# BIOLOGICAL PLANT SIZING

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BIOLOGICAL PLANT SIZING
Ing. Alberto Scaunich

STATISTIC ELABORATION
EXISTING PLANT (or available data flowrate and pollutants concentration) - Number of values N Average Value M Standard Deviation s WHICHEVER DISTRIBUTION NORMAL Typical Values M+ M+2 3 75% 91% 68.3% 95.4% 99,7% STATISTIC ELABORATION Generally are available data for: Flow Q [m3/d] Pollutant concentration c [mg/l] Pollutant Load C [kg/d] = Q*c/1000

EXISTING PLANT (or available data flowrate
and pollutants concentration) When are available a lot of data, it’s better to eliminate single data (only flow or only concentration). Hence you proceed in statistic elaboration. At the end, when you have average values of flow and loads, calculate the value ratio: average load (concentration) average flow which generally is different from concentration average values and is more significant, representing the weighted average of concentrations.

NOT EXISTING PLANT MUNICIPAL WASTE WATER
You have to refer your design to the SPECIFIC CONTRIBUTION PER CAPITA, which generally result prudential values. 2. INDUSTRIAL WASTE WATER You have to refer your design to the available SPECIFIC CONTRIBUTION PER UNIT OF PRODUCTS, adopting some security factors.

POLLUTANTS BALANCE In biological plant sizing the ratio COD/BOD and BOD/TKN (or COD/TKN) are very important In Denitrification you need organic load to remove Nitrogen. assume: 3 kgBOD/kg(N-NO3)DEN sizing oxidation 4 kgBOD/kg(N-NO3)DEN sizing post-denitrification (methanol requirements) Calculate Pollutants balance for these following cases (to verify section sizing): M (BOD) + M(TKN) M(BOD) + M+2s (TKN) M+2s (BOD) + M(TKN)

TKNin+(N-NO2)in+(N-NO3)in =
NITROGEN BALANCE TKNin+(N-NO2)in+(N-NO3)in = = TKNSED+(N-NO3)DEN+TKNox+TKNout+(N-NO2)out+(N-NO3)out Where: TKNin = inlet Nitrogen (organic ed ammonia) (N-NO2)in = inlet Nitrogen (nitrite): generally absent (N-NO3)in = inlet Nitrogen (nitrate): present only in industrial wastewater TKNSED = organic Nitrogen removed in primary sedimentation: 10÷15% TKNin TKNin(N-NO3)DEN = nitrogen to remove by denitrification TKNox = TKN removed by bacterial metabolism (5% BOD removed in biological treatment = 0,05 (BODin Den – BODout) TKNout = outlet Nitrogen (organic ed ammonia) - assume: 1 mg/l (N-NO2)out = outlet Nitrogen (nitrite) - negligible (N-NO3)out = outlet Nitrogen (nitrate) - project requirement(10÷15 mg/l) Normally you can’t have in the same time significant values of (N-NH3)out and (N-NO3)out

DENITRIFICATION DESIGN
DENITRIFICATION VELOCITY (municipal effluents) (nD)T = (nD)20 * qT-20 Where: (nD)T [gN-NO3/kgVSS*d] = Denitrification velocity:actual operative conditions (temperature = T); (nD)20 [gN-NO3/kgVSS*d] = Denitrification velocity: max value at T = 20 °C, without any limiting factor; q = Temperature correction coefficient (higher value, higher T dependence)

PRE-DEN Inizial velocity
DENITRIFICATION VELOCITY DENITRIFICATION INTERNAL CARBON PRE-DEN Inizial velocity PRE-DEN Average vel. POST-DEN Average vel. VOCE Unità di misura Scaunich vecchio Scaunich attuale Forte influenza T Esercizio attuale Debole influenza T Organic fraction SSV/SST 0,7 Temperature correction coefficient 1,12 1,065 1,200 1,080 1,030 Denitrification velocity a °C 20 gN-NO3/kgSSTxd 70,0 56,0 504,0 70,7 50,4 18 55,8 49,4 350,0 60,6 47,5 16 44,5 43,5 243,1 52,0 44,8 14 35,5 38,4 168,8 44,6 42,2 12 28,3 33,8 117,2 38,2 39,8 10 22,5 29,8 81,4 32,7 37,5 gN-NO3/kgSSVxd 100,0 80,0 720,0 101,0 72,0 79,7 70,5 500,0 86,6 67,9 63,6 62,2 347,2 74,2 64,0 50,7 54,8 241,1 60,3 40,4 48,3 167,4 54,6 56,8 32,2 42,6 116,3 46,8 53,6

DENITRIFICATION VOLUME CALCULATION
(N-NO3)DEN V = (nD)T * X Where: V [m3] = Minimum design Denitrification volume T [°C] = Minimum design Temperature (N-NO3)DEN [kg N-NO3/d] = nitrogen to remove by denitrification X [kgSSV/m3]: = Volatile Suspended Solids concentration in biological basins (Denitrification – Nitrification) Note: It’s opportune to assure a minimum residential time of 3÷4 h at the maximum flow, to give to mixed liquor enough time to reduce its O2 content (DO concentration of 0,5 mg/l reduce denitrification efficiency to 10%)

MIXED LIQUOR TO RECYCLE CALCULATION
1000 * (N-NO3)DEN QML = QR 24 * N-NO3 out Where: QML [m3/h] = flowrate of recirculated Mixed Liquor QR [m3/h] = return sludge flowrate (N-NO3)DEN [kg N-NO3/d] = nitrogen to remove by denitrification N-NO3 out [g/m3] = concentration of nitrogen in outlet stream (design value) 1000 = conversion factor (kg  g) 24 = conversion factor (d  h)

MIXING - DENITRIFICATION
Above 8÷10 W/m3 energy density is required (normal submersible mixers) Mixer rotation velocity must be chosen as low as possible (< 700 rpm)

OXIDATION DESIGN PRELIMINARY SIZING BODin V = --------------- X * F/M
Where: BODin [kgBOD/d] = Inlet BOD, coming from Denitrification X [kgSST/m3] = Total Suspended Solids concentration in biological basins (Denitrification – Nitrification): Values: 4÷6 SSV/SST = Organic fraction: typical = 0,7 F/M [kgBOD/kgSST*d] = Ratio Food/Mass: Typical values range - extended aeration , (0,06÷0,09) - nitrification (according T) , (0,12÷0,18) - carbon removal only (h =85-90%) , (0,2÷0,35)

OXIDATION DESIGN NITRIFICATION VERIFING
Where: (nn)T = Nitrification velocity: actual operative conditions (temperature = T [gTKN/kgSSV/d]; (nn)20 = Nitrification velocity: max value at T = 20 °C, without any limiting factor; [gTKN/kgSSV/d]; q = Temperature correction coefficient; KTKN, KO = semisaturation constants, relating to TKN and DO [mg/l]; TKN, O.D.= TKN and Oxygen concentrations in biological basins [mg/l]

NITRIFICATION VERIFING
OXIDATION DESIGN NITRIFICATION VERIFING

OXIDATION DESIGN CALCULATION OF NITRIFICANT BACTERIA FRACTION Where:
y N = nitrificant bacteria cellular yield coefficient [kgSSV/kg/TKN] y = heterotrophic bacteria cellular yield coefficient [gSSV/gBOD] S0 = inlet organic matter [mg/l] Se = outlet organic matter [mg/l] TKN0 = inlet TKN [mg/l] TKNe = outlet TKN [mg/l] y/yN = 4,72 (Bonomo, 2008)

OXIDATION DESIGN NITRIFICATION VOLUME CALCULATION Where:
x = Total Suspended Solids concentration in biological basins [kgSST/m3] XN = Total nitrificant bacteria in nitrification basins [kgSST]

OXIDATION DESIGN RETURN SLUDGE FLOWRATE Where:
xr = Total Suspended Solids concentration in return sludge [kgSST/m3]

Qr Va OXIDATION DESIGN (Q + Qr)Va = Qr Vr
RETURN SLUDGE FLOWRATE – IMHOFF CONE (Q + Qr)Va = Qr Vr Qr Va = Q Vr - Va If Vr = 1 l/l Q Va

OXIDATION DESIGN RETURN SLUDGE FLOWRATE SVI (sludge volume index)
Where: x = Total Suspended Solids concentration in biological basins [g/l] Qr x = Q /SVI - x Imhoff cone – 30 min [ml/l] or [cc/l] Imhoff SVI = x

EXCESS SLUDGE FLOWRATE CALCULATION
OXIDATION DESIGN EXCESS SLUDGE FLOWRATE CALCULATION

OXIDATION DESIGN ACTUAL OXYGEN REQUIREMENTS (AOR) & STANDARD OXYGEN REQUIREMENTS (SOR) Where: a = Carbon removal coefficient = 0,5 kgO2/kgBOD b = Endogenous respiration coefficient = 0,08 kgO2/kgSST/d N da nitrificare = N to remove in nitrification [kgN-NH4/d] 2,86 KgO2/KgNDEN = Oxygen recovery

OXIDATION DESIGN ACTUAL OXYGEN REQUIREMENTS (AOR) & STANDARD OXYGEN REQUIREMENTS (SOR) Where: a = rapporto tra il coefficiente di trasferimento relativo al liquido reale a 20°C e quello relativo alle condizioni standard, fissato pari a 0,70; b = rapporto tra la concentrazione di ossigeno a saturazione nel liquido reale in condizioni di esercizio e quella in acqua pulita in condizioni di esercizio; Cs,T = concentrazione di ossigeno a saturazione in acqua pulita alla temperatura di esercizio T; Cw,T = concentrazione di ossigeno nel liquido reale alle condizioni di esercizio, fissata pari a 2 mg/l; Cs,* = concentrazione di saturazione in acqua pulita in condizioni standard (20 °C); T = Temperatura nelle condizioni di esercizio

OXIDATION DESIGN AIR DEMAND Where: 24 = days hours;
0,28 = Kg O2 / mc air in standard conditions (20°C – 0 m a.s.l.); h = transfer efficiency O2 = 5% / m depth.

SEDIMENTATION DESIGN Hydraulic head (mc/mqxh) Ci=Q/A 0,20 – 0,30
- Q (mc/h), flowrate - A (mq), area Solid load (kg SST/mqxd) Cs = G/A < 5 a Q24 <9 a Qmax - G (kgSST/d), solid flowrate = 2,5 Qr X - X (kgSST/mc), activated sludge concentration - Qr (mc/h), return sludge flowrate = 1 – 1,5 Q24 Height (m) ≥3m Bridge Suction bridge

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