Recalcitrant Molecules Research Articles

Application of ESI FT-ICR MS to Study Kraft Lignin Modification by the Exoenzymes of the White Rot Basidiomycete Fungus TrametesHirsutaLE-BIN 072

Trameteshirsuta is a wood rotting fungus that possesses a vast array of lignin degrading enzymes, including7 laccases, 7 ligninolyticmanganese peroxidases, 9 lignin peroxidases and 2 versatile peroxidases. In this study,electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS)was used to examine kraft lignin modification by the enzymatic system of this fungus.The observed pattern of lignin modification suggested that before the 6th day of cultivation,the fungal enzymatic system tended to degrade more oxidized moleculesand, hence, less recalcitrant molecules, with the production of hard-to-modify reduced molecular species. At some point after the 6th day of cultivation,the fungal enzymatic system tended to degrade more oxidized moleculesand, hence, less recalcitrant molecules, with the production of hard-to-modify reduced molecular species. At some point after the 6th day of cultivation,the fungus started to degrade less oxidized, more recalcitrant, compounds, converting them into the more oxidized forms. The altered pattern of lignin modification enabled changes in the fungal enzymatic system. These changes were further attributed to the appearance of the particular ligninolyticmanganese peroxides enzyme(MnP7), which was added by the fungus to the mixture of enzymes that had already been secreted (VP2 and MnP5).
 Keywords: wood rotting fungi, kraft lignin, mass spectrometry, peroxidases

Dry anaerobic digestion of the fine particle fraction of mechanically-sorted organic fraction of municipal solid waste in laboratory and pilot reactor.

High-solid anaerobic digestion of the very small particle fraction of mechanically-sorted organic fraction of municipal solid waste (OFMSW) was examined in mesophilic digestion tests in a conventional laboratory (0.013m3) and a pilot (0.300m3) reactor. The non-biodegradable and recalcitrant molecules together with the low protein and starch contents of the small-particles of OFMSW limited the methane generation potential of substrate. In the conventional AD system, methane yields remained low at 0.139 m3kgVS-1 due to formation of a non-reacting layer on digestate surface, which restricted utilization of the available in OFMSW digestible organics. The absence of surface solid crust in the pilot unit favoured consumption of a greater proportion of volatile solids of the OFMSW. Dry AD was remarkably stable over the entire period and negligibly effected by the toxic H2S yields. Methane generation (0.167 m3kgVS-1) was increased 1.2-fold compared to the conventional system due to a better mixing of substrate and microorganisms achieved inside the pilot reactor, which led to an increase of the digested volatile organics. Digestate presented low stability and high heavy metal content, both of which restrain its implementation as soil conditioner or fertilizer in agriculture. A secondary co-digestion treatment may be required for the neutralization of digestate.

Biodegradation of azo dye-containing wastewater by activated sludge: a critical review.

The effluent from the textile industry is a complex mixture of recalcitrant molecules that can harm the environment and human health. Biological treatments are usually applied for this wastewater, particularly activated sludge, due to its high efficiency, and low implementation and operation costs. However, the activated sludge microbiome is rarely well-known. In general, activated sludges are composed of Acidobacteria, Bacillus, Clostridium, Pseudomonas, Proteobacteria, and Streptococcus, in which Bacillus and Pseudomonas are highlighted for bacterial dye degradation. Consequently, the process is not carried out under optimum conditions (treatment yield). Therefore, this review aims to contextualize the potential environmental impacts of azo dye-containing wastewater from the textile industry, including toxicity, activated sludge microbiome identification, in particular using the matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) as a novel, rapid and accurate strategy for the identification of activated sludge microbiome (potential to enhance treatment yield).

Identification of processes mobilizing organic molecules and arsenic in geothermal confined groundwater from Pliocene aquifers

Organic matter (OM) has been accepted as an important trigger fueling Fe(III) oxide reduction and arsenic release in the late Pleistocene-Holocene anoxic aquifers, whereas its fates and roles on arsenic mobility in the Pliocene aquifer are unclear. To fill this gap, groundwaters from a confined Pliocene aquifer (CG) and an unconfined Holocene aquifer (UG) were sampled in the Guide Basin, China, to monitor evolutions of groundwater geochemistry and OM molecular signatures along the groundwater flow path. The outcomes showed that groundwater pH, temperature, and arsenic concentrations in the CG samples generally increased along the groundwater flow path, which were much higher than those in the UG samples. The numbers and intensities of recalcitrant molecules (polycyclic aromatics and polyphenols) in the CG samples remarkably increased along the path, but relatively labile molecules (highly unsaturated and phenolic compounds and aliphatic compounds) showed the opposite trends. The arsenic-poor (<10 μg/L) UG samples contained more labile molecules than the arsenic-rich CG samples. High groundwater pH, temperature, and sediment age in the confined aquifers may be responsible for the selective mobilization of the unique polycyclic aromatics and polyphenols. The mobilized recalcitrant organic molecules may enhance arsenic release via electron shuttling, complexation, and competition. Furthermore, high temperature and pH may also facilitate arsenic desorption. The study provides molecular-scale evidences that the mobilization of recalcitrant organic molecules and arsenic were concurrent in the geothermal confined groundwater.

Production of lipopeptide biosurfactant by Kurthia gibsonii KH2 and their synergistic action in biodecolourisation of textile wastewater

Textile dyes are recalcitrant molecules and contain a high level of chemicals and colour which poses a serious challenge to surrounding environments. Therefore, this study aims to produce biosurfactant and investigate the synergistic action on decolourisation of textile dyes by the combination of bacteria and biosurfactant. An effective dye degrading strain and biosurfactant-producer, Kurthia gibsonii KH2, was isolated from textile wastewater using molasses as the only source of carbon and energy. The isolates were identified and screened for biosurfactant production using haemolytic activity, oil spreading technique, drop collapse test and emulsification index. Fourier Transform Infrared Spectrum (FTIR) and Thin Layer Chromatography (TLC) analyses were carried out to detect the type of biosurfactant. The effect of different physicochemical parameters on textile wastewater decolourisation was assessed within 24 h. The Kurthia gibsonii KH2 showed positive results for haemolytic activity, oil spreading technique, and drop collapse test. The emulsification test (E24) revealed that Kurthia gibsonii KH2 had a higher emulsification index of 63%. FTIR and TLC analyses indicated that the biosurfactant was a lipopeptide and was formed with a yield of 2 gL −1 . The synergistic activity of Kurthia gibsonii KH2 and lipopeptide biosurfactant resulted in decolourisation levels of 85% at 100 mg/L concentration and pH 7 was recorded at 168 h of incubation. The high attributes of these combinations and the phytotoxicity tests implied that the metabolites were less toxic, making it a promising option for the biodecolourisation and biodegradation of industrial textile wastewater and various environmental conditions. • Textile wastewater treatment using utilisation of microbial biocatalysts is vital. • The lipopeptide biosurfactant was derived from the bacteria Kurthia gibsonii KH2. • The strain showed synergistic action in textile dyes removal efficiency. • Decolorisation process was the dominant removal mechanism.

Suitability of Different Titanium Dioxide Nanotube Morphologies for Photocatalytic Water Treatment.

Photocatalysis has long been touted as one of the most promising technologies for environmental remediation. The ability of photocatalysts to degrade a host of different pollutants, especially recalcitrant molecules, is certainly appealing. Titanium dioxide (TiO2) has been used extensively for this purpose. Anodic oxidation allows for the synthesis of a highly ordered nanotubular structure with a high degree of tunability. In this study, a series of TiO2 arrays were synthesised using different electrolytes and different potentials. Mixed anatase-rutile photocatalysts with excellent wettability were achieved with all the experimental iterations. Under UVA light, all the materials showed significant photoactivity towards different organic pollutants. The nanotubes synthesised in the ethylene glycol-based electrolyte exhibited the best performance, with near complete degradation of all the pollutants. The antibacterial activity of this same material was similarly high, with extremely low bacterial survival rates. Increasing the voltage resulted in wider and longer nanotubes, characteristics which increase the level of photocatalytic activity. The ease of synthesis coupled with the excellent activity makes this a viable material that can be used in flat-plate reactors and that is suitable for photocatalytic water treatment.

Real effluents and fractionation in the supply of COD: Rapid adaptation and high efficiency to treat mine drainage combined with industrial by-products

The biological treatment of mine drainage (MD) using sulfate-reducing bacteria (SRB) is a technology in growing exploitation. The use of by-products as sources of electrons can make this treatment more environmentally and economically advantageous. However, the high chemical oxygen demand (COD) and the presence of recalcitrant molecules can lead to the accumulation of metabolic intermediates that acidify the system, thus interrupting the treatment. Besides, the adaptation of the inoculum to the establishment of sulfidogenesis with MD and by-product may be slow. This study aimed to investigate prompt adaptation and operation strategies that do not require additives to enable the sulfidogenic process to occur while maintaining a pH close to neutrality. The sources of electrons tested were trub (brewery residue) and crude glycerol – CG (residue from the biodiesel production). The inoculum from a methanogenic reactor was stored with a real MD for a month. The adapted inoculum was applied in a batch reactor for 168 h of hydraulic detention time, and promoted 75.8 ± 4.3% of sulfate removal from an MD with 3756.4 ± 258 mg.L−1 of sulfate using CG in a COD/SO42− ratio of 3 ratio. With higher initial substrate concentrations, acidification occurred and the treatment was interrupted. Using trub instead of CG, the acidification occurred at a COD/SO42− ratio of 3. Acidification was prevented and the best efficiencies in sulfate removal were obtained when the amount of substrate corresponding to COD/SO42− ratio of 3 was fractioned into equal parts and added over six days in the CG reactor. It was achieved 94.15 ± 1.76% of sulfate removal. With trub, the same procedure in which this COD was divided into seven parts, and resulted in a sulfate removal of 88.49 ± 1.02%. The removal of metals and metalloids were greater than 94.5% in all the systems in which the substrate supply was made fractionally, and the effluent generated presented alkalinity between 3370 and 4242 mg CaCO3.L−1, and pH between 6.8 and 7. The method of adaptation and operation applied allowed the realization of a MD treatment with quick establishment of sulfidogenesis and without the use of neutralizing additives. Finally, the effluent presented characteristics considered favorable for a later stage of post-treatment of the effluent with methane generation.

Ozonation as a pre-treatment of landfill leachate

Ozone is an oxidizing agent with a potential for removing complex molecules, including those of difficult microbiological decomposition, such as the molecules found in landfill leachates. This effluent presents high organic content, including recalcitrant molecules. Therefore, this study evaluated the efficiency of ozonation in the treatment of raw leachate at the Primavera landfill, located in Mato Grosso, Brazil. The experiments were carried out using the batch system. The leachate pH value was set at 7 and 10, and the contact times between the gas and the leachate were 20, 40, 60, 80, and 100 minutes. Throughout the study, we analyzed color, turbidity, pH value, chemical oxygen demand (COD), and ultraviolet absorbance at 254 nm (UV abs) of the leachate, both before and after ozonation. Results show that ozonation presented high removal of color, COD and UV abs when pH was 7. In contrast, turbidity removal was higher when the pH value was 10. Regarding contact time, we observed a high removal of color (between 80% and 90%) and UV abs (between 60% and 70%) at 40 minutes, depending on the pH value. Removal was also high for turbidity (approximately 75%) starting at 20 minutes with the pH value at 10, and at 70 minutes with pH at 7. The removal relation within all analyzed parameters (due to ozone consumption) decreased throughout the reaction time. Thus, we concluded that ozonation as a pre-treatment of leachate is indeed satisfactory because of its great capacity for organic material removal.

Supercritical water oxidation of recalcitrant acetaminophen with methanol, ethanol, n-propanol, isopropanol and glycerol as co-fuels

Pharmaceuticals are recalcitrant molecules that demand advanced treatment techniques for their complete elimination in wastewater streams. Supercritical water oxidation has been proved as an effective technology to remove the recalcitrant molecules from wastewater streams. Supercritical water oxidation of acetaminophen was performed in the presence of various co-fuels such as methanol, ethanol, n-propanol, isopropanol, and glycerol. The key operating parameters such as temperature (400–500 °C) and oxidation coefficient (OC: 1–3) have been varied to note total organic carbon (TOC) removal efficiency at different conditions. Temperature and OC showed a positive impact on the removal efficiency for all the co-fuels implemented. The addition of co-fuels has increased the free radicals that act on the organics and thereby enhanced TOC removal efficiency. Near-complete removal efficiencies (99.7%) were attained with ethanol and n-propanol at an operating temperature of 500 °C with an oxidation coefficient of 3. The gas composition analysis reflects the highest H2 volume fraction for ethanol followed by glycerol and n-propanol at the lowest supercritical temperature 400 °C and OC 1. However, with the rise in temperature (500 °C) and OC 3, the CO2 mole fraction increased confirming the acceleration of oxidation reactions.

Integrated Electro-Fenton and Membrane Bioreactor System for Matured Landfill Leachate Treatment

Abstract Most matured landfill leachate contains organic recalcitrant molecules that cannot be easily separated by biological processes alone. Integrating an advanced oxidation process (AOP) and a ...

Effect of Detritus Manipulation on Different Organic Matter Decompositions in Temperate Deciduous Forest Soils

Soil organic matter supply is mainly derived from plant litter. The early stages of litter degradation is a very dynamic process. Thus, its study is important for understanding litter degradation and the control factors of different biomes and ecosystems. In the frame of the Síkfőkút DIRT (Detritus Input and Removal Treatments) Project, the effect of organic matter treatment was studied on the rate of decomposition of organic matter by applying different kinds of organic materials (leaf and wood litter, green and rooibos tea material, and cellulose cotton wool). During long-term experiments, we intended to investigate how the different organic matter manipulations changed by the soil microbial community and how it affects the degradation of different quality organic matter in the soil. The important main purpose of the research was to investigate litter degradation and its main regulators, contributing to both current and future climate scenarios. According to our results, in the case of litter-doubling treatments, we experienced a greater loss of organic matter compared to the weight of the litter bags placed in the soil of organic matter-withdrawal treatments. Furthermore, based on our results, we found that the decomposition rate is influenced by litter quality (leaf and cellulose wool) that is to be decomposed and by the applied litter treatments depending on the time allowed for decomposition. A drier climate by slowing down the degradation processes and by increasing the proportion of recalcitrant molecules in the detritus may increase the turnover time, which may lead to an increase in soil organic carbon (SOC).

Molecular Evidence of Arsenic Mobility Linked to Biodegradable Organic Matter.

Molecular characteristics of natural organic matter (NOM) and their potential connections to arsenic enrichment processes remain poorly understood. Here, we examine dissolved organic matter (DOM) in groundwater and water-soluble organic matter (WSOM) in aquifer sediments being depth-matched with groundwater samples from a typical arid-semiarid basin (Hetao Basin, China) hosting high arsenic groundwater. We used Fourier transform ion cyclotron resonance mass spectrometry to determine molecular characteristics of DOM and WSOM and evaluate potential roles of biodegradable compounds in microbially mediated arsenic mobility at the molecular level. High-arsenic groundwater DOM was generally enriched in recalcitrant molecules (including lignins and aromatic structures). Although potential contribution of recalcitrant compounds to arsenic enrichment cannot be ruled out, preferential degradation of the labile molecules coupled with reduction of Fe(III) (oxyhydr)oxides seemed to dominate arsenic mobilization. Both the number and the intensity of biodegradable compounds (including aliphatic/proteins and carbohydrates) were higher in WSOM than those in DOM in depth-matched high-arsenic groundwater (arsenic >0.67 μmol/L or 50 μg/L). Groundwater arsenic concentration generally increased with the increase in the number and the intensity of unique biodegradable compounds (especially N-containing compounds) in WSOM at matched depths. Anoxic incubations of sediments and deionized water show that more arsenic and Fe(II) were released from aquifer sediments with greater numbers and intensities of consumed biodegradable compounds in WSOM (especially N-containing compounds), with a higher proportion of microbially derived compounds produced. These observations indicate that the biodegradation of aliphatic/proteins and carbohydrates (especially CHON formulas) in WSOM fueling the reductive dissolution of Fe(III) (oxyhydr)oxides predominantly promotes arsenic release from aquifer solids. Our unique data present a better understanding of arsenic mobilization shaped by microbial degradation of labile organic compounds in anoxic aquifers at the molecular level.

Degradation mechanism of tributyl phosphate by UV/H2O2 treatment and parameters optimization towards the design of a pilot reactor

ABSTRACT While activated sludge treatment is currently the preferred process for the removal of tributyl phosphate (TBP) at the mg.L−1 level, it is well known that this recalcitrant molecule is incompletely degraded, stimulating research into alternative approaches, such as advanced oxidation. The aim of this study was to characterize the degradation mechanism of TBP during ultraviolet/H2O2 treatment using 31P NMR, ionic chromatography and total organic carbon analysis. The effects of initial pH, amount of oxidant and pollutant concentration were also assessed using an experimental design approach. The results of this parametric study show that ultraviolet/H2O2 photo-oxidation efficiently degrades TBP at concentrations up to 600 mg.L−1, with >90% phosphate release and up to 95% removal of total organic carbon within 1 h. The data also show that the main reaction intermediates are short carboxylic acids, resulting from the released alkyl groups, meaning that an interesting application of this process may be to rapidly pre-treat industrial effluent upstream of activated sludge reactors.

Analysis of trace malachite green, crystal violet, and their metabolites in zebrafish by surface-coated probe nanoelectrospray ionization mass spectrometry

Malachite green (MG) and crystal violet (CV) are the typical triphenylmethane dyes, which are recalcitrant molecules exerting mutagenic and carcinogenic effects on living organisms. Characterization of the residues of MG, CV, and their metabolites in biological organisms is of importance, especially for in vivo and in situ characterization. In this study, a method for determination of trace MG, CV, and their leuco metabolites in zebrafish by surface-coated probe nanoelectrospray ionization mass spectrometry (SCP-nanoESI-MS) was developed. A microscale solid-phase microextraction (SPME) probe was developed and used for extraction and enrichment of trace MG, CV, and their leuco metabolites in zebrafish after exposure. After that, the loaded SPME probe was directly employed for nanoESI-MS analysis under ambient and open-air conditions. Under the optimum conditions, the method demonstrated good linearity, with correlation coefficient values (r2) no less than 0.9925. The limits of detection and quantification were 0.014–0.023 ng mL−1 and 0.046–0.077 ng mL−1, respectively. By using the proposed method, the bioaccumulation of MG and CV in zebrafish was investigated, and the distribution of MG, CV, and their leuco metabolites in different organs of zebrafish was studied. MG, CV, and their leuco metabolites were all found in zebrafish tissues including brain, muscle, heart, and kidney after exposure, with highest concentration in intestine followed in ovary.

Role of bacterivorous organisms on fungal-based systems for natural tannin degradation

Tannery wastewater presents high concentrations of organic load and pollutant recalcitrant molecules (e.g. tannins), which reduce the efficiency of biological treatment processes. Recent studies showed that several fungal species and strains are effective in the degradation of tannins. However, high bacterial load can negatively affect fungal growth, reducing system stability and degradation performances.The aim of the present study was to evaluate the effects of the introduction of bacterivorous grazers (ciliates and/or rotifers) in batch scale experiments using fungi to remove Tara tannin, i.e. to check the potential synergistic effect between fungi and bacterivorous grazers in the degradation of recalcitrant compounds. In this context, the ciliated grazers Paramecium calkinsi, Tetrahymena sp., Pseudovorticella sp., and the rotifer Lecane inermis, preliminary selected according to their ability to grow in a solution prepared with Tara tannin, were separately tested. Activated sludge, including a complex mixture of native grazers, was used as experimental control. The following parameters were monitored: bacterial load, number of grazers/mL and Soluble Chemical Oxygen Demand (SCOD). Colony Forming Unit (CFU)/grazers ratio was also calculated. Particular attention was paid to: i) bacterial load reduction and ii) enhancement of recalcitrant compounds degradation, and we observed that in all experimental conditions where grazers occurred bacterial load was significantly reduced and the system achieved a higher SCOD removal in a shorter time. Our findings provide useful insights for the stabilization of fungal-based systems in non-sterile conditions.

Low temperature design of titanium dioxide anatase materials decorated with cyanuric acid for formic acid photodegradation

The influence of cyanuric acid (CA) on the structural, textural, electronic, morphological properties and the photocatalytic activity of titanium dioxide materials (TNCA) were herein evaluated. TNCAs samples were prepared through the sol gel method. The novelty of this work that cyanuric acid; the so far most recalcitrant molecule, is used here as reservoir of nitrogen. The synthesis of TNCAs nanomaterials are performed at low temperature in presence of quaternary ammonium as co-catalyst for anatase growth. Samples were characterized by means of nitrogen adsorption-desorption isotherms at 77 K, X-ray diffraction (XRD), Infrared (ATR), Raman, diffuse reflectance ultraviolet-visible, photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic activities of TNCAs and their free counterpart nanomaterials were then evaluated in the photocatalytic degradation of formic acid (FA) as model molecule under UV.X-ray and Raman show success of anatase phase formation at low temperature without any post-calcination. IR-ATR analysis confirms CA grafting onto TiO2 identified by formation of vibration band between Ti and triazine. SEM mapping shows that C, O, Ti, and N are homogeneously distributed in the nanomaterial. Nitrogen adsorption-desorption measurements at 77 K show developed textural properties; the heat of N2 adsorption seems to be affected by CA loading. PL and UV-visible spectroscopies show simultaneously (i) electron trapping by the oxygen vacancy identified by Raman spectroscopy by redshift of Eg1 mode and (ii) the hole is confined by nitrogen. Therefore, the excited electron can move from TiO2 VB to the new sublevels initiated by the introduction of nitrogen which results in quenching of the photoluminescence intensity. The photocatalytic activity of the various TNCAs nanomaterials increases versus CA loading. The highest kLH of TNCA2 (5 wt%) could be explained by short migration time conjugated with lower bulk recombination of the photogenerated electron hole.

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Persistence of dissolved organic matter explained by molecular changes during its passage through soil

Dissolved organic matter affects fundamental biogeochemical processes in the soil such as nutrient cycling and organic matter storage. The current paradigm is that processing of dissolved organic matter converges to recalcitrant molecules (those that resist degradation) of low molecular mass and high molecular diversity through biotic and abiotic processes. Here we demonstrate that the molecular composition and properties of dissolved organic matter continuously change during soil passage and propose that this reflects a continual shifting of its sources. Using ultrahigh-resolution mass spectrometry and nuclear magnetic resonance spectroscopy, we studied the molecular changes of dissolved organic matter from the soil surface to 60 cm depth in 20 temperate grassland communities in soil type Eutric Fluvisol. Applying a semi-quantitative approach, we observed that plant-derived molecules were first broken down into molecules containing a large proportion of low-molecular-mass compounds. These low-molecular-mass compounds became less abundant during soil passage, whereas larger molecules, depleted in plant-related ligno-cellulosic structures, became more abundant. These findings indicate that the small plant-derived molecules were preferentially consumed by microorganisms and transformed into larger microbial-derived molecules. This suggests that dissolved organic matter is not intrinsically recalcitrant but instead persists in soil as a result of simultaneous consumption, transformation and formation. Dissolved organic matter is persistent in soil owing to continuous consumption and transformation rather than owing to its recalcitrant molecular properties, according to analyses of molecular changes of dissolved organic matter as it passes through soil.

Fate of Labile Organic Carbon in Paddy Soil Is Regulated by Microbial Ferric Iron Reduction.

Global paddy soil is the primary source of methane, a potent greenhouse gas. It is therefore highly important to understand the carbon cycling in paddy soil. Microbial reduction of iron, which is widely found in paddy soil, is likely coupled with the oxidation of dissolved organic matter (DOM) and suppresses methanogenesis. However, little is known about the biotransformation of small molecular DOM accumulated under flooded conditions and the effect of iron reduction on the biotransformation pathway. Here, we carried out anaerobic incubation experiments using field-collected samples amended with ferrihydrite and different short-chain fatty acids. Our results showed that less than 20% of short-chain fatty acids were mineralized and released to the atmosphere. Using Fourier transform ion cyclotron resonance mass spectrometry, we further found that a large number of recalcitrant molecules were produced during microbial consumption of these short-chain fatty acids. Moreover, the biotransformation efficiency of short-chain fatty acids decreased with the increasing length of carbon chains. Ferrihydrite addition promoted microbial assimilation of short-chain fatty acids as well as enhanced the activation and biotransformation of indigenous stable carbon in the soil replenished with formate. This study demonstrates the significance of ferrihydrite in the biotransformation of labile DOM and promotes a more comprehensive understanding of the coupling of iron reduction and carbon cycling in paddy soils.

Measuring the organic amendment properties of the liquid fraction of digestate

The liquid fraction (LF) of digestate has usually been proposed as a substitute for mineral fertilizers because of the presence of high N content, above all in easily available form (ammonia). The LF was reported to contain about 66% of dry matter from the digestate. This study reports the characterization of the organic carbon (OC) contained in the LF of digestates obtained from full scale plants by screw-press solid/liquid separation, to find out about their organic amendment properties. Results indicate that LF contains stable OC because of the concentration during anaerobic digestion of recalcitrant molecules, and that its biological stability, measured by oxygen uptake rate, was similar to that of compost, i.e. 40 ± 15 mg O2 g DM−1 20 h−1 and 41.1 ± 5.1 mg O2 g DM−1 20 h−1. 13C NMR indicated that LFs were similar each other and were constituted of recalcitrant Alkyl-C (34.82 ± 5.28% OC) derived from plant and fecal material, Aromatic-C (11.10 ± 2.2% OC) derived from lignin-like structures and O/N-alkyl (44.91 ± 4.87% OC) derived from cellulose/hemicelluloses and protein material. A simple simulation of the real C dosed by using LF as N-fertilizers indicated that amendment properties cannot be ignored. All these results seem to indicate good amendment properties for LFs, contrary to the common opinion.