modelling full sale granular sludge sequening tank … · 2019. 11. 14. · net reactor solids...
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Peter Dold, Bill Alexander*, Mark Fairlamb, Gillian Burger, Daniela Conidi, Chris Bye and Weiwei Du EnviroSim Associates Ltd., Hamilton ON Canada; * Alexander Process Consulting, Sandton, South Africa
MODELLING FULL-SCALE GRANULAR SLUDGE SEQUENCING TANK PLANT PERFORMANCE
GRANULAR SLUDGE SEQUENCING TANK (GSST) OPERATION IN
BioWin
MIXING PHASE
• Granules and mixed liquor well mixed.
• Aeration continuous or on/off.
• DO setpoint or air flowrate.
SETTLING PHASE
• Granules immediately settled on base of the reactor (with a void volume).
• Mixed liquor solids settle on top of the granular sludge.
• Waste activated sludge (WAS) withdrawn from bottom layer of settled mixed liquor solids.
• Granules not removed during wasting - only bulk mixed liquor.
FEED PHASE
• Influent feed typically commences well into the settling period.
• Upper section of the reactor should be well-clarified liquid.
• Distributed across the base - into granular sludge voidage.
• Plug-flow up through the reactor.
• Displaced liquid overflows into launders as effluent.
DECANT PHASE
• Small decant of clarified liquid to drop the liquid level below the launders.
• Avoid spillage of mixed reactor contents when next cycle starts.
MODELLING APPROACH
• Granular sludge based on BioWin’s 1D biofilm model. Biofilm thickness equivalent to granule radius.
• Settling of mixed liquor (non-granule) solids based on 1D flux model. Liquid above bed of settled granules divided into n equal-depth layers during settling.
• Full BioWin ASDM applied throughout.
• Detailed phys-chem modelling (pH, chemical precipitation, gas/liquid mass transfer, etc.).
….. CONSEQUENCES AND LIMITATIONS
• Does not predict new granule “formation”.
• Diameter of granules changes dynamically depending on loading, and solids impingement/erosion.
• Granule size distribution not considered.
• No steady state solution. GSST model simulated from initial values for approximately 4 SRTs to reach quasi-steady-state.
Parameter Unit Modelled Measured
Net reactor solids concentration kg m-3 10.3 > 8
Percent total mass in the granular phase % 81 > 80
Sludge production kg d-1 4,050 3,900
Effluent
Concentration
TSS mgSS/L 18 20
TCOD mgCOD/L 68 64
BOD5 mg/L 4.2 9.7
TP mgP/L 0.9 0.9
Soluble PO4-P mgP/L 0.4 0.4
TN mgN/L 7.1 6.9
Ammonia mgN/L 0.8 1.1
MODELLING A FULL-SCALE SYSTEM
BioWin GSST model calibrated to the full-scale Nereda® process at Garmerwolde, Netherlands*:
• Buffer tank followed by two parallel GSSTs with a total volume of 19,200 m3 (9,600 m3 each).
• Average dry weather influent flow is 28,600 m3/d.
*Pronk, M., de Kreuk, M.K., de Bruin, B., Kamminga, P., Kleerebezem, R. and M.C.M van Loosdrecht. (2015), Full scale performance of the aerobic granular sludge process for sewage treatment. Wat. Res., 84, 207-217.
TYPICAL SIMULATION RESULTS
User specifies:
• Initial granule settled volume fraction (FG).
• Initial granule diameter (D).
• Voidage fraction (E) in settled granule bed.
• Operating cycle.
TYPICAL RANGES:
• D from 0.6 to 1.5 mm.
• E from 20 to 28%.
• Granular surface area to tank volume ratio [A/Vt] from 300 to 500 m2/m3.
Dynamic behaviour in the system is quite complex:
• BioWin GSST model captures ability of these systems to remove N and P.
• Growth (and decay) of different biomass species within the granule and bulk mixed liquor.
User-defined parameters used to calculate a base granular surface area (A) [in metric units] :
Modelling results demonstrate capacity of the GSST to biologically remove nitrogen and phosphorous.