Higher Organic Matter Degradation Research Articles

Organomineralization of dolomite in hypersaline microbial mats from Qatar sabkhas visualized by TEM & STXM

Deep insight into the low-temperature mineralization mechanism of dolomite in sediments has remained elusive. This issue is popularly termed “The Dolomite Problem” due to its multifactorial nature. Dolomite has been observed to mineralize in the exopolymeric substances produced by microbial mat communities (Bontognali et al. 2013), where productivity is high. One working hypothesis suggests that degrading organic matter in hypersaline environments releases the necessary component ions, increasing saturation with respect to dolomite (DiLoreto et al. 2019, Dupraz et al. 2009, Petrash et al. 2017). Other models suggest a dissolution-reprecipitation reaction of calcite to dolomite (Rivers 2023). High-resolution micro-spectroscopy techniques (such as transmission electron microscopy, TEM; and scanning transmission X-ray microscopy, STXM) can be used to determine chemical changes in crystals nucleating in a matrix, however to date very little studies have focused on observing dolomite mineralization at the nano-scale. The present study investigates microbial mats collected from hypersaline salt flats in the Persian gulf at micro- to nano-meter scales using high-spatial and -energy resolution TEM (Thermo Scientific Talos 200X at the Canadian Centre for Electron Microscopy) and STXM (PolLux Beamline at the Swiss Light Source at Paul Scherrer Institut), specifically to see changes in carbonate mineralization due to interactions with organic matter. C, Ca and O elemental maps of carbonate crystals were obtained with EDXS (energy-dispersive X-ray spectroscopy) in TEM. These crystals were also indexed by SAED (selected area electron diffraction in TEM). Fine spectral signatures (near-edge X-ray absorption fine structures, or NEXAFS) at the C K-edge (280-290 eV) and Ca L2,3-edge (344-356 eV) in STXM were used to determine the chemical identity of carbonate minerals and surrounding organic matter of the microbial mats. The results of the study show that dolomite nucleates in close association with the organic matter of the mats, where degradation is highest (defined in our adjacent study as the increase in C:N ratio). In TEM, polycrystalline dolomite is seen mineralizing in the matrix of the microbial mat organic material (Fig. 1). In STXM, the identity of the carbonate mineral changes from calcite on the outside to dolomite on the inside of the microbial mat particle (Fig. 2). In addition, our microsensor observations of elevated H2S concentrations, surface oxygenation from oxygenic phototrophy, high reduction potential, high organic carbon, high Mg:Ca ratio and high organic matter degradation (by C:N ratio) in each of the studied microbial mats confirms that the ideal dolomite mineralization conditions according to models of the dolomite problem are present in each case.

Optimization of P25/CaTiO3nanorod Composite Photocatalysts for High Organic Matter Degradation Performance

Wastewater is discharged into rivers and oceans without any treatment, causing significant damage to animal health and destroying ecosystems. Semiconductor photocatalysts are attracting attention as an effective means for solving this problem. Among them, titanium-based perovskite semiconductors are expected to be the next-generation photocatalysts because of their wide range of properties, including chemical and optical stability. CaTiO3, in particular, has attracted attention because of its excellent corrosion resistance, low cost, and ease of material synthesis. In this study, CaTiO3 nanorods (CaTiO3NR) were prepared by hydrothermal synthesis. The photocatalytic activity was improved by forming a heterostructure between TiO2 particles (P25) and CaTiO3NR and by optimizing the mass ratio of P25 to CaTiO3NR. Methylene blue solution was used as a pollutant model to evaluate the degradation performance of photocatalysts under UV irradiation. The results showed that controlling the mass ratio of P25 /CaTiO3NR can significantly improve the photocatalytic performance and has better degradation than P25/CaTiO3nanocuboids composite photocatalysts. The highest photocatalytic performance was achieved by the P25 /CaTiO3NR=3:1 composite photocatalyst, which had about 60% more decomposition performance compared to P25.

Exploring the Microbial Dynamics of Organic Matter Degradation and Humification during Co-Composting of Cow Manure and Bedding Material Waste

The present study investigated the effects of bedding material (BM) waste on physicochemical properties, organic matter (OM) degradation, microbial community structure and metabolic function during composting. The results showed that bedding material (CK-0, S1-40%, S2-25%) optimized the composting conditions for lignocellulose and OM biodegradation. The highest OM degradation and humic substance (HS) synthesis rates were observed in the 40% BM addition group. Firmicutes was more abundant in the bedding material addition groups, whereas Proteobacteria was more abundant in the group without bedding material. Functional prediction showed higher carbohydrate and amino acid metabolism in the BM groups than that in control group. Animal and plant pathogens were almost eliminated, and saprotrophs were the dominant fungal trophic modes after 40% BM addition composting. Cellulose, hemicellulose, and organic matter had strong associations with microbial communities, such as Lysinibacillus and Corynebacterium (bacteria), compared to the associations of Aspergillus, Candida, and Sordariomycetes (fungi) (p value < 0.05). Network analysis revealed closer microbial community interactions in 40% BM addition group than in other groups. These findings provide detailed information about the coupling of material conversion, of bacterial and fungal succession during composting, and that bedding materials waste can also be used as an effective compost amendment.

Use of corn stover as bulking agent in dairy manure composting toward Japanese circular dairy farming.

In response to the recent development of ear corn feeding systems and the shortage of bulking agents for manure composting in the Hokkaido region, the plausibility of using corn stover (a residue of ear corn harvesting) as an alternative bulking agent for dairy manure composting was tested. The temperature profile, quality of the final product, and greenhouse gas emissions were evaluated and compared with the values obtained from manure that used wheat straw, a typical bulking agent. A sufficiently high temperature profile (>70°C) and active organic matter degradation were achieved by mixing in corn stover. After active organic matter degradation for 8 weeks, CO2 production was significantly lower and the stable final products were obtained. The total solids level increased significantly, to 48.8–50.4%, while the C/N ratio dropped significantly, from 19.9–21.8 to 11.2–12.8. Methane emission from the corn-stover-based pile was 0.36% of initial volatile solids, while nitrous oxide emission was 0.58% of initial N, proving that the use of corn stover can mitigate greenhouse gas emission and that its mitigating effect was comparable to those of other bulking agents. Together, the results showed that the use of corn stover can be a suitable alternative bulking agent for dairy manure composting and can serve as part of an ecologically friendly and “circular” method of dairy farming.

Toward Sustainability in Rural Areas: Composting Palm Tree Residues in Rotating Bioreactors

Huge quantities of palm tree residues are available annually in Saudi Arabia; they are often disposed of by burning, leading to large environmental pollution and health problems. Enclosed composting may be a successful method for utilizing these residues. Effective composting in a rotary bioreactor depends on the composting materials and the frequencies of the rotation–aeration process. Here, we attempted to determine the optimal method for composting these residues in a bioreactor. Four identical pilot-scale bioreactors (D1–D4) were used. The respective aeration–rotation frequencies were continuous (D1), and 20 min per 1 h (D2), 2 h (D3), and 3 h (D4); the rotation speed of the bioreactors was 3 rpm. Three periods were analyzed; their names and their respective lengths for D1, D2, D3, and D4 were as follows: the lag period was 10 h for each, the mesophilic periods were 13, 14, 89, and 231 h, and the thermophilic periods were 0, 55, 71, and 17 h. The peak compost temperatures (Tc, max) for D1, D2, and D3 were 65.2, 57.2, and 46.9 °C, and were achieved at 36, 71, and 108 h of operation, respectively. In D1, Tc quickly declined after reaching Tc, max due to limited microbial activity at Tc > 60 °C. In D2, a Tc of 50–57.2 °C was maintained for 61 h, and the highest organic matter degradation (OMD) of 0.30 was achieved. During the composting period, the carbon to nitrogen (C/N) ratio and moisture contents (MC) remained in the optimal ranges for microorganisms and did not affect the composting process. The results indicated that combined aeration–rotation for 20 min every hour (D2) gave the best results for composting palm tree residues, it ensured the hygiene safety of the end product, and it also consumed less power for aeration and rotation than D1.

A comparison of various bulking materials as a supporting matrix in composting blackwater solids from vacuum toilets

This study discusses the influence of six bulking materials (peat, bark, oat husks, sawdust, food waste, and wheat bran) on the composting of blackwater solids (feces, urine and toilet paper) from low flush vacuum toilets (0.8 L/flush). The focus was on faecal indicator reduction, nutrient recycling, and carbon dioxide and methane emissions. In a composting experiment lasting 60 days, bulking materials were combined and mixed with blackwater solids, composted without stirring and with controlled aeration in a bench scale experiment. The bulking materials combination of oat husks, wheat bran and bark and of oat husks and wheat bran composted with blackwater solids showed the best results in terms of faecal indicator reduction (2.8 log10 reduction of Escherichia coli and 3.2 log10 reduction of faecal streptococci, respectively). Oat husks, bark and wheat bran combination had the smallest nutrient losses of 7.5% total nitrogen, 3.8% total phosphorus and 28% total potassium, while the highest accumulation in total phosphorus was 76.4% occurred in the mixture with oat husks and wheat bran. Peat and food waste improved the sorption of ammonia. The highest methane emissions (average 15.4%) were detected after 28 days of composting in the mixture with bran and food waste. Methane and carbon dioxide levels decreased in all the mixtures towards the end of composting indicating high organic matter degradation. Our findings show that a variety of natural and inexpensive materials can be used and adapted when composing blackwater in remote and sensitive areas.

Role of Ca-bentonite to improve the humification, enzymatic activities, nutrient transformation and end product quality during sewage sludge composting

This study was aimed to examine the response of Ca-bentonite (CB) amendment to improve the sewage sludge (SS) composting along with wheat straw (WS) as bulking agent. Five treatments (SS + WS) were mixed with or without blending of discrepant concentration of CB (2%, 4%, 6%, and 10%), respectively, and without CB added treatment applied as the control. The results showed that compared to control and 2%CB blended treatments, while the 6–10%CB -amended treatment indicated maximum enzymatic activities with the composting progress and highest organic matter degradation and loss. The amendment of 6–10%CB increased the humic acid, HA/FA ratio, DON, NH4+-N, NO3 and DOC but reduced the fulvic acids content and the maturity period by 2 weeks as compared to control. In addition, maturity parameters also confirmed that the highest seed germination was observed with the 10%CB applied compost followed by 6%CB, 4%CB and 2%CB applied treatments, respectively.

Benefits to decomposition rates when using digestate as compost co-feedstock: Part II – Focus on microbial community dynamics

Linkage between composting reactor performance and microbial community dynamics was investigated during co-composting of digestate and fresh feedstock (organic fraction of municipal solid waste) using 25L reactors. Previously, the relationship between composting performance and various physicochemical parameters were reported in Part I of the study (Arab and McCartney, 2017). Three digestate to fresh feedstock ratios (0, 40, and 100%; wet weight basis) were selected for analysis of microbial community dynamics. The 40% ratio was selected because it was found to perform the best (Arab and McCartney, 2017). Illumina sequencing results revealed that the reactor with a greater composting performance (higher organic matter degradation and higher heat generation; 40% ratio) was associated with higher microbial diversity. Two specific bacterial orders that might result in higher performance were Thermoactinomycetaceae and Actinomycetales with a higher sequence abundance during thermophilic composting phase and during the maturing composting phase, respectively. Galactomyces, Pichia, Chaetomium, and Acremonium were the four fungal genera that are probably also involved in higher organic matter degradation in the reactor with better performance. The redundancy analysis (RDA) biplot indicated that among the studied environmental variables, temperature, total ammonia nitrogen and nitrate concentration accounted for much of the major shifts in microbial sequence abundance during the co-composting process.

Synergistic effect of co-digestion to enhance anaerobic degradation of catering waste and orange peel for biogas production.

Catering waste and orange peel were co-digested using an anaerobic digestion process. Orange peel is difficult to degrade anaerobically due to the presence of antimicrobial agents such as limonene. The present study aimed to examine the feasibility of anaerobic co-digestion of catering waste with orange peel to provide the optimum nutrient balance with reduced inhibitory effects of orange peel. Batch experiments were conducted using catering waste as a potential substrate mixed in varying ratios (20-50%) with orange peel. Similar ratios were followed using green vegetable waste as co-substrate. The results showed that the highest organic matter degradation (49%) was achieved with co-digestion of catering waste and orange peel at a 50% mixing ratio (CF4). Similarly, the soluble chemical oxygen demand (sCOD) was increased by 51% and reached its maximum value (9040 mg l-1) due to conversion of organic matter from insoluble to soluble form. Biogas production was increased by 1.5 times in CF4 where accumulative biogas was 89.61 m3 t-1substrate compared with 57.35 m3 t-1substrate in the control after 80 days. The main reason behind the improved biogas production and degradation is the dilution of inhibitory factors (limonene), with subsequent provision of balanced nutrients in the co-digestion system. The tCOD of the final digestate was decreased by 79.9% in CF4, which was quite high as compared with 68.3% for the control. Overall, this study revealed that orange peel waste is a highly feasible co-substrate for anaerobic digestion with catering waste for enhanced biogas production.

Methane and nitrous oxide annual emissions from an old eutrophic temperate reservoir

Two greenhouse gases –methane (CH4) and nitrous oxide (N2O) - were monitored monthly during one year (2011) at the Eguzon Reservoir in France. The objective of the study was to quantify for the first time in a temperate area the total emissions of these gases through the main emission pathways (diffusion and bubbling from the reservoir, degassing and downstream diffusion). The reservoir was impounded in 1926 and had, in 2011, a eutrophic status promoting high organic matter degradation and nitrification-denitrification, all favouring CH4 and N2O production. CH4 and N2O emissions were dominated by diffusion from the reservoir surface (respectively 78.0% and 92.3%). Ebullition was only observed for CH4 and accounted for 14.0% of total CH4 emissions. Downstream degassing and diffusion represented 8.1% of the total CH4 emissions and 7.7% of the total N2O emissions.

Assessing the influence of oil and grease and salt content on fish canning wastewater biodegradation through respirometric tests

Fish canning industry wastewaters have high organic matter, oil and grease and salt (NaCl) content, which make difficult a proper treatment before discharge. In this work, their treatment was evaluated via activated sludge aerobic biological process through respirometric tests. Inhibition was found to be significant for NaCl concentrations higher than 17.5 g/L. On the other hand, the oil and grease content affects the wastewater biodegradability in the same way that the organic matter content expressed as chemical oxygen demand: the lower oil and grease and organic matter concentrations, the lower the percentage of wastewater biodegradability. As a final conclusion, the aerobic biological treatment process by activated sludge proved to be appropriate to treat fish canning industrial wastewaters, leading to high organic matter degradation rates (average value of 4900 mgO2/gCOD.d). Additionally, the experimental results achieved with the respirometric tests may be useful for the design of activated sludge plants to treat this type of wastewaters.

Composting of wastewater treatment sludge with different bulking agents

ABSTRACTThe main objectives of this study were to investigate the compostability of wastewater treatment sludge (WTS) containing different bulking agents (BAs) and to determine the most efficient BA. Four different compost trials consisting of mixtures of wheat straw (WS), plane leaf (PL), corncob (CC) and sunflower stalk (SS) with WTS were performed in laboratory reactors. In all experiments, a mixture of 60% WTS and 40% BA (wet basis) was used. The temperature, dry matter (DM), organic matter (OM), pH, electrical conductivity (EC) and C/N ratio were monitored during the composting process. Evaluation of the operational parameters showed that the highest organic matter degradation (i.e. 37.6%), loss of dry matter (i.e. 29.6%) and temperature (i.e. 64 °C) were achieved for the WTS-CC mixtures. Results also showed that the WTS-SS mixture was also successful in terms of these operational parameters. Use of bulking agents for the treatment of wastewater treatment sludge in composting process is an important issue with regards to process efficiency, economy and disposal of agricultural waste. Corncob and sunflower stalk that were previously not used for the composting of WTS from food industry were shown to be highly successful BA materials in this study.Implications: The compostability of wastewater treatment sludge from the food industry with different bulking agents was studied. Wheat straw, plane leaf, corncob, and sunflower stalk were used as bulking agents. The required microbial stabilization and degree of mineralization were achieved with corncobs and sunflower stalks.

Subcritical water extraction of organic matter from sedimentary rocks

Subcritical water extraction of organic matter containing sedimentary rocks at 300°C and 1500psi produces extracts comparable to conventional solvent extraction. Subcritical water extraction of previously solvent extracted samples confirms that high molecular weight organic matter (kerogen) degradation is not occurring and that only low molecular weight organic matter (free compounds) are being accessed in analogy to solvent extraction procedures. The sedimentary rocks chosen for extraction span the classic geochemical organic matter types. A type I organic matter-containing sedimentary rock produces n-alkanes and isoprenoidal hydrocarbons at 300°C and 1500psi that indicate an algal source for the organic matter. Extraction of a rock containing type II organic matter at the same temperature and pressure produces aliphatic hydrocarbons but also aromatic compounds reflecting the increased contributions from terrestrial organic matter in this sample. A type III organic matter-containing sample produces a range of non-polar and polar compounds including polycyclic aromatic hydrocarbons and oxygenated aromatic compounds at 300°C and 1500psi reflecting a dominantly terrestrial origin for the organic materials. Although extraction at 300°C and 1500psi produces extracts that are comparable to solvent extraction, lower temperature steps display differences related to organic solubility. The type I organic matter produces no products below 300°C and 1500psi, reflecting its dominantly aliphatic character, while type II and type III organic matter contribute some polar components to the lower temperature steps, reflecting the chemical heterogeneity of their organic inventory. The separation of polar and non-polar organic compounds by using different temperatures provides the potential for selective extraction that may obviate the need for subsequent preparative chromatography steps. Our results indicate that subcritical water extraction can act as a suitable replacement for conventional solvent extraction of sedimentary rocks, but can also be used for any organic matter containing mineral matrix, including soils and recent sediments, and has the added benefit of tailored extraction for analytes of specific polarities.

Hybrid alkali-hydrodynamic disintegration of waste-activated sludge before two-stage anaerobic digestion process.

The first step of anaerobic digestion, the hydrolysis, is regarded as the rate-limiting step in the degradation of complex organic compounds, such as waste-activated sludge (WAS). The aim of lab-scale experiments was to pre-hydrolyze the sludge by means of low intensive alkaline sludge conditioning before applying hydrodynamic disintegration, as the pre-treatment procedure. Application of both processes as a hybrid disintegration sludge technology resulted in a higher organic matter release (soluble chemical oxygen demand (SCOD)) to the liquid sludge phase compared with the effects of processes conducted separately. The total SCOD after alkalization at 9 pH (pH in the range of 8.96–9.10, SCOD = 600 mg O2/L) and after hydrodynamic (SCOD = 1450 mg O2/L) disintegration equaled to 2050 mg/L. However, due to the synergistic effect, the obtained SCOD value amounted to 2800 mg/L, which constitutes an additional chemical oxygen demand (COD) dissolution of about 35 %. Similarly, the synergistic effect after alkalization at 10 pH was also obtained. The applied hybrid pre-hydrolysis technology resulted in a disintegration degree of 28–35 %. The experiments aimed at selection of the most appropriate procedures in terms of optimal sludge digestion results, including high organic matter degradation (removal) and high biogas production. The analyzed soft hybrid technology influenced the effectiveness of mesophilic/thermophilic anaerobic digestion in a positive way and ensured the sludge minimization. The adopted pre-treatment technology (alkalization + hydrodynamic cavitation) resulted in 22–27 % higher biogas production and 13–28 % higher biogas yield. After two stages of anaerobic digestion (mesophilic conditions (MAD) + thermophilic anaerobic digestion (TAD)), the highest total solids (TS) reduction amounted to 45.6 % and was received for the following sample at 7 days MAD + 17 days TAD. About 7 % higher TS reduction was noticed compared with the sample after 9 days MAD + 15 days TAD. Similar results were obtained for volatile solids (VS) reduction after two-stage anaerobic digestion. The highest decrease of VS was obtained when the first stage, the mesophilic digestion which lasted 7 days, was followed by thermophilic digestion for 17 days.

The Aeration Control during Co-Composting of Sewage Sludge and Wooden Chips in a Rotary Drum Reactor

To optimize the aeration control during the co-composting process of sewage sludge and wooden chips in a rotary drum reactor, it was proposed to study the implementation of different control strategies. A series of pilot scale experiments were carried out in a rotary drum reactor with a volume of 3.14m3, using 800 kg sewage sludge from 2nd wastewater treatment plant of Kunming and 400 kg wooden chips collected from parks in Kunming as compost materials. Temperature, oxygen concentrations, volatile solid contents and moisture content were followed during the composting process as important variables to compare different aeration control strategies (continuous, intermittent and two stage temperature feedback aeration control strategies). The obtained results have shown that two stage temperature feedback aeration control strategy is the optimal, because it can effectively control the temperature during composting, with better moisture removal and higher organic matter degradation than the other strategies, obtaining a stabilized product with less nutrient elements losses.

Initial air pressure influence on in-vessel composting for the biodegradable fraction of municipal solid waste in Morocco

This study aimed to determine the initial air pressure influence on the in-vessel composting for the biodegradable fraction of municipal solid waste in Morocco. For this purpose, representative composting mixture was prepared in which C/N ratio was 26 and moisture content was 70 %. The in-vessel bioreactor was designed and used specially to evaluate the initial air pressure effect on composting process in this study. Thus, daily changes of internal air pressure and temperature were monitored, and physicochemical properties of different composts obtained were also analyzed and compared. Experimental results showed a significant increase in internal pressure corresponding to the initial air pressure of 0.6 bar and a slight increase for the other initial air pressures. The initial air pressure which equal to 0.6 bar allowed maximum value of temperature and final composting product with good physicochemical properties as well as higher organic matter degradation and higher gas production. Composts obtained from experiments under 0.4 and 0.8 bar showed good maturity levels and may also be used for agricultural applications.

Co-composting as an oxygen stabilization of an organic fraction of municipal solid waste and industrial sewage sludge

The purpose of this work is to study the characteristics of the co-composting of municipal solid waste (MSW), sewage sludge, grass and sawdust. Differing proportions of biodegradable waste were investigated through changes of temperature, oxygen consumption, organic matters, moisture content, carbon, nitrogen, C/N ratio as well as heavy metals and pathogen microorganisms content. The present study has shown that addition of MSW above 10% had a negative impact on the composting process. The initial C/N of the mixtures with a higher MSW content was below 18. Lower losses of organic matter occurred during composting for the mixture with the highest addition of MSW. Although studies have shown that composting is a good method for the disposal of organic waste additional research is required in order to optimize the organic and nitrogen compounds degradation during the co-composting process. In conclusion, a 1:4:4:1 mixture of MSW:sewage sludge:grass:sawdust is recommended because it can achieve high temperature as well as the highest organic matter degradation and highest N content in the final composting product. The concentration of heavy and light metals in all composts was within the limits of regulation of the Polish Minister of Agriculture and Rural Development.

<i>In vitro</i> fermentation of diets incorporating carob pulp using inoculum from rabbit caecum

The aim of this work was to evaluate the nutritive value of carob pulp for rabbits using the in vitro digestibility and gas production techniques with inocula from caecal content of rabbits. Experimental diets contained 0% (D1), 10% (D2), 20% (D3) and 100% (D4) carob pulp on a dry matter (DM) basis and were incubated in glass syringes for 72 h at 39ºC. Carob pulp contained 313 g neutral detergent fibre/kg DM with a high acid detergent fibre (263 g/kg DM) content, resulting in a low hemicellulose content of 50 g/kg DM. Potential gas production ranged from 123 (D1) to 179 (D4) mL/g DM and was similar for the D1 (123 mL/g DM), D2 (126 mL/g DM) and D3 (130 mL/g DM) treatments. The lowest pH value of 6.47 and the highest organic matter degradation (OMD, 64.3%) were observed in the 100% carob pulp (D4) treatment, while its inclusion at 10% and 20% tended to improve the OMD of the diets. These results show that carob pulp is well fermented by the caecal micro-organisms of rabbits. Although its inclusion at 20% did not improve in vitro fermentation and degradation of the commercial concentrate, it was concluded that carob pulp has potential as an unconventional feed resource for rabbits. Its utilization could have a positive effect on intestinal microbiota owing to its high content of soluble fibre.Keywords: Ceratonia siliqua, by-product, chemical composition, gas production, organic matter degradation

Effect of initial moisture content on the in-vessel composting under air pressure of organic fraction of municipal solid waste in Morocco

This study aimed to evaluate the effect of initial moisture content on the in-vessel composting under air pressure of organic fraction of municipal solid waste in Morocco in terms of internal temperature, produced gases quantity, organic matter conversion rate, and the quality of the final composts.For this purpose, in-vessel bioreactor was designed and used to evaluate both appropriate initial air pressure and appropriate initial moisture content for the composting process. Moreover, 5 experiments were carried out within initial moisture content of 55%, 65%, 70%, 75% and 85%. The initial air pressure and the initial moisture content of the mixture showed a significant effect on the aerobic composting. The experimental results demonstrated that for composting organic waste, relatively high moisture contents are better at achieving higher temperatures and retaining them for longer times.This study suggested that an initial moisture content of around 75%, under 0.6 bar, can be considered as being suitable for efficient composting of organic fraction of municipal solid waste. These last conditions, allowed maximum value of temperature and final composting product with good physicochemical properties as well as higher organic matter degradation and higher gas production. Moreover, final compost obtained showed good maturity levels and can be used for agricultural applications.

Comparison of organic matter degradation and microbial community during thermophilic composting of two different types of anaerobic sludge

Changes in organic matter degradation and microbial communities during thermophilic composting were compared using two different types of anaerobic sludge, one from mesophilic methane fermentation, containing a high concentration of proteins (S-sludge), and the other from thermophilic methane fermentation, containing high concentrations of lipids and fibers (K-sludge). The difference in the organic matter degradation rate corresponded to the difference in the organic matter constituents; the CO 2 evolution rate was greater in the composting of S-sludge than of K-sludge; moreover, the NH 3 evolution resulting from the protein degradation was especially higher in the composting of S-sludge. Then the differences in the microbial communities that contributed to each composting were determined by the PCR-DGGE method. Ureibacillus sp., which is known as a degrader with high organic matter degradation activity, was observed during the composting of S-sludge, whereas Thermobifida fusca, which is a well known thermophilic actinomycete that produces enzymes for lignocellulose degradation, were observed during the composting of K-sludge.