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The AFC Process

The AFC Process. What Is AFC?. UF System. Permeate. Effluent. Balance Tank. Feed. AFC Reactor. Retentate. Concentrate Return. Inert Blowdown. Chemical Treatment. Key Operations are Balancing of incoming waste streams Thermophilic activated sludge (AFC) to oxidise the organic load

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The AFC Process

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  1. The AFC Process

  2. What Is AFC? UF System Permeate Effluent Balance Tank Feed AFC Reactor Retentate Concentrate Return Inert Blowdown Chemical Treatment • Key Operations are • Balancing of incoming waste streams • Thermophilic activated sludge (AFC) to oxidise the organic load • Ultrafiltration to separate the biomass from the treated effluent • Chemical treatment to hydrolyse excess biomass and make it biodegradable 2003

  3. The advantages of AFC technology • Simple, robust and flexible process • Able to treat high strength wastes (COD 20,000 – 200,000 mg.l-1) • Thermophilic process which generates its own heat • Able to digest biological solids • Complete retention of biomass within the system • Complete destruction of excess biomass generated or biomass added in feed stream • No sludge disposal off-site • Conversion of nitrogenous compounds to ammonia • Conversion of phosphorus compounds to phopshate • Flexible plant with small footprint • Potential for heat, ammonia, phosphate and carbon dioxide recovery 2003

  4. Ultrafiltration - principles 2003

  5. Ultrafiltration – key points • Ultrafiltration using ceramic membranes to remove biological solids from the treated effluent • Complete retention of solids; permeate solids level at <50 mg.l-1 • Independent of physical form of the biomass • Does not require a flocculant sludge • Ceramic membranes used because • Stable at operating temperatures employed • Resistant to biological fouling • Resistant to aggressive cleaning regimes • Unit sized on basis of permeate flow through a unit membrane area • Membranes arranged into four filtration units, each skid containing four membrane assemblies • Circulation flow around the UF system is designed at 6 times the permeate flow • Provided with Clean In Place (CIP) skid to allow any one membrane skid to be cleaned at a time 2003

  6. Ultrafiltration – ceramic membrane module 2003

  7. Chemical Treatment – key points • Continuous chemical process to partially solubilise and oxidise • the excess biomass generated in the AFC process • the non-degradable portion of the biological fermentation solids input • any other recalcitrant COD • biosurfactants that could cause foaming • Treated material returned to AFC system for further treatment • Uses concentrated biomass returned from UF as feedstock • Process uses • Hydrogen peroxide (oxidant) at dose of 1 part per 4 parts VSS • Acidic conditions (pH 3-5) using sulphuric acid • High temperature (>65C) • Minimum 8 hour retention time • Or use ferrous sulphate as catalyst to accelerate hydrolysis and oxidation reactions • Raw materials fed in proportion fo feed flow to chemical tank • Vents to atmosphere • Blowdown from AFC system • To control build up of inorganics (principally struvite - magnesium ammonium phosphate) • Based on magnesium feed to AFC system • Blowdown from ultrafilter concentrate return line to existing WWTP 2003

  8. AFC Operating Conditions • Principle operating conditions for the AFC bioreactor are • Loading rate • 200-400 mg COD per litre per hour (4.8 – 9.6 kg COD/m3/d) • Dissolved Oxygen Concentration • Maintained in the range 1-3 mg per litre • Mixed Liquor Suspended Solids • Contains both active thermophilic biomass and waste fermentation biomass for destruction • In the range 25-35,000 mg per litre • pH • In the range 6.5-8.5 • Temperature • 45C- 70C 2003

  9. AFC Plant at GSK 2003

  10. Ultrafiltration Plant at GSK 2003

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