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Activated Sludge System Audit Presentation

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Wastewater Treatment System Evaluation Pulp and Paper Mill Northern United States

Paul Klopping-Callanand Brooks
Mike Foster -Environmental Business Specialists, LLC
April 17, 2008

Purpose of Visit

  • Review wastewater treatment operation in the context of anticipated changes when the one of the two mills discharging to the treatment system ceases operation this summer.
  • Assist mill in developing a strategy for transitioning from current operating conditions to future ones.

Growth Pressures or “Limiters”

  • BOD5,COD or TOC (Type and amount of food)
  • pH
  • Toxicity and Inhibition
  • Dissolved Oxygen
  • Hydraulic retention time and flow patterns
  • Nutrients (N&P)
  • Temperature
  • Amount and health of biomass

Type and amount of foodBOD5 and COD

  • Current BOD Loading to Lagoons
    • Mill #1 -32,000 lb/day
    • Mill #2 -54,500 lb/day
  • Average loading to UNOX -60,300 lb/day
  • BOD removed across both lagoons -26,200 lb/day
  • Amount removed in each lagoon is unknown -testing recommended
  • Change in type of food -relative biodegradability

pH

  • Concern is that pH will be significantly higher under new operation
  • Three issues:
    • pH for optimum UNOX performance
    • pH for effluent compliance
    • pH for odor minimization
  • Between pH 5.0 -9.5, lagoons will “self buffer”
  • Influent of 6.0 -8.5 is fine for UNOX
  • A pH control (trim) system is needed for those times when lagoon outlet pH is unstable
  • Final effluent pH will be higher, but more stable (less dissolved CO2)

Dissolved Oxygen

  • Current oxygen usage average is ~90,000 lb/day
  • At future anticipated BOD loading of 22,000 -30,000 lb/day, oxygen requirement will be 35,000 -50,000 lb/day
  • Projected need is well below output of one compressor

Nutrients

  • Nutrient demand is stoichiometericwith BOD loading
  • Mill currently runs at target for P, but frequently above target for N
  • P method is very accurate and precise. Ammonia method is less so.
  • Future nutrient demand will drop proportionally to BOD loading decrease
  • Lower loading makes switch from anhydrous ammonia to aqueous ammonia or urea-ammonium nitrate more attractive
  • A potential scenario for improved nutrient control is to tie nutrient feed to oxygen flow to UNOX reactors

Temperature

  • Mill 1 mill effluent is 5 -15 degrees hotter than Mill 2 effluent.
  • UNOX influent temperature must stay below 104 F
  • Cooling is critical in summer
  • Two scenarios
    • Run both lagoons at ~7 MGD each (4 days). Same heat transfer potential via coolers/aerators. Twice as much potential cooling due to ambient cooling
    • Put all cooling /aeration equipment in one lagoon
      • Pros
        • Better mixing
        • More thorough aeration
      • Con
        • Less time for cooling
        • Cost for redesign
    • Both options being evaluated by equipment consultant

Amount and Health of Biomass

  • Target MLSS
  • Sludge age
  • Future primary/secondary ratio
  • Future polymer chemistry
  • Improve solids capture on gravity tables
  • Mass balance spreadsheet
  • State point analysis -Solids load to clarifiers -(1, 2, or 3 clarifiers)

Secondary Clarifier Capacity

  • Depends upon SVI, Flow, MLSS conc.
  • 3 clarifiers recommended initially
  • Assess sludge quality and MLSS…
    • 2-clarifier operation may be possible
      • SVI ≤ 125 mL/g
      • Q ≤ 18 MGD
      • MLSS ≤ 3,200 mg/L
  • Hypochlorite (filament control) is essential

Summary

  • What will happen following mill shutdown?
  • Compliance -expect success
    • Honor past practices but be prepared to change strategy and tactics.
    • Re-allocate and or modify assets.
      • Temp (lagoon modifications), pH trim, nutrient optimization, UNOX 1-train &cryomodifications, dewatering optimization, secondary clarifier optimization.
  • Capable facility, competent people, pride of ownership
    • Best in Class Performance (people and process)

Activated Sludge System

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