Effect of Pb2+ on the production of hydroxyl radical during solid-state fermentation of straw with Phanerochaete chrysosporium

Evolution of humic substances and the forms of heavy metals during co-composting of rice straw and sediment with the aid of Fenton-like process

The Fenton-like process was established by Fe₃O₄ nanomaterials (NMs) and Phanerochaete chrysosporium or oxalate, and applied to the co-composting of rice straw and sediment to study its effect on the formation of humic substance and the bioavailability of Cd, Cu, and Pb. Results shown that the application of Fenton-like process significantly promoted the passivation of Cd and Cu, while not shown obvious enhancement for Pb. The decrease of exchangeable fraction Cd (EXC-Cd) and the humic acid (HA) content in pile B with Fe₃O₄ NMs and oxalate were highest, which were 22.35% and 20.3 g/kg, respectively. Redundancy analyses (RDA) manifested that the Fenton-like process enhanced the influence of humus substance on the bioavailability of Cd, Cu, and Pb. Excitation-emission matrix (EEM) fluorescence spectra analysis suggested that Fenton-like process could obviously enhance the generation of humic substance. This research provides a new perspective and way for composting to remediate heavy metals pollution.

Efficient degradation of sulfamethazine in simulated and real wastewater at slightly basic pH values using Co-SAM-SCS /H2O2 Fenton-like system

The presence of antibiotics in aquatic environments has attracted global concern. Fenton process is an attractive yet challenging method for antibiotics degradation, especially when such a reaction can be conducted at neutral pH values. In this study, a novel composite Fe/Co catalyst was synthesized via the modification of steel converter slag (SCS) by salicylic acid-methanol (SAM) and cobalt nitrate (Co(NO₃)₂). The catalysts were characterized by N₂-Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The results indicated that the Co-SAM-SCS/H₂O₂ Fenton-like system was very effective for sulfamethazine (SMZ) degradation at a wide pH range. At initial pH of 7.0, the degradation rate of SMZ in Co-SAM-SCS/H₂O₂ system was 2.48, 3.20, 6.18, and 16.21 times of that in Fe-SAM-SCS/H₂O₂, SAM-SCS/H₂O₂, Co(NO₃)₂/H₂O₂ and SCS/H₂O₂ system, respectively. The preliminary analysis suggested that high surface area of Co-SAM-SCS sample and synergistic effect between introduced Co and SAM-SCS are responsible for the efficient catalytic activity. During the degradation, three main intermediates were identified by high performance liquid chromatography-mass spectrometry (HPLC-MS) analysis. Based on this, a possible degradation pathway was proposed. The SEM images, XRD patterns and XPS spectra before and after the reactions demonstrate that the crystal and chemical structure of Co-SAM-SCS after five cycles are almost unchanged. Besides, the Co-SAM-SCS presented low iron and cobalt leaching (0.17 mg/L and 2.36 mg/L, respectively). The studied Fenton-like process also showed high degradation of SMZ in river water and municipal wastewater. The progress will bring valuable insights to develop high-performance heterogeneous Fenton-like catalysts for environmental remediation.

Degradation of di (2-ethylhexyl) phthalate in sediment by a surfactant-enhanced Fenton-like process

This is the premier study reporting the remediation of di (2-ethylhexyl) phthalate (DEHP) contaminated sediment by a surfactant-enhanced Fenton-like system. Three widely used non-ionic surfactants were tested, and the order for desorption and solubilization of DEHP was determined as Tween 80 > Triton X-100 > Brij 35. The degradation of DEHP was studied at a near natural pH of 6.0 by two Fenton treatments: (i) Fe³⁺/H₂O₂ and (ii) Fe³⁺/PCA/H₂O₂. Results show that the addition of PCA can significantly enhance DEHP removal from 48.9% to 92.5%. This is consistent with observation that PCA maintained at a relative high level of iron ions, which can catalyze H₂O₂ to generate the reactive hydroxyl radicals (OH). Most of the added Tween 80 and a portion of OM were co-oxidized together with DEHP due to the non-selective nature of OH, which leaded to an increase in DOC content and decreases in sediment pH and total N content. The results provide an efficient and eco-friendly technique for the remediation of DEHP contaminated sediment, and also give insight to its environmental implications.

Effect of Phanerochaete chrysosporium inoculation on bacterial community and metal stabilization in lead-contaminated agricultural waste composting

The effects of Phanerochaete chrysosporium inoculation on bacterial community and lead (Pb) stabilization in composting of Pb-contaminated agricultural waste were studied. It was found that the bioavailable Pb was transformed to stable Pb after composting with inoculum of P. chrysosporium. Pearson correlation analysis revealed that total organic carbon (TOC) and carbon/nitrogen (C/N) ratio significantly (P<0.05) influenced the distribution of Pb fractions. The richness and diversity of bacterial community were reduced under Pb stress and increased after inoculation with P. chrysosporium. Redundancy analysis indicated that C/N ratio, total organic matter, temperature and soluble-exchangeable Pb were the significant parameters to affect the bacterial community structure, solely explained 14.7%, 11.1%, 10.4% and 8.3% of the variation in bacterial community composition, respectively. In addition, the main bacterial species, being related to organic matter degradation and Pb stabilization, were found. These findings will provide useful information for composting of heavy metal-contaminated organic wastes.

Tween 80 surfactant-enhanced bioremediation: toward a solution to the soil contamination by hydrophobic organic compounds

The occurrence of hydrophobic organic compounds (HOCs) in the soil has become a highly significant environmental issue. This problem has been exacerbated by the strong sorption of HOCs to the soils, which makes them unavailable for most remediation processes. More and more works show that surfactant-enhanced biological technologies offer a great potential to clear up HOCs-contaminated soils. This article is a critical review of HOCs removal from soils using Tween 80 (one of the mostly used nonionic surfactants) aided biological remediation technologies. The review begins with a discussion of the fundamentals of Tween 80-enhanced desorption of HOCs from contaminated soils, with special emphasis on the biotoxicity of Tween 80. Successful results obtained by Tween 80-enhanced microbial degradation and phytoremediation are documented and discussed in section 3 and section 4, respectively. Results show Tween 80-enhanced biotechnologies are promising for treating HOCs-contaminated soils. However, considering the fact that most of these scientific studies have only been conducted at the laboratory-scale, many improvements are required before these technologies can be scaled up to the full-scale level. Moreover, further research on mechanisms related to the interaction of Tween 80 with degrading microorganisms and the plants is in high demand.

Lignocellulose-degrading enzymes, free-radical transformations during composting of lignocellulosic waste and biothermal phases in small-scale reactors

Environmentally friendly strategies of waste management are both part of legal solutions currently in place and a focus of interest worldwide. Large-scale composting plants are set up across various regions while home composting is becoming increasingly popular. A variety of microbial groups are successively at work during composting and enzymatic activities detected in the composting mass fluctuate accordingly. Changes in the activities of oxidoreductases and hydrolases, i.e. glucose oxidase, horseradish peroxidase, lignin peroxidase, laccase, xylanase, superoxide dismutase and keratinase, low-molecular weight compounds, i.e. methoxyphenolic and hydroxyphenolic compounds, and the relative level of superoxide radicals and glucose were determined periodically in water extracts of composts to investigate the process of biochemical transformations of ligninocellulose in relation to biothermal phases and to identify a potential priming effect in two composts containing different ratios of lignocellulosic waste and chicken feathers. Composting was conducted for 30weeks. An important aim of the study was to demonstrate that a positive priming effect was induced during composting of a variety of lignocellulosic waste types using native keratin (chicken feathers) as a source of N. The effect was more evident in compost containing grass, which was related to a more rapid depletion of easily available sources of C and energy (glucose) during composting. Ligninolytic enzymes known to biodegrade recalcitrant organic matter were induced in subsequent biothermal phases of composting. Compost I enriched with grass (pine bark, grass, sawdust and chicken feathers) exhibited a higher enzymatic activity than compost II which did not contain any grass but which had a greater number of hardly-degradable components (pine bark, wheat straw, sawdust, chicken feathers). Similar observations were made for the concentrations of low-molecular weight compounds. The enzymes activities and concentration of low-molecular weight compounds listed above can be used to estimate the biodegradation of lignocellulose during composting.

A combined biological removal of Cd(2+) from aqueous solutions using Phanerochaete chrysosporium and rice straw

The removal of Cd(2+) from aqueous solutions by agricultural residues rice straw combined with white rot fungus Phanerochaete chrysosporium (P. chrysosporium) was investigated. The results showed that over 99% of the total Cd(2+) (initial concentration of 150mgL(-1)) was removed at the optimal operating conditions (pH 5.0 at 35°C). We also found that P. chrysosporium could survive under Cd(2+) stress even with an initial Cd(2+) concentration of 250mgL(-1). But when Cd(2+) concentration increased to 250mgL(-1), fungus growth and reproduction were remarkably restrained, and as a result, Cd(2+) removal dropped to 59.2%. It was observed that the fungus biomass and activities of ligninolytic enzymes decreased at some degree under high concentration of Cd(2+) (above 100mgL(-1)). Also, we found that a moderate Cd(2+) stress (below 150mgL(-1)) could stimulate P. chrysosporium's production of the heavy metals chelator - oxalate. This study will provide useful information for the application of biological removal of heavy metal irons from wastewater.

Degradation of atrazine by a novel Fenton-like process and assessment the influence on the treated soil

This is the premier study reporting the remediation of atrazine contaminated soil with steel converter slag (SCS) catalyzed Fenton-like process. The effects of various operating parameters, such as SCS loads and H2O2 concentrations were evaluated with respect to the removal efficiency of atrazine. Results show the optimal SCS load and H2O2 concentration were 80gkg(-1) and 10%, respectably. The graded modified Fenton's oxidation with a 3-time addition of 10% H2O2 was able to remove 93.7% of total atrazine in the contaminated soil and maintain soil temperature within 50°C. In contrast to traditional Fenton treatment, a slight pH increase has been observed due to the addition of SCS. More importantly, experiment conducted at natural conditions with SCS gave the similar atrazine removal to the experiments with the other catalysts (e.g., FeSO4 and Fe2O3). One thing should be noted that after the treatment, dissolved organic carbon (DOC) content increased to 1.206gkg(-1) from an initial value of 0.339gkg(-1).

Study of the degradation of methylene blue by semi-solid-state fermentation of agricultural residues with Phanerochaete chrysosporium and reutilization of fermented residues

The degradation of methylene blue (MB) by semi-solid-state fermentation of agricultural residues rice straw with Phanerochaete chrysosporium and the reutilization of fermented residues was investigated. A maximum decolorization of 84.8% for an initial dye concentration of 0.4 g/L was observed at the optimal operating conditions (temperature 35 °C, pH 5). As compared to the previous results obtained using synthetic materials as substrate, the results in the present study revealed an excellent performance of the bioreactor in decolorizing the wastewater containing MB, which is due to this type of cultivation reproducing the natural living conditions of the white rot fungi. Among the two ligninolytic enzymes that are responsible to the decolorization, manganese peroxidase (MnP) activity was found better correlated with decoloration percentage. Our results also provide a first step to recycling the fermented residues for the removal of MB from aqueous solutions, the maximum adsorption capacity of the fermented residues reached 51.4 mg/g.

Photocatalytic degradation of phenol by the heterogeneous Fe3O4 nanoparticles and oxalate complex system

A novel approach for phenol removal using Fe₃O₄ nanoparticles and oxalate was proposed via a radical mechanism.