What Is a Biofilter Septic System?

Nothing is more disheartening than realizing your septic tank could be polluting groundwater. Faulty septic systems can release untreated liquid waste containing pathogens and chemicals that are harmful to humans, wildlife and fish.

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What Is a Biofilter Septic System?

A biofilter septic system is an advanced onsite wastewater treatment solution you install on your property. It uses natural bacteria to purify liquid waste from your septic tank. This secondary wastewater treatment sits between the septic tank and the drain field. Liquid effluent from septic tanks contains dissolved organic matter and nutrients such as phosphorus and nitrogen. These are harmful to the environment and humans. Septic effluent also holds suspended solids, harmful bacteria and pathogens. Septic biofilters remove these organisms to produce gray water that is safe for non-potable use and environmentally friendly.

How Does a Septic Biofilter System Work?

There are two types of biofilter: those that use anaerobic (oxygen-free) bacteria and those using aerobic (oxygen-loving) microorganisms.

How Does an Anaerobic Biofilter System Work?

Anaerobic biofilter systems use bacteria that thrive in an environment without oxygen. The system has the following components:

• Septic tank: Anaerobic biofilter systems use a standard two-chamber septic tank. Bacteria in the septic tank digest the organic matter, converting it into liquid, sludge and gas. The liquid leaving the tank contains dissolved solids, bacteria and viruses.

• Effluent filter: Septic tanks may have an effluent filter to collect undissolved solids like hair and fibers. Wastewater filtration prevents blockages in the drain field.

• Biofilter: The sealed fixed media biofilter contains anaerobic bacteria that further break down the effluent. There are several types of septic biofilters. The Ecoflo septic system uses coconut husk filters, while the Puraflo filter uses peat filters. Other types have textile filters or special absorbent foam ( Waterloo biofilter).

• Drainage system: The clean effluent, with virtually no pathogens, is now safe for discharge into the environment, usually through an existing drain field.

How Does an Aerobic Treatment Unit Work?

This form of biofilter uses aerobic bacteria that thrive on oxygen in the air. The components of an ATU septic system include:

• Septic tank pretreatment: Raw domestic sewage collects in a holding tank. Usually, this is a conventional septic tank that partially digests the waste. Alternatively, you may use a pre-treatment tank where the solids settle.

• Aeration tank: The liquid waste flows from the septic or pretreatment tank into a separate aeration chamber. The chamber has an air blower to feed a continuous supply of fresh air into the tank through a diffuser. Oxygen-loving bacteria digest the waste, leaving a clear liquid that significantly lowers pathogen levels.

• Clarifier: The effluent still has some solids and passes into a clarifier for effluent polishing before discharge.

• Dispersal: The clean effluent flows into a drain field before percolating into the soil.

Tertiary Effluent Treatment

Although the effluent after a septic biofilter has low pathogen levels, some remain. Also, the effluent contains nutrients such as phosphorus and nitrogen. Tertiary effluent treatment produces gray water suitable for irrigation and discharge into a watercourse. These steps include:

• Effluent disinfection: If you plan to reuse the effluent or discharge it into a watercourse, you must disinfect it to kill remaining pathogens. Ultraviolet disinfection is effective for domestic systems and requires minimal maintenance. Alternatives include chlorination and ozone treatment.

• Phosphorus removal: Phosphorus is a common constituent in household cleaning products and waste. Unfortunately, it acts as a fertilizer and causes algae blooms in lakes. You can remove phosphorus from septic effluent using a specialized media filter or by chemical dosing.

• Nitrogen removal: Nitrogen is another product often found in human waste and cleaning products, and causes many of the same problems as phosphorus. Nitrogen reduction is a feature of standard biofilters, although you may need additional treatment to bring nitrogen levels down to meet environmental standards.

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Local Environmental Regulations

While biofilters and ATUs treat domestic waste to higher standards, they must still follow local environmental regulations. Most states require a permit for a biofilter and installers need relevant licenses for installing these alternative waste management systems. Distance requirements, such as to the nearest well and property boundaries, still apply, although many jurisdictions relax these requirements to an extent.

All equipment should comply with the relevant National Sanitation Foundation (NSF) and American National Standards Institute (ANSI) requirements ( NSF/ANSI 40). Systems near the coast and lakes must remove at least 50% of the nitrogen in the effluent ( NF/ANSI 245) and those reusing treated effluent should comply with NSI/ANSI 350.

How Does a Biofilter Differ From Traditional Septic Systems?

An important part of learning what a biofilter septic system is is understanding the difference between advanced septic systems and standard septic tank solutions. Differences include:

• Improved effluent treatment: The quality of the effluent is better as it has fewer solids, less nitrogen and phosphorus and significantly lower levels of pathogens.

• Suitability for poor soils: The higher quality of the effluent allows for the disposal of the effluent in poorer soils and where there's limited soil cover.

• Suitable as a high water table septic solution: With the addition of tertiary effluent treatment, you can use septic biofilters and ATUs in areas with a high water table.

• Suitable for small lot septic systems: You can use these systems in small lots because they need a smaller drain field. Depending on the location, the required drain field is 30% to 50% smaller than for an equivalent septic tank.

• Sustainability: Septic biofilters remove more pollutants and pathogens and mostly use biodegradable biofilter media.

• Odor-free: Septic biofilters and aerobic tank units produce fewer odors than septic systems.

• Maintenance requirements: Biofilter maintenance requirements are higher, primarily due to the need to inspect systems annually and to clean the septic biofilter media. You must inspect the blower and control system on aerobic treatment units every year.

• Cost: Advanced septic treatment units cost more and annual maintenance costs are higher. These are offset by the improved quality of the effluent and the lower environmental impact.