Process for treating an aqueous fluid whereby a biogas is produced in an installation comprising a bioreactor and a separate container, the process comprising (i) a bioreactor feeding stage; (ii) a batch reaction stage, wherein biogas is formed and formed biogas is temporarily stored in the separate container, and at least one further stage (iii) comprising a settling stage and/or an aqueous fluid effluent discharge stage, wherein the biogas stored in the separate container is used to reduce fluctuations in a biogas exit flow from the installation. An installation for carrying out the process and the use thereof.