As a result of anthropological activities, various pollutants, for example heavy metals, enter the environment in significant quantities. They have the potential to accumulate in living organisms and are not biodegradable in the environment. This poses a major threat to the health and life of living organisms and the environment. Therefore, the search for effective technologies to reduce anthropic pollutants in the environment is so important. Currently, membrane techniques, chemical precipitation, electrolysis, coagulation, ion exchange and adsorption, among others, are used to remove heavy metal ions. The most versatile method is adsorption on adsorbents. It is a relatively simple method, but very expensive. This prompts a constant search for new, effective and inexpensive adsorbents. Coffee is one of the most important foodstuffs and agricultural commodities in the world. From the point of view of the circular economy, by-products from the processing of coffee beans have become a valuable raw material in other areas of life. An important way to manage waste from the coffee bean processing industry is to produce adsorbents using it. There are data from laboratory studies indicating that it is possible to produce effective and low-cost adsorbents using by-products from the agro-food industry to remove pollutants from the aquatic environment and wastewater. Laboratory studies prove the high efficiency of heavy metal removal when using coffee-processing waste as adsorbents. However, data from real-world studies are still lacking. In addition, there is a lack of data from analyses on the impact of alternative adsorbents on economic, environmental and social aspects.

Wastewater treatment plants are considered to be not only as treatment facilities, but also essential elements of the circular economy. Wastewater treatment plants can be essential chains of the circular economy cycle. Despite this, sewage sludge management and utilization are mostly limited to biodegradation and further agricultural uses or incineration. The recovery of valuable products is mainly limited to nitrogen and phosphorus compounds. Fewer analyses focus on generating, recovering, and removing various polymers from sewage sludge, such as cellulose or extracellular polymeric substances (EPS). On the other hand, sewage sludge also contains polymeric pollutants, such as microplastics. The recovery and use of biopolymers is significant considering the problems connected with the presence and effects of artificial polymers (microplastics) in the environment. Despite the technical possibilities, not many technical scale installations are operated. Law regulations should make some incentives to develop the technologies and sell the recovered polymers in the market not as waste material, but as a valuable product. This paper presents state-of-the-art technologies for selected polymers’ recovery from sludge, including technical parameters of the processes and possible applications of recovered products, but it also considers the possibility of microplastics’ removal from this waste material.

Sludge dewatering is a key element in sludge’s processing and management. Solid-phase separation, sludge volume reduction and the separation of a high-quality supernatant are the main tasks of the dewatering devices. The effectiveness of this task, in turn, results from the selection of the dewatering method and conditioning of the sludge before dewatering. The aim of the research was to determine the influence of conditioning substances (polyelectrolyte, fly ash and zeolite) on the efficiency of dewatering at variable filtration pressure. The use of polyelectrolyte in sludge conditioning was a solution that increased the efficiency of the filtration process. On the contrary, the use of structure-forming substances (fly ash and zeolite) slows the process but reduces the hydration of the filter cake. The same trends were obtained in dual conditioning combining dosing of polyelectrolyte and ash or zeolite. It was also shown that the dewatering efficiency of conditioned sludge with these two different substances (ash and zeolite) was the same. The use of zeolite in independent or dual conditioning was important for the quality of the supernatant.

The article presents an analysis of the possibilities of biogas production in the process of methane fermentation of sonicated excess sludge. The greater the percentage of methane in biogas, the higher its calorific value. In order to increase the intensity of biogas production containing approximately 70% of methane, sewage sludge is disintegrated. In particular, excess sludge formed as a result of advanced wastewater treatment by the activated sludge method shows low biodegradability. The study aim was to examine the effect of the ultrasonic field disintegration of excess sludge on biogas production. As a result of subjecting the sludge to disintegration by ultrasonic field, there was an increase in the digestion degree of sewage sludge. In the methane fermentation process of modified sludge, an increase of the biogas yield was noted, which confirmed the supportive action of ultrasonic field on the excess sludge biodegradation. In the case of disintegration of excess sludge by ultrasonic field, for the ultrasonic field intensity value of 4.3 W cm⁻² and a sonication time equal to 300 s, the highest values of soluble chemical oxygen demand (SCOD), total organic carbon (TOC), and volatile fatty acids (VFAs) concentrations were obtained. In the process of conventional methane fermentation, biogas yield value was 0.303 L g VSS⁻¹, while in the process of methane fermentation of sonicated excess sludge, the value 0.645 L g VSS⁻¹.

This study verified the possibility of sludge conditioning before dewatering using a combination of factors such as iron coagulant, polyelectrolyte, and the magnetic field generated by a solenoid. It was assumed that further conditioning with the magnetic field, leads to the formation of a rigid structure of sludge flocs by the destabilized and flocculated solid phase particles in the sludge (using the conditioning dual chemical method: PIX—polyelectrolyte). The resulting structure can increase the efficiency of sludge cake filtration by reducing sludge compressibility and maintaining the porosity necessary for the flow of removed water through the filter cake. The effects of the exposure of conditioned sludge (after the dual chemical method) to the magnetic field depended on two factors. The first factor was the direction of sludge flow through the magnetic field. This was a key factor in improving the efficiency of sludge conditioning using this method. The sludge flow through the solenoid in the direction opposite to the magnetic field had a strong effect on the particles. The second factor was the rate of sludge flow through the magnetic field. Better results were obtained for a flow rate of 1.0 L/min than for pumping sludge through a coil at a rate of 2.0 L/min. At a flow rate of 1.0 L/min, the exposure time of the sludge to the magnetic field was 6.6 s. Too high a flow rate may lead to the deterioration of filtration efficiency by adverse changes in the structure of sludge flocs. This may be due to the mechanical destruction of the flocs structure of sludge by a too turbulent flow.