| ON-SITE SEWAGE SYSTEM MANAGEMENT FOR FOOD SERVICE ESTABLISHMENTS | |
Robert Simmons and Richard Burleigh | |
Restaurants: A Risky Business for On-site Sewage Systems | |
| Food service establishments risk significant problems with their on-site sewage disposal systems. On-site sewage systems were originally designed for domestic, residential applications. Sewage, or wastewater, from food service establishments is "stronger" than wastewater from typical households because it contains more oils, greases, food particles, and disinfectants. Food service establishments also often discharge large volumes of high temperature wastewater from dishwashers. | |
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The Basic Operation of an On-site Sewage System | |
A typical on-site sewage system has three working parts: septic tank, drainfield and the soil below the drainfield. The primary function of the septic tank is to separate wastewater into three main components: sludge, heavy solids which settle on the bottom of the tank; effluent, the clarified middle liquid layer; and scum, the lighter components of wastewater such as greases and oils which float on the surface of the effluent layer. Bacterial action in the septic tank partially decomposes some of the solids. The drainfield distributes the effluent discharged from the septic tank over a large subsurface area of soil. The soil provides the final treatment and disposal of septic tank effluent. Many eating establishments also have a grease trap before the septic tank to reduce the amount of grease and oil entering the septic tank. When some of the scum or sludge in the tank is allowed to flow out to the drainfield, it has the potential to clog the pores in the soil. Such clogging reduces the ability of the soil to allow the effluent to slowly percolate downward. When the soil becomes excessively clogged and can no longer accept the amount of wastewater discharged, the wastewater may flow to the surface, indicating drainfield failure. Ignoring the additional risk factors associated with food service establishment wastewater will lead to an increased chance of a drainfield failure. However, managers can offset these risks by managing wastewater generation at the source and by establishing a timely sewage system maintenance plan. The elements of managing wastewater generation include the management of flow, strength, temperature, and toxic compounds. | |
Managing Wastewater Flow | |
Every reduction in wastewater flow that you achieve will increase the amount of time wastewater remains in the septic tank. Extended treatment time allows increased separation of solids, liquids, and oils, as well as additional bacterial breakdown in the septic tank. This increased treatment will result in clearer effluent leaving the septic tank, possibly extending the lifespan of the drainfield. Practicing water conservation is the best method to reduce flow:
For some restaurants, holidays and three-day weekends are often periods of excessive flow. Periods of excessive flow, or "surge" periods, can cause serious system damage by stirring up previously settled solids and carrying them over to the drainfield. If you routinely have your tank(s) pumped one or more times a year, consider scheduling a pumpout to occur just before a known surge period (your busiest several consecutive days) in order to minimize its effect. If you are operating a seasonal kitchen such as for a school, campground, or summer resort, consider having your septic tank pumped before season opening. | |
Managing Wastewater Strength | |
When it comes to managing the strength of your wastewater, the single most important person in your organization is the dishwasher. He/she should make every effort to minimize the amount of grease, oil, and food products that find their way into your wastewater stream. Garbage disposal units are not recommended since they discharge large amounts of food products into the septic tank. Installing a large removable screen basket in your first rinse sink will greatly reduce the amount of food being discharged into the septic tank. On-site sewage systems are especially susceptible to damage from oils which can pass through the septic tank to the drainfield. Consider scraping food from dishes into the trash with a rubber spatula before washing. If the dishes are oily, also consider wiping them with disposable paper towels. This is especially important for pans containing cooking oils and salad dishes coated with salad oil or mayonnaise. Consider a grease recycling company for storing and collecting used greases and oils. (Call 1-800-RECYCLE for a list of facilities serving your area.) | |
Managing Temperature | |
| Proper sanitation often requires the use of high temperature water. Discharging this into the septic tank may liquify some of the solidified greases in the scum layer. This could pose a problem during periods of high flow when these liquified portions of the scum layer could be carried over to the drainfield. Run your dishwashing machine only when it is fully loaded and spread its usage throughout the day as much as possible. Maintain the machine in good working order and check it frequently to insure that the flows are correct and that the rinse temperature is not excessively high (over 185°F). Teach your staff to practice water conservation at the sink and use cold water whenever possible. Consider using a chemical sanitizer instead of hot water rinses. If you do use chemicals to sanitize, check to insure that the proper amount and concentrations are being used. Any product advertised as a disinfectant can also kill the beneficial bacteria in your septic tank and soil if it is used improperly. | |
Managing Toxins | |
Most substances that are toxic to humans are just as toxic to the biological activity within your septic tank. You can reduce your use of many toxic substances by observing the product label which should contain one of the following federally required signal words:
"Non-Toxic" or "Septic Safe" are advertising terms with no regulatory meaning. Small amounts of cleaning compounds and sanitizers are obviously necessary and generally not harmful. Use those that are least toxic and still do the job. Use cleaning compounds in recommended concentrations and do not allow overzealous employees to believe that twice as strong cleans twice as well. This just wastes money. Liquid chlorine bleach is a popular sanitizer. One tablespoon of household liquid bleach in two gallons of water is the proper concentration for wiping surfaces and one tablespoon in four gallons of water is adequate for immersion sanitizing. Some chemicals are exceptionally harmful. These include the strong caustics or solvents that are used in many oven cleaners, drain openers, and ventilation system cleaners. Keep these substances out of your sewage system. If staff or professional contractors clean your vent hoods and filters, make sure that they do not dispose of the cleaning solvents in your sewage system. The use of septic tank additives is not recommended. None have proven helpful and some have proven harmful. Drainfield damage has occurred in some cases. The most important factor in proper on-site sewage system maintenance is knowing your system and equipment. Talk to your septic tank pumper about your system and ask him/her to measure the sludge and scum layers prior to pumping. Record the information. Keep track of the rate at which solids accumulate. This will allow you to determine how often your tank needs to be pumped. If your septic tank or grease trap is full of solids at the time of pumping, you need to pump more frequently. Failure to do so will cause permanent damage to your drainfield. On the other hand, if the sludge and scum depths are small, you may decrease pumping frequency. If possible, pump your septic tank before peak usage periods. If you have a grease trap in your system, it will also need periodic cleaning, usually more often than your septic tank. Pump chambers, pressure distribution systems, and most pretreatment devices also require periodic inspection and specific maintenance actions in order to operate properly. Some designers, installers, and pumpers offer these necessary services. Check with your local Health Department for guidance and assistance. Keep kitchen and bathroom equipment in good repair, especially the dishwashing machine and sink fixtures. If you contract with commercial cleaning services check to see what wastes and chemicals they are putting into your sewage system. | |
A Final Word | |
The best management practices in the world cannot protect your on-site sewage system from problems if it is not properly designed to support your current operations. A system designed ten years ago for another owner may not be adequate for your use if your wastewater flow or strength is greater. If you are in doubt, do not hesitate to seek the services of a reputable designer/installer or contact your local health department for assistance. Having your effluent sampled and your system performance analyzed is a relatively simple and worthwhile investment. High-risk establishments should consider sampling effluent strength every six to twelve months to insure they are not exceeding drainfield capacity. These samples may indicate the need for a pretreatment device or surge tank in the system. There are a growing number of effective and reliable pretreatment systems and system modifications available. Many of these are capable of reducing commercial wastewater concentrations to that of residential wastewater. It is important to add such a system if your wastewater strength warrants it. Do not wait until your system has failed and your kitchen is closed to seek help in solving a problem. Good managers agree: It is wiser to prevent problems than to have to react to them. | |
Additional Information | |
More information is available from the following WSU Extension bulletins: Properly Managing Your Septic Tank System, EB1671 The Care and Feeding of Septic Tanks, EB0707 Properly Managing Your Pressure Distribution System, EB1673 Properly Managing Your Sand Filter System, EB1670 Properly Managing Your Mound System, EB1672 Septic System Waste Treatment in Soil, EB1475 Creative Cleaning, Back to Basics, EB1758 Disposal of Household Hazardous Waste, EB1522 Other sources of information include your local Health Agency or Natural Resources Conservation Service Office, or write to: Washington State Department of Health, Office of Community Environmental Health, Mail Stop LD-11 OLYMPIA, WA 98504. | |
By Robert Simmons, Extension Faculty, and Richard Burleigh, Program Assistant, Washington State University Cooperative Extension, Mason County Washington State University Cooperative Extension bulletins contain material written and produced for public distribution. You may reprint written material, provided you do not use it to endorse a commercial product. Please reference by title and credit Washington State University Cooperative Extension. To reproduce material used with permission (such as a photo or chart) in this publication, please contact the original source. College of Agriculture and Home Economics Issued by Washington State University Cooperative Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8 and June 30, 1914. Cooperative Extension programs and policies are consistent with federal and state laws and regulations on nondiscrimination regarding race, color, gender, national origin, religion, age, disability, and sexual orientation. Evidence of noncompliance may be reported through your local Cooperative Extension office. Trade names have been used to simplify information: no endorsement is intended. Published November 1995. Subject code 375. A. EB1807 | |
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