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.     

Evaluation of the transformation of organic matter to humic substances in compost by coupling sec-page

Humic acids (HAs) from soil and compost at the beginning (S0) and at the end of the stabilization process after 130 days (S130) have been fractionated by coupling size exclusion chromatography (SEC) and polyacrylamide gel electrophoresis (PAGE). Preparative quantities of HA fractions (HAFs) with different molecular sizes (MSs) and exactly defined electrophoretic mobility (EMs) have been obtained from all samples and the HAFs weight content has been studied. A high degree of similarity in HAFs weight content between soil HA and a stabilized compost HAs130 has been observed. Such data seem to be reliable for monitoring the evolution of the compost organic matter to humic substances for their agricultural uses.     

Composition variability of spent mushroom compost in Ireland

Spent mushroom compost (SMC) has proven to be an attractive material for improving soil structure in tilled soils and increasing dry matter production in grassland soils, owing to its high organic matter content and availability of essential plant nutrients. Because of this, it is important to identify the variability in composition of SMC in order to evaluate its merit as a fertilizer/soil conditioner. For this reason, a study was carried out involving the analysis of SMC samples obtained from five mushroom growers using compost from each of the 13 mushroom composting yards currently operating in both Northern Ireland (5 yd) and the Republic of Ireland (8 yd). The selected parameters measured include dry matter, organic matter, total N, P and K, C/N ratio; plant-available P and K, pH, EC, total Ca, Mg, Na, Cu, Zn, Fe, Mn, Cd, Cr, Ni, Pb; and cellulose, hemicellulose and lignin constituents. Yield of mushroom data were also collected from the selected growers. There were significant differences (P<0.05) within two compost production yards for some parameters, therefore, for the most part, the uniformity of SMC within each yard is relatively consistent. However, significant differences (P<0.05) were evident when comparing SMC obtained from growers supplied with compost from Northern Ireland and the Republic of Ireland independently, particularly among total and available phosphorus and potassium values. The results obtained show that, while SMC has fertilizer merit, its variability of composition must be taken into account when assessing this value. The variability of composition is also of particular interest in the context of recent emphasis on plant nutrient management in agriculture.     

Molecular analysis of bacterial community succession during prolonged compost curing

The compost environment consists of complex organic materials that form a habitat for a rich and diverse microbial community. The aim of this research was to study the dynamics of microbial communities during the compost-curing phase. Three different methods based on 16S rRNA gene sequence were applied to monitor changes in the microbial communities: (1) denaturing gradient gel electrophoresis of PCR-generated rRNA gene fragments; (2) partial rRNA gene clone libraries; and (3) a microarray of oligonucleotide probes targeting rRNA gene sequences. All three methods indicated distinctive community shifts during curing and the dominant species prevailing during the different curing stages were identified. We found a successional transition of different bacterial phylogenetic groups during compost curing. The Proteobacteria were the most abundant phylum in all cases. The Bacteroidetes and the Gammaproteobacteria were ubiquitous. During the midcuring stage, Actinobacteria were dominant. Different members of nitrifying bacteria and cellulose and macromolecule-degrading bacteria were found throughout the curing process. In contrast, pathogens were not detected. In the cured compost, bacterial population shifts were still observed after the compost organic matter and other biochemical properties had seemingly stabilized.     

Changes in the chemical characteristics of water-extractable organic matter during composting and their influence on compost stability and maturity

Composting is the biochemical transformation of waste organic matter by microorganisms whose metabolism occurs in the water-soluble phase. Therefore, a study of the changes occurring in compost dissolved organic matter can be useful for assessing its stability and maturity. In light of the variety of parameters generally utilized to study composting processes, this work aims at identifying the major chemical processes that occur in solution and their influence on the attainment of stability and maturity with composting time. Compost stability, assessed by means of respirometric analysis which determined oxygen demand as a result of mineralization of the compost's organic matter, and compost maturity evaluated with Lepidium sativum L. seed bioassays, were found to be highly related to the nature and content of water-soluble organic matter. Moreover, fractionation of the water-extractable organic carbon showed that the ratio of hydrophobic to hydrophilic carbon increased to values greater than unity for stabilized compost. These results together with the analysis for non-cellulosic polysaccharides, phenolic compounds and organic nitrogen within the water extracts, confirmed the influence of solubilization, mineralization and organic matter transformation on the quality of the final compost.     

Characterization of dairy cattle manure/wallboard paper compost mixture

The aim of this research was to evaluate the use of manufacturing wallboard paper scraps as an alternative bulking agent for dairy cattle manure composting. The characteristics of the composting process were studied based on the changes in physico-chemical parameters and final compost quality. Composting of dairy cattle manure with wallboard paper was performed in a 481-L cylindrical reactor with vacuum-type aeration. Rapid degradation of organic matter was observed during the thermophilic stage of composting due to high microbial activity. High temperature and alkaline pH conditions promoted intense ammonia emission during the early stage of composting. The number of mesophilic and thermophilic microorganisms were found to be affected by changes in temperature at different composting stages. The total nitrogen (N), phosphorus (P), potassium (K), and sodium (Na) concentrations of the mixture did not change significantly after 28days of composting. However, the presence of gypsum in the paper scraps increased the calcium content of the final compost. The wallboard paper had no phyto-inhibitory effects as shown by high germination index of final compost (GI=99%).     

Modeling long-term compost application effects on nitrate leaching

Application of compost to agricultural soils may be beneficial for crop production by increasing soil fertility and supplying plant nutrients, however, any raise of the soil organic matter content may increase the potential for unintended groundwater contamination by nitrate leaching. In this paper, the effect of long-term compost applications on nitrate leaching, soil organic matter content, and crop production is analyzed using results of simulation scenarios for agricultural sites with loamy and sandy soils. Simulations were carried out using the Danish Nitrogen Simulation System (DAISY) which describes the nitrogen balance in a one-dimensional soil-plant-atmosphere system and considers compost type and application rate as well as management and cropping practice. Estimations of hydraulic and solute transport parameters are based on pedotransfer functions. Data from a 4.5-year period of field experiments with compost applications in northern Germany as well as from laboratory experiments with compost amended soil are used for model calibration. Simulation results suggest that: (i) with respect to nitrogen turnover the differences between compost types (i.e., non-matured and matured) are small compared to site-specific properties (i.e., soil temperature and water balance) and management practices (i.e., crop rotation) when considering a compost application period of 50 years; (ii) with respect to nitrate leaching the effect of different compost application scenarios is highly sensitive at the sand and relatively small at the loam site; and (iii) relatively high crop yields and acceptably low nitrate concentrations in the drainage water are obtained at the sand site when applying a combination of 10 t compost/ha/yr and soil- N_min adjusted mineral nitrogen additions of about 20 kg/ha/yr to a winter-grain dominated crop rotation. Further optimization may be possible by applying reduced rates of the (economically interesting) non-matured compost. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date. This revised version was published online in June 2006 with corrections to the Cover Date.     

Microbiological parameters as indicators of compost maturity

AIMS: The objectives of this study were to determine the changes of microbial properties of pig manure collected from pens with different management strategies and composted using different turning and moisture regimes; relate their association with humification parameters and compost temperature; and identify the most suitable microbial indicators of compost maturity. METHODS AND RESULTS: Six different microbial parameters, including total bacterial count, oxygen consumption rate, ATP content, dehydrogenase activity, and microbial biomass C and N, along with humification parameters [humic acid (HA), fulvic acid (FA) and HA : FA ratio] and compost temperature were monitored during composting. Significant positive correlations were found between temperature and microbial properties, including O2 consumption rate, ATP content, dehydrogenase activity, and microbial biomass N. The humification parameters also showed significant correlations with microbial properties of the manure compost. For instance, HA contents of pig manures was positively correlated with total aerobic heterotrophs, and microbial biomass N and C; and negatively correlated with O2 consumption rate, ATP content, and dehydrogenase activity. Among the six microbial parameters examined, dehydrogenase activity was the most important factor affecting compost temperature and humification parameters. Composting strategies employed in this study affected the speed of composting and time of maturation. If the moisture content is maintained weekly at 60% with a 4-day turning frequency, the pig manure will reach maturity in 56 days. CONCLUSIONS: The composting process went through predictable changes in temperature, microbial properties and chemical components despite differences in the initial pig manure and composting strategies used. Among the six microbial parameters used, dehydrogenase activity is the most suitable indicator of compost maturity. Compared with respiration rate, ATP content and microbial biomass procedures, dehydrogenase activity is the simplest, quickest, and cheapest method that can be used to monitor the stability and maturity of composts. SIGNIFICANCE AND IMPACT OF THE STUDY: The results presented here show that microbial parameters can be used in revealing differences between composts and compost maturity. The statistical relationship established between humification parameters and microbial parameters, particularly dehydrogenase activity, demonstrates that it is possible to monitor the composting process more easily and rapidly by avoiding longer and more expensive analytical procedures.     

Assessing the agronomic and environmental effects of the application of cattle manure compost on soil by multivariate methods

Multivariate analysis was used for interpreting data from a pot experiment using samples of three Spanish soils. Samples of soil fertilized with compost were compared with untreated control samples. We also compared the effect of adding the compost to soil with a controlled moisture content of 50% of its water holding capacity (WHC), and to a near-saturated soil (95% WHC). Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were used; they perfectly differentiated sample groups both as a function of the treatment applied and by sampling date. The compost samples were characterized by higher pH, electrical conductivity (EC), organic matter (OM) content and cation exchange capacity (CEC), together with nutrient concentrations than the control pots. The pots with a soil–compost mixture at 95% WHC presented lower values of EC, CEC, inorganic N, K, Na and B than the mixtures at 50% WHC. Multivariate methods may therefore be useful for the analysis and interpretation of a large number of data in soil research.     

UV spectroscopy: a tool for monitoring humification and for proposing an index of the maturity of compost

Composting organic matter is an interesting way to valorize waste. Compost is a product obtained after a humification process. The humification of organic matter during composting was studied by the quantification and monitoring of the evolution of humic substances. The final objective was to be able to evaluate the state of humification based on a spectrum of total humic substances using the method of UV spectral deconvolution. This study presented a new index obtained by UV spectroscopy using the deconvolution of an unknown spectrum of compost with 3 reference spectra. This index was compared to the maturity indices usually used, such as total extraction of humic substances (rate of extraction), IP (index of polymerization) or the humic acid to fulvic acid ratio. This new parameter, which was easy and quick to determine, gave precise information about the quality of the compost. It made it possible to disregard the values of aberrant concentrations caused by the classical protocol of extraction. Compared to the humic acid to fulvic acid ratio, the new index obtained by UV spectral deconvolution showed more representative results: the humic acid to fulvic acid ratio for an apparently non-mature compost was abnormally high, suggesting that the compost was mature, whereas the UV index proposed showed that the compost was really young and not yet humified.     

Microbial degradation of polycyclic aromatic hydrocarbons in soils affected by the organic matrix of compost

This paper describes the degradation of naphthalene, phenanthrene, anthracene, fluoranthene, and pyrene in soil and soil/compost mixtures. Compost addition facilitated the degradation of 500 mg naphthalene/kg soil and 100 mg/kg each of other polycyclic aromatic hydrocarbons (PAH) within 25 days in soil systems with water contents below the water-holding capacity. By means of a humic acid extraction, it was demonstrated that the decrease of PAH concentrations after compost addition was not caused by a sorption to organic matter preventing PAH analysis. The enhanced PAH degradation was examined in a series of batch experiments with contaminated soil to evaluate whether the effect of compost addition is caused by the microorganisms of the compost itself, by the properties of the organic matrix of the compost material, or by water-soluble fertilising substances. The experiments revealed that the release of fertilising substances from the compost and the shift of soil pH brought about by the compost did not cause the stimulatory effect. The microorganisms inherent to the compost were also not necessary for the enhanced degradation. Sterilised compost was recolonised by soil microorganisms after a lagphase yielding a degradation activity similar to that of the non-sterilised compost. The presence of the solid organic matrix of the compost seemed to be essential for the enhanced degradation. The soil/compost microflora, which was separated from the organic matrix in liquid cultures, exhibited a much lower degrading activity than in the presence of the solid organic material.     

Characterization of different compost extracts using Fourier-transform infrared spectroscopy (FTIR) and thermal analysis

Compost extract or “compost tea” is a liquid extract of compost obtained by mixing compost and water for a defined period of time. Compost tea contains nutrients and a range of different organisms and is applied to the soil or directly to plants with the principal aim of suppressing certain plant diseases. In addition, the application of compost tea supplies nutrients and organic matter to the soil. Thermal analysis and Fourier transform infrared spectroscopy (FTIR) are two widely applied analytical techniques for establishing the stability of compost, and although numerous studies have evaluated the capacity of compost tea to suppress plant diseases, there are no studies employing these techniques to characterize compost-tea. For the present study, 12 compost extracts were produced under varying conditions in a purpose-built reactor. Two different composts, an stable compost produced from manure and an unstable compost produced from municipal solid waste, respectively, two aeration systems (aerated and non-aerated extracts) and three temperatures (10, 20 and 30°C) were used in these experiments. The extracts were freeze-dried and subsequently analysed, together with the two composts, by means of FTIR and thermal analysis. Extracts produced from high stability compost, independently of the conditions of aeration and temperature, showed very similar results. In contrast, differences among extracts produced from the unstable compost were more noticeable. However, the different conditions of aeration and temperature during the production of the extracts only explained partially these differences, since the transformations undergone by compost over the 3 months that the experiments lasted were also reflected in the composition of the extracts. In spite of everything, extraction process favoured the degradation of easily oxidizable organic matter, which was more abundant in unstable compost. This degradation was more intense for non-aerated processes, probably due to the longer duration of these (10 days) with respect to aerated extractions (2 days). The effect of temperature was not clear in these experiments, although high temperatures could increase micro organism activity and consequently favour the degradation of easily oxidizable organic matter.     

Chemical and biological changes during composting of different organic wastes and assessment of compost maturity

Changes in organic C, total N, C:N ratio, activities of cellulase, xylanase and protease, and microbial population were determined during composting of different organic wastes such as mixture of sugarcane trash and cattle dung, press mud, poultry waste and water hyacinth biomass. There were losses of N in poultry waste and water hyacinth with the effect an initial increase in C:N ratio was observed which decreased later on due to decomposition. The activities of cellulase, xylanase and protease were maximum between 30 and 60 days of composting in various wastes. Similar trend was observed with respect to mesophilic bacterial and fungal population. Various quality parameters like C:N ratio, water soluble C (WSC), CO(2) evolution and level of humic substances were compared after 90 day composting. There was statistically significant correlation between C:N ratio and CO(2) evolution, WSC and humic substances. Significant correlation between CO(2) evolved and level of humic substances was also observed. The study shows that no single parameter can be taken as an index of compost maturity. However, C:N ratio and CO(2) evolved from finished compost can be taken as the most reliable indices of compost maturity.     

Improving the quality of municipal organic waste compost

The effects of different municipal organic waste (MOW) management practices (shredding, addition of carbon-rich materials and inoculation with earthworms) on organic matter stabilization and compost quality were studied. Four static piles were prepared with: (i) shredded MOW; (ii) shredded MOW+woodshavings; (iii) non-shredded MOW; and (iv) non-shredded MOW+woodshavings. After 50 days, a part of each pile was separated for vermistabilization, while the rest continued as traditional thermophilic composting piles. At different sampling dates, and in the finished products, the following parameters were measured: pH, electrical conductivity, carbon dioxide evolution, and concentrations of organic matter, total nitrogen, water-soluble carbon, nitrate nitrogen, ammonium nitrogen, and extractable phosphorus. Shredded treatments exhibited faster organic matter stabilization than non-shredded treatments, evidenced specially by earlier stabilization of carbon dioxide production and shorter thermophilic phases. Woodshavings addition greatly increased quality of final products in terms of organic matter concentration, and pH and electrical conductivity values, but decreased total nitrogen and available nutrient concentrations. Vermicomposting of previously composted material led to products richer in organic matter, total nitrogen, and available nutrient concentrations than composting only, probably due to the coupled effect of earthworm activity and a shorter thermophilic phase.     

Composting of bio-waste, aerobic and anaerobic sludges--effect of feedstock on the process and quality of compost

In-vessel composting of three stocks with originally different degree of organic matter degradation was conducted for: (1) kitchen source-separated bio-waste (BW), (2) aerobic (AS) as well as (3) anaerobic sludges (AnS) from municipal wastewater treatment plant. Composting experiment lasted over a year. The highest activity of the process was in the BW compost. It was implied by the highest temperature, CO(2) release, ammonification and nitrification, intensive accumulation and removal of low-weight carboxylic acids (water- and NaOH-extractable). Between the sludges higher mineralization and CO2 release was in AnS, while ammonification and nitrification were higher in AS compost; no significant difference between sludge composts was noticed for dynamics of pH, conductivity, concentrations of LWCA, and some nutrient compounds and heavy metals. Nitrogen content of the final compost increased in BW, but decreased in AS and AnS. Phytotoxicity of Lepidium sativum was eliminated faster in sludge composts compared to BW compost.     

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.     

Development of compost maturity and Actinobacteria populations during full-scale composting of organic household waste

AIMS: This study investigates changes in microbiological and physicochemical parameters during large-scale, thermophilic composting of a single batch of municipal organic waste. The inter-relationships between the microbial biomass and community structure as well as several physicochemical parameters and estimates of maturation were evaluated. METHODS AND RESULTS: Analyses of signature fatty acids with the phospholipid fatty acid and ester-linked methods showed that the total microbial biomass was highest during the early thermophilic phase. The contribution of signature 10Me fatty acids from Actinobacteria indicated a relatively constant proportion around 10% of the microbial community. However, analyses of the Actinobacteria species composition with a PCR-denaturing gradient gel electrophoresis approach targeting 16S rRNA genes demonstrated clear shifts in the community structure. CONCLUSIONS: This study demonstrates that compost quality, particularly maturity, is linked to the composition of the microbial community structure, but further studies in other full-scale systems are needed to validate the generality of these findings. SIGNIFICANCE AND IMPACT OF THE STUDY: The combination of signature lipid and nucleic acid-based analyses greatly expands the specificity and the scope for assessing the microbial community composition in composts. The results presented in this study give new information on how the development of the compost microbial community is connected to curing and maturation in the later stages of composting, and emphasizes the role of Actinobacteria in this respect.     

Evaluation of city refuse compost maturity: a review

Evaluation of the maturity of domestic refuse compost has been widely recognized as one of the most important problems concerning the composting process and the application of this product to the land. This has given rise, in recent years, to a great amount of information in the literature. Arranging and clarifying this information is the fundamental aim of the present paper. In the first place, the effects of insufficiently-matured compost on the soil-plant system are studied, and the criteria and methods proposed for the determination of compost maturity are described. The conditions or characteristics which the compost must meet to assure an acceptable degree of maturity are also established. Numerous studies make clear that the most notable effect of immature compost is the biological blockage of soil-available nitrogen which may give rise to serious N-deficiencies in crops with consequent depressive effects. The rapid decomposition of an immature compost may cause a decrease of the O₂-concentration and soil Eh and as a result, the creation of an anaerobic and strongly-reducing environment at the level of the root system. This causes an increase of the solubility of heavy metals in the soil and inhibition of plant seed germination by the production of phytotoxic substances, fundamentally ammonia, ethylene oxide and organic acids. The plant reacts to the inhibitory environment conditions by lowering its metabolic rate, reducing root respiration, decreasing nutrient absorption and slowing the gibberellin and cytokinin synthesis and transport. Many criteria or methods have been proposed to establish the degree of maturity and avoid these risks. They may be grouped into five types. Physical tests: temperature, odour and colour. Study of microbial activity parameters: measuring metabolic activity, biomass count and the study of the easily-biodegradable constituents. These include: respirometric studies, ATP and hydrolytic enzyme activity determinations, hydrolysable polysaccharide content, relation between total organic carbon and soluble glucides, and ratio of carbon in reducing sugars to total carbon. Study of humified organic matter: determining the richness in total humus and the degree of polymerization of humic compounds by means of paper chromatography and photocolorimetric methods. Chemical methods: C/N ratio in solid phase and in water extracts, pH, cation-exchange capacity and tests for ammonia, hydrogen sulphide, nitrates and nitrites. Biological methods: based on the determination of the germination index of seeds incubated in water extracts of the compost.     

Electrofocusing the compost organic matter obtained by coupling SEC-PAGE

Humic acids (HA)-like extracted from compost at the beginning (t(0)) and after 130 days of composting (t(130)) were fractionated by coupling size exclusion chromatography to polyacrylamide gel electrophoresis (SEC-PAGE). HA-like fractions with the same molecular size (MS) and electrophoretic mobility were pooled and further characterised by analytical polyacrylamide gel electrofocusing (EF) and compared with HA separated from a Typic Chernozem soil. During the composting process all fractions were subjected to quantitative and qualitative modifications: the high MS fraction was degraded, the mid MS fractions were qualitatively changed, the content of low MS fractions increased and changed qualitatively. The main changes in EF pattern of the non fractionated HA-like t(130) were associated to low MS fractions. Such data seem to be reliable for explanation what mechanisms and monitoring of the evolution of the compost organic matter for their agricultural uses.