Analysis of branched-chain fatty acids in humic substances as indices for compost maturity by pyrolysis–gas chromatography/mass spectrometry with tetramethylammonium hydroxide (TMAH-py–GC/MS)

Parameters that affect the degree of humification for humic substances (HSs) are deeply related to the maturity of the compost. In general, the matured composts contain HSs with a higher degree of humification. In addition, microbial activities during composting are also one of the indices for compost maturation. Branched-chain fatty acids are metabolites as the result of microbial activities in a soil environment. Such branched-chain fatty acids, regarded as humic precursors, are incorporated into HSs during the composting process. To determine whether branched-chain fatty acids in HSs can be used as biomarkers during composting processes or not, HSs were extracted from three types of composts with the different maturation, and the branched-chain fatty acids in the HSs were analyzed by pyrolysis–gas chromatography/mass spectrometry with tetramethylammonium hydroxide (TMAH-py–GC/MS). HSs with a higher degree of humification (higher aromaticity and lower molecular weight) contained higher levels of branched-chain fatty acids. These results show that branched-chain fatty acids in HSs from matured compost samples can be used as biomarkers, which indicate the history of microbial activities during overall composting process.     

Humification index of composts originating from three types of woody biomass

Composting is a good method for recycling surplus manure and stabilizing organic matter from biowastes. Compost is used as a soil amendment and recently, for restoration of vegetation in barren areas. We investigated the relationship between the type of woody biomass (using Robinia pseudoacacia, Japanese larch and apple) and the humification index (HI) of the resulting compost. This study evaluated the difference in HI between the three compost types, and the structural features of composts and extracted humic acids (HAs). The HIs for R. pseudoacacia and apple were larger than that for Japanese larch after composting for 11 months. The structural features of the Japanese larch compost were also different from the apple and R. pseudoacacia, with a very high carbon/nitrogen ratio. The average molecular weights and ultraviolet–visible spectra (A600/C) of HAs extracted from composting samples at 0 and 11 months indicate that the humification rate of Japanese larch was slower than that of R. pseudoacacia and apple. During composting, the average molecular weights of apple and R. pseudoacacia decreased, while their A600/C values increased, but the reverse was observed for Japanese larch. The humification rate was found to depend on the type of woody biomass being composted.     

Techniques for the evaluation of maturity for composts of industrially contaminated lake sediments

Composting was applied as a bioremediation methodology for the reclamation of dredged sediments of Isnapur, Khazipally and Gandigudem lakes polluted with industrial wastes. The present study is an attempt to elaborate upon organic matter transformations and define the parameters for product maturity adapting chemical and spectroscopic methods during composting. The stability and maturity of sediments were evaluated by assessing parameters like C/N ratio, nitrification index (NH(4)-N/NO(3)-N), water-soluble organic carbon concentration, CO(2) evolution rate, cation exchange capacity and indices such as humification index, E4/E6 ratio, compost mineralization index (ash content/oxidizable carbon), germination index, dehydrogenase, polyphenoloxidase activities and FTIR spectroscopy. The results showed that the changes in the above chemical and biological parameters can be employed as reliable indicators of stability and maturity. The FTIR spectra revealed enrichment in the aromatic groups and a degradation of the aliphatic groups indicating stabilization of the final compost.     

A full-scale study of treatment of pig slurry by composting: kinetic changes in chemical and microbial properties

Since the indiscriminate disposal of pig slurry can cause not only air pollution and bad odours but also nutrient pollution of ground waters and superficial waters, composting is sometimes used as one environmentally acceptable method for recycling pig manure. The aim of this study was to evaluate the effect of composting pig slurry on its sanitation (evaluated by ecotoxicity assays and pathogen content determination), as well as to determine the effect of a carbon-rich bulking agent (wood shavings, WS) and the starting C/N ratio on the changes undergone by different chemical (volatile organic matter, C and N fractions) and microbiological (microbial biomass C, ATP, dehydrogenase activity, urease, protease, phosphatase, and beta-glucosidase activities) parameters during composting. Pig slurry mixed with bulking agent (P+WS) and the solid faction separated from it, both with (PSF+WS) and without bulking agent (PSF), were composted for 13 weeks. Samples for analysis were taken from composting piles at the start of the process and at 3, 6, 9, and 13 weeks after the beginning of composting. The total organic carbon, water soluble C and ammonium content decreased with composting, while Kjeldahl N and nitrate content increased. The nitrification process in the PSF+WS pile was more intense than in the PSF or P+WS composting piles. The pathogen content decreased with composting, as did phytotoxic compounds, while the germination index increased with compost age. Piles with bulking agent showed higher values of basal respiration, microbial biomass carbon, ATP and hydrolase activities during the composting process than piles without bulking agent.     

Fertilization of maize with compost from cattle manure supplemented with additional mineral nutrients

An alternative approach for cattle manure management on intensive livestock farms is the composting process. An industrial-scale composting plant has been set up in northwest Spain for producing compost from cattle manure. Manure composting involved an increase in pH, electrical conductivity (EC), cation exchange capacity (CEC) and NO3(-)--N concentration, and a decrease in temperature, moisture content, organic matter (OM) content, NH4+--N concentration and C/N ratio. Cu, Zn and Ni concentrations increased due to the reduction of pile mass during the composting process. The resulting compost was applied to a field to study the viability of applying this compost combined with a nitrogen mineral fertilizer as a replacement for the mineral fertilization conventionally used for maize (Zea mays L.). The thermophilic phase of the composting process was very prolonged in the time, which may have slowed down the decomposition of the organic matter and reduced the nitrification process, leading to an over-short maturation phase. The humification and respirometric indexes, however, determined immediately after compost application to the soil, showed it to be stable. Compost application did not decrease the grain yield. A year later, soil pH, OM content and CEC were higher with the compost treatment. Total P, K, Ca and Na concentrations in compost-amended plots were higher than in mineral-fertilized ones, and no significant differences between treatments were found in soil concentrations of NH4+--N,NO3- --N, available P, Mg and B. Compost caused no heavy metal pollution into the soil. Therefore, this compost would be a good substitute for the mineral fertilizers generally used for basal dressing in maize growing.     

Sewage sludge composting: Influence of initial mixtures on organic matter evolution and N availability in the final composts

The influence of bulking agents on organic matter (OM) stability and nitrogen (N) availability in sewage sludge composts was investigated. The same sludge was composted on an industrial plant with different mixtures of bulking agents. The composting process included an active phase and a curing phase, both lasting 6 weeks, separated by the screening of composts. The OM evolution was characterised by carbon (C) and N mass balances in biochemical fractions. The OM stability and N potential availability of final composts were measured during soil incubations. During composting, the C and N losses reached more than 62% of the initial C and more than 45% of the initial N, respectively, due to C mineralisation or N volatilisation and screening. The bulking materials mostly influenced OM evolution during the active phase. They contributed to the mitigation of N losses during the active phase where N immobilisation through active microbial activity was favoured by bulking agents increasing the C:N ratio of the initial mixtures. However, the influence of bulking agents on OM evolution was removed by the screening; this induced the homogenisation of compost characteristics and led to the production of sludge composts with similar organic matter characteristics, C degradability and N availability.     

Change of the chemical composition and biodegradability of the Van Soest soluble fraction during composting: A study using a novel extraction method

Van Soest fractionation is widely employed to characterize exogenous organic matter. The soluble fraction of Van Soest fractionation (SOL, extracted using hot water and then neutral detergent) often increases in line with compost maturity, although it is generally considered as labile. We have developed an alternative extraction method that comprises four successive steps (extraction using hot water, sodium tetraborate, dichloromethane/methanol and chelating resin) in order to clarify the chemical nature of the SOL fraction and explain its biodegradability. This method was tested on municipal solid waste compost sampled during the thermophilic phase (MSWi) and after 8 months of composting (MSWm). Both methods extracted similar proportions of organic matter. The composition of the residues was similar in MSWm although differences were noted for the extraction of polysaccharides and lipids in the case of MSWi. The hot water extractable fraction decreased during composting. Its high biodegradability in MSWi was linked to the high polysaccharide content revealed by pyrolysis–GC/MS and FTIR spectroscopy. The increase in the sodium tetraborate extractable fraction mainly explained the increase in the SOL fraction during composting. This was made up of N-containing compounds, polysaccharides and lipids in the immature compost, and a majority of N-containing compounds in the mature compost. During composting, the stabilization of organic matter in the SOL fraction extractable by sodium tetraborate and EDTA might principally involve N-containing structures through the formation of complexes of organic matter with metal ions, especially Ca²⁺, which may be broken down during extraction of the Van Soest soluble fraction. These mechanisms still need to be investigated.     

Study of the organic matter evolution during municipal solid waste composting aimed at identifying suitable parameters for the evaluation of compost maturity

In this work the composting process of municipal solid wastes was studied in order to characterize the transformations of organic matter, particularly humic acid (HA). A composting process, lasting three months, was monitored by chemical methods; the following parameters were measured: water-soluble carbon concentration (WSC) and humic substances content (humic and fulvic acid (FA)). The effects of humification on the molecular structure of humic acid (HA) were also evaluated by Fourier transform infrared (FT-IR) and (13)C NMR spectroscopy. WSC concentration rapidly increased reaching a maximum at day-14 of the composting process and then declined. The humic and fulvic acid content (HA and FA, respectively) slightly increased during the process. The FT-IR and (13)C NMR spectra of HA indicate a high rate of change in structure during composting. The groups containing aromatic and carboxylic C increased, while polysaccharides and other aliphatic structures degraded during composting, resulting in HA structures of higher aromaticity. Therefore, spectrometric measurements could provide information significantly correlated to conventional chemical parameters of compost maturity.     

Composting anaerobic and aerobic sewage sludges using two proportions of sawdust

Sawdust has been proven to be a good bulking agent for sludge composting; however, studies on the most suitable ratio of sludge:sawdust for sludge composting and on the influence of the sludge nature (aerobic or anaerobic) on the composting reaction rate are scarce. In this study two different sewage sludges (aerobic, AS, and anaerobic, ANS) were composted with wood sawdust (WS) as bulking agent at two different ratios (1:1 and 1:3 sludge:sawdust, v:v). Aerobic sludge piles showed significantly higher microbial activity than those of anaerobic sludge, organic matter mineralization rates being higher in the AS mixtures. The lowest thermophilic temperatures during composting were registered when the anaerobic sludge was mixed with sawdust at 1:1 ratio, suggesting the presence of substances toxic to microorganisms. This mixture also showed the lowest decreases of ammonium during composting. All this matched with the inhibitory effect on the germination of Lepidium sativum seeds of this mixture at the first stages of composting, and with its low values of microbial basal respiration. However, the ANS+WS 1:3 compost developed in a suitable way; the higher proportion of bulking agent in this mixture appeared to have a diluting effect on these toxic compounds. Both the proportions assayed allowed composting to develop adequately in the case of the aerobic sludge mixture, yielding suitable composts for agricultural use. However, the ratio 1:1 seems more suitable because it is more economical than the 1:3 ratio and has a lower dilution effect on the nutritional components of the composts. In the case of the anaerobic sludge with its high electrical conductivity and ammonium content, and likely presence of other toxic and phytotoxic substances, the 1:3 ratio is to be recommended because of the dilution effect.     

Soil bioassays as tools for sludge compost quality assessment

Composting is a waste management technology that is becoming more widespread as a response to the increasing production of sewage sludge and the pressure for its reuse in soil. In this study, different bioassays (plant germination, earthworm survival, biomass and reproduction, and collembolan survival and reproduction) were assessed for their usefulness in the compost quality assessment.Compost samples, from two different composting plants, were taken along the composting process, which were characterized and submitted to bioassays (plant germination and collembolan and earthworm performance). Results from our study indicate that the noxious effects of some of the compost samples observed in bioassays are related to the low organic matter stability of composts and the enhanced release of decomposition endproducts, with the exception of earthworms, which are favored. Plant germination and collembolan reproduction inhibition was generally associated with uncomposted sludge, while earthworm total biomass and reproduction were enhanced by these materials. On the other hand, earthworm and collembolan survival were unaffected by the degree of composting of the wastes. However, this pattern was clear in one of the composting procedures assessed, but less in the other, where the release of decomposition endproducts was lower due to its higher stability, indicating the sensitivity and usefulness of bioassays for the quality assessment of composts.     

Effect of composting on the Cd,Zn and Mn content and fractionation in feedstock mixtures with wood chips from a short-rotation coppice and bark

Micronutrient content and availability in composts may be affected by the addition of wood chips or tree bark as a bulking agent in the compost feedstock. In the first part of this study, micronutrient levels were assessed in bark and wood of poplar and willow clones in a short-rotation coppice. Large differences between species were observed in bark concentrations for Cd, Zn and Mn. In the second part of the study, we aimed to determine the effect of feedstock composition and composting on Cd, Zn and Mn concentrations and availability. By means of three composting experiments we examined the effect of (a) bark of different tree species, (b) the amount of bark, and (c) the use of bark versus wood chips. In general, compost characteristics such as pH, organic matter and nutrient content varied due to differences in feedstock mixture and composting process. During the composting process, the availability of Cd, Zn and Mn decreased, although the use of willow and poplar bark or wood chips resulted in elevated total Cd, Zn or Mn concentrations in the compost. Cd concentrations in some composts even exceeded legal criteria. Cd and Zn were mainly bound in the reducible fraction extracted with 0.5 M NH₂OH?HCl. A higher acid-extractable fraction for Mn than for Cd and Zn was found. Higher Cd concentrations in the compost due to the use of bark or wood chips did not result in higher risk of Cd leaching. The results of the pH-stat experiment with gradual acidification of composts illustrated that only a strong pH decline in the compost results in higher availability of Cd, Zn and Mn.     

Coffee husk composting: An investigation of the process using molecular and non-molecular tools

Various parameters were measured during a 90-day composting process of coffee husk with cow dung (Pile 1), with fruit/vegetable wastes (Pile 2) and coffee husk alone (Pile 3). Samples were collected on days 0, 32 and 90 for chemical and microbiological analyses. C/N ratios of Piles 1 and 2 decreased significantly over the 90 days. The highest bacterial counts at the start of the process and highest actinobacterial counts at the end of the process (Piles 1 and 2) indicated microbial succession with concomitant production of compost relevant enzymes. Denaturing gradient gel electrophoresis of rDNA and COMPOCHIP microarray analysis indicated distinctive community shifts during the composting process, with day 0 samples clustering separately from the 32 and 90-day samples. This study, using a multi-parameter approach, has revealed differences in quality and species diversity of the three composts.     

Functional changes in culturable microbial communities during a co-composting process: Carbon source utilization and co-metabolism

Microbial communities in sewage sludge and green waste co-composting were investigated using culture-dependent methods and community level physiological profiles (CLPP) with Biolog Microplate. Different microbial groups characterized each stage of composting. Bacterial densities were high from beginning to end of composting, whereas actinomycete densities increased only after bio-oxidation phase i.e. after 40 days. Fungal populations become particularly high during the last stage of decomposition. Cluster analyses of metabolic profiles revealed a similar separation between two groups of composts at 67 days for bacteria and fungi. Principal component analysis (PCA) applied to bacterial and fungal CLPP data showed a chronological distribution of composts with two phases. The first one (before 67 days), where the composts were characterized by the rapid decomposition of non-humic biodegradable organic matter, was significantly correlated to the decrease of C, C/N, organic matter (OM), fulvic acid (FA), respiration, cellulase, protease, phenoloxidase, alkaline and acid phosphatases activities. The second phase corresponding to the formation of polycondensed humic-like substances was significantly correlated to humic acid (HA) content, pH and HA/FA. The influent substrates selected on both factorial maps showed that microbial communities could adapt their metabolic capacities to the particular environment. The first phase seems to be focused on easily degradable substrate utilization whereas the maturation phase appears as multiple metabolisms, which induce the release of metabolites and their polymerization leading to humification processes.     

Modelling of organic matter dynamics during the composting process

Composting urban organic wastes enables the recycling of their organic fraction in agriculture. The objective of this new composting model was to gain a clearer understanding of the dynamics of organic fractions during composting and to predict the final quality of composts. Organic matter was split into different compartments according to its degradability. The nature and size of these compartments were studied using a biochemical fractionation method. The evolution of each compartment and the microbial biomass were simulated, as was the total organic carbon loss corresponding to organic carbon mineralisation into CO₂. Twelve composting experiments from different feedstocks were used to calibrate and validate our model. We obtained a unique set of estimated parameters. Good agreement was achieved between the simulated and experimental results that described the evolution of different organic fractions, with the exception of some compost because of a poor simulation of the cellulosic and soluble pools. The degradation rate of the cellulosic fraction appeared to be highly variable and dependent on the origin of the feedstocks. The initial soluble fraction could contain some degradable and recalcitrant elements that are not easily accessible experimentally.     

Bacterial community patterns and thermal analyses of composts of various origins.

During composting, the degradation of organic waste is accompanied and driven by a succession of microbial populations exhibiting a broad range of functional capabilities. Detailed inventories of the microbial communities in mature compost, however, are not available. Mature composts, originating from biowaste as well as sewage sludge and anaerobic sludge, were studied by denaturing gradient gel electrophoresis-fingerprints after polymerase chain reaction (PCR) amplification of the 16S rRNA genes using three different universal primer pairs, as well as by differential scanning calorimetry and thermogravimetry. The composts of different origin had different bacterial communities. The influence of different 16S rDNA primer sets on the same batches of compost DNA was evaluated. The clearest separation of different compost types was obtained by using the PCR primer pair 338f + 518r which is suggested for future applications. Communities from the different biowaste compost samples clustered together and could be separated from sewage sludge communities indicating the establishment of different microbial consortia. A similar differentiation of composts was found with the thermogavimetric analyses. It may thus be concluded that the resulting humus quality is closely linked to the microbial communities involved.     

Production of well-matured compost from night-soil sludge by an extremely short period of thermophilic composting

The effect of various operational conditions on the decomposition of organic material during the composting of night-soil treatment sludge was quantitatively examined. The optimum composting conditions were found to be a temperature of ca. 60 °C and an initial pH value of 8. Rapid decomposition of organic matter ceased by the sixth day of composting under these optimum conditions, and the final value of the cumulative emission of carbon (E_C), which represents the degree of organic matter decomposition, was less than 40%, indicating that the sludge contained only a small amount of easily degradable organic material. A plant growth assay using Komatsuna (Brassica campestris L. var. rapiferafroug) in a 1/5000a standard cultivation pot was then conducted for the compost at various degrees of organic matter decomposition: the raw composting material, the final compost obtained on day 6, and the 2 intermediate compost products (i.e., E_C = 10% and 20%). It was found that the larger the E_C, the greater the yield of Komatsuna growth. It was also found that 6 days of composting is sufficient to promote Komatsuna growth at the standard loading level, which is equivalent to a 1.5 g N/pot, since the promotion effect was as high as that obtained using chemical fertilizer. It can therefore be concluded that well-matured compost could be obtained in a short period of time (i.e., as early as 6 days), when night-soil sludge is composted under optimum conditions.     

Maturity assessment of compost from municipal solid waste through the study of enzyme activities and water-soluble fractions

In this work the dynamics of biochemical (enzymatic activities) and chemical (water-soluble fraction) parameters during 100 days of municipal solid wastes composting were studied to evaluate their suitability as tools for compost characterization. The hydrolase (protease, urease, cellulase, beta-glucosidase) and dehydrogenase activities were characterized by significant changes during the first 2 weeks of composting, because of the increase of easily decomposable organic compounds. After the 4th week a "maturation phase" was identified in which the enzymatic activities tended to gently decrease, suggesting the stabilisation of organic matter. Also the water-soluble fractions (water-soluble carbon, nitrogen, carbohydrates and phenols), which are involved in many degradation processes, showed major fluctuations during the first month of composting. The results obtained showed that the hydrolytic activities and the water-soluble fractions did not vary statistically during the last month of composting. Significant correlations between the enzymatic activities, as well as between enzyme activities and water-soluble fractions, were also highlighted. These results highlight the suitability of both enzymatic activities and water soluble fractions as suitable indicators of the state and evolution of the organic matter during composting. However, since in the literature the amount of each activity or fraction at the end of composting depends on the raw material used for composting, single point determinations appear inadequate for compost characterization. This emphasizes the importance of the characterization of the dynamics of enzymatic activities and water-soluble fractions during the process.     

Effects of alkyl polyglycoside (APG) on composting of agricultural wastes

Composting is the biological degradation and transformation of organic materials under controlled conditions to promote aerobic decomposition. To find effective ways to accelerate composting and improve compost quality, numerous methods including additive addition, inoculation of microorganisms, and the use of biosurfactants have been explored. Studies have shown that biosurfactant addition provides more favorable conditions for microorganism growth, thereby accelerating the composting process. However, biosurfactants have limited applications because they are expensive and their use in composting and microbial fertilizers is prohibited. Meanwhile, alkyl polyglycoside (APG) is considered a “green” surfactant. This study aims to determine whether APG addition into a compost reaction vessel during 28-day composting can enhance the organic matter degradation and composting process of dairy manure. Samples were periodically taken from different reactor depths at 0, 3, 5, 7, 14, 21, and 28 days. pH levels, electrical conductivity (EC), ammonium and nitrate nitrogen, seed germination indices, and microbial population were determined. Organic matter and total nitrogen were also measured.Compared with the untreated control, the sample with APG exhibited slightly increased microbial populations, such as bacteria, fungi, and actinomycetes. APG addition increased temperatures without substantially affecting compost pH and EC throughout the process. After 28 days, APG addition increased nitrate nitrogen concentrations, promoted matter degradation, and increased seed germination indices. The results of this study suggest that the addition of APG provides more favorable conditions for microorganism growth, slightly enhancing organic matter decomposition and accelerating the composting process, improving the compost quality to a certain extent.     

Pelleted organo-mineral fertilisers from composted pig slurry solids, animal wastes and spent mushroom compost for amenity grasslands

In Ireland, conversion of biodegradable farm wastes such as pig manure spent mushroom compost and poultry litter wastes to pelletised fertilisers is a desirable option for farmers. In this paper, results obtained from the composting of pig waste solids (20% w/w) blended with other locally available biodegradable wastes comprising poultry litter (26% w/w), spent mushroom compost (26% w/w), cocoa husks (18% w/w) and moistened shredded paper (10% w/w) are presented. The resulting 6-mo old 'mature' composts had a nutrient content of 2.3% total N, 1.6% P and 3.1% K, too 'low' for direct use as an agricultural fertiliser. Formulations incorporating dried blood or feather meal amendments enriched the organic N-content, reduced the moisture in mature compost mixtures and aided the granulation process. Inclusion of mineral supplements viz., sulphate of ammonia, rock phosphate and sulphate of potash, yielded slow release fertilisers with nutrient N:P:K ratios of 10:3:6 and 3:5:10 that were suited for amenity grasslands such as golf courses for spring or summer application and autumn dressing, respectively. Rigorous microbiological tests carried out throughout the composting, processing and pelletising phases indicated that the formulated organo-mineral fertilisers were free of vegetative bacterial pathogens.     

Home composting versus industrial composting: Influence of composting system on compost quality with focus on compost stability

Stability is one of the most important properties of compost obtained from the organic fraction of municipal solid wastes. This property is essential for the application of compost to land to avoid further field degradation and emissions of odors, among others. In this study, a massive characterization of compost samples from both home producers and industrial facilities is presented. Results are analyzed in terms of chemical and respiration characterizations, the latter representing the stability of the compost. Results are also analyzed in terms of statistical validation. The main conclusion from this work is that home composting, when properly conducted, can achieve excellent levels of stability, whereas industrial compost produced in the studied facilities can also present a high stability, although an important dispersion is found in these composts. The study also highlights the importance of respiration techniques to have a reliable characterization of compost quality, while the chemical characterization does not provide enough information to have a complete picture of a compost sample.