Monitoring the variations of the oxygen transfer rate in a full scale membrane bioreactor using daily mass balances Available to Purchase

Oxygen transfer in biological wastewater treatment processes with high sludge concentration, such as membrane bioreactor (MBR), is an important issue. The variation of α-factor versus mixed liquor suspended solids (MLSS) concentration was investigated in a full scale MBR plant under process conditions, using mass balances. Exhaustive data from the Supervisory Control And Data Acquisition (SCADA) and from additional online sensors (COD, DO, MLSS) were used to calculate the daily oxygen consumption (OC) using a non-steady state mass balance for COD and total N on a 24-h basis. To close the oxygen balance, OC has to match the total oxygen transfer rate (OTR_tot) of the system, which is provided by fine bubble (FB) diffusers in the aeration tank and coarse bubbles (CB) in separate membrane tanks. First assessing OTR_CB, then closing the balance OC=OTR_tot allowed to calculate OTR_FB and to fit an exponential relationship between OTR_FB and MLSS. A comparison of the α-factor obtained by this balance method and by direct measurements with the off-gas method on the same plant is presented and discussed.