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.     

Effects of the maturity of wood waste compost on the structural features of humic acids

An analytical scheme for the separation of humic substances (HSs) and non-humic substances (non-HSs) was established to estimate the humification index (HI), which was defined as the ratio of HS carbon content to non-HS carbon content. The alkaline compost-extract contained a mixture of HSs and non-HSs, while acidification of the compost-extract resulted in precipitation of humic acid (HA). The acidified supernatant contained fulvic acid (FA) and non-HSs. In the present study, DAX-8 resin was used to separate FA and non-HSs. HI values, which were estimated to evaluate the maturity of wood waste compost, increased with composting duration. To determine the effects of compost maturity on HA structural features, correlations between HI and indicators of the degree of HA humification (atomic ratios, acidic functional group contents, spectroscopic parameters and molecular weight) were investigated. HI values were significantly related to the indicators of the extent of HA humification during composting.     

Influence of humic substances on bioavailability of Cu and Zn during sewage sludge composting

Influence of humic substances (HS) on bioavailability of Cu and Zn was characterized during 120 days co-composting of sewage sludge and maize straw. At the initial stage of composting, Cu and Zn in sewage sludge were released as organic matter was degraded, and water soluble Cu and Zn increased markedly. Water soluble Cu and FA content decreased after 21 days whereas water soluble Zn increased during the whole process. Both HA-Cu and HA-Zn were significantly and positively correlated with HA and H/F, respectively. At the end of composting, the distribution coefficients of HA-Cu and HA-Zn reached 27.50% and 3.33% respectively with HA-Cu/HA-Zn ratio increased from 1.29 to 2.73. The results suggest that Cu combined with HA more strongly than Zn, and composting treatment could decrease bioavailability of Cu markedly.     

Humic substances in straw compost with rock phosphate

The production of humic substances and their retention capacities for phosphorus and calcium released during composting of wheat straw with two types of low-grade rock phosphate were examined. Relative quantities of humic acids increased with increase of composting time, while fulvic acids production decreased after 30 days of composting. The addition of both Mussoorie and Hyperphos retarded humic acids production and enhanced fulvic acids production. Molasses incorporation had no effect on humic acids but increased fulvic acids production. The production of humic acids and their retention capacity for P and Ca were greater in the presence of Mussoorie phosphate than in the presence of Hyperphos, but fulvic acids formation was higher with Hyperphos. About 80–85% P and 90–95% Ca retained by the total humic substances were found in the fulvic acids fraction.     

Comparison of the changes in mushroom (Agaricus bisporus) compost during windrow and bunker stages of phase I and II

The changes in thermophilic fungi and biochemical characteristics, during windrow and bunker stages of phase I and phase II composts, were compared in this investigation. Composts prepared by the two phase I systems differed in a number of key parameters including mean straw length, population of Scytalidium thermophilum, dry matter, conductivity, nitrogen dry matter, ammonia, fibre content and ash. S. thermophilum populations in phase I composts were significantly higher in windrow compared to bunker‐composted materials as a result of the larger high temperature (65‐80°C) core in bunker treatment, which inhibited microbial activity. Assessment of the composts for loss of matter during composting has revealed that the bunker system can conserve fresh matter better than the windrow production system, possibly due to lower microbial activities during bunker composting. The productivity of the phase II composts prepared from windrow and bunker systems was compared in trials using commercial growers.     

Nitrogen Incorporation into Lignite Humic Acids during Microbial Degradation

Previous study showed that nitrogen content in lignite humic acids (HA) increased significantly during lignite biodegradation. In this paper we evaluated the factors responsible for the increased level of N in HA and the formation of new nitrogen compound following microbial degradation. When the ammonium sulfate concentration in lignite medium was < 0.5%, the N-content in HA was higher than that in the crude lignite humic acid (cHA); when the ammonium sulfate concentration was ≥ 0.5%, both the biodegraded humic acid (bHA) N-content and the content of bHA in lignite increased significantly, but at 2.0% no increase was observed. This indicated that HA incorporated N existing in the lignite medium, and more HA can incorporate more N with the increase of bHA amount in lignite during microbial degradation. CP/MAS ¹⁵N NMR analysis showed that the N incorporated into HA during biotransformation was in the form of free or ionized NH₂-groups in amino acids and sugars, as well as NH₄ ⁺. We propose nitrogen can be incorporated into HA biotically and abiotically. The high N content bHA has a potential application in agriculture since N is essential for plant growth.     

Characterization of natural organic matter (NOM) derived from sewage sludge compost. Part 1: chemical and spectroscopic properties

In this study changes in the properties of natural organic matter (NOM) were studied during composting of sewage sludge in a laboratory experiment using the pile method. Typical physicochemical parameters were measured during 53 days of composting including humic fractions. The effects of humification on the molecular properties of humic acids (HA) were investigated by 13C CP/MAS NMR spectroscopy. On the basis of chemical analyses, 53 days of composting sewage sludge with structural material can be divided into three phases: (i) domination of rapid decomposition of non-humic, easily biodegradable organic matter (two to three weeks), (ii) domination of organic matter humification and formation of polycondensed, humic-like substances (the next two weeks), (iii) stabilization of transformed organic material and weak microbial activity. Spectroscopic characterization (13C NMR) of compost humic acids reveals changes in their structures during maturation. The changes are highly correlated with the processes taking place in bulk compost.     

Transformation of organic matter during co-composting of pig manure with sawdust

Co-composting of pig manure with sawdust was studied in order to characterize the organic transformation during the process, using both chemical and spectroscopic methods. Humic acids (HA) and fulvic acids (FA) were fractionated from immature and mature pig manure compost, and characterized. After 63 days of composting, the ratio of total organic carbon and soluble organic carbon decreased to a satisfactory low level and the solid and soluble C/N ratios decreased rapidly for the first 35 days before attaining a constant value, indicating compost maturity. Humification could be responsible for the increase in humic acid proportion during composting. The increase in the aromatic bonds after composting, as indicated by the reduction of C/H and C/O ratios of HA and FA, resulted in a more stabilized product. A substantial increase in high molecular weight compounds along with a small increase in low molecular weight compounds was found in mature compost. Moreover the HA also had more complex organic compounds at this stage. Fluorescence spectral analysis showed an increase in the maximum wavelength of HA associated with the contents of aromatic structures in solution. A decrease in relative absorbance of HA at 1160 cm(-1), 2950 cm(-1) and 2850 cm(-1) was seen in the FTIR spectra indicating the decomposition of complex organic constituents, into simpler ones. Increase in the aromatic compounds with higher stability could account for the relative increase in the absorbance of HA at 1650 cm(-1) and 1250 cm(-1) of the mature compost. The composition of FA was not much altered, indicating most of the degradation of organic matter occurred in HA. Data from organic carbon, C/N ratio, elemental analysis, E(4)/E(6) ratio, gel chromatography, fluorescence and FTIR spectra indicated an increase in polycondensed structures and the presence of more stable organic matter in the mature compost.     

Successions of bacterial community in composting cow dung wastes with or without hyperthermophilic pre-treatment

Comparative analyses of bacterial community successions in the composting materials were done for a conventional windrow post-treatment (WPOT) process with the hyperthermophilic pre-treatment (HTPRT) and simple windrow composting (SWC; without the HTPRT). Multidimensional scaling profiles based on data of terminal restriction fragment length polymorphisms of the bacterial population in the samples of every 7 days composting material and analyses of the 16S rRNA gene-based clone library of the 7 and 21 days composting materials suggested that bacterial communities of the composting materials differed much between these two processes until the 35 days of composting, whereas that they were closely related to each other at the final composting stage (42 days of composting). Detailed phylogenetic analysis clarified that all WPOT clone libraries contained many clones of the lineages of aerobic bacteria (for example, bacilli). However, the most abundant clones retrieved from all SWC materials were affiliated with a clone cluster closely related to identified and classified members of the phylum Firmicutes that have strictly anaerobic metabolism pathways. From these results, we conclude that the HTPRT process contributed to easily establish an aerobic ecosystem from the early stage to the final stage of WPOT composting with plowing the materials only once a week.     

Changes in physical,chemical and microbial parameters during the composting of municipal sewage sludge

Changes in physical, chemical and microbial parameters were investigated during the composting of municipal sewage sludge. Raw sewage sludge (30% dry matter) was mixed with compost from sewage sludge (85% dry matter) in 3:1 ratio (v/v). The mixture was divided into 4 windrows which were composted under the same conditions except the turning factor. The turning was every 7, 10, 15 days and according to the temperature which must be (55–65°C) for windrow 1 (W1), windrow 2 (W2), windrow 3 (W3) and windrow 4 (W4), respectively. Water was added to adjust the moisture content (40–60%). The composting process consisted of 2 periods; fermentation (12 weeks) and maturation (4 weeks). The results showed that the temperature reached the maximum after 12 weeks for W1 and 11 weeks for W2, W3 and W4 and then decreased. The final compost was nearly odourless and black, especially in case of W4. The general trend indicates a decrease in organic matter, organic carbon and nitrogen (N), whereas ash, potassium (K) and phosphorus (P) increased and consequently C/K and C/P ratios decreased. There was a slight increase in C/N ratio. The pH increased and then decreased to near neutrality at the end. The mesophilic bacteria increased during the fermentation period and decreased after that, whereas the thermophilic ones increased with increasing of temperature, decreased after 2 weeks and increased again during the fermentation period and then decreased. The mesophilic and thermophilic fungi were present during the first week and disappeared after that. The final compost was pathogens-free as indicated by the counts of coliforms and Salmonella.     

Changes in functional abilities of the microbial community during composting of manure

The objective of this study was (a) to detect changes of the functional abilities of the microflora during composting of manure as a result of windrow turning frequency and (b) to detect differences between distinct zones within the windrows. Biolog GN microtiter plates containing 95 different carbon sources were inoculated with diluted suspensions of compost material containing 15,000 microorganisms per well (120 l). We found a dramatic shift in functional microbial community structure during the 8-week composting process. The shift was more rapid when the compost windrows were turned. The substrate use pattern in the outer, well-aerated zone of the unturned windrow was similar to that of the turned windrows. Microbial biomass and respiration decreased more rapidly in the turned than in the unturned windrows, indicating a different pace of compost maturation. The data suggest that the Biolog assay may be a suitable approach to determine compost maturity. Correspondence to: H. Insam     

Chemical and structural evolution of humic acids during organic waste composting

The effects of the composting process on the chemical and structural properties of humic acids have been studied in seven different organic waste mixtures from different origin. Only slight changes in elemental composition have been found in the humic acids after the composting process pointing to a more aromatic structure with higher proportions of oxygen and nitrogen. Functional groups were the most sensitive to the changes caused by the composting process showing a marked increase in the total acidity and phenolic, carboxyl and carbonyl groups. Gel permeation chromatography showed a slight increase in the average molecular weight of the humic acids. Infrared spectroscopy did not show important differences in humic acid structure but a clear decrease in the intensity of the bands in the region 3000–2850 cm^-1 corresponding to the aliphatic fractions. As a general result, the composting process yields humic acids in which the elemental and functional composition are closer to that of the more humified soil humic acids.     

Sludge stabilization by composting: a Jordanian case study

Municipal sludge handling is a major problem facing wastewater treatment plants due to the high costs of treatment and disposal. This issue is of special importance in Jordan because of the critical economic situation as well as the lack of financial support for such nonprofit projects. This study investigates the possibility of solving this problem by testing a method of sludge stabilization that requires minimum initial and operating costs. The method tested here is sludge stabilization by composting which is an attempt to transform sludge into a safe, nuisance free, humus like product that can be applied safely to land and can become a source of income that would recover the costs of processing. Two types of composting systems were tested in this study, aerated static pile and windrow. Results obtained indicate that composting of dried sludge was not possible due to the extremely low moisture content; which was overcome by sludge seeding and mixing with amendment and bulking agents. This resulted in efficient stabilization and reduction of the amount of organic matter in the final compost. The experimental results obtained also indicate that both systems (aerated static pile and windrow) are efficient. The organic content of the sludge was reduced in the windrow system by 46% and in the aerated static pile by 66%. In addition, the total volatile solids had decreased in the windrow and the aerated pile by 26 and 73%, respectively. The heavy metals content of the final compost was examined and found to comply with the international standards.     

Chemical and infra-red spectroscopic study of humic and fulvic acids from composted poplar bark

Humic (HA) and fulvic (FA) acids were extracted from poplar bark after 12 and 30 months of composting and characterized through functional groups analysis and FT-IR spectra. The extraction and purification procedures were those recommended by the International Humic Substances Society (IHSS). Total acidity and COOH, total OH and CO contents of FA were always greater than those of the corresponding HA. Carboxyl groups were the major components of total acidity. Phenolic OH groups content of HA was always higher than that of the corresponding FA, whilst the alcoholic OH groups content was higher in FA than in HA. There were no significant differences between HA extracted after 12 and 30 months of composting, but some differences were shown by the corresponding FA.     

Effect of humic acids from Leonardite on the stability of soil aggregates and melon roots under greenhouse conditions

Leonardite is an oxidized form of lignite carbon, which is obtained from fossilized organic materials. Such materials are used for the extraction of humic acids (HA). The result of the addition of HA of organic origin on soil structure is known; however, the effects of adding HA of Leonardite on soil structure have been scarcely investigated. The objectives of this research were (1) to determine the influence of humic acids derived from Leonardite in increasing the aggregate stability of an Aridisol under greenhouse conditions, and (2) evaluate the morphology of the root xylem during the phenological development of melon plants (Cucumis melo L.). Three treatments of HA solution application to the soil were used: soil without solution application (HA0), and application of HA solution to the soil with pH 6 (HA6) or (HA7). Aggregate stability (As) and bulk density (Da) were evaluated as soil variables. Development and quantification of xylem area were studied on plants. There were significant differences in aggregate stability. Also, there was an increase in the root xylem area, and the best treatment was when AH7 solution was applied. Humic acids derived from Leonardite increased the stability of soil aggregates when plants grew under greenhouse conditions, and fostered the development of xylem conduits during the fruiting stage.     

Dynamics of pruning waste and spent horse litter co-composting as determined by chemical parameters

Co-composting of pruning waste and horse manure was monitored by different parameters. A windrow composting pile, having the dimensions 2.5m (height) x 30m (length) was established. The maturation of pruning waste and horse manure compost was accompanied by a decline in NH(4)(+)-N concentration, water soluble C and an increase in NO(3)(-)-N content. Organic matter (OM) content during composting followed a first-order kinetic equation. This result was in agreement with the microbiological activity measured by the CO(2) respiration during the process. The correlation at a high level of probability found between the OM loss and CO(2) evolution showed that both parameters could be used to indicate the degree of OM degradation that is the maturity and stability phases of the compost studied. Humification parameters data from the organic matter fractionation did not show a clear tendency during the composting time, suggesting that these parameters are not suitable for evaluating the dynamics of the process.     

Chemical characterization of humic substances extracted from organic-waste-amended soils

Humic substances were extracted from a soil treated, in a 4-year experiment, at different rates with a sludge from anaerobic treatment of combined civil and industrial wastes, and with agricultural manure. Elemental and chemical analyses, molecular weight (MW) distribution and infrared (IR) spectroscopy were performed on the purified humic acids (HA). Organic wastes significantly increased the HA content of the treated soils and improved CEC. The C/N, C/H and C/O ratios of HA extracted from the original wastes showed a higher degree of humification for sludge than for manure. This difference was also noticed for the C/N ratio of soil humic extracts, indicating a faster humification process for the sludges in soil. The content of oxygen-containing functional groups was lower than the ‘model’ HA reported in the literature, and even more so for HA from sludges, reflecting their anaerobic formation. MW distribution and E₄/E₆ ratios showed that the sludge material had a higher molecular complexity than manure, supporting the high degree of humification attributed to the former. HA extracted from sludge-treated soils revealed a molecular dimension increasing with the application doses of waste material. Infrared spectra showed that HA formed in soils after waste additions reflected the chemical composition of the original organic material, which was rich in aliphatic groups and peptides for sludge and in carbohydrates for manure. On the basis of this study, it is concluded that not only are organic waste additions able to build up the HA content in soils but the HA formed assume the chemical characteristics and the degree of humification of the original material.     

Characterization of different decomposition stages of biowaste using FT-IR spectroscopy and pyrolysis-field ionization mass spectrometry

The decomposition stage and stabilization of organic matter in biowaste (mixture of yard waste and kitchen waste), originating from an open windrow process, were investigated using Fourier transform infrared (FT-IR) spectroscopy and pyrolysis-field ionization mass spectrometry (Py-FIMS). These investigations provided detailed information about chemical constituents and their behavior during the composting process. The chemical compounds were classified by their molecular signals in Py-FIMS. Multivariate statistical analysis revealed, that during the composting process, the group containing lipids, fatty acids and other chemical compounds with aliphatic skeletons changed the most. Corresponding with Py-FIMS findings changes were observed in absorbance bands of infrared spectra that reflect this group of organic compounds: the aliphatic methylene bands at 2925 and 2850cm^-1, the band of C=O vibrations of carboxylates at 1640cm^-1, the O=H in-plane bend of carboxylic acids, the CO₂ stretch of carboxylates and the CH₂ group of alkanes at around 1430cm^-1. During decomposition these bands decreased up to a steady level that indicated stabilization. The band at 1260–1240cm^-1 that can be assigned to the C=O stretch of carboxylic acids or to the C=N stretch of amides and the band of aromatic amines at 1320cm^-1 disappeared completely. The nitrate band at 1384cm^-1 appeared at a later stage of the composting process. The relative increase of chemical compounds like moieties of lignin, humic acids and tannins in the composted material contributed to the aromatic C=C band at around 1640cm^-1.     

Contribution of bacterial cell nitrogen to soil humic fractions

Summary Living cells ofSerratia marcescens, uniformly labelled with¹⁵N, were added to samples of maple (Acer saccharum) and black spruce (Picea mariana) forest soils. After different periods of incubation from zero time to 100 days, the soils were subjected to alkali-acid and phenol extraction to provide humic acid, fulvic acid, humin and humoprotein fractions. Significant amounts of the cell nitrogen were recovered in the humic and fulvic acids immediately after addition. After incubation, less cell, nitrogen appeared in the humic acid and more in the fulvic acid. The amount of cell nitrogen recovered in the humin fraction increased with incubation. Roughly 5 to 10 per cent of the added cell nitrogen was found as amino acid nitrogen from humoprotein in a phenol extract of the humic acid. The data are consistent with the occurrence of co-precipitation of biologically labile biomass nitrogen compounds with humic polymers during the alkaline extraction procedure involved in the humic-fulvic fractionation.     

Modification of humic acids by the compost-dwelling deuteromycete Paecilomyces inflatus

The soil mold Paecilomyces inflatus is capable of modifying and partially mineralizing synthetic and natural humic acids (HAs) in compost environments. HA degradation studies using a synthetic HA (¹⁴C-HA) in autoclaved compost microcosms showed that, after 12 weeks of cultivation, P. inflatus mineralized approximately 5% of the ¹⁴C-labeled HA to¹⁴CO₂, while 6% of the ¹⁴C-HA was converted into ¹⁴C-labeled water-soluble fragments (fulvic-acid-like fraction). About 40% was still present as NaOH-soluble HA representing unmodified or only slightly modified humic material (compared with 60% in the controls). Modification of natural HAs extracted from compost was followed by their partial decolorization (30%) in liquid cultures of P. inflatus. Bleaching of the medium was accompanied by moderate changes in the molecular mass distribution of both the HA and fulvic-acid fractions, which were analyzed with high-performance size exclusion chromatography. HA modification was most pronounced during the primary growth phase of the fungus and was associated with increased laccase activity.