QUESTION: Why care about something like plastic microbeads?
ANSWER: The starting point in any discussion about the life span and effectiveness of individual sewage treatment systems is making sure effluent coming out of the septic tank does not exceed about 160 mg/L BOD and 60 mg/L suspended solids. When BOD levels are consistently above 160 mg/L and certainly over 200 mg/L, it is common to recommend additional pretreatment to reduce the levels before discharge to the soil for final treatment and dispersal. This keeps biomat development in check and within the long-term acceptance rate parameters for soil. At these levels, it is assumed with proper maintenance (septic tank cleaned at regular intervals, excess water avoided, etc.) the system will last indefinitely.
One of the primary purposes of these limits – other than initial treatment through anaerobic digestion in the tank – is to hold the larger solids in the tank. This involves allowing time for particles that are heavier than water to settle, forming the sludge layer in the bottom of the tank and keeping the floating solids – soap scum and grease – in the tank for cleaning. Effluent passed on to the soil treatment area should come from the clear zone in the tank. Having proper baffles along with regular cleaning ensures that the tank will provide this function.
To make sure that larger solids are not reaching the soil treatment area, most states have started requiring installation of an effluent screen. This screen promotes regular cleaning, and if there is an upset in the tank, the solids are captured and plug the screen instead of passing through and plugging the soil treatment area. This is all good practice, and it works.
SUSPENDED SOLIDS …
However, we need to have another discussion about solids – those that remain suspended and are small enough to move readily through the screen and into the soil treatment area. If these solids are small pieces of organic material, they will break down or be consumed in the soil. However, if they are inert particles such as clay soil particles or plastics or other synthetic materials, they will not break down in the soil environment and will plug the soil pores, permanently reducing the ability of the soil to accept septic tank effluent. There is no fix when this happens other than replacement.
When septic service professionals get together, talk often turns to situations where a system is having problems and the homeowner is using certain cleaning products or bath oils or a variety of other products. The conclusion is that this is somehow affecting the system, but most of it is anecdotal and without a lot of research to back it up. Nevertheless, we encourage homeowners to not use excessive amounts of soap or cleaning products.
Enter the microbeads: small plastic pellets used in personal care products such as hand soap, exfoliating scrubs and toothpaste. When these products are used by consumers and are washed down the drains of sinks and showers, the microbeads end up in wastewater treatment systems. Some of these beads are heavy and they sink and are contained in the sludge in the bottom of the tank. Others float, ending up as a suspended solid in the septic tank.
Interestingly, it is not our industry that has highlighted these beads as being a problem, but researchers looking at the outflow from municipal treatment plants where the beads have been discharged to the surface waters and are then consumed by fish, causing potential environmental and health concerns.
SAY NO TO MICROBEADS
For us, though, these microbeads or microplastics – less than 5 mm in their longest dimension and often smaller, down to 0.335 mm – will easily pass through the effluent screens we have in place and continue on to the soil treatment area. And they are common in many products that would be used by a homeowner.
These include toothpaste, soap, exfoliating creams and lotions, and bathroom cleaning products. In my view, this supports some of the anecdotal discussion about cleaners and soaps causing problems in certain areas. We certainly want to limit the use of these products to protect the soil treatment part of the system.
This year has seen a number of states, including California, Illinois and Minnesota, ban the use of products containing microbeads. A number of other Great Lakes states are also considering bans. The good news is that these personal care and cleaning product manufacturers have recognized the problems and are eliminating their use.
As a service provider, you should be supportive of any moves to eliminate these beads from products. A smartphone app is available to scan ingredient lists to determine if these products contain plastics that make up microbeads. Continuing to have conversations with clients and homeowners about not overusing products will also help prolong the life of that wastewater treatment system in their backyard.