High-tech process optimisation in biogas plants

At present, Germany has to import expensive and mostly fossil-based energy sources in order to supply industry and private households with sufficient energy. Economic dependencies and political uncertainties are the inevitable consequences. In order to become more independent from these energy imports in the near future, industrial energy production has to diversify, taking new directions, such as the establishment of sustainable bio-based processes to supplement existing power generation. In ESE-BIOGAS the research partners together with BRAIN are introducing bio-based energy production processes through the consistent use of renewable raw materials. This covers one of the priority fields of current German research and development programs. ESE-BIO-GAS (reference number FKZ: 03SF0424D) is therefore part of the National Research Strategy Bioeconomy 2030.

In Germany, biogas as energy source accounts for more than 50% of the electrical power produced from biomass and other industrial waste streams. With the clear goal not to compete with carbon sources needed for food and feedstuff production, BRAINs focus is to optimise the use of substrates such as straw, scrap wood and liquid manure, which by using microbial consortia are converted to biogas.

The biochemical conversion of biomass into biogas is a highly complex process in which a diverse microbial consortium is needed. The complexity of this community in a reactor so far largely precludes reliable control of the fermentation process, which until today restricted the use of this technology in a validated industrial setting. Apart from this deficit in process control the initial breakdown of polymeric biomass into fermentable monomers is fairly slow, which currently determines the speed of the entire process and thus constitutes a further limitation. Another well-known problem in the operation of biogas plants is acidification of the fermentation resulting in heavy disturbance of the process through inhibition of susceptible methane producing bacteria. The consequential failure in degradation/ bioconversion is inevitably connected to economic losses.

The new process established by BRAIN addresses these problems, leading to an increase in stability, sustainability and efficiency of the entire fermentation process. The output-raising improvement comprises three interacting modules for optimal effect: an exo-enzyme farm, an electro-biogas fermenter and a biosensor. “The newly established exo-enzyme farm provides a defined enzyme cocktail that increases the efficiency of the waste substrate breakdown and subsequent metabolic degradation by 20%. Advantages of this process step are an improved space-time yield and a reduced final waste volume. At the core of the reactor is a new electro-biogas fermenter. Herein, the degradation steps of the substrate can be controlled individually by directly implemented fuel cells. In parallel, the energy equivalents (electrons) that are released during the enzymatic reactions are used directly for additional power generation. In comparison to existing combined heat and power plants this works far more efficiently“, explains Dipl. Ing. Marc Gauert, project leader at BRAIN. “The last process component is a microfluidic biosensor which monitors the process intermediate propanoic acid, enabling easier process control”.

“Within a very short time span, Marc Gauert and his BRAIN team succeeded in effectively optimising of the process of biogas production. Special thanks also go to Prof. Dr. Johannes Gescher from KIT in Karlsruhe, whose excellent experience in microbial fuel cells as well as in exo-electrogenic and methanogenic microorganisms contributed essentially to the positive outcome“, adds Dr. Guido Meurer, Unit Head Strain Development at BRAIN.

At the end of 2014, 7,820 biogas plants were in operation in Germany. They had an installed capacity of around 3,500 MW. Compared to the year 2000 the number of plants increased sevenfold. German biogas plants thus replace more than two nuclear power plants and provide more than 10 million households with 27 billion kilowatt-hours of electricity per year (4.3% of the gross power generation). In Germany alone, the biogas sector employed around 40,000 people in 2013 who achieved total sales of EUR 6.6 billion. International business accounted for about 40% of the sales.