Food Service/Food Preparation Wastewater Discharge Information...

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General Information On Wastewater Discharged From Food Service/Food Preparation Facilities

Wastewater discharged from food service/preparation facilities (restaurants, commercial kitchens, schools, convenience stores, and some large office buildings with cafeterias) generally has two common characteristics. The first being fat, oil and grease (FOG), which, can stick to the insides of sewer pipes and over time, build up and cause blockages. These blockages cause problems for both the discharger and the County and must be removed in order for the sewer to function properly. Second, the discharge will have biochemical oxygen demand (BOD) and total suspended solids (TSS) concentrations that will vary depending on the wastewater's strength and will probably result in additional treatment costs.

The surcharge program in Hanover County, similar to most municipalities, assigns an additional fee or surcharge, to sewer bills for customers that discharge strong waste. Strong waste is defined as any wastewater that is stronger than household or domestic wastewater. Customers that discharge strong waste will be charged this additional fee to offset increased operation, maintenance and treatment costs.

It is important to note that you have some control over this surcharge by lowering FOG discharges and controlling your BOD/TSS concentrations. Actions taken to reduce FOG and BOD/TSS are often the same. The following is a listing of some actions to consider that may help reduce surcharges and backups.

Minimizing the amount of food discharged down drains of kitchen sinks and dishwashers. Modification of employee actions should be the first and least costly preventive measure in the effort to reduce strong waste discharges. Food service personnel should be instructed to put as much of the discarded food material into trashcans as possible and not wash it down the drain.

Use sink and dishwasher strainers to capture as much of the solid material as possible. Consider purchasing, or fabricating, strainers with smaller holes to capture more food particles.

Maintain existing grease traps and grease interceptors on a frequency that will assure proper function of the device. Internal grease traps generally cost less to install, but also capture less grease. External grease interceptors are more expensive to install but are typically more efficient in reducing waste. External grease interceptors are usually more effective than internal grease traps because:

• They provide greater settleability of solids;
• They provide a greater detention time, thereby allowing the temperature of the discharge to be lowered which promotes grease accumulation in the grease trap rather than the sewer; and
• They need to be cleaned less frequently.

It should be noted that external interceptors should be pumped, not "skimmed." Accordingly, pumping, rather than skimming, will likely result in a greater reduction in waste. In addition, periodic "jet cleaning" of the lateral, including the grease trap/interceptor, can keep the line open and free flowing and has a tendency to lower the FOG and BOD/TSS concentrations.

Garbage disposals contribute excessive organic material to the sanitary sewer system. This translates to higher BOD/TSS concentrations resulting in higher surcharges. It is not unusual to see large reductions in BOD/TSS when garbage grinders are removed.

Make sure that plumbing in the food preparation area actually goes to the grease interceptor or grease trap. Make certain that floor drains and sinks do not bypass the traps/interceptors. Where possible do not locate the drain from a deep fryer next to a floor drain. The temptation is often great to discharge the fryer oil into the floor drain instead of the recycling barrel.

Finally, it is important to note that a certain amount of BOD is soluble in water; therefore, it will not be removed from a wastewater discharge by mechanical devices. More elaborate pretreatment methods may need to be employed for further BOD reduction.