A sewer system is an important infrastructure of every settlement. A sewer system is a set of construction facilities used for the quick removal of wastewater from the humans’ immediate environment and its transport to a wastewater treatment plant or direct discharge into an appropriate recipient. In order for the sewer system to perform its purpose properly, its proper maintenance is required. Maintenance of a sewer system is very demanding since the system is mostly underground which makes it difficult to be accessed and maintained. The maintenance of a sewer system can be preventive (regular) or corrective (reactive). The regular maintenance occurs at certain intervals, whereas the reactive maintenance occurs in the case of some unforeseen event. This paper presents the history of sewer systems, as well as basic and alternative types of sewer systems. Furthermore, challenges that arise during sewer system maintenance and difficulties that maintenance employees face in their work are presented in this paper, as well as the ways in which sewer systems are maintained.

The operations and maintenance phase is typically the longest phase within the building life cycle. Proper and consistent building maintenance is imperative for several reasons, including extending the life of buildings, improving occupants’ comfort and safety, and ultimately saving on long-term costs. Budgets for maintenance should be foreseen. The costs of statutory periodic inspections, the costs of replacing worn materials and elements, the costs of periodic works and repairs, the costs of reactive maintenance and the costs of operation will be shown for the analyzed building—a school. This paper outlines the development of a 15-year maintenance plan and program for the building, covering the period from 2024 to 2038. The plan incorporates a discount rate of 3.64% and accounts for inflation when calculating costs. The present value of the costs of maintenance and operation of the building for 15 years is EUR 1,978,292.20 and the largest share of these costs is the operation cost of the building with EUR 1,599,002.18 (80.83%). A sensitivity analysis was conducted by varying the discount rate and analysis period, resulting in recalculated present values for maintenance costs. The analysis reveals a correlation of 26.73% between the present value of maintenance and operation costs over a 15-year period and the associated capital costs.

A sewer system is an indispensable part of every settlement which contributes to the protection of the environment and people. There are many types of sewer systems. In addition to the standard sewer systems (mixed, separated, etc.), there are the alternative, non-standard systems, and one of them is a vacuum sewer system. In order for a sewer system to function correctly and to perform its tasks successfully, it needs to be maintained properly and regularly. Generally speaking, maintenance is considered to be a series of activities performed in order to achieve that constructed buildings allow an adequate use and functionality for the purpose they were designed for. Considering these systems are relatively new and still rarely used, there is no general practice or rules for use and maintenance of the same, and, most importantly, there is no user experience or people responsible for managing the work and maintenance. The paper will present the general characteristics and parts of vacuum sewer systems. Maintenance recommendations will be given, and maintenance costs specified making reference to the literature available to the authors.

Maintenance costs of all types of buildings are most often ignored since they are incurred in the future. Potential investors are interested in capital costs—construction costs—while maintenance costs are considered as unimportant in the life cycle of a building. If there were a larger number of maintenance cost estimation models, it would be possible to estimate these costs and present them to potential investors more easily, thus making it easier and more effective to apply life cycle cost methods. A study on the characteristics and costs of the maintenance of sewer systems in the Republic of Croatia was conducted, wherein questionnaires were sent to companies operating public sewer systems. The data requested in the questionnaires were general data on enterprises, maintenance, data on sewer systems, quantities of sewer discharge, sewer pipes and data on maintenance costs of sewer systems. It was established that it is possible to use linear regression when creating a model for estimating the maintenance costs of a sewer system.

Possibilities of using expert methods for sewer system maintenance optimisation This paper provides an overview of the state-of-the-art research on the possibilities of using expert methods (artificial neural networks, genetic algorithms, expert systems, decision trees, Markov chains, and ant colony algorithm) for optimising maintenance of sewerage systems. Timely maintenance of sewerage systems is significant as it ensures their proper functioning, repair cost reductions, basic operation of the system, drainage of waste water from households to wastewater treatment plants, and discharge to the receiving water body. Possible uses of expert methods for optimising maintenance of sewerage systems, aimed at reducing maintenance costs, are presented.