Microbiology and performance of a methanogenic biofilm reactor during the start-up period

Monitoring Candida parapsilosis and Staphylococcus epidermidis Biofilms by a Combination of Scanning Electron Microscopy and Raman Spectroscopy

The biofilm-forming microbial species Candida parapsilosis and Staphylococcus epidermidis have been recently linked to serious infections associated with implanted medical devices. We studied microbial biofilms by high resolution scanning electron microscopy (SEM), which allowed us to visualize the biofilm structure, including the distribution of cells inside the extracellular matrix and the areas of surface adhesion. We compared classical SEM (chemically fixed samples) with cryogenic SEM, which employs physical sample preparation based on plunging the sample into various liquid cryogens, as well as high-pressure freezing (HPF). For imaging the biofilm interior, we applied the freeze-fracture technique. In this study, we show that the different means of sample preparation have a fundamental influence on the observed biofilm structure. We complemented the SEM observations with Raman spectroscopic analysis, which allowed us to assess the time-dependent chemical composition changes of the biofilm in vivo. We identified the individual spectral peaks of the biomolecules present in the biofilm and we employed principal component analysis (PCA) to follow the temporal development of the chemical composition.

Control of VOCs from printing press air emissions by anaerobic bioscrubber: Performance and microbial community of an on-site pilot unit

A novel process consisted of an anaerobic bioscrubber was studied at the field scale for the removal of volatile organic compounds (VOCs) emitted from a printing press facility. The pilot unit worked under high fluctuating waste gas emissions containing ethanol, ethyl acetate, and 1-ethoxy-2-propanol as main pollutants, with airflows ranging between 184 and 1253 m³ h^-1 and an average concentration of 1126 ± 470 mg-C Nm^-3. Three scrubber configurations (cross-flow and vertical-flow packings and spray tower) were tested, and cross-flow packing was found to be the best one. For this packing, daily average values of VOC removal efficiency ranged between 83% and 93% for liquid to air volume ratios between 3.5·10^-3 and 9.1·10^-3. Biomass growth was prevented by periodical chemical cleaning; the average pressure drop was 165 Pa m^-1. Rapid initiation of anaerobic degradation was achieved by using granular sludge from a brewery wastewater treatment plant. Despite the intermittent and fluctuating organic load, the expanded granular sludge bed reactor showed an excellent level of performance, reaching removal efficiencies of 93 ± 5% at 25.1 ± 3.2 °C, with biogas methane content of 94 ± 3% in volume. Volatile fatty acid concentration was as low as 200 mg acetic acid L^-1 by treating daily average organic loads up to 3.0 kg COD h^-1, equivalent to 24 kg COD m^-3 bed d^-1. The denaturing gradient gel electrophoresis (DGGE) results revealed the initial shift of the domains Archaea and Bacteria associated with the limitation of the carbon source to a few organic solvents. The Archaea domain was more sensitive, resulting in a drop of the Shannon index from 1.07 to 0.41 in the first 123 days. Among Archaea, the predominance of Methanosaeta persisted throughout the experimental period. The increase in the proportion of Methanospirillum and Methanobacterium sp. was linked to the spontaneous variations of operating temperature and load, respectively. Among Bacteria, high levels of ethanol degraders (Geobacter and Pelobacter sp.) were observed during the trial.

Microbiology and Molecular Biology Tools for Biogas Process Analysis, Diagnosis and Control

Many biotechnological processes such as biogas production or defined biotransformations are carried out by microorganisms or tightly cooperating microbial communities. Process breakdown is the maximum credible accident for the operator. Any time savings that can be provided by suitable early-warning systems and allow for specific countermeasures are of great value. Process disturbance, frequently due to nutritional shortcomings, malfunction or operational deficits, is evidenced conventionally by process chemistry parameters. However, knowledge on systems microbiology and its function has essentially increased in the last two decades, and molecular biology tools, most of which are directed against nucleic acids, have been developed to analyze and diagnose the process. Some of these systems have been shown to indicate changes of the process status considerably earlier than the conventionally applied process chemistry parameters. This is reasonable because the triggering catalyst is determined, activity changes of the microbes that perform the reaction. These molecular biology tools have thus the potential to add to and improve the established process diagnosis system. This chapter is dealing with the actual state of the art of biogas process analysis in practice, and introduces molecular biology tools that have been shown to be of particular value in complementing the current systems of process monitoring and diagnosis, with emphasis on nucleic acid targeted molecular biology systems.

Sequential operation of a hybrid anaerobic reactor using a lignocellulosic biomass as biofilm support

Agro-industries are facing many economic and environmental problems associated with seasonal generation of liquid and solid waste. In order to reduce treatment costs and to cope with seasonal variation, we have developed a hybrid anaerobic reactor operated sequentially by using lignocellulosic biomass (LB) as biofilm carrier support. Six LBs were tested to evaluate the treatment performance during a succession of two start-up periods, separated by a non-feeding period. After a short acclimation phase of several days, all the reactors succeeded in starting-up in less than 1month to reach an organic loading rate of 25gCODL(-1)d(-1). In addition, they restarted-up successfully in only 15days after a 3month non-feeding period, indicating that biofilms conserved their biological activities during this last phase. As a consequence, the use of LB as a biofilm support gives the potential to sustain seasonal variations of wastewater loads for industrial application.

Anaerobic treatment of tequila vinasses under seasonal operating conditions: start-up, normal operation and restart-up after a long stop and starvation period

This study examines the performance of an anaerobic fixed-film bioreactor under seasonal operating conditions prevailing in medium and small size Tequila factories: start-up, normal operation and particularly, during the restart-up after a long stop and starvation period. The proposed start-up procedure attained a stable biofilm in a rather short period (28 days) despite unbalanced COD/N/P ratio and the use of non-acclimated inoculum. The bioreactor was restarted-up after being shut down for 6 months during which the inoculum starved. Even when biofilm detachment and bioreactor clogging were detected at the very beginning of restart-up, results show that the bioreactor performed better as higher COD removal and methane yield were attained. CE-SSCP and Q-PCR analyses, conducted on the biofilm prokaryotic communities for each operating condition, confirmed that the high COD removal results after the bioreactor clogging and the severe starvation period were mainly due to the stable archaeal and resilient bacterial populations.

Biofilm development during the start-up period of anaerobic biofilm reactors: the biofilm Archaea community is highly dependent on the support material

To evaluate the impact of the nature of the support material on its colonization by a methanogenic consortium, four substrata made of different materials: polyvinyl chloride, 2 polyethylene and polypropylene were tested during the start-up of lab-scale fixed-film reactors. The reactor performances were evaluated and compared together with the analysis of the biofilms. Biofilm growth was quantified and the structure of bacterial and archaeal communities were characterized by molecular fingerprinting profiles (capillary electrophoresis-single strand conformation polymorphism). The composition of the inoculum was shown to have a major impact on the bacterial composition of the biofilm, whatever the nature of the support material or the organic loading rate applied to the reactors during the start-up period. In contrast, the biofilm archaeal populations were independent of the inoculum used but highly dependent on the support material. Supports favouring Archaea colonization, the limiting factor in the overall process, should be preferred.

Changes in microbial communities in a hybrid anaerobic reactor with organic loading rate and temperature

Poor understanding of the response of microbial communities to sudden changes in organic and hydraulic loads is one of the major reasons for the inability to prevent operational instabilities in anaerobic reactors. Effect of changes in hydraulic retention time (HRT) and organic loading rate (OLR) on reactor performance and its anaerobic microbial community were investigated in two anaerobic hybrid reactors operated at 37 and 55 °C. HRT was reduced stepwise, while OLR was increased along with influent chemical oxygen demand at fixed HRT until the performance of reactor deteriorated. The profile of archaeal 16S rRNA gene amplicons, resolved by denaturing gradient gel electrophoresis, reflected system status during disturbances. The more diverse archaeal community in the reactor operated at 37 °C showed better performance than the communities present at 55 °C at higher OLR and shorter HRT, suggesting that higher diversity is indicative of more stable operation of reactors despite organic and hydraulic shocks.

Distinctive responses of metabolically active microbiota to acidification in a thermophilic anaerobic digester

Acidification is one of the most common and serious problems inducing process failure in anaerobic digesters. The production of volatile fatty acids (VFAs) mainly triggers acidic shock. However, little is known about the bacteria involved in the processes of acidogenic metabolism, such as fermentation and reductive acetogenesis. Here, the metabolic responses of a methanogenic community to the acidification and resulting process deterioration were investigated using transcriptional profiling of both the 16S rRNA and formyltetrahydrofolate synthetase (FTHFS) genes. The 16S rRNA-based analyses demonstrated that the dynamic shift of bacterial populations was closely correlated with reactor performance, especially with VFA accumulation levels. The pH drop accompanied by an increase in VFAs stimulated the metabolic activation of an uncultured Chloroflexi subphylum I bacterium. The subphylum has been characterized as a fermentative carbohydrate degrader using culture- and molecular-based ecophysiological assays. At the beginning of VFA accumulation, FTHFS genes were expressed; the transcripts were derived from phylogenetically predicted homoacetogens, suggesting that reductive acetogenesis was operated by hitherto unidentified bacteria. When acetate concentrations were high, the FTHFS expression ceased and Thermoanaerobacterium aciditolerans proliferated selectively. This thermoacidophilic bacterium would play a decisive role in acetate production via fermentative metabolism. The results of this study reveal for the first time that an uncultured Chloroflexi, T. aciditolerans, and novel homoacetogens were metabolically associated with acidic shock and subsequent VFA accumulation in an anaerobic digester.