A new process for removing mercury from the wastewaters containing various forms of inorganic mercury was investigated. In this process pulverized iron (II) sulfide was added to the wastewater to convert the mercury to mercury sulfide after the adjustment of pH between 6.0 to 8.0. In this range of pH, hydrogen sulfide gas liberated from the water was hardly detected and the solubility of mercury sulfide was extremely small. The wastewater comprising 1 per cent iron sulfide by weight was agitated for 8 hours and the resulting precipitate was then removed together with unreacted iron sulfide by centrifugal separation. The concentration of residual mercury in the treated water was below 0.0035 mg·l^-1 when the concentration of mercury in the wastewater was between 0.02 to 1.00 mg·l^-1. And a result of reaching test of sludge consisting of the precipitate and the residual iron sulfide showed that the concentrations of mercury in the leaching solutions were not more than 0.0025mg·l^-1 except for a few samples.
Key words : removal of mercury, addition of pulverized iron (II) sulfide, mercury sulfide, depression of hydrogen sulfide, pH control of wastewater

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An experimental study has been conducted to analyze an aerobic wastewater treatment using a draft tube air-lift reactor suspended with biologically active carbon particles. The liquid circulation rate and the volumetric gas-liquid mass transfer coefficient were measured under suspending fresh activated carbon particles. Effects of initial substrate concentration, dissolved oxygen concentration and reaction temperature upon the substrate removal rate were measured under the liquid batch operation. The experiments for liquid continuous operation were also performed to obtain conversion versus space time data.
The substrate removal rate is found to obey 0-th order kinetics for the substrate concentration greater than 150 mg·l^-1 and Monod kinetics for the substrate concentration smaller than 150 mg ·l^-1. In the 0-th order kinetics region, the reaction rate increases with the dissolved oxygen concentration in proportion to the power of 0.2 for the oxygen concentration and the apparent activation energy for the reaction is found to be 33.5 kJ·mol^-1. The substrate conversion data for the liquid continuous operation can be predicted well by the model analysis assuming the liquid flow in the draft tube reactor to be a completely mixed flow.

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[in Japanese]

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[in Japanese]

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