Method and device to optimize plug flow in an aerobic biological wastewater treatment reactor

The invention relates to a method for the treatment of wastewater in a biological treatment reactor, comprising the steps of (a) introducing wastewater influent at the bottom part of the reactor while simultaneously decanting treated wastewater effluent at the operational water level in the top part of the reactor, (b) an aeration step and (c) a settling step wherein the biomass is allowed to settle; wherein step (a) is performed under vertical plug flow conditions, wherein during step (a) the equal distribution of the influent wastewater across the distributor pipes and/or the degree of plug-flow in the reactor is monitored, and when a suboptimal distribution or a suboptimal degree of plug-flow is detected the influent distributor system and/or effluent decanter system is cleaned by removing fouling and/or blockage.The invention also relates to a liquid influent system and to an installation for the use in such method for the treatment of wastewater.