Comparison of static,in-vessel composting of MSW with thermophilic anaerobic digestion and combinations of the two processes

The biological stabilisation of the organic fraction of municipal solid waste (OFMSW) into a form stable enough for land application can be achieved via aerobic or anaerobic treatments. To investigate the rates of degradation (e.g. via electron equivalents removed, or via carbon emitted) of aerobic and anaerobic treatment, OFMSW samples were exposed to computer controlled laboratory-scale aerobic (static in-vessel composting), and anaerobic (thermophilic anaerobic digestion with liquor recycle) treatment individually and in combination. A comparison of the degradation rates, based on electron flow revealed that provided a suitable inoculum was used, anaerobic digestion was the faster of the two waste conversion process. In addition to faster maximum substrate oxidation rates, anaerobic digestion (followed by post-treatment aerobic maturation), when compared to static composting alone, converted a larger fraction of the organics to gaseous end-products (CO₂ and CH₄), leading to improved end-product stability and maturity, as measured by compost self-heating and root elongation tests, respectively. While not comparable to windrow and other mixed, highly aerated compost systems, our results show that in the thermophilic, in-vessel treatment investigated here, the inclusion of a anaerobic phase, rather than using composting alone, improved hydrolysis rates as well as oxidation rates and product stability. The combination of the two methods, as used in the DiCOM^® process, was also tested allowing heat generation to thermophilic operating temperature, biogas recovery and a low odour stable end-product within 19 days of operation.     

Methods to improve the composting process of the solid fraction of dairy cattle slurry

Cattle slurry solid fraction (SF) with different dry matter (DM) contents was collected from two dairy farms and composted in static and turned piles, with different sizes and cover types, to investigate the effects of pile conditions on the physical and chemical changes in SF during composting and to identify approaches to improve final compost quality. Thermophilic temperatures were attained soon after separation of SF, but the temperature of piles covered with polyethylene did not increase above 60 degrees C. The rate of organic matter (OM) mineralisation increased for turned piles in comparison to static piles, but the maximum amount of mineralisable OM (630-675gkg(-1)) was similar for all pile treatments. The C/N ratio declined from over 36 to a value of 14 towards the end of composting, indicating an advanced degree of OM stabilisation. Mature compost was obtained from raw SF feedstock as indicated by the low compost temperature, low C/N ratio, and low content of NH(4)(+) combined with increased concentrations of NO(3)(-). The efficiency of the composting process was improved and NH(3)-N losses were minimized by increasing DM content of the SF, reducing the frequency of pile turning and managing compost piles without an impermeable cover.     

Enhancement of dry anaerobic batch digestion of the organic fraction of municipal solid waste by an aerobic pretreatment step

The start-up of the dry anaerobic batch digestion by the BIOCEL-concept of the organic fraction of municipal solid waste (MSW) is unbalanced when a methanogenic inoculum (digested sewage sludge) is added to a total solids concentration of 35%. The unbalanced conditions are the result of the rapid degradation of easily-degradable compounds which are present in the organic fraction. Enhancement of the first start-up of the dry batch digestion was tried by applying an aerobic partial-composting step. By this aerobic treatment the easily degradable compounds are removed. After the composting step the anaerobic digestion will be limited by the conversion of the ligno-cellulose part of the organic fraction. It appeared that at least 19·5% of the volatile solids (VS) should be converted during the aerobic composting period before acid formation in the digestion was in balance with the methane formation. This amount of aerobically degraded VS means a 40% loss of potential biogas. The loss of a part of the biogas is a major drawback to the partial composting as a method for enhancing the start-up of the dry anaerobic digestion. A shorter composting period which is combined with another start-up method might be a feasible method to decrease the energy input of the dry digestion process.     

Microbial degradation and humification of the lawn care pesticide 2,4-dichlorophenoxyacetic acid during the composting of yard trimmings.

The fate of the widely used lawn care herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) during the composting of yard trimmings consisting of primarily leaves and grass is an important unexplored question. In this study, we determined the extent of 2,4-D mineralization, incorporation into humic matter, volatilization, and sorption during the composting of yard trimmings. Yard trimmings (2:1 [wt/wt] leaves-grass) were amended with 14C-ring-labeled 2,4-D (17 mg/kg of dry weight) and composted in a temperature-controlled laboratory scale compost system. During composting, thermophilic microbes were numerically dominant, reaching a maximum of 2 x 10(11)/g. At the end of composting, 46% of the organic matter (OM) present in the yard trimmings was lost and the compost was stable, with an oxygen uptake rate of 0.09 mg of O2 per g of OM per h, and was well humified (humification index, 0.39). Mineralization of the OM temporally paralleled mineralization of 2,4-D. In the final compost, 47% of the added 2,4-D carbon was mineralized, about 23% was complexed with high-molecular-weight humic acids, and about 20% was not extractable (humin fraction). Less than 1% of the added 14C was present in water expressed from the finished compost, suggesting a low potential for leaching of 2,4-D. Very little volatilization of 2,4-D occurred during composting. It is of interest that our results indicate active mineralization of 2,4-D at composting temperatures of 60 degrees C because microbial 2,4-D degradation at thermophilic temperatures has not been previously documented.     

烟草废弃物在堆肥领域的研究进展

在烟草生产及加工过程中,通常会产生大量的烟草废弃物,如何有效利用这些废弃物以避免环境污染和资源浪费,已成为烟草行业亟需解决的问解。研究发现,烟草废弃物堆肥化处理是规模化利用废弃资源的有效途径之一,对烟草农业的绿色、低碳、循环、可持续发展具有重要意义。从有机肥堆肥制备技术、肥效研究等方面进行了系统综述,从整体上展示了烟草废弃物堆肥技术的发展现状,以期为国内烟草废弃物源堆肥未来技术的研发及产业化提供一定的参考。通过分析发现,在堆肥制备技术方面,主要有微生物菌剂添加技术、共堆肥技术和烟草材料预处理技术3种,此外还衍生出液态有机肥和厌氧发酵联产有机肥技术;在堆肥肥效研究方面,烟草废弃物堆肥可明显改善土壤的物性参数、化学参数以及生物学参数,显著钝化土壤重金属元素,进而提高作物的产量或品质,其中堆肥与化学肥料配施的效果相对较好;堆肥的多功能化是未来堆肥创新利用的重要途径。     

Composting winery waste: sludges and grape stalks

The composting of winery waste is an alternative to the traditional disposal of residues, and also involves a commitment to reducing the production of waste products. We studied two residues (sludge and grape stalks), mixed in two proportions (1:1 and 1:2 sludge and grape stalks (v/v)), and we also examined the effects of grinding the grape stalks. Our results showed that composting the assayed materials was possible. Best results were obtained in the compost heap in which the residues were mixed in the proportion 1:2, and where the grape stalks had been previously ground. Optimum results required a moisture around 55% and a maximum temperature around 65 degrees C and an oxygen concentration not lower than 5-10%. The resulting compost had a high agronomic value and is particularly suitable for the soils of the vineyards which have a very low organic matter content. The compost can be reintroduced into the production system, thereby closing the residual material cycle.     

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.     

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.     

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.     

Co-composting of oil exhausted olive-cake, poultry manure and industrial residues of agro-food activity for soil amendment

The co-composting of exhausted olive-cake with poultry manure and sesame shells was investigated. These organic solid wastes were watered by the confectionary wastewater which is characterized by its high content of residual sugars raising its COD. Four aerated windrows were performed to establish the effects of confectionary by-products on the compost process. Different mixtures of the agro-industrial wastes were used. During the composting process, physico-chemical parameters (temperature, moisture, pH, electrical conductivity, total carbon and total nitrogen) were studied. The stability of the biological system was noticed after 70 days. The final products were characterized by their relatively high organic matter content, and low C/N ratio of 14-17. The humidification of the windrows with the wastewater seemed to have accelerated the composting process in comparison to a windrow humidified with water. In addition, the organic matter degradation was enhanced to reach 55-70%. The application of the obtained composts to soil appeared to significantly improve the soil fertility. Indeed, field experiments showed an increase in potato yield; the production was 30.5-37.5 tons ha(-1), compared to 30.5 tons ha(-1) with farm manure.     

Characterization of natural organic matter (NOM) derived from sewage sludge compost. Part 2: multivariate techniques in the study of compost maturation

This study presents the results of chemometric data analysis which describes the maturation of sewage sludge compost. The compost was characterized at different stages of maturation by various chemical and spectroscopic parameters including carbon and nitrogen content, humic substances content, UV-Vis and 13C NMR. The data set of compost characteristics was analyzed using multivariate methods: cluster analysis (CA) and principal component analysis (PCA). The results enabled the determination of three groups of compost samples at different stages of maturation that correspond to three stages of composting: (i) domination of rapid decomposition of non-humic, easily biodegradable organic matter, (ii) domination of organic matter humification and formation of polycondensed, humic-like substances (the next 2 weeks), (iii) stabilization of transformed organic material and weak microbial activity. The multivariate techniques also enabled the identification of main parameters that change during different stages of composting the most.     

玉米秸秆堆肥的田间积制和原位还田肥效

针对我国西南丘陵山区玉米秸秆随处堆放或就地焚烧,既浪费资源又污染空气的情况,研究一种适合当地有机肥就地积制利用的方法.试验将玉米秸秆直接堆放于田边地角,接种菌剂,添加增氮和保氮剂,覆盖薄膜,腐熟后的堆肥配施化肥原位施入烟地.结果表明: 与对照(自然堆肥,CK)相比,生物堆肥(玉米秸秆+菌剂+增氮剂+保氮剂+覆盖薄膜)的物料升温快(2～3 d,>35 ℃),高温期(≥50 ℃)持续时间长(约15 d),降温慢;微生物种群在高温期减少,但细菌数量比CK高2～3个数量级;经90 d的积制,玉米秸秆呈深褐色或黑色,为碎屑或粉末状态,完全腐熟,含水量低于25%, pH 6.14,活性有机质和氮磷钾养分含量显著高于CK.在烤烟栽培中,生物堆肥配施50%的化肥可显著提高烟叶产量、均价、产值,改善烟叶品质.说明这种生物堆肥方式实现了玉米秸秆资源化利用,消除了由此引起的空气污染,适合于丘陵山区.     

Transformation of buffalo manure by composting or vermicomposting to rehabilitate degraded tropical soils

The addition of composted buffalo manure may lead to qualitative and quantitative improvement of the organic matter content of degraded tropical agricultural soils in Northern Vietnam. The objectives of this study were to follow the biochemical changes occurring during composting of buffalo manure with and without earthworms during 3 months and to study the effect of the end products (compost and vermicompost) on soil biochemical parameters and plant growth after two months of incubation under controlled conditions in an open pot experiment. Our conceptual approach included characterisation of organic matter of the two composts before and after addition to soil by elemental, isotopic analysis and analytical pyrolysis and comparison with conventional fertilisation. We also analysed for lignin content and composition.Our results showed that composting in the presence of earthworms led to stronger transformation of buffalo manure than regular composting. Vermicompost was enriched in N-containing compounds and depleted in polysaccharides. It further contained stronger modified lignin compared to regular compost. In the bulk soil, the amendment of compost and vermicompost led to significant modification of the soil organic matter after 2 months of exposure to natural weather conditions. The lignin component of SOM was unaffected whatever the origin of the organic amendment. Compost and vermicompost amendments both enhanced aggregation and increased the amount of organic matter in water stable aggregates. However, vermicompost is preferable to compost due to its beneficial effect on plant growth, while having similar positive effects on quantity and quality of SOM.     

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.     

Anaerobic digestion of thin stillage for energy recovery and water reuse in corn-ethanol plants

Recycling of anaerobically-digested thin stillage within a corn-ethanol plant may result in the accumulation of nutrients of environmental concern in animal feed coproducts and inhibitory organic materials in the fermentation tank. Our focus is on anaerobic digestion of treated (centrifugation and lime addition) thin stillage. Suitability of digestate from anaerobic treatment for reuse as process water was also investigated. Experiments conducted at various inoculum-to-substrate ratios (ISRs) revealed that alkalinity is a critical parameter limiting digestibility of thin stillage. An ISR level of 2 appeared optimal based on high biogas production level (763 mL biogas/g volatile solids added) and organic matter removal (80.6% COD removal). The digester supernatant at this ISR level was found to contain both organic and inorganic constituents at levels that would cause no inhibition to ethanol fermentation. Anaerobic digestion of treated-thin stillage can be expected to improve the water and energy efficiencies of dry grind corn-ethanol plants.     

A multi-criteria ranking of different technologies for the anaerobic digestion for energy recovery of the organic fraction of municipal solid wastes

This paper describes a conceptual framework and methodological tool developed for the evaluation of different anaerobic digestion technologies suitable for treating the organic fraction of municipal solid waste, by introducing the multi-criteria decision support method Electre III and demonstrating its related applicability via a test application. Several anaerobic digestion technologies have been proposed over the last years; when compared to biogas recovery from landfills, their advantage is the stability in biogas production and the stabilization of waste prior to final disposal. Anaerobic digestion technologies also show great adaptability to a broad spectrum of different input material beside the organic fraction of municipal solid waste (e.g. agricultural and animal wastes, sewage sludge) and can also be used in remote and isolated communities, either stand-alone or in conjunction to other renewable energy sources. Main driver for this work was the preliminary screening of such methods for potential application in Hellenic islands in the municipal solid waste management sector. Anaerobic digestion technologies follow different approaches to the anaerobic digestion process and also can include production of compost. In the presented multi-criteria analysis exercise, Electre III is implemented for comparing and ranking 5 selected alternative anaerobic digestion technologies. The results of a performed sensitivity analysis are then discussed. In conclusion, the performed multi-criteria approach was found to be a practical and feasible method for the integrated assessment and ranking of anaerobic digestion technologies by also considering different viewpoints and other uncertainties of the decision-making process.     

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.     

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.     

Composting of the solid fraction of olive mill wastewater with olive leaves: organic matter degradation and biological activity

The flocculated solid fraction of olive mill wastewaters, obtained from two different olive oil extraction systems (FOMW1 and FOMW2) was composted, with olive leaves (OL) as bulking agent, by the static pile system (Rutgers). The dynamic of organic matter (OM) degradation during composting and its relationship with the basal respiration and fluorescein diacetate (FDA) hydrolytic activity, as indicators of biological activity, were studied. Two mixtures were prepared: C1, from 65% FOMW1 plus 35% OL; and C2, from 74% FOMW2 plus 25% OL and 1% urea. The biooxidative phase of composting in C1, which had a high initial C/N ratio, was long, leading to a high OM degradation, mainly of the lignocellulosic compounds. The water-soluble organic carbon content, C/N ratio and the urea supplied as a N source for the C2 compost make this mixture more adequate for composting, as it had a shorter composting time than C1, and developed a microbial population with a high metabolic activity. The results for basal respiration in C1 and C2 were correlated at a high probability level with those of FDA hydrolysis, and both parameters can be used for establishing the degree of biological stability of the composting material.     

Chemical properties and hydrolytic enzyme activities for the characterisation of two-phase olive mill wastes composting

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated during the extraction of olive oil by the two-phase centrifugation system. Among all the available disposal options, composting is gaining interest as a sustainable strategy to recycle TPOMW for agricultural purposes. The quality of compost for agronomical use depends on the degree of organic matter stabilization, but despite several studies on the topic, there is not a single method available which alone can give a certain indication of compost stability. In addition, information on the biological and biochemical properties, including the enzymatic activity (EA) of compost, is rare. The aim of this work was to investigate the suitability of some enzymatic activities (beta-glucosidase, arylsulphatase, acid-phosphatase, alkaline-phosphatase, urease and fluorescein diacetate hydrolysis (FDA)) as parameters to evaluate organic matter stability during the composting of TPOMW. These enzymatic indices were also compared to conventional stability indices. For this purpose two composting piles were prepared by mixing TPOMW with sheep manure and grape stalks in different proportions, with forced aeration and occasional turnings. The composting of TPOMW followed the common pattern reported previously for this kind of material with a reduction of 40-50% of organic matter, a gradual increase in pH, disappearance of phytotoxicity and formation of humic-like C. All EA increased during composting except acid-phosphatase. Significant correlations were found between EA and some important conventional stability indices indicating that EA can be a simple and reliable tool to determine the degree of stability of TPOMW composts.