A steady state model was developed for evaluating the sulfur cycle based SANI(®) process. The model comprises: 1) a COD-based anaerobic hydrolysis kinetics model to determine removal of biodegradable COD and sulfate under different hydraulic retention time (HRT) and sludge retention time (SRT), 2) an element (C, H, O, N, P, S), COD and charge mass balanced stoichiometric part for prediction of the concentrations of alkalinity (H(2)CO(3)(*) alkalinity + H(2)S alkalinity), COD, sulfate, sulfide, nitrate and free saline ammonia in anaerobic sulfate reduction, anoxic autotrophic denitrification and aerobic autotrophic nitrification, and 3) an inorganic carbon (HCO(3)(-)) and sulfide (H(2)S/HS(-)) mixed weak acid/base chemistry part for pH prediction. Through characterization of the sewage organic matter and determination of the anaerobic hydrolysis kinetic rate and other relevant parameters, the steady state model was calibrated to a pilot plant for the SANI(®) process. The model predictions agreed well with the experimental data of the pilot-scale trial, demonstrating that the model developed from this study can explain the causes and conditions for the different bioprocesses and minimal sludge production in the SANI(®) process.
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