Abstract: A biofiltering device for treating wastewater comprises a housing having an inlet for receiving the wastewater to be treated and an outlet for discharging the treated wastewater, a bed of peat disposed inside the housing between the inlet and outlet, the peat defining a biofiltering medium having a predetermined biofiltering capacity, and an air vent for aerating the peat. The device further includes a fluid flow control system arranged over the bed of peat and in fluid flow communication with the inlet, for distributing the wastewater through the bed of peat in a manner such that when the wastewater enters the system at a flow rate greater than the biofiltering capacity of the peat, the wastewater discharged from the system flows through the bed of peat at a flow rate no greater than the biofiltering capacity. The biofiltering device according to the invention enables one to efficiently treat incoming wastewater irrespective of its flow rate.