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Sewage sludge (SS) formed in wastewater treatment plants can contain organic matter and nutrients in concentrations that are valuable for amending poor soil. This work aims to compare the performance of six residues not only as drying adjuvants of SS but also as improvers agents in agronomic properties of the final product. According to criteria in line with circular economy and industrial ecology, the selected adjuvants were weathered coal fly ash (CFA), bottom biomass ash (BBA), green liquor dregs (GLD), lime mud (LM), eggshell (ES), and rice husk (RH). The main physicochemical properties of these materials were determined. Then, small cylinders with and without 0.15 g adjuvant/g SSwet basis were shaped at room temperature and dried at 130 oC in a moisture analyzer to evaluate the drying kinetics. The profiles were modeled, and the main parameters determined. Furthermore, several relevant parameters for agronomic applications of the final products were determined, such as pathogen contamination, acid neutralization capacity (ANC), and oxygen uptake rate (OUR). Adding BBA to SS (named as SS_BBA product) promoted the highest diffusion coefficient (2.55·10−7 m2/s) and drying rate (41.6 g H2O/kg min). On the other hand, SS_ES showed a positive impact in almost all agronomic parameters, with an ANC of 0.166 g CaCO3/g, OUR of 10.18 mmol O2/kg organic matter h, and germination index of 29.1%. In general, the results indicate that several residues can be used to improve not only sludge drying but also the final properties of the product for soil applications.

Air pollution control residues (APCr) from municipal solid waste (MSW) incineration are hazardous waste, and their management requires holistic approaches within technical, economical, legislative, and environmental constraints. This work deals with the recycling of APCr for producing lightweight aggregates (LWA) commonly manufactured by firing natural clay. The main objectives are to evaluate the environmental impacts of LWA with and without incorporating APCr and assess whether APCr recycling in LWA is beneficial, based on the life-cycle assessment (LCA) methodology. The system boundary included raw material extraction, grinding, mixture, firing, cooling, and packing (cradle-to-gate). Results were analysed following the impact assessment methods recommended by the International Reference Life Cycle Data System. Results pointed out a reduction of impacts in all categories when 3% of natural clay are replaced by APCr. The highest gains occurred for toxicity categories (HTc, HTnc) and resulted mainly from avoiding landfill of APCr. For non-toxicity categories, impacts were dominated by the emissions from the kiln firing process, which were similar for both LWA; therefore, impact reductions from APCr use in LWA in these categories were modest. LCA results show that the valorisation of APCr in LWA may be an environmentally sound solution to avoid landfill disposal practices.

The classification of wastes regarding hazardous property HP 14 (ecotoxicity) is essential for proper waste management. In the EU, HP 14 has been estimated based on waste chemical composition rather than using biotests, and guidelines for experimental assessment are still lacking. This study aims at evaluating the potential ecotoxicological impacts of weathered coal fly ash (CFA) from a landfill, as a case study to assess the current EU methodology used to classify wastes regarding HP 14. A large amount of CFA is still landfilled, but its valorisation would be of interest. The analysis was based on the chemical composition of CFA (in ClassifyMyWaste software), and on a battery of five biotests applied to eluates, with Lepidium sativum, Aliivibrio fischeri, Raphidocelis subcapitata, Lemna minor and Daphnia magna. Through chemical analysis, most of the simulations with data from the literature indicated "Possible Hazard", including the sample of this work. Biotests revealed low impairment for most endpoints. D. magna was the most sensitive organism, but the inhibitory effect was significantly reduced after pH adjustment of the eluate. The test with A. fischeri does not seem to be adequate to assess CFA due to the high variability observed in results. The methodology involving a simple battery of bioassays was proven to be enlightening, providing relevant results for HP 14 assessment. The chosen battery of biotests (excluding the A. fischeri test) may be a good starting point to represent the aquatic environment in this context. In short, it seems that weathered CFA can be considered non-hazardous, and therefore the material under analysis could be valorised in practical applications without significant ecotoxic effect on the environment.

Mining is an essential human activity, but results in several environmental impacts, notably the contamination of ground and surface water through the presence of toxic substances such as metals and sulfates in mine drainage. Permeable reactive barriers (PRB) have been applied to remediate this environmental impact, but the high costs associated with the maintenance of this system are still a challenge. The main objective of this study was to evaluate the use of kraft pulp mill alkaline residues, known as dregs and grits, as material for PRB, and to determine their capacity for retaining copper and sulfate. The work was carried out in laboratory adsorption kinetics assays, batch assays and column tests. Tests for elemental characterization, point of zero charge, acid neutralization capacity, total porosity, bulk density and moisture of the dregs and grits were conducted. The results showed high retention of Cu due to a chemical precipitation mechanism, notably for dregs (99%) at 5 min in adsorption kinetics. The grits presented similar results after 180 min for the same assay. Sulfate retention was effective at pH below 5, with an efficiency of 79% and 89% for dregs and grits, respectively. Dregs presented the best results for acid drainage remediation, notably with a solid:liquid (S:L) ratio of 1:10.

The high toxicity/volatility and low biodegradation of phenolic compounds are serious concerns in terms of environmental and health impact—their recommended max. value for drinking water is 0.005 mg/L. They are usually removed from effluents by adsorption, but they show a complex interaction behavior with adsorbents, because the hydroxyl group and the hydrophobic aromatic ring are very close. In this work, the versatility of Si chemistry was explored to tailor the surface chemistry of silica aerogels and improve their adsorption performance towards phenolic compounds. Methyltrimethoxysilane and tetramethylorthosilicate were combined to adjust the hydrophobicity of the obtained aerogels. In the next stage, β-cyclodextrin, with its highly hydrophobic cavity, was grafted into the gels to improve the capturing of aromatic rings. For a sustainable linkage of β-cyclodextrin to silica, the methyltrimethoxysilane/tetramethylorthosilicate precursor system was modified by adding an epoxy functionalized silane. A first screening of the adsorption performance shows a 1.5–2-fold increase of the adsorption capacity and removal efficiencies of the epoxy-cyclodextrin-modified aerogel toward phenol and p-cresol when compared to aerogel counterpart without modification. Freundlich isotherm model was the most suitable to describe the equilibrium data of aerogels with or without β-cyclodextrin, with the curves showing favorable profiles, more evident in the case of aerogels with β-cyclodextrin. Apart from the improving of the sorption capacity for phenolic compounds (achieving a maximum of 60 mg g−1 in the case of p-cresol), the utilization of the biodegradable β-cyclodextrin moiety obtained from natural and sustainable resources is a further asset of the epoxy-cyclodextrin-modified aerogel.

This study aims to evaluate a new biosorbent derived from co-composting eggshell with other organic materials (potato peels, grass clipping, and rice husk) for uptaking Pb(II) from an aqueous medium. This biosorbent contains a high amount of eggshell (30 % w/w; CES) and its performance was compared to mature compost without eggshell (CWES) and natural eggshell (ES). Sorption kinetics and equilibrium data were fitted to pseudo-second-order and Langmuir models, respectively. From a kinetic point of view, lead sorption into CES was fast, attaining equilibrium within less than 180 min. Batch experiments indicated that maximum sorption capacity of Pb into CES is 23 mg g−1. The sorption capacity of CES was not significantly dependent on pH within the range of 2–5.5. In comparison to ES, organic matter of CES provided supplementary sites for lead sorption and an increase of 43 % in the sorption capacity was observed. Nevertheless, CWES was the biosorbent with higher sorption capacity. Still, this study points out the potential of new use of CES as an effective biosorbent to lead removal from aqueous matrices.