In Poland, in recent years, there has been a rapid accumulation of sewage sludge -a by-product in the treatment of urban wastewater. This has come about as a result of infrastructure renewal, specifically, the construction of modern sewage treatment plants. The more stringent regulations and strategic goals adopted for modern sewage management have necessitated the application of modern engineering methodology for the disposal of sewage sludge. One approach is incineration. As a consequence, the amount of fly ash resulting from the thermal treatment of municipal sewage sludge has grown significantly. Hence, intensive work is in progress for environmentally safe management of this type of waste.The aim of the experiment was to evaluate the possibility of using the fly ash that results from municipal sewage sludge thermal treatment (SSTT) as an additive to hardening slurries. This type of hardening slurry with various types of additives, e.g. coal combustion products, is used in the construction of cut-off walls in hydraulic structures.The article presents the technological and functional parameters of hardening slurries with an addition of fly ash obtained by SSTT. Moreover, the usefulness of these slurries is analysed on the basis of their basic properties, i.e. density, contractual viscosity, water separation, structural strength, volumetric density, hydraulic conductivity, compressive and tensile strength. The mandated requirements for slurries employed in the construction of cut-off walls in flood embankments are listed as a usefulness criteria.The article presents the potential uses of fly ash from SSTT in hardening slurry technology. It also suggests directions for further research to fully identify other potential uses of this by-product in this field.

The growing number of municipal sewage treatment plants in Poland raises the problem of managing more and more sludge. The thermal treatment of municipal sewage sludge (TTMSS), which significantly reduces the volume of waste, results in an increase in the concentration of heavy metals in the fly ashes – the final products of the process. The search for methods of utilization of fly ash from TTMSS resulted in attempts to use it in hardening slurries widely used in hydro-engineering. Due to the nature of the application of this material in the cut-off walls (exposure to groundwater flow) one of the key issues is the degree of heavy metal immobilization. The paper attempted to determine the degree of leaching of selected heavy metals from the hardened hardening slurry, composed of fly ash from TTMSS. For this purpose, the eluates were prepared from samples, after various periods of curing, using a dynamic short-term method called “Batch test”. The liquid used for leaching was: distilled water and 0.1 molar EDTA solution – to determine the amount of potentially mobile heavy metal forms. The results show the possibility of the safe usage of fly ash from TTMSS as an additive for hardening slurries.

The article discusses the results of examining the impact of aggressive solutions on specimens of mortars with a slag-ash binder. Bar specimens were exposed to unidirectional diffusion of sodium chloride and sodium sulphate for 90 days. Next, the specimens were subjected to flexural and compressive strength tests, ion content tests, XRD phase composition tests, and microstructural SEM-EDS tests. The test results indicated that aggressive solution action resulted in decreased flexural strength, however, it did not impact the compressive strength of mortars. A minor impact of chloride ions on the pH of the pore liquid was recorded, while the tests did not show any influence of sulphate ions. Furthermore, aggressive ion concentration decreased in deeper specimen slices. Specimen phase composition testing after chloride ion action indicated the presence of a small amount of Friedel’s salt, while regular sodium chloride crystals were identified in the microscopic image. The performance properties of mortars exposed to the action of aggressive solutions were maintained.

One of the basic threats in terms of concrete used for tanks or ducts applied in wastewater management is the phenomenon of biogenic sulphate corrosion (BSC). BSC is a particular case of corrosion caused by the action of sulphuric acid (IV), which is formed as a result of a number of biochemical processes, which can take place, e.g. in an environment encountered within the aforementioned structures. Ions present in sulphuric acid react with cement hydration products, which leads to replacing the primary cement matrix components with compounds easily-soluble or highly-swelling during crystallization. The outcome of advanced corrosion is usually an observed formation of a white, amorphous, sponge-like mass, which is easily separated from the underlying concrete. The article discusses a case study of a BSC process in a newly constructed primary settling tank in a municipal wastewater treatment plant.

Owing to the increasing popularity of the thermal treatment of municipal sewage sludge (TTMSS) in Poland, constant growth in the quantity of ash generated within this process has been recorded. Due to their properties, it is difficult to utilize this type of ash within the concrete production technology. One of the methods of waste utilization is to add it to hardening slurries, used in, among others, cutoff walls. The slurry operating conditions (contact with groundwater) and elevated heavy metal content in ash raise justified concerns in terms of environmental safety of the aforementioned methods. In the study, the release of heavy metals from a matrix, namely, the hardened slurry has been examined. The so-called "batch test" dynamic leachability testing method was applied for this purpose. A high level of heavy metal immobilization in the slurry was achieved. The obtained results indicate an environmentally safe possibility of using TTMSS ash in hardening slurries in cut-off walls.