Microplastics (MPs) and nanoplastics (NPs) are emerging aquatic contaminants that pose environmental and public health risks due to their persistence, ubiquity, and ability to adsorb co-contaminants. This scoping review synthesises findings from 57 experimental studies and five review studies published between 2019 and 2025 on the use of biocharbased materials for the removal of microplastics from water and wastewater. Guided by the hypothesis that surface-modified biochars, such as magnetised, surfactant-coated, or chemically activated forms, achieve high removal efficiencies through multimodal mechanisms (e.g., electrostatic attraction, hydrophobic interactions, π–π stacking, and physical entrapment), this review applies PRISMA-based protocols to systematically evaluate biochar feedstocks, pyrolysis conditions, surface modifications, polymer types, removal mechanisms, and regeneration approaches. Scopus, Web of Science, and PubMed were searched until 30 May 2025 (English-only), and 62 studies were included. The review was not registered, and no protocol was prepared. The results confirm a high removal efficiency (>90%) in most experimental studies, particularly under controlled laboratory conditions and using pristine polystyrene. However, the performance declines significantly in complex matrices (e.g., wastewater and surface water) owing to dissolved organic matter, ionic competition, and particle heterogeneity, thus supporting the guiding hypothesis. This review also identifies critical methodological gaps, including narrow plastic typologies, a lack of standardised testing protocols, and limited field-scale validation. Addressing these gaps through environmentally realistic testing, regeneration optimisation, and harmonized methods is essential for transitioning biochar from a promising sorbent to a practical water treatment solution.

Municipal sewage sludge (MSS) has been identified as a promising feedstock for producing biochar with potential applications as a soil conditioner and animal feed. However, the high heavy metal content and limited availability of nutrients, such as phosphorus (P), pose significant challenges. This study aimed to improve the quality of MSS-derived biochar through copyrolysis with wheat straw (rich in K and Si) and bakery waste husks (rich in K) at temperatures of 500, 650, and 900 °C. Thermodynamic equilibrium calculations (TEC) were performed using FactSage and HSC Chemistry to predict the stability of P-bearing compounds and the fate of heavy metals in the biochars. The morphology and physicochemical properties of the biochars were examined by using SEM and Brunauer-Emmett-Teller (BET) analyses. The results indicate that increasing the proportions of wheat straw and bakery waste husks, along with higher pyrolysis temperatures, reduced the biochar yield. TEC demonstrated that these blends enhanced the formation of plant-available phosphates compared with pure MSS biochar. This improvement was primarily because of the formation of K/Mg-bearing phosphates in different amorphous and crystalline phases, such as K2P2O7, CaK2P2O7, KPMgO4, and KZnPO4, instead of Fe/Al-based phosphates. Additionally, copyrolysis reduced the concentrations of heavy metals such as cadmium (Cd), lead (Pb), and zinc (Zn) in the biochars compared to MSS pyrolysis alone. However, it had no significant effect on the copper (Cu), chromium (Cr), and nickel (Ni) levels. In conclusion, copyrolysis with wheat straw and bakery waste husks not only improved the nutrient profile and physicochemical properties of MSS-derived biochar but also mitigated heavy metal contamination. Additionally, this method reduced the presence of heavy metals, making it a more suitable alternative to biochar produced through monopyrolysis for use in agricultural applications.

Municipal sewage sludge (MSS) contains significant amounts of trace elements including zinc, copper, cadmium, and lead. This study investigated the behavior of these trace elements in municipal sewage sludge biochar during the pyrolysis of both anaerobically digested and undigested sludge at temperatures ranging from 500 °C to 900 °C using a rotary pyrolyzer. Microwave plasma-atomic emission spectroscopy (MP-AES) was used to measure the concentrations of trace elements in the biochars. Additional analyses included Fourier-transform infrared spectroscopy (FTIR), thermogravimetric analysis to determine the activation energies, and Brunauer–Emmett–Teller (BET) analysis coupled with scanning electron microscopy to assess the porosity, specific surface area, and morphology at different temperatures. Thermodynamic equilibrium calculations (TECs) were utilized to understand the speciation of trace elements under varying thermal conditions. The results demonstrated that as the pyrolysis temperature increased, both the undigested and digested biochars exhibited higher surface areas and total porosity volumes, along with a decrease in the average pore size. The digested biochar showed a higher surface area and pore volume at 500 °C than the undigested biochar. However, both types processed at 900 °C had similar average pore diameters of approximately 7.5 nm, according to BET analysis. All biochars had H/C ratios below and around 0.2, indicating strong degradation resistance. TECs results indicated that, at 500 °C, the thermal volatility sequence of the trace elements was established as Cr < Ni < Cu < Mn < Zn < Pb < Cd. Consequently, higher temperatures led to reduced concentrations of Cd, Pb, and Zn in all biochars while Cr, Ni, and Cu were largely retained in the biochar. Phosphorous (P) was enriched in the biochars at all temperatures for both MSS, however anaerobically digested MSS biochar exhibiting higher concentration of nutrient such as P, higher porosity and a finer pore structure compared to undigested one. Biochar yield decreases as pyrolysis temperature rises (500–900 °C) for both digested (BSS) and undigested (LSS) sludge, with BSS consistently yielding more than LSS.

To achieve a closed nutrient cycle and more sustainable food production, enhanced nutrient recycling in the agri-food system is a necessity. Pyrolysis is an emerging technology to recycle the nutrient content of sewage sludge. The produced biochar can be used to reduce the need for mineral fertilizers; in addition, pyrolysis can also handle potential pollutants such as microplastics and pathogens present in sewage sludge. In this research, a life cycle assessment (LCA) was carried out to determine the environmental impact of sewage sludge pyrolysis as an alternative to current practices of two different cases of sewage sludge treatment in two municipalities in Sweden. The results indicated that avoiding mineral fertilizer production by using biochar has a significant influence on the environmental benefits. Furthermore, it showed that an integrated system of anaerobic digestion followed by pyrolysis could perform as the most environmental-friendly option for sewage sludge treatment with a lower risk of transferring pollution to the soil.

Phosphorus (P) recovery and recycling play a crucial role in improving resource efficiency, sustainable nutrient management and moving toward circular economy. Increasing demand for fertilizers, signs of geopolitical constraints, and high discharge of P to waterbodies are the other reasons to pursue the circularity of P. Various research have been carrying out and several processes have been developed for P-recovery from different resources. However, there is still a huge unexplored potential for P-recovery specially in the regional framework from the four main P-rich waste resources: food waste, manure, mining waste, and sewage sludge. This study reviews recovery methods of P from these secondary resources comprehensively. Additionally, it analyzes the Nordic viewpoint of P-cycle by evaluating Nordic reserves, demands, and secondary resources to gain a systematic assessment of how Nordic countries could move toward circular economy of P. Results of this study show that secondary resources of P in Nordic countries have the potential of replacing mineral fertilizer in these countries to a considerable extent. However, to overcome the challenges of P-recovery from studied resources, policymakers and researchers need to take decisions and make innovation along each other to open the new possibilities for Nordic economy.

The present study investigates how the original sewage sludge characteristics influence the composition of sewage sludge-based chars for land applications. Sewage sludge from two different wastewater treatment plants in Sweden was pyrolyzed at 500, 700, and 900 °C, and the resulting chars were analyzed. Thermodynamic equilibrium calculations (TEC), together with chemical fractionation, were implemented to simulate the char after the pyrolysis process at different temperatures. The results showed that, in general, for both the municipal sewage sludge (MSS), phosphorus (P) was significantly retained in the char at various temperatures. However, no specific correlation could be found between the pyrolysis temperature and the amount of P remaining. With regard to the heavy metals removed from the char after the pyrolysis reaction, the concentrations of copper, chromium, lead, nickel, zinc, and cadmium were below the limits of the Swedish regulations for farmland application.

Effects of Elm tree sawdust pretreatments using alkali and alkaline earth metals (NaCl, KCl, CaCl2, MgCl2 and Elm tree ash) and deashing solutions (water, HCl, HNO3 and aqua regia) before the carbonization process on the porosity of produced activated carbons and Pb (II) and Cr (VI) adsorption were studied. The activated carbons were characterized by pore size distribution, surface area, FTIR, and SEM-EDX analysies. Based on the results, HCl leaching pretreatment of the biomass increased the activated carbon adsorption capacity of Cr (VI) from 114 to 190 mg g−1. The treatment of biomass with alkali and alkali earth metal salts, especially MgCl2, remarkably increased the activated carbon adsorption capacity of Pb (II) from 233 to 1430 mg g−1. The results indicated that Pb (II) adsorption was attributed to both the mesoporous structure of activated carbon and the abundance of Mg on the activated carbon's surface. On the other hand, the micropores played a major role in Cr (VI) adsorption capacity. The development of the micro- or mesoporous structure of activated carbons through pretreatment of lignocellulosic precursor could be an approach for providing high performance activated carbons for Pb (II) and Cr (VI) removal from aqueous solutions.

Sewage sludge is regarded as a potential source for soil fertilizer However, the direct utilization of sewage sludge in agricultural land is restricted since it also contains heavy metals, pathogens, and toxic compounds. Pyrolysis of the sewage sludge destroys the organic pollutants and partly volatilizes the heavy metals. In this study, pyrolysis of sewage sludge was carried out in order to determine the optimum residence time and temperature to recover the phosphorous and remove heavy metals from the resultant sewage sludge char (SSC). Pyrolysis was conducted on dried sewage sludge (DSS) by means of thermogravimetric analysis (TGA) and high-temperature oven with an N2-atmosphere. Microwave Plasma-Atomic Emission Spectroscopy (MP-AES) was used to determine the concentration of P and trace elements in the resulting solid char fraction. A combination of chemical fractionation (step-by-step leaching) of the DSS and thermodynamic equilibrium calculations were utilized to estimate the availability of phosphorous and removal of heavy metals in the SSC fraction at different temperatures. The results from the thermodynamics calculation were in line with the measured chemical composition of the SSC. Furthermore, the energy contents of the SSC obtained at different temperatures were measured. The pyrolysis evaluation results indicate that phosphorous was enriched in the char, while lead, zinc, and cadmium were significantly removed.

Phosphorus has been identified as a critical element by the European Union and recycling efforts are increasingly common. An important phosphorus-containing waste stream for recycling is municipal sewage sludge (MSS), which is used directly as fertilizer to farmland. However, it contains pollutants such as heavy metals, pharmaceutical residues, polychlorinated bi-phenyls (PCBs) and nano-plastics. The interest in combustion of MSS is continuously growing, as it both reduces the volume as well as destroys the organic materials and could separate certain heavy metals from the produced ashes. This results in ashes with a potential for either direct use as fertilizer or as a suitable feedstock for upgrading processes. The aim of this study was to investigate co-combustion of MSS and biomass to create a phosphorus-rich bottom ash with a low heavy metal content. A laboratory-scale fixed-bed reactor in addition to an 8 MWth grate-boiler was used for the experimental work. The concentration of phosphorus and selected heavy metals in the bottom ashes were compared to European Union regulation on fertilizers, ash application to Swedish forests and Swedish regulations on sewage sludge application to farmland. Element concentrations were determined by ICP-AES complemented by analysis of spatial distribution with SEM-EDS and XRD analysis to determine crystalline compounds. The results show that most of the phosphorus was retained in the bottom ash, corresponding to 9-16 wt.% P2O5, while the concentration of cadmium, mercury, lead and zinc was below the limits of the regulations. However, copper, chromium and nickel concentrations exceeded these standards.

The aim of this study was to investigate the effects of temperature and reaction time on the primary pyrolysis of cellulose and xylan. Fast pyrolysis of cellulose and xylan was carried out with a micropyrolyser connected to a gas chromatograph-mass spectrometer/flame ionisation detector (GC–MS/FID) to separate and identify volatile components, both qualitatively and quantitatively. This set-up meant a minimum amount of secondary reactions, low impact of the heating period and at the same time provided rapid and accurate analyses. The two biomass components investigated were: cellulose and hemicellulose (represented by xylan). They were pyrolysed during 0.5, 1, 2 and 5 s (s) and within a temperature range of 400–600 °C. The results showed that levoglucosan (1, 6-anhydro β-D-glucopyranose) is the main chemical compound released during cellulose pyrolysis. It increased with increasing temperature and time. The main volatile compounds produced from pyrolysis of xylan are: 1-hydroxy-2-butanone, 4-hydroxy-5, 6-dihydro-(2 H)-pyran-2-one, 1-hydroxy-2-propanone (acetol), acetaldehyde and hydroxyacetaldehyde (HAA). HAA was the most abundant chemical compound released during xylan pyrolysis, increasing with higher temperatures and time. Acetol and acetaldehyde also showed similar behaviour. The chemical compounds released from cellulose and xylan fast pyrolysis are primary products and assumed to be produced directly from both cellulose and xylan molecules and not from secondary degradation. In this study, possible reaction routes during biomass primary pyrolysis are also suggested based on the product distribution from the thermal decomposition of cellulose and xylan.