Microbial succession during a composting process as evaluated by denaturing gradient gel electrophoresis analysis

Microbial succession during a laboratory-scale composting process of garbage was analysed by denaturing gradient gel electrophoresis (DGGE) combined with measurement of physicochemical parameters such as temperature, pH, organic acids, total dissolved organic carbon and water-soluble humic substance. From the temperature changes, a rapid increase from 25 to 58 degrees C and then a gradual decrease, four phases were recognized in the process as follows; mesophilic (S), thermophilic (T), cooling (C) and maturing (M). The polymerase chain reaction-amplified 16S rDNA fragments with universal (907R) and eubacterial (341F with GC clamp) primers were subjected to DGGE analysis. Consequently, the DGGE band pattern changed during the composting process. The direct sequences from DGGE bands were related to those of known genera in the DNA database. The microbial succession determined by DGGE was summarized as follows: in the S phase some fermenting bacteria, such as lactobacillus, were present with the existing organic acids; in the T phase thermophilic bacillus appeared and, after the C phase, bacterial populations were more complex than in previous phases and the phylogenetic positions of those populations were relatively distant from strains so far in the DNA database. Thus, the DGGE method is useful to reveal microbial succession during a composting process.     

Composting of municipal solid waste

This paper reviews the literature on the composting process, which is one of the technological options for the processing of municipal solid wastes (MSWs). The process assumes a great significance, particularly from the point of its economic viability, capability for recycling of nutrients and waste minimization with minimum environmental problems. A number of studies on various aspects of the composting process, including process control and monitoring parameters such as temperature, pH, moisture content, aeration, and porosity are reviewed. Salient observations on microbial properties of composting are described and details of vermicomposting, as well as a detailed analysis of patents on composting of MSW, are presented.     

微生物在有机固废堆肥中的作用与应用

好氧堆肥是实现有机固体废弃物资源化利用的主流处理方式。堆肥腐熟是一个由微生物主导的生理生化过程,堆料通过微生物发酵实现矿质化、腐殖化和无害化,转变成腐熟的有机肥。传统的好氧堆肥存在发酵周期长、养分损失、恶臭及温室气体排放等不足。在堆肥过程中添加微生物是弥补传统好氧堆肥缺陷、提高堆肥品质和功效的有效方法。近年来,国内外在好氧堆肥过程中主要微生物类群与其演替规律、外源添加微生物的作用与功能等方面取得了较大进展。本文简述好氧堆肥基本过程与主要影响因素,以及这个过程中主要微生物类群与其演替规律,重点介绍有关微生物添加剂在好氧堆肥中的应用及其作用方面的研究进展。同时,我们对目前微生物添加剂在应用中存在的问题进行分析并对解决途径进行探讨。     

Microbial Community Growth and Utilization of Carbon Constituents During Thermophilic Composting at Different Oxygen Levels

Composting is characterized by dramatic changes in microbial community structure, to a high extent driven by changes in temperature and in the composition of the organic substrate. This study focuses on the interrelationships between decomposition of major classes in the organic material and dynamics in microbial populations during thermophilic composting of source-separated organic household waste. Experiments were performed in a 200-L laboratory reactor at 16, 2.5, and 1% O₂ in the compost atmosphere. Major classes of carbon constituents were analyzed by chemical methods, and the microbial biomass and community structure determined by fatty acid analyses with phospholipid fatty acids (PLFA) and total ester-linked fatty acids (EL) methods. At all three O₂ levels, the process was characterized by a rapid increase in microbial activity and biomass in the early thermophilic phase, although this period was delayed at the lower O₂ concentrations. Starch and fat were the main substrates utilized at all three O₂ levels during this period. The depletion of the starch fraction coincided with the beginning of a microbial biomass decrease, suggesting thatstarch is an important carbon substrate for the growth of thermophilic microorganisms during composting. Growth yields in the microbial community based on consumption of major carbon constituent classes in the high-activity period fell between 22 and 28%. Multivariate statistical analysis of changes in fatty acid composition revealed small, but statistically significant differences in the microbial community succession. At 16% O₂, 10Me fatty acids from Actinomycetes and cyclopropyl fatty acids (from Gram-negative bacteria) became more important with time, whereas 18:1ω7t was characteristic at 2.5 and 1% O₂, indicating a more stressed bacterial community at the lower O₂ concentrations. Although adequate composting was achieved at O₂ levels as low as 2.5 and 1%, it is not recommended to compost at such low levels in large-scale systems, because the heterogeneous gas transport through the material in these systems might lead to anaerobic conditions and inefficient composting.     

Response of compost maturity and microbial community composition to pentachlorophenol (PCP)-contaminated soil during composting

Two composting piles were prepared by adding to a mixture of rice straw, vegetables and bran: (i) raw soil free from pentachlorophenol (PCP) contamination (pile A) and (ii) PCP-contaminated soil (pile B). It was shown by the results that compost maturity characterized by water soluble carbon (WSC), TOC/TN ratio, germination index (GI) and dehydrogenase activity (DA) was significantly affected by PCP exposure, which resulted in an inferior degree of maturity for pile B. DGGE analysis revealed an inhibited effect of PCP on compost microbial abundance. The bacteria community shifts were mainly consistent with composting factors such as temperature, pH, moisture content and substrates. By contrast, the fungal communities were more sensitive to PCP contamination due to the significant correlation between fungal community shifts and PCP removal. Therefore, the different microbial community compositions for properly evaluating the degree of maturity and PCP contamination were suggested.     

Physical and Chemical Correlates of Microbial Activity and Biomass in Composting Municipal Sewage Sludge

Various physical and chemical parameters were monitored to evaluate their influence on the microbial communities present in composting municipal sewage sludge. Temperature, moisture content, depth, pH, protein content, total nitrogen, total carbon, lipid phosphate biomass, and the rates of microbial incorporation of substrates into lipids were measured at several times throughout the 17- to 19-day composting runs. Temperature was found to have the most consistent and dramatic effect on microbial activity and biomass. When temperatures exceeded 55 to 60°C, microbial activity fell dramatically, usually by more than 1 order of magnitude. Microbial activity was generally greatest in samples taken from the 35 to 50°C areas of the composting piles. Changes in the composition of the compost over time included increased pH, increased protein content, and decreased total organic content. The changes in these parameters appeared to reflect the microbial activity and biomass present. The results of this study indicate that the rate of composting may best be optimized by controlling the composting temperatures, provided that the other parameters fall within reasonable limits in the starting material.     

Emission of Climate-Relevant Trace Gases and Succession of Microbial Communities during Open-Windrow Composting

Determination of different indicators of microbial biomass, community structure, and bioactivity by the fumigation extraction method, as well as determination of phospholipid fatty acids (PLFAs) and their subfractions and the measurement of trace gases, respectively, provides valuable information about microbial succession in composting processes. The emission rates of carbon dioxide (CO(inf2)), methane (CH(inf4)), and nitrous oxide (N(inf2)O) increased successively during compost maturation: initially in the presence of easily degradable nutrients, during high temperature, and after the temperature had cooled down, respectively. The emission rate patterns of these trace gases corresponded to the concentrations of PLFAs and their particular subfractions. (i) Similar to the CO(inf2) emission rates, microbial biomass estimations by fumigation extraction and by determination of the amount of total PLFAs showed a discontinuous decrease during the composting process, with a slight increase at the end of the observation period. (ii) An increase in ether lipids, indicating the enhanced presence of archaean methanogens, and an elevated CH(inf4) emission were observed at the same time. (iii) The period of enhanced N(inf2)O emission corresponded to the increase in beta and omega hydroxy fatty acids derived from the outer membrane. Additionally, the continuous increase in branched-chain fatty acids suggested an increase in gram-positive bacteria and actinomycetes, and the decrease in polyunsaturated fatty acids indicated a decrease in eukaryotic cells during the composting.     

变性梯度凝胶电泳在堆肥微生物研究中的应用

对当前堆肥中微生物种群分布及其对有机物分解作用的研究进行分析,论述了分子生物技术中的变性梯度凝胶电泳(DGGE)的特点。将DGCE与PCR扩增技术相结合,可用于研究自然菌种堆肥和人工培养驯化菌种堆肥过程中微生物的演替规律,为研究和筛选堆肥中的微生物提供更加有效、快速的信息,促进堆肥技术的发展。     

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%).     

翻堆频率对堆肥减量化、腐殖化和稳定化的影响

好氧堆肥是有机固体废弃物处理处置的有效手段之一,堆肥还田也是贫瘠土壤改良的常用措施。但好氧堆肥是一个典型的CO_2等温室气体的释放过程。如何减少堆肥过程中的CO_2释放,强化堆肥的腐殖化过程对于实现有机固体废弃物的低碳化堆肥、提高作为优良土壤改良剂的腐殖质产量具有重要意义。本文选取农林秸秆和餐厨垃圾作为堆肥原料,研究不同翻堆频率对堆肥过程中的物料减量化、腐殖化和稳定化的影响,以期发现一个较低碳的堆肥工艺,并从微生物角度初步探索了其影响机制。研究结果显示,不同的翻堆频率(分别为每2 d、4 d和6 d翻堆一次),堆料的减量化和腐殖化程度有一定差异,翻堆频率为4 d的堆肥工艺物料减量率最高为50.5%,但碳减量率最低为77.4%;而翻堆频率为2 d的堆肥工艺腐殖质产量最高;3种堆肥工艺经62 d堆肥都达到了腐熟程度,翻堆频率为4 d的堆肥工艺腐熟化程度最高。不同的翻堆频率可能通过影响堆肥过程中堆料的温度、含氧量等因素从而改变堆料中活性微生物量、种类和生物酶活性,进而影响堆料的矿化和腐殖化进程。     

The stimulatory effects of surfactants on composting of waste rich in cellulose

The chemical surfactant Tween 80 and biosurfactant rhamnolipid were respectively added to the composting substrate, a mixture of rice straw and bran, and their effects on the composting process were investigated. Samples were analysed for microbial communities of bacteria, actinomycetes and fungi, carboxymethylcellulose hydrolysis (CMCase) and xylanase activities, cellulose and hemicellulose fractions, water-soluble carbon (WSC) contents in the substrates, organic matter contents and pH values during the composting process. The results showed that both Tween 80 and rhamnolipid had slight stimulatory effects on the microbial populations of bacteria, actinomycetes and fungi. In addition, rhamnolipid increased the peak xylanase activity 15% higher than that of the control, while Tween 80 increased the maximum CMCase activity 35% higher than that of the control. As a result of the increased enzyme activities, treatments with Tween 80 and rhamnolipid were of higher WSC contents than the control during the whole composting process. Accordingly, the composting process was accelerated by the surfactants, since the organic matter was decomposed more quickly and the breakdown of cellulose and hemicellulose was better in the treatments with Tween 80 and rhamnolipid.     

Comparison of microbial communities in four different composting processes as evaluated by denaturing gradient gel electrophoresis analysis

AIMS: We aimed to systematically understand the composting processes by a comparison of microbial communities during four full-scale composting processes. METHODS AND RESULTS: Microbial communities during the four different full-scale composting processes were analysed by denaturing gradient gel electrophoresis combined with measurement of physicochemical parameters. Two composting processes utilized sewage sludge and two utilized food-waste. Comparison of the four processes indicated that the concentration of dissolved organic carbon was higher in the food-waste-composting than in the sewage-sludge-composting processes, and microbial communities varied with composting substrate. The tendency for different microbes to appear in the composting process with different concentrations of dissolved organic carbon agreed with a previous study that showed that microbial succession occurred with a decrease in dissolved organic carbon in a laboratory-scale food-waste-composting process. CONCLUSIONS: Our results suggested that the main factor affecting microbial communities in the composting process is the concentration of dissolved organic materials. SIGNIFICANCE AND IMPACT OF THE STUDY: In addition to studying microbial communities involved in composting, this research is also the first to study composting mechanisms using molecular methods. The results of our studies may be helpful in the design and management of composting processes.     

Composting Process Control Based on Interaction Between Microbial Heat Output and Temperature

Rational composting process control involves the interrelated factors of heat output, temperature, ventilation, and water removal. The heat is released microbially at the expense of organic material; temperature is an effect and, because it is a determinant of microbial activity, it is also a cause of heat output; ventilation supplies oxygen and removes heat, mainly through the vaporization of water; water removal results from heat removal. These relationships were implemented in a field-scale process of static-pile configuration, using a mixture of sewage sludge and wood chips. Heat removal was matched to heat output through a temperature feedback control system, thereby maintaining biologically favorable temperatures. The observations indicate that fundamentally there are two kinds of composting systems: those that are and those that are not temperature self-limiting. The self-limiting system reaches inhibitive temperatures (>60°C) which debilitate the microbial community, suppressing decomposition, heat output, and water removal. In contrast, non-self-limiting temperatures (<60°C) support a robust community, promoting decomposition, heat output, and water removal.     

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.     

城市生活垃圾堆肥发酵中微生物菌群变化规律的研究

通过对垃圾处理厂静态堆肥不同区域的微生物菌群与数量的分析,表明了城市生活垃圾堆肥发酵中微生物菌群的变化规律,温度与微生物菌群的相关性,指出了高温微生物菌群数量影响堆肥的效率。建议在静态一次堆肥发酵周期中,增加通气量和翻堆频率,有利于增强微生物菌群的活力和提高堆肥质量。     

城市垃圾堆肥过程中的生物学问题研究

介绍了城市垃圾堆肥处理的主要工艺,详细分析了垃圾堆肥过程中的生物化学变化和微生物学原理及研究现状。提出了可以将耗氧速率、C/N比、pH值作为堆肥腐熟度在线监测指标及在堆肥过程中,添加高效复合微生物接种剂可加快有机物的分解,缩短发酵周期,减少恶臭气体的产生,提高堆肥制品质量。     

Changes in Bacterial and Fungal Communities across Compost Recipes,Preparation Methods,and Composting Times

Compost production is a critical component of organic waste handling, and compost applications to soil are increasingly important to crop production. However, we know surprisingly little about the microbial communities involved in the composting process and the factors shaping compost microbial dynamics. Here, we used high-throughput sequencing approaches to assess the diversity and composition of both bacterial and fungal communities in compost produced at a commercial-scale. Bacterial and fungal communities responded to both compost recipe and composting method. Specifically, bacterial communities in manure and hay recipes contained greater relative abundances of Firmicutes than hardwood recipes with hay recipes containing relatively more Actinobacteria and Gemmatimonadetes. In contrast, hardwood recipes contained a large relative abundance of Acidobacteria and Chloroflexi. Fungal communities of compost from a mixture of dairy manure and silage-based bedding were distinguished by a greater relative abundance of Pezizomycetes and Microascales. Hay recipes uniquely contained abundant Epicoccum, Thermomyces, Eurotium, Arthrobotrys, and Myriococcum. Hardwood recipes contained relatively abundant Sordariomycetes. Holding recipe constant, there were significantly different bacterial and fungal communities when the composting process was managed by windrow, aerated static pile, or vermicompost. Temporal dynamics of the composting process followed known patterns of degradative succession in herbivore manure. The initial community was dominated by Phycomycetes, followed by Ascomycota and finally Basidiomycota. Zygomycota were associated more with manure-silage and hay than hardwood composts. Most commercial composters focus on the thermophilic phase as an economic means to insure sanitation of compost from pathogens. However, the community succeeding the thermophilic phase begs further investigation to determine how the microbial dynamics observed here can be best managed to generate compost with the desired properties.     

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.     

Effects of Continuous Thermophilic Composting (CTC) on Bacterial Community in the Active Composting Process

The method of continuous thermophilic composting (CTC) remarkably shortened the active composting cycle and enhanced the compost stability. Effects of CTC on the quantities of bacteria, with a comparison to the traditional composting (TC) method, were explored by plate count with incubation at 30, 40 and 50°C, respectively, and by quantitative PCR targeting the universal bacterial 16S rRNA genes and the Bacillus 16S rRNA genes. The comparison of cultivatable or uncultivatable bacterial numbers indicated that CTC might have increased the biomass of bacteria, especially Bacillus spp., during the composting. Denaturing gradient gel electrophoresis (DGGE) analysis was employed to investigate the effects of CTC on bacterial diversity, and a community dominated by fewer species was detected in a typical CTC run. The analysis of sequence and phylogeny based on DGGE indicated that the continuously high temperature had changed the structure of bacterial community and strengthened the mainstay role of the thermophilic and spore-forming Bacillus spp. in CTC run.     

环境条件对猪粪好氧堆肥过程的影响

禽畜粪便的大量排放给环境造成了巨大污染,其中猪场粪便和污水是最主要的污染源。为了实现猪粪的无害化、减量化和资源化,好氧堆肥是目前普遍应用和效果良好的实用技术。为了探明堆肥过程的生物学和化学过程,论本文主要从几个影响因素如温度、调理剂、含水率、通风方式、微生物菌剂等对猪粪好氧堆肥技术方面进行了综述。