Ozonation in Advanced Wastewater Treatment : Practical Aspects and Development of a Prediction Tool for Pharmaceutical Removal
Abstract: Pharmaceuticals that are not completely metabolized in the human body are excreted in wastewater and may find their way into surface waters, where they can have harmful effects on aquatic fauna and flora. The implementation of ozonation at wastewater treatment plants (WWTPs) can reduce the amount of pharmaceuticals discharged to the environment. Despite the technology readiness level of ozone treatment, some practical aspects remain to be addressed to facilitate the installation of full-scale ozonation units at WWTPs.In this work, the ozonation process was investigated to optimize the treatment and to facilitate its full-scale implementation. The operating conditions and properties of the wastewater were investigated on pilot and laboratory scale to determine their effects on removal efficiency. In addition, a tool was developed based on chemical oxygen demand (COD) and suspended solids (SS) for the prediction of ozone demand and pharmaceutical removal. Finally, the formation of the undesired by-product bromate during ozonation, and its subsequent reduction using a denitrifying biofilm process was evaluated on laboratory scale.No significant effects were observed on the efficiency of pharmaceutical removal when varying the hydraulic retention time, ozone dispersion method or wastewater temperature in pilot-scale ozonation experiments. Shorter hydraulic retention times allow more compact ozonation units, reducing both capital expenditure and space requirements. Ozonation performed slightly better after post-precipitation than after the activated sludge process, which led to further studies on the effects of SS.Laboratory-scale ozonation experiments showed comparable results regarding pharmaceutical removal when the ozone dose was normalized to the COD and dissolved organic carbon (DOC). Dissolved matter had a greater effect on the removal efficiency than particles at moderately elevated concentrations of ~25 mg SS/L. However, extremely elevated concentrations of particles, of ~100 mg SS/L, had greater negative effects on slow-reacting pharmaceuticals than fast-reacting ones. A tool was developed for the prediction of the removal of pharmaceuticals,using the parameters typically used in wastewater modelling and monitoring (COD and SS) as input. The predictions agreed with empirical data from pilot-scale ozonation, with deviations of less than 10% for several pharmaceuticals.Such a COD/SS-based tool could contribute to a more practical approach to predicting pharmaceutical removal at WWTPs.The results of the experiments on the microbial reduction of bromate indicated the potential of reducing the formed bromate in bromide-rich ozonated wastewater using the denitrifying biofilm process after ozonation. A reduction of 80% of the initial bromate to bromide using carriers from a full-scale moving-bed biofilm reactor could be achieved after 60 minutes.
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