What is a septic system?

PIRANA Systems designs innovative solutions for septic system repair, cleaning, and maintenance. In order to understand how the innovative Pirana Method works, it is necessary to have answer the question, “What is a septic system?” A septic system is designed to be either conventional, without air added to the liquid, or aerobic, with air added to the liquid. While septic systems come in different configurations, their central purpose remains the same: establish and maintain a place for household sewage to be stored and treated. Learn about septic systems below.

A septic system is comprised of three parts: a tank, disposal field, and soil. The purpose of the three parts is simple and easy to understand. First, the purpose of the tank is to remove most of the solid waste from the water. Then, it allows for the “break down” of sewage into water that can be dispersed naturally throughout the soil.

Conventional septic tanks, without air added to the liquid, simply store the solid waste until you remove the solid waste by pumping the tank. Aerobic tanks, with air added to the liquid, grow oxygen breathing bacteria that remove solid waste by digesting it.

Second, the purpose of the disposal field is to spread the liquid from the tank over a large underground area of soil, so the liquid can be absorbed or soaked up by the soil.

Third, the purpose of the soil is to do the final treatment or to purify the liquid from the tank.
Large numbers of tiny life forms called microbes live in the soil. These microbes eat the remaining waste in the liquid. This purifies the liquid so it is safe for humans and will not pollute drinking water or the environment.

What is a conventional septic system?

A conventional septic system is comprised of three parts. The first is the conventional anaerobic (without oxygen) septic tank that receives the solid and liquid waste (called influent) from the house or business that's connected to it. The second is the disposal field that receives liquid waste (called effluent) from the septic tank. The effluent is distributed throughout the disposal field so that it can be absorbed into the surrounding soils. The third is the soil that purifies the effluent.

How the Septic System Works

The way the three parts operate is simple and easy to understand. Within the residence or business, solid waste is put into water so gravity can move it away and into the septic tank. The conventional septic tank is designed to remove the majority of these solids from the water used to carry it to the septic tank. This is accomplished by retaining the influent for several days in the septic tank to allow separation of floatable solids (scum) and sinking solids (sludge) from one another.

Intestinal bacteria from human bodily wastes survive within the conventional septic tank and there secrete enzymes that assist in breaking down the solid wastes into these two forms. By this method, 70% to 90% of the solids that were originally put into water are removed and contained within the septic tank. Over time, these solids build up within the septic tank and have to be removed by pumping and disposal off-site. Typically this means taking the contents or the septic tank (septage) to the local municipal wastewater plant for treatment (digestion) and disposal.

The clarified liquid (effluent) between the two forms of solids, then over flows out of the septic tank as new influent comes in, and is piped to a disposal field. The disposal field can be of many designs and constructions. Most typical is the leach line, though all disposal fields have the same function. This function is to expose the liquid effluent to aerobic soils (with oxygen) that can absorb it. Within the aerobic portions of the soil, there is an abundant community of aerobic microbes, including many species of bacteria that digest the remaining organic matter, purify it, and recycle the liquid back into the environment. The part of a conventional septic system that fails is the disposal field.

The Purpose of the Typical Septic System

The traditional purpose of anaerobic septic systems is to safely recycle the water component of sewage on the site where the sewage is produced. The vast majority of organic matter (solids) entering a septic system is retained in the anaerobic septic tank for periodic removal off site for treatment and disposal (hopefully with a low level of pollution). The requirement for any septic system to have an anaerobic septic tank is the evidence that only the disposal of contaminated water is the purpose.

The soil on the site provides the final treatment, or purifies the water, unless mechanical disinfection is allowed. All onsite septic systems are expected to protect humans from disease, water sources from contamination, and the ecosystems from environmental damage from human sewage.

Human waste enters a septic tank as organic solids (other than urine). The general septic industry to date has not considered the disposal of organic matter and solids onsite because there was no means or method to dependably recycle organic solids on site whether by anaerobic or aerobic septic systems until the introduction of the Pirana System in 2000.

What is Final Treatment?

“Final treatment” means the complete removal, or reduction to government-approved “acceptable levels of concentration,” of specific chemical and biological contaminants contained in the contaminated water from the septic tank prior to contact with humans, exposure to the environment or introduction into surface and ground waters. If effluent cannot receive final treatment by native soil, some approved method of disinfection must be provided. Native soils act as a filter, purifying the contaminated water by capturing and holding biological and organic contaminants in the water for eventual destruction by naturally occurring, aerobic soil microbes.

Default Septic System Design

For the past century, anaerobic septic tanks with disposal fields (hereafter called “conventional septic systems”), and cesspools have been generally accepted in the USA and worldwide as the default designs for onsite disposal of the water component of sewage.

Conventional septic systems and cesspools are essentially a series of three filters. The first filter is the septic tank that separates solids from the water into settled sludge and floating scum and holding these solids in the tank for eventual removal by pumping and transport off site. The septic tank is a very efficient filter as it removes 80% to 90% of solids entering a septic tank. Removing a portion of a flow of material through an apparatus is technically a filtering process no matter how the removal is accomplished. The contaminated water containing soluble and suspended particulate matter from feces and hazardous bacteria and microbes leaving a septic tank is commonly called “effluent.”

The second filter is the disposal field construction. Suspended organic particulates in the effluent will settle out and soluble organic matter will partially coagulate out while trapping a portion of the bacteria and microbes in the contaminated water from the septic tank. This settling out is another form of filtering.

The third filter is the aerobic native soils. The native soil is an excellent filter. After the effluent passes through three to five feet of native soil, all of the remaining organic and biological contaminates are filtered out of the water and held in the soil for digestion and destruction by soil microbes thereby purifying the water so it can safely be recycled.

A cesspool functions as a combined septic tank and disposal field in one construct. The functional life of a typical cesspool is expected to be dramatically shorter than a conventional septic system in comparable soils. The cesspool and conventional septic system both fail from the same biological process.

Soil structure is or should be the determining factor in cesspool and disposal field designs. The right design is critical in projecting how long either will function properly. In the USA, Federal EPA guidelines outline that if a disposal field functions properly for +/- “hoped for” 20 years before a symptom of failure occurs, it is generally considered a properly designed and installed disposal field. What is critical to property owners is this 20-year “hoped-for period” before failure makes septic systems affordable. Unfortunately in many areas of the US, being “affordable” is often not considered in modern septic system designs.

So what ultimately causes failure? The answer is simple. All anaerobic septic systems will eventually fail from biomat clogging of cesspool or disposal field infiltrative soils.

What is biomat?

“Biomat” is the accumulation of natural, very viscous colloidal slimes secreted by obligate anaerobic intestinal bacteria colonizing all of the infiltrative soil surfaces that absorb the contaminated water from cesspools or septic tanks.

Biomat is a slime layer that is bio-chemically resistant to the movement of water through the slime layer. Over time, the accumulation of biomat reduces the permeability of the disposal field design, causing contaminated water to collect in the drain field void spaces or within the vertical column of a cesspool. According to the USA EPA, 95+% of conventional septic system failures are from anaerobic biomat slime clogging the surfaces of the infiltrative soil.

How Biomat Causes Disposal Field Failure

There are positive and negative aspects of anaerobic septic systems. Both are from how modern man deals with bodily waste. First, waste is put in water to take it away from homes and businesses. Then, the water and waste is stored in a cesspool or septic tank that quickly becomes anaerobic as organic waste solubilizes and suspends in the effluent. The organic waste and dissolved oxygen in the water bond together, removing the oxygen from the water and creating anaerobic conditions (no available oxygen for aerobic respiration).

Obligate anaerobic intestinal bacteria that secrete biomat in the drain field soils do not survive outside of human bodies, primarily because they cannot tolerate exposure to oxygen. Oxygen is toxic to them. The development of anaerobic conditions of the water in septic tanks allows biomat-secreting, anaerobic intestinal bacteria to survive in the septic tank. The anaerobic, contaminated water leaving a septic tank or stored within a cesspool eventually creates anaerobic conditions throughout the disposal field construct and in the infiltrative surfaces of the native soil (including cesspool infiltrative soil surfaces).

Native soils are naturally aerobic. Anaerobic bacteria cannot survive in aerobic soils. As within the anaerobic septic tank, anaerobic conditions in the disposal field and infiltrative soil surfaces allow biomat secreting intestinal bacteria to survive. When they finally colonize all of the infiltrative surfaces of the native soil in a drain field or around a cesspool, failure will occur.

Biomat is bio-chemically resistant to the passage of water through its structure. It will eventually reduce the passage of contaminated water through it so that some of the contaminated water entering the disposal field from the septic tank each 24-hour period, or into a cesspool, cannot pass into the native soil. A tiny volume remains in the disposal field void spaces or within the cesspool eventually creating a vertical liquid depth.

Initially, the stored anaerobic effluent in the cesspool or the void spaces of the disposal field rises to a vertical depth that creates hydraulic pressure that forces the anaerobic effluent through the restrictive biomat layer more efficiently. A temporary equilibrium between what enters the drain field or cesspool in our 24-hour living cycle is established.

The vertical depth of the stored anaerobic effluent that created the initial hydraulic pressure remains, but it doesn’t increase. The hydraulic pressure, however, “pushes” anaerobic effluent further into the soil creating a deeper anaerobic soil environment. The anaerobic soil conditions allow more biomat-producing bacteria ever deeper into the soil while supplying nutrients to support their continued survival.

Greater depth penetration creates greater resistance to the passage of anaerobic effluent that eventually requires more hydraulic pressure. The temporary equilibrium is destroyed. Again, a small volume of effluent remains each day in the drain field void spaces. The liquid level in the cesspool or disposal field void spaces increases continuously. Each step forces biomat bacteria further into the native soil causing the requirement for more hydraulic pressure to another temporary equilibrium. Eventually the process runs out of vertical height in the disposal field or cesspool to increase hydraulic pressure. A failure event will then occur.

Symptoms or Definitions of Septic System Failure

It is important to understand that “failure” doesn’t mean no septic effluent enters the soil for final treatment. Biomat isn’t an impermeable layer that doesn’t allow any effluent to be absorbed. In nearly all cases of failure, 99+% of the septic effluent will continue to be absorbed into the native soil for final treatment. The small amount of effluent that can’t enter the soil in our 24-hour living cycle is then “excess” effluent that causes some form of failure. It is this small excess that we see surfacing or is stored in the septic system that eventually backs up toilets and plumbing from rising septic tank liquid levels.

There are classic symptoms of cesspools or conventional septic systems that can presage an event that would be defined as failure:

A. Occasional and Increasing Frequency of Slow Draining Fixtures and Gurgling When Toilets Are Flushed with Occasional Sewer Odors When Toilet Is Flushed
B. Periodic Episodes of Sewage Upwelling into a Tub or Shower
C. Green Stripping from Vigorous Plant Growth over Disposal Field
D. Plant Dead Zone over Disposal Field
E. Occasional Damp or Wet Spots over Disposal Field or around the Cesspool and Septic Tank
F. Back Flow from the Disposal Field into the Septic Tank When the Septic Tank Is Pumped

The five classic descriptions of septic system failure are:

(1) Noxious Odors with Permanent Swampy Areas or Surfacing Effluent over a Drain Field or over a Cesspool or Septic Tank Are Most Common.
(2) Permanent Slow Draining or over Flowing Toilets and Plumbing Fixtures in the House or Building That Make Using the Septic System Difficult or Impossible (Most Disturbing to a House or Building Owner)
(3) Polluted Surface Waters by Liquid Drainage or “Seep” off Site That Can Be Proven to Originate from a Particular Cesspool or Conventional Septic System (Rare)
(4) Potable Water Source (Well or Spring) Contaminated with Human Intestinal Bacteria Where the Source of the Contamination Is a Cesspool or Septic System (Rare in Industrial Countries)
(5) Change in Government Codes or Ordinances That Re-Defines an Existing Septic System as Failed (Occurs Frequently in Industrial Countries)

Summary of the Function of Septic Systems

Anaerobic cesspools and conventional septic systems are only designed to recycle the water component of sewage. They do relatively little to dispose and recycle the organic load or pollutants that enter a septic system. Because a conventional septic system or cesspool is essentially a series of filters, and only the first filter can be cleaned, they are essentially designed to fail over time.

95+% of failures are from the same cause: biomat clogging the infiltrative native soils. Failure isn’t defined as zero absorption of effluent. Failure is defined as any volume of septic effluent, even a tablespoon of effluent, that isn’t purified by the native soil, or approved disinfection method, before contact with human beings, the environment, ground and surface waters, or the plumbing in your home ceases to function properly.

For 17 years, the septic industry has resisted recommending or using the superior capabilities of the Pirana System. The general public depends in most cases on the septic industry for information and solutions. Learn about the Pirana System and see how it is making septic cleaning and maintenance a safer, more efficient process.

Contact PIRANA Systems and place your order for a septic cleaning kit. Products are available to customers around the world.