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Let's calculate an estimate of the solids retention time for a number of aerobic installations using the iterative formula - all data self-explanatory. Please be aware that these calculations are a simplification of the actual project data. For example, actual solids inventories could be smaller or larger and all other derived magnitudes adjusted accordingly. SRT is thus about ballpark.
| SRT Sludge Age Sizer | Dairy Biological Nutrient Removal | ||||||||||||
| T | 20 | °C | T | 20 | °C | T | 20 | °C | |||||
| Yoc | 0.5 | Yon | 0.31 | Ydn | 2.28 | ||||||||
| Kd | 0.200 | Kd | 0.200 | Kd | 0.200 | ||||||||
| flow in | 2000 | m3/d | 0.528 | mgd | |||||||||
| CODin | 483 | mg/L | 2126 | lbCOD/day | 964 | kgCOD/day | TKNin | 44 | mg/L | ||||
| TKNin | 44 | mg/L | (for nitrif!) | 194 | lbTKN/day | 88 | kgTKN/day | ||||||
| Nitrates | 44 | mg/L | 194 | lbCOD/day | 88 | kgNO3/day | 0 | used up for COD removal/growth | |||||
| nVSS | 0 | mg/L | 0 | lbSS/day | 0 | kgSS/day | TKNin used for growth | 0 | mg/L | ||||
| Percent | 100 | % Treated | 964 | kgCOD/day | TKNin avail for nitrification | 44 | mg/L | ||||||
| Percent | 95 | % COD removed | 916 | kgCOD/day | |||||||||
| Vreactor | 899300 | gallon | 3404 | m3 | (from order of magnitude sizing) | ||||||||
| 0.8993 | mg | 0.28 | kgCOD/day per m3 | ||||||||||
| Target MLVSS | ballpark bug mix | ||||||||||||
| 1086 | mg/L | heterotrophs | 3690 | kg heterotrophs | 1086 | mg/L | 68 | % of Target MLVSS | |||||
| 61.5 | mg/L | nitrifiers | 209 | kg nitrifiers | 62 | mg/L | 4 | % of Target MLVSS | |||||
| 450 | mg/L | denitrifiers | 1529 | kg denitrifiers | 450 | mg/L | 28 | % of Target MLVSS | |||||
| 0 | mg/L | other solids | 0 | kg other | 0 | mg/L | 0 | % other | (this entry's not used) | ||||
| 1598 | mg/L | ||||||||||||
| 1598 | mg/L | 11967 | lb bugs | 5428 | kg bugs | ||||||||
| Heterotrophic Calcs | |||||||||||||
| SRT | 30.04 | days | (iterates automatically) | ||||||||||
| Yn = | 0.134 | ||||||||||||
| biomass yield = | 123 | kg/day bugs | |||||||||||
| Global Sludge Age | |||||||||||||
| Nitrifiers | 30.01414 | 181 | kg/day | ||||||||||
| SRT | 30.16 | days | (iterates automatically) | synthesis | |||||||||
| Yn = | 0.083 | ||||||||||||
| biomass yield = | 7 | kg/day bugs | |||||||||||
| Denitrifiers | |||||||||||||
| SRT | 29.93 | days | (iterates automatically) | ||||||||||
| Yn = | 0.612 | ||||||||||||
| biomass yield = | 51 | kg/day bugs | |||||||||||
| HRT = V / Q = | 1.7 | days | |||||||||||
| 41 | hours | ||||||||||||
Let's calculate an estimate of the required solids retention time for a small petroleum refinery stream containing benzene (1850 ppm -> COD = 1850* 3.08 = 5700 mg/L). Please be aware that these calculations are a simplification of the actual project data. For example, actual solids inventories could be smaller or larger and all other derived magnitudes adjusted accordingly. SRT is thus about ballpark.
| SRT Sludge Age Sizer | ||||||||||||
| T | 25 | °C | ||||||||||
| Yoc | 0.5 | Petroleum Refinery Stream | ||||||||||
| Kd | 0.250 | (also called b) | Stream containing about 1850 ppm benzene | |||||||||
| Carbonaceous Removal Sludge Age | ||||||||||||
| flow in | 240 | m3/d | 0.063 | mgd | ||||||||
| CODin | 5700 | mg/L | 3011 | lbCOD/day | 1366 | kgCOD/day | applied | |||||
| 0 | kgCOD/day | via denitrif | ||||||||||
| 1366 | ||||||||||||
| Percent | 100 | % Treated | 1366 | kgCOD/day | ||||||||
| Percent | 98 | % COD removed | ||||||||||
| Vreactor | 190440 | gallon | 721 | m3 | (from order of magnitude sizing) | |||||||
| 0.19044 | mg | 1.89 | kg applied COD/day per m3 | (Residual OK) | ||||||||
| Target MLVSS | 1.89 | kg applied + from denitri COD d/m3 | ||||||||||
| 5320 | mg/L | 8439.463 | lb bugs | 3828 | kg bugs | total bugs in tank but say only | 100.0 | % heterotrophs | ||||
| 5320 | mg/L | 8439.463 | lb bugs | 3828 | kg bugs | (heterotrophic biomass) | ||||||
| SRT | 20.04 | days | (iterates automatically) | |||||||||
| Ync | 0.143 | ok | f/m | 0.357 | kg AppliedCOD d per total kg bugs (Residual OK) | |||||||
| f/m | 0.357 | kg Applied + From Dentir / total kg bugs | ||||||||||
| biomass yield = | 191 | kg/day bugs | due to appliedCOD | |||||||||
| HRT = V / Q = | 3.0 | days | ||||||||||
| 72 | hours | ok | ||||||||||
