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

RESIDUALS TREATMENT AND DISPOSAL

MFMicrofiltration (MF) membranes:
 Microfiltration membranes are typically hollow-fibers with a pore size range of approximately 0.1 – 0.2 μm (nominally 0.1 μm)./UFUltrafiltration (UF) membranes:
 Ultrafiltration membranes are typically hollow-fibers with a pore size range of approximately 0.01 – 0.05 μm (nominally 0.01 μm). membrane units will produce backpulseBackpulse 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. and 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. residualsResiduals:
  Residuals refers to all waste streams from a treatment process.  For membrane systems it could include the backwash wastewater, clean-in-place wastewaters, rinse waters, and concentrates. which must be properly handled and disposed of. Additionally, MF/UF systems operated in a cross-flowCross-flow configuration:
 A cross-flow configuration is the application of water at high velocity tangential to the surface of a membrane to maintain contaminants in suspension. connection rather than dead-endDead-end configuration:
Dead end filtration refers to a hydraulic configuration in membrane systems in which all the feed water passes through the membrane and no concentrate is produced. may generate a concentrateConcentrate:
 Concentrate refers to the waste stream created in reverse osmosis and nanofiltration systems or any membrane system in which not all the feed water passes through the membrane. The water that does not pass through the membrane will have a much higher concentration of dissolved solids and/or particulates. stream that requires disposal, but since cross-flow is not a typical MF/UF configuration, disposal of its concentrate will not be discussed here.


Backpulse residuals. Considerations and treatment options for backpulse residuals include:

• In some MF/UF membrane treatment systems, a coagulantCoagulant aids:
 Coagulant aids are often polymers used to assist primary coagulants such as alum or ferric salts in order to achieve better settling or better filtering flocs. and/or polymer may be added in-line in which case the backpulse residuals will be similar to those from conventionalConventional treatment:
Conventional treatment refers to older established water treatment process such as coagulation, flocculation, and rapid sand filters. treatment. However, in many cases no coagulant or polymer is added in which case the amount of solids will be less than conventional treatment and may pose fewer problems.

• Disposal options are similar to those in conventional treatment and include

1) Discharge to a surface water,

2) Discharge to a sanitary sewer, or

3) On-site treatment that returns the suprenatantSupernatant:
  Supernatant is the relatively clearer water that forms at the top of a water in a clarifier or sedimentation tank. to the head of the plant and disposes of the solids.

• Discharge to a surface water or sanitary sewer must of course meet all state and local regulations and discharge to a surface water will require a permit.

• If the backpulse includes chemical wastes, then the treatment/disposal options may be more complex. If chlorine is added to the backpulse water, then the chlorine may require quenching prior to discharge. If acids, bases, surfactantsSurfactant:
  Surfactants are essentially soaps or detergents that lower the surface tension of water to allow particulates to be more easily removed from surfaces. or proprietary chemicals will be present in the backpulse, then consideration must be given to their treatment/disposal according to any state and local regulations.

• On-site treatment options are similar to those for conventional treatment. These include clarifiers, settling lagoons, gravity thickeners, centrifuges, belt filter presses or a combination. Coagulant aids may or may not be necessary. Additionally, the supernatant is typically returned to the plant influent and the residual solids ultimately sent to a landfill.


Chemical cleaning residuals. Chemicals used to clean the membranes can include chlorine or other oxidant, acids and bases, surfactants and proprietary chemicals. Often much of these chemicals can be recovered for reuse (90% in some cases). However, chemical cleaning residuals that will be discharged are generally treated on-site and discharged to a surface water or sanitary sewer in accordance with state and local regulations . Chlorine and other oxidants are quenched and acids and bases neutralized prior to discharge. Treatment of surfactants and proprietary chemicals may be more complex. Additionally, the rinse water that is applied after cleaning will contain some level of chemicals and may require treatment prior to discharge.

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