ABSTRACT
Collection system operators use the term grease to refer mainly to restau rant fats. Fats are defined as triglyceride esters of fatty acids. Animal fats are the usual culprit in clogging arteries and sewer systems. Fat, oil, and grease (FOG) discharges to the collection system are usually limited to between 200 and 300 mg/L. Full-service restaurants generate about 4-1/2 pounds of grease per 150 meals served (The Cleaner, 4-95). Grease is hydrophobic: it is not water soluble. Grease readily comes out of suspension to cling to itself, pipe walls, manhole inverts, and roots. Acidity and Alkalinity
pH is a measure of acidity and alkalinity. The scale runs from 1 to 14. pH 1 is extremely acidic, and pH 14 is a very strong base. A pH of 7 is neutral. The pH of wastewaters discharged to the collection system is limited to between 5 and 9. Highly alkaline substances form large, hard deposits in sewer pipes. Acids corrode concrete pipes and manholes. Diluting strong acids or bases with water is not an acceptable alternative to neutralization. Acid neutraliza tion tanks are interceptors filled with limestone chips. Their maintenance con sists of “stirring the rocks” and effluent sampling. Viscosity
Many substances, such as waxes, flour pastes, greases, oils, paraffins, pro teins, and gums congeal or solidify. They reduce internal pipe diameter and clog the collection system. They should be discharged to an approved interceptor. Solids
The Uniform Plumbing Code prohibits the discharge to the sanitary sewer system of all harmful solids, which includes any solid that has the potential to clog the sewer pipes. Sand traps at car washes are designed to collect and retain solids. Wastewater collection systems move liquids to the treatment plant. Solids settle out and interfere with liquid flow.
