distillation unit called a still as

distillation unit called a still as the final treatment step before storage and distribution. The high temperatures and liquid- to-vapor phase change in a still generally ensure that a distil- late will meet bacterial contamination limits. Two types of stills commonly are used: vapor compression (VC) and multi-effect (ME).A VC still may require only a softener and an activated- carbon bed as pretreatment.An ME still requires high-quality feed water. EDI commonly is used in conjunction with an ME still in pharmaceutical water treatment systems. Pre–membrane water treatment methods To understand why EDI currently is regarded so favorably, it is helpful to consider pharmaceutical water treatment methods of the past.Figure 1 shows an example of pre–membrane water treat- ment methods. In the past, membrane water treatment generally meant RO membrane water treatment.Presently,membrane water treatment includes microfiltration, ultrafiltration, nano- filtration, hyperfiltration (i.e., RO), EDI, and electrodialysis.