Seasonal microbial community dynamics in a flowerpot-using personal composting system for disposal of household biowaste

Microbial community dynamics in a flowerpot-using solid biowaste composting (FUSBIC) process were monitored seasonally by quinone profiling and conventional microbiological methods. The FUSBIC system, which consisted of three flowerpots (14 L or 20 L capacity) with 5-6 kg each of a soil-compost mixture (SCM) as the primary reactors, was loaded daily with household biowaste from November 1998 to October 1999. The monthly average waste reduction rate was 88.2% for the 14-L system and 92.5% for the 20-L system on a wet weight basis. The direct total microbial count detected in the 14-L primary reactors ranged from 4.5 to 9.6x10(11) cells.g(-1) of dry wt of SCM, and the viable count of aerobic heterotrophic bacteria recovered on agar plates at 28 degrees C varied from 1.9 to 5.7x10(11) CFU.g(-1) of dry wt. The quinone content of SCM samples from the 14-L and 20-L systems ranged from 160 to 353 nmol.g(-1) of dry SCM. Ubiquinones, unsaturated menaquinones, and partially saturated menaquinones constituted 15.0-36.4, 14.8-22.0, and 41.8-61.6 mol% of the total content, respectively. The major quinone types detected were usually MK-8(H(2)), MK-9(H(2)), and Q-10. Variations in quinone profiles were evaluated numerically by using two parameters, the dissimilarity index (D) and microbial divergence index (MD(q)). The upper limit of seasonal changes in the microbial community structure was about 30% as expressed by D values. The MD(q) values calculated ranged from 18 to 22. A significant positive correlation was found between seasonal temperature and bacterial populations containing partially saturated menaquinones. These results indicated that the FUSBIC system contained highly diverse microbial populations that fluctuated to some extent depending on seasonal temperature. Members of the Actinobacteria were suggested to be the major constituents of the total population present.     

Degradation of household biowaste in reactors.

Household derived biowaste was degraded by biological methods. The system involves the combined method of low-solids (up to 10% w/v of total solids (TS)) anaerobic digestion and aerobic degradation for the recovery of energy (biogas) and the production of fine humus-like material which can be used as a soil amender or a substrate for further thermal treatment (pyrolysis, gasification). The performance of batch and continuous processes carried out in bioreactors (stirred tank reactor, air-lift) of working volume 6 and 18 dm(3), at different temperatures (25-42 degrees C) was monitored by reduction of TS, volatile solids, chemical oxygen demand, total organic carbon, C/N in time. The application of continuous process with recirculation (33%) caused that for residence time of 8-16 h the obtained degree of organic load reduction was similar to that obtained after 72-96 h of the batch process. The experimental data of batch aerobic degradation was also subjected to kinetic analysis. The sequence of the two processes: aerobic and anaerobic or anaerobic and aerobic showed that the degree of organic load reduction was similar in both cases, while the amount of produced biogas was four times higher when the first stage was anaerobic. The final product after dewatering was subjected to pyrolysis and gasification. The gases obtained were characterised by a high heat of combustion of about 11-15 MJ Nm(-3).     

Microbial population dynamics during fed-batch operation of commercially available garbage composters

Microbial populations in terms of quantity, quality, and activity were monitored during 2 months of start-up operation of commercially available composters for fed-batch treatment of household biowaste. All the reactors, operated at a waste-loading rate of 0.7 kg day^–1 (wet wt), showed a mass reduction efficiency of 88–93%. The core temperature in the reactors fluctuated between 31°C and 58°C due to self-heating. The pH declined during the early stage of operation and steadied at pH 7.4–9.3 during the fully acclimated stage. The moisture content was 48–63% early in the process and 30–40% at the steady state. Both direct total counts and plate counts of bacteria increased via two phases (designated phases I, II) and reached an order of magnitude of 10¹¹ cells g^–1 (dry wt) at the steady state. Microbial community changes during the start-up period were studied by culture-independent quinone profiling and denatured gradient gel electrophoresis (DGGE) of PCR-amplified 16S rDNA. In all the reactors, ubiquinones predominated during phase I, whereas partially saturated menaquinones became predominant during phase II. This suggested that there was a drastic population shift from ubiquinone-containing Proteobacteria to Actinobacteria during the start-up period. The DGGE analysis of the bacterial community in one of the reactors also demonstrated a drastic population shift during phase I and the predominance of members of the phyla Proteobacteria and Bacteroidetes during the overall period. But this molecular analysis failed to detect actinobacterial clones from the reactor at any stage.     

Microbial community related to volatile organic compound (VOC) emission in household biowaste

Malodorous emissions and potentially pathogenic microorganisms which develop during domestic organic waste collection are not only a nuisance but may also pose health risks. The aim of the present study was to determine whether the presence of specific microorganisms in biowastes is directly related to the composition of the emitted volatile organic compounds (VOCs). The succession of microbial communities during 16 days of storage in organic waste collection bins was studied by denaturing gradient gel electrophoresis (DGGE) of amplified 16S ribosomal DNA in parallel with a classical cultivation and isolation approach. Approximately 60 different bacterial species and 20 different fungal species were isolated. Additionally, some bacterial species were identified through sequencing of excised DGGE bands. Proton transfer reaction mass spectrometry (PTR-MS) was used to detect VOCs over the sampling periods, and co-inertia analyses of VOC concentrations with DGGE band intensities were conducted. Positive correlations, indicating production of the respective VOC or enhancement of microbial growth, and negative correlations, indicating the use of, or microbial inhibition by the respective compound, were found for the different VOCs. Measurement of the VOC emission pattern from a pure culture of Lactococcus lactis confirmed the positive correlations for the protonated masses 89 (tentatively identified as butyric acid), 63 (tentatively identified as dimethylsulfide), 69 (likely isoprene) and 73 (likely butanone).     

Microbial community dynamics in bioaugmented sequencing batch reactors for bromoamine acid removal

Sphingomonas xenophaga QYY with the ability to degrade bromoamine acid (BAA) was previously isolated from sludge samples. The enhancement of BAA removal by strain QYY in sequencing batch reactors (SBRs) was investigated in this study. The results showed that augmented SBRs exhibited stronger abilities to degrade BAA than the non-augmented control one. In order to estimate the relationship between community dynamics and function of augmented SBRs, a combined method based on fingerprints (ribosomal intergenic spacer analysis, RISA) and 16S rRNA gene sequencing was used. The results indicated that the microbial community dynamics were substantially changed, and the introduced strain QYY was persistent in the augmented systems. This study suggests that it is feasible and potentially useful to enhance BAA removal using BAA-degrading bacteria, such as S. xenophaga QYY.     

Microbial community succession and lignocellulose degradation during agricultural waste composting

The changes of microbial community during agricultural waste composting were successfully studied by quinone profiles. Mesophilic bacteria indicated by MK-7 and mesophilic fungi containing Q-9 as major quinone were predominant and seemed to be important during the initial stage of composting. Actinobacteria indicated by a series of partially saturated and long-chain menaquinones were preponderant during the thermophilic period. While Actinobacteria, fungi and some bacteria, especially those microbes containing MK-7(H4) found in Gram-positive bacteria with a low G+C content or Actinobacteria were found cooperate during the latter maturating period. Since lignocellulsoe is abundant in the agricultural wastes and its degradation is essential for the operation of composting, it’s important to establish the correlation between the quinone profiles changes and lignocellulose degradation. The microbes containing Q-9 or Q-10(H2) as major quinone were found to be the most important hemicellulose and cellulose degrading microorganisms during composting. While the microorganisms containing Q-9(H2) as major quinone and many thermophilic Actinobacteria were believed to be responsible for lignin degradation during agricultural waste composting.     

堆肥过程中的微生物种群结构

堆肥化是有机固体废物无害化、减量化、资源化的根本途径。有机固体废弃物的堆肥化研究一直是环境科学领域研究的热点之一。产品中含有有机质、P、K等多种植物所需的养分,可以提高农林等产品的产量,改善土壤结构,提高土壤肥力。微生物是堆肥过程的工作主体,早期对堆肥中微生物的研究主要采用分     

Microbiological aspects of biowaste during composting in a monitored compost bin

AIMS: To determine the microbial succession of the dominating taxa and functional groups of microorganisms and the total microbial activity during the composting of biowaste in a monitored process. METHODS AND RESULTS: Biowaste (vegetable, fruit and garden waste) was composted in a monitored composting bin system. During the process, taxonomic and functional subpopulations of microorganisms were enumerated, and dominating colonies were isolated and identified. All counts decreased during the thermophilic phase of the composting, but increased again when the temperature declined. Total microbial activity, measured with an enzyme activity assay, decreased during the thermophilic phase, increased substantially thereafter, and decreased again during maturation. Bacteria dominated during the thermophilic phase while fungi, streptomycetes and yeasts were below the detection limit. Different bacterial populations were found in the thermophilic and mesophilic phases. In fresh wastes and during the peak-heating phase, all bacterial isolates were bacilli. During the cooling and maturation phase the bacterial diversity increased, including also other Gram-positive and Gram-negative bacteria. Among the fungi, Aspergillus spp. and Mucor spp. were predominant after the thermophilic phase. CONCLUSIONS: The microbial abundance, composition and activity changed substantially during composting and compost maturity was correlated with high microbial diversity and low activity. SIGNIFICANCE AND IMPACT OF THE STUDY: A more complete overview of the whole composting process of biowaste, based on microbial counts, species diversity and functional groups and abiotic parameters is presented, and the potential of a simple enzyme assay to measure total microbial activity was demonstrated.     

Bench-scale reactors for composting research

Laboratory-size reactors for composting have been constructed to investigate precisely some parameters which usually cannot be evaluated, such as respiration rate of microorganisms. This paper reports the effects of different nitrogen additives including Calcium cyanamide in view of improving the composting of solid urban wastes.     

Microbial community dynamics alleviate stoichiometric constraints during litter decay

Under the current paradigm, organic matter decomposition and nutrient cycling rates are a function of the imbalance between substrate and microbial biomass stoichiometry. Challenging this view, we demonstrate that in an individual‐based model, microbial community dynamics alter relative C and N limitation during litter decomposition, leading to a system behaviour not predictable from stoichiometric theory alone. Rather, the dynamics of interacting functional groups lead to an adaptation at the community level, which accelerates nitrogen recycling in litter with high initial C : N ratios and thus alleviates microbial N limitation. This mechanism allows microbial decomposers to overcome large imbalances between resource and biomass stoichiometry without the need to decrease carbon use efficiency (CUE), which is in contrast to predictions of traditional stoichiometric mass balance equations. We conclude that identifying and implementing microbial community‐driven mechanisms in biogeochemical models are necessary for accurately predicting terrestrial C fluxes in response to changing environmental conditions.     

New insights into the structure and dynamics of actinomycetal community during manure composting

Despite advancing knowledge about the functional role of actinomycetes in degrading lignocellulosic materials, definitive knowledge concerning the diversity and dynamics of the actinomycetal community in composting is still lacking. In this study, real-time polymerase chain reaction (PCR) coupled with denaturing gradient gel electrophoresis (DGGE) and clone library construction were applied to investigate actinomycetal diversity and dynamics in a pilot-scale composting. Quantitative real-time PCR data revealed that actinomycetes accounted for 18–86 % of bacteria and that the fraction peaked during the maturing phase, indicating that Actinobacteria were critical to the compost ecosystem. Qualitatively, actinomycetal communities displayed distinct temporal variations during composting. Fourteen distinct genera of actinomycetes and an unknown group were observed in manure composts. Redundancy analysis indicated that temperature exerted an influence over the actinomycetal communities. Specifically, pathogenic Corynebacterium species dominated in the initial phase, whereas the genera Saccharomonospora and Thermobifida were abundant in the thermophilic phase. In maturing composts, mesophilic Micrococcineae members were most prevalent. The dominant thermophiles along with Micrococcineae may jointly facilitate the degradation of lignocellulosic materials during composting. Together, our research revealed a more detailed ecological and potential functional role for actinomycetes in the compost ecology.     

Microbial community composition and dynamics in high-temperature biogas reactors using industrial bioethanol waste as substrate

Stillage, which is generated during bioethanol production, constitutes a promising substrate for biogas production within the scope of an integrated biorefinery concept. In this study, a microbial community was grown on thin stillage as mono-substrate in a continuous stirred tank reactor (CSTR) at a constant temperature of 55 °C, at an organic loading rate of 1.5 g_oTS/L*d and a retention time of 25 days. Using an amplicon-based dataset of 17,400 high-quality sequences of 16S rRNA gene fragments (V2–V3 regions), predominance of Bacteria assigned to the families Thermotogaceae and Elusimicrobiaceae was detected. Dominant members of methane-producing Euryarchaeota within the CSTR belonged to obligate acetoclastic Methanosaetaceae and hydrogenotrophic Methanobacteriaceae. In order to investigate population dynamics during reactor acidification, the organic loading rate was increased abruptly, which resulted in an elevated concentration of volatile fatty acids. Acidification led to a decrease in relative abundance of Bacteria accompanied with stable numbers of Archaea. Nevertheless, the abundance of Methanosaetaceae increased while that of Methanobacteriales decreased successively. These findings demonstrate that a profound intervention to the biogas process may result in persistent community changes and reveals uncommon bacterial families as process-relevant microorganisms.     

Effect of seed sludge microbial community and activity on the performance of anaerobic reactors during the start-up period

In this study, two laboratory-scale anaerobic batch reactors started up with different inoculum sludges and fed with the same synthetic wastewater were monitored in terms of performance and microbial community shift by denaturant gradient gel electrophoresis fingerprinting and subsequent cloning, sequencing analysis in order to reveal importance of initial quality of inoculum sludge for operation of anaerobic reactors. For this purpose, two different seed sludge were evaluated. In Reactor1 seeded with a sludge having less diverse microbial community (19 operational taxonomic unit (OTU’s) for Bacterial and 8 OTU’s for Archaeal community, respectively) and a methanogenic activity of 150 ml CH₄ g TVS⁻¹ day⁻¹, a chemical oxygen demand (COD) removal efficiency of 78.8 ± 4.17% was obtained at a substrate to microorganism (S/X) ratio of 0.38. On the other hand, Reactor2, seeded with a sludge having a much more diverse microbial community (24 OTU’s for Bacterial and 9 OTU’s for Archaeal communities, respectively) and a methanogenic activity, 450 ml CH₄ g TVS⁻¹ day⁻¹, operated in the same conditions showed a better start-up performance; a COD removal efficiency of over 98% at a S/X ratio of 0.53. Sequence analysis of Seed2 revealed the presence of diverse fermentative and syntrophic bacteria, whereas excised bands of Seed1 related to fermentative and sulfate/metal-reducing bacteria. This study revealed that a higher degree of bacterial diversity, especially the presence of syntrophic bacteria besides the abundance of key species such as methanogenic Archaea may play an important role in the performance of anaerobic reactors during the start-up period.     

Microbial characterization during composting of municipal solid waste

This study investigates the prevailing physico-chemical conditions and microbial community; mesophilic bacteria, yeasts and filamentous fungi, bacterial spores, Salmonella and Shigella as well as faecal indicator bacteria: total coliforms, faecal coliforms and faecal Streptococci, present in a compost of municipal solid waste. Investigations were conducted in a semi-industrial pilot plant using a moderate aeration during the composting process. Our results showed that: (i) auto-sterilization induced by relatively high temperatures (60–55°C) caused a significant change in bacterial communities. For instance, Escherichia coli and faecal Streptococci populations decreased, respectively, from 2×10⁷ to 3.1×10³ and 10⁷ to 1.5×10³ cells/g waste dry weight (WDW); yeasts and filamentous fungi decreased from 4.5×10⁶ to 2.6×10³ cells/g WDW and mesophilic bacteria were reduced from 5.8×10⁹ to 1.8×10⁷ bacteria/g WDW. On the other hand, the number of bacterial spores increased at the beginning of the composting process, but after the third week their number decreased notably; (ii) Salmonella disappeared completely from compost by the 25th day as soon as the temperature reached 60°C; and (iii) the bacterial population increased gradually during the cooling phase. While Staphylococci seemed to be the dominant bacteria during the mesophilic phase and at the beginning of the thermophilic phase, bacilli predominated during the remainder of the composting cycle. The appearance of gram-negative rods (opportunistic pathogens) during the cooling phase may represent a serious risk for the sanitary quality of the finished product intended for agronomic reuse. Compost sonication for about 3 min induced the inactivation of delicate bacteria, in particular gram-negatives. By contrast, gram-positive bacteria, especially micrococcus, spores of bacilli, and fungal propagules survived, and reached high concentrations in the compost.     

Microbial community and biomass characteristics associated severe membrane fouling during start-up of a hybrid anoxic-oxic membrane bioreactor

In MBR, severe membrane fouling is often observed in the initial phase in which biomass is yet fully acclimated and stabilized in terms of microbial community structure and biomass characteristics. The focus of this study was to investigate the microbial community development and its influence on biomass characteristics and membrane fouling during start-up of a hybrid anoxic-oxic MBR. PCR-DGGE analysis indicated that the microbial community shifted in start-up period when a severe membrane fouling was observed. Small particle size, high fractal dimension (DF) and high EPS production, which were closely associated with microbial community, were found to be the major contributors to the severe fouling. Microbial community development was most likely the ultimate factor responsible for the severe membrane fouling.     

Microbial community dynamics during production of the Mexican fermented maize dough pozol

The dynamics of the microbial community responsible for the traditional fermentation of maize in the production of Mexican pozol was investigated by using a polyphasic approach combining (i) microbial enumerations with culture media, (ii) denaturing gradient gel electrophoresis (DGGE) fingerprinting of total community DNA with bacterial and eukaryotic primers and sequencing of partial 16S ribosomal DNA (rDNA) genes, (iii) quantification of rRNAs from dominant microbial taxa by using phylogenetic oligonucleotide probes, and (iv) analysis of sugars and fermentation products. A Streptococcus species dominated the fermentation and accounted for between 25 and 75% of the total flora throughout the process. Results also showed that the initial epiphytic aerobic microflora was replaced in the first 2 days by heterofermentative lactic acid bacteria (LAB), including a close relative of Lactobacillus fermentum, producing lactic acid and ethanol; this heterolactic flora was then progressively replaced by homofermentative LAB (mainly close relatives of L. plantarum, L. casei, and L. delbrueckii) which continued acidification of the maize dough. At the same time, a very diverse community of yeasts and fungi developed, mainly at the periphery of the dough. The analysis of the DGGE patterns obtained with bacterial and eukaryotic primers targeting the 16S and 18S rDNA genes clearly demonstrated that there was a major shift in the community structure after 24 h and that high biodiversity-according to the Shannon-Weaver index-was maintained throughout the process. These results proved that a relatively high number of species, at least six to eight, are needed to perform this traditional lactic acid fermentation. The presence of Bifidobacterium, Enterococcus, and enterobacteria suggests a fecal origin of some important pozol microorganisms. Overall, the results obtained with different culture-dependent or -independent techniques clearly confirmed the importance of developing a polyphasic approach to study the ecology of fermented foods.     

Microbial community structure changes during bioremediation of PAHs in an aged coal-tar contaminated soil by in-vessel composting

The microbial community structure changes of an aged-coal-tar soil contaminated with polycyclic aromatic hydrocarbons (PAHs) were investigated during simulated bioremediation at the laboratory-scale using an in-vessel composting approach. The composting reactors were operated using a logistic three-factor factorial design with three temperatures (T=38, 55 or 70 °C), four soil to green-waste amendment ratios (S:GW=0.6:1, 0.7:1, 0.8:1 or 0.9:1 on a dry weight basis) and three moisture contents (MC=40%, 60% or 80%). Relative changes in microbial populations were investigated by following the dynamics of phospholipid fatty acid (PLFA) signatures using a ¹³C-labeled palmitic acid internal standard and sensitive GC/MS analysis during in-vessel composting over 98 days. The results of this investigation indicated that fungal to bacterial PLFA ratios were significantly influenced by temperature (p<0.05), and Gram-positive to Gram-negative bacterial ratios were significantly influenced by temperature (p<0.001) and S:GW ratio (p<0.01) during in-vessel composting. Additionally, the Gram-positive to Gram-negative bacterial ratios were correlated to the extent of PAH losses (p<0.005) at 70 °C.