An Onsite Wastewater Treatment System Owner’s Manual

A septic tank with soil dispersal trenches is a common wastewater treatment system that uses an underground tank designed to collect and pre-treat WASTEWATER from your home or establishment. As WASTEWATER flows into the tank, heavier materials settle to the bottom and form a SLUDGE layer, while lighter greases and fats float to the top, forming a SCUM layer. Clarified EFFLUENT is discharged from the center layer of the tank into a soil treatment system where it is dispersed into the surrounding soils. However, if solids leave the tank, the soil at the bottom of the dispersal trenches can clog. When clogging occurs, WASTEWATER is not dispersed or treated effectively, which can cause WASTEWATER to back up into the building or come to the ground surface. It can potentially lead to expensive repairs or replacement of the soil treatment system.

The use of EFFLUENT screens is becoming more common. Usually, an EFFLUENT screen is placed in the outlet tee of the septic tank to enhance solids retention in the tank, helping to prevent blockages and clogging that can damage the soil treatment system. Screens come in a variety of shapes and sizes and can often be retrofitted into existing septic tanks or can be installed in a separate basin following the septic tank.

How an Effluent Screen Works

The simplest EFFLUENT screens are slotted cartridges that are inserted in the septic tank’s outlet tee with seals so that WASTEWATER must pass through the slots to leave the tank. Any solids that are larger than the slots will be retained in the tank. Over time, retained solids collect on the screen and clog the slots. Although this indicates the screen is working, screens must be cleaned periodically to avoid sluggish drains, SEWAGE backups, or sewage tank overflows.

Various types of EFFLUENT screens are available; some are more efficient at retaining solids and/or require less frequent cleaning. For example, the size of retained solids may be from 1/8 inch down to 1/32 inch, or even smaller to prevent clogging of small holes in some types of pressure systems. Some screens have more than one stage to filter out successively smaller solids.

To decrease how often screens need to be cleaned, larger screen surface areas can be used. Some screen designs promote solids falling off and back into the tank. Another way to decrease MAINTENANCE is to connect multiple screens using a manifold at the tank outlet. This can also increase the flow capacity of an EFFLUENT screen system.

A high water alarm is recommended to alert the system OWNER if their EFFLUENT screen clogs. The alarm would be activated by a float when the WASTEWATER level in the tank rises above normal. In pressure systems, high water alarms are necessary because of potential pump MALFUNCTIONS as well as filter clogging.

Benefits of using EFFLUENT screens include:

• Screens reduce solids discharged into dispersal trenches and prevent or delay clogging;
• Screens are relatively inexpensive (compared to replacing the soil treatment system);
• Screens are simple to maintain; and
• Screens can be installed in new systems or retrofitted into existing systems.

EFFLUENT screens are used in many wastewater treatment systems. The U.S. Environmental Protection Agency has established five management models with progressively increasing management controls as sensitivity of the environment and/or treatment system complexity increases. MANAGEMENT MODEL I specifies appropriate program elements and activities where treatment systems are owned and operated by individual PROPERTY OWNERS in areas of low environmental sensitivity.

The objective of this model is to ensure that:

• Systems are designed and installed in accordance with appropriate state and local regulations;
• Homeowners are knowledgeable of their particular system and provide routine MAINTENANCE (INSPECTIONS and pumping) necessary for the system to operate properly; and
• Homeowners ensure a MALFUNCTIONING system is repaired in accordance with Missouri law.

This model is generally appropriate for septic tank systems including an EFFLUENT screen. However, in some sensitive environments or where an EFFLUENT screen is part of an aeration treatment unit or system with a pump, MANAGEMENT MODELS II, III, or IV may be recommended.

EFFLUENT screens can retain solids in your sewage tank and help protect other components in your system. The screen must be cleaned regularly to continue that protection and prevent SEWAGE backups.

Design and Construction

Simple EFFLUENT screens are molded of plastic; however, screens may be made of stainless steel, stacked plastic plates and spacers, filter bristles, plastic discs, etc.

EFFLUENT screens must be accessible for cleaning; they may be:

• A septic tank outlet screen, which must be accessible – septic tank manhole access recommended;
• A screen pump basket or screened pump vault, which must be accessible through a pump tank manhole; and
• A pressure line screen, which must be accessible through a pump tank manhole, in a separate basin, or in a component box.

To be effective and not require cleaning too frequently, EFFLUENT screens must have:

• A large enough surface area and be designed to handle the anticipated maximum daily flow; and
• The slot, screen, or rating necessary to retain the size of solids necessary to prevent clogging soil dispersal trenches and other components of the system.

A screen or filter with more surface area or rated capacity than necessary could pay off in the long term by requiring less frequent cleaning.

Maintenance - Inspections and Cleaning

Some EFFLUENT screens that are located in the septic tank outlet can be inspected and cleaned by the OWNER, with some important precautions.

• Never enter a septic tank; poisonous gasses or a lack of oxygen can be fatal;
• Wear protective clothing, including gloves and eye protection;
• Wash your hands and clothing when finished; and
• Secure the tank lid to prevent accidental entry.

System OWNERS may also hire a REGISTERED ONSITE WASTEWATER TREATMENT SYSTEM installer or qualified SERVICE PROVIDER to perform the necessary MAINTENANCE. When a screen pump basket, screened pump vault, or other type of screen is used in the system, it may be located near the bottom of a tank or may be harder to service. These are best serviced by a REGISTERED ONSITE WASTEWATER TREATMENT SYSTEM PROFESSIONAL or other qualified SERVICE PROVIDER.

EFFLUENT screen in septic tank outlet:

• Remove the access cover over the tank outlet;
• Observe the WASTEWATER level in the tank in relation to the outlet level;
• If the WASTEWATER level is high, it must be lowered before inspecting and cleaning the filter. Lower the level by allowing WASTEWATER to drain while using no water in the house or establishment or by contracting for the removal and sanitary disposal of WASTEWATER and SLUDGE from the tank;
• If the WASTEWATER level is at the bottom of the outlet pipe, remove the screen;
• Follow manufacturer’s recommendations. Clean the screen over the tank inlet manhole using water spray and direct the solids and spray into the tank;
• Replace the screen; and
• Secure the tank access cover(s).

EFFLUENT screens in other locations:

• Remove access cover(s);
• If necessary, pump out WASTEWATER to the next system component or with a vacuum truck;
• Disable the pump;
• If possible, close valves to isolate screen(s);
• Remove and inspect the condition of the screen;
• Follow the manufacturer’s recommendations. Spray the screen to clean it over a tank access and direct the solids and spray into the tank, or alternatively, replace with a clean screen and take the clogged screen off site for cleaning;
• Replace the screen, open valves, and enable the pump;
• Check for WASTEWATER leaks; and
• Secure all access covers.

Homeowner's Instructions

• DO NOT ENTER a septic tank for any reason! Noxious gasses that are in septic tanks can cause serious injury or death.
• Wear waterproof, disposable gloves and safety glasses. Remove the septic tank manhole cover where the screen is located and note the liquid level in the tank. The liquid level should be at the bottom of the outlet pipe. If the liquid level is above the outlet pipe or the EFFLUENT screen, do not remove the screen. This is a sign of problems somewhere in the system, such as a clogged screen, pump failure, or clogged soil treatment system. Call a REGISTERED ONSITE WASTEWATER TREATMENT SYSTEM PROFESSIONAL and have the tank’s contents pumped before removing the screen.
• If the liquid level is at the bottom of the outlet pipe, remove the screen from its casing. Note the condition of the screen and the extent of build-up to help determine when to clean the screen. Using a garden hose, spray off the screen over the first manhole (closest to inlet pipe). Be careful to prevent splashing onto your body or clothes or into the yard. Do not clean the EFFLUENT screen in the grass next to the septic tank; SEWAGE in your yard is a public health risk.
• Return the screen to its casing once it has been cleaned.
• Secure the manhole cover once you are finished. The solids from the screen cleaning will settle and get removed the next time the tank is pumped during routine MAINTENANCE. Make sure the screen is reinstalled correctly to ensure proper OPERATION.
• Once the job is complete, dispose of the gloves and wash your hands thoroughly with soap and warm water. If your clothes were contaminated, remove them immediately and launder in hot water and dry on high heat.

Effluent Screen Do’s and Don’ts

Large volumes of WASTEWATER generated in a short period of time can result in turbulence in your septic tank and reduce retention time, which can lead to solids clogging the EFFLUENT screen.

Do’s

• Limit the use of water-using fixtures to one at a time.
• Disconnect water treatment devices such as water softeners from your sewage tank.
• Do laundry throughout the week, rather than doing it all in one day.
• Add a lint filter to the outlet hose of your washing machine.
• Avoid or limit the use of garbage disposal and scrape all dishes well before placing in a dishwasher. Dispose of food waste by composting or in the trash.
• Replace filter if found in disrepair.
• If your septic alarm signals, don’t ignore it!

Don’ts

• Your sewage system is not a trash can. Don’t put dental floss, feminine hygiene products, flushable wipes, condoms, diapers, cotton swabs, cigarette butts, coffee grounds, cat litter, paper towels, paint, pesticides, or other hazardous chemicals into your system.
• Reduce the amount of strong cleaning chemicals and antibacterial soaps used in the home. These can interfere with treatment in the septic tank or aeration treatment unit.
• Do not flush unused or expired medications; take them to a prescription drug collection site.