Humic-like Acids Research Articles

Characteristics of humic-like acid of <I>Aphodius</I>-processed cow manure and natural cow manure compost

分别用焦磷酸钠和氢氧化钠浸提新鲜牛粪、蜉金龟堆肥(APCM)和自然堆肥(腐熟牛粪)产物中的类胡敏酸, 采用元素组成、红外光谱及差热分析研究了其结构特征。元素分析结果表明, 蜉金龟堆肥焦磷酸钠浸提物--类胡敏酸(NaHLA)的芳香性低于新鲜牛粪和自然堆肥, 而碳水化合物及氮元素含量增加。蜉金龟堆肥氢氧化钠浸提物--类胡敏酸(PAHLA)的碳水化合物和氮元素含量也高于新鲜牛粪和自然堆肥, 而自然堆肥PAHLA的芳香性略低于新鲜牛粪和蜉金龟堆肥。红外光谱分析结果表明, 与自然堆肥NaHLA相比, 蜉金龟堆肥NaHLA中羧酸脂类化合物、酮类化合物、脂肪族化合物及碳水化合物有所增加。与新鲜牛粪PAHLA相比, 蜉金龟堆肥和自然堆肥PAHLA的碳水化合物、脂肪族化合物、酚类化合物及纤维素酯类减少, 同时蜉金龟堆肥PAHLA的酰胺化合物在蜉金龟消化过程中被其吸收。差热分析结果表明, 自然堆肥NaHLA的热稳定性高 于新鲜牛粪和蜉金龟堆肥, 而蜉金龟堆肥NaHLA的脂族化合物、外围官能团和分子内部芳香结构含量较高, 分子结构较复杂。蜉金龟堆肥PAHLA存在两个放热峰, 而新鲜牛粪和自然堆肥的中温放热峰消失。综上, 蜉金龟堆肥和自然堆肥采用两种提取液浸提出类胡敏酸的结构特征存在差异性。

Influence of the composition of the initial mixtures on the chemical composition, physicochemical properties and humic-like substances content of composts

The influence of the proportion of C- and N-rich raw materials (initial C/N ratio) and bulking agent on the chemical functional groups composition, humic-like substances (HS-like) content and physicochemical properties of composts was assessed. To achieve these goals, seven initial mixtures (BA1–6 and C1) of dog food (N-rich raw material) were composted with wheat flour (C-rich raw material). Composts were analyzed in terms of chemical functional groups, physicochemical, maturity and stability parameters.The C-rich raw material favored the formation of oxidized organic matter (OM) during the composting process, as suggested by the variation of the ratios of the peaks intensity of FT-IR spectra, corresponding to a decrease of the polysaccharides and an increase of aromatic and carboxyl-containing compounds. However, although with high proportion of C-rich raw material, mixtures with low initial C/N seems to have favored the accumulation of partially oxidized OM, which may have contributed to high electrical conductivity values in the final composts. Therefore, although favoring the partial transformation of OM into stabilized HS-like, initial mixtures with high proportion of C-rich raw material but with low initial C/N led to unstable composts.On the other hand, as long as a high percentage of bulking agent was used to promote the structure of biomass and consequently improve of the aeration conditions, low initial C/N was not a limiting factor of OM oxidation into extractable stabilized humic-like acids.

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 345/435nm 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.

Surrogate descriptors of C-storage processes on crusted semiarid ecosystems

Arid and semiarid crusted ecosystems occupy a large extent of the Earth's surface. In these ecosystems there is a delicate balance between C sequestration and biodegradation that could easily be altered due to human disturbance or global warming. These environments are characterized by the presence of biological soil crusts (BSCs) coexisting with shrubs in the interspaces. BSCs play an important role in the C-cycle in arid and semiarid areas, but there has been little research regarding C-storage in crusted soils. In this research, representative BSCs were studied in three different crusted semiarid ecosystems in Southern Spain. Chemical fractionation and characterization of the organic matter in BSCs and underlying soils were undertaken to compare the total amount and quality of humic substances and find surrogate indicators of the soil organic matter quality. After isolating the major organic fractions (particulate fraction, humic acid-like (HA) and fulvic acid (FA)), the macromolecular, HA fraction was studied by derivative visible spectroscopy and resolution-enhanced infrared (IR) spectroscopy. Our results show quantitative differences in organic matter fractions, in agreement with the structural characteristics of the HA-type substances. The more stable crusted ecosystem with more evolved vegetation cover tend to be associated with HAs with broadband IR profiles, high optical density and macromolecular condensation and presence of polycyclic fungal biomarker compounds. In contrast, in the crusted ecosystem with very low or almost absent vascular vegetation cover, the C sequestration depends almost exclusively on the activity of crust-inhabiting organisms. It is suggested that the organic matter in BSCs shares characteristics with aquatic humic matter derived from non-lignified plants, including structurally complex HA-type substances which may have been originated by abiotic condensation of unsaturated lipids and/or diagenetic alteration of aliphatic biomacromolecules. Although these humification mechanisms have not been extensively studied in terrestrial soils they may be very active mechanisms for C sequestration in some types of crusted ecosystems. In particular, the spectroscopic characteristics in the visible and IR ranges of the crust-isolated HA-type substances provide the above-indicated biogeochemical proxies informing on the organic matter stability and quality and their bearing on the potential of crusted ecosystems for maintaining their properties after external disturbance.

Thermal treatment of rice bran by portion-wise addition in the presence of an organo-iron catalyst

For raw organic wastes (ROWs) that are produced on a daily basis, a thermal treatment using an organo-iron catalyst with the ROW added in portion was examined for conversion to compost-like materials (CLMs). The mixture of initial materials (rice bran as a model ROW, red loam as a bulking agent, and an organo-iron catalyst) was incubated at 60 °C for 5 days. It was then heated at 170 °C for 8 h, and small portions of a mixture of rice bran and catalyst were added. This process was repeated a total of 45 times. The qualities of the CLMs were evaluated, based on the degree of humification of humic-like acids (HLAs) that were contained in the products. Thus, the HLAs were extracted from the prepared CLMs, and the levels of unsaturated carbons and oxygen- and nitrogen-containing compounds were analyzed and used as indices of the degree of humification. The influence of the initial materials on the degree of humification of the HLAs was investigated, and the highest degree of humification was obtained when red loam and the catalyst were both added with the initial materials.

Characterization of dissolved organic matter extracted from fermentation effluent of swine manure slurry using spectroscopic techniques and parallel factor analysis (PARAFAC)

Dissolved organic matter (DOM) is the most active component in environmental system, and its chemical and structural characteristics are most likely to affect its biodegradation. DOM has several different fluorophores whose fluorescent characteristics contain a lot of information about structure and functional groups. Fluorescence spectroscopy and Fourier-transform infrared (FTIR) were used to examine the structural and biodegradable characteristics of DOM extracted from fermentation effluent of swine manure slurry. Humic-like acid, fulvic-like acid and protein-like fluorophores were observed in fluorescence spectra. Fluorescence index (FI) indicated that the fluorophores in the samples were representative of both terrestrial and microbially-derived organic matter. FTIR spectroscopy showed that DOM featured aliphatic CH, aromatic CC and carbohydrate CO functional groups. With PARAFAC model, four fluorescent components were identified: component 1 (protein-like), component 2 (soluble microbial byproduct-like), component 3 (non-humic like) and component 4 (fulvic-like). Component 1 was a dominant fluorescent component. Components 2, 3 and 4 were degraded by microorganisms as the anaerobic fermentation processes. The C/N ratio of DOM in F1 has a more significant decrease than that in F0, indicating the loss of carbon (CH4 and CO2) during this process. The C/N ratio of DOM in F2 obviously increased when additional swine manure slurry was added.

Enhanced humification by carbonated basic oxygen furnace steel slag – I. Characterization of humic-like acids produced from humic precursors

Carbonated basic oxygen furnace steel slag (hereinafter referred to as “steel slag”) is generated during iron and steel manufacturing and is often classified as waste. The effect of steel slag on humification process was investigated. Catechol, glycine and glucose were used as model humic precursors from degraded biowastes. To verify that humification occurred in the system, humic-like acids (HLAs) were isolated and characterized structurally by elemental analysis, FTIR spectra, solid-state CP-MAS 13C NMR spectra, and TMAH-Py-GC/MS. Characteristics of the steel slag-HLA were compared with those of HLAs formed in the presence of zeolite and birnessite, and with that of mature compost humic acid. The results showed that steel slag-HLA, like zeolite- and birnessite-HLA, is complex organic material containing prominent aromatic structures. Steel slag substantially accelerated the humification process, which would be highly significant for accelerating the stabilization of biowastes during composting (e.g. municipal solid waste, sewage sludge, and food waste).

The Relationship between THMFP and the Variation of Fluorescence Characteristic of DOM among the Different Bio-Treatment Processes

Dissolved organic matter (DOM) from different biological treated wastewater in secondary effluent of different municipal wastewater treated plants are isolated and fractionated using resin adsorption into five different fractions: hydrophobic bases (HOB), hydrophobic acids (HOA), hydrophilic bases (HIB), hydrophilic acids (HIA) and hydrophilic neutrals (HIN). The characteristics of three dimensional excitation emission matrix fluorescence spectroscopy (3DEEM) and disinfection by-products formation potential (THMFP) of each fraction are investigated. The objective of this study is to investigate the influence of different biological processes on THMs generation and transformation. The results show that for each municipal wastewater treated plant, HIA and HOA fractions content more fulvic-like acid and humic-like acid, which are the important matter to result the higher THMFP. THMFP of HIA rang from 736μg/L to 359μg/L in the secondary effluent. It shows that acidic organic matters are important THMs precursors, especially fulvic-like acids and humic-like acids. The Orbal oxidation ditch process can lead to the highest THMFP, and secondly is the Convert A2/O process.

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.

Spectroscopic investigations of humic-like acids formed via polycondensation reactions between glycine, catechol and glucose in the presence of natural zeolites

Polycondensation reactions between low-molecular-weight compounds, such as amino acids, sugars and phenols, are crucially important processes in the formation of humic substances, and clay minerals have the ability to catalyze these reactions. In the present study, catechol (CT), glycine (Gly) and glucose (Gl) were used as representative phenols, amino acids and sugars, respectively, and the effects of the catalytic activities of natural zeolites on polycondensation reactions between these compounds were investigated. The extent of polycondensation was evaluated by measuring the specific absorbance at 600 nm ( E 600) as an index of the degree of darkening. After a 3-week incubation period, the E 600 values for solutions that contained zeolite samples were 4–10 times greater than those measured in the absence of zeolite, suggesting that the zeolite had, in fact, catalyzed the polycondensation reaction. The humic-like acids (HLAs) produced in the reactions were isolated, and their elemental composition and molecular weights determined. When formed in the presence of a zeolite, the nitrogen contents and molecular weights for the HLAs were significantly higher, compared to the HLA sample formed in the absence of zeolite. In addition, solid-state CP-MAS 13C NMR spectra and carboxylic group analyses of the HLA samples indicated that the concentration of carbonyl carbon species for quinones and ketones produced in the presence of zeolite were higher than the corresponding values for samples produced in the absence of a zeolite. Carbonyl carbons in quinones and ketones indicate the nucleophilic characteristics of the samples. Therefore, a nitrogen atom in Gly, which serves as nucleophile, is incorporated into quinones and ketones in CT and Gl. The differences in the catalytic activities of the zeolite samples can be attributed to differences in their transition metal content (Fe, Mn and Ti), which function as Lewis acids.

Humic substances change during the co-composting process of municipal solid wastes and sewage sludge

The change of the degree of stability of compost during the composting process was a kind of guideline for our study. This stability was estimated by monitoring the chemical fractionation (extraction of humic and fulvic acids, and humin) during two cycles of composting. Change of humin (H), humic-like acid carbon (CHA) and fulvic-like acid carbon (CFA) fractions during the composting process of municipal solid wastes were investigated using two windrows W1 (100% of municipal solid wastes) and W2 (60% of municipal solid wastes and 40% of dried sewage sludge). Humin and fulvic acid fractions in the two windrows decreased since the start of composting process and tend to stabilize. At the end of composting process, humic acid fraction is more important in the windrow without sludge (W1) than the one with sludge (W2). The humification indexes used in this study showed that the humic-like acid carbon fraction production takes place largely during the phase of temperature increase (thermophilic phase), and it appeared very active in the windrow W2. At the end of composting process, the E4/E6 ratio value indicated that the compost of W1 is more mature than the compost of W2. The humification ratio (HR) allowed a correct estimation of compost organic matter stabilization level.

Urban wastes as sources of valuable chemicals for sustainable development: surfactants, dispersing polymers and polyelectrolytes of biological origin

Following previous work indicating urban wastes to be sources of valuable products with remarkable surface activity properties, a new humic acid-like (HAL) substance (cHAL3) was isolated from green residues composted for 7 days. This material was characterized for its chemical composition by elemental analysis, nuclear magnetic resonance and infrared spectroscopy, and potentiometric titration of carboxylic and phenol groups, for its surface activity properties in aqueous solution at pH 7 and for its molecular weight. The results indicate that cHAL3 has good surface activity properties mostly due to molecules with molecular weight up to 1 kg/mol; it also contains larger ionic polymeric molecules or aggregates with molecular weight up to 267 kg/mol. In the attempt to obtain evidence for possible source–structure–properties relationships, cHAL3 was compared with other previously reported HAL substances (i.e. cHAL2) isolated from the same green residues before composting and cHAL isolated from a mix of kitchen and green residues composted for 15 days. The results show that cHAL3 and cHAL2 have slightly different chemical compositions but similar surface activity properties in aqueous solution at pH 7 (i.e. critical micellar concentration (cmc) 0.91–0.97 g/L and surface tension at the cmc (γ cmc ) 38 mN/m). By comparison, the cHAL biosurfactant is less polar and less hydrophilic and exhibits enhanced surface activity (i.e. cmc = 0.40 g/L and γ cmc = 36 mN/m). Thus, composting in the 0–7-day range does not appear to result in chemical composition changes in the isolated HAL substances, which can significantly affect surface tension properties. However, changing both the biomass nature and the composting time seems to affect significantly the surface activity and the content of ionic functional groups in the humic-like isolates. The results offer scope for a long-range process and product development study aiming to the valorization of biomass wastes as source of high-value chemical auxiliaries.

Combined UV–Vis absorbance and fluorescence properties of extracted humic substances-like for characterization of composting evolution of domestic solid wastes

Open-air composting evolution of domestic solid wastes (DSW) collected during 150 days from a neighborhood of Santiago del Estero, Argentina, was investigated using several standard methods of compost analysis, in combination with steady-state UV–Vis absorption and fluorescence measurements of their extracted total humic substance-like (HSL), fulvic acid-like (FAL), and humic acid-like (HAL) molecules. The UV-spectra of the HSL were fitted with a two Gaussian-like bands model, allowing the calculation of the absorption ratio between the electron-transfer and benzenoid band components, A o,ET/ A o,Bz, which provided information about the type and degree of substitution into the aromatic chromophores. In addition, the variation of the absorbance ratio E 4/E 6 of the HSL was mainly sensitive to the fraction of FAL substances. Fluorescence quantum yields ( Φ F) and full-width at half-maximum (FWHM) for the different humic extracts were also valuable parameters for tracking the evolution of these substances during composting. The excitation–emission matrix (EEM) of the different extracts showed the presence of two fluorescence maxima, namely P1 ( λ exc < 280 nm) and P2 ( λ exc > 280 nm) respectively. Only the location of the P2 of HAL was sensitive to the evolution of composting, indicating the continuous modification of the fluorophore during the process. The present results indicate the suitability of combined absorption and emission spectroscopical properties in the characterization of both HSL and evolution of composting.

Effect of an allophanic soil on humification reactions between catechol and glycine: Spectroscopic investigations of reaction products

Adduction of amino acids to phenols is a possible humification reaction pathway [F.J. Stevenson, Humus Chemistry: Genesis, Composition, Reaction, second ed., Wiley, New York, 1994, pp. 188–211; M.C. Wang, P.M. Huang, Sci. Total Environ. 62 (1987) 435; M.C. Wang, P.M. Huang, Soil Sci. Soc. Am. J. 55 (1991) 1156; M.C. Wang, P.M. Huang, Geoderma 112 (2003) 31; M.C. Wang, P.M. Huang, Geoderma 124 (2005) 415]. To elucidate the reaction kinetics and products of abiotic humification, the effects of an allophanic soil on the adduction of amino acids to phenols were investigated using catechol (CT) and glycine (Gly) as a model phenol and amino acid, respectively. An aqueous solution containing CT and Gly (pH 7.0) in the presence of allophanic soil was incubated for 2 weeks, and the kinetics of the humification reactions were monitored by analysis of absorptivity at 600 nm ( E 600). A mixture of CT and Gly in the absence of allophanic soil was used as a control. The E 600 value increased markedly in the presence of allophanic soil. In addition, unreacted CT was detected in the control reaction mixture, but not in the allophane-containing reaction mixture. Under the sterilized conditions, absorbance at 600 nm for the control reaction mixture was significantly smaller than that for the allophanic soil-containing reaction mixture, which indicates there was no microbial participation during incubation. These results indicate that the allophanic soil effectively facilitated humification reactions between CT and Gly. The reaction mixtures were acidified and humic-like acid (HLA) was isolated as a precipitate. The elemental composition, acidic functional group contents, molecular weight, FT-IR, solid-state CP-MAS 13C NMR, and 1H NMR spectra of the purified HLAs were analyzed. The results of these analyses indicate that the nitrogen atom of Gly binds to the aromatic carbon of CT in the HLA products.

Fluorescence analysis of humic-like substances extracted from composts: influence of composting time and fractionation

Humic-like acids (HLA0, HLA70, HLA130, HLA730) were extracted from composts obtained from sewage sludges and trimmings after 0, 70, 130 and 730 days of composting, respectively. In addition, HLA130 was fractionated using SEC-PAGE set-up. Fluorescence spectroscopy revealed that HLA0 was the only sample to contain emission bands characteristic of protein-like compounds (λexc/λem: 280/350) and chlorophyll (λexc/λem: 420/660). Emission intensities above 400 nm and HIX both varied in the order: HLA70 > HLA130 > HLA730 > HLA0 and increased as the fraction molecular size decreased. Thus, the formation of long wavelength emitting fluorophores during composting is connected to the humification process. These fluorophores are mainly concentrated in the low molecular size fraction obtained by SEC-PAGE fractionation of composts

Evaluation of photochemical properties of compost humic-like materials

Humic-like acids (HLA) were extracted from compost at the beginning and after 70, 130 and 730 days of maturation in order to be investigated for their ability to induce the transformation of 2,4,6-trimethylphenol under irradiation at 365 nm. The rate of 2,4,6-trimethylphenol phototransformation in the presence of HLA (25 mg l −1) varied within HLA 0 << HLA70 ≈ HLA 130 ≈ HLA 730. The changes of photoinductive capacity paralleled the changes of HLAs absorptivity indicating that the formation of photoinductive constituents is related to that of the colored moieties. The polyacrylamide gel electrophoresis analysis showed that intensity of all humic electrophoretic fractions significantly increased during the first 70 days of maturation but did not undergo significant changes for longer composting times. These data confirm the changes of HLS during composting.

Using EEFM (Excitation Emission Fluorescence Matrix) to Differentiate the Organic Properties of the Effluents from the Ozonated Biofilters

This study conducted a two-stage experiment. The first stage attempted to establish biostable filter beds. Two parameters, total bacterial count (TBC) and non-purgeable dissolved carbon (NPDOC), measured by passing through a 0.2 μm membrane filter, were selected to compare the difference of biostability of a filtration system with recirculation with different O3-to-NPDOC ratios of filtered water. The excitation emission fluorescence matrix (EEFM) was used as an effective tool for understanding information regarding organic characteristics by comparing source filtered water before and after ozonation and the effluent during biostablizing filter. During the second stage, a biostable filter was used to compare differences in biodegradability of ozonated products sodium oxalate and sodium acetate. Experimental results demonstrate that both parameters, NPDOC removal and TBC, can be utilized to evaluate the biostabilty of a filter bed. With each parameter, a plateau was reached in roughly 20 days. The source water from Chen Ching Lake (CCL) contained a protein-like substance determined by the EEFM. This protein-like substance was also destroyed by O3/NPDOC = 1.1. Soluble microbial products (SMPs) released from the biostablizing filter into the effluent have two peaks in the EEFM, identified as protein-like and humic-like acid. The NPDOC removal for the biostabilizing filter using O3/NPDOC = 1.7 was less than that using O3/NPDOC = 1.1. Bacterial counts in the effluent from the biostabilizing filter using O3/NPDOC = 1.1 was better than that of O3/NPDOC = 1.7. This difference can be explained by the high ratio of O3/NPDOC producing by-products of ozonation that were easily utilized by microorganisms; however, filter bed also released relatively more SMPs owing to increased proliferation of microorganisms attached to glass pellets in the filter. Regarding the differences in decomposition of the by-products of ozonation by the biostable filter, such as sodium oxalate, the NPDOC removal at O3/NPDOC = 1.1 was better than that at O3/DOC = 1.7. This phenomenon can be explained as previously mentioned.

Humic acid-like fractions in raw and vermicomposted winery and distillery wastes

Three different substrates from winery and distillery wastes including a spent grape marc (SGM), a mixture of SGM and lees cake (SGML) and a mixture of biosolid vinasse and vine shoots (BvS) were vermicomposted with Eisenia andrei for 8 months. The chemical changes occurring in the bulk substrates and in their humic acid-like (HAL) fractions were investigated. Vermicomposting produced a decrease of total organic C content and C/N ratio, and an increase of total extractable C and humic acid C contents in the three substrates. The HAL fractions in the initial substrates were characterized by a marked aliphatic character, small acidic functional group content, a marked presence of proteinaceous materials and polysaccharide-like structures, extended molecular heterogeneity and small degrees of aromatic ring polycondensation, polymerisation and humification. After vermicomposting, the chemical and structural characteristics of HAL fractions approached those typical of soil humic acid. In particular, a loss of aliphatic, polypeptidic and carbohydrate components, and an increase in oxygenated and acidic functional groups occurred. Results obtained showed that vermicomposting is a suitable treatment for transforming fresh organic matter in SGM, SGML and, especially, BvS into humified forms, thus enhancing the quality of these materials as soil organic amendments. Further, the mixture SGML yielded slightly better results in terms of HAL fraction quality and humification degree of the final product, with respect to SGM.

Acid−Base Properties of Humic and Fulvic Acids Formed during Composting

The soil acid-base buffering capacity and the biological availability, mobilization, and transport of macro- and micronutrients, toxic metal ions, and xenobiotic organic cations in soil are strongly influenced by the acid-base properties of humic substances, of which humic and fulvic acids are the major fractions. For these reasons, the proton binding behavior of the humic acid-like (HA) and fulvic acid-like (FA) fractions contained in a compost are believed to be instrumental in its successful performance in soil. In this work, the acid-base properties of the HAs and FAs isolated from a mixture of the sludge residue obtained from olive oil mill wastewater (OMW) evaporated in an open-air pond and tree cuttings (TC) at different stages of composting were investigated by a current potentiometric titration method and the nonideal competitive adsorption (NICA)-Donnan model. The NICA-Donnan model provided an excellent description of the acid-base titration data, and pointed out substantial differences in site density and proton-binding affinity between the HAs and FAs examined. With respect to FAs, HAs were characterized by a smaller content of carboxylic- and phenolic-type groups and their larger affinities for proton binding. Further, HAs featured a greater heterogeneity in carboxylic-type groups than FAs. The composting process increased the content and decreased the proton affinity of carboxylic- and phenolic-type groups of HAs and FAs, and increased the heterogeneity of phenolic-type groups of HAs. As a whole, these effects indicated that the composting process could produce HA and FA fractions with greater cation binding capacities. These results suggest that composting of organic materials improves their agronomic and environmental value by increasing their potential to retain and exchange macro- and micronutrients, and to reduce the bioavailability of organic and inorganic pollutants.

Olive Pomace Amendment in Mediterranean Conditions: Effect on Soil and Humic Acid Properties and Wheat (Triticum turgidum L.) Yield

The effects of the addition of either crude or exhausted olive pomace at two rates (10 and 20 t ha(-)(1)) on soil and soil humic acid (HA) properties and durum wheat (Triticum turgidum L.) yield were investigated in open-field Mediterranean conditions. Soil amendment with olive pomaces produced a significant increase of total organic, total extractable, humified and nonhumified C forms, and available K contents. With respect to control soil HA, humic-like acids isolated from crude and exhausted olive pomaces were characterized by larger phenolic OH group contents, smaller carboxyl group contents, a prevalent aliphatic character, extended molecular heterogeneity, and smaller aromatic polycondensation and humification degrees. In general, application of olive pomaces to soil produced a number of modifications in soil HAs, including the increase of O and acidic functional group contents, C/N ratio, and aliphaticity and the decrease of C/H ratio and N and C contents. Wheat grain yield increased significantly as an effect of olive pomace amendment. In particular, the increases were related to kernel weight, kernel number per square meter, and soil organic matter content. Possibly, the enhanced amount of soil organic matter in olive-pomace-amended soils relieved wheat of drought stress from anthesis to maturity by promoting a good soil structure, thereby reducing water loss by evaporation.