Section 58.01.08.522 - SURFACE WATER TREATMENT: FILTRATION USING DIATOMACEOUS EARTHThe use of these filters may be considered for application to surface waters with low turbidity and low bacterial contamination, and may be used for iron removal for groundwaters providing the removal is effective and the water is of satisfactory sanitary quality before treatment.
01.Conditions of Use. Diatomaceous earth filters are expressly excluded from consideration for the following conditions:c. Turbidity removal where either the gross quantity of turbidity is high or the turbidity exhibits poor filterability characteristics; ord. Filtration of waters with high algae counts.02.Treated Water Storage. Treated water storage capacity in excess of normal requirements must be provided to allow operation of the filters at a uniform rate during all conditions of PWS demand at or below the approved filtration rate, and guarantee continuity of service during adverse raw water conditions without by-passing the system.03.Number of Units. A minimum of two (2) units for redundancy must be provided for filtration such that plant design capacity can be maintained with any component out of service for maintenance or repairs.04.Precoat. A uniform precoat must be applied hydraulically to each septum by introducing a slurry to the tank influent line and employing a filter-to-waste recirculation system.05.Body Feed. A body feed system to apply additional amounts of diatomaceous earth slurry during the filter run is required to avoid short filter runs or excessive head losses. a. The rate of body feed is dependent on raw water quality and characteristics and must be determined in the pilot plant study in accordance with Subsection 501.19.b. Continuous mixing of the body feed slurry is required.06.Filtration Requirements.a. Rate of filtration must be controlled by a positive means.b. Head loss must not exceed thirty (30) psi for pressure diatomaceous earth filters, or a vacuum of fifteen (15) inches of mercury for a vacuum system.c. A recirculation or holding pump must be employed to maintain differential pressure across the filter when the unit is not in operation in order to prevent the filter cake from dropping off the filter elements. A minimum recirculation rate of one-tenth (0.1) gallon per minute per square foot of filter area must be provided.d. The septum or filter elements must be structurally capable of withstanding maximum pressure and velocity variations during filtration and backwash cycles, and must be spaced such that no less than one (1) inch is provided between elements or between any element and a wall.e. The filter influent must be designed to prevent scour of the diatomaceous earth from the filter element.07.Backwash. A satisfactory method to thoroughly remove and dispose of spent filter cake must be provided.08.Appurtenances. The following must be provided for every filter: a. Sampling taps for raw and filtered water.b. Loss of head or differential pressure gauge.c. Rate-of-flow indicator.d. A throttling valve used to reduce rates below normal during adverse raw water conditions.e. Evaluation of the need for body feed, recirculation, and any other pumps.f. Provisions for filtering to waste with appropriate measures for backflow prevention.09.Monitoring. A continuous monitoring turbidimeter with recorder is required on each filter effluent for plants treating surface water.Idaho Admin. Code r. 58.01.08.522