If you have a septic system, you have probably used, or considered using, a septic additive. The advertisements make them sound like a cheap and natural way to maintain your tank and system. For just a few dollars, you can remove more sludge from your tank by flushing their additives down your toilet. But do they really work as advertised? Are they worth the money? Can they help with your failing septic system?
The simple answer is no. Your septic tank already has all the bacteria it needs to work properly, as long as you routinely pump it every 3-5 years.
But couldn’t the additives still help?
Well, no. Most septic tank additives contain beneficial bacteria or enzymes, or a combination of both, that the companies claim will help digest or breakdown the sludge (or waste solids) in your tank. But one of the main purposes of your tank is to collect human waste, which is loaded with the necessary bacteria species to digest the waste solids. Studies have shown that a typical, 1,000-gallon septic tank contains an average population of 3.64 billion to 3.64 trillion bacteria cells per gallon. Additives claim to add up to several billion bacteria cells per treatment. Though that sounds like a lot, it would only account for 0.1 – 1% of what is already present in your tank.
Couldn’t a little still go a long way?
The answer is still no. Numerous research studies have tested the effect that additives have on septic sludge volume and water quality. Some studies used lab-based, batch reactors (essentially, small septic tank simulations) and others tested numerous home septic tanks. All of the studies concluded that additives did not show any significant sludge reduction or increase in bacterial populations. One additive actually introduced a negative effect by increasing total suspended solids (the small particles in liquid waste) that could impede the normal flow of the drain field. Studies also suggested that additives should not be used as a substitute for, or as a means to reduce, septic tank pumping frequency.
Don’t Forget The Bottom Line!
Septic additives cost approximately $4-10/month, or $50-120/year. One of the most important maintenance tasks to ensure a properly functioning septic systems is to routinely pump your septic tank. The University of Maryland Extension recommends that you pump your tank every three to five years. The national average for pumping a septic tank is $380. That means that the expense of additives would cover the cost of routinely pumping your tank.
So the bottom line on septic tank additives is that they aren’t worth the money. Just call your local pumper and schedule a pump-out.
This post was co-written by Daphne.
Breathing Room 
Please, what are the things to look for when constructing a drain field? Thanks.
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Hello: There are numerous considerations in a septic drainfield. First is that the site and soil has been evaluated to ensure that the soil can take the appropriate amount of wastewater daily per design specifications (based on occupancy and soil characteristics) and effect proper treatment to protect human and environmental health. The soil is where the vast majority of treatment (nutrient reduction and pathogen elimination) occurs. If you have a design plan, that will inform you of how much soil dispersion (drainfield) area is needed to handle the design daily flow. The design will take into account the type of drainfield also. If you don’t have a design and your soils have not been evaluated, that is the first step. Not all soils make for an adequate wastewater treatment septic system! County health departments are usually the agency that regulate and design septic systems and they should have a list of area installers. Also most states require septic systems to be designed and installed by certified or licensed individuals. Due to the potential contamination of nearby water wells, proper design and installation is critical to public and environmental health!
On the drainfield question, there are many types and the use depends on the soil and deign daily flow. A conventional drainfield uses preforated pipe in gravel trenches, then there are plastic chambers which don’t use gravel and are easy to install. Important with all drainfields, in addition to soil quality which is most important, are proper installation to ensure even flow to entire soil dispersion area. Proper elevation from house to tank to distribution box (if applicable) to each drainfield trench is critical.
Please see the following links for more specific information: https://www.co.hendricks.in.us/egov/documents/1488484070_73465.pdf
https://content.ces.ncsu.edu/septic-systems-and-their-maintenance
https://content.ces.ncsu.edu/septic-system-owners-guide
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Hi Andy, thanks for this expository piece. Are there ways to increase bacterial load in a septic system? I mean human intervention.
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Hello. As to considering ways to increase bacteria to your septic system, it is important to understand that household wastewater is loaded with bacteria, both beneficial and pathogenic. Much of this population comes from our digestive and intestinal tract. Our wastewater contains from 4 to 350 billion cells per gallon naturally, which amounts up to 500 trillion cells per septic tank. More than enough to help digest the organic matter in waste. However, that enormous load of bacteria requires a tremendous amount of oxygen to efficiently convert wastes including the initial form of nitrogen, ammonia to nitrate, which then is subsequently converted to nitrogen gas by bacteria in the absence of oxygen. This nitrogen gas can ultimately be released to the air, which is made up of 78%, (hence is recycled). Allowing air (oxygen) to reach the underground drainfield component of the system will aid in this conversion to nitrate. An Advanced treatment unit or Best Available Technology (BAT) unit essentially is feeding the bacteria with air to provide for enhanced organic matter and nutrient breakdown.
So, given the natural population of bacteria in wastewater, there is no need to supplement it. For more informations on this topic see the resource on our webpage: https://extension.umd.edu/well-and-septic/resources.
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