Combining calcium precipitation and electro-coagulation-flotation to treat wastewater with high-concentration-arsenic
Date Issued
2005
Date
2005
Author(s)
Hsu, Hsei-Ching
DOI
zh-TW
Abstract
Because gallium arsenide (GaAs) becomes a new material in the semiconductor industry, the problem of treating high-arsenic-containing wastewater has newly risen. Arsenic has already been proved to be in relation to lung cancer, liver cancer and skin cancer. Excessive uptake of arsenide will cause death. Therefore, treating arsenic wastewater well is an important issue for environmental engineers nowadays.
The treatment of arsenic is mostly aimed at low-concentration in the past and the process for high-arsenic-containing wastewater is limited. A common method for removing arsenic from wastewater is principally in calcium precipitation. But the treatment of calcium precipitation cannot reach the discharge standards of wastewater. It therefore needs to combine with other processes. Moreover, the sludge of calcium arsenates is very difficult to precipitate and collect. The costs of arsenic sludge treatments are five times to the ones of the normal sludge. Therefore, this study expects to develop a feasible and effective method to remove arsenic in high-arsenic-containing wastewater.
This study combined precipitation of calcium, and electro-coagulation- flotation to treat the wastewater with 500ppm of As. The effects of the additions of calcium, type and concentration of the surfactants, current densities, pH, and interference ions on arsenic removal efficiency were eximed.
The results indicated that the additions of calcium dramatically influenced the efficiency of arsenic removal. The removal efficiency increased from 78.8% to 99.9% as calcium was added. SDS facilitated to flotation efficiency. The current density is an important operating factor influencing arsenic removal and flotation efficiency. The best operating system of this study was the following, the dosages of calcium =1.962g/L(Ca/As molar ratio=2), the additions of SDS=50mg/L, the current density= 17.86mAcm-2, the reaction time=15 minutes. Under this operating system, the residual concentration of arsenic was less than 0.5ppm and SS was less than 30mg/L in the effluent.
The final pH is more important than initial pH for arsenic removal. The changes of pH value caused the changes of zeta potential of particles. The optimum flotation efficiency occurs at the zero point of surface charged. The co-existing of anions compete the calcium with arsenate and the active cites with SDS. This fact cause the decrease the efficiencies of arsenic removal and SS removal. The series of the influence is PO43- > SiO32- > SO42- > CO32-.
Subjects
砷系廢水
電聚浮除法
界面活性劑
arsenic-containing wastewater
electro-coagulation- flotation
surfactants
SDGs
Type
thesis
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