What kinds of sewage treatment methods are there?

Generally speaking, it is physics, chemistry and biology.

The principle of biological removal of ammonia nitrogen by A/O method: Under the condition of oxygenation (O stage), ammonia nitrogen in sewage is nitrated into nitrate nitrogen by nitrifying bacteria, and a large amount of nitrate nitrogen flows back to A stage. Under anoxic conditions, organic matter in sewage is used as electron donor and nitrate nitrogen is used as electron acceptor, so that nitrate nitrogen wave is reduced to pollution-free nitrogen and escapes to the atmosphere, thus achieving the ultimate goal of denitrification.

Nitrification reaction: NH4++2o2→ NO3-+2h+H2O.

Inverse digestion reaction: 6NO3-+5CH3 OH (organic matter) → 5CO2 ↑+7H2O+6OH-+3N2 ↑.