Fermentor

Fermentation

•       Group of chemical reactions induced by microorganisms or enzymes that split complex organic compounds into relatively simple substance

         Anaerobic conversion of sugar to carbon dioxide and alcohol by yeast 

Fermentor

•       Available – varying sizes – total volume capacity

•       Small laboratory fermentors – 1 – 15 lts

•       Pilot plant fermentors – 25-100-2000 gallons

•       Range – 5000 – 10,000 gallons

•       Actual operating volume – less than that of total volume

•       Head space – top – above the liquid medium – splashing, foaming and aeration

•       Head space – a fifth to a quater

Fermentor Design

•       Fermentor – strong enough to withstand the pressure of large volumes of aqueous medium

•       Fermentor vessel – capable of operating aseptically – number of days

•       Adequate aeration and agitation – provided – meet the metabolic requirements of m/o – mixing should not damage the organism

•       Power consumption should be as low as possible

•       A system of temperature control should be provided

•       A system of PH control should be provided

•       Sampling facilities – provided

•       Evaporation losses = not excessive

•       Additional inoculum or seed tanks – small sized Fermentor – inoculum is produced – added directly to the fermentor

•       Drain or mechanism – bottom of fermentor – remove the completed fermentation broth

•       Vessel should be designed – require minimal use of labour in operation, harvesting, cleaning and maintenance

•       Smooth internal surfaces

•       Material of vessel – withstand repeated steam sterilization cycles

•       Small scale – Glass or stainless steel

•       Glass –smooth surfaces, non-toxic, corrosion proof and easy to monitor

Impeller

•       Impeller(stirrer)

•       Agitation  -

•       Air dispersion

•       Oxygen transfer

•       Heat transfer

•       Maintain uniform environment throughout the vessel

•       Enhancement of mass transfer between dispersed phases

Baffles

•       Four baffles to eight  – incorporated – vessel – prevent vortex – improve aeration efficiency

•       Metal strips roughly one tenth of vessel diameter – attached radially to the wall

•       Baffle should be installed – gap between the vessel wall  and baffle – scouring action – minimizes the microbial growth on the baffles and fermentor walls

Sparger – Aeration System

•       Device – introducing air – liquid – Fermentor

Three types

1. Porous sparger
2. Orifice sparger
3. Nozzle sparger

•       Pipe – minute holes

•       Hole size – 1/64 – 1/32 inch or larger

•       Allows air under pressure to escape as tiny air bubbles into the liquid medium. Small size hole – requires great air pressure

Sterilization of Air Supply for Fermentation

•       Sterile air – large volumes – aerobic fermentation process

•       Heating and filtration – main methods of sterilization

•       Heating is generally too cost for full scale operation

•       Glass wool, glass fiber – filter material

Cooling Coil

•       Temperature – important factor

•       High temperature – ferments – destroyed

•       Very low temperature – reaction – slow

•       Optimum temperature – maintained

•       Growth temp of M/o ----- may or may not coincide with optimum temp of fermentation

•       To maintain optimum temp – fermentor should be cooled

•       Passing cold water –inside wall of tank or jacketed walls of tank

Sterile Filter

•       Sterilization of air – entering fermentor – sterile filter

•       Composed cotton wool – trap m/o in air

•       Form the filter – air – carried through sterile piping – bottom of the fermentor – beneath the impeller blade

Antifoam

•       Aeration and agitation - liquid medium – foam – if media containing protein or peptides

•       Not controlled –raise to headspace – tank – along with spent air

•       Condition may cause – contamination  and limits the gas exchange between the medium and the atmosphere of the head space

•       Antifoaming agents – Lowers the surface tension and decreases the stability of the foam bubbles – burst

•       Two types

•       Inert antifoam agents – Silicone compounds

•       Too expensive – adv – Not utilized by m/o and non-toxic

•       Antifoams – crude organic materials – animal or vegetable oils – Lard oil, corn oil and soyabean oil or long chain alcohols like octadecanol

•       Not inert, toxic, provide additional nutrients to the m/o

•       Fatty acid of the antifoam – lower the PH of the medium

•       Added – manually or automatic

•       Automatic – sensing mechanism used – foam risen into headspace of fermentor – product touches the electrode – current produced – activate pump to add antifoam agent

Sterilization of Medium

•       Pure culture fermentation – medium to be sterilized

•       Small scale – medium placed directly – fermentor – autoclaved

•       Large tanks – not feasible

•       Medium+ water - --- pumped into retention tubes and heat exchangers before passing into fermentation tank

•       Retention tube contain  - steam jet heaters – inject high pressure steam in to the medium  - to sterilize it as it passes through the pipes

•       Rate of passage – adjusted – provide complete media sterilization without overcooking

Summary

•       Anaerobic conversion of sugar to carbon dioxide and alcohol by yeast

•       Fermentor vessel

•       Baffles

•       Impeller

•       Cooling coil

•       Antifoam agent