Idaho Administrative Code › Title IDAPA 58 - Environmental Quality, Department of › Rule 58.01.08 - IDAHO RULES FOR PUBLIC DRINKING WATER SYSTEMS › Section 58.01.08.525 - FACILITY AND DESIGN STANDARDS: LOW PRESSURE MEMBRANE FILTRATION

Current through August 31, 2023
Low pressure filtration, as used herein, refers to
				microfiltration or ultrafiltration processes. Low pressure membrane systems can
				provide greater than 3-log removal of Giardia lamblia and Cryptosporidium, and
				ultrafiltration systems can also provide up to 2-log virus removal. The
				Department will determine maximum available removal credits for the specific
				membrane under consideration. The actual log removal credit that a low pressure
				membrane filtration system will receive is the lower of the values determined
				by the following: the removal efficiency demonstrated during challenge testing,
				or the maximum log removal that can be verified by direct integrity testing
				required during the course of normal operation. Membrane systems shall contain
				sufficient design to allow for offline direct integrity testing of all units or
				modules at the required interval while retaining the capability to supply
				maximum day demand to the water system. Membrane systems shall have at least
				two (2) units unless it can be demonstrated to the satisfaction of the
				Department that a secondary source or treatment component can supply the
				required minimum plant design capacity. (3-24-22)
01.
Membrane Selection and Design
			 Considerations
. (3-24-22)
a. Challenge
			 Testing. Challenge testing involves seeding feed water with an organism or
			 particulate and measuring the log reduction of the organism or particulate
			 between the feed and filtrate. It is a one-time productspecific test event
			 performed by an approved third party designed to demonstrate the removal
			 ability of the membrane. Challenge testing shall be conducted by the third
			 party entity in general conformance with the USEPA Membrane Filtration Guidance
			 Manual referenced in Subsection
			 002.02 (Membrane Filtration
			 Guidance Manual). The challenge test report shall be submitted to the
			 Department along with the preliminary engineering report for the project. The
			 Department may accept another state's challenge test report approval.
			 (3-24-22)
b. Water Quality
			 Considerations for Design. A review of historical source water data shall be
			 conducted to determine the degree of pretreatment needed if any, the
			 feasibility of membrane filtration, and an estimated cost of the system. At a
			 minimum, the following parameters shall be investigated: Seasonal temperature
			 and turbidity profiles, total organic loading, occurrence of algae, microbial
			 activity, iron, manganese, and hardness levels, and any other inorganic or
			 physical parameters determined to be necessary by the Department. The data
			 shall be used to determine anticipated fouling and scaling, backwash and
			 cleaning cycles and regimens, acceptable transmembrane pressure differentials,
			 and design flux, especially during lowest anticipated water temperature.
			 (3-24-22)
c. Pilot Study. A pilot
			 study shall be conducted for a period that shall be determined by the design
			 engineer and approved by the Department. The duration should include the season
			 of lowest water temperatures and the season including the highest anticipated
			 turbidity, algal bloom, TOC, and iron/manganese event or otherwise cover four
			 seasons of source water quality conditions. The Department may approve a
			 shorter duration proof pilot to verify design criteria that affect the reliable
			 production capacity of the membrane system. The Department may approve the use
			 of a full scale pilot study where the full scale facility will act as the pilot
			 study. The Department may also waive the pilot study requirement. Proof pilot
			 studies, full scale pilot studies, and the waiving of the pilot study
			 requirement will only be approved in circumstances where source water
			 conditions and fouling characteristics are already well understood. Such source
			 waters include but are not limited to ground water under the influence of
			 surface water, waters with existing membrane plants, waters where sufficient
			 pilot test data has already been generated, and extensively used or tested
			 membrane products where production or test data on similar waters is available
			 (i.e., same lake, reservoir, or same reach for stream sources). In addition to
			 the requirements in Subsection
			 501.19, the pilot study shall
			 include: (3-24-22)
i. A means to identify the
			 best membrane to use for the anticipated water quality; (3-24-22)
ii. Analysis of any need for pretreatment;
			 (3-24-22)
iii. Range of anticipated
			 flux rates; (3-24-22)
iv. Operating
			 and transmembrane pressure; (3-24-22)
v. Fouling and scaling potential;
			 (3-24-22)
vi. Backwash and recovery
			 cleaning, cleaning processes, and intervals; (3-24-22)
vii. Efficiency and process mass balance;
			 (3-24-22)
viii. Waste stream
			 volume, characterization, and disposal method; (3-24-22)
ix. Turbidity; and (3-24-22)
x. Integrity testing results and procedures.
			 (3-24-22)