Biomass-to-biofuel conversion represents a critical component of the global transition to renewable energy. One of the most accessible types of biomass is sewage sludge (SS). This by-product from wastewater treatment plants (WWTPs) contains microplastics (MPs) originating from household, industrial and urban runoff sources. Due to their small size (<5 mm) and persistence, MPs present a challenge when they are removed from sewage systems, where they mainly accumulate (~90%). The presence of MPs in SS poses environmental risks when biosolids are applied as fertilizer in agriculture or incinerated for the purpose of energy production. The key problem is the efficient and reliable identification and reduction of MPs in sewage systems, due to the lack of standardized procedures. The reduction methods for MPs might involve physical, chemical, biological, and hydrothermal approaches, including hydrothermal carbonization (HTC). The HTC of SS produces hydrochar (HC), a solid biofuel, and presents a cutting-edge approach that simultaneously addresses secondary microplastic pollution and renewable biomass-derived energy production. In this article, we review briefly the MPs content in biosolids from different countries, and present HTC as a promising method for their removal from SS. In conclusion, HTC (i) effectively reduces the abundance of MPs in biosolids, (ii) produces an improved solid source of energy, and (iii) contributes to circular SS management.

Wastewater-derived microplastics (WW-MPs) are increasingly recognised as reactive vectors for aromatic organic contaminants (AOCs), yet their role in contaminant fate remains insufficiently constrained. This review synthesises current knowledge on the transformation of microplastics in wastewater treatment plants, including fragmentation, oxidative ageing, additive leaching, and biofilm formation, and links these processes to changes in sorption capacity toward phenols, PAHs and their derivatives, and organochlorine pesticides (OCPs). We summarise the dominant adsorption mechanisms-hydrophobic partitioning, π-π interactions, hydrogen bonding, and electrostatic and, in some cases, halogen bonding-and critically evaluate how wastewater-relevant parameters (pH, ionic strength, dissolved organic matter, temperature, and biofilms) can modulate these interactions. Evidence in the literature consistently shows that ageing and biofouling enhance WW-MP affinity for many AOCs, reinforcing their function as mobile carriers. However, major gaps persist, including limited data on real wastewater-aged MPs, lack of methodological standardisation, and incomplete representation of ageing, competitive sorption, and non-equilibrium diffusion in existing isotherm and kinetic models. We propose key descriptors that should be incorporated into future sorption and fate frameworks and discuss how WW-MP-AOC interactions may influence ecological exposure, bioavailability, and risk assessment. This critical analysis supports more realistic predictions of AOC behaviour in wastewater environments.

Microplastics (MPs) represent a persistent class of emerging contaminants, of which significant amounts can be found in sewage sludge. In this study, the effect of hydrothermal carbonization (HTC) temperature on MPs and the properties of digested sewage sludge (DSS) was evaluated. The HTC process was carried out at temperatures of 200, 210, and 220 °C for 2 h in a batch reactor, and the solid products were subjected to (i) mass balance and fuel properties and (ii) microplastic occurrence analysis using Confocal Raman Microspectroscopy and Scanning Electron Microscopy. In digested sludge, 2700 ± 475 MP particles/100 g d.m. were detected, mostly fragments with ~350 ± 100 fibers. Hydrocharcontained only black and brown fragments in the following amounts: 4175 ± 575 (200 °C), 4450 ± 700 (210 °C), and 1450 ± 590 (220 °C), respectively, after 2 h. The microplastic removal rate was 54% for the highest temperature. Polystyrene (PS) was identified in untreated sludge, while only PE was detected after HTC at 200–210 °C, and no MPs were identifiable at 220 °C. The surfaces of post-MPs exhibited progressive degradation with increasing HTC temperature. The results confirm that HTC lowers the content and alters the physicochemical properties of microplastics, reducing their thermal stability and degrading their structure, while simultaneously improving the fuel properties of hydrochars by increasing the calorific value and carbon content.

The presence of pharmaceuticals in the aquatic environment is known to scientists and is constantly being investigated. Such micropollutants with bactericidal, virucidal, or fungicidal properties are commonly used in households, which results in their presence in raw sewage flowing to wastewater treatment plants. The content of pharmaceuticals may vary depending on the lifestyle of the inhabitants or the intensity of drug consumption. This study analysed the content of antibiotics, virucidal and fungicidal substances in raw and treated sewage from one of city located in southern Poland with a population equivalent of 680,000. Furthermore, the study was conducted in the summer and autumn-winter seasons.Microplastics are one of the largest pollutants in the world. Since the 1970s, it has already existed, but there has been no better alternative than plastic. It is related to easy and cheap production, high availability, and specific properties of plastics, such as plasticity, chemical resistance, and lightness.In the research, samples of stabilized sewage sludge were analyzed in terms of quantitative and qualitative analysis. The separation of microplastics was carried out in two stages. First, the sample matrix was digested with 15% hydrogen peroxide. The next step was density separation, where a saturated solution of calcium chloride was used. Separated microplastics were counted and their sources of origin were analyzed using a Raman confocal microscope and ATR FT-IR spectrometer. The samples were divided according to the month of their collection.The production of organic-mineral fertilizers from sewage sludge is one of the ecological possibilities of their management. Pharmaceuticals and their derivatives, as well other micropollutants which get in the sludge during the treatment of wastewater, can be a problem. The negative impact of these micropollutants on the environment has been scientifically proven, and the pharmaceuticals and microplastics contained in the sludge may also be detected in fertiliser products.Acknowledgments: Research supported by the Polish National Agency for Academic Exchange in the Bekker programme (no. PPN/BEK/2020/1/00243/) as well by the Polish National Science Centre (grant no. 2022/45/B/ST10/02108). Research was partially supported by the program ‘Initiative for Excellence – Research University’ for the AGH University of Krakow. Research supported under the Implementation Doctorate in the program of the Ministry of Science and Higher Education.