I had a question recently about what would be the “best” system to treat wastewater from a restaurant. This led me to thinking about how things have changed concerning how we look at and have dealt with systems serving restaurants or bars.

            Back in what I like to term the “old days,” there were a lot of anecdotal reports from service providers that restaurants they serviced with conventional septic tank soil treatment systems had high rates of failure. As we turned our attention to these systems, one of the first things that became apparent was septic tank effluent from tanks sized to handle residential wastewater were much higher in organic matter than typical, actually on the order of three to four times or more. In addition, it was noted restaurants had large levels of oil and grease in their effluent, even with the presence of grease traps.

            Initial recommendations were to increase the size and number of septic tanks serving the facility. Doubling tank capacity was the standard rule of thumb. This seemed to work for some restaurants and not for others. This just highlighted the difficulty to define a typical restaurant to base designs on. Each restaurant has its own set of unique customers and the way they run their operation. It makes designing, installing and maintaining systems a challenge. So, the answer to what is the best system depends on several factors in the business itself in addition to the soil and site characteristics.

REDUCE PEAK FLOWS

            One problem I often see with struggling restaurant systems is the size of the area available for expanding or moving the soil treatment portion of the system. By the time you take out the area dedicated to parking, food deliveries, garbage pickup and setback requirements, available area is limited. This problem is exacerbated if the restaurant has difficult soils and the daily flows have been underestimated, resulting in the soil treatment area being undersized. In these situations, the solution is going to be some type of advanced pretreatment and selection dictated by what imposes the smallest footprint on the site.

            Actions can be taken as part of the restaurant operation to reduce daily and peak flows and the amount of organic material, fats, oil and grease delivered to the system to improve system efficiencies. Ideally, effluent from the system pretreatment components to the soil treatment area should have a biochemical oxygen demand about 170 mg/L; total suspended solids less than 60 mg/L and fats, oil and grease at 20 mg/L.

            It is important for restaurant operators/owners to control or reduce flows by using as many low-flow, high-efficiency fixtures as possible. They need to recognize the system has a finite capacity and anything done to reduce flows (both daily and peak) will protect the system and increase longevity.

            It is also important the fixtures are kept in good operating condition. How many times have you visited a restroom to find the faucet or toilet running continuously? Any additional water is going to be detrimental to long-term operation.

            Where daily flows vary widely throughout the week, adding storage capacity and then timing release of effluent through the week to even out peak flows is often a good strategy. Where I live, restaurants utilizing onsite systems are often closed one or two days a week with very large flows on Friday fish fry night and Saturday prime rib special night. Storing and controlling daily flows to spread flow throughout the week can keep the system from being stressed during busy periods.

A RECIPE FOR SUCCESS

            Actions can be taken in the kitchen to reduce BOD and FOG levels. The grease trap should be large enough and regularly maintained to capture oils before they move into the treatment system. Use of degreasers in cleaning that are washed down the drain and through the system should be minimized. Simple things such as cleaning pots and pans during times of lower flows and avoiding peak business hours help maintain the grease trap.

            All of this requires the cooperation and diligence of the owner/operator, so developing a good client relationship is important.

            In home systems I often highlight that garbage disposal units are a problem since they introduce large quantities of undigested food bacteria that have to break down in the system, large quantities of water are used, and the material is ground up finely which can increase the TSS in the effluent. Obviously, it is difficult not to have a garbage disposal in a restaurant, but the amount of material delivered through it can be reduced by scraping plates before rinsing.

TRAIN THE WORKERS

            It is important that all employees and the owner are on the same page relative to activities necessary to help protect the system and the reasons why. A regular training program for new and current employees is important. This is key with seasonal employees who are unfamiliar with proper care and usage of septic systems.

            As a service provider, it is important to have a regular monitoring and maintenance program for system components. The frequency of maintenance activities will depend on the components present, and flows generated. Annual or seasonal visits may be in order. Where additional pretreatment or storage tanks are part of the system, visits will depend on operation requirements of each component.

            Additional pretreatment components may be aerobic treatment units or media filters if effluent requirements cannot be met through increased septic tank capacity. So the answer is there is no “best” system other than it is the one that can handle the flow requirements for the restaurant.