Selection of solids Retention Time and loading Criteria The common parameters used are the solids retention time (SRT), the food to biomass (F/M ratio(also known as food to microorganism ratio), and the volumetric organic loading rate(Ly) Solids retention time The SRT, in effect, represents the average period of time during which the sludge has remained in the system. SrT is the most critical parameter for activated-sludge design as SRT affects the treatment process performance, aeration tank volume, sludge production, and oxygen requirements
Selection of Solids Retention Time and Loading Criteria The common parameters used are the solids retention time (SRT), the food to biomass (F/M) ratio (also known as food to microorganism ratio), and the volumetric organic loading rate(Lv). Solids Retention Time The SRT, in effect, represents the average period of time during which the sludge has remained in the system. SRT is the most critical parameter for activated-sludge design as SRT affects the treatment process performance, aeration tank volume, sludge production, and oxygen requirements
Sludge production Sludge will accumulate in the activated-sludge process if it cannot be processed fast enough by an undersized sludge-handling facility The observed yield decreases as the Srt is increased due to biomass loss by more endogenous respiration. The yield is higher when no primary treatment is used, as more nbVSS remains in the influent wastewater(A-B)
Sludge Production Sludge will accumulate in the activated-sludge process if it cannot be processed fast enough by an undersized sludge-handling facility. The observed yield decreases as the SRT is increased due to biomass loss by more endogenous respiration. The yield is higher when no primary treatment is used, as more nbVSS remains in the influent wastewater(A-B)
Oxygen Requirements As an approximation, for BOD removal only, the oxygen requirement will vary from 0.90 to 1.3 kg O,/kg BOd removed for Srts of 5 to 20 d Nutrient Requirements Using the formula CsH,NO,, for the composition of cell biomass, about 12. 4 percent by weight of nitrogen will be required. The phosphorus requirement is usually assumed to be about one-fifth of the nitrogen value. As a general role, for SrT values greater than 7 d, about 5 g nitrogen and 1 g phosphorus will be required per 100 g of bod to provide an excess of nutrients
Oxygen Requirements As an approximation, for BOD removal only, the oxygen requirement will vary from 0.90 to 1.3 kg O2 /kg BOD removed for SRTs of 5 to 20 d . Nutrient Requirements Using the formula C5H7NO2 , for the composition of cell biomass, about 12.4 percent by weight of nitrogen will be required. The phosphorus requirement is usually assumed to be about one-fifth of the nitrogen value. As a general role, for SRT values greater than 7 d, about 5 g nitrogen and 1 g phosphorus will be required per 100 g of BOD to provide an excess of nutrients
Other Chemical requirements The amount of alkalinity required for nitrification, taking into account cell growth, is about 7.07 g Caco /g NH-N In addition to the alkalinity required for nitrification, additional alkalinity must be available to maintain the pH in the range from 6.8 to 7. 4. Typically the amount of residual alkalinity required to maintain pH near a neutral point (i. e, pHa 7)is between 70 and 80 mg/L as Caco3
Other Chemical Requirements The amount of alkalinity required for nitrification, taking into account cell growth, is about 7.07 g CaCO3 /g NH4 -N. In addition to the alkalinity required for nitrification, additional alkalinity must be available to maintain the pH in the range from 6.8 to 7.4. Typically the amount of residual alkalinity required to maintain pH near a neutral point (i.e., pH ≈ 7) is between 70 and 80 mg/L as CaCO3