Performance evaluation and kinetic modeling of an upflow anaerobic sludge blanket septic tank for domestic wastewater treatment

Abstract

This work evaluated the UASB-septic tank performance using different kinetic models that correlated process efficiency and methane production with hydraulic and organic loading rates through experiments with five different HRT (48 h, 36 h, 24 h, 18 h, and 12 h) using synthetic domestic wastewater. The modified Stover-Kincannon model provided the best fitting to calculate kinetics constants, with an R² above 98% for linear regression, and predicted the effluent COD more accurately than the other models. Methane yield was 0.3294 L CH₄/g COD removed, being closer to the theoretical value, and the Van der Meer and Heertjes model had the highest R² for methane production. Organic matter and solids removal were 45% for TS, 70% and 68% for total and soluble COD, and 85% for TSS. Pollutant removal markedly decreased when the reactor operated HRT below 24 h; thus, it is recommended to operate the UASB-septic tank at this HRT.

Keywords: Anaerobic baffled reactor; Bacterial growth models; Decentralized wastewater treatment; Modified septic tank; Substrate utilization models; UASB reactor.