Biotechnological Conversion Processes

ever since ever: Traditional Biomass
then: Coal (peak around 1910)
then: Oil, Gas (peak around 1970)
then: Nuclear Energy (no real peak, more like a plateau, start around 1940)
then: Renewable Energy (starting in late 1970)

BRISC = Brazil, Russia, India, China, South Africa

EU

Salmonella spp. can be transferred by many different manures.

E. coli can be transferred by cattle manures.

Yersinia enterocolitica can be transferred by pig manures.

Codigestion refers to the simultaneous anaerobic digestion of multiple organic wastes in one digester. Codigestion is used to increase methane production from low-yielding or difficult to digest materials (i.e., feedstocks).

Ammonia is a commonly encountered inhibitor in anaerobic digestion systems. Ammonium ion (NH₄⁺) and free ammonia (NH₃) are directly and indirectly inhibitory. Process inhibition is also related to the pH, temperature, and concentrations of ammonium and ammonia.

Inhibition of the biogas process by ammonia results in an enhanced accumulation of acetate and propionate. This leads to a decreased pH (due to the accumulation of acetate)

> pH adjustment

> dilution of batch medium

The methanogenic bacteria die off

The Renewable Energy Sources Act or EEG (German: Erneuerbare-Energien-Gesetz) is a series of German laws that originally provided a feed-in tariff (FIT) scheme to encourage the generation of renewable electricity.  

Tariffs  in the EEG paid for Biogas Plants starting in 2009.

The purpose of this Act is to enable the energy supply to develop sustainably in particular in the interest of mitigating climate change and protecting the environment, to reduce the costs to the economy not least by including long-term external effects, to conserve fossil energy resources and to promote the further development of technologies to generate electricity from renewable energy sources.

Two main reasons:

a) the economical crisis that heats the EU after 2010

b) reticence and pushbacks on issues relating the energy security, environmental sustainability, and the cost-effectiveness of the use of biogas technology (food vs fuel).

Because the big biogas installations use more fuels for their run, need more amounts of feedstocks (food crops) and they do not ensure energy security at the end when all inputs are taken into consideration.

The small biogas installations use biowaste from the nearby farms, unlike big ones that have to spend a lot of fuel to transport the feedstock from elsewhere. 

Chances of breakdowns in energy supply are lowered if you have a more decentralized system with smaller plants and when one or two get e.g. contaminated it is less severe than when you have big plants and one of them gets affected in some way

By the end of the 20th century, governments and policymakers around the world faced three key issues:

i) worries about energy security;

ii) commitment to economic development, including the creation and sustaining of jobs, particularly in agriculture; and

iii) the need to mitigate global climate change and achieve lower GHG emissions.

More advanced technologies in terms of substrate pretreatment and microbiological methods lead to higher throughput and more efficient processes.  

Another reason was the introduction of the tariff legislation-EEG that was set up in relation to these discussions.

The Renewable Energy Sources Act or EEG (German: Erneuerbare-Energien-Gesetz) is a series of German laws that originally provided a feed-in tariff (FIT) scheme to encourage the generation of renewable electricity.

> Investment protection through guaranteed feed-in tariffs and connection requirements.

> No charge to German public finances.

> Innovation by decreasing feed-in-tariffs.

Hydroelectric, Wind power, Solar power, Biomass, Geothermal.

The Kyoto basket encompasses the following six greenhouse gases: carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and the so-called F-gases(hydrofluorocarbons and perfluorocarbons) and sulfur hexafluoride (SF6). Each gas is weighted by its global warming potential and aggregated to give total greenhouse gas emissions in CO2 equivalents.

1. worries about energy security (oil crisis)

2. economic development, both in the developed world and developing countries, including the creation or sustaining of jobs in agriculture

3. the need to mitigate climate change and achieve lower greenhouse gas (GHG) emissions.

Two different fermentation processes:

Anaerobic (absence of oxygen): (Alcoholic) fermentation - mainly products produced

vs

Aerobic (presence of oxygen): Composting - mainly biomass produced (a lot of ATP)

Anaerobic metabolism: Alcoholic fermentation (digestion) from Saccharomyces -> not so much energy but we have a high yield of product (methane, H2, ethanol, CO2)

Aerobic metabolism: Composting -> A lot of energy (36 ATP), produce more cells and products (biomass, water, CO2)

> Substrate (energy crops or biowaste, slurry or manure)

> (pretreatment)

> Biogas Reactor

> Biogas (CHP cogeneration heat & power, NGG national gas grid) + Digestion Residue

> fertilizer

> acre

> Substrate

During the first two steps, polymers (lipids, proteins, carbohydrates, etc.) are converted to soluble monomers (long-chain fatty acids, glycerol, amino acids, sugars, etc.), which are subsequently further converted via various fermentation reactions to short-chain fatty acids, alcohols, H2 and CO2 . In the next step the acids and alcohols are degraded through anaerobic oxidation by proton-reducing syntrophic acetogens to form H2 , CO2 and acetate, which are used by the methanogens in the final step for the production of biogas (methane, H2).

The acetogenesis is combined with the methanogenesis because of the free energy change (ΔG, Gibbs standard: under standard conditions) -> energetically more feasible

• Ethanol fermentation (Acetate) ΔG+

• Methanogenesis (Methane production) ΔG-

• Syntrophic, coupled reaction ΔG-

ΔG- after the biological stage, it means ΔG+ for the bacteria.

-> The bacteria seem to be exchanging electrons during the coupled reaction

Both reactions occur simultaneously, nonetheless it is speculated that the energy transfer between methanogenic and acetogenic bacteria could take place via pili structures. Because of this, it is important to know that excessive stirring would increase the shear stress in the culture broth which could harm the overall methanation process and/ or drive them apart.

We can't cultivate these microbial cultures separately.