Static solid state bioreactor and method for using same

Abstract

A static solid state bioreactor and method of using same. The bioreactor comprises a vessel having an upper end and a lower end, the upper end having a sealable opening. A gas distribution system in communication with the upper end and the lower end of the vessel. A liquid distribution system in communication with the upper end of the vessel. A liquid recovery system in communication with the lower end of the vessel. A material removal system disposed at the lower end of the vessel for removing biomass from the vessel.

Description

FIELD[0001]The present patent document relates to static solid state bioreactors and methods for using the same.BACKGROUND[0002]Fermentation may be broadly defined as the controlled cultivation of microorganisms for the transformation of an organic compound into a new product. Therefore, the term “fermentation” includes conventional alcohol fermentation, which is typically performed using some type of living ferment, such as yeast, and involves the enzymatically controlled anaerobic conversion of simple sugars, including those produced through saccharification, into carbon dioxide and alcohol. Depending on the organic compounds employed and fermentative microorganism(s) employed, however, a host of other fermentation products may be generated in addition to, or in the alternative to, alcohol.[0003]Recently, conversion of biomass through fermentation into ethanol or other useful products as a replacement for fossil fuels has garnered considerable attention. Biomass for such conversio...

AI Technical Summary

Benefits of technology

[0027]According to a further embodiment, the lower end of the vessel may be conically shaped. In one implementation, the lateral wall of the conically shaped lower end includes a plurality of openings to allow communication with the gas distribution system and / or the liquid recovery system at the lower end. In such an embodiment, the communication with the gas distribution system and liquid recovery system can be spread out over a large area, namely the surface of the conically shaped lower end, while at the same time the biomass may be directed towards a material removal system disposed at the apex of the conically shaped lower end. The conically shaped lower end, therefore, allows for even distribution of gas and liquid while facilitating easy and efficient material removal from the bioreactor.

[0042]In one embodiment, the bioreactor may further comprise a plurality of manifolds, the plurality of manifolds being disposed to connect the plurality of openings with the plurality of gas ports and the plurality of liquid ports. Preferably at least one gas port is located above at least one liquid port on at least one manifold. This allows the liquid to naturally separate from the gas and enter the liquid recovery system while minimizing the amount of liquid that enters the gas distribution system.

Problems solved by technology

While biomass has the potential to provide an attractive fossil fuel alternative, substantial difficulties still remain.

Although SSF has been practiced for hundreds of years in the preparation of traditional fermented foods, its application to the production of fermentation products within the context of modern biotechnology has been fairly limited.

This is because historically it has been notoriously difficult to control the fermentation conditions within SSF.

In practice, for example, temperature control, fluid channeling, excessive pressure drop, and evaporation have posed major problems to the development of a commercially viable SSF reactor and process that is suitable for large scale, industrial applications.

Numerous drawbacks exist with using the SLF process, however.

Two principal drawbacks of SLF processes is that they tend to be capital intensive and have high operating costs, making them less than optimum for producing many fermentation products, including alternative fuels, such as ethanol, on an industrial scale and at a competitive price.

Stirring adds complexity and significant cost to the bioreactor.

Static systems are sometimes used because the microorganism used in the fermentation process can not withstand the disruption caused during stirring.

These designs have been mostly for laboratory use and are not effective or efficiently designed to be scaled for use at an industrial level.

One of the major problems in utilizing a static SSF bioreactor on a large scale is temperature control.

This leads to localized elevated temperatures within the biomass in the reactor.

The elevated temperatures within the SSF bioreactor can result in temperatures well above the optimum for microbial growth, which in turn can inhibit the fermentation process from occurring efficiently.

This is primarily due to the fact that it is difficult to remove the localized heat uniformly from the biomass using a remote heat sink.

Numerous problems exist with present forced aeration bioreactor designs.

First, the gas introduced at the bottom of the reactor tends to reduce the temperature of the biomass near the bottom of the reactor, but has a lesser effect on the biomass as it passes up through the reactor.

As gas is introduced, it absorbs heat from the biomass at the bottom of the reactor, which in turn raises the temperature and humidity of the gas, and makes it less effective at cooling as it passes up through the reactor.

Furthermore, the pressure drop typically increases as the height increases making forced aeration more difficult.

This creates a problem, however, because by keeping the height small, large areas are required in order to scale up existing bioreactor designs, which in many cases will be impracticable due to the availability and / or cost of the required land.

While this solution effectively keeps the height of the biomass small while allowing the bioreactor to increase in height, the tray stacking design and implementation is too expensive and impractical to scale to the industrial levels necessary for many potential applications, including for cost effective alternative fuel production.

A further problem with forced aeration SSF reactors is the drying effect of the aeration process.

Further, the increase in temperature towards the top of the bioreactor can cause further evaporation, drying the biomass more.

In addition to the reduced efficiency of the fermentation processes, the drying of the biomass has a secondary effect.

This reduction in volume will cause channeling and cause the biomass to pull away from the sides of the reactor.

Channeling reduces the flow of gas to large parts of the volume of biomass causing localized temperature increases and an overall increase in the temperature gradients and thus, a reduction in process efficiency.

Further, contemporary thinking is that liquid can not be effectively used in a static SSF bioreactor because the liquid can not be evenly dispersed throughout the biomass.

The addition of liquid to static SSF reactors can result in flooding and inhibit the fermentation process.

The permeability of biomass, depending on the source, is usually very limited and tends to decrease as the biomass depth is increased.

While stirring can have positive effects, stirring mechanisms are complicated to build and become extremely expensive to construct and operate when scaled.

Even if stirring equipment on a large scale is effectively designed, the process of stirring will be extremely expensive for a large scale SSF reactor.

Wet biomass requires large amounts of energy to mix or stir because of its weight.

In addition, as mentioned above, stirring can have a deleterious effect on the microorganisms used in the fermentation process.

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