function by passing the effluent through the media, either via gravity or through an effluent pumping system. As the effluent passes through the media, it filters out larger particles and bacteria living on the media consume and reduce dissolved solids and nutrients in the effluent. The result is a much higher level of wastewater treatment that can meet government discharge regulations.

Effluent treatment systems usually have the following things in common:

• A media is used, such as sand, gravel, peat, or crushed glass;

• As effluent passes through the media, organic matter is trapped and consumed by bacteria; and

• These systems require some form of pre-treatment from devices like septic tanks or grease traps. Excessive grease or organic material may clog media filters, making them ineffective.

Media Filters

As mentioned above, there are many types of media that can be used to effectively filter effluent. These systems are relatively easy to build and operate.

Designing and planning effluent filter systems requires knowledge of the media itself, and how many liters of effluent can be applied per square meter each day. Once designed, filter media systems are constructed step-by-step.

Step 1. Build a box.

Step 2. Install a waterproof liner so that the bottom and sides of the box are covered.

Step 3. Install an underdrain piping system to catch the treated effluent after it is filtered.

Step 4. Fill the box with media.

Step 5. Install the effluent distribution piping.

The example shown here is a sand filter designed for a housing complex of 20 units, each with its own septic tank. It serves between 40 and 50 people and producesa high quality effluent that can be discharged into a drip irrigation system.

Constructed Wetlands