This paper presents the case of a small wastewater treatment plant taken out of service due to insufficient design and equipment installed. Design assumptions and decisions made for plant restoration based on treatment requirements are outlined and plant operation aspects regarding revealed wastewater characteristics, process efficiency, sludge settling behaviour and equipment control, are discussed. The importance of wastewater characterization as a necessary procedure prior to plant design and construction, is stressed and the feasibility of nutrient removal in small wastewater treatment plants under minimum supervision, is assessed. A simplified mathematical model, as a useful tool to operators, for plant performance evaluation and prediction, is presented.