*2.8. Scanning Electron Microscopy*

Sludge samples were fixed in 2.5% glutaraldehyde in phosphate-buffered saline for 2 h at 4 ◦C and postfixed in 1% osmium tetroxide in the same buffer for 1 h. The samples were dehydrated in a graded ethyl alcohol series, critical point-dried, gold coated, and viewed under a JSM-5410 scanning electron microscope (JEOL Ltd., Tokyo, Japan).

#### **3. Results and Discussion**
