What is the tank retention time of the MBBR tank?
MBBR (Moving Bed Biofilm Reactor) is an efficient biological treatment technology used for wastewater treatment. It combines the advantages of activated sludge and biofilm systems by adding high-fill-rate suspended fillers to the reactor to increase the attachment and growth space for microorganisms, thus improving treatment efficiency.
Calculation of Hydraulic Retention Time
Hydraulic Retention Time (HRT) refers to the average residence time of wastewater in the reactor. The formula for calculating the hydraulic retention time of an MBBR pool is as follows:
HRT = QV
Where:
V is the effective volume of the reactor (m3), considering that the reactor is not completely filled with water in actual operation, the volume corresponding to the actual water depth is usually taken.
Q is the influent flow rate (m3/h).
How to calculate the Sludge Retention Time?
Sludge Retention Time (SRT), also known as biomass retention time, refers to the average residence time of biomass (sludge) in the system.
In the MBBR system, calculating SRT directly is complex due to the system's design specificity (biofilm attached to the filler instead of freely suspended in water). SRT is usually indirectly managed by controlling the system's sludge discharge and monitoring the biofilm thickness rather than being calculated directly.
For MBBR systems, because most of the biological treatment occurs on the biofilm surface on the filler, the system's efficiency depends not only on the hydraulic retention time but also on the thickness and activity of the biofilm. Therefore, the key to controlling and optimizing MBBR systems is not only through calculating and adjusting HRT but also monitoring and maintaining the health of the biofilm on the filler.
For more specific calculations and system designs, factors such as wastewater characteristics, treatment objectives, reactor design parameters, etc., need to be considered. Adjustments and optimizations may require specific engineering practices and experience.
For traditional activated sludge treatment systems, we can calculate Sludge Retention Time (SRT), also known as Solid Retention Time (SST) or Biomass Retention Time. Here's a simple calculation example to help you understand how to calculate SRT.
Assumptions:
Daily influent volume: 10,000 m3/day
Influent Suspended Solids (SS) concentration: 200 mg/L
Effluent SS concentration: 30 mg/L
Daily sludge discharge: 200 m3/day
Sludge SS concentration: 10,000 mg/L
Mixed Liquor Suspended Solids (MLSS) concentration in the reactor: 3,000 mg/L
Effective volume of the reactor: 5,000 m3
Steps for calculating SRT:
Calculate the daily SS load (i.e., the total amount of SS entering and leaving the reactor).
Influent SS total = Influent volume × Influent SS concentration = 10,000 m3/day × 200 mg/L
Effluent SS total = Effluent volume × Effluent SS concentration = 10,000m3/day × 30 mg/L
Sludge SS total = Sludge discharge × Sludge SS concentration = 200 m3/day × 10,000 mg/L
Calculate the total SS in the system (MLSS).
Total SS in the system = Effective volume of the reactor × MLSS concentration = 5,000 m3 × 3,000 mg/L
Calculate SRT.
SRT (Sludge Retention Time) = Total SS in the system / (Influent SS total - Effluent SS total + Sludge SS total)
Let's calculate the specific values.
According to the above calculation, the Sludge Retention Time (SRT) of this activated sludge treatment system is approximately 4.05 days. This means that the average residence time of sludge in the system is 4.05 days before it is discharged from the system. This value is essential for understanding and controlling the sludge's biological decomposition rate, the system's treatment efficiency, and necessary maintenance operations (such as sludge discharge).