A comprehensive microbial insight into single-stage and two-stage anaerobic digestion of oxytetracycline-medicated cattle manure

At present, there is a distinct lack of understanding to the effect of antibiotic contamination of a substrate on two-stage anaerobic digestion (AD) processes. The aim of this study was to investigate how oxytetracycline (OTC) influences the structure of the microbial community and the production of methane in two-stage anaerobic cattle manure digesters. Ion Torrent sequencing and PCR-DGGE analysis were used to detect microbial community changed in response to the addition of oxytetracycline. Illumina sequencing was also performed to detect antibiotic resistance genes (ARGs). Digestion studies utilized samples of manure produced by cattle which had been therapeutically treated using a standard OTC solution of 50 mL per 20 mg kg(-1) cattle weight. According to the results of the PCR-DGGE and Ion Torrent sequencing, the bacterial diversity of acidogenic digesters was higher than those of single-stage digesters during the digestion period. An assessment of single-stage and two-stage AD data highlighted that Methanosarcina and syntrophic acetate-oxidizing bacteria are critical to the production of biogas. The overall results indicated that changes in the structure of a microbial community lead to changes in biodegradation capacity of antibiotics and occurrence of ARGs. (C) 2016 Elsevier B.V. All rights reserved

Stochastic prediction of natural frequencies of laminated composite beams by using a high-order statistical moment based approach

Statistical Moment (SM) based modelling is a quite straightforward approach in stochastic modelling of uncertain structures. However, the method still has deficiencies including determination of SMs of natural frequencies of vibratory structures, and it has not been tested yet for realistic structures. This study aims such verification by employing high-degree statistical moments in stochastic equations. In this respect, SM approach is applied for two different uncertainty cases. In the first case, uncertain parameters are experimentally reproduced from the batch of laminated composite beams. Then, those uncertainties are fed to SM equations used in finite element model to obtain descriptive statistical quantities (mean, variance, skewness, and kurtosis) of stochastic natural frequencies. Next, Pearson model is utilized to obtain probability density function of the natural frequency by using standardized SMs. Beside this, uncertain fundamental natural frequency of fifty samples of composite beams is measured by experimental modal tests. All SM based predictions and modal test results are also compared with numerical Monte Carlo Simulations. The latter case examines composite beams having non normal uncertain thickness. Since the results are in good harmony with each other, it is concluded that high order SM based approach may effectively be used in uncertainty modelling of realistic structures

Application of next-generation sequencing methods for microbial monitoring of anaerobic digestion of lignocellulosic biomass

The anaerobic digestion of lignocellulosic wastes is considered an efficient method for managing the world's energy shortages and resolving contemporary environmental problems. However, the recalcitrance of lignocellulosic biomass represents a barrier to maximizing biogas production. The purpose of this review is to examine the extent to which sequencing methods can be employed to monitor such biofuel conversion processes. From a microbial perspective, we present a detailed insight into anaerobic digesters that utilize lignocellulosic biomass and discuss some benefits and disadvantages associated with the microbial sequencing techniques that are typically applied. We further evaluate the extent to which a hybrid approach incorporating a variation of existing methods can be utilized to develop a more in-depth understanding of microbial communities. It is hoped that this deeper knowledge will enhance the reliability and extent of research findings with the end objective of improving the stability of anaerobic digesters that manage lignocellulosic biomass

Operating conditions influence microbial community structures, elimination of the antibiotic resistance genes and metabolites during anaerobic digestion of cow manure in the presence of oxytetracycline

The way that antibiotic residues in manure follow is one of the greatest concerns due to its potential negative impacts on microbial communities, the release of metabolites and antibiotic resistant genes (ARGs) into the nature and the loss of energy recovery in anaerobic digestion (AD) systems. This study evaluated the link between different operating conditions, the biodegradation of oxytetracycline (OTC) and the formation of its metabolites and ARGs in anaerobic digesters treating cow manure. Microbial communities and ARGs were determined through the use of quantitative real-time PCR. The biodegradation of OTC and occurrence of metabolites were determined using UV-HPLC and LC/MS/MS respectively. The maximum quantity of resistance genes was also examined at the beginning of AD tests and concentration was in the order of: tetM > tetO. The numbers of ARGs were always higher at high volatile solids (VS) content and high mixing rate. The results of the investigation revealed that relationship between mixing rate and VS content plays a crucial role for elimination of ARGs, OTC and metabolites. This can be attributed to high abundance of microorganisms due to high VS content and their increased contact with elevated mixing rate. An increased interaction between microorganisms triggers the promotion of ARGs

Enhancing methane production from anaerobic co-digestion of cow manure and barley: Link between process parameters and microbial community dynamics

The effects of selected process parameters (i.e., temperature, inoculum to substrate ratio [I:S], and inoculum source) on methane production and microbial community structure were investigated in lignocellulose-based anaerobic digestion tests. The results highlighted that dynamic response of microbial communities in changing process parameters subsequently affected anaerobic digestion performance. Co-inoculation of cow rumen fluid to the seed sludge improved the methane yield by 18%. The overall highest methane yield (278 mL CH4/g volatile solids) was obtained when cow rumen fluid was co-inoculated with anaerobic seed sludge with an I:S ratio of 1:2 at mesophilic temperature. Based on 16S rRNA gene amplicon sequencing results, Clostridium, Bacteroides, and Bacillus were the predominant bacterial genera in all anaerobic digesters. The highest relative abundances of Clostridum and Bacillus were detected in the thermophilic anaerobic digester. The relative abundance of Rikenella; known for high cellulolytic activity, was significantly higher only in the cow rumen fluid-added digester. Comparatively higher abundances of these lignocellulose-degraders synergistically affected volatile fatty acids as well as methane production in these anaerobic digestion set ups. Methanobacterium was the most abundant methanogen in the digesters inoculated only with anaerobic seed sludge; whereas, Methanobrevibacter dominated the digester that was co-inoculated with cow rumen fluid

Biological pretreatment with Trametes versicolor to enhance methane production from lignocellulosic biomass: A metagenomic approach

The presence of poorly biodegradable components in lignocellulosic biomass limits the methane recovery in anaerobic digesters. The main reason to go for aerobic pretreatment before anaerobic digestion (AD) is to enable enzymatic cleavage of the aromatic rings in lignin by oxygen since it cannot be efficiently degraded under anaerobic conditions. In this study, the advantage of highly-cellulolytic white-rot fungi Trametes versicolor was taken by aerobic pretreatment prior to anaerobic co-digestion of cow manure and selected cereal crop materials (i.e. wheat, rye, barley, triticale) harvested at different stages. Fungal pretreatment improved the methane yield by 10%-18% and cellulose degradation up to 80%. Furthermore, higher volatile fatty acid (VFA) speciation was found in the anaerobic digesters upon fungal pretreatment. 16S rRNA gene amplicon sequencing revealed a more diverse microbial community in the fungal-pretreated anaerobic digesters. Generally, typically-detected bacterial species dominated the digesters; except that Synergistetes was only enriched in the fungal-pretreated digesters. Although Methanosarcianease was the predominant methanogenic archaea, a more diverse methanogenic population was identified in the fungal-pretreated digesters in which Methanobacteriaceaa and Methanomibrobiaceae also took role during biomethanation. Comparatively more unique microbiome of biogas reactors upon fungal pretreatment synergistically affected VFA production, cellulose degradation and eventually methane yield in an affirmative way. Considering the functional importance of bacterial and methanogenic archaeal populations, elevated knowledge of the microbial structures is essential for minimizing process failures and for creating strategies for process optimization of lignocellulose based-AD

Composting practice for sustainable waste management: a case study in Istanbul

Increased demand in municipal and industrial facilities has caused growing number of solid wastes generation in the last decades. In this regard, it is necessary to develop sustainable management strategies for maintaining environmental quality. As a developing country, waste management is recognized as a priority issue in Turkey and new policies are in progress to overcome existing obstacles. According to the national strategy, it is planning to reduce the amount of biodegradable wastes to be disposed in landfill facilities by evaluating recycling, composting, or energy/material recovery methods. The aim of this study was to implement a composting system to a housing estate located in Istanbul for reducing organic waste loads to sanitary landfill areas and providing soil amendment for estate's garden. In this scope, two compost tumbler systems with 1ton/year capacity were set up in the pilot area. Kitchen waste was used in the first system and shredded before composting, whereas second system was only fed with yard wastes and tumblers were turned manually once a day. Final composts' qualities were evaluated according to national regulations. Heavy metal concentrations of two composts were below the regulatory limits (Cd<1mg/kg, Co<20mg/kg, Cr<100mg/kg, Cu<50mg/kg, Mo<10mg/kg, Ni<30mg/kg, Pb<50mg/kg, Zn<150mg/kg). C/N ratios were calculated as 42.7 and 19.3 for kitchen waste and yard waste composts, respectively. According to the national regulations, C/N ratio of a final compost product must be <35. Therefore, it is suggested to use the mixture of these two types of composts for soil application

Fungal bioaugmentation of anaerobic digesters fed with lignocellulosic biomass: What to expect from anaerobic fungus Orpinomyces sp.

Energy-efficient biogas reactors are often designed and operated mimicking natural microbial ecosystems such as the digestive tracts of ruminants. Anaerobic fungi play a crucial role in the degradation of lignocellulose-rich fiber thanks to their high cellulolytic activity. Fungal bioaugmentation is therefore at the heart of our understanding of enhancing anaerobic digestion (AD). The efficiency of bioaugmentation with anaerobic fungus Orpinomyces sp. was evaluated in lignocellulose-based AD configurations. Fungal bioaugmentation increased the methane yield by 15-33% during anaerobic co-digestion of cow manure and selected cereal crops/straws. Harvesting stage of the crops was a decisive parameter to influence methane production together with fungal bioaugmentation. A more efficient fermentation process in the bioaugmented digesters was distinguished by relatively-higher abundance of Synergistetes, which was mainly represented by the genus Anaerobaculum. On the contrary, the composition of the methanogenic archaea did not change, and the majority of methanogens was assigned to Methanosarcina

Anaerobic co-digestion of cow manure and barley: Effect of cow manure to barley ratio on methane production and digestion stability

Anaerobic co-digestion of cow manure (CM) and barley (Hordeum vulgare, HV) was evaluated in terms of biochemical methane potentials with respect to five different CM to HV mixing ratios of 1:0, 2:1, 1:1, 1:2, and 0:1 based on volatile solids (VS) contents. Bacterial community composition of the seed sludge was examined using 454 pyrosequencing of 16S rRNA gene sequences. Based on the taxonomic classification, major bacterial phyla belonged to the Firmicutes (42%) and Bacteroidetes (22%). Co-digestion of CM and barley was superior at all mixing ratios when compared with the digestion of CM alone. The digestion systems failed at the ratio of 0:1, and there was no methane production. The presence of barley caused high acidification, but there was no volatile fatty acids accumulation at the end of the digestion. Highest specific methane productions were obtained at CM to HV mixing ratios of 2:1 and 1:1 as 216 CH4/g VS and 230 CH4/g VS, respectively. Because of the highest specific methane production, the optimal CM to HV mixing ratio was found to be 1:1 in this study. (c) 2015 American Institute of Chemical Engineers Environ Prog, 35: 589-595, 201