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| levels |
||||
|---|---|---|---|---|
| factor | factor code | low | center | high |
| pH | A | 4.0 | 6.5 | 9.0 |
| amount of adsorbent (mg) | B | 200.0 | 600.0 | 1000.0 |
| contact time (min) | C | 5.0 | 25.0 | 45.0 |
