Patrice Ramm

Production, characterization, and biogas application of magnetic hydrochar from cellulose

Hydrothermal carbonization (HTC) produces carbon-rich nano-micro size particles. In this study, magnetic hydrochar (MHC) was prepared from model compound cellulose by simply adding ferrites during HTC. The effects of ferrites on HTC were evaluated by characterizing solid MHC and corresponding process liquid. Additionally, magnetic stability of MHC was tested by magnetic susceptibility method. Finally, MHC was used as support media for anaerobic films in anaerobic digestion (AD). Ash-free mass yield was around 50% less in MHC than hydrochar produced without ferrites at any certain HTC reaction condition, where organic part of MHC is mainly carbon. In fact, amorphous hydrochar was growing on the surface of inorganic ferrites. MHC maintained magnetic susceptibility regardless of reaction time at reaction temperature 250°C. Pronounced inhibitory effects of magnetic hydrochar occurred during start-up of AD but diminished with prolong AD times. Visible biofilms were observed on the MHC by laser scanning microscope after AD.

Demand-driven biogas production from sugar beet silage in a novel fixed bed disc reactor under mesophilic and thermophilic conditions

A newly developed fixed bed disc reactor (FBDR) which combines biofilm formation on biofilm carriers and reactor agitation in one single system was assessed for its applicability to demand-driven biogas production by variable feeding of sugar beet silage. Five different feeding patterns were studied at an organic loading of 4gVSL-1d-1 under mesophilic and thermophilic conditions. High methane yields of 449-462LNkgVS were reached. Feeding variable punctual loadings caused immediate response with 1.2- to 3.5-fold increase in biogas production rates within 15min. Although variable feeding did not induce process instability, a temporary decrease in pH-value and methane concentration below 40% occurred. Thermophilic temperature was advantageous as it resulted in a more rapid, higher methane production and less pronounced decrease in methane content after feeding. The FBDR was demonstrated to be well-suited for flexible biogas production, but further research and comparison with traditional reactor systems are required.

Magnetic Biofilm Carriers: The Use of Novel Magnetic Foam Glass Particles in Anaerobic Digestion of Sugar Beet Silage

The use of recently developed magnetic foam glass particles for immobilization of microbial biomass was tested. The effect of the particles was illustrated at the production of biogas from sugar beet silage as the sole substrate. Lab-scale fermentation experiments were conducted using a mesophilic completely stirred tank reactor and a magnetic separator. Microscopic analysis revealed biofilm coverage of 50–60% on the surface of the particles within 110 days. It was possible to recover 76.3% of the particles from fermentation effluent by means of a separation procedure based on magnetic forces. Comparing a particle charged reactor with a control reactor showed a small performance gain. The methane rate was increased from to  L L−1 d−1 and the methane yield was increased from to  L g−1 (volatile solids) at an organic loading rate of  g L−1 d−1 (volatile solids). Maximum methane rates of 1.42 L L−1 d−1 at an organic loading rate of 4.60 g (volatile solids) L−1 d−1 (reactor including magnetic particles) and 1.34 L L−1 d−1 at 3.73 g L−1 d−1 (control reactor) were achieved. Based on the results, it can be concluded that the use of magnetic particles could be an attractive option for the optimization of biogas production.

Microbial communities involved in biogas production exhibit high resilience to heat shocks

We report here the impact of heat-shock treatments (55 and 70 °C) on the biogas production within the acidification stage of a two-stage reactor system for anaerobic digestion and biomethanation of grass. The microbiome proved both taxonomically and functionally very robust, since heat shocks caused minor community shifts compared to the controls, and biogas yield was not decreased. The strongest impact on the microbial profile was observed with a combination of heat shock and low pH. Since no transient reduction of microbial diversity occured after the shock, biogas keyplayers, but also potential pathogens, survived the treatment. All along the experiment, the heat-resistant bacterial profile consisted mainly of Firmicutes, Bacteroidetes and Proteobacteria. Bacteroides and Acholeplasma were reduced after heat shocks. An increase was observed for Aminobacterium. Our results prove the stability to thermal stresses of the microbial communities involved in acidification, and the resilience in biogas production irrespectively of the thermal treatment.

The Relationship Between Bioreactor Design and Feedstock for Optimal Biogas Production

This chapter presents an overview of bioreactor configurations for the production of biogas with an investigation of different enhancement strategies for the conversion of organic biomass to methane. Initially anaerobic digestion (AD) microbial processes are introduced. Subsequently, optimal bioreactor design is examined. The AD process is capable of converting a large variety of feedstocks to carbon dioxide and methane. The performance of microbial conversion is closely linked to feedstock characteristics. As such bioreactor concepts are explored with reference to these feedstock characteristics, and are categorized as either: liquid and low solid content AD; or high-solid AD. Enhancement strategies include the enrichment of active biomass within the reactor through immobilization of microbes, separation of process stages, solid-liquid phase separation, improvement of mass transfer, and conversion of hydrogen and carbon dioxide to methane. Recent reactor developments are considered in each section.