This project entitled ‘Expansion and modernisation of the waste water treatment plant in Grabce Józefpolskie’ will be carried out at a waste water treatment plant located north-east of the town of Mszczonów, in the municipality of Mszczonów, in the Mazowieckie Province. The facilities of the sewage treatment plant are located on plots Nos 57/2, 58/2, 59/8, 60/2, 61/2, 62/2, 63/4, 63/7. The existing sewage treatment and sludge treatment plant is used to treat urban wastewater supplied by sanitary sewage from: Mszczonów, Grabce Józefpolskie, Adamówek, Kamionka, Sosnowica, Wymysłów and Badowo-Dańki as well as slurry vehicles transported from the commune. After the extension, the installation will be able to receive waste water from the planned areas of the Municipality of Mszczonów and from the recreational complex of the ‘Suntago’ Water Park in Wręcza near Mszczonów. Therefore, the necessity to implement the project results from the obligation to comply with the conditions of Directive 91/271/EEC, i.e. the so-called Environmental Protection Directive. The Wastewater Directive. According to the report on the implementation of the KPOŚK for 2023, the wastewater treatment plant in Grabce Józefpolskie does not meet the second and third conditions of the Wastewater Directive. In connection with the development of the municipality, the planned expansion and modernisation of the waste water treatment plant in Grabce Józefpolskie was to meet the assumptions regarding the improvement of the operation of the plant in question, which indicated that, due to the increase in the average daily supply of waste water to the treatment plant, the infrastructure should be adapted to the higher load on the plant along with the need to maintain the level of waste water treatment at an appropriate level. Activities related to the reconstruction and expansion of the Sewage Treatment Plant in Grabce Józefpolskie, carried out in the first part of the project, were based on the use of existing sewage treatment technology and sludge treatment. Following the preparation of the required documentation and the implementation of works related to the extension and modernisation of the waste water treatment plant in question, it was demonstrated that additional modernisation works should be planned to comprehensively improve the operation of the waste water treatment plant in question. The most important factor suggesting the adoption of this decision are particularly problematic raw sewage entering the Wastewater Treatment Plant in Grabce Józefpolskie and the need to adapt some elements of the infrastructure to their adoption. Expansion and modernization of the wastewater treatment plant in Mszczonów has been fully implemented to increase the efficiency of wastewater treatment in the wastewater treatment plant in Grabce Józefpolskie. However, during the stage of implementation of the investment, control of the parameters of the treatment plant and changes related to the amount and composition of wastewater entering the treatment plant, it was considered necessary to extend the scope of the project to include infrastructure task No 2 Increasing the possibility of raw wastewater flow between chambers at the wastewater treatment plant in Mszłonów in order to improve the flow of raw wastewater and the possibility of treating pipelines and separation chambers from solid wastewater. The planned implementation of this task is mandatory for the comprehensive improvement of the operation of the wastewater treatment plant and its adaptation to the load of raw wastewater and its composition, containing a high concentration of particulate matter. It should be emphasized that failure to implement task 2 will result in task 1 not fulfilling its purpose, and the waste water treatment plant will not meet the conditions of the Waste Water Directive. In this case, it is important to maintain the third condition of the Wastewater Directive, i.e. the standard of wastewater treatment regardless of the type of incoming wastewater.