Method for manufacturing a fibrous web

The invention relates to a method for manufacturing a fibrous web， such as web of paper， board， tissue or the like. The method comprises obtaining at least one fibre suspension of lignocellulosic and/or cellulosic fibres and feeding the fibre suspension into an intermediate residence entity， such as pulper， storage tower or broke tower. Fibre suspension， which comprises bacterial endospores， is discharged out of the intermediate residence entity via an outlet after a residence time of at least 2 hours in the intermediate residence entity and after a time delay the fibre suspension is formed into a fibrous web. Bacterial endospores are sensitised for germination by adding a germinant surfactant， which comprises a primary or secondary ammonium head group and a linear unsubstituted C12-alkyl tail， to the fibre suspension at an addition point， which is located at the lower part of the intermediate residence entity or after the outlet of the intermediate residence entity， but before the formation of the fibrous web. The invention relates also to a treatment system.