A dynamic model of the activated sludge process was used to analyze and optimize the operation of an SBR treating slaughterhouse wastewater. The existing treatment cycle (duration of fill, aeration, mix, decanting and wasting periods) was found to be inadequate for meeting effluent requirements under a number of different loading scenarios. Modelling analysis indicated that the aeration phase was too long and the settling phase too short. Simulation of a new SBR cycle operation, in which the superfluous time in the aeration phase was distributed to the settling phase and a new anoxic phase, confirmed that the unit could meet the stringent effluent requirements. Using an iterative approach, optimal cycle settings were determined for each of the loading and temperature scenarios investigated.

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Data from an intensive inter-stage sampling project at an advanced wastewater treatment plant, which characterized congeners of the flame retardants polybrominated diphenyl ethers (PBDEs), were used to calibrate a fate model of the treatment plant. Flow and solids balances were first established, followed by predicting of the fate of the different congeners through the treatment plant. A biodegradation rate coefficient value of 1E-05 L/mg VSS-h was used for all congeners in the absence of any published values. Sensitivity analysis was used to assess the effect of varying the magnitude of the biodegradation rate coefficient on the fate of different representative congeners. Most of the PBDEs (approximately 90%) are predicted to partition to the wastewater residual solids, with most of the remaining mass discharged in the treated effluent. Biodegradation may account for a small mass of the lower brominated congeners. Air emissions were predicted be very small. Estimates of the mass of PBDEs discharged nationally by U.S. POTWs were calculated based on flows reported in the 2004 EPA Needs Survey.