Water Treatment Technology Assistance CenterUniversity of New HampshireUniversity of Tennessee-KnoxvilleMembrane SystemsLimestone Contractors ModuleUV Disinfection Module

  • List of Contents

  • Introduction
  • Process Description
    • Process Description
    • Membranes
    • Challenge Testing
    • Theory
    • Typical Pressure & Vacuum Systems
    • Integrity Testing
    • Indirect Integrity Monitoring
    • Post Treatment
    • Residuals Treatment & Disposal
  • Typical Membrane Unit
    • Typical Membrane Unit
    • Screening
    • Pretreatment
    • Membranes
    • Typical Pressure & Vacuum
    • Post-Treatment
    • Backpulsing
    • Chemical Cleaning
    • Residuals Treatment & Disposal
    • Integrity Testing
    • Indirect Integrity Monitoring
  • Design Criteria
    • Design Criteria
    • Theory
  • Example Plans & Specifications
  • Treatment Performance
  • Operation
    • Operation
    • Indirect Integrity Monitoring
    • Direct Integrity Testing
      • Testing Requirements
      • Determining UCL
  • Automation Potential
    • Automation Potential
    • Example SCADA Screens
  • Advantages
  • Limitations & Concerns
  • Pilot Plant Objectives
  • Costs
  • References
  • Contacts

CHALLENGE TESTING

The LT2ESWTRLT2ESWTR:
  The Long Term 2 Enhanced Surface Water Treatment Rule (LT2ESWTR) is an EPA regulation targeting control of Cryptosporidium and other microbial contaminants.  It mandates treatment efficiency, i.e., log removal values, and gives credit to various treatment technologies to achieve the needed treatment efficiency. mandates that membrane filtration units must establish their log removalLog removal value (LRV) or log reduction credit:
  The log removal value or log removal credit is the filtration removal efficiency for a target organism, particulate, or surrogate expressed as log10(feed concentration) – log10(filtrate concentration). value (LRV)Log removal value (LRV) or log reduction credit:
  The log removal value or log removal credit is the filtration removal efficiency for a target organism, particulate, or surrogate expressed as log10(feed concentration) – log10(filtrate concentration). through challenge testingChallenge testing:
 Challenge tests are conducted to determine the efficiency of removal of target particulates such as a microbe or a surrogate in order to calculate the log removal value of the membrane module. if they are used to meet the CryptosporidiumCryptosporidium:
 According to the U.S. Center for Disease Control, Cryptosporidium is a microscopic parasite that causes the diarrheal disease cryptosporidiosis. Both the parasite and the disease are commonly known as "Crypto." There are many species of Cryptosporidium that infect humans and animals. The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very tolerant to chlorine disinfection. While this parasite can be spread in several different ways, water (drinking water and recreational water) is the most common method of transmission. Cryptosporidium is one of the most frequent causes of waterborne disease among humans in the United States. treatment rules of the LT2ESWTR. The challenge test would typically be performed on the product by the manufacturer and would be applicable to any site assuming that the membrane system was not significantly modified from the original test. Although the manufacturer would most likely conduct the test, any entity could perform the test if they had the necessary skills and capabilities.

Individual state regulatory agencies can decide whether to accept the results of challenge testing. The EPA Membrane Filtration Guidance Manual (2005) provides extensive further recommendations on conducting challenge testing.

Challenge testing requirements of the LT2ESWTR (40 CFR 141.719(b)(2)) include:

• The membrane module tested must be identical in material and construction to that used in the full-scale membrane system.

• The particulates used in challenge testing must either be Cryptosporidium oocysts or a surrogate particulate that is not removed more efficiently than Cryptosporidium oocysts. The concentration of challenge particulates must be able to be quantified directly rather than using gross measurements such as turbidityTurbidity:
  Turbidity is a measure of  the cloudiness of a water as well as a gross measure of the amount of suspended solids in a water..

• The maximum feed concentration of the challenge particulate is 3.16•106 times the detection limit of challenge particulate in the filtrateFiltrate:
  Filtrate is the water that has passed through the membrane.. This would then allow a log removal of up to 6.5 to be shown.

• "Challenge testing must be conducted under representative hydraulic conditions at the maximum design fluxFlux:
  Flux is the flow rate of water applied per unit area of the membrane and has units of volume/unit area/time. and maximum design process recovery specified by the manufacturer for the membrane module." … "Recovery is defined as the volumetric percent of feed waterFeed water:
 The feed water is the water stream applied to the membrane unit. that is converted to filtrate over the course of an operating cycle uninterrupted by events such as chemical cleaningClean-in-place (CIP) or in-situ chemical cleaning:
 Clean-in-place is a procedure performed periodically to clean a membrane more thoroughly than backwashing can achieve in order to restore the permeability of the membrane towards baseline levels. The process uses chemicals such as citric acid and chlorine or others to remove accumulated foulants on the membrane. or a solids removal process (i.e., backwashingBackpulse or backwash:
 1) Backwash is a procedure in which periodically the flow direction is reversed through the membrane for a short period of time in order to remove particulates accumulated at the membrane surface. 
2) Backwash also refers to the waste water produced as a result of the backwash procedure.)."

• Removal efficiency of a membrane module is "expressed as a log removal value (LRV) according to the following equation: LRV = Log10(Cf) – Log10(Cp), where LRV is the log removal value demonstrated during the challenge test, Cf is the feed concentration measured during the challenge test, and Cp is the filtrate concentration. If the challenge particulate is not detected in the filtrate, the term Cp is set equal to the detection limit for the purpose of calculating the LRV. An LRV must be calculated for each membrane module evaluated during the challenge test."

• "The removal efficiency of a membrane filtration process demonstrated during challenge testing must be expressed as a log removal value (LRVC-Test). If fewer than 20 modules are tested, then LRVC-Test is equal to the lowest of the representative LRVs among the modules tested. If 20 or more modules are tested, then LRVC-Test is equal to the 10th percentile of the representative LRVs among the modules tested. The percentile is defined by (i/(n+1)) where i is the rank of n individual data points ordered lowest to highest. If necessary, the 10th percentile may be calculated using linear interpolation."

• "The challenge test must establish a quality control release value (QCRV) for a non-destructive performance test that demonstrates the Cryptosporidium removal capability of the membrane filtration module. This performance test must be applied to each production membrane module used by the system that was not directly challenge tested in order to verify Cryptosporidium removal capability. Production modules that do not meet the established QCRV are not eligible for the treatment credit demonstrated during the challenge test." The non-destructive test could be either a bubble-point test, diffusive airflow test, or a pressure or vacuum decay test or other. Also note that each state must decide what an acceptable QCRV procedure is.

• "If a previously tested membrane is modified in a manner that could change the removal efficiency of the membrane or the applicability of the non-destructive performance test and associated QCRV, additional challenge testing to demonstrate the removal efficiency of, and determine a new QCRV for, the modified membrane must be conducted and submitted to the State."

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