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Wastewater treatment steps

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Tertiary: Effluent polishing, Nutrient and Toxins Removal (chemical, also ... Bioassays (response of fathead minnow, water flea, others, over time) ... – PowerPoint PPT presentation

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Title: Wastewater treatment steps


1
Wastewater treatment steps
  • Primary solids removal (physical)
  • Secondary BOD treatment (biological)
  • Tertiary Effluent polishing, Nutrient and Toxins
    Removal (chemical, also possibly physical and
    biological)

2
Tertiary (advanced) treatment
  • Secondary treatment
  • removes 85 - 95 of BOD and TSS
  • removes 20 - 40 P
  • removes 0 - 50 N
  • Tertiary treatment
  • removes over 99 of pollutants
  • very high cost

3
Goals of tertiary treatment
  • Effluent polishing (BOD, TSS)
  • Nutrient removal (N, P)
  • Toxin removal
  • (pesticides, VOCs, metals)

4
Effluent polishing
  • Removal of additional BOD and TSS
  • Granular media filter beds
  • gravity or pressurized
  • require frequent backwashing
  • air-washing
  • Microstraining/ microscreens
  • 20-micrometer openings

5
Nutrient management
  • Nutrient plants require them for growth
  • Potential problems from nutrients
  • water quality
  • aquatic ecosystem
  • human animal health
  • Approaches
  • dilution
  • treatment (biological or physicochemical)
  • plant uptake

6
Nitrogen
  • Biochemically interconvertable forms
  • organic N (proteins, urea)
  • ammonia gas (NH3)
  • ammonium ion (NH4)
  • nitrate (NO3)
  • nitrite (NO2)
  • elemental N2 gas (78 of air)
  • Mobile (esp. nitrate)
  • Limiting nutrient in salt waters

7
Nitrification-denitrification
  • Two-step biological method
  • Step 1 Aerobic Nitrification
  • Ammonia to nitrate conversion
  • now nontoxic to fish
  • m.o.s Nitrosomonas and Nitrobacter
  • Step 2 Anoxic-anaerobic Denitrification
  • nitrate to N2 conversion
  • requires carbon source
  • m.o. Pseudomonas

8
On-site biological methods
  • Upflow anaerobic sand filter
  • uses septic tank effluent as carbon source
  • must monitor and manage recycle ratio
  • too low incomplete denitrification
  • too high excess O2 shuts down denitrification
  • 75 removal possible

9
On-site biological methods...
  • Aerobic chamber plus deep sand filter
  • uses methanol as carbon source
  • must manage methanol dosing rate
  • 85 - 95 removal possible

10
On-site biological methods...
  • Bardenpho system
  • uses wastewater as carbon source
  • alternating anoxic and aerobic STRs
  • must monitor and manage sludge recycle ratio
  • Oxidation ditch
  • endless loop of anoxic and aerobic zones
  • less removal efficiency than Bardenpho

11
Physical-chemical N removal
  • Approach
  • convert all N to ammonia
  • then treat the ammonia
  • Three methods
  • Breakpoint chlorination
  • Ion exchange
  • Ammonia stripping
  • Often impractical for on-site systems

12
Ammonia stripping
  • Two-step physical-chemical method
  • Step 1 Raise pH to 10.5-11.5
  • convert ammonium ions to ammonia gas
  • Step 2 Air-strip
  • cascade wastewater countercurrent to air flow
  • ammonia gas escapes to atmosphere
  • Pro less costly, no sludge or Cl by-products
  • Cons acids/bases, scale, freezing problems

13
Phosphorus
  • Forms
  • organic phosphorus
  • orthophosphate (PO4)
  • polyphosphates
  • phosphorus-containing rocks
  • Binds to soils and sediments
  • Limiting nutrient in fresh waters

14
Biological P removal
  • Luxury uptake
  • anaerobically- stressed m.o.s ingest more P than
    needed
  • Methods
  • Bardenpho
  • Sequencing Batch Reactor
  • 1 tank, 5 steps
  • fill, aerate, settle, decant, idle

15
Physical-chemical P removal
  • Chemical precipitation (3 options)
  • add alum (Al2SO4) to form aluminum phosphate
  • add ferric chloride (FeCl3)
  • add lime (CaO)
  • Coagulation / flocculation
  • Clarifier/settler

16
More on P precipitation
  • Pros
  • can also serve as effluent polishing step if
    added after 2ndary treatment
  • lime can aid ammonia stripping too
  • Cons
  • expensive more tanks, clarifiers, and filters
  • must closely manage pH, chemical dosing, and
    precipitate removal
  • produces a LOT of sludge

17
Toxin treatment and removal
  • Types of toxins
  • Organics (pesticides, solvent, petroleum,...)
  • Metals (lead, cadmium, mercury,...)
  • Sources of toxins
  • Impact on wastewater treatment systems when
    toxins hit

18
Toxicity testing
  • Test for specific chemicals
  • Bioassays (response of fathead minnow, water
    flea, others, over time)
  • Human toxicity (carcinogenicity, acute or chronic
    disease)

19
Toxin strategy
  • Prevention
  • Protection
  • equalization basins
  • holding tanks
  • contingency plans
  • Treatment
  • no universal treatment method
  • each toxin different

20
Toxin Tertiary Treatment
  • Organics
  • Biological treatment (incl. co-metabolism)
  • Oil-water separator
  • Air stripping
  • Thermal treatment (incineration, desorption,
    distillation, evaporation)
  • Chemical oxidation
  • Sorption (activated carbon, kitty litter)
  • Land farming

21
Toxin Tertiary Treatment
  • Metals
  • Chemical precipitation and filtration
  • Biological transformation
  • Sorption
  • Solidification (cement, asphalt, plastic
    polymers)
  • Encapsulation
  • Plant uptake /phytoremediation (note sludge
    application implications)
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