Abstract
Adsorption method of orthophosphate on activated alumina was examined as a tertiary treatment to remove it from the wastewater also containing calcium ions.
Activated alumina of 0.2g was added to the 100ml solution being adjusted at pH of 7 and containing phosphate of 5.0 mg·l-1, total alkali of 100 mg·l-1 and calcium of 23.2 mg·l-1. After shaking the solution for 12h, 90% removal ratio of phosphate was observed, while in the absence of calcium ions the ratios lay between 60-64%. The amount of phosphate removed was significantly influenced by the pH of the solution, it increased at lower pH but decreased at higher pH. The existence of calcium ions participated in relaxation of the strong pH-dependence.
The solution containing phosphate of 5.0 mg·l-1, total alkali of 100 mg·l-1, calcium of 23.2 mg·l-1 and being adjusted at pH of 7.0 was passed through the column at SV=10 h-1 packed with activated alumina of 2.0g. The sum volume of the effluent passed was 12 times as large as that without the calcium ions until the concentration of phosphate in the effluent reached 1.5 mg·l-1. In the same experimental condition the molar ratio of calcium to orthophosphate removed was about 2.1 immediately after the effluent of 28l had passed.
