Structural characterization of humic acids, extracted from sewage sludge during composting, by thermochemolysis–gas chromatography–mass spectrometry

Effect of municipal sludge-based biochar produced at different pyrolysis temperatures on humification and oxytetracycline degradation of pig manure composting

This study explored the influence of pyrolysis temperatures on the properties of municipal sludge-based biochar (MSB) and evaluated the impact of MSB on humification and oxytetracycline (OTC, a broad-spectrum antibiotic) degradation in pig manure composting. Three types of MSB were produced from sewage sludge pyrolyzed at 300 °C, 500 °C, and 700 °C, respectively. Results indicated that pyrolysis temperature adjusted the formation sequence of the functional groups in MSB, and higher pyrolysis temperatures enriched the aromaticity of the biochar and augmented the concentrations of humic precursor compounds. The MSB addition to pig manure composting enhanced the peak temperature and prolonged the thermophilic phase. Moreover, the MSB addition significantly increased the HI (humic acid/fulvic acid) values (1.6-2.57) compared with the control (1.28), with a more pronounced effect observed at higher biochar pyrolysis temperatures. Furthermore, the MSB reduced the half-life of OTC degradation (1.47-2.44 d) during composting, accelerating its degradation compared with the control (2.66 d). The study demonstrated that the MSB provided a substantial amount of humic precursor materials into the composting process while also expediting the degradation of organic matter, thereby enhancing the humification process. Moreover, the extended duration of the thermophilic phase accelerated the degradation of OTC and shortened its half-life. Notably, the MSB at 700 °C had the best performance compared with other MSBs.

New insights into the sustainable use of soluble straw humic substances for the remediation of multiple heavy metals in contaminated soil

This study addresses the research gap in understanding the differences in straw decomposition and variations in humic substances (HS) extracted from various treatment conditions. The aim is to explore the potential of soluble straw HS in remediating heavy metal pollution in soils. The study characterizes straw decomposition structures using scanning electron microscopy (SEM) and X-ray diffraction (XRD), while employing gel permeation chromatography (GPC) and fluorescence spectroscopy (EEM) to analyze the molecular weight and degree of humification of extracted straw HS. The removal efficiency of HS for heavy metals is assessed, with a focus on aerobic humic substances (AE-HS) showing the highest potential for heavy metal removal. Spectral analysis and mass spectrometry analysis reveal the role of phenolic compounds, carboxylic acids, and aromatic compounds in AE-HS, forming humates or complexes to remove heavy metals from contaminated soil. Notably, the optimized AE-HS achieved the highest removal efficiency of 96.18 %, 82.75 %, 60.43 %, and 41.66 % for cadmium, copper, zinc, and lead, respectively. This study provides new insights into the preparation of straw for use as a heavy metal remover and has implications for the use of straw humic substances in soil remediation.

Effect of inoculating thermophilic bacterial consortia on compost efficiency and quality

The objective of this study was to investigate the potential effects of thermophilic bacterial consortia on compost efficiency and quality. The application of bacterial consortia resulted in an earlier onset of the thermophilic period (THP), an increased upper temperature limit, and an extended duration of the THP by 3-5 days compared to the control group (CK). Microbial inoculation significantly improved the efficiency of organic matter degradation, as well as the content of water-soluble nitrogen (WSN) and humic acid-carbon (HAC). In the case of consortium Ⅱ inoculation (T2), the activities of cellobiohydrolase, β-glucosidase, and protease were increased by 81.81 %, 70.13 %, and 74.09 % at the THP respectively compared to CK. During the maturation stage, T2 also exhibited the highest PV, n/PIII, n value (1.33) and HAC content (39.53 mg·g-1), indicating that inoculation of consortium Ⅱ effectively promoted substrate maturity and product quality. Moreover, this inoculation effectively optimized the bacterial communities, particularly the growth of Planococcus, Chelatococcus, and Chelativorans during the composting, which were involved in carbon and nitrogen conversion or HAC synthesis. Carbohydrate and amino acid metabolism, and membrane transport were predominant in the consortia-inoculated samples, with an increased gene abundance, suggesting that inoculation contributed to promoting the biodegradation of lignocellulose and the exchange of favorable factors. In conclusion, this study demonstrates that inoculating thermophilic bacterial consortia has a positive impact on enhancing the resource utilization efficiency of agricultural waste and improving the quality of compost products.

Emerging disposal technologies of harmful phytoextraction biomass (HPB) containing heavy metals: A review

Phytoextraction is an effective approach for remediation of heavy metal (HM) contaminated soil. After the enhancement of phytoextraction efficiency has been systematically investigated and illustrated, the harmless disposal and value-added use of harmful phytoextraction biomass (HPB) become the major issue to be addressed. Therefore, in recent years, a large number of studies have focused on the disposal technologies for HPB, such as composting, enzyme hydrolysis, hydrothermal conversion, phyto-mining, and pyrolysis. The present review introduces their operation process, reaction parameters, economic/ecological advantages, and especially the migration and transformation behavior of HMs/biomass. Since plenty of plants possess comparable extraction abilities for HMs but with discrepancy constitution of biomass, the phytoextraction process should be combined with the disposal of HPB after harvested in the future, and thus a grading handling strategy for HPB is also presented. Hence, this review is significative for disposing of HPB and popularizing phytoextraction technologies.

Thermal Hydrolysis Pretreatment-Anaerobic Digestion Promotes Plant-Growth Biostimulants Production from Sewage Sludge by Upregulating Aromatic Amino Acids Transformation and Quinones Supply

Micromolecular plant-growth biostimulants (micro-PBs) production from sewage sludge is attracting increasing interest, as it is expected to enhance the fertilizing effect of sludge for land application. This study attempted to promote effective micro-PBs production from sewage sludge through thermal hydrolysis pretreatment-anaerobic digestion (THP-AD) and explore the underpinning regulation mechanisms. Results showed that the highest effective micro-PB production in digested sludge was achieved in THP(160 °C)-AD by day 12, with 80.73 mg/kg volatile solid (VS) of phytohormones and 417.75 mg/kg VS of allelochemicals, and these effective micro-PBs all originated from aromatic amino acids (AAAs). The metabolomic and metagenomic results revealed that, as compared with THP(120 °C)-AD and AD without THP, THP(160°C)-AD uniquely upregulated AAAs biosynthesis and consequently improved AAAs metabolism toward effective micro-PBs production. Further exploration of related microbial pathways and metabolites suggested that the upregulated AAAs biosynthesis in THP(160 °C)-AD in the early stage was partially attributed to the enhanced carbohydrate release. More importantly, the results showed that the amount of quinones, which probably facilitate energy generation via acting as electron-transfer mediators, was significantly positively correlated with the abundance of AAAs biosynthesis genes (R² = 0.93). Hence, the improved initial release and biosynthesis of quinones are critical in enhancing the AAAs biosynthesis in THP(160 °C)-AD. Moreover, the enhanced quinones supply and the consequent active AAAs transformation in THP(160 °C)-AD reinforced the humification process, highly supporting effective micro-PBs stabilization. The important roles of quinones in effective micro-PBs production and stabilization in sludge anaerobic digestion should be considered in technology development for micro-PBs recovery.

Optimization of tomato waste composting with integration of organic feedstock

Valorization of waste by composting converts organic waste into valuable organic supplements. Physicochemical characteristics of tomato waste (TW) limit the efficiency of the composting process. To overcome these challenges, different mixtures were investigated by integration of olive pumice (OP), sheep manure (SM), chicken manure (CM), and sawdust as bulking agents for the optimization of the composting process. Evaluations of the composting process and compost quality were carried out to measure the temperature profile, organic matter (OM) losses, concentrations of humic substances, and macro-nutriments. The results showed that the type and ratio of feedstock in the mixture influenced the temperature of the composting process. In mixtures with SM and OP, the temperature exceeded 55 °C for more than 2 weeks, ensuring hygienization. Additionally, phosphorus and potassium significantly increased when SM and CM were added to the composting mixture. The addition of OP increased the concentrations of humic acid-like carbon (C_HA) and fulvic acid-like carbon (C_FA). Higher content of humic substances was recorded when SM and OP were used as composting feedstock. Using SM in the mixture was found to be more efficient than CM and constitutes a suitable feedstock for composting of tomato waste, achieving successful co-operation of agronomic and animal farm sectors.

Effect of bamboo sphere amendment on the organic matter decomposition and humification of food waste composting

The aim of this study is to examine the effect of bamboo sphere on the organic matter decomposition and humification of food waste composting. Food waste composting were carried out on four treatments, namely control (CK), 3% (T1), 6% (T2) and 9% (T3) (w/w) bamboo sphere treatments. Results showed that adding bamboo sphere facilitated the organic matter decomposition and increased the seed germination index. The number of cells in T2 treatment was always the highest during the composting process. Furthermore, the final humic substances and humic acid contents increased by 41.08% and 68.3%, respectively, in 6% bamboo sphere treatment. Fourier transform infrared and excitation-emission matrix fluorescence spectroscopy analysis revealed that adding bamboo sphere accelerated the humification of composting with more aromatic structures and humic acid-like substances. GC-MS studies revealed that the compost products of 6% bamboo sphere treatment had more ring structures, and thus enhanced the humification.

Protein-derived structures determines the redox capacity of humic acids formed during hyperthermophilic composting

Humic acid (HA) in compost has received widespread attention for its high redox activity, which can mediate the degradation of organic pollution and the passivation of heavy metals in the environment. Hyperthermophilic composting (HTC) can accelerate HA formation. However, few studies have examined whether and how the structures of different organics affect the formation of the HA and HA redox structure at the molecular level in HTC. Detailed molecular information and the redox capacity (electron transfer capacity, ETC) of HA in HTC and thermophilic composting (TC) were characterized using pyrolysis gas chromatography/mass spectrometry and the electrochemical method, respectively. HTC promoted the formation of redox structure, leading to the improvement of the ETC of HA. Aromatics and N-containing compounds were mainly derived from protein components, and the rate at which they were transferred into HA was accelerated in HTC, while the relative abundance of lipids decreased. Partial least squares regression and correlation analysis demonstrated that protein-derived compounds were the key factor determining the HA redox capacity. Finally, partial least squares path modeling suggested that the influence mechanism of protein-derived structures on HA redox capacity might differ in HTC and TC. HTC may promote the relative abundance of N-containing components into the C-skeleton and accelerate the accumulation of the aromatic products, thereby improve the HA redox capacity. These findings provided new insight into how the redox capacity of the HA in compost could be improved and how compost products could be prepared for use in environmental remediation.

Bulk and water-extractable organic matter from compost: evaluation of the selective dissolution in water using infrared absorbance ratios

Land application of composts affects concentration and composition of dissolved organic matter (OM) which plays important roles in soil functioning and may have effects on spreading of environmental pollution. Linking between the composition of bulk compost OM and its water-soluble fraction may, therefore, allow better understanding and prediction of the environmental impact of compost added to soil. The objectives of this study were to (i) examine composition-based links between bulk compost OM and water-extractable OM (WEOM), and (ii) evaluate and quantify selectivity of bulk compost OM dissolution, based on infrared (IR) absorbing functional groups. For that, 8 different composts and their freeze-dried WEOMs were characterized by mid-IR transmission spectroscopy. Compositions of compost OM and of WEOM were characterized in terms of ratios (R) defined on the basis of both areas and heights of specific IR absorbance bands in relation to absorbance by aliphatic CH groups. A simple novel approach is suggested, whereby selective dissolution of compost OM components is quantified by relating the R values determined for WEOM to those associated with compost OM. Significant similarities of IR spectra found in a series of WEOMs (and, to a lesser extent, in a series of compost OMs) suggest significant contributions of OM carboxylic groups to various bands. IR absorbance of compost OM contributed by hydrophilic and, specifically, carboxyl and carboxylate groups, when related to absorbance by aliphatic CH groups, can be used for predicting the indices characterizing WEOM composition, such as IR absorbance-based R values and aromaticity estimated from specific UV absorbance.

Humification in extracellular polymeric substances (EPS) dominates methane release and EPS reconstruction during the sludge stabilization of high-solid anaerobic digestion

High-solid anaerobic digestion (HAD) can directly treat dewatered sewage sludge (total solid content ≥15%) with superior volume efficiency. Sludge stabilization during HAD is expected to achieve by throughout organic degradation and conversion towards methane-rich biogas release and humic formation. Sewage sludge is the combination of microbial zoogleas and theirs adsorption of organic and inorganic matter, in which the extracellular polymeric substances (EPS) account 60-80% of total sludge organic matter, inevitably participating most extracellular metabolic pathways. The interactions between EPS transformation and genetically annotated metabolic pathways were found in this research. In brief, noticing the highly cross-linked structures in EPS with major active components of humic substances (HS) and protein (PN), as PN hydrolysis and decomposition in EPS were enhanced in the high-solid anaerobic condition, the exposure of aromatic groups and sites in HS were considerable. HS release was the main factor shifting the electron exchange capacity and activity, which aided in energy metabolism of sludge microorganisms involved in redox reactions, especially the methanogenesis, thus in turn facilitating the PN degradation; Then, the screened humic groups and active protein derives might act as the beneficial precursors to regenerate neo-humic structures, whose significant bridging effect and signal role on stimulating amino acid biosynthesis, member transport and metallic complexation could further contribute to proteolytic condensation and EPS reconstruction. Hence, the in-depth sludge stabilization mechanism during HAD process was established for developing enlightening strategies.

Hyperthermophilic composting of sewage sludge accelerates humic acid formation: Elemental and spectroscopic evidence

Application of thermophilic composting (TC) is limited due to poor efficiency and long composting period. Hyperthermophilic composting (HTC) could effectively overcome this defect. Here, the transformation of humic acid (HA) in both HTC and TC was characterized and compared to investigate the roles of HTC toward accelerating the formation of HA. In HTC, the highest temperature was 96.6 °C, and the hyperthermophilic and thermophilic phases exceed 18 days. The degree of polymerization (DP) in HTC increased to 1.27 on day 27, while it only increased to 1.15 at the end of TC. The elemental composition of the HA in HTC showed higher O atomic content (36.3%) and lower C/N atomic ratio (6.5) compared with TC. These changes indicated that HTC could significantly accelerate oxidized and polycondensed reactions for HA formation, which resulted in the shortening of composting period to 27 days. The maximum fluorescence intensity (F_max) of humic-like components were achieved faster in HTC (F_max = 1649.9) than in TC (F_max = 1316.9), implying that HTC promoted the polycondensation of small molecular components to form HA with larger molecular weight and higher degree of aromatization. Two-dimensional FTIR correlation spectroscopy (2D-FTIR-COS) analysis demonstrated that HTC prevented the HA precursor from condensing before it was deeply oxidized, and increased the content of small molecules rich in carboxyl moieties. Based on the evolution of the molecular structure of HA, the level of oxidation of HA precursors was a key factor to determine the degree of polymerization and the degree of HA humification.

Physiological characteristics and toxin production of Microcystis aeruginosa (Cyanobacterium) in response to DOM in anaerobic digestion effluent

The ecological implications of livestock production intensification have received sustained attention across the globe. Anaerobic digestion is the main process for livestock waste treatment. However, the ecological consequences of dissolved organic matter originating from anaerobic digestion (AD-DOM) in eutrophic water bodies remain elusive. In this study, the physiological responses of a bloom-forming cyanobacterium, Microcystis aeruginosa, to AD-DOM were investigated. Moreover, the composition of AD-DOM was identified by using thermochemolysis followed by gas chromatography-mass spectrometry (GC-MS) analysis. The growth of M. aeruginosa FACHB905 was not sensitive to low levels (0.625-1.25%, V/V) of AD-DOM but was inhibited by high levels (2.5-5%, V/V) of AD-DOM, resulting from photoinhibition damage to photosystem II (PSII). The main target of AD-DOM in PSII was the electron accepting side (ψ₀) or the electron donor side (φ P₀), depending on time variables. The reactive oxygen species (ROS) level showed a positive correlation with AD-DOM addition; however, it was higher than that of the control for 3.75-5% AD-DOM on the 6th day. The intracellular microcystin contents (including MC-LR and Dha⁷-MC-LR) decreased in response to AD-DOM addition, but extracellular microcystin increased after 6 days of exposure. In addition, GC-MS detection showed that AD-DOM is mainly composed of lignin-derived aromatic compounds, alkanes/alkene, nitrogen-containing compounds, and sterols. The results presented in this study suggested that AD-DOM released from the livestock industry may play a subtle role in affecting harmful algal blooms through level-dependent variables. In addition, the ecological consequences of microcystin released by toxin-producing species under AD-DOM stress are still worth considering.

Chemical and microbiological responses of heavy metal contaminated sediment subject to washing using humic substances

Washing of contaminated soils or sediments using humic substances (HS) extracted either from source-rich materials or compost has been tested effective to remove various heavy metals. Nevertheless, the remaining chemical fractionation of metals and post-washing biological responses were not discussed in previous research. In this study, we used a HS extracted from green waste compost to wash off Cd, As, and Ni from a contaminated sediment, and evaluated the washing effect on sediment microbes by measuring a series of indexes with regard to microbial biomass and enzyme activities. Results showed that HS washing was more effective in removing the cationic metals Cd and Ni than the anionic metal As. The highest HS dose of 2000 mg L^-1 resulted in 24.5-, 33.1-, and 12-fold increases of removal for Cd, Ni, and As, respectively. The remaining Cd and As were found to migrate to less stable fractions, whereas the remaining Ni was dominantly found in the residual fraction. Increases of metal removal efficiency, microbial biomass, and dehydrogenase activity were found to correlate with the increase of HS concentrations. Increasing doses of HS slightly altered sediment pH to the lower range but did not cause any significant effect on microbial activities. The study proves that HS washing is indeed a more environmental-friendly strategy than many existing washing agents which have exerted various side effects on soil properties.

Influence of Ligneous Bulking Agents on the Complexation of Heavy Metals to Humic Substances Formed in Pig Manure Composting

In order to investigate the influence of different lignin sources on humic substance formation during composting, this study selected two lignin sources, including wood sawdust and maize straw, to be co-composted with pig manure. Humic substances (HS) were characterized based on their fluorescence characteristics and complexing behaviors with heavy metals. The results showed that lignin sources, especially wood sawdust, were more conducive in promoting the formation of humic acids (HAs) than inorganic matter. The fluorescence excitation-emission matrix spectra also proved the positive effects of lignin on the formation of HAs during the humification process. The binding capacities of HAs isolated from mature composts for Cu and Cd followed the order of WS-90 > MS-90 > I-90, indicating that organic bulking agents are superior at increasing the complexing capacity of HAs. This finding suggests that the co-composting of pig manure with ligneous bulking agents is more advantageous at reducing the environmental risk of heavy metals.

Humic substances from green waste compost: An effective washing agent for heavy metal (Cd, Ni) removal from contaminated sediments

In this study, humic substances (HS) selected from 8 composting groups (peanut straw, sesame straw, corn straw and deciduous leaves, with or without grape marc) were used to remove Cd and Ni from artificially contaminated sediments. Sesame straw compost appeared to have the highest removal capacity for heavy metals through a series comparison on Cd removal efficiency, yield of HS and fulvic acids (FA), and seed germination index. The selected sesame HS was further used to wash two contaminated sediments of varying properties (a clay type for sediment 1 and a silty loam for sediment 2). Batch desorption experiments were conducted to determine the optimum HS concentration, equilibrium time, pH, solid-to-liquid ratio, and washing frequency. Under optimum conditions, a triple washing removed 74.16% of Cd and 42.91% of Ni from sediment 1, and 86.88% of Cd and 43.84% of Ni from sediment 2, respectively, whereas a commercial FA only achieved half of the efficiency. After washing, both sediments were identified with increased contents of total organic matter total nitrogen and phosphorus. Therefore, HS from the sesame straw compost is a cost-effective, efficient and environmental-friendly washing agent to remove heavy metals from contaminated sediments.

The changes in carbon, nitrogen components and humic substances during organic-inorganic aerobic co-composting

In this article, the changes in carbon, nitrogen components, and humic substances during organic-inorganic aerobic co-composting, with adding biochar as an additive or not, were studied. Results showed that adding a certain amount of inorganic fertilizers had no adverse effects on the compost fermentation process. Biochar enhanced the temperature, pH, oxygen content in the compost piles and ultimately hastened the fermentation process. Biochar contributed to the decomposition of hemicellulose, cellulose, lignin and promoted compost humification. Adding biochar increased the contents of acid hydrolysis nitrogen, amino acid nitrogen, amino sugar nitrogen, unidentified organic nitrogen and decreased the content of ammonia organic nitrogen thus improved nitrogen transformation and reduced nitrogen loss. The addition of biochar increased the nutrients contents in mature composts. The amendment of 10-15% biochar by weight as an additive would be optimum for the co-composting of organic-inorganic materials. These results contributed to produce value-added composting fertilizers.

Effect of aromatic repolymerization of humic acid-like fraction on digestate phytotoxicity reduction during high-solid anaerobic digestion for stabilization treatment of sewage sludge

Humification plays an important role in the sewage sludge stabilization treatment and probably influences the end-product ecotoxicity, which are not fully understood for high-solid anaerobic digestion (AD) process. This study monitored the aromaticity degree of humic acid-like fraction (HA) and detected digestate phytotoxicity during a 48-d high-solid AD. Significant repolymerization of aromatic structures in HA. Electrical conductivity (EC) of digestate changed negatively with the aromaticity degree in HA, and the digestate with high EC had low seed germination index (SGI). A positive correlation between SGI and the aromaticity degree of HA was found. Aromatic repolymerization of HA supplies more aromatic electron-rich sites to form neo-humic polymers and to determine the distribution of organic and/or inorganic phytotoxic compounds; thus, aromatic repolymerization of HA may control the digestate phytotoxicity by reducing excessive salinity. The results showed the effect of HA repolymerization on digestate stabilization and phytotoxicity reduction during the high-solid AD process. The inadequate phytotoxicity reduction efficiency (SGI ≤ 17%) may be ascribed to unaccomplished HA repolymerization, creating a demand for humification intensification studies.

Effects of forest fire on the properties of soil and humic substances extracted from forest soil in Gunma, Japan

Increases in global wildfires and fire severity are expected to result from global warming. Severe wildfires not only burn surface vegetation but also affect forest soil. Humic substances play key roles in the transport of nutrients and the carbon cycle in terrestrial ecosystems. In this study, we evaluated the effects of forest fires on the chemical properties of fulvic acid (FA) and humic acid (HA) extracted from non-burned and burned forest soils in Gunma, Japan. The differential thermal analysis of FA indicated that the intensity of exothermic reaction peak at 400 °C was 2-fold higher than that from non-burned soil. Based on pyrolysis-gas chromatography-mass spectrometry analysis with tetramethyl ammonium hydroxide, the amount of pyrolysate compounds in FA from burnt soil was significantly lower than that in FA from non-burnt soil. Therefore, we can conclude that the forest fire caused the significant change in the properties of FA such as increasing the aromaticity and refractory. In addition, the concentration of dissolved organic carbon with low molecular weight in surface soil increased after forest fire. This study suggests that the denaturation of soil organic matter by wildfire can affect the carbon cycle in terrestrial ecosystems.

Impacts of delayed addition of N-rich and acidic substrates on nitrogen loss and compost quality during pig manure composting

Delayed addition of Nitrogen (N)-rich and acidic substrates was investigated to evaluate its effects on N loss and compost quality during the composting process. Three different delayed adding methods of N-rich (pig manure) and acidic substrates (phosphate fertilizer and rotten apples) were tested during the pig manure and wheat straw is composting. The results showed that delayed addition of pig manure and acidic materials led two temperature peaks, and the durations of two separate thermophilic phase were closely related to the amount of pig manure. Delayed addition reduced total N loss by up to 14% when using superphosphate as acidic substrates, and by up to 12% when using rotten apples as acidic substrates, which is mainly due to the decreased NH₃ emissions. At the end of composting, delayed the addition of pig manure caused a significant increase in the HS (humus substance) content, and the highest HS content was observed when 70% of the pig manure was applied at day 0 and the remaining 30% was applied on day 27. In the final compost, the GI in all treatments almost reached the maturity requirement by exceeding 80%. The results suggest that delayed addition of animal manure and acidic substrates could prevent the N loss during composting and improve the compost quality.

Role and multi-scale characterization of bamboo biochar during poultry manure aerobic composting

The objective of the present study was to study the changes in compost particle and its relationship with other physicochemical process during aerobic composting employing 5%, 10%, 20% or 0% biochar. Changes of physicochemical and biological parameters and gases emissions indicated that appropriate biochar addition improved both degradation rate and final degree of the organic matter and simultaneously reduced CO₂, CH₄, N₂O and NH₃ emissions. Beneficial properties like stability and high porosity of biochar could optimize composting environment, accelerate the process of composting and facilitate microbial growth during the thermophilic composting stage, with increases of 1.3×10¹⁰ to 1.5×10¹¹cfu/g. Analysis of microstructure characterization of the changes in compost particle indicated that biochar amended contributed to better degradation of compost particle with smaller sizes and a higher degree of looseness. Ultimately, 10% biochar addition optimized organic matter degradation, while reducing ammonia and greenhouse gas emissions and costs.

Assessment of mobility and bioavailability of mercury compounds in sewage sludge and composts

Content of heavy metals, including mercury, determines the method of management and disposal of sewage sludge. Excessive concentration of mercury in composts used as organic fertilizer may lead to accumulation of this element in soil and plant material. Fractionation of mercury in sewage sludge and composts provides a better understanding of the extent of mobility and bioavailability of the different mercury species and helps in more informed decision making on the application of sludge for agricultural purposes. The experimental setup comprises the composing process of the sewage sludge containing 13.1mgkg^-1 of the total mercury, performed in static reactors with forced aeration. In order to evaluate the bioavailability of mercury, its fractionation was performed in sewage sludge and composts during the process. An analytical procedure based on four-stage sequential extraction was applied to determine the mercury content in the ion exchange (water soluble and exchangeable Hg), base soluble (Hg bound to humic and fulvic acid), acid soluble (Hg bound to Fe/Mn oxides and carbonates) and oxidizable (Hg bound to organic matter and sulphide) fractions. The results showed that from 50.09% to 64.55% of the total mercury was strongly bound to organo-sulphur and inorganic sulphide; that during composting, increase of concentrations of mercury compounds strongly bound with organic matter and sulphides; and that mercury content in the base soluble and oxidizable fractions was strongly correlated with concentration of dissolved organic carbon in those fractions.

Characterization of lignocellulosic compositions' degradation during chicken manure composting with added biochar by phospholipid fatty acid (PLFA) and correlation analysis

Biorefractory high polymer lignocellulosic compositions may limit rapid composting and stable decomposition. Because their degradation during composting is not well understood, the correlation with microbial community profiles was assessed to reveal degradation mechanism of lignocellulosic compositions. Testing of chicken manure aerobic composting with added biochar was performed using phospholipid fatty acid (PLFA) and correlation analysis. Results demonstrated a good composting effect with good dynamic correlation between microbial characteristic (PLFA) and lignocellulosic compositions' degradation ratio. The prediction model for hemicellulose degradation ratio (R²=0.97, SEP=3.24) and the prediction model for cellulose degradation ratio (R³=0.94, SEP=3.09), built using PLFA 16:0-18:2ω6c and PLFA 18:2ω6c-18:3ω3 as the arguments had good predictive ability. Based on microbial analysis and quantitative characterization of the degradation ratio, the prediction models provided methodological support for delineating the mechanism of lignocellulosic compositions' degradation during chicken manure aerobic composting with added biochar.

Heavy metal variation and characterization change of dissolved organic matter (DOM) obtained from composting or vermicomposting pig manure amended with maize straw

A mixture of pig manure and maize straw was vermicomposted with Eisenia fetida or naturally composted for 60 days; basic parameters, heavy metal variation, dissolved organic matter (DOM) content, and its characterization were determined, aiming to explore different dynamics of DOM characterization and heavy metal variation during composting or vermicomposting. The results showed that vermicomposting led to higher pH, TC, and available P but lower EC, TN, available N, and available K in the substrate residues compared with natural composting; the total or available Cu/Zn content in the substrate residues similarly increased after composting or vermicomposting, but Cu was easily enriched in earthworm bodies and its intestinal vermicompost while vermicomposting enhanced the formation of dissolved Zn in DOM; moreover, much more fulvic and humic acid-like materials and much greater aromaticity were exhibited in DOM obtained from vermicomposting residues compared with DOM from composting residues, which may contribute to the variations of Cu/Zn enrichment in earthworms and its migration to the vermicomposting residues or its DOM.

Kinetics of organic matter removal and humification progress during sewage sludge composting

This study investigated the kinetics of organic matter (OM) removal and humification during composting of sewage sludge and lignocellulosic waste (wood chips, wheat straw, leaves) in an aerated bioreactor. Both OM degradation and humification (humic substances, HS, and humic acids, HA formation) proceeded according to 1. order kinetics. The rate constant of OM degradation was 0.196 d(-1), and the rate of OM degradation was 39.4 mg/g OM d. The kinetic constants of HS and HA formation were 0.044 d(-1) and 0.045 d(-1), whereas the rates of HS and HA formation were 3.46 mg C/g OM d and 3.24 mg C/g OM d, respectively. The concentration profiles of HS and HA indicated that humification occurred most intensively during the first 3 months of composting. The high content of HS (182 mg C/g OM) in the final product indicated that the compost could be used in soil remediation as a source of HS for treating soils highly contaminated with heavy metals.

Alkali-solubilized organic matter from sludge and its degradability in the anaerobic process

This study investigates alkali-solubilized dissolved organic matter (DOM) and its fate in the anaerobic treatment process. DOM was fractionated into high molecular weight (HMW) protein-like substances (PL), HMW saccharide-like substances (SL), low molecular weight (LMW) PL, LMW SL, and humic acid-like substances (HAL). The results indicate alkali-solubilized DOM is primarily composed of LMW PL, HMW SL, and HAL. Alkaline pretreatment improved the overall anaerobic degradability of DOM in sludge (removal efficiency of total DOM increased by 28.4%). However, certain DOM fractions (mainly HMW PL and HAL) exhibited low degradability during anaerobic treatment, primarily caused by the low degradability of aromatic groups (such as aromatic amine groups from tryptophan-like PL). Alkaline pretreatment also resulted in an increase of residual DOM, which is mainly composed of HAL (52.9%) and HMW SL (49.9%).

Feasibility of using humic substances from compost to remove heavy metals (Cd, Cu, Ni, Pb, Zn) from contaminated soil aged for different periods of time

There is a need for inexpensive, readily-available and environmentally-friendly soil washing agents to remediate polluted soils. Thus, batch washing experiments were performed to evaluate the feasibility of using a solution of humic substances (HS) extracted from compost as a washing agent for simultaneous removal of Cu, Cd, Zn, Pb and Ni from artificially contaminated soils aged for 1 month, 12 months and 24 months. The efficiency of metal removal in single and multiple washings and kinetic constants (equilibrium metal concentration qe and rate constant k from the second-order kinetic equation) were determined. On average, triple washing removed twice as much metal as that removed with a single washing. At pH 7 and a HS concentration of 2.2 g C L(-1), metal removal from all soils decreased in this order: Cd (79.1-82.6%) > Cu (51.5-71.8%) > Pb (44.8-47.6%) > Ni (35.4-46.1%) > Zn (27.9-35.8%). However, based on qe (mg kg(-1)), metal removal was in this order: Pb > Zn ≈ Cu > Ni > Cd. This difference was due to different concentrations of metals, which is typical for multi-metal contaminated soils. Regardless of washing mode, removal of Cd and Pb was not affected by soil age, whereas removal of Cu, Ni and Zn was higher in soils that had been aged for a shorter time. These results indicate that HS are suitable for remediating soil contaminated with multiple heavy metals in extremely high concentrations.

Humic substances from sewage sludge compost as washing agent effectively remove Cu and Cd from soil

Although commercially available biosurfactants are environmentally friendly and effectively remove heavy metals from soil, they are costly. Therefore, this study investigated whether inexpensive humic substances (HS) from sewage sludge compost could effectively remove copper (Cu) and cadmium (Cd) from highly contaminated sandy clay loam (S1) and clay (S2). The optimum HS concentration and pH were determined, as well process kinetics. Under optimum conditions, a single washing removed 80.7% of Cu and 69.1% of Cd from S1, and 53.2% and 36.5%, respectively, from S2. Triple washing increased removal from S1 to almost 100% for both metals, and to 83.2% of Cu and 88.9% of Cd from S2. Triple washing lowered the potential ecological risk (Er(i)) of the soils, especially the risk from Cd. HS substances show potential for treating soils highly contaminated with heavy metals, and HS from other sources should be tested with these and other contaminants.

The change of organic matter in sewage sludge composting and its influence on the adsorption of pentachlorophenol (PCP)

Due to the abundance of organic matter in compost, the addition of compost to soil can promote the adsorption of pesticides. However, few studies have examined the influence of the composting duration on the organic matter (OM) transformation and adsorption capacity of the compost. In this study, a mixture of sewage sludge and straw was composted, and then the physicochemical properties of various OM were studied. Additionally, the sorption capacities of humic acid (HA), humin (HM), humic acid + humin, and fulvic acid (FA) + humic acid + humin extracted from composts of different stages toward pentachlorophenol (PCP) were compared. The sorption data can be well-described by the Freundlich model, and the sorption capacity of PCP on HM is the strongest of all organic components. After 120 days of composting, the sorption abilities of HA and HM increased by 54.76 and 36.73%, respectively, which corresponds with increases in the aromatization degree, BET specific area, and pore volume and with a decrease in acid functional groups. The sorption ability of HA and HM increased by 54.76 and 36.73% due to the increase of the aromatization degree. However, the sorption capacity of the compost decreased by 51.2%, which resulted from a decrease in total organic matter content and from the interaction between organic components in composts. This could be verified by the sequence of the sorption capacity: HM > HM + HA > HM + HA + FA > HA. The contribution of humus to the sorption of PCP onto compost is approximately 41 to 55%, and it increases with composting time. Therefore, it is possible that other components are present that affect the adsorption of PCP on composts.

Organic matter humification in vermifiltration process for domestic sewage sludge treatment by excitation-emission matrix fluorescence and Fourier transform infrared spectroscopy

Performance of a conventional biofilter (BF) and two vermifilters (VFs, different heights) containing earthworms was investigated for domestic sewage sludge (DWS) treatment. Humic-acid like (HAL) fraction isolated from the influent sludge (IS) and effluent sludge of BF (ESBF) and VFs (ESVFs) were determined the elemental and functional composition, and structural characteristics using various analytical approaches. Results showed that performance of DWS treatment in the VFs was preferable to that in the BF. With respect to IS-HAL and ESBF-HAL, ESVFs-HAL had low C, H and N contents and C/O ratio, and high O, carboxyl and phenolic OH group contents, and C/N, C/H and E4/E6 ratios, and large molecular weight. The excitation-emission (Ex/Em) matrix spectra revealed that an additional peak was found at Ex/Em wavelength pairs of 345/435 nm in ESVFs-HAL. Further, Fourier transform infrared spectra showed that vermifiltration led to the loss of aliphatic materials and carbohydrates, and the enrichment of carbonyl and phenolic OH groups in HAL fractions. Additionally, the increase in VF height seemed to accelerate humification degree of organic matter in the effluent sludge. In summary, vermifiltration is alternate technology for transformation of organic matter into humic substances, and thus improves quality of DWS as soil organic fertilizer.

pH influence on the complexation site of Al(III) with protocatechuic acid. A spectroscopic and theoretical approach

Electronic spectroscopy techniques with the aid of quantum chemical calculations, and notably the Time-Dependent Density Functional Theory, can be used to probe the structure of metal complexes in solution. Here, we report the characterization of Al(III)-protocatechuate in aqueous solution, at pH=6.5. The exploitation of the UV-vis spectra of the system by chemometric methods highlights the formation of a single complex of stoichiometry 1:1. From different structural hypothesis, the comparison of theoretical and experimental spectra shows that Al(III) forms a monodentate complex with the carboxylate function. This hypothesis is confirmed by the calculation of the complexation reaction pathways. Previous studies report the formation of a chelate involving the ortho-dihydroxyl group, at pH=3.5. These results illustrate the important dependence of the protonation state of the carboxylic function on the Al(III) fixation site on the studied ligand.

Evaluation of DNA extraction methods for freshwater eukaryotic microalgae

The use of molecular methods to investigate microalgal communities of natural and engineered freshwater resources is in its infancy, with the majority of previous studies carried out by microscopy. Inefficient or differential DNA extraction of microalgal community members can lead to bias in downstream community analysis. Three commercially available DNA extraction kits have been tested on a range of pure culture freshwater algal species with diverse cell walls and mixed algal cultures taken from eutrophic waste stabilization ponds (WSP). DNA yield and quality were evaluated, along with DNA suitability for amplification of 18S rRNA gene fragments by polymerase chain reaction (PCR). QiagenDNeasy(®) Blood and Tissue kit (QBT), was found to give the highest DNA yields and quality. Denaturant Gradient Gel Electrophoresis (DGGE) was used to assess the diversity of communities from which DNA was extracted. No significant differences were found among kits when assessing diversity. QBT is recommended for use with WSP samples, a conclusion confirmed by further testing on communities from two tropical WSP systems. The fixation of microalgal samples with ethanol prior to DNA extraction was found to reduce yields as well as diversity and is not recommended.

Biological pretreatment for production of lignocellulosic biofuel

Lignocellulosic biomass was submitted to a biological pretreatment prior to a catalytic hydroliquefaction in order to produce biofuel. The biodegradation process was conducted over 3 months in a reactor under controlled conditions. During the biodegradation process the organic matter was characterised and its evolution was correlated with physico-chemical parameters. In parallel with the analysis of the lipidic fraction, analytical pyrolysis was used to monitor bacterial activity. The alterations of branched to linear fatty acids ratio and of mono- to diacids ratio were compared when determined by thermochemolysis and observed in the directly extractable lipids. The evolution of the phytol to the corresponding isoprenoic ketone ratio was observed to be dependent on the desorption technique since it decreases using headspace while it increases using pyrolysis. "Humic"/"fulvic acids" ratio, infrared spectroscopy and thermodifferential analysis were used to determine the degree of OM complexification.

Organic matter transformations and kinetics during sewage sludge composting in a two-stage system

The use of different proportions of rape straw and grass as amendments in the composting of dewatered sewage sludge from a municipal wastewater treatment plant was tested in a two-stage system (first stage, an aerated bioreactor and second stage, a periodically turned windrow). The composition of feedstock affected the temperature and organic matter degradation in the bioreactor and the formation of humic substances, especially humic acids (HA), during compost maturation in the windrow. The total HA content (the sum of labile and stable HA) increased according to first-order kinetics, whereas labile HA content was constant and did not exceed 12% of total HA. ΔlogK of 1.0-1.1 indicated that HA was of R-type, indicating a low degree of humification. Temperature during composting was the main factor affecting polymerization of fulvic acids to HA and confirmed the value of the degree of polymerization, which increased only when thermophilic conditions were obtained.

Optimization of conditions for thermal treatment of rice bran using an accelerator including an organo-iron compound

A method for thermal conversion of raw organic waste (ROW) to a compost-like material (CLM) with higher levels of unsaturated carbohydrates, nitrogen- and oxygen-containing compounds was developed, in which rice bran and an organo-iron compound were employed as a model ROW and the accelerator, respectively. To evaluate the qualities of CLMs, organic substances of an acid insoluble fraction of alkaline extracts (AIAEs) from a CLM were structurally characterized by elemental analysis, pyrolysis-gas chromatography/mass spectrometry and FT-IR. The levels of unsaturated carbohydrates, and nitrogen- and oxygen-containing compounds in the CLM samples were increased by long-term treatment (60°C for 5 days, 170°C for 3 days). In particular, the high lipid content of the AIAEs, which was indicative of inadequate digestion of CLM components, was dramatically reduced in the presence of the accelerator.

Compositional and functional features of humic acid-like fractions from vermicomposting of sewage sludge and cow dung

The chemical changes occurring in five different substrates of sewage sludge spiked with different proportions of cow dung after vermicomposting with Eisenia foetida for 90 days were investigated. Their humic acid-like (HAL) fractions were isolated to determine the elemental and functional composition, and structural and functional characteristics using ultraviolet/visible, Fourier transform infrared (FT-IR) and fluorescence spectroscopies and scanning electron microscopy. After vermicomposting, the total organic C and C/N ratio decreased, and the total extractable C and humic acid (HA) C increased in all substrates. In the HAL fractions, the C and H contents, C/N and C/O and aliphatic structures, proteinaceous components and carbohydrates decreased, while the O and N and acidic functional group contents and C/H ratio, aromaticity and polycondensation structures increased. Further, the results suggest that the addition of cow dung to sewage sludge could improve the quality of organic matter humification of the substrates. The structures of HAL fractions in vermicomposts resembled those typical of soil HA, especially the vermicompost of cow dung alone. Scanning electron microscopy showed the microstructure of HAL fraction in final product became close-grained and lumpy. Overall results indicate that vermicomposting was an efficient technology for promoting organic matter (OM) humification in sewage sludge and cow dung alone, as well as in mixtures of both materials, improving their quality and environmental safety as a soil OM resource for utilization as soil amendments.

Evaluation of the maturity of organic waste composts

Olive-mill wastes represent a significant environmental problem in Mediterranean areas due to their significant production during a short period of time. Their high polyphenol, lipid and organic acid concentrations make them phytotoxic wastes. Composting is one of the technologies used for the valorization of those wastes, producing a fertilizer useful for poor soils. The present study is an attempt to elaborate upon organic matter transformations and define the parameters for product maturity by adapting chemical and spectroscopic methods during composting. The aim of this work was to study the changes involved in the composting process of four piles during 200 days, and follow up the maturity of the final product during composting. Fourier transform infrared (FTIR) spectroscopy has been proven to be an appropriate analytical method for the qualitative assessment of compost stability. FTIR spectroscopy results revealed enrichment in aromatic structures and a degradation of the aliphatic and alcoholic structures indicating stabilization of the final compost. The results showed that stability of the final product was reached after 7 months of composting. The phytotoxic effects of olive mill wastes and animal manures was assessed by germination index. Indeed, the germination indices of piles 1, 2, 3 and 4 reached 131.31%, 72%, 90.56%, and 105.37%, respectively, at the end of the process. This demonstrated the absence of phytotoxicity in the majority of mature composts.

Structural study of humic acids during composting of activated sludge-green waste: elemental analysis, FTIR and 13C NMR

The humic acids extracted from a compost of activated sludge at different stages of maturity were characterized by various chemical techniques. Elemental analysis showed the reduction of H, and the H/C and C/N ratios and an increase in the proportion of N and S. At the end of composting C% and O% presented the same values as initially, although they increased in the intermediate stage. Based on the ratios of FTIR absorbance it was shown that the end product was enriched in etherified and peptidic compounds absorbing at 1384, 1034 and 1544 cm(-1). The alkyl and other N-rich and oxidized recalcitrant structures compose the new humic polymers produced during composting. In principal components analysis, the first axis, PC1: 49.75% considers the variability between structures in decomposition from the other parameters that concern the stable new humic polymers formed after composting. PC2 (40.5%) shows a negative correlation between (aromatic carbon, FA level) and (aliphatic carbon, HA level) during composting.

Stability and maturity of a green waste and biowaste compost assessed on the basis of a molecular study using spectroscopy, thermal analysis, thermodesorption and thermochemolysis

The organic matter (OM) of a green waste and bio waste compost was characterised over 8months and the observed evolution was correlated with physico-chemical parameters (temperature, pH, carbon content, C/N ratio). Thermochemolysis and thermodesorption were used to monitor bacterial activity (stability) whereas diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) and thermodifferential analysis (TDA) permitted to determine the degree of OM humification (maturity). DRIFT spectroscopy and TDA provide two indicators of maturity since, with these two techniques, the signals associated with the biodegradable organic matter decrease relatively to the signals associated with refractory organic matter. This increase in R(TG) and R(IR) ratios between aromatic to aliphatic signals constitutes a proof for OM complexification. It correlates with humic acids/fulvic acids ratio known to be a maturity index. Pyrolysates are mainly constituted of lignin moieties, terpenoids, nitrogen containing compounds, carbohydrates (furanosic moiety), mono- and diacids (as methyl esters), and methoxyesters. The R(branched/linear) ratio between branched to linear acids traduces the evolution of the bacterial activity during composting. Moreover the R(di/mono) ratio between aliphatic mono to diacids correlates with the latter showing that diacids can occur from the biological oxidation of monoacids. These two ratios determined by thermochemolysis are useful to monitor the stability of compost. VOC, observed by thermodesorption are mainly constituted of terpenes, light acids, aldehydes and ketone. An unexpected result was obtained since the amount of phytol increases relatively to the isoprenoid ketone considered to originate from the latter.

Occurrence and composition of extracellular lipids and polysaccharides in a full-scale membrane bioreactor

The aim of this study was to characterize the polysaccharides and lipid fractions of membrane foulants in a full-scale membrane bioreactor (MBR) treating municipal wastewater. Both of these polymeric compounds are major components of bacterial lipopolysaccharides and are impacting membrane fouling; however most of the data so far have been collected by determining sum parameters rather than the detailed composition of these polymers. Photometric analysis of sugars showed that uronic acids (glucuronic, mannuronic and galacturonic acid) as common units of bacterial polysaccharides accounted for 8% (w/w) of extracellular polymeric substances (EPS) in activated sludge flocs. Further the so-called polysaccharide peak of EPS, with a molecular weight >10 kDa according to size exclusion chromatography, was proven to contain bacterial sugar units as shown by high resolution LC-MS. Interestingly, only traces of uronic acids could be detected in EPS of the membrane fouling layer. A far more dramatic enrichment in the fouling layer was revealed for the lipid fraction of EPS, which was determined as fatty acid methyl esters by GC-MS. The weight percentage of fatty acids in EPS extracted from fouled ultrafiltration membranes was much higher (10%) than in the activated sludge itself (1-3%). The fatty acids accumulated on the membrane fouling layer were obviously not only of microbial origin (C16:0, C18:0) but also derived from the raw wastewater itself (C9:0). Hydrophobic interaction of lipids with the PVDF (polyvinylidene fluoride) membrane material therefore seems a plausible explanation for the observed fouling phenomenon. The results suggest that fatty acids from bacterial lipopolysaccharides as well as from synthetic sources are of much higher relevance to membrane fouling than previously assumed.

Application of three methods used for the evaluation of polycyclic aromatic hydrocarbons (PAHs) bioaccessibility for sewage sludge composting

Three chemical approaches were compared to assess the bioaccessibility of PAHs during four sewage sludge composting. In the present study solid phase extraction with Tenax-TA and two non-exhaustive/mild-solvent extraction techniques with n-butanol (BtOH) and hydroxypropyl[beta]cyclodextrin (HPCD) have been applied. The content of the PAHs sum in individual sludges ranged from 2.83 to 9.95 mg/kg. Mainly 4-ring PAHs predominated in all sludges. The content of the bioaccessible fraction of PAHs determined using the BtOH and HPCD methods was usually twice higher than with the use of Tenax-TA adsorbent. The share of the bioaccessible fraction depended on the method applied and sewage sludge type. In the case of the PAH sums it ranged from 28.1% to 54.5% (Tenax-TA), from 25.7% to 80.9% (BtOH) and from 60.2% to 83.5% (HPCD). As a result of composting, the share of the bioaccessible fraction decreased by about 50% in most of the sludges examined. The reliable prediction of individual PAHs losses was observed for many of the PAHs; however, for a number of them, this was confirmed in more than two of the sludges examined.

Physico-chemical analysis of tannery solid waste and structural characterization of its isolated humic acids after composting

In Marrakech, solid by-products from tanneries are highly polluting, generating large amounts of nitrogenous and organic matter. In the present study composting is tested as a cost-effective method for waste management to overcome many of the environmental hazards and produce a stable, rich material for soil fertilization. Two composting trials were conducted after neutralization by ammonia or lime. The aim of the neutralization was to avoid the antimicrobial effects of the acidity in the tannery waste, thus ensuring correct composting. Different techniques such as elemental analysis and 13C NMR spectroscopy were applied to analyse humic acids isolated from raw and composted materials, and to monitor the process of tannery waste composting, and the stability and maturity of the final product according to the means of neutralization. Comparison of data showed similar behaviour in both trials, but the composting process appeared to be more complete following neutralization with lime. The C, H and N content decreased, while the O increased. The FTIR and 13C NMR spectra show the decrease of aliphatic compounds demonstrated by the reduction of absorbance around 2922cm(-1) and of the resonance in the C-alkyl area around 0-55ppm. The humic acids newly formed during composting were richer in the O-N alkyl and oxidized aromatic structures that increased almost twofold on composting after neutralization with lime. The first principal component axis PC1 (54%) separated C-aliphatic, C-carboxylic and other less stable and less polycondensed compounds such as polyphenols from the more polycondensed O-N alkyl and oxidized C-aromatic compounds.

Structural study of the fulvic fraction during composting of activated sludge-plant matter: elemental analysis, FTIR and 13C NMR

The starting fulvic structures isolated from an initial mixture of activated sludge and plant matter presented abundant peptide structures and hydrocarbons that absorb in FTIR spectra around (1650 and 1560 cm(-1)) and 1072 cm(-1), respectively. They also present a high resonance signal in the O- and N-alkyl areas of (13)C NMR spectra. As composting proceeded, some changes led to the formation of the molecular structures of fulvic fraction as demonstrated by a decrease of intensity of compounds absorbing around 1072 cm(-1) and an increase of those absorbing around 1140 cm(-1). The resonance of O- and N-substituted alkyl carbon also decreased from 55.7% to 33.8%, with an increase in the intensity of aromatic carbons, alkyls and carboxyls. These data indicate that the microbial community that developed during composting used polysaccharides as an energy source, structures which are supplied in abundance in the initial material. The fulvic fraction of the final compost is much richer in aromatic structures and aliphatic ethers/esters, which are most likely preserved from the original material but probably also synthesized through the microbial activities. The occurrence of alkyl ethers/esters at the end of composting is demonstrated by strong absorbance around 1140 cm(-1) in the FTIR spectra and large peaks at 32 and 174 ppm in the NMR spectra. These structures could also be produced following the creation of ether/ester bonds during the humification process.

Characterization of humic and fulvic acids extracted from landfill by elemental composition, 13C CP/MAS NMR and TMAH-Py-GC/MS

Humic acid (HA) and fulvic acid (FA) extracted from landfills at different landfill ages were characterized by elemental composition, (13)C CP/MAS NMR, and TMAH-Py-GC/MS. The elemental composition analysis revealed high O/C and low H/C ratios in the FA, indicating a high proportion of O-alkyl and carboxylic acids in the FA. The analytical results of (13)C CP/MAS NMR suggested that there were more oxygenated aliphatic carbons and fewer aromatic carbons in FA than in HA. The Py-GC/MS products showed that the HA and FA extracted from the refuse in the landfill were mainly composed of various lignin-derived compounds. Oxidized aromatic acid derivatives originated from the oxidation of side-chains of lignin-like compounds, and this process played a significant role in the process of HA and FA formation in the landfill. All of the results demonstrated that the degree of humification increased with landfill age.