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The Challenge of Emerging Contaminants

Emerging contaminants are substances recently identified in water sources that may pose risks to human health or the env

High Organic Loading

Wastewater streams frequently carry organic loads 5-50x higher than domestic sewage, demanding robust biological or physical-chemical treatment capacity.

Variable Conditions

Temperature, pH, flow, and concentration swings between production shifts create treatment instability without proper equalisation and buffering.

Biological Sensitivity

Shock loads, toxins, or pH extremes can kill beneficial biomass. Protection mechanisms like equalisation and pH correction are essential.

Fat, Oil & Grease

High FOG content causes pipe blockage, flotation cell failure, and membrane fouling. Effective pre-treatment prevents downstream operational issues.

Complex Chemistry

Variable chemical composition from cleaning agents, process chemicals, and raw materials requires adaptable treatment chemistry and dosing control.

Regulatory Pressure

Discharge consents are tightening continuously. Treatment must not only meet current limits but accommodate future reductions without major rebuild.

PFAS Treatment with GAC

Per- and Polyfluoroalkyl Substances

Understanding PFAS

PFAS (per- and polyfluoroalkyl substances) are a group of man-made chemicals that have been used in industry and consumer products since the 1940s. Their strong carbon-fluorine bonds make them resistant to degradation, earning them the nickname"forever chemicals." Common PFAS include:

  • PFOA (Perfluorooctanoic acid) - formerly used in Teflon production
  • PFOS (Perfluorooctanesulfonic acid) - used in firefighting foams
  • GenX - replacement for PFOA
  • Short-chain PFAS (PFBA, PFBS, PFHxA) - increasingly common
90-99% Removal

GAC effectively removes long-chain PFAS (PFOA, PFOS) with proper system design. Removal efficiency depends on carbon type, EBCT, and PFAS chain length.

Design Considerations

  • EBCT: 15-30 minutes minimum
  • Carbon type: Coconut shell preferred
  • Pretreatment: pH adjustment may help
  • Series configuration: Lead-lag recommended
  • Monitoring: PFAS-specific analysis

Performance Factors

  • Chain length: Longer chains adsorb better
  • Functional group: Sulfonates vs carboxylates
  • Competing organics: Reduce capacity
  • pH: Lower pH generally improves removal
  • Temperature: Lower is better

Short-Chain PFAS Challenge

Short-chain PFAS (C4-C6) are more difficult to remove with GAC due to their higher water solubility and smaller molecular size. Removal rates may be 50-80% compared to 95-99% for long-chain compounds. For sites with significant short-chain PFAS, consider:

  • Longer EBCT (20-30+ minutes)
  • Speciality carbons with enhanced microporosity
  • Combination with ion exchange (IX)
  • Reverse osmosis for complete removal

Regulatory Context

PFAS regulations are evolving rapidly. The US EPA has established Maximum Contaminant Levels (MCLs) of 4 ng/L for PFOA and PFOS individually. The EU Drinking Water Directive sets a limit of 100 ng/L for the sum of 20 PFAS compounds. GAC is a proven BAT (Best Available Technology) for PFAS compliance.

Pharmaceuticals & Personal Care Products

PPCP Removal with GAC

Pharmaceutical Compounds

Pharmaceuticals enter water sources through human excretion, improper disposal, and manufacturing discharge. Common compounds include antibiotics, hormones, analgesics, and psychiatric medications. GAC can effectively remove many of these compounds, though removal efficiency varies significantly by compound.

Compound ClassExamplesGAC Removal
AntibioticsSulfamethoxazole, Ciprofloxacin, Erythromycin70-95%
AnalgesicsIbuprofen, Acetaminophen, Diclofenac80-99%
HormonesEstradiol, Ethinyl estradiol, Testosterone85-99%
PsychiatricCarbamazepine, Diazepam, Fluoxetine75-95%
Lipid regulatorsBezafibrate, Clofibric acid60-85%
X-ray contrastIopromide, Iomeprol30-60%

Personal Care Products

Personal care products including fragrances, sunscreen agents, and preservatives are increasingly detected in water sources. GAC removal effectiveness varies:

  • Musk fragrances: 90-99% removal (highly adsorbable)
  • UV filters (benzophenone): 80-95% removal
  • Parabens: 85-98% removal
  • Triclosan: 90-99% removal
  • DEET: 70-90% removal

Other Emerging Contaminants

GAC Treatment Effectiveness

Industrial Chemicals

  • 1,4-Dioxane: Poor removal (<30%)
  • NDMA: Poor removal with GAC alone
  • Chlorinated solvents: 90-99% removal
  • MTBE: 70-90% removal
  • BTEX: 95-99% removal

Pesticides & Herbicides

  • Atrazine: 85-95% removal
  • Glyphosate: 60-80% removal
  • 2,4-D: 80-95% removal
  • Metolachlor: 90-98% removal
  • Neonicotinoids: 70-90% removal

Endocrine Disruptors

  • Bisphenol A (BPA): 90-99% removal
  • Nonylphenol: 95-99% removal
  • Phthalates: 85-98% removal
  • Alkylphenols: 90-98% removal

Microplastics

  • Physical filtration: >50 microns removed
  • Smaller particles: Limited removal
  • Combined approach: GAC + membrane recommended
  • Adsorption: Not primary mechanism

Design Recommendations

Optimising GAC for Emerging Contaminants

Extended EBCT

For emerging contaminants, longer empty bed contact times are typically required compared to conventional applications:

  • PFAS: 15-30 minutes
  • Pharmaceuticals: 15-25 minutes
  • PPCPs: 10-20 minutes
  • Multiple contaminants: 20-30 minutes

Series Configuration

Lead-lag configuration is strongly recommended for emerging contaminants to maximise carbon utilisation and ensure consistent effluent quality:

  • Lead vessel: Primary removal
  • Lag vessel: Polishing & backup
  • Rotation: When lead approaches breakthrough
  • Monitoring: Critical for both vessels

Carbon Selection

Not all activated carbons perform equally for emerging contaminants:

  • Coconut shell: Best for PFAS, small molecules
  • Coal-based: Good general performance
  • Wood-based: Better for larger molecules
  • Testing: Always recommended

Pilot Testing

For emerging contaminants, pilot testing is essential before full-scale design:

  • Rapid small-scale column tests (RSSCT)
  • Isotherm studies
  • Breakthrough curve development
  • Competing substance evaluation

Related Pages

Gac Fundamentals

Learn the science behind granular activated carbon adsorption.

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Gac Operation

Operate and maintain GAC filters effectively.

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Gac Regeneration

Thermal regeneration and reactivation of spent activated carbon.

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Gac System Design

Design GAC adsorption systems for your application.

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Gac Vs Pac

Compare granular and powdered activated carbon.

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