Method for starting up and controlling a biological process for ammonium removal by the action of autotrophic bacteria in wastewater

The present invention is related to a method for starting up and controlling a biological process for removing nitrogen contained in wastewater through a combined stage of nitrification and anaerobic oxidation of ammonium ion (Anammox), in which an aerobic reaction of partial nitrification of the ammonium contained in the wastewater to nitrite with oxidizing bacteria and addition of oxygen, and a nitrogen production anoxic reaction with ammonium and nitrite autotrophic denitrifying bacteria, of the phylum Planctomycetes, take place at the same time, both bacterial populations being arranged in the form of biofilm in the same reactor such that the oxidizing bacteria are on the outside of the biofilm contacting an aerobic zone inside the reactor and the autotrophic bacteria are inside the biofilm creating an anoxic zone, characterized in that the reactor is fed with a wastewater flow and air/oxygen are injected into the same continuously until its shutdown, i.e. aeration is facilitated in the entire reaction stage, keeping the dose of dissolved oxygen in the reactor at a level higher than 0.6 mg/l. In order to ensure the stability of the process, the air/oxygen supply to the reactor, the hydraulic residence time and the alkalinity in the feed are controlled such that the (Alkalinity input -Alkalinity output )/(Conductivity input -Conductivity output ) ratio must be kept, ideally, below 13 mM/(mS/cm 25ºC ). In order to maintain a high efficiency of the process, the alkalinity at the output of the reactor must be between 5% and 25% of the alkalinity at the input. Ideally, this process is applied to nitrogen removal from effluent from anaerobic digesters that preferably can be previously pretreated in a tank the objective of which is to laminate the water flow to be treated in the biological unity and to decant the solids found in said effluent from anaerobic digestion.