In relation to a waste water treatment plant which stage or process is related to fluids and particles?

In the sewage treatment process, one of the most important steps is the separation of liquids and solids, in this process, we can give several examples of processes:

1. Water-Oil Separation - oils are used to receive effluent and oil and grease contaminated water from maintenance areas, vehicle and machine washing and mechanical workshops. Water - oil separators employ physical methods and work by density, using the tendency of oil to float in water;

2. Decanting and Decanters - Decanting is a physical method of separation such as filtration, coagulation, flocculation, flotation, etc., working by density. Sludge settlers use lower settling rates;

3. Flotation - Flotation in effluent and water treatment separates liquids from solids with clouds of air microbubbles that drag suspended impurities to the surface facilitating removal;

4. Drag Column - Removal of Contaminant Gases - The removal processes of Ammonia, VOC's, Radon, Carbonic Gas (CO2) and BTEX and mainly water nitrogen are usually based on biological oxidation (nitrification-denitrification);

5. Water filters: Sand, Coal, Zeolites, MnO2, Anthracite, etc. - The waters contain salts, suspended solids, microorganisms and debris that must be removed. Filters generally remove particles and improve color, odor, and taste.

answer; i do believe the correct answer is (river); /// good luck

not clear