A photocatalysis hybrid system for effluent organic matter (EfOM) removal from biologically treated sewage effluent (BTSE)

Publication Type:
Thesis
Issue Date:
2008
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NO FULL TEXT AVAILABLE. Access is restricted indefinitely. ----- The interest in water reuse and reclamation has been growing persistently due to the increasing pressure of freshwater deficiency. Detailed studies have been carried out on numerous technologies, including biofiltration, advanced disinfection and membrane filtration in order to find the most practical, efficient and low-cost technique. The possible use of photocatalysis with Ti0₂ in wastewater treatment has been the focus of many studies in recent years. The objective of this study is to investigate the performance of the hybrid photocatalysis - submerged membrane system in the removal of effluent organic matter (EfOM) from the biologically treated sewage effluent (BTSE). An investigation of the adsorption behaviors of two catalysts, namely UV light responsive titanium dioxide (P25) and visible light responsive titanium dioxide (Vis-Ti0₂) indicated that the Freundlich model fitted well with the experimental data. In addition, the photocatalytic kinetics of both materials were well described and predicted by the Linear Driving Force Approximation (LDF A) model. A series of batch experiments was conducted to optimize the photocatalytic oxidation in terms of catalyst dose, pH, flow rate, residence time and ultraviolet (UV) light intensity for maximum degradation of EfOM. The results indicated that the photo-oxidation process was significantly affected by catalyst dose, pH as well as the detention time. An optimal concentration of 1.0 g/L of P25 yielded approximately 65% of DOC removal efficiency. An increase of 20% in the removal efficiency was attained by adjusting the pH from neutral (pH= 7.8) to more acidic (pH= 4.0). Lowering the flow rate, i.e. increasing the detention time appeared to allow more time for the mineralizing of organic compounds. Upon photooxidation, treated water was pumped into the submerged membrane reactor to retain the photocatalysts. The results showed an increase of 1 0% in organic removal was achieved after the filtration. This raised the total DOC removal of the hybrid system to 70- 75% and enabled it to operate consistently at the feed rate of 50 mL/min to the photoreactor and the flux rate of 40 L/m².h for a 240-minute testing. The results also indicated that pre- photooxidation with Ti0₂/UV could effectively reduce membrane fouling and enhance the critical flux of the submerged membrane reactor. Pre-treatment by flocculation was considered to facilitate the degradation rate of photocatalysis and improve the effluent quality. It was found the optimal coagulant doses were around 50-60 mg/L of FeCl₃ and pH ranged between 5.5 and 6.5. The removal of organic matter was increased by 30% after flocculation, resulting in a total removal efficiency of nearly 98%. In other word, pre-treatment by flocculation was able to significantly enhance photocatalytic process as well as the effluent quality. The determined operating conditions were applied for the treatment of real biologically treated sewage effluent (BTSE) collected from the Homebush Bay's Water Reclamation Plant. The hybrid system obtained a relatively high removal efficiency of 80% with preflocculation (50mg/L of FeCl₃). In addition, the photocatalysis and membrane hybrid system was employed as the last polishing process of the MBR effluent in the practice of water reuse. A low concentration of Ti0₂ of 0.1 g/L and the minimal light intensity of 46.61 mW/cm² Ied to almost 90% of DOC removal efficiency. One of the advantages of photocatalysis over the treatment of persistent organic pollutant (POP) was demonstrated with the decomposition of trimethoprim, an antibiotic most frequently detected in municipal wastewaters and surface waters. A high removal efficiency of approximately 70% was obtained by the Ti0₂/UV irradiation compared to <10% removal efficiency of microfiltration. In addition, the filtration flux of microfiltration was improved to 60 L/m² .h. The transmembrane pressure (TMP) increased slightly from 8 to 9.5 kPa after 4 hours of operation while the quality of the permeate remained sustainably.
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