Due to its produced quantity, sewage sludge is a serious environmental problem not only in Slovakia, but also on a global scale. The submitted study deals with the current state of sewage sludge treatment with a focus on assessing the advantages and disadvantages of selected technologies. The main objective of the review study is to evaluate the advantages and limitations of individual sewage sludge processing technologies. Based on the evaluation of the advantages and limitations, another objective of the study was to determine the most suitable, less suitable, or unsuitable technologies for sewage sludge processing. Another objective of the study was to evaluate innovative technologies (not only commonly used ones). The purpose of this objective was to monitor the most current trends in sewage sludge processing technologies and, by evaluating them, to expand knowledge in this scientific field. The presented analysis of sewage sludge treatment was carried out in accordance with current European directives. The main novelty of the review study is a comprehensive assessment of sludge processing technologies with a focus on their main advantages and limitations. Another novelty is the focus of the study on innovative methods of sewage sludge processing. As part of the analysis, the evaluated sludge treatment technologies were divided into three categories: conventional, alternative, and innovative. As a conventional method, composting is currently the dominant method of sewage sludge management in the Slovak Republic. Mono-incineration, which is one of the conventional methods, allows for an effective reduction of the volume of sewage sludge while removing all unwanted hazardous components at the same time. However, this sludge treatment technology causes simultaneously the loss of most of the valuable nutrients, contained in sewage sludge. Pyrolysis and gasification as alternative technologies are effective in terms of removing hazardous components, but they are complex technologies, and their economic viability depends on their ability to maximise efficiency and produce high-value energy carriers. Hydrothermal liquefaction has a major advantage over all other thermal sewage sludge treatment processes because it does not require sludge drying. Innovative methods of sewage sludge treatment such as bio-electrochemical system, supercritical water oxidation, and biodiesel production require a more detailed examination by the scientific community to implement these methods in practice due to the lack of information from operational experiments. Given the extensiveness of the sludge treatment issue, we plan to address the economic aspect of the technologies in a separate study in the future.

Kitchen waste presents a significant problem in waste management because of its large volume and other properties. Technologies for the treatment of kitchen waste are more or less tested in laboratory, semi-operational, or operational conditions. The main current technologies for the treatment of kitchen waste are anaerobic digestion, composting, incineration, and landfilling. However, new methods for kitchen waste treatment are currently being developed that combine the advantages and eliminate the disadvantages of current technologies. This review provides an overview, critically comparing the current methods of kitchen waste treatment. The comparison has been made primarily from the point of view of environmental advantages and disadvantages. This review does not take into account economic factors, which are difficult to evaluate as their value has to be related to a specific process and unit of capacity. In addition, we summarize some innovative methods for kitchen waste treatment that have already been tested under laboratory conditions.

Environmental contamination of rubber from waste tyres poses a risk to the environment. Rubber particles from tyres enter the environment due to the abrasiveness of the road surface. The aim of the scientific work was to observe the biological degradability of waste tyres in aquatic environment and its ecotoxicity. Biodegradability was observed under aerobic and anaerobic conditions that simulate both aerobic and anaerobic conditions in the aquatic natural environment. Aerobic conditions in the aquatic environment take place in flowing fresh water, sea water, lakes. Leachate was prepared to simulate the behaviour of tyres in an aqueous environment. Aerobic degradability was evaluated through complete biodegradability using a 301 F manometric respirometry test. Anaerobic biodegradability was evaluated by measuring biogas production using OECD 311 Anaerobic Biodegradability of Organic Compounds in Digested Sludge. For a better simulation of the natural environment, the pH of the leachates from the tyres was adjusted to a neutral range. It should be noted that standard degradability tests were extended by 7 days due to low biodegradability. Adjusting the pH during the biodegradability test is also a modification of the original test. This modification was used to better simulate biodegradability when the pH of tyres in the natural environment is reduced by acid rain. An essential part of monitoring the behaviour of waste tyres was the assessment of ecotoxicity using standard tests. The contribution of the scientific article lies in the evaluation of the course of decomposition in aerobic and anaerobic conditions with and without pH adjustment and in the use of modified biodegradability tests. The benefit of the scientific work is in the determination of the biodegradability of waste tyres with and without pH treatment, which simulate a comparison of the degradability of tyres in an acid rain environment. Another benefit of the scientific work is the depiction of biodegradation using 3D modelling with calculations of 100% degradability at different input concentrations of waste tyres. Modelling was used for the time for the absolute decomposition of tyres without pH adjustment (outside the acid rain environment) and with pH adjustment (in the acid rain environment). By monitoring, it is possible to determine whether acid rain as an anthropogenic activity influences the degradability of waste tyres in the natural environment. Biodegradability tests confirmed the low biological degradability of waste tyres. The highest average rate of biological degradability—15% was recorded at the input concentration of waste tyres of 350 mg/L. The aerobic degradability test confirmed the improvement of tyre decomposition when adjusting the pH to the level of 6.5–7.5. On the contrary, the anaerobic degradability test confirmed the improvement of the decomposition in the alkaline region compared to the neutral pH values of the mixture. By mathematical–statistical evaluation of aerobic decomposition with preservation of degradability trends at three input concentrations, the time of absolute decomposition of waste tyre particles at a concentration of 370 mg/L was found to be approximately 336 days. By adjusting the pH to the neutral range during aerobic decomposition, the total decomposition time was reduced to 126 days. The ecotoxicity tests performed confirmed the toxic effect of tyre leachate on selected tested organisms. In the future, the authors propose to focus on a more detailed assessment of the ecotoxicity of the waste conditions and to modify the biodegradability tests by changing the conditions (wider range of input pH value, longer biodegradability time, temperature) for a better simulation of different types of environments. Adjusting the pH to a neutral environment increased aerobic degradability but had no significant effect on anaerobic degradability. Therefore, it is important to focus future research on the adjustment of various conditions to support the degradability of tyres, of which pH has clearly been confirmed as an important factor.

Microplastics (MPs) currently cause an environmental risk due to their transport to all components of the environment. The review article aims to evaluate and compare selected methods for the sampling of different matrices and detection of microplastics. To choose suitable sampling methods, the available equipment, goal of research, and kind of environment should be considered. Through the separation of microplastics from samples, NaI and ZnBr₂ can provide high recovery rates (99%) and tight error bars. There exist image analysis software and also computer vision based systems (e.g., SMACC) that can be used for the identification, automatic calculation, and classification of MPs in the environment with shorten data calculation time and reduction of human error. Fourier-transform infrared microscopy and Raman spectroscopy were found to be the most appropriate methods for the characterization of MPs.

Information about how different conditions affect the course of sorption is variously scattered and needs to be consolidated. The paper primarily focuses on identifying the optimal sorption conditions for acid and neutral mine drainages. In this review, key parameters were assessed, including temperature, pH level, sorbent dose, initial metal concentrations, and sorption duration. This overview also includes a comparison of the advantages and disadvantages of selected types of sorbents. The sorption of many metals tends to be optimal at circumneutral pH values. The adsorptive capacity decreases with an increase in temperature for exothermic processes, whereas it increases in the case of an endothermic one. Increasing the initial concentration has a positive effect on adsorption until the sorbent is fully saturated, leading to a plateau in adsorption capacity. The knowledge gained from this research extends the spectrum of the potential sorption applications, especially in the processes of recovering the metals and sorbents by desorption.

This study aimed to investigate the adsorption efficiency of Cd and Mn using natural sorbents—bentonite, zeolite and stabilized digested dewatered waste sludge. The main contributions of the scientific article are in adding to the scientific knowledge of the use of natural and waste sorbents in the removal of heavy metals from neutral mine effluents. Current studies mainly focus on metal removal by sorption using natural sorbents from acid mine drainage. This study investigates sorption in neutral mine drainage. The efficiency of the sorption process was evaluated using the following parameters: efficiency (%) of metal ion removal, Freudlich and Langmuir adsorption isotherm constant. The AES–ICP method (atomic emission spectrometry with inductively coupled plasma) was used for the initial metal analysis of the materials used. The atomic absorption spectrometry (AAS) method was used for the analysis of Cd and Mn in the sorption process. The maximum efficiency of Mn removal by bentonite at the end of the test was approximately 90%. The removal of Mn by zeolite was considerably lower—about 20% compared to the use of sludge—80%. Based on the sorption efficiency, the sludge was suitable for sorption. Much higher levels of Cd sorption were achieved using sludge compared to using natural bentonite and zeolite. The main novelty of the work lies in the sorption of metals using dewatered digested sludge. Previous studies have focused on metal sorption using activated sludge. Most previous studies focused on sorption from acid mine drainage. The novelty of this study is that we focused on the sorption of neutral mine drainages, which are typical for the location we are monitoring.