In this graduate thesis, the conceptual design of the wastewater treatment plant of the Rab agglomeration was made. The input data required for defining the hydraulic and biological load are taken from the Feasibility Study for the application of the Rab agglomeration project, for co-financing from EU funds. Based on the input data, and in accordance with the current legislation, the required degree of purification is defined. Furthermore, hydraulic calculations were carried out that defined the optimal dimensions of the facilities and devices located within the treatment plant. A design, functional and technical solution of the water line, audit shafts, mechanical pretreatment building, pumping station, aerated grit chamber, the primary settling plant, the sand classifier building, the sludge treatment building and the administrative building were given. Also, an estimate of the cost of building the plant until its release into permanent operation was carried out. In the graphic annexes to the conceptual design, there are designs that define the position of the plant in space, and the constructive solution and dimensions of each individual object.