Tomato Residue Management from a Biorefinery Perspective and towards a Circular Economy.

The tomato industry is a relevant socio-economic activity in the European Union, while it generates a large variety of residues. Tomatoes unfit for consumption, tomato peels, seeds, industrial pomace, and plants are examples of residues of this industry. Commonly, some of the residues can be left in the field, composted, used for animal feeding, or valorized through anaerobic digestion. However, more economic value can be attributed to these residues if a biorefinery approach is applied. Indeed, many value-added compounds can be obtained by the integration of different processes while closing the carbon and nutrient loops. The extraction of bioactive compounds followed by anaerobic digestion and composting seems to be a viable proposal for a biorefinery approach. Thus, this study aims to review the biorefinery strategies for valorizing tomato residues, highlighting the main processes proposed. The recovery of lycopene, ß-carotene, and phenolic compounds has been widely studied at the lab scale, while energy recovery has already been applied at the industrial scale. Although techno-economic analysis is scarce for tomato residue valorization processes, positive net present values (NPV) and low payback times (PBT) have been reported in the literature. Thus, more work comparing multiple extraction technologies and biorefinery strategies coupled with economic and environmental assessment should be performed to select the most promising management route for tomato residues.

Phosphorus removal from urban wastewater through adsorption using biogenic calcium carbonate.

Phosphorus (P) removal from urban wastewater is increasingly relevant in the wastewater treatment sector. The present work aims to contribute to the study of the adsorption process as a P removal technology. Biogenic calcium carbonate from industrial eggshell waste prepared by milling and calcination was used as an adsorbent. Batch adsorption experiments were conducted using real wastewater with 40 mg P/L (orthophosphate), original pH 7.33, under stirring conditions (100 rpm). The adsorbent was characterized using SEM-EDS, XRD, and FTIR-ATR before and after adsorption. From an initial screening of calcination times (15, 30, 60, and 120 min) and considering a balance between P removal and energy saving, the adsorbent selected was eggshell calcined at 700 °C for 60 min. The Langmuir isotherms describe the experimental data with a maximum adsorption capacity of 4.57 mg P/g at 25 °C. The adsorption process reached equilibrium within 120 min for different dosages (5, 10, and 20 g/L at 25 °C). Batch experiments showed that SO42-, at a concentration of 2689 mg/L reduced the P adsorption selectivity for dosages ≤10 g/L at 25 °C. Characterization of the loaded adsorbent shows that P adsorption from real wastewater is mostly electrostatic attraction, with the contribution of ligand exchange and microprecipitation. The adsorption capacity and behavior of the selected adsorbent seem promising for P removal from urban wastewater compared with other low-cost adsorbents.

Grape Pomace as a Natural Source of Phenolic Compounds: Solvent Screening and Extraction Optimization.

The optimization of extraction by using solvents of phenolic compounds (TPh) of grape pomace (GP) based on a central composite design was investigated. The GP was characterized, and preliminary assays were conducted with five different solvents (water, ethanol, acetone, methanol, and butanol) and the aqueous mixtures thereof. Ethanol and acetone were revealed to be the best solvents for TPh extraction. The main extraction parameters (temperature-T, time-t, solvent concentration, and liquid-solid ratio-L/S) were optimized by using a central composite design. The optimized conditions for the ethanol extraction (T = 60 °C, t = 1.5 h, L/S = 25 mL/gdryGP) and for acetone (T = 50 °C, t = 1.5 h, L/S = 25 mL/gdryGP) were determined. Single-stage extraction revealed a TPh of 45.18 ± 9.51 mgGAE/gdryGP for acetone and a TPh of 38.70 ± 3.64 mgGAE/gdryGP for ethanol. The characterization of the extracts revealed the presence of gallic acid, caffeic acid, syringic acid, vanillic acid, chlorogenic acid, and p-coumaric acid, where the concentration of the first three compounds stands out in all extracts. A three-stage extraction increased the yield of ethanol to 63.3 mg GAE/gdryGP and the yield of acetone to 59.2 mg GAE/gdryGP. Overall, both solvents allow the extraction of phenolic compounds of grape pomace, but ethanol is commonly considered a greener solvent for this purpose.

Increasing Value of Winery Residues through Integrated Biorefinery Processes: A Review.

The wine industry is one of the most relevant socio-economic activities in Europe. However, this industry represents a growing problem with negative effects on the environment since it produces large quantities of residues that need appropriate valorization or management. From the perspective of biorefinery and circular economy, the winery residues show high potential to be used for the formulation of new products. Due to the substantial quantities of phenolic compounds, flavonoids, and anthocyanins with high antioxidant potential in their matrix, these residues can be exploited by extracting bioactive compounds before using the remaining biomass for energy purposes or for producing fertilizers. Currently, there is an emphasis on the use of new and greener technologies in order to recover bioactive molecules from solid and liquid winery residues. Once the bio compounds are recovered, the remaining residues can be used for the production of energy through bioprocesses (biogas, bioethanol, bio-oil), thermal processes (pyrolysis, gasification combustion), or biofertilizers (compost), according to the biorefinery concept. This review mainly focuses on the discussion of the feasibility of the application of the biorefinery concept for winery residues. The transition from the lab-scale to the industrial-scale of the different technologies is still lacking and urgent in this sector.

Supported TiO2 in Ceramic Materials for the Photocatalytic Degradation of Contaminants of Emerging Concern in Liquid Effluents: A Review.

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.

Beneficial use of lime mud from kraft pulp industry for drying and microbiological decontamination of sewage sludge.

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.

From wastewater to fertilizer products: Alternative paths to mitigate phosphorus demand in European countries.

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 thermo-chemical 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.

Isothermal drying kinetics of sewage sludge using weathered coal fly ash as adjuvant for agronomic application.

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-1 of SSwet basis (wb). By fitting appropriate models to the experimental drying curves, it is possible to observe an improvement of 1-17% in the diffusion coefficient and 7-19% in the kinetic constants, using CFA. The best drying conditions are achieved with CFA as an adjuvant at 130 °C, where the drying rate is 31.61 gH2O kg-1 SSwb min-1. Phytotoxicity and growth assays are performed to evaluate the effect of the produced materials in the soil. The product with SS and CFA shows the potential to improve soil condition due to (i) the organic matter, N, P, and K content, (ii) the lower phytotoxic effect when compared to raw SS; (iii) the soil pH correction. Thus, not only the addition of weathered CFA facilitates the drying of SS but also the final product has benefits to soil conditions.

Assessment of hazardous property HP 14 using ecotoxicological tests: a case study of weathered coal fly ash.

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.

Kraft pulp mill dregs and grits as permeable reactive barrier for removal of copper and sulfate in acid mine drainage.

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.

Thermal dehydration of urban biosolids with green liquor dregs from pulp and paper mill.

This study aims to investigate the sewage sludge (SS) drying process by incorporating a by-product formed in the pulp and paper industry (green liquor dregs - GLD) as drying adjuvant. Through an innovative approach, the drying kinetics was modelled, and the final dried product was tested for soil applications. After the characterization phase, small cylinders of SS without and with 0.15 g GLD g SS-1wb (SS_GLD) were dried in isothermal conditions at 70, 100, and 130 °C. The experimental data were fitted by Fick's second law and thin-layer models, and good results were achieved in both cases (R2 > 0.98 and RMSE <0.05). Although only a slight improvement was observed, the best conditions for drying biosolids were found with the addition of GLD at 130 °C, where the drying rate was 30.88 gH2O kg-1 SSwb min-1. In this condition, a decrease of 8% in the energy required for moisture evaporation was observed. Regarding the phytotoxicity tests with Lepidium sativum L. (garden cress), 60% improvement in EC50 was noticed for the sample with GLD when compared to the raw SS. The dried product SS_GLD complied with the regulations for soil applications regarding the potentially toxic metals (Cr, Ni, Cu, Pb, Zn, and Cd), and promoted an increase in soil organic matter and pH. However, further and in-depth studies should be conducted to assess the potential of SS_GLD application in agricultural soil.

Legal situation and current practice of waste incineration bottom ash utilisation in Europe.

Almost 500 municipal solid waste incineration plants in the EU, Norway and Switzerland generate about 17.6 Mt/a of incinerator bottom ash (IBA). IBA contains minerals and metals. Metals are mostly separated and sold to the scrap market and minerals are either disposed of in landfills or utilised in the construction sector. Since there is no uniform regulation for IBA utilisation at EU level, countries developed own rules with varying requirements for utilisation. As a result from a cooperation network between European experts an up-to-date overview of documents regulating IBA utilisation is presented. Furthermore, this work highlights the different requirements that have to be considered. Overall, 51 different parameters for the total content and 36 different parameters for the emission by leaching are defined. An analysis of the defined parameter reveals that leaching parameters are significantly more to be considered compared to total content parameters. In order to assess the leaching behaviour nine different leaching tests, including batch tests, up-flow percolation tests and one diffusion test (monolithic materials) are in place. A further discussion of leaching parameters showed that certain countries took over limit values initially defined for landfills for inert waste and adopted them for IBA utilisation. The overall utilisation rate of IBA in construction works is approximately 54 wt%. It is revealed that the rate of utilisation does not necessarily depend on how well regulated IBA utilisation is, but rather seems to be a result of political commitment for IBA recycling and economically interesting circumstances.

Analysis of potentially toxic metal constraints to apply sewage sludge in Portuguese agricultural soils.

The application of sewage sludge (SS) in the soil can be a valuable way to increase its content of organic matter. However, the concentration of potentially toxic metal (PTM) in both SS and soil can hinder this route of management. Thus, the main objective of this work was to evaluate the compliance with the restrictions related to PTM contained in SS from wastewater treatment plants (WWTP) for agricultural land application. The regulatory constraints associated with SS and soil in respect to PTM (Cd, Cr, Cu, Ni, Pb, and Zn) were analyzed. These metals showed a deleterious effect on germination of Lepidium sativum seeds, and their phytotoxicity may be ranked as Cd > Cu > Cr(VI) > Cr(III) ~ Zn ~ Ni > Pb. Portuguese SS samples from different WWTP, from a national sludge management operator, and from the literature were considered. The results revealed that the content of these metals, in general, complies with the regulatory threshold values. The content of PTM in the soil is not restrictive to receive SS in at least 90% of the national territory. The assessment of ecological risk based on the geoaccumulation index (Igeo), pollution index (PI), and potential ecological risk index (PERI) showed low risk for all metals. The exception was Igeo of Cd, Cu, and Zn, which presented moderate to high level of pollution. According to the state of the art, no significant negative impacts have been detected on human health and the environment due to SS applications in the soil. Thus, in a country with low carbon content in the land and whenever compliance with regulations is achieved, the main route for SS management may be agricultural soil.

Recovery of phosphate from aqueous solutions using calcined eggshell as an eco-friendly adsorbent.

Phosphorus scarcity has become a significant issue in the European Union (EU) during 21st Century, due to its relevance as an irreplaceable macronutrient for life, and because of the total dependency of EU regarding imports. This work aims to evaluate the phosphorus recovery by adsorption in batch and fixed-bed column, using a thermally modified eggshell as an adsorbent. The screening phase revealed that calcined eggshell at 700 °C (CES700) is the most suitable material compared with the other thermally modified eggshells tested. Thus, CES700 was characterized regarding the specific surface area, pore volume, zero-point charge pH, total dissolved solids and organic matter. The influence of pH and adsorbent dosage was investigated in batch conditions. Langmuir-Freundlich model described the equilibrium data and the maximum adsorption capacity was about 39 mg P-PO4/g. The kinetics follows a pseudo-first order model, with constants between 0.063 and 0.224 min-1. Fixed-bed studies indicated that increasing fluid superficial velocity and feed concentration led to an early saturation of the adsorbent. Yoon-Nelson, Thomas and Bohard-Adams empirical models properly adjusted the breakthrough curves with R2 ≥ 0.98. Germination tests using CES700 loaded with phosphate revealed a germination index of 120 and 124% to 48 and 72 h, respectively. CES700 is statically better than the other tested materials, which opens the possibility of its use as fertilizer. This study showed that the developed material, CES700, can be applied in batch or fixed-bed processes to recover phosphate ions from liquid effluents, and the loaded adsorbent has potential to be further used as fertilizer.

Single and binary sorption of Cr(III) and Ni(II) onto modified pine bark.

This study aims to investigate the single and binary biosorption of Cr(III) and Ni(II) by pine bark chemically treated with NaOH solution (MPB). The studies involved the effect of initial pH in the equilibrium, as well as kinetic uptake using synthetic solutions. Equilibrium tests were also conducted with an industrial effluent. The kinetic model of pseudo-second order described well the data of single and binary systems. The equilibrium data were better described by the Langmuir model for both metals. The maximum adsorption capacity (qmax) to single system was 31.4 and 23.7 mg/g for Cr(III) and Ni(II), respectively. To analyse the competitive sorption between chromium and nickel ions, the modified Langmuir and Freundlich models were tested for two different concentration (mEq/L) ratios Cr(III)/Ni(II) of 1:1 and 2:1. The modified Langmuir model is also the best to fit the experimental data for both syntetic and industrial effluents. In the synthetic effluent, the qmax value for Cr(III) in MPB was about 25 mg/g, while qmax for Ni(II) decreased from 12.4 to 5.5 mg/g. The results showed that Ni(II) did not significantly interfere in Cr(III) adsorption capacity, whereas Cr(III) decreased the uptake of Ni(II). The industrial effluent contains several species, and thus, the sorption capacities for Cr(III) and Ni(II) were significantly affected.

Technologies for the management of MSW incineration ashes from gas cleaning: New perspectives on recovery of secondary raw materials and circular economy.

Environmental policies in the European Union focus on the prevention of hazardous waste and aim to mitigate its impact on human health and ecosystems. However, progress is promoting a shift in perspective from environmental impacts to resource recovery. Municipal solid waste incineration (MSWI) has been increasing in developed countries, thus the amount of air pollution control residues (APCr) and fly ashes (FA) have followed the same upward trend. APCr from MSWI is classified as hazardous waste in the List of Waste (LoW) and as an absolute entry (19 01 07*), but FA may be classified as a mirror entry (19 0 13*/19 01 14). These properties arise mainly from their content in soluble salts, potentially toxic metals, trace organic pollutants and high pH in contact with water. Since these residues have been mostly disposed of in underground and landfills, other possibilities must be investigated to recover secondary raw materials and products. According to the literature, four additional routes of recovery have been found: detoxification (e.g. washing), product manufacturing (e.g. ceramic products and cement), practical applications (e.g. CO2 sequestration) and recovery of materials (e.g. Zn and salts). This work aims to identify the best available technologies for material recovery in order to avoid landfill solutions. Within this scope, six case studies are presented and discussed: recycling in lightweight aggregates, glass-ceramics, cement, recovery of zinc, rare metals and salts. Finally, future perspectives are provided to advance understanding of this anthropogenic waste as a source of resources, yet tied to safeguards for the environment.

Phytotoxicity assessment of olive mill solid wastes and the influence of phenolic compounds.

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 (GI) 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.

Assessment of co-composting process with high load of an inorganic industrial waste.

This study aims to investigate the co-composting of an inorganic industrial waste (eggshell - ES) in very high levels (up to 60% w/w). Since composting is a process in which solid, liquid and gaseous phases interact in a very complex way, there is a need to shed light on statistical tools that can unravel the main relationships structuring the variability associated to this process. In this study, PCA and data visualisation were used with that purpose. The co-composting tests were designed with increasing quantities of ES (0, 10, 20, 30 and 60%ES w/w) mixed with industrial potato peel and rice husks. Principal component analysis showed that physical properties like free air space, bulk density and moisture are the most relevant variables for explaining the variability due to ES content. On the other hand, variability in time dynamics is mostly driven by some chemical and phytoxicological parameters, such as organic matter decay and nitrate content. Higher ES incorporation (60% ES) enhanced the initial biological activity of the mixture, but the higher bulk density and lower water holding capacity had a negative effect on the aerobic biological activity as the process evolved. Nevertheless, pathogen-killing temperatures (>70°C for 11h) were attained. All the final products obtained after 90days were stable and non-phytotoxic. This work proved that valorisation of high amounts of eggshell by co-composting is feasible, but prone to be influenced by the physical properties of the mixtures.

Influence of N-rich material in valorization of industrial eggshell by co-composting.

Industrial eggshell (ES) is an animal by-product (ABP) involving some risk if not properly managed. Composting is a possible treatment approved for its safe use. This study aims to assess the influence of using N-rich material (grass clippings (GC)) to improve co-composting of ES mixtures for reaching sanitizing temperatures imposed by the ABP regulation from the European Union. Two sets of mixtures (M1 and M2) were investigated, each containing industrial potato peel waste, GC and rice husks at 3:1.9:1 and 3:0:1 ratios by wet weight. In each set, ES composition ranged from 0% to 30% (w/w). Co-composting trials were performed in self-heating reactors for 25 days, followed by maturation in piles. Results showed that only M1 trials attained temperatures higher than 70°C for nine consecutive hours, but N-losses by stripping on average were four- to five-fold higher than M2. In the absence of N-rich material, biodegradability of mixtures was 'low' to 'moderate' and organic matter conversion was impaired. Physical, chemical and phytotoxic properties of finished composts were suitable for soil improvement, but M1 took 54 more days to achieve maturity. In conclusion, co-composting ES with N-rich materials is important to assure the fulfilment of sanitizing requirements, avoiding any additional thermal treatment.

Immobilisation of lead and zinc in contaminated soil using compost derived from industrial eggshell.

This study aims to evaluate the capacity of a compost obtained by co-composting of industrial eggshell (CES) to immobilise lead (Pb) and zinc (Zn) in an acidic soil contaminated by mining activities. Mature compost without eggshell (CWES) and natural eggshell (ES) were also tested as soil amendments for comparison purposes. Three different application rates were used for each material, ensuring the same quantity in terms of neutralizing capacity. Incubation experiments were conducted under controlled conditions and CO2 emissions monitored for 94 days. The environmental availability of Pb and Zn in the amended soil was assessed and bioassays were performed at the end of the incubation period. When eggshells were present, the CES compost raised the soil pH to values higher than 6 and reduced the soil mobile fraction for both Pb and Zn, in more than 95%. Soil toxicity towards Vibrio fischeri was also suppressed and environmental risk decreased to "low level". However, the immobilisation in the acid insoluble soil component was significantly achieved only for Zn. In addition, regarding soil carbon dynamics the CO2-C emissions were enhanced, mainly in the case of the highest rate of amendment. Both first order-E and parallel first order models may adequately describe the kinetic data of CO2-C cumulative release. Without eggshells, the CWES compost revealed limited effect on heavy metals immobilisation, likely due to its small capacity to correct soil acidity, at lower application rates. Using solely eggshells, the ES waste had similar outcomes when compared with CES, but at the higher application rate, CO2 emissions were enhanced with the eggshell compost due to the contribution of biotic carbon present therein. Therefore, this study points out that CES is an effective liming material and may be used for in situ remediation of contaminated soil with Pb and Zn.