Mass balance of a wastewater loaded canal system: case study of Bangkok

Abstract A dynamic water quality model was applied in order to investigate self-purification processes in highly loaded canals in the centre of Bangkok, capital city of Thailand. Oxygen production by aquatic plants induces a significant diurnal variation of the dissolved oxygen concentration. The corresponding profiles of heterotrophic growth and BOD 5 concentration demonstrate the limiting impact of oxygen shortage during night time. Both self-purification mechanisms -biological degradation and settling -are considered and water-sediment interactions are calculated. Simulation results and measurement data are summarized by mass balance schemes which offer a telling characterization of the complex system

Anaerobic model for high-loaded or high-temperature digestion - additional pathway of acetate oxidation

Current digestion models cannot properly simulate processes that are operated under high loadings or high temperatures. A modification to existing models has been implemented by adding important missing degradation pathways, to accommodate these high loaded and high temperature anaerobic systems without artificially recalibrating the model parameters. This degradation pathway relies on the use of an alternate acetate oxidizing mechanism that is more tolerant to ammonia than the aceticlastic pathway. Inhibition values have been estimated and a logistic function has been used to apply ammonia inhibition. The model also relates metabolic activity to unionised species such as undissociated acetic acid as substrate (though not obligatory for all organisms) and unionized ammonia as inhibitor. The model also incorporates all important chemical species and activity coefficients in the equilibrium chemistry module (such as the phosphate buffer), resulting in more accurate pH predictions which is crucial for proper modeling of CO and NH stripping. This model can now be used to simulate processes that are operated under conditions where free ammonia inhibition can be an important factor for process efficiency and substrate conversions

Anaerobic model for high-solids or high-temperature digestion - additional pathway of acetate oxidation

Current anaerobic digestion models cannot properly simulate processes that are operated under high solids concentrations or high temperatures. A modification to existing models has been implemented by adding important missing degradation pathways, to accommodate these systems without artificially recalibrating the model parameters. Specifically, we implemented the alternate acetate oxidizing mechanism that is more tolerant to ammonia than the standard aceticlastic pathway. Inhibition values were estimated and an empirical function has been used to apply ammonia inhibition. The model also relates metabolic activity to un-ionised species such as undissociated acetic acid as substrate (although not obligatory for all organisms) and unionised ammonia as inhibitor. The model relies on an equilibrium chemistry module (e.g. including the phosphate buffer), resulting in more accurate pH predictions, which is crucial for proper modeling of CO and NH stripping. Calibration results from three case-studies modeling thermal hydrolysis and subsequent digestion of sludge are presented