Investigation on the simultaneous removal of fluoride, ammonia nitrogen and phosphate from semiconductor wastewater using chemical precipitation

This study investigates the simultaneous removal of the total ammonia nitrogen (TAN), phosphate (PO4-P) and fluoride (F−) from semiconductor wastewater by chemical precipitation. The lab-scale experiment results revealed that the fluoride removal by using magnesium salts produced a good performance. The fluoride present could significantly inhibit the struvite crystallization, in this process. The inhibition ratio of the fluoride on struvite crystallization remarkably increased with an increase in the fluoride concentration and a drop in the pH value. The optimal pH for struvite precipitation in the semiconductor wastewater was taken as 9.5, the value at which the fluoride effect significantly decreased. Therefore, to further lower the fluoride effect, an overdose of the magnesium source was required in the process of struvite precipitation. The experimental results thus indicated that overdosing the bittern was the more effective method to treat the semiconductor wastewater compared with a brucite overdose; this was because large amounts of un-reacted brucite remained in the solution, causing increased costs and operation difficulty when it was employed as magnesium source. The pilot-scale study demonstrated that 97% of the PO4-P, 58% of the TAN and 91% of the F− could be removed from semiconductor wastewater by a two-stage precipitation process. An economic analysis showed that the treatment cost of the process proposed was approximately 1.58 $/m3.