Çağrı Akyol

Microbial monitoring of ammonia removal in a UASB reactor treating pre-digested chicken manure with anaerobic granular inoculum

Performance and microbial community dynamics in an upflow anaerobic sludge bed (UASB) reactor coupled with anaerobic ammonium oxidizing (Anammox) treating diluted chicken manure digestate (Total ammonia nitrogen; TAN=123±10mg/L) were investigated for a 120-d operating period in the presence of anaerobic granular inoculum. Maximum TAN removal efficiency reached to above 80% with as low as 20mg/L TAN concentrations in the effluent. Moreover, total COD (tCOD) with 807±215mg/L in the influent was removed by 60-80%. High-throughput sequencing revealed that Proteobacteria, Actinobacteria, and Firmicutes were dominant phyla followed by Euryarchaeota and Bacteroidetes. The relative abundance of Planctomycetes significantly increased from 4% to 8-9% during the late days of the operation with decreased tCOD concentration, which indicated a more optimum condition to favor ammonia removal through anammox route. There was also significant association between the hzsA gene and ammonia removal in the UASB reactor.

Performance and microbial community variations in thermophilic anaerobic digesters treating OTC medicated cow manure under different operational conditions.

This study aimed to determine the fate and effect of oxytetracycline (OTC) and its metabolites during thermophilic anaerobic digestion of cow manure. OTC-medicated and non-medicated digesters were operated at 55°C with different volatile solids (VS) concentrations (4% and 6%) and mixing rates (90 and 120rpm). OTC and its metabolites were measured by HPLC and LC/MS/MS, respectively. Microbial community dynamics were monitored by denaturing gradient gel electrophoresis (DGGE) and real-time PCR (qPCR). Approximately 2mg/L initial OTC concentration caused 10-30% inhibition on biogas production and higher inhibition was observed as mixing rate increased. DGGE results indicated that OTC caused a shift in bacterial community structure and several species became dominant with time. Archaeal community decreased throughout the digestion period. RNA based qPCR analyses showed that gene copy numbers of bacteria and Methanomicrobiales declined in all digesters whereas gene copy numbers of Methanobacteriales and Methanosarcinales increased in high mixing rate digesters.

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.

Bioaugmentation with Clostridium thermocellum to enhance the anaerobic biodegradation of lignocellulosic agricultural residues

This study aimed to improve biomethane production from lignocellulosic biomass by assessing the impact of bioaugmentation with Clostridium thermocellum on the performance of anaerobic digesters at different inoculation ratios. The outputs of the digestion experiments revealed that bioaugmentation strategies with C. thermocellum increased the methane yield up to 39%. The sequencing analysis indicated that the indigenous microbial community was modified by the bioaugmentation. During the process of bioaugmentation, in the digester that was inoculated at the ratio of 20% (v:v), an increase in the abundance of Ruminococcaceae family led to a decrease in the Bacteroidaceae and Synergistaceae families. Furthermore, the metabolic products of the bioaugmented strains greatly influenced the diversity of the archaeal community and an increase in the abundance of Methanomicrobiales was observed.

Acidification of non-medicated and oxytetracycline-medicated cattle manures during anaerobic digestion

Possible adverse effects of a commonly used veterinary antibiotic, oxytetracycline (OTC), on acidogenic phase of anaerobic digestion of cattle manure along with optimum operating conditions were investigated. A standard veterinary practice of 50 ml OTC solution (20 mg/kg cattle weight) was injected into the muscles of cattle and then manure samples were collected for 5 days following the injection. The 5-day samples were equally mixed and used throughout digestion experiments. Preliminary batch tests were conducted to obtain the optimum pH range and observe volatile fatty acids (VFAs) production. In this regard, different sets of batch digesters were operated at pH ranging from 5.2±0.1 to 5.8±0.1 at mesophilic conditions with total solids content of 6.0±0.2%. The pH of 5.5±0.1 was found to be the optimum value for acidification for both non-medicated and OTC-medicated conditions. Under predetermined conditions, maximum total VFA (VFAtot) of 830±3 mg (as acetic acid)/L was produced and maximum acidification rate was evaluated as 11% for OTC-medicated cattle manure, whereas they were 900±6 mg (as acetic acid)/L and 12% for non-medicated manure. Digestion studies were further continued in a semi-continuous mode at pH 5.5±0.1 and SRT/HRT of 5 days. VFAtot concentrations and maximum acidification rate increased up to 2181±19 mg (as acetic acid)/L and 29% for non-medicated cattle manure. For OTC-medicated cattle manure, lower acidification rate of 18% was observed.

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.