4/26/2011 SEWER COMMISSION Minutes

Home Browse Search

Page 21 however, the system must be shut down during freezing conditions, all bridge crossings should be drained and all air release valve assemblies should be protected with appropriate insulation. Residential Connections Residential sewage is conveyed to a 1,000-gallon, or occasionally 1,500-gallon, single-compartment septic tank through a standard building sewer. In effluent systems, they are often referred to as interceptor tanks. Tanks for commercial sites range from a single 1,500-gallon size, to several tanks in series, to very large poured-in-place tanks. The interceptor tank serves several physical functions critical to every system: 1) It provides sufficient hydraulic retention time for capturing grease, grit and other substances that settle or float. Minimum retention times from 6 to 24 hours are considered adequate. 2) It allows sufficient storage capacity for sludge and scum so that septage pumping intervals are infrequent. 3) It provides reserve space adequate for 24 to 48 hours of normal operation before a system malfunction must be corrected, thus eliminating the need for emergency maintenance. The reserve space must also allow for adequate tank ventilation back through the inlet plumbing. 4) It provides an operating zone sufficient to modulate peak inflows without causing nuisance alarms or excessive hydraulic gradients. In addition to its physical functions, the tank provides conditions conducive to biological treatment of the captured organic matter. The organic(volatile solids) reduction is a result of facultative and anaerobic digestion that converts organic matter to gases. Facultative microbes solubilize the complex organic material to volatile organic acids while strict anaerobes ferment the volatile organic acids to gases (methane, carbon dioxide, etc.). Volatile solids reduction may vary from 30 to 70 percent. The mineral or inorganic(fixed) solids content may range between 40 and 60 percent of the total solids. The organic solids content of tanks that are well managed generally exceeds 80 percent. On the average, therefore, about 55 percent of the organic matter is reduced biologically, extending the septage pumping frequency by a factor of 2.2 ±. These tanks provide highly efficient treatment, yielding an effluent that is relatively free of fats, oils, greases, solids and other constituents that can clog and foul collection and disposal equipment. More than 45 percent of the ultimate treatment of the wastewater is accomplished in the septic tank. And anoxic digestion can reduce the solids handling requirements of the treatment facility by as much as 80 percent. These issues should not be overlooked when comparing alternatives. An interceptor tank maintains a lower liquid level than does a typical septic tank followed by a drainfield. If a pumping system malfunctions, a resident can continue to use water for about two days before using up the reserve space. The need for emergency maintenance, then, is minimized. During a power outage, the safe period of use is probably even longer since washing machines and water heaters do not function, lessening water use. -To avoid abuse of a system's interceptor tanks, cooperation of users is essential and best accomplished through community education.To explain a district's policies and property owners' responsibilities, a list of"Do's and Don'ts"should be provided to patrons and updated regularly. Users should be warned against disposing inappropriate solid-waste into the sewer. Tampons, cigarette butts, Handy Wipes, disposable diapers, prophylactics, rags, plastics, excessive grease, petroleum oils, cutting oils, coffee grounds, egg shells, kitty litter (clay), chemicals,water softener backwash, and any non-biodegradable substances should be disposed in trash containers at approved solid or hazardous waste sites. The best practice is not to discharge anything into a