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Technical Description Because of this additional hydraulic loading, 7H further recommends the use of dual filters which are designed to use the filtrate of one filter to backwash the other. Since the filtrate is already part of the system hydraulic loading, nothing is added. In order to obtain the desired solids holding ca- pability, the media must allow penetration into the depth of the bed rather than simply retaining solids on the media surface. Conventional filter sands, as used in potable water filtration, provide only this surface removal and retention effect. This is satisfactory for the low solids concentra- tions involved in freshwater filtration. However, in wastewater filtration, solids concentrations are significantly higher and tend to rapidly seal the surface. During backwash of conventional filter sand media, another phenomenon occurs which contrib- utes to this surface straining effect. When the bed is fluidized, the less dense, smaller grain-size media tends to accumulate as the top layer in the bed. This provides for efficient particle removal during filtration, but precludes any penetration beyond the surface layer. A more efficient media system incorporating varied media layers is recommended. The different materials are always different specific gravities and are usually made up of various sizes of gravel, garnet, sand, and anthracite coal. The denser filter media are placed below the coarser but less dense coal, thus allowing deeper penetration in the direction of flow and maintain- ing a coarse surface layer even after backwash. BOD5 concentrations that are trapped in the suspended solids of the secondary effluent can be effectively removed in a well-designed tertiary filter; however, standard multimedia filtration has little or no measurable effect on the removal of soluble BUD which is generally less than 10 mi- crons in size. The most important consideration in the sizing of tertiary filters, and one requiring considerable engineering judgment, is selection of the application rate, which is expressed as gallons per minute applied per square foot of filter surface area. In many cases, the maximum application rate is fixed by a regulatory agency. Some factors that must be considered in selection of the rate of application include: 1) efficiency of the secondary treatment process; 2) flow pattern; 3) filter cycle duration and backwash water production; and 4) capital cost of equipment. With the Bio-Pure system, designed-in plant flow equalization allows filter flow rate selections based on equalized flow rates, which removes the problems that result from periodic surge flows. With the unique batch design of the Bio-Pure secondary process, daily flow patterns (as well as peak flow rates) are near constant, thus a set schedule can be maintained for backwashing the fil- ter media during low system flow periods. COMPUTERIZED/ELECTRONIC/ELECTRICAL CONTROL SYSTEM The Bio-Pure system control unit provided by 7H manages and monitors the operational functions of the entire treatment system with solid-state memory and micro-processor computerized sys- tems. These systems are capable of monitoring and controlling down stream effluent disposal and reclaimed water systems. This system provides 7-H with capability of monitoring all remote sys- tems from their Headquarters in Grass Valley, California. They can coincidentally provide the client with the same information of monitored systems by modem or Internet Access to 7-H's Web Page.