(31)In order to ensure the proper implementation of this Directive and in particular respect for the emission limit values, it is important to monitor discharges of treated urban wastewater into the environment. The monitoring should be done through the establishment at national level of a mandatory system for prior regulations or specific authorisations, or both, in order to discharge the treated urban wastewater into the environment. In addition, in order to prevent unintentional discharges of biomedia into the environment from urban wastewater treatment plants using biomedia, it is essential to include in the discharge authorisations or regulations, or both, specific obligations to continuously monitor and prevent such discharges. Such biomedia are usually made of plastic and might include, inter alia, biocarriers, biobeads or polystyrene beads.