Along with the increase in popularity of the sewage sludge thermal treatment methods in Poland

resulting from the implementation of European Union law, a management problem with ash, which is produced

as a result of this process, appeared. The paper analyses the chemical composition and physical properties of fl y

ash from thermal treatment of municipal sewage sludge in terms of its use in concrete technologies in relation to

EN 450-1 Fly ash for concrete. Defi nition, specifi cations and conformity criteria (2012) and EN 197-1 Cement.

Composition, specifi cations and conformity criteria for common cements (2011) standards. The tested material did

not meet the requirements related to use of fl y ash for concrete production (chemical composition, low activity

index, high water demand and fi neness), and as main and minor components for cement production. On the basis

of the carried out research and analyses, it was found that the hardening slurry technology creates the greatest

possibilities related to the management of fl y ash from thermal treatment of municipal sewage sludge.

An increasing number of municipal sewage treatment plants in Poland, desirable from an environmental perspective, raises the problem of managing the growing volume of sewage sludge. The thermal treatment of municipal sewage sludge (TTMSS) method, by greatly reducing the waste volume, increases the heavy metal concentration in fly ash (primary, end product of the treatment process), which may constitute a risk factor when attempting to utilize them economically. The research paper concentrates on determining the TTMSS fly ash heavy metal leaching level. For this purpose, ash samples were subjected to leaching with the batch and percolation tests, and the heavy metal content in eluates was determined by the FAAS method. The obtained results served as a base to determine the level of heavy metal immobilization in the ash, the element release mechanism (percolation test), and the impact of the L/S (liquid to solid) ratio and pH on the heavy metal leaching intensity (percolation test). The conducted research indicated high immobilization of heavy metals in TTMSS fly ash, regardless of the applied study method, which corresponds to the results of other researchers. Lead was the most intensively eluted metal.

In recent years, there has been a marked increase in the amount of municipal waste generated in Poland. In 2020, 21.6% of all municipal waste was subjected to a thermal treatment process. Consequently, the amount of ashes generated is significant. Due to their properties, it is difficult to utilize this type of waste within concrete production technology. One of the waste utilization methods is to add it to hardening slurries used in, among others, cut-off walls. The article assesses the possibility of using ashes from municipal waste incineration as an additive to hardening slurries. It also discusses the technological properties of hardening slurries with the addition of the ashes in question. The experiment showed that it is possible to compose a hardening slurry based on tested ashes with technological properties suitable for use as a cut-off wall. Further research directions were proposed.

Missing data in test result tables can significantly impact the analysis quality, especially in relation to technical sciences, where the mechanism generating missing data is often non-random, and their presence depends on the non-observed part of studied variables. In such cases, the application of an inappropriate method for dealing with missing data will lead to bias in the estimated distribution parameters.
The article presents a relatively simple method to implement in dealing with missing data generated as a result of the MNAR mechanism, which utilizes the censored random variable. This procedure does not modify the variable distribution form, which is why it ensures objective and efficient estimation of distribution parameters within studies affected by certain restrictions of technical or physical nature (censored distribution), with a relatively low workload. Furthermore, it does not require the application of specialized software. A prerequisite for using this method is the knowledge of the frequency and cause of missing data.
The method for estimating the random variable censored distribution parameters was shown based on the example of studying the leachability of selected heavy metals from a hardening slurry. The analysis results were compared with classical methods for dealing with missing data, such as, ignoring missing data observations (listwise or pairwise deletion), single imputation and stochastic regressive imputation.

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.

Cut-off walls built using self-hardening slurries are an important tool for modern engineering pursuing Sustainable Development Goals. Much like cement concrete, this material is affected by the challenges posed by the increasing human pressure on the environment, although it is used significantly less widely than concrete; for this reason, relatively little comprehensive literature data is available describing the interaction of self-hardening slurries with the environment. This article provides a review that complements the current state of knowledge on self-hardening slurries in this area, with a particular focus on the durability of the material and its pollutant immobilization capabilities. To provide context, the material’s operating conditions, properties and components are briefly characterized. The resistance of self-hardening slurries to environmental aggression is described extensively, as it is a key factor in ensuring the durability of the material. A sample analysis of the material’s carbon footprint in several representative composition variants is presented. The subject of pollutant immobilization by self-hardening slurries is outlined. Lines of further research are proposed to fill gaps in the available knowledge.