Taiwan: Chinese Institute of Environmental Engineering
Treatment of drinking water from the water reservoir (e.g., Shihman reservoir, located in southern Taipei) is a challenging work due to the highly cultivated region of the upstream.Abundance of micrometer sized or even nanometer sized particulates causing high turbidity water was easily seen in recently years, especially after the incidents of heavy rain showers or typhoons.Relative longer retention time of particle sedimentation was necessary to meet the need of further treatment. Two alternative methods to treat reservoir water containing high turbidity were used in the present study. Particle removal efficiency of micrometer-sized (average D50 = 6.5 μm) with high turbidity (500, 1500 and 3000 NTU, Nephelometric Turbidity Unit) reservoir water was tested either by electro-aggregation or conventional coagulation jar test. Blank tests of artificial high turbidity water (500 NTU) with kaolinite and high conductive solution (0.00 and 0.6 M NaCl) were also performed for comparison of the results. The optimum dosage of poly aluminum chloride for 500 NTU sample was 50 mg L-1 to achieve the lowest turbidity (3 NTU) of the treated water by coagulation. As for the electro-aggregation, the optimum controlling parameters for the same sample were: 280 V of power supply, hydraulic retention time of 128 s and aluminum plates as the conductive chambers to achieve the clarified effluent of 4 NTU after 30 min further settling. The aluminum plates may play the roles of dipole phenomena and releasing aluminum ions as coagulant.Blank tests of pure electrolytes (0.003 M NaCl) in electro-aggregation enhances the electroconductivity and further releasing aluminum ion (117 mg L-1) under the conditions of 280 V and 128 s of retention time, while water was almost boiling with 0.6 M NaCl in a short period of time. Although the formation of aluminum ions in kaolinite solution (low electro-conductivity) is not significant (3 mg L-1), it does reduce the effluent turbidity (from 510 to 140 NTU) at 280 V and 128s retention time.
Journal of Environmental Engineering and Management 17(5), pp.371-375