| dc.description.abstract | The objectives of this study were first to investigate the quantity and quality of filter backwash wastewater (FBW) in Ping-Jan Water Treatment Plant (WTP), and then further to evaluate the possibility for treating and reusing of FBW. In addition, the strategies of reducing the quantities of FBW in this plant were also explored based on the daily information of filter operations.
The survey results showed that the year average quantities of FBW from Hardinge and Wheeler filters were 4,587 and 9,871 CMD, respectively in the year of 2007. Thus, the FBW from Wheeler filters was the primary source of wastewaters in Ping-Jan WTP. In addition, the production quantity of FBW was independent on the turbidity of raw water and settled water, whereas directly correlated to the time of filter run. The results of water quality analysis indicated that the major component of pollutants in FBW was the total suspended solid (TSS). At the season of raw water with low turbidity, the TSS concentration in FBW was 417 mg/L and 184 mg/L for Hardinge filters and Wheeler filters, respectively. Also, the average particle size of TSS was in the range of 24~57 μm. However, as raw water with high turbidity, the TSS concentration in FBW from Hardinge filters was increased significantly to 801 mg/L. It was also observed that the FBW generally contained low organic contents with average DOC concentration was about 4.0 mg/L.
The experimental results revealed that the turbidity in FBW could be effectively removed by pre-sedimentation followed by UF membrane process. The turbidity removal efficiency was 93% after sedimentation, and the residue turbidity after pre-sedimentation and UF process were 7.9 NTU and 0 NTU, respectively. In contrast, the DOC removal efficiency for pre-sedimentation and UF process were only 7% and 23%, respectively. These results elucidated the need of further study on water quality improvement for FBW reuse. Finally, in order to meet the goals of FBW reduction and zero discharge in Ping-Jan WTP, four strategies, including on-schedule examination and maintenance of filters, setting the new guideline for start-up filter backwashing operation, shortening the time need for backwash, and reusing and recycling of FBW with proper treatment, were recommended.
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