In locations with low population density or constraints in technology, resources, and personnel, the use of centralized wastewater treatment systems is not be justified. In such areas, decentralized wastewater treatment systems offer several advantages overcentralized systems. In these systems, the treatment and disposal of effluent is close to the source of waste water production, which reduces investments in a long sewage network and enables the application of other methods of wastewater transport, such as pressure sewerage and vacuum sewerage. A significant advantage of decentralized systems is their ability to be installed quickly, while also enabling local water reuse and implementation of the principles of circular economy, thereby enhancing productivity. In Serbia, according to the 2011 census, there are 449 settlements with more than 2,000 equivalent inhabitants whose wastewater should undergo at least secondary biological treatment. Given that approximately 80% of these settlements have populations ranging from 2,000 to 10,000, the implementation of decentralized wastewater treatment systems becomes imperative for sustainable water protection in Serbia. This paper provides a brief overview of decentralized wastewater treatment systems and, using the example of the municipality of Pirot, highlights the advantages and significance of implementing decentralized treatment to ensure a safe, reliable, economically justified, and ecologically sound solution for protecting water resources from pollution.

Excavation of tunnels with a small overburden inevitably implies surface settlements, especially when they are carried out in soft soil or weak rock masses. Subsidence becomes a critical aspect when the construction of tunnels is realized in narrower urban areas, directly below occupied residential buildings. Taking as an example the Kobilja Glava tunnel, which will represent part of the main project connecting Vogošća with Sarajevo and at the same time the connection of the narrowest city center of Sarajevo with the A1 motorway on the Vc corridor, surface deformations were monitored during the excavation and installation of the primary support of the left tunnel tube. Special attention was dedicated to excavation from the entrance side on a certain section of the tunnel where the height of the overburden was less than 2D. During the excavation of the left tunnel tube of the Kobilja Glava tunnel, which was carried out from the entrance portal at chainage km 3+543,202 in the direction of Vogošće, multiple surface settlements were measured from the very entrance to the place where the excavation was stopped (chainage km 3+615,56) compared to the predicted values obtained by assessment. The main reason for stopping the further progress of the excavation of the left tunnel tube from the chainage km 3+615.56 lies in the fact that the direction of the geological layers coincided with the direction of the progress of the excavation, which had a significant negative impact on the movement of the soil itself, and therefore on the increase surface deformations. After a comprehensive analysis of the above, as well as consideration of optional possibilities, it was decided to approach the excavation of the left tunnel tube from another attack point, i.e. to start the excavation from cross passage No. 1 in the direction towards the entrance. In this way, it was possible that the direction of the geological layers under these cirrcustamces positively contributes to the reduction of surface subsidence caused by the progress of the tunnel excavation by over 50%.