WAS Rate to Hold Target SRT (Sludge Age)
The daily wasting decision: how much sludge to waste today to hold a target SRT.
Example
You enter
- Aeration volume (MG) 2
- Mixed-liquor solids MLSS (mg/L) 3000
- Target SRT (days) 10
- WAS concentration (mg/L) 8000
- Effluent flow (MGD) 5
- Effluent TSS (mg/L) 15
You get
- Solids to waste (lb) 5004
- Q was (MGD) 0.0656
- Q was (GPM) 46
Details, formula, and sources
Q_WAS = (system_solids/SRT - effluent_solids) / (WAS x 8.34), in MGD and gpm. The inverse of a sludge-age readout; effluent solids over the weir count as wasted and cut the pump rate. SRT lags ~one SRT, so change gradually.
system_solids = V x MLSS x 8.34; solids_to_waste = system_solids / SRT; effluent_solids = Qeff x TSSeff x 8.34; Q_WAS = (solids_to_waste - effluent_solids) / (WAS x 8.34); Q_WAS_gpm = Q_WAS x 1e6 / 1440.
WAS rate for a target SRT (MCRT/SRT control; WEF operator training), by name.
The SRT-control solids-balance relation is a public wastewater-operations method; the process trend and the operator govern the actual set point.
Estimate. AHJ and licensed professional govern.
Field names used by the API: aeration_volume_mg, mlss_mg_l, target_srt_days, was_conc_mg_l, effluent_flow_mgd, effluent_tss_mg_l, solids_to_waste_lb, q_was_mgd, q_was_gpm
- Solids to waste solids_to_waste = system_solids / SRT; the effluent solids reduce the required WAS pumpingSRT control
- Slow response SRT reacts over roughly one SRT; change the wasting gradually rather than chasing a single readingWEF operator training