Biological health risk associated with resource recovery,sorting of recycle waste and composting

Numbers of airborne microorganisms, fungi, Gram-negative bacteria, thermophilic microorganisms, endotoxins and dust have been monitored in resource recovery plants and composting plants. The work is still in progress, so this paper decribes only preliminary results. Only low levels (< 15 ng m^?3) of endotoxins were found at all locations. Levels of microorganisms, fungi, Gram-negative bacteria and dust changed with quality of waste, activity in the plant etc. Levels of airborne microorganisms, endotoxins and dust could be considerably decreased in resource recovery plants if only waste of good quality, e.g. presorted materials, is handled. For composting plants the highest levels of airborne microorganisms were found during aeration, especially by indoor composting where levels of 8.3 × 10⁵ CFU of mesophilic microorganisms were found.     

Profiling of bacterial community in a full-scale aerobic composting plant

Changes in temperature, pH, moisture, C/N ratio, and bacterial community were monitored in Istanbul full-scale composting plant. C/N ratio steadily decreased during composting and final mature compost products had a C/N ratio of less than 20. During the composting process, temperature was mostly above 55 °C and decreased to mesophilic conditions in the matured stages. Different types of bacteria were dominant in every stage of composting and bacterial diversity changed mainly by temperature. Bacillus species were dominant in early stages of composting while Acinetobacter and Sphingobacterium strains were detected in thermophilic and maturing stages. Bacteria were mainly active in the degradation of cellulose and toxic organics while some strains had denitrification ability. Generally, thermophilic stages were more rich in bacterial diversity than mesophilic and hyperthermophilic conditions significantly changed the bacterial community.     

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.     

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.     

Composting of palm press fibre

The effects of composting palm press fibre alone, palm press fibre supplemented with poultry layer deep-litter and urea, and palm press fibre supplemented with poultry broiler floor-litter and urea were studied. The initial C:N ratios of the three mixtures were 40:1, 33:1 and 26:1, respectively. After 8 weeks of composting the C:N ratios of the mixtures were 26:1, 17:1 and 16:1, respectively. The temperature in the heaps rose to 60–70°C in the first 3 weeks of composting but stabilized at between 30 and 40°C after 8 weeks. The ratio of thermophilic to mesophilic fungi increased during composting, and even after the compost had cooled the thermophilic fungal counts remained high. The mesophilic bacteria were not influenced by temperature fluctuation in the heaps and bacterial numbers remained high even during the peak heating phase. Decreases in cellulose and carbon corresponding with increases in nitrogen, lignin and ash were evident after composting. Preliminary studies indicate that the compost mixed in sand and loam may enhance crop production.     

Description of heterotrophic bacteria occurring in paper mills and paper products

AIMS: To isolate aerobic mesophilic bacilli and thermophilic bacteria from different paper mill samples and to evaluate their potential harmfulness. METHODS AND RESULTS: A total of 109 mesophilic and 68 thermophilic isolates were purified and characterized by automated ribotyping and partial 16S rDNA sequencing. The mesophilic isolates belonged to the genera Bacillus (13 taxa), Brevibacillus (three taxa) and Paenibacillus (five taxa). The thermophilic bacteria represented seven taxa of Bacillus, Geobacillus or Paenibacillus, four of proteobacteria and one of actinobacteria. The most frequently occurring bacteria were Bacillus cereus, B. licheniformis, Pseudoxanthomonas taiwanensis and bacteria closely related to Paenibacillus stellifer, P. turicensis or Leptothrix sp. One mill was contaminated throughout with bacteria of a novel mesophilic genus most closely related to Brevibacillus centrosporus and another with bacteria of a novel thermophilic genus most closely related to Hydrogenophilus thermoluteolus. One B. cereus isolate producing haemolytic diarrhoeal enterotoxin was detected and all the tested B. licheniformis isolates produced a metabolite toxic to boar sperm cells. CONCLUSIONS: The bacilli and thermophilic bacteria isolated represent species which should not present occupational hazards in paper mill environments. The most harmful bacterium detected was B. licheniformis and potentially also B. cereus. SIGNIFICANCE AND IMPACT OF THE STUDY: Knowledge of the microbial diversity in a paper mill provides a rational basis for development of an effective controlling programme. A database constructed from the fingerprints generated using automated ribotyping helps to identify and trace the contamination routes of bacteria occurring in paper mills.     

Characterization of lactic acid bacteria strains on the basis of neutral volatile compounds produced in whey

AIMS: Seventy-eight strains of lactic acid bacteria belonging to five genera and showing six different phenotype combinations of Lac (lactose fermentation), Prt (proteolytic activity) and Cit (citrate degradation) characters were investigated for their main flavouring properties with the aim to detect variability among and within the groups. METHODS AND RESULTS: High resolution gas chromatography-mass spectrometry analysis of neutral volatile compounds produced in whey showed that, considering both neo-formation compounds and substances quantified in the whey cultures at different concentrations in comparison to the extract from sterile whey, the groups of lactococci, enterococci, thermophilic streptococci and mesophilic lactobacilli produced a higher number of volatiles than thermophilic lactobacilli and leuconostocs. Applying principal component analysis (PCA) to the results, enterococci, mesophilic lactobacilli and thermophilic streptococci showed a broad diversity, while lactococci included rather similar strains as well as strains with special flavouring properties. Applying PCA to thermophilic streptococci and enterococci, to lactococci and enterococci, to lactococci and thermophilic streptococci, or to mesophilic and thermophilic lactobacilli, the strains gathered consistently with their systematic position. CONCLUSION: The study evidenced strains producing some volatile compounds responsible for food flavouring. Flavouring properties were variable among the systematic groups and in some cases different within the same bacterial group. SIGNIFICANCE AND IMPACT OF THE STUDY: The potential of the findings is discussed with reference to the development of flavouring adjuncts for the dairy industry.     

Microbial population,stability and maturity analysis of rotary drum composting of water hyacinth

Water hyacinth is a noxious aquatic weed growing over a wide variety of wetland. One of the effective methods of its treatment is rotary drum composting. Hence, microbial succession in the rotary drum composting of water hyacinth was studied along with stability and maturity. Different ratios of water hyacinth, cow dung and sawdust, i.e. 8: 1: 1, 7: 2: 1, 6: 3: 1, 5: 4: 1 and 10: 0: 0 (control), respectively, were taken. A total weight of 150 kg was maintained. Maximum degradation was observed in the trial 3 (6: 3: 1), which showed maximum temperature rise up to 56.5°C. The total mesophilic bacterial count changed from 4.73 × 10¹² to 2.5 × 10⁷ colony forming unit (CFU)/g compost during the composting period. Spore forming population reached the highest count of 3.3 × 10¹⁰ CFU/g in the thermophilic phase of composting. Actinomycetes, streptomycetes and fungi counts decreased to about 2.4 × 10⁷ CFU/g, 6.5×10⁵ CFU/g and 6.79 × 10⁵ CFU/g, respectively, at the end of composting period. A maximum reduction of 78.7% in oxygen uptake rate and 90.6% in CO₂ evolution rate was observed. This showed the highest stability of the compost sample. But the maximum volatile solids reduction of 45.9% signified the high content of recalcitrant lignocellulosic material. Indicator organisms were reduced to acceptable standards of sanitation.     

Phylogenetic and physiological characterization of mesophilic and thermophilic bacteria from a sewage sludge composting process in Sapporo,Japan

The phylogenetic and physiological characteristics of mesophilic and thermophilic bacteria isolated from a field-scale sewage sludge composter were determined by 16S rDNA and phenotype analyses. Of the 34 mesophilic isolates, 5 (15%), 16 (47%), and 3 (9%) displayed amylase, protease, and lipase activities, respectively. Among these isolates, the following species were identified based on their 16S rRNA gene sequences: Aneurinibacillus aneurinilyticus, Bacillus fortis, Bacillus subtilis, Brachybacterium paraconglomeratum, Brevibacterium otitidis, Dietzia maris, Pseudomonas xiamenensis, Staphylococcus lentus, Thermobifida fusca, Ureibacillus thermosphaericus, and Vagococcus lutrae. However, 15 isolates could not be identified as known taxa, thus indicating new bacterial taxa. Of these new taxa, it is likely that NoID A plays an important role in organic matter decomposition during composting based on its physiological characteristics. Sapporo sewage sludge compost contains a microbial ecosystem with novel bacterial biodiversity, comprising a high percentage of previously unrecognized species. This study improves our knowledge of the unique bacteria in sewage sludge compost, providing a future resource for bacterial genetic information and bacterial species of agricultural benefit.     

Bioaerosol emissions in a poultry litter burning plant

This study investigates the exposure of workers to biological particles in a poultry litter burning plant in operation. The microorganism concentrations were examined at different workplaces during procedures leading to increased emissions. The concentrations of culturable airborne mesophilic, xerophilic and thermophilic microorganisms in the ambient air were tested inside and outside of the burning plant using two different methods of measuring. The focus of this study was on the quantitative evaluation of culturable bacteria as well as the quantitative and qualitative evaluation of gram-negative bacteria, fungi and thermophilic actinomycetes. The maximum airborne concentrations were found in the delivery hall. Mesophilic bacteria concentrations reached up to 1.7 × 10⁶ CFU/m³; gram-negative bacteria up to 9.1 × 10² CFU/m³. Fungal propagule concentrations for xerophilic fungi were between 1.2 × 10³ and 2.9 × 10⁴ CFU/m³ and for mesophilic fungi between 4.4 × 10² and 2.9 × 10⁴ CFU/m³. Among fungi, Aspergillus niger, Eurotium herbariorum and Scopulariopsis brevicaulis species were dominant. Thermophilic actinomycetes reached airborne concentrations of 8.7 × 10⁴ CFU/m³, with increased concentrations of the pathogens causing extrinsic allergic alveolitis. The high concentrations of airborne microorganisms in poultry litter burning plants and the potential hazard of the intake of microorganisms including potential pathogens require the introduction of consistent measures in both technical areas and personnel management.     

Dehydrogenase activity as a method for monitoring the composting process

Dehydrogenase enzymatic activity was determined to monitor the biological activity in a composting process of organic fraction of municipal solid waste. Dehydrogenase activity is proposed as a method to describe the biological activity of the thermophilic and mesophilic stages of composting. The maximum dehydrogenase activity was detected at the end of the thermophilic stage of composting, with values within 0.5-0.7mgg dry matter(-1)h(-1). Also, dehydrogenase activity can be correlated to static respiration index during the maturation mesophilic stage.     

The microbial signature of aerosols produced during the thermophilic phase of composting

Aims:  The microbial diversity of bioaerosols released during operational activities at composting plants is poorly understood. Identification of bacteria and fungi present in such aerosols is the prerequisite for the definition of microbial indicators that could be used in dispersal and exposure studies.
Methods and Results:  A culture-independent analysis of composting bioaerosols collected at five different industrial open sites during the turning of composting piles in fermentation was performed by building 16S rDNA and 18S rDNA libraries. More than 800 sequences were analysed. Although differences in the phylotypes distribution were observed from one composting site to another, similarities in the structure of microbial diversity were remarkable. The same phyla dominated in the five bioaerosols: Ascomycota among fungi, Firmicutes and Actinobacteria among bacteria. For each phylum, some dominant phylotypes were common to at least four bioaerosols. These common phylotypes belonged to Thermomyces , Aspergillus , Penicillium , Geobacillus, Planifilum , Thermoactinomyces , Saccharopolyspora , Thermobifida and Saccharomonospora .
Conclusions:  The microbial signature of aerosols produced during the thermophilic phase of composting was determined. The similarities observed may be explained by the selection of thermophilic and sporulating species.
Significance and Impact of the Study:  Several bacteria and fungi identified in this study may represent potential indicators of composting bioaerosols in air.     

The effect of a commercial UV disinfection system on the bacterial load of shell eggs

AIMS: To study the effect of UV irradiation on the bacterial load of shell eggs and of a roller conveyor belt. METHODS AND RESULTS: The natural bacterial load on the eggshell of clean eggs was significantly reduced by a standard UV treatment of 4.7 s; from 4.47 to 3.57 log CFU per eggshell. For very dirty eggs no significant reduction was observed. Eggs inoculated with Escherichia coli and Staphylococcus aureus (4.74 and 4.64 log CFU per eggshell respectively) passed the conveyor belt and were exposed to UV for 4.7 and 18.8 s. The reduction of both inoculated bacteria on the eggshell was comparable and significant for both exposure times (3 and 4 log CFU per eggshell). Escherichia coli was reduced but still detectable on the conveyor rollers. The internal bacterial contamination of eggs filled up with diluent containing E. coli or S. aureus was not influenced by UV irradiation. Conclusions: There is a significant lethal effect of UV irradiation on the bacterial contamination of clean eggshells and recent shell contamination, contamination of rollers can be controlled and the internal contamination of eggs is not reduced. SIGNIFICANCE AND IMPACT OF THE STUDY: The penetration of UV into organic material appears to be poor and UV disinfection can be used as an alternative for egg washing.     

Mesophilic and thermophilic biotreatment of BTEX-polluted air in reactors

This study compares the removal of a mixture of benzene, toluene, ethylbenzene, and all three xylene isomers (BTEX) in mesophilic and thermophilic (50 degrees C) bioreactors. In the mesophilic reactor fungi became dominant after long-term operation, while bacteria dominated in the thermophilic unit. Microbial acclimation was achieved by exposing the biofilters to initial BTEX loads of 2-15 g m(-3) h(-1), at an empty bed residence time of 96 s. After adaptation, the elimination capacities ranged from 3 to 188 g m(-3) h(-1), depending on the inlet load, for the mesophilic biofilter with removal efficiencies reaching 96%. On the other hand, in the thermophilic reactor the average removal efficiency was 83% with a maximum elimination capacity of 218 g m(-3) h(-1). There was a clear positive relationship between temperature gradients as well as CO(2) production and elimination capacities across the biofilters. The gas phase was sampled at different depths along the reactors observing that the percentage pollutant removal in each section was strongly dependant on the load applied. The fate of individual alkylbenzene compounds was checked, showing the unusually high biodegradation rate of benzene at high loads under thermophilic conditions (100%) compared to its very low removal in the mesophilic reactor at such load (<10%). Such difference was less pronounced for the other pollutants. After 210 days of operation, the dry biomass content for the mesophilic and thermophilic reactors were 0.300 and 0.114 g g(-1) (support), respectively, reaching higher removals under thermophilic conditions with a lower biomass accumulation, that is, lower pressure drop.     

Change in Microbial Numbers during Thermophilic Composting of Sewage Sludge with Reference to CO(2) Evolution Rate

Dewatered sewage sludge was composted in a laboratory-scale autothermal reactor in which a constant temperature of 60 degrees C was kept as long as possible by regulating the air feed rate. The change in CO(2) evolution rate was measured continuously from the start up through the cessation of compositing. The succession of mesophilic bacteria, thermophilic bacteria, and thermophilic actinomycetes was also observed during the composting. Specific CO(2) evolution rates of thermophilic bacteria and actinomycetes in the constant-temperature region of 60 degrees C were assessed quantitatively. It was found that the CO(2) evolution rate was attributed to thermophilic bacteria at the initial stage of 60 degrees C and to thermophilic actinomycetes at the later stage of 60 degrees C.     

The growth of Bacillus stearothermophilus on stainless steel

AIMS: To determine the potential for Bacillus stearothermophilus cells to form biofilms of significance in dairy manufacture. METHODS AND RESULTS: The ability of isolates of B. stearothermophilus from dairy manufacturing plants to attach to stainless steel surfaces was demonstrated by exposing stainless steel samples to suspensions of spores or vegetative cells and determining the numbers attaching using impedance microbiology. Spores attached more readily than vegetative cells. The attachment of cells to stainless steel was increased 10-100-fold by the presence of milk fouling the stainless steel. The growth of B. stearothermophilus as a biofilm on stainless steel surfaces was determined using a continuously flowing experimental reactor. Vegetative cells were released in greater numbers than spores from biofilms of most strains studied. Biofilms of one strain (B11) were studied in detail. Biofilms of > 106 cells cm-2 formed in the reactor and released approximately 106 cells ml-1 into milk passing over the biofilm. A doubling time of 25 min was calculated for this organism grown as a biofilm. CONCLUSION: The formation of biofilms of thermophilic Bacillus species within the plant appears to be a likely cause of contamination of manufactured dairy products. Methods to control the formation of biofilms in dairy manufacturing plants are required to reduce the contamination of dairy products with thermophilic bacilli. SIGNIFICANCE AND IMPACT OF THE STUDY: Biofilms of B. stearothermophilus growing in dairy manufacturing plants can explain the contamination of dairy products with these bacteria.     

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.     

Quantitative analysis of bacterial aerosols in two different dental clinic environments.

Microbial aerosols are generated during dental treatments and may represent an important source of infection. This study was designed to quantify bacterial air contamination during dental treatments in both a closed dental operatory and a multichair dental clinic. Air was sampled by using a slit type of biological air sampler. Following air sampling, blood-supplemented Trypticase soy agar plates were incubated at 37 degrees C under anaerobic conditions for 7 days. The maximum levels of air contamination in the closed dental operatory were observed while dental treatments were being performed (four trials; 216 +/- 75 CFU/m3 for ultrasonic scaling treatments and 75 +/- 22 CFU/m3 for operative treatments). At 2 h after completion of the treatments, the bacterial counts were about the same as the pretreatment levels (12 to 14 CFU/m3). In the second part of the study, a multichair dental clinic was divided into four areas, and air contamination was monitored at each site. Three sites were located in active dental treatment areas, whereas no dental treatments were performed within an 11-m radius of the fourth site. At 3 h after the beginning of dental treatments, the highest bacterial counts were obtained in the three active dental treatment areas (76 to 114 CFU/m3). However, there was noticeable contamination in the inactive dental treatment area (42 CFU/m3). Thus, bacterial aerosols were able to spread into areas where there was no dental activity. My data show that dental treatments significantly increased the levels of bacterial air contamination in both a closed dental operatory and a multichair dental clinic.(ABSTRACT TRUNCATED AT 250 WORDS)     

微生物菌剂对猪粪堆肥中细菌群落结构的影响

以猪粪和小麦秸秆做堆肥试验,处理组添加外源微生物菌剂,利用常规方法对堆肥样品进行理化性状测定,采用高通量测序技术分析堆肥过程中细菌群落特征。理化性状测定结果表明: 添加外源菌剂可延长堆肥高温时间,降低堆肥发酵末期的pH,增加全氮含量,加快C/N的下降。主成分分析表明: 外源菌剂影响堆肥样品细菌群落的稳定性。门分类水平上,厚壁菌门、变形菌门和绿弯菌门的相对丰度在处理组中较高;纲分类水平上,梭状芽孢杆菌纲、α-变形菌纲和γ-变形菌纲在处理组的升温期和高温期相对丰度增加;科分类水平上,小单孢菌科和梭状芽孢杆菌纲的消化链球菌科、梭菌科以及盐厌氧菌科的相对丰度在处理组的升温期和高温期均呈上升趋势。Pearson相关性分析表明,盐胞菌属与外源菌剂呈显著正相关,而氨苄芽孢杆菌属与外源菌剂呈显著负相关。研究表明,猪粪堆肥中添加外源菌剂可使堆肥的理化性质和细菌群落结构均发生显著变化。     

Relative contributions of archaea and bacteria to microbial ammonia oxidation differ under different conditions during agricultural waste composting

The aim of this study was to compare the relative contribution of ammonia-oxidizing archaea (AOA) and bacteria (AOB) to nitrification during agricultural waste composting. The AOA and AOB amoA gene abundance and composition were determined by quantitative PCR and denaturing gradient gel electrophoresis (DGGE), respectively. The results showed that the archaeal amoA gene was abundant throughout the composting process, while the bacterial amoA gene abundance decreased to undetectable level during the thermophilic and cooling stages. DGGE showed more diverse archaeal amoA gene composition when the potential ammonia oxidation (PAO) rate reached peak values. A significant positive relationship was observed between the PAO rate and the archaeal amoA gene abundance (R2=0.554; P<0.001), indicating that archaea dominated ammonia oxidation during the thermophilic and cooling stages. Bacteria were also related to ammonia oxidation activity (R2=0.503; P=0.03) especially during the mesophilic and maturation stages.