Question:
There are several laundry machine lint filters on the market. What are the benefits as you see them? If the septic tank has an effluent filter in the outlet tee, would this negate the benefit of blocking laundry lint from entering the septic tank? For a heavily used septic system, is it reasonable to divert the laundry water to a few chambers, with an overflow back to a tee in front of or even after the septic tank? Let's assume that surface distribution of laundry water is not an option.
Answer:
I will address each of your questions:
What are the benefits of laundry machine lint filters as you see them?
When clothes are washed, some fine material is removed from the fabric. This fine material, called lint, ends up in the wash and rinse water, which ends up in the sewage tank.
The fine particles of lint will easily be carried by the flowing wastewater. How much of the lint gets into the soil treatment system is another question. This would depend on the liquid volume of the septic tank, the tank having compartments to slow the flow, and the volume of wastewater discharged by each cycle of the automatic washer.
The liquid moves slowly through a large tank, or not at all when there is no flow into the tank. Some of the lint will settle to the bottom of the tank and become a part of the sludge layer.
I am not aware of research about the amount of lint entering a sewage tank and the amount leaving the tank. I also am not aware of any studies confirming lint to be a major problem clogging the distribution media in a soil treatment system. It is certainly good practice to keep as much solid matter as possible out of the soil treatment system.
An effective filter on the wastewater discharge line from the automatic washer should catch most of the fine lint particles.
If the septic tank has an effluent filter in the outlet, would this negate the benefit of blocking laundry lint from entering the septic tank?
No. A filter in the outlet tee of the septic tank will not affect the flow of sewage into the sewage tank.
The purpose of the outlet filter on a septic tank is to prevent fine solids from being discharged with the effluent. Many different types of outlet filters are available. An outlet filter must be cleaned periodically to be effective in removing solids. Filters should be selected for ease of maintenance, as well as effectively removing solids from the effluent.
An onsite system can benefit from having both a laundry wastewater filter and an effluent outlet filter in the septic tank.
As an aside, when outlet filters are placed in sewage tanks, installers should offer homeowners a service contract. Servicing the outlet filter is not considered a desirable job by the average homeowner. Yet the outlet filter does need periodic service to effectively remove fine solids. A service contract will be beneficial both to the homeowner and to the installer.
For a heavily used septic system, is it reasonable to divert the laundry water to a few chambers, with an overflow back to a tee in front of or even after the septic tank?
First of all, a septic system should be sized adequately for the average daily sewage flow. Thus, there should be little difference in the flow pattern between systems, and no system considered “heavily used.”
In some state codes, septic tanks are required to have chambers. Two chambers is usually the accepted number. The laundry water should not be discharged into the second chamber of a two-chamber septic tank. That sewage liquid would flow much faster to the tank outlet, carrying more lint particles out of the septic tank.
If the tank has more than two chambers, the laundry wastes definitely should not be discharged closer to the tank outlet. All of the wastewater should flow through the sewage tank and as slowly as possible.
Most tank compartments have an opening in the compartment wall through which the sewage flows from one compartment to the next. A much better way to provide effective treatment and slower flow is the use of an outlet tee on the compartment wall. As the sewage flows into the tank, the liquid level rises in the first compartment and begins to flow into the second compartment.
The liquid level in the second compartment should be at least two inches lower than in the first compartment. This forces the liquid in the second compartment to rise before effluent flows out of the sewage tank. This slowing of the flow is called “attenuation” of the flow. Sewage tanks with an outlet tee in the compartment wall and a lower liquid elevation in the second compartment will have a much slower flow out of the tank.
The slowest possible flow through the tank will result in the best effluent quality. Good effluent quality is essential for an extended life of the soil treatment system.
The laundry water must not be discharged “after the septic tank.” All sewage wastes from a home must flow into the inlet tee of the septic tank.
