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Commercial Septic System Operation and Maintenance

For some commercial establishments, the sources and characteristics of wastewater may be quite similar to those of residential wastewater. For other businesses and institutions, however, wastewater may be very different: for example, it may contain harsh industrial-strength cleaners or high concentrations of oils, or it may derive from processes (e.g., small-scale manufacturing) that introduce chemicals and other substances not found in residential wastewater. Accordingly, many commercial septic system owners face a couple of special considerations in operating and maintaining their systems.

Fats, Oils and Grease

The most serious problem that plagues commercial septic systems is the carry-over of fats, oils and grease (sometimes referred to as FOG) into the drainfield. This may be the result of improper maintenance and/or poor system design. When carry-over occurs, these materials tend to cling to the infiltrative surface (biomat) of the drainfield or alternative treatment system (e.g., sand filter), reducing the absorption capacity of the system. Over time, this leads to system overflows (i.e., breakout), at which point, depending on the extent of damage, the drainfield will need to be repaired, extended or even replaced. Fats, oils and grease are particularly pernicious because they are slow to biodegrade (given that the enzymes that break them down are less active in the lower temperatures found in the septic tank and drainfield soil) and hence simply accumulate in the soil.
The drainfield of a well-designed and maintained system can handle small amounts of FOG, such as natural body oils carried over from a household's shower water. However, drainfields or alternative treatment systems cannot accommodate significant (i.e., more than about 30 mg/L) concentrations of FOG, such as that produced by restaurants, bakeries, cafeterias and camps (and even households that are heavy garbage disposal users and regularly pour cooking grease down their drains).

Grease Traps 

For this reason, many states require the use of grease traps (also called grease interceptors) by restaurants and similar commercial establishments. Grease traps are holding tanks, often modified septic tanks, that receive kitchen wastewater prior to the passage of that wastewater to the main septic tank. Other non-kitchen wastewater from the establishment (e.g., from bathrooms, laundry facilities) flows directly to the septic tank. In the grease trap, wastewater is slowed and allowed to cool somewhat, giving fats, oils and grease have a chance to settle out before the effluent passes to the septic tank, where further settling occurs. Some states mandate the use of three grease traps in a series, a configuration shown to be effective in reducing restaurant grease and oil concentrations to acceptable levels before effluent reaches the drainfield.
Traditionally, grease traps have been used in a range of commercial establishments, including garages, automotive facilities and other commercial/industrial situations. Grease traps at these facilities are being phased out, with zero discharge becoming the standard by 2003. Septic systems may be used for domestic or toilet wastewater at these establishments, but not for wastewater generated by automotive/industrial processes. (Under EPA guidelines, this wastewater must be collected separately and disposed/recycled off-site.) Going forward, grease traps will mainly be used at restaurants and other facilities were food is served/processed.
Location of grease traps is mandated by local ordinances. Typically, these traps are located as close to the source of the FOG as possible. Grease traps generally range in size from one to three times the average daily flow that will be discharged into it. For example, a restaurant serving 100 customers daily who contribute 10 gallons per day of kitchen wastewater will require a grease trap that is between 1,000 to 3,000 gallons. As with the main septic tank, proper sizing of the grease trap is critical to its ability to fulfill its function.

Good Operation and Maintenance 

Good operation and maintenance practices enable the grease trap and septic tank to work effectively in reducing grease and oil. Restaurants and other establishments should scrape food scraps and congealed fats into the garbage, use drain covers and sink baskets and strainers to prevent solids from entering the flow of wastewater and eliminate, or at least limit, the use of a garbage disposal. Cooking oil and grease should never be poured down the drain. Finally, commercially available septic system additives that claim to reduce oils and grease should not be used. Although these additives do indeed dissolve oils and grease, this only increases the likelihood that these materials will be carried over to the drainfield rather than remaining in the grease trap and septic tank where they can be slowly broken down and pumped out at regular intervals. Carried-over oils and grease, as noted above, clog the biomat, decrease the absorption capabilities of the drainfield and eventually can lead to system failure.
A note about dishwashers and grease traps: some experts recommend that wastewater from dishwashers not be discharged into the grease trap but rather flow directly into the septic tank. This is because the high rate of flow and high temperature of the dishwasher wastewater can cause excessive turbulence in the grease trap (usually smaller in size than the septic tank) and emulsify FOG, resulting in carry-over to the septic tank and from there to the drainfield.
Perhaps above all else, the key to the effectiveness of the grease trap is regular, frequent pumping. Depending on the size of the grease trap and the strength and flow of wastewater at a given commercial establishment, required pumping frequency may range from twice per month to once every three or six months. A proper pumping does not just remove the liquid in the grease trap but scours the grease trap and the associated lines to eliminate caked-on substances and oily residue. Pumping should be done by a licensed pumper who will dispose of grease and oils properly (e.g., at approved recycling sites). Rogue pumpers or commercial septic owners who dump fats, oils and grease illegally into municipal sewers cause significant damage to the sewer systems and cost billions of dollars in damage.

Tank Pumping Frequency

As with residential systems, regular, scheduled pumping of the septic tank is arguably the most essential element of commercial septic system maintenance. The important difference lies in the frequency of pumping: commercial septic tanks typically require (much) more frequent pumping than their residential counterparts. 
There are several reasons for this:

 Faster rate of wastewater flow, resulting in greater likelihood of solids carry-over to drainfield

 Greater strength of wastewater (higher "organic load," that is, higher concentrations of solids and fats, oils and grease), resulting in faster accumulation of solids in septic tank

 Presence of harsh cleaners and other chemicals not normally found in household wastewater, potentially resulting in harm to bacteria that breakdown wastewater in the septic tank

 Varied and changeable group of system users (employees and customers), resulting in somewhat lessened ability to control/enforce good maintenance practices (as compared to household)

How frequently you will need to have your particular tank pumped depends on a number of factors, including:

 Type and size of your establishment

 Size of your septic tank

 Volume and rate of wastewater flows

 Amount of organic matter (e.g., waste solids, food scraps, fats/oils/grease) in your establishment's wastewater

The first two factors are essentially fixed. If, however, your septic tank is undersized, you may need to replace it with a larger tank to improve the quality of wastewater treatment. The second two factors can be significantly influenced by your operational practices.
Here are some things you can do to avoid overstressing your septic system over the long term and using pumping (which will always be necessary, whatever your maintenance habits) as a substitute for good operational basics:

 In restrooms: make sure plumbing fixtures don't leak; install automatic shut-off faucets; provide hand dryers instead of paper towels

 In kitchens: divert kitchen wastewater to grease trap; scrape plates into the garbage, not the sink; install drain covers and sink baskets/strainers to prevent solids (food scraps, FOG) from entering your system; avoid use of garbage disposal; use water-saving dishwasher cycle; use mild detergents, not harsh industrial cleaners; use paper towels rather than rags to mop up grease from counters, grills, etc.

 In laundry facilities: avoid use of harsh detergents; space out laundry over the course of the week rather than doing establishment's washing all at once

 
An inspection of your septic system by a licensed septic inspector (which should be an annual event) can help you determine the pumping frequency your tank requires. You should schedule pumping with a licensed pumper based on your required frequency (e.g., every three months, twice a year). This same pumper may also be able to pump out your grease trap. Note, however, that grease traps will almost always require more frequent pumping than your septic tank to function effectively. Pumping generally costs $200-$350 per 1,000 gallons of septic tank volume.
The bottom line for commercial septic systems is: have a knowledgeable septic professional determine how frequently your tank and grease trap requires pumping, set a maintenance schedule based on that and stick to it!

Septic tank risers

An important part of septic system maintenance, inspection and pumping must be performed through the septic tank inspection ports and service lids.  An effective method of providing proper access is through the installation of septic tank access risers.  This allows the maintenance professional to access the lids on the tank without having to unearth them each time the system needs service.  The installation of risers can usually be completed in one or two hours.  Most pumpers offer this service.

Septic Tank Effluent Filter

A filter placed at the outlet of the septic tank to trap suspended solids that are not heavy enough or had had insufficient time to sink to the bottom of the tank. Effluent filters must be periodically cleaned (e.g., when tank is pumped out) so that they do not clog up and back effluent into the house. Effluent filters come in many shapes and sizes, a licensed service provider can determine which filter is best suited for your system.