SLUDGE CALCULATION
Sewage sludge is the residual, semi-solid material that is produced as a byproduct of treatment of municipal or industrial wastewater.
Sludge age is defined as the average time in days the suspended solids remain in the entire system. It may also be defined as the amount of time in days that bacteria are under aeration.
The BOD loading is calculated by multiplying the concentration of BOD entering the aeration tanks by the influent flow per day to the aeration tanks by the weight constant of wastewater.
The amount of microorganisms in the process consists of the mass of Mixed Liquor Volatile Suspensed Solids (MLVSS) in the online aeration tanks.
Hydraulic Retention Tank (HRT) is the amount of time in hours for wastewater to pass through the aeration tank. HRT of an aeration tank is determined by dividing the volume of the aeration tank by the flow rate through the aeration tank.
The Mean Cell Residence Time (MCRT) is the amount of time, in days, that solids or bacteria are maintained in the activated sludge process. MCRT is also known as Solids Retention Time (SRT). The MCRT of an activated sludge process is calculated by dividing mass of MLSS in the activated sludge process by the pounds of suspended solids leaving the activated sludge.
Mixed Liquor Volatile Suspended Solids (MLVSS) represents the population size of bacteria within the activated sludge process.
Sludge Volume Index (SVI) is used to measure the settling character of the mixed liquor or activated sludge.
SVI = volume of settled solids after 30 minutes / concentration of MLSS
