Answer to Question 1
Any four of the following:
dewatering such as screw presses, belt presses, vacuum filters
ultrasound
electric and magnetic fields
screening
filtering
centrifuging
skimming
settling
coagulation or flocculation
trickling filters
activated sludge tanks and ponds
anaerobic digestion
Answer to Question 2
When BOD levels are high, more treatment of the wastewater will be required.