After leaving the aeration basin (the tank that contains the microbes and the wastewater to be treated), the water proceeds to a secondary clarifier. The secondary clarifier serves to separate the biomass (i.e. the flocced microorganisms) from the clarified effluent. After secondary treatment, in many instances, water can go directly to a disinfection step because the level of treatment would have been sufficient for EPA (or local) permit requirements. However, more stringent water discharge regulations are being implemented causing many plants to have to retrofit their facilities for further treatment. Further treatment (i.e. tertiary or advanced) can be in the form of activated carbon filters (the same mechanism as a Brita), sand filters, and further nutrient removal.