Fermentor
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A fermentor or fermentation chamber is a type of bioreactor for containing and controlling fermenter microorganisms. Fermentation is an important economical route to important raw materials (ethanol, lactic acid) and fermented foods. A fermenter must control temperature and keep the chamber anaerobic and free of oxygen to optimize conditions for desired microbial fermentation. Fermentation is a basic and highly developed art and also pursued by hobbyists. Necessary public information is available to create an economical and high performance OSE version to complete certain product ecologies.
Fermentation
Fermentation is a way for microorganisms to continue metabolism when there is no exogenous electron acceptor. Microorganisms are forced to use an electron acceptor that is available endogenously, usually an organic compound. The organism gains high energy electrons by converting the molecule to lower energy forms by catalyzing the breakdown of oxygen functional groups to a lower redox state. The breakup of sugars into a large amount of modified small organic molecules such as ethanol, lactic acid, or acetic acid is useful to an OSE context for its ability to process agricultural feedstocks into desirable materials and foods. Fermentation is carried out by yeast and bacteria, in liquid and anaerobic solids. Silage is an example of solid state fermentation and fermentors are used for solution state fermentation.
Open source projects
In addition to the numerous beer brewing fermentor designs publicly available there are efforts to create an open source laboratory grade bioreactors.
Universidad del Valle, Cali, Colombia contains CAD designs and arduino controller program code. The design calls for a polycarbonate material, which can be sterilized in an autoclave.
The projects description is copied below: This project aims at using an Arduino board to monitor and control a bioreactor from a web interface. A first prototype was build at the Universidad del Valle, Cali, Colombia as an attempt to produce a cost effective and easily maintainable alternative to usually very expensive genuine bioreactors. The setup encompasses a home made bioreactor, an Arduino Mega 2560 board for control and monitoring, an embedded Alix computer as a server and a router.
The features of the reactors are as follows: pH monitoring pH control using pinch valves (to be added soon) NH4+ monitoring (to be added soon) temperature monitoring and regulation (3 point measurement and heating regulation) regulation of the motor used for agitation liquid level monitoring semi-batch operation using two peristaltic pumps gas inlet control for 3 different gases.
Open Wet Ware DIYbio has a list of resources for DIY fermentors.
OSE fermentor
Prototype 1
The fermentor should be designed to control the conditions necessary to raise any nonphototrophic microorgansism (see Photobioreactor). An initial prototype should be built to control the conditions for lactic acid and ethanol fermenters. Anaerobic and aseptic conditions must be maintained by being sealed to the outside. Initial designs will be for batch production but allow for configuration for continuous runs with proper attachments. Gas hookups will allow gas exchange with the atmosphere or injection of gas hookups. Top or side ports would allow the removal of broth and addition of substrates. The fermentor will be designed based upon proven laboratory and industry designs, and open source designs.
An initial prototype design is proposed to be a cylinder made of polycarbonate with a closed bottom and a lip around the upper rim for an airtight seal with the lid using clamps. The cover plate will be a circle of polycarbonate of a corresponding size with holes necessary for pumps and probes.
Design factors to consider
Agitation
Standard design calls for agitation to be driven by an impeller connected to a motor through the cover plate, baffles may be included to interrupt vortexes. Alternatively a magnetic stirrer could be built into the base plate, there are concerns that cells may be damaged by the sir bar. Rotary motion is the standard method of stirring, but creates undesirable action in the culture media, including vortex movement and cell damage. Linear movement that moves a stir cylinder up and down through the media presents many advantages and is being explored.
Temperature control
Consideration must be given to sources of heat; either a heated support, internal cartridge heater, or heat jacket. A heated support would be through the use of an external cartridge heater and would be a simple design, but there may be issues with heat transfer. An internal heater cartridge would be the most efficient means to provide heat to the culture, however there would most likely be local overheating. A heat jacket allows heating and cooling of the culture but adds a layer of design complexity. Radiation infrared heating is a new technique that shows promise, an infrared heat source is placed in a metal reflector and placed under the reservoir. A combination of these methods may be used.
OSE fermentor specifications
- Ability to maintain anaerobic conditions, while removing product and adding substrate
- Internal dimensions
- Internal volume - 5 l, can be operated at less than maximum capacity
- Sealed cyclinder that can be disassembled to reservoir and cover plate for sterilization
- Material - polycarbonate
Advanced features
In order to facilitate high productivity, reproducible results, and rapid experimentation with a variety of substrates, organisms, and growth parameters advanced features that integrate electronic sensors and automated control should be a goal in the initial prototype. 1. Configurable to allow different component hookup such as aeration, dialysis and inputs allowing continuous run 2. pH measurement with automatic base addition 3. Sensors for temperature, dissolved oxygen, liquid level sensor, nutrient density and cell density (via turbidity). 4. Growth programs
Design rationale
An OSE fermentor will be designed for small scale production of desired chemical material rich broth from agricultural materials. The design of the fermentor will allow for anaerobic microorganism fermentation to be conducted in a controlled environment with control over many of the impactful parameters of growth and metabolism. The fermentor will be shaped and ported for removal of spent broth, overgrowth of microorganisms, and addition of feed, gases, salts. The design will incorporate key features found in industrial and laboratory fermentors including agitation, level sensors, removal of media and addition of feed during the run for continuous operation, and pH sensing and automatic base addition to maintain an optimal internal environment. Agitation is necessary to maintain optimal mixing of the feedstock with the microorganisms and will be controllable in the range of 1-200 rpm. A level sensor is necessary to accurately control the removal of spent broth and the addition of feed for continuous operation. An electronic pH sensor will be necessary to measure this aspect of internal environment and control the acidification of the environment through the addition of a base. A turbidity sensor, that measures the absorbance at a specific adjustable wavelength (~600 nm), will be used quantify cell density and maintain optimal density for continuous run operations.