Treatment of high-level arsenic-containing wastewater by fluidized bed crystallization process

Gallium arsenide technology has been widely applied in the communication and optical electronics industries. The process of chip manufacturing produces a stream of wastewater unique in its low flow rate and high arsenic concentration. Fluidized bed crystallization (FBC) technology combines the advantages of a fluidized bed reactor and crystallization. It is highly efficient with low capital and operational costs, while producing no sludge. The waste from the FBC is small in volume, high in crystal purity and recyclable. Jar tests were first performed to evaluate the precipitation of arsenic sulfide. Then a lab-scale fluidized bed reactor was applied to screen critical operational parameters and the process was optimized to meet the wastewater discharge standard. The results obtained in this study confirmed that the FBC process is capable of treating wastewater containing high concentrations of arsenic, reducing the concentration to μg L^-1 levels. Sulfide dosage and operating pH are the two most significant parameters determining the residual arsenic concentration of the effluent, with optimum conditions of pH = 2 and S/As = 2.2 to meet the local discharge limit.