Soluble organic substances extracted from compost as amendments for Fenton-like oxidation of contaminated sites

Novel process for organic wastewater treatment using aerobic composting technology: Shifting from pollutant removal towards resource recovery

In this study, an organic wastewater treatment process based on aerobic composting technology was developed in order to explore the transition of wastewater treatment from pollutants removal to resource recovery. The novelty of the process focuses towards the microbial metabolic heat that is often ignored during the composting, and taking advantage of this heat for wastewater evaporation to achieve zero-discharge treatment. Meanwhile, this process can retain the wastewater's nutrients in the composting substrate to realize the recovery of resources. This study determined the optimum condition for the process (initial water content of 50 %, C/N ratio of 25:1, ventilation rate of 3 m3/h), and 69.9 % of the total heat generated by composting was used for wastewater treatment under the condition. The HA/FA ratio of composting substrate increased from 0.07 to 0.53 after wastewater treatment, and the retention ratio of TOC and TN was 52.3 % and 61.7 %, respectively, which proved the high recycling value of the composting products. Thermoduric and thermophilic bacteria accounted for 44.3 % of the community structure at the maturation stage, which played a pivotal role in both pollutant removal and resource recovery.

Direct humification of biowaste with hydrothermal technology: A review

Hydrothermal humification of biowaste, in comparison to the traditional coal-based humic acid extraction process, better aligns with the goals of carbon neutrality and sustainability. This article provided a comprehensive review on the current advancements in hydrothermal humification of biowaste. Hydrothermal humic acid (HHA) derived from different biowaste sources was compared, exhibiting significant differences in their hydrophobicity, oxygen-containing functional group content, and structural characteristics. The influence of key parameters, including reaction temperature, residence time, pH and the action of catalysts on HHA yield was analyzed. The pathways through which biowaste and its major components transform into HHA were elucidated. Coal-like hydrochar has shown significant potential for producing HHA through hydrothermal treatment, with HHA selectivity exceeding 65 %. HHA also exhibits promising performance in agriculture and environmental remediation, offering comparable value to commercial humic acid. Future research should concentrate on establishing the correlation between hydrothermal conditions and the efficiency of biowaste humification, thereby facilitating the development of a predictive model for assessing efficiency. Additionally, exploring the application value of hydrothermal-synthesized HHA with diverse chemical characteristics will guide the optimization of hydrothermal conditions and selection of suitable feedstock.

Binding characteristics of humic substances with Cu and Zn in response to inorganic mineral additives during swine manure composting

Composting is suitable for recycling livestock manure into valuable organic fertilizer, which can improve soil quality while mitigating potential risk of heavy metal pollution. Humic substances (HS) in compost have been demonstrated to play a key role in regulating the redistribution of heavy metal fractions. However, limited direct information have been reported on how different components of HS complexes with heavy metals to affect their bioavailability during composting. In this study, sequential extraction procedures (H₂O, KCl, Na₄P₂O₇, NaOH and HNO₃) were used to assess the characteristics that HS bound with Cu and Zn during composting of swine manure and straw added either 5% boron waste (BW) or 5% phosphate rock (PR). Organically complexed fraction extracted by Na₄P₂O₇ contained only 33-41% of the Cu but most of the Zn (81-87%). During composting, initially mobile fractions of Cu and Zn (extracted by H₂O or KCl) changed into more stable fractions (extracted by NaOH and HNO₃), and both organic matter and fulvic acids (FA) were identified as critical factors to explain this redistribution based on redundancy analysis. Over 80% of Cu and Zn were complexed with FA of HS. However, exogenous additives (phosphate rock and boron waste) enhanced Cu conversion by promoting humification (Humic acid/Fulvic acids, HA/FA) whereas they had limited influence on Zn, due to the relatively weak binding relationship between Zn and HA.

Recent Developments in Advanced Oxidation Processes for Organics-Polluted Soil Reclamation

Soil pollution has become a substantial environmental problem which is amplified by overpopulation in different regions. In this review, the state of the art regarding the use of Advanced Oxidation Processes (AOPs) for soil remediation is presented. This review aims to provide an outline of recent technologies developed for the decontamination of polluted soils by using AOPs. Depending on the decontamination process, these techniques have been presented in three categories: the Fenton process, sulfate radicals process, and coupled processes. The review presents the achievements of, and includes some reflections on, the status of these emerging technologies, the mechanisms, and influential factors. At the present, more investigation and development actions are still desirable to bring them to real full-scale implementation.

Application of Chelating Agents to Enhance Fenton Process in Soil Remediation: A Review

Persistent organic contaminants affecting soil and groundwater pose a significant threat to ecosystems and human health. Fenton oxidation is an efficient treatment for removing these pollutants in the aqueous phase at acidic pH. However, the in-situ application of this technology for soil remediation (where pHs around neutrality are required) presents important limitations, such as catalyst (iron) availability and oxidant (H2O2) stability. The addition of chelating agents (CAs), forming complexes with Fe and enabling Fenton reactions under these conditions, so-called chelate-modified Fenton process (MF), tries to overcome the challenges identified in conventional Fenton. Despite the growing interest in this technology, there is not yet a critical review compiling the information needed for its real application. The advantages and drawbacks of MF must be clarified, and the recent achievements should be shared with the scientific community. This review provides a general overview of the application of CAs to enhance the Fenton process for the remediation of soils polluted with the most common organic contaminants, especially for a deep understanding of the activation mechanisms and influential factors. The existing shortcomings and research needs have been highlighted. Finally, future research perspectives on the use of CAs in MF and recommendations have been provided.

Heavy metals passivation driven by the interaction of organic fractions and functional bacteria during biochar/montmorillonite-amended composting

The aim of this study was to identify critical driving factors and pathways of mitigating heavy metals (HM) bioavailability during biochar/montmorillonite-amended composting: emphasize on the interaction effect between organic constituents and functional bacteria. Organic components, such as humus (HS), humic (HA) and fulvic acid (FA) and dissolved organic carbon (DOC), exhibited indivisible links with Cu and Zn speciation, which confirmed their vital roles on deactivating Cu and Zn. Network analysis indicated that biochar/montmorillonite obviously increased the diversity of Cu resistant/actor and Zn actor bacteria, which aided in HM passivation. Although multiple pathways were involved in regulating Cu/Zn passivation, the interaction of bacteria and organic constituents was the most critical driving factor. Given that, promoting potential HM resistant/actor bacteria utilizing and transforming low-humification organic fractions coupling with elevating high-humification constituents were the optimal pathway. This study is helpful to practical application of biochar/montmorillonite to inactivate HM for industrial composting.

Lignocellulose Biomass as a Multifunctional Tool for Sustainable Catalysis and Chemicals: An Overview

Today, the theme of environmental preservation plays an important role within the activities of the scientific community and influences the choices of politics and the common population. In this context, the use of non-fossil substances should be promoted for different reasons: to avoid the depletion and damage of the areas involved in the fossil fuel extraction, decrease the impact of emissions/by-products related to the industrial transformation of fossil-based products and possibly exploit residual biomasses as sources of carbon. This latter aspect also can be viewed as a way to revalorize lignocellulose waste, generally destined to dump as putrescible matter or to be incinerated. In this review, we are aiming to present a concise overview of the multiple functions of lignocellulose biomass in the broad field of catalysis for a sustainable development. The originality of the approach is considering the lignocellulose-derived matter in three different aspects: (i) as a precursor to convert into platform molecules, (ii) as an active material (i.e., humic-like substances as photosensitizers) and (iii) as a green support for catalytic applications. We find that this perspective can widen the awareness level of scientists involved in the catalysis field for the exploitation of residual biomass as a valuable and complementary resource.

An analysis of the versatility and effectiveness of composts for sequestering heavy metal ions, dyes and xenobiotics from soils and aqueous milieus

The persistence and bioaccumulation of environmental pollutants in water bodies, soils and living tissues remain alarmingly related to environmental protection and ecosystem restoration. Adsorption-based techniques appear highly competent in sequestering several environmental pollutants. In this review, the recent research findings reported on the assessments of composts and compost-amended soils as adsorbents of heavy metal ions, dye molecules and xenobiotics have been appraised. This review demonstrates clearly the high adsorption capacities of composts for umpteen environmental pollutants at the lab-scale. The main inferences from this review are that utilization of composts for the removal of heavy metal ions, dye molecules and xenobiotics from aqueous environments and soils is particularly worthwhile and efficient at the laboratory scale, and the adsorption behaviors and effectiveness of compost-type adsorbents for agrochemicals (e.g. herbicides and insecticides) vary considerably because of variabilities in structure, topology, bond connectivity, distribution of functional groups and interactions of xenobiotics with the active humic substances in composts. Compost-based field-scale remediation of environmental pollutants is still sparse and arguably much challenging to implement if, furthermore, real-world soil and water contamination issues are to be addressed effectively. Hence, significant research and process development efforts should be promptly geared and intensified in this direction by extrapolating the lab-scale findings in a cost-effective manner.

The role of soil organic matters and minerals on hydrogen peroxide decomposition in the soil

Application of H₂O₂ in in-situ chemical oxidation (ISCO) for soil remediation has been limited by its rapid decomposition. However, effect of main factors involving in this phenomenon are not well understood. In this contribution, H₂O₂ decomposition in the six types of natural soils was investigated by kinetic analyses and soil characterizations. The grassland soil (GS) and red soil (RS) have the highest H₂O₂ decomposition rates (respective 0.048 and 0.069 min^-1), while the paddy soil (PS) shows the lowest one (0.004 min^-1). The decomposition mainly takes place on the surface adsorption sites of soil particles. PS has the highest content of SOM, which can block the active adsorption sites for H₂O₂ decomposition. The effects of dissolved organic matter (DOM) and biological debris in the soil are minor. Iron and manganese containing minerals are significantly influential on H₂O₂ decomposition, and the soil with a higher content of clay can induce faster H₂O₂ decomposition. The immobilized goethite (GM) and birnessite (BM) on montmorillonite were synthesized to simulate soil minerals. Results show H₂O₂ decomposition rates in BM is even faster than GM when the former dosage is two orders of magnitude lower than that of the latter. This indicates the crucial role of manganese minerals although their contents are generally much lower than that of iron in the soils. This study advanced the understanding of H₂O₂ decomposition in the soil and bring insights for H₂O₂ based ISCO technology in soil remediation.

Humic acids extracted from compost as amendments for Fenton treatment of diesel-contaminated soil

In this study, we investigate the performance of a Fenton-like process carried out adding as amendments humic acids extracted from compost obtained from organic wastes. Namely, Fenton-like lab-scale tests with different dosages of the extracted humic acids and traditional stabilizing agent (KH₂PO₄) were performed on a diesel-contaminated soil collected in a former gasoline station. The performed tests showed a beneficial effect of the extracted humic acids on the hydrogen peroxide stability. Namely, the H₂O₂ lifetime in the tests carried out without the addition of any amendments proved to be quite limited, resulting equal to around 1 h. The adoption of the extracted humic acids alone entailed a limited increase of the hydrogen peroxide stability that anyhow was detected in solution for 24 h using 10 g/L of extracted HA. When the humic acids (10 g/L) were used in combination with KH₂PO₄ (8.2 g/L), the hydrogen peroxide lifetime increased up to around 150 h. A beneficial effect of the humic acids extracted from compost for a Fenton-like process was also observed in terms of diesel removal. Namely, without any amendment, a contaminant removal of around 55% was observed. Using KH₂PO₄ or HA alone, the contaminant removal raised up to around 75% while using the traditional stabilizer together with the humic acids extracted from compost, it was possible to remove up to 90% of the initial diesel content of the soil.

Unveiling the Dependence between Hydroxyl Radical Generation and Performance of Fenton Systems with Complexed Iron

Humiclike substances (HLS) have been demonstrated to be useful auxiliaries to drive the (photo)-Fenton process at mild pH, by avoiding iron inactivation via formation of active complexes. However, the actual performance of the process is affected by a manifold of opposite processes. In this work, the generation of hydroxyl radical-like reactive species in the Fentonlike process has been investigated using electron paramagnetic resonance, employing 5,5-dimethyl-1-pyrroline-N-oxide as a probe molecule. The signal obtained with the Fe(II)-HLS-H2O2 system at pH = 5 was very intense but decreased with time, in line with the difficult reduction of the formed Fe(III) to Fe(II). On the contrary, the signal of the Fe(III)-HLS-H2O2 system was weak but stable. The most intense signal was observed at HLS concentration of ca. 30 mg/L. Interestingly, the performance of the Fenton system at pH = 5 to degrade caffeine followed the same trends, although caffeine removal was very low after 1 h of irradiation. The results were more evident in a solar simulated photo-Fenton process, where an increase in the abatement of caffeine was observed until an HLS concentration of 30 mg/L, where 98% removal was reached after 1 h.

Degradation of haloacetic acids with the Fenton-like and analysis by GC-MS: use of bioassays for monitoring of genotoxic, mutagenic and cytotoxic effects

In this study, a method was developed to evaluate the degradation of haloacetic acids (HAAs) in water by a heterogenous Fenton-like process catalyzed by cobalt-doped magnetite nanoparticles (Fe_{3 - x}Co_xO₄), extraction of the contaminants by liquid-liquid extraction (LLE), and analysis by gas chromatography-mass spectrometry (GC-MS). The developed method was efficient in the degradation of HAAs, with the following degradation values: 63%, 62%, 30%, 39%, 37%, 50%, 84%, 41%, and 79% for monochloroacetic acid, monobromoacetic acid, dichloroacetic acid, trichloroacetic acid, bromochloroacetic acid, dibromoacetic acid, bromodichloroacetic acid, dibromochloroacetic acid, and tribromoacetic acid compounds, respectively. Through the application of the Allium cepa test, the cytotoxicity, genotoxicity, and mutagenicity of HAAs were evaluated. The results confirm its genotoxic and mutagenic effects on Allium cepa meristematic cells. Through this study, it was possible to verify the effectiveness of the developed method and its potential as a proposal for environmental remediation.

Use of iron ore tailing from tailing dam as catalyst in a fenton-like process for methylene blue oxidation in continuous flow mode

The global demand for iron ore with high iron contents to supply the steel industry is associated, in most countries, with the generation of tailings from mineral processing. The chemical compositions of iron ore tailings (basically Fe₂O₃ and SiO₂) make them an excellent candidate as a catalyst for advanced oxidation processes (AOPs), especially the Fenton process and its derivatives. Therefore, this paper aimed to transform iron ore tailings from tailing dams into catalysts able to activate H₂O₂ for the purpose of treating, in a continuous flow, effluents contaminated with organic dyes, employing methylene blue as a model molecule. The mineralogical characteristics of in natura tailings, such as the associations between iron oxides and quartz and the particle sizes of iron oxides, are favourable points for their transformation into catalysts by Fenton-like processes. Different pellet geometries and binding agents were evaluated to optimize the dye removal. Pellet pretreatment in a CH₄ atmosphere at 550 °C for 2 h with 10% bentonite as a binding agent (RCSP sample) resulted in the removal of approximately 80% of dye. Kinetic removal data show the good stability of the catalyst in the flow system. Significant catalytic activity loss was not observed after four runs, and data from TG-MS indicate that there is a synergetic mechanism between the adsorption, radical attack and desorption processes of the substrate on the catalyst surface.

Optimization of integrated ultrasonic-Fenton system for metal removal and dewatering of anaerobically digested sludge by Box-Behnken design

This study reveals the optimization of ultrasonic-Fenton process for the treatment of sludge taken from a local municipal wastewater treatment plant after anaerobic digestion. Box-Behnken design (BBD), a common approach of response surface methodology (RSM), was applied to evaluate and optimize the individual and interactive effects of three process variables, namely Fe²⁺ dose, H₂O₂ amount and sonication time for Fenton-ultrasonication method. Five dependent parameters including total organic carbon (TOC), extracellular polymeric substances (EPS), as LB-EPS and TB-EPS, and metals such as Zn and Cu were considered as the responses to investigate. According to the results of analysis of variances (ANOVA), five modelling equations are proposed that can be used to operate the design space with high regression coefficient R². Modelling results suggest that Fenton parameters, such as: H₂O₂ and Fe²⁺ dosage had the significant effects on the overall removal of TOC; whereas, sonication improved the metal removal from the sludge sample. Based on response surface methodology, best performance is achievable under the following conditions: 36 mM of Fe²⁺, 320 mM H₂O₂ with 30 min of sonication respectively for all of the responses.

New Route for Valorization of Oil Mill Wastes: Isolation of Humic-Like Substances to be Employed in Solar-Driven Processes for Pollutants Removal

The valorization of olive oil mill solid wastes (OMW) has been addressed by considering it as a possible source of humic-like substances (HLSs), to be used as auxiliary substances for photo-Fenton, employing caffeine as a target pollutant to test the efficiency of this approach. The OMW-HLS isolation encompassed the OMW basic hydrolysis, followed by ultrafiltration and drying. OMW-HLS structural features have been investigated by means of laser light scattering, fluorescence, size exclusion chromatography, and thermogravimetric analysis; moreover, the capability of OMW-HLS to generate reactive species under irradiation has been investigated using spin-trap electronic paramagnetic resonance. The caffeine degradation by means of photo-Fenton process driven at pH = 5 was significantly increased by the addition of 10 mg/L of OMW-HLS. Under the mechanistic point of view, it could be hypothesized that singlet oxygen is not playing a relevant role, whereas other oxidants (mainly OH^• radicals) can be considered as the key species in promoting caffeine degradation.