How to Add a Biofilter to a Septic Tank Drain Field

What You'll Need
Appropriate biofilter material
Perforated piping

Adding a biofilter to a drain field is becoming a requirement in many areas. The biofilter will help to break down sewage material faster as they remove nasty bacteria. This is better for the environment, and will reduce the load the soil has to pull in the drain field. Installing a biofilter isn't the easiest task, but it may be necessary for many homeowners. 

Step 1: Prepare the Field

It's much easier to install a biofilter in a new drain field. If you are upgrading your current system, the field will need to be done again from scratch. You will need to remove the backfill, the pipes, and the gravel. The most effective biofilters are placed at the bottom of the drain field under the piping system. These are called trickling biofilters. Once you have the field prepared, you will need to contact your county inspectors to ensure you are following proper codes, and the biofilter is suitable for your area.

Step 2: Choose the Biofilter

There are several types of tricking biofilters to choose from. Some systems use a fiberglass basin filled with an absorbent material that will remove bacteria and digest solids. This is best for small drain fields. These systems can be monitored remotely to alert you of a problem before it gets out of hand. Other types of biofilters will use a peat fiber as the filtering media. As effluent is passed through the pipes, the perforations pass the material over the peat fiber. This absorbs, assimilates microbes, and breaks down ammonia and other pathogens. This is a more expensive filter, but is best for large drain fields.

Step 3: Lay Out the Filter

Once you have chosen the filter that's best for your field, you can begin to lay the filter out according to the manufacturers instructions. There usually needs to be a slight gap between the perforated pipes and the biofilter. This gap will eventually get filled with gravel or backfill, but will allow the effluent to be evenly distributed over the filter. The gaps can be created with small stakes if the directions call for it.

Step 4: Place the Pipes

Once the filter is in place, you can start to place the pipes in the trenches. This will be done no differently than laying out an ordinary drain field piping system. Once the pipes are back in place, be sure the perforations are oriented so they will allow effluent to pass over the filter. 

Step 5: Add Gravel and Backfill

With the pipes in place, you can begin to add the gravel over the pipes. Some of the gravel will settle naturally under the pipes, this is normal and fine. With the gravel placed in the trenches, you can begin to add backfill. 

If you already have a drain field in place, and don't want to deal with the hassle of digging it up, there are above-ground filters available. These are usually just as complicated to install, and won't work as effectively. You can check with your local home improvement store, or do a simple Internet search to find these units.