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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 feasibility of recycling red mud waste by its direct transformation into highly-porous cellular ceramics was successfully demonstrated. Ceramic materials with designed cellular porosity were processed by emulsification of red mud suspensions with liquid paraffin. Taguchi method was used to study the effects provided by varying the red mud load in the suspension, gelatine content and emulsion stirring time on the micro structural features of the cellular ceramics. Additional experiments analysed the effects of the organic to suspension ratio and firing temperature. Emulsification of paraffin followed by gelatine consolidation, drying, elimination of the droplets of the discontinuous organic phase and firing, allowed one to design cellular ceramic pieces with open porosity up to 75%, consisting in interconnected cells with adjustable cell size and low resistance to percolation. These results allow one to consider prospective applications of red mud-based cellular ceramics with designed microstructures as highly-porous membranes for the capture of pollutants.

This work presents an updated overview of waste lubricant oil (WLO) management practices in Europe to promote a circular economy. The characteristics of virgin and waste oil, their hazardous proper...

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.

This study aims to evaluate the effect of weathered coal fly ash (CFA) as a drying adjuvant of sewage sludge (SS) to produce a soil amendment. The high amount of SS and CFA creates a complex waste management problem in many countries, requiring more research efforts. Towards a circular economy, CFA can be viewed as an anthropogenic inorganic by-product with valuable nutrients (e.g. K), which can be recovered in combination with SS (rich in organic matter, N, and P). Different temperatures (70, 85, 100, 115, and 130 °C) are tested to dry small SS cylinders, without and with 0.15 g CFA g

Green liquor dregs (GLD) are a major waste of the pulp and paper industry, and their correct classification is important to finding alternatives to landfill disposal. In the European Union, the met...

The application of TiO2 as a slurry catalyst for the degradation of contaminants of emerging concern (CEC) in liquid effluents has some drawbacks due to the difficulties in the catalyst reutilization. Thus, sophisticated and expensive separation methods are required after the reaction step. Alternatively, several types of materials have been used to support powder catalysts, so that fixed or fluidized bed reactors may be used. In this context, the objective of this work is to systematize and analyze the results of research inherent to the application of ceramic materials as support of TiO2 in the photocatalytic CEC removal from liquid effluents. Firstly, an overview is given about the treatment processes able to degrade CEC. In particular, the photocatalysts supported in ceramic materials are analyzed, namely the immobilization techniques applied to support TiO2 in these materials. Finally, a critical review of the literature dedicated to photocatalysis with supported TiO2 is presented, where the performance of the catalyst is considered as well as the main drivers and barriers for implementing this process. A focal point in the future is to investigate the possibility of depurating effluents and promote water reuse in safe conditions, and the supported TiO2 in ceramic materials may play a role in this scope.

In the European Union (EU), waste is classified according to the List of Waste (LoW) and relying on the assessment of 15 hazardous properties (HPs). Incineration bottom ash (IBA) from municipal solid waste is a mirror entry in the LoW, which leads to extremely different management options within the EU. IBA has shown potential for different applications under a circular economy perspective, contributing both to avoiding waste landfilling and the consumption of natural resources, such as sand and gravel. In this context, IBA evaluation and classification play a significant role in understanding which protection measures should be taken. This work aims to present an assessment of the 15 HPs and the consequent classification of IBA using data from the industry. Each HP is assessed based on knowledge of waste, chemical composition considering concentration limits for hazardous substances, and/or through tests (chemical, physical, or biological). According to the criteria followed, 5 out of 6 samples from a Portuguese Waste-to-Energy plant were considered non-hazardous. Only one sample was classified as hazardous due to the assignment of HP 10, which resulted from Pb content (0.36%) above the concentration limit established for this property (0.3%). Nonetheless, although most hazardous entries in the LoW have this classification based on HP 14, the results obtained for the samples of this work seem to indicate IBA from this study is non-ecotoxic. Moreover, it has been suggested that IBA could possibly achieve the End-of-Waste status according to the Waste Framework Directive. For such purpose, clear criteria should be laid down to safely use the material, and testing is a crucial step.

This work aims to contribute to the discussion of using a waste (sewage sludge) to obtain a valuable product (organic-rich fertilizer), based on a circular economy perspective. The compo- sition of sewage sludge (SS) was considered, highlighting important characteristics as raw ma- terial for fertilizer production (e.g., macronutrients, microbiological contamination, phytotoxicity). Particularly, the biological stability of SS was evaluated measuring the oxygen uptake rate (OUR) using the Oxitop® method, and the phytotoxicity using germination tests. The potential of thermal drying to stabilize the SS was evaluated at two temperatures (100 and 130◦C). The results showed that the organic matter (OM), N, and P levels are within the range of interest for agronomic valorization, while the content of some potentially toxic metals (e.g., Zn and Cu) may exceed the legal limits. The phytotoxicity assessment showed that raw SS samples negatively impacted the germination phase. Concerning the biological stability, results showed that raw anaerobic digested samples were characterized by OUR values above 50 mmol O2/kg OM.h (the limit for stable SS). Although thermal treatment of SS at 100 and 130◦C eliminated pathogens and significantly stabilized SS to OUR values below 50 mmol O2/kg OM.h, it was not enough to reach the limit established for a stable fertilizer (25 mmol O2/kg OM.h). Globally, SS has potential for soil application, within the scope of circular economy, but it is essential to control its microbiological contamination and stability. info:eu-repo/semantics/publishedVersion

The biorefinery approach must be boosted in the management of agro-residues in the future. The present study aims to investigate the valorization of tomato production residues, namely rotten tomato (unfit for consumption - RT), green tomato (GT), and tomato branches (TB). The assessment involves the recovery of value-added compounds through the extraction process followed by biogas production through anaerobic digestion. A thorough characterization of the three residues (RT, GT, and TB) was carried out, including the identification of volatile compounds by solid-phase microextraction (SPME) and gas chromatography/mass spectrometry (GC/MS). The volatiles analysis revealed the presence of flavor enhancer compounds and molecules with insecticidal properties. A solid-liquid extraction with ethanol allowed the recovery of value-added compounds in the extracts, in particular phenolic compounds, β-carotene, and lycopene, which contributed to the antioxidant activity. RT and TB extracts were found to be richer in total phenolic compounds (~27 mg GAE/gdb dry basis) and exhibited higher antioxidant activity (IC50 = 0.911 and 0.745 mg/mL). The tomato branches extract had the highest concentration of carotenoids with 37.23 and 3.08 mg/kgdb of β-carotene and lycopene, respectively. The biochemical methane potential (BMP) was assessed in sealed reactors operating in anaerobic conditions for all the raw (RT, GT, and TB) and extracted substrates waste (RTe, GTe, and TBe). While the BMP of RT and GT was in the range of 232–285 mL CH4/g VS, a lower value of 141 mL CH4/g VS was obtained for TB. The methane production for each pair of raw and extracted substrates (RT/RTe, GT/GTe, and TB/TBe) was considered statistically similar at a 95 % confidence level. Overall, the value-added compounds recovery through ethanolic extraction did not compromise the methane production of the materials.

Sewage sludge (SS) is a global environmental, social, and economic problem that requires a sustainable management approach. Still, the production of other industrial wastes, such as lime mud (LM), has recently gained considerable attention to avoid landfilling. This work aims to present a new approach for converting SS and LM into value-added products within the circular economy perspective. In particular, the effect of LM and calcined lime mud (CLM) as drying adjuvants and SS sanitation agents are investigated. Two out of three SS samples show Escherichia coli contamination above the Portuguese limit established for soil application, while no Salmonella spp. was detected in the searched samples. The addition of CLM to SS in a ratio between 0.05 and 0.15 g CLM/gwb, lead to complete elimination of the microbiological contamination in almost all cases. Contrarily, the use of LM does not seem efficient to act as a sanitation agent. Both LM and CLM show a positive impact on the drying process when compared to the raw SS, increasing the drying rate, and reducing the drying time. The most favourable drying conditions to maximize the drying rate and minimize the drying time (until 30% of moisture) are 130 °C, 0.15 g adj/gwb, and 2.5 mm of plate thickness. The thermal treatment (100 and 130 °C) without adjuvants reduces the microbiological contamination below the legal limit. Overall, a beneficial effect is observed by adding CLM to SS, open the possibility of producing a safer organic soil improver.

Municipal solid waste (MSW) incineration in waste-to-energy plants plays an important role in waste management systems of developed countries, since the increasing amounts of waste cannot be all recycled, and diverting waste from landfilling is a priority. On the other hand, proper MSW management is a fundamental part of sustainable development, which requires the balance of the economic, social, and environmental dimensions. Thus, this chapter explores sustainability issues about MSW incineration with energy recovery. For this purpose, an overview of the MSW management systems is presented and incineration technology is highlighted. Subsequently, the three dimensions of sustainable development are explored regarding MSW incineration with energy recovery. Environmental considerations related to air emissions and solid residues from MSW incineration are discussed. Concerning economic issues, the costs and revenues of incineration treatment are reviewed. Finally, the social context of this management option is provided, pointing out public concerns and studies addressing these aspects.

The agro-industry of tomato generates three types of residues: ripe rotten tomato (unfit for consumption) (RT), green (unripe) tomato (GT), and tomato branches including leaves and stems (TB). These materials are commonly wasted or used as feed for livestock. Energy production through anaerobic digestion is an alternative way to manage and simultaneously valorise these materials. Initially, the operating conditions of mono anaerobic digestion were investigated using RT. Thus, a design of experiments based on a two-level fractional factorial design with resolution V was performed to determine the factors that affect biochemical methane potential (BMP). The substrate to inoculum ratio (SIR), total volatile solids concentration (VSt), working volume (WV), presence of nutrients (Nu), and the pre-incubation of the inoculum (Inc) were investigated. The results showed that SIR is the most important factor. The maximum BMP for RT was 297 NmLCH4/gVS with SIR = 0.5, tVS = 20 g/L, WV = 20%, no pre-incubation and the presence of nutrients. Using these optimum operating conditions, co-digestion was investigated through a mixture design approach. The substrates RT and GT presented similar BMP values, whereas TB led to a significantly lower BMP. Indeed, when high concentrations of TB were used, a significant decrease in methane production was observed. Nonetheless, the highest BMP was achieved with a mixture of 63% RT + 20% GT + 17% TB, with a production of 324 NmLCH4/gVS, corresponding to a synergetic co-digestion performance index of about 1.20. In general, although the substrate RT generates the highest BMP, the mixture with GT did not impair the methane yield. Overall, the co-digestion of tomato residues must be conducted with SIR close to 0.5 and the content of tomato branches in the reaction mixture should be kept low (up to 20%).

Phosphorus (P) is a non-renewable resource, irreplaceable for life and food production, and currently considered a Critical Raw Material to the European Union (EU). Due to concerns about the rate of consumption and limited reserves in countries with sensitive geopolitical contexts, it is urgent to recover P from urban and industrial flows. Indeed, the municipal wastewater treatment plants (WWTP) are considered relevant sources with several hot spots, especially sewage sludge with estimated recovery efficiencies of >80%. The most promising recovery strategies are based on thermal treatments (e.g., incineration of sludge) following by wet-chemical or thermochemical leaching, precipitation, and adsorption. The direct application of sludge on soil is no longer a primary route for P reintegration in the value-chain for countries as Switzerland, Germany, and The Netherlands. In fact, Switzerland and Austria paved the way for implementing P recovery legislation, focusing on recovery from raw sewage sludge or ashes. Indeed, industrial technologies with sludge ash as input show high recovery efficiencies (Ashdec® and Leachphos® with 98 and 79%) and lower environmental impacts, whereas Pearl® technology has about 12% recovery efficiency with wastewater as input. After all, struvite emerges as the most recovered product with recent access to the internal market of EU fertilisers and similar growth performance compared to triple-super-phosphate. However, several studies leave open the possibility of introducing loaded adsorbents with P as soil amendments as a new alternative to conventional desorption. Briefly, P recovery should be a compromise between efficiency, environmental impacts, and economic revenues from the final products info:eu-repo/semantics/publishedVersion

Electrochemical reduction of iron oxides into zero-valent iron (ZVI, Fe0) is a promising alternative to the traditional methods used for iron production. The electrochemical deposition of Fe0 from hematite and hematite-based Fe2−xAlxO3 ceramic in alkaline suspensions (10 M of NaOH) was assessed at relatively low temperature (90 °C). Ceramic compositions aimed to mimic the main components of red mud waste from the alumina refining industry for iron valorisation purposes. The impact of aluminium content on the electroreduction and microstructure of the deposited Fe0 films was demonstrated and discussed. Trapping and following the leaching of the aluminium species during deposition causes drastic morphological changes and induces significant porosity. Faradaic efficiencies of the reduction to Fe0 were found to decrease from 70% to 32% for Fe2O3 and Fe1.4Al0.6O3, respectively. The results highlight possible effects imposed by aluminium presence during Fe0 electrodeposition for future iron recycling from, for example, red mud or other aluminium containing wastes by electrowinning in alkaline conditions.

Water treatment sludge is an industrial by-product which has recently been classified as a waste by the European Commission. The main goal of this work is to valorise this waste to produce lightweight aggregates. Formulations with sludge substituting expanded clay up to 50 wt% were produced. The physical properties of the lightweight aggregates such as bloating index, density and porosity were studied. The introduction of the sludge without expanding properties, reduced the expandability of the clay and the porosity of the aggregates. The density increased from 0.32 g/cm3 in aggregates without sludge to 1.46 g/cm3 in aggregates with 50 wt% of sludge. It is shown that lightweight aggregates can be produced using mixtures of expanded clay and water treatment sludge, with low substitution percentages (up to 15 wt% of sludge). Aggregates up to 15 wt% of sludge were further studied. The compressive strength increased with sludge wt.%, and the concentrations of heavy metals and metalloids, assessed through leaching tests, were well below the stablished limits. Two preliminary tests of lightweight aggregate concrete were produced: LWAC 1 was formulated with commercial lightweight aggregates and LWAC 2 with aggregates containing 7 wt% of the sludge and commercial lightweight aggregates. The physical, mechanical and thermal properties of LWAC 1 and LWAC 2 were found to be very similar. Our work demonstrates the feasibility in using water treatment sludge as a by-product to produce lightweight aggregates suitable for thermal insulation and lightweight applications.

In this study, the performance of chemically modified pine bark for removal of Cr(III) from solutions was investigated. Initially, several chemicals were tested (NaOH, C5H9NO4, H3PO2 and CS2). The xanthate pine bark (XPB) obtained with CS2, was screened as the best adsorbent and thus, it was characterized in respect to morphological and textural properties. Sulfur groups after xanthation reaction were identified on XPB by FTIR and EDS spectroscopies. Equilibrium isotherm and kinetics were determined. The equilibrium data were well described by the Langmuir isotherm allowing to calculate the maximum adsorption capacity (56.5 mg/g). The kinetics is fast and follows a pseudo-second order model. Furthermore, an ion-exchange sorption mechanism between Cr(III) and Na+ was proposed. Among the desorbing agents tested, the best results were achieved with 2.0 M H2SO4. Moreover, in the column tests, a reduction on the breakthrough time and the stoichiometric time from 36.5 and 22.8%, respectively, was observed, when the feed concentration increased from 230 to 500 mg/L. The breakthrough curves were well modeled by Bohard-Adams, Thomas or Yoon-Nelson equations. Globally, XPB revealed to be a promising adsorbent for uptake Cr(III). The scale-up design and the economic assessment indicated potential applicability for the treatment of real effluents.

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.

This work aims to study the removal of contaminants from waste lubricating oil (WLO) with distinct properties by solvent extraction to recover the base oil. 1-Butanol and methyl ethyl ketone (MEK) were selected as green solvents. Three WLO samples (class A, B, and C) with substantially different properties were considered. Class A is the most common type of WLO; Class B corresponds to mineral oil with low level of contaminants (e.g. oxidation products and additives); Class C is mainly constituted by synthetic ester base oils. The analysis involved the response surface methodology and the desirability function to model two response variables (Yield and percent sludge removal - PSR) and to find the best operating conditions for the most influential factors (solvent/oil ratio and KOH dosage). The rates of contaminant removal were very dependent on the type of WLO. The maximum PSR achieved were 8.5 and 6.5% using 1-Butanol for class A and C oils, respectively, while 6.3 and 4.7% were observed for MEK. Thus, 1-Butanol is the most efficient extracting agent than MEK for both classes A and C. The extraction process was not effective for class B (PSR ≈ 0%), and this oil can bypass the deasphalting stage, saving materials and energy. The addition of KOH as flocculation agent in class C was less effective than to other classes due to the saponifiable matter content in the oil. However, the solvent extraction is a suitable treatment route for the regeneration of synthetic ester-based oils (class C). Reasonably accurate models regarding the response variables were obtained for both solvents and class A and C oils. Considering desirability functions, a solvent/oil ratio of 5 w/w and KOH dosage of 1.5 or 2 g/L were found as optimal conditions.

Iron oxides are attractive for a variety of applications, since they offer unique physical and chemical properties, while being abundant and environmentally friendly. Some of those potential applications, including electrochemical and catalytic systems, require ceramics with designed porosity and well-developed percolation networks. In the present work, representative Al- and Mg-substituted hematite and magnetite- based cellular ceramics were processed by emulsification of mixed oxide suspensions. Reactive firing conditions were adjusted to attain a reasonable compromise between designed porosity, percolation and phase composition. The impact of firing conditions on the cellular ceramics microstructure, porosity, phase content and interconnectivity of the cells was studied and discussed. Thus, the applicability of the proposed emulsification of ceramic suspensions method was demonstrated for iron oxide-based ceramics.

This work aims to analyse the dynamic behavior of a fixed-bed column to remove Cr(III) from a synthetic effluent. The adsorbent was prepared by mercerizing pine bark (MPB). The dynamic study of the sorption process was based on the breakthrough curves obtained experimentally and modelled by a mechanistic approach, empirical models and multivariate regression analysis. The experimental results showed that the maximum fraction of saturated bed (FSB) was 0.65 when the inlet concentration was 100 mg/L, the height of the bed (H) 6.5 cm and the superficial velocity ( u 0 ) 14.4 × 10−2 cm/s. The mechanistic model includes equilibrium parameters and the linear driving force (LDF) approach to express the intraparticular mass transport. The prediction of the experimental profiles was very acceptable, and the parameters used are valuable for the further design of fixed-bed column. The fitting through empirical models (Bohard-Adams, Thomas and Yoon-Nelson) are similar or even better than the mechanistic model. Aiming at the optimization of the column operation, a multivariate linear regression model (MRM) was developed based on a full factorial design. Thus, relationships between the variable responses FSB and Δtads (defined as the difference between the breakthrough time and exhaustion time) and two input variables (H and u 0 ) were developed. This model was validated and used to predict the optimal operating conditions to maximize FSB (0.65) and minimize Δtads (133 min). Finally, the regeneration of the adsorbent was assessed using nitric acid. The MPB adsorbent tested demonstrated a good capacity for uptaking Cr(III) from liquid effluents in column configurations.

Waste lubricant oil (WLO) is an absolute hazardous entry in the European List of Waste that requires proper treatment. Solvent extraction is one of the most effective deasphalting processes for the regeneration of WLO, with a strong contribution to the circular economy. This study aims to propose a new methodology for the selection of solvents for WLO regeneration, which balances technical, economical, and greenness criteria. The method involves two phases for screening a list of 154 solvents. In the first phase, five criteria were used: water and acidic properties; selectivity toward the base oil and flocculation capacity; number of carbon atoms between three and five; melting point lower than 10 °C and a boiling point between 60 and 130 °C; and yield greater than 85%. In the second phase, three metrics of sustainability were employed: greenness, efficiency, and cost. Globally, a score was attributed to each solvent based on the assessment of the individual metric. From a list of 154 solvents, 1-butanol,...

Measurements of viscosity, density and surface tension of waste lubricant oil (WLO) were conducted at different temperatures. The dataset was constituted by nine WLO samples from different producers. The main objective of the work is the investigation of the temperature dependence of viscosity, including the glass transition, T g , and dynamic crossover, T x , temperatures. In addition, different correlations were evaluated to predict viscosity and surface tension starting from a property easily obtained such as density. WLO show rapid decrease of viscosity with shear rate, followed by an extensive and well defined Newtonian plateau. The temperature dependence of viscosity at the Newtonian plateau of WLO deviated from the Arrhenius behavior, and was accurately described by four different models: Williams–Landel–Ferry (WLF), MYEGA, power law and Ghatee. The minimum and maximum absolute average relative deviation (AARD) were 0.08% and 0.9%, respectively. T g predicted by WLF equation varied between T = 170.5 K and T = 198.7 K, while MYEGA tends to predict lower T g (about T = 20 K). The power law and Ghatee models estimate T x nearly with the same accuracy. A ratio T x / T g of about 1.28 ± 0.03 was obtained for WLO, which agrees with the literature. Waste oil is a moderately fragile glass forming fluid with a fragility parameter, m , ranging from 47.8 and 64.5. New correlations were developed for the prediction of viscosity and surface tension from density at different temperatures. AARD of 7% was observed for viscosity and 2% for surface tension.

Coagulation phenomena can occur in certain types of waste lubricant oils (WLO) during regeneration processes involving alkaline treatments, causing plant shutdowns. In this context, this study addresses the nature of the compounds responsible for the coagulation phenomena after the alkaline treatment. For such, an empirical test was developed to assess the coagulation behaviour of WLO, consisting in the addition of KOH to the WLO followed by heating under stirring conditions. This test was performed on 133 samples and four coagulation classes were identified: A; B1; B2 and C. Moreover, a physicochemical characterization of WLO was carried out regarding viscosity at 40°C, saponification number (SN), total acid number (TAN), surface tension, water content, elemental analysis and functional groups (FTIR). 56 samples of fresh lubricant oils for different applications were also characterized and their properties assessed and compared. Multivariate methods were applied to WLO to discriminate among coagulation classes based on FTIR spectra. It was found that coagulation classes A and B1 exhibit statistically similar patterns for all properties determined. Spectral discriminating analysis did not reveal discriminant peaks for class B1 samples, and the presence of specific additives was pointed as the possible factor underlying the increase in viscosity in this oils. Class B2 presents the absence of additives and oxidation products as differentiating features. In addition, B2 samples showed lower TAN SN, and lower concentration of some elements. Lubricants from gear or hydraulic applications can give rise to this class of WLO. Oils of Class C are mainly composed by synthetic ester type base oils, which hamper regeneration processes using alkaline pretreatments. In future studies, WLO type A and B1 can be classified as a single class. The coagulation phenomena classification becomes A - negative, B - precipitate formation and C - positive.

This work aims for the development and characterization of a new biosorbent with enhanced capacity for recovery of Cr(III) from aqueous solutions. The adsorbent was developed by chemical modification of pine bark (Pinus pinaster) (PB). Initially, several chemical agents (HCl, H2SO4, HNO3, H3PO4, citric acid, acetic acid, NaOH) were tested, but the best results were obtained with NaOH. The adsorbent developed was characterized regarding chemical composition and thermal behaviour before and after adsorption tests. Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) showed the morphology and the most relevant elements on the surface before and after adsorption of Cr(III). Fourier transform infrared spectroscopy (FTIR) revealed the important role of carboxylate groups in Cr(III) uptake. The adsorption process was studied under different conditions, namely for testing the particle size (in the ranges from 0.088 to 0.149 and 0.250 to 0.595 mm). The equilibrium isotherms showed that Cr(III) adsorption is strongly dependent on particle size. According to the Langmuir model, the maximum adsorption capacity of Cr(III) increased from 17.15 to 31.40 mg/g as the particle range decreased. The experimental Cr(III) removal efficiencies as a function of the adsorbent dosage were well predicted by the mass balance equation for the batch adsorption process coupled with the equilibrium isotherm. This article is protected by copyright. All rights reserved

The main objective of this work is to evaluate the phytotoxicity of olive mill solid wastes (OMW) produced in two different centrifugation technologies and also the toxicity associated with specific phenolic compounds. Two samples of waste were collected in two-phase (2P-OMW) and three-phase (3P-OMW) centrifugation olive oil production processes, and cress bioassays with Lepidium sativum L. were employed to evaluate phytotoxicity. Although both OMW have similar total phenolic content (TPh), results confirmed that 2P-OMW is more phytotoxic than 3P-OMW. When extracts from 2P-OMW at liquid to solid ratio of 10 L kg−1 were applied none of the seeds germinated, i.e. germination index ( G I ) was 0%, while for 3P-OMW GI was 94.3%. Growth tests in soil and mixtures with OMW also led to more favorable results for 3P-OMW, whereas worse results than those obtained in the control experiments were observed. In order to discriminate the individual influence of eleven phenolic compounds, gallic acid, protocatechuic acid, cinnamic acid, syringic acid, 3,4,5-trimethoxybenzoic acid, 4-hydroxybenzoic acid, vanillic acid, p-coumaric acid, caffeic acid, veratric acid and phenol were tested in the concentration range of 5–500 mg L−1. Results showed that cinnamic acid is the most phytotoxic, with EC50 of 60 mg L−1, which is related with its hydrophobicity. Moreover, increasing -OH and -OCH3 groups in these molecules seem to reduce phytotoxicity. Tests with a mixture of six phenolic compounds demonstrated there are neither synergistic nor additive effects. The phytotoxicity appears to be determined by the presence of the most lipophilic phenolic molecule.

Nowadays the European guidelines boost the concept of “circular economy” which is focused on catalysing sustainable development. “Closing the loop” is particularly important for improving the recycling rates, and thus waste and by-products can be turned into a resource with benefits to the economy and environment. Within this scope, this work reviews and updates the potential of valorisation and legal framework of an anthropogenic biomineral with high content of calcium carbonate. Namely, the waste under consideration is the industrial eggshell waste (ES) resulting from egg breakage. This is considered an animal by-product (ABP) and thus some constraints may limit ES applications. The flux of this ABP mainly within the European region is also indicated and the estimated data highlight that significant amount of this biomineral is being produced. Despite legal restrictions, countries such as the UK, Spain and Portugal have been able to find practical application for ES, avoiding landfilling. The literature shows that applications for industrial eggshell may be grouped into two categories: raw material and operating supply. In the first case, the options are food additive, soil amendment, purified calcium carbonate, cosmetics and biomaterial composite. As operating supply, ES may be used as catalyst and sorbent. Although the economic profit should be evaluated in each case, the environmental benefit of those potential applications is in general high. Considering ES properties and the soil properties in large areas of Europe (acidic pH and low topsoil organic carbon content) the production of Ca-rich compost obtained through composting seems to be a particularly interesting approach toward “circular economy”.

Waste lubricant oil (WLO) management systems across Europe can be very heterogeneous, with significant discrepancies in their performance. The objectives towards a circular economy represent a challenge to continuously maximize the collection and regeneration of this hazardous waste. The quality of WLO is a limiting factor towards its potential for regeneration, in which producers have a great responsibility on the handling phase. In this context, the main objectives of this work are the evaluation and improvement of a national management system, based on the physicochemical characteristics of WLO collected by different producers (garage, industry and others). Data of critical parameters (sediments, water, chlorine and PCB) of 30,242 samples collected from 2008 to 2015 were analyzed. About 4.8% of those samples exceeded the Portuguese regulatory limit regarding sediments (3 wt %) and 22.3% for water plus sediments (8 wt %). On the contrary, 0.73% of the samples did not comply with the limit of chlorine (2000 ppm) and only 0.08% for PCB (50 ppm). Chlorine nonconformities were mostly registered in industrial producers. In addition, 60 samples collected in 2015 were characterized regarding other important properties, namely density, kinematic viscosity at 40 °C, total acid number, saponification number, elemental analysis and functional groups. These results gave important clues about the performance of the different producers. In particular, FTIR analysis revealed that about 60% of the samples may be contaminated with glycol compounds regardless the type of producer. The overall management system can be improved by preventing contamination with chlorine from industry WLO or glycol-containing compounds (such as brake fluid and antifreeze) for all producers.

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.

Electrochemical reduction of iron oxides into zero-valent iron (ZVI, Fe0) is a promising alternative to the traditional methods used for iron production. The electrochemical deposition of Fe0 from hematite and hematite-based Fe2−xAlxO3 ceramic in alkaline suspensions (10 M of NaOH) was assessed at relatively low temperature (90 °C). Ceramic compositions aimed to mimic the main components of red mud waste from the alumina refining industry for iron valorisation purposes. The impact of aluminium content on the electroreduction and microstructure of the deposited Fe0 films was demonstrated and discussed. Trapping and following the leaching of the aluminium species during deposition causes drastic morphological changes and induces significant porosity. Faradaic efficiencies of the reduction to Fe0 were found to decrease from 70% to 32% for Fe2O3 and Fe1.4Al0.6O3, respectively. The results highlight possible effects imposed by aluminium presence during Fe0 electrodeposition for future iron recycling from, for example, red mud or other aluminium containing wastes by electrowinning in alkaline conditions.