Method for generation of bio-gas

Improved method for the production of bio-gas incorporating a magnetic field to situate magnetotactic bacteria in the reactive zone of a bio-gas producing digester.

FIELD OF THE INVENTION 
This invention relates to bio-gas production and more particularly to a 
method for producing bio-gas more efficiently through the use of 
magnetotactic bacteria. 
BACKGROUND OF THE INVENTION 
According to recent reports, two billion tons of organic waste per year are 
available on United States farms. These organic wastes can readily be 
converted to a methane containing gas, or bio-gas, by fermentation of the 
wastes in a digester. One such process is disclosed in U.S. Pat. No. 
3,973,043. 
It has been determined that one ton of manure will produce approximately 
two thousand cubic feet of bio-gas. Therefore, approximately four thousand 
billion cubic feet of bio-gas could be produced per year in the United 
States. Since two hundred twenty cubic feet of bio-gas is approximately 
equivalent to one gallon of gasoline, approximately nine gallons of 
gasoline could be recovered from one ton of manure, or approximately 
eighteen billion gallons from two billion tons. 
In terms of electrical energy, since twenty cubic feet of bio-gas is 
approximately equivalent to one Kilo Volt Ampere (K.V.A.), approximately 
two hundred billion K.V.A.'s could be generated per year. 
Obviously, there is great energy generation potential through this type 
conversion. However, to data the economics of operation to produce bio-gas 
have not been favorable enough to make bio-gas production readily 
acceptable. As a consequence, several means for optimizing this type 
production have been proposed. One such means is disclosed in U.S. Pat. 
No. 4,100,023. Another is disclosed in the co-pending application of 
Carter entitled "Improved Bio-Gas Generating Digester," Ser. No. 187,466, 
filed Sept. 15, 1980. 
Accordingly, one object of the present invention is the provision of a more 
efficient means of producing bio-gas by preventing the loss of bacteria 
from the digester as sludge is withdrawn therefrom. 
Another object of the present invention is the provision of a more 
efficient means of producing bio-gas by situating bacteria in the zone of 
the digester where the bacteria will be the most productive. 
Still another object of the present invention is the provision of a more 
efficient means of producing bio-gas by increasing the flow rate of 
material through the digester. 
SUMMARY OF THE INVENTION 
In practice, bio-gas is normally produced in a digester by the fermentation 
of organic wastes. Often bacteria is added to the organic wastes to 
facilitate the fermentation therof. The particular bacteria chosen for 
addition varies depending on the composition of the organic wastes. 
Although bacteria addition can be beneficial in producing bio-gas, certain 
processing problems are commonly encountered when bacteria are added to 
the organic wastes. First of all, bacteria become entrapped in sludge 
which is formed in the digester and are lost as the sludge is withdrawn 
from the digester. This loss becomes greater as the flow rate of material 
through the digester is increased. One way to reduce this loss is to 
reduce such flow rate, but, of course, this reduces the amount of organic 
wastes that can be processed in a given time period. 
A better way to reduce the loss of bacteria from the digester is to 
initially use magnetotactic (magnetically sensitive) bacteria and prohibit 
bacteria from exiting the digester with the sludge by creating a magnetic 
field to situate bacteria apart from the sludge. Since the bacteria can be 
kept apart from the sludge by utilizing such a magnetic field, sludge can 
be withdrawn from the digester at a more rapid rate and more organic 
wastes processed in a given time period. 
Furthermore, by properly positioning the magnetic field the magnetotactic 
bacteria can be made to occupy the area of the digester where they will be 
most productive and thereby make the entire bio-gas generation operation 
more efficient. 
Other objects, features and advantages of the present invention will become 
apparent from a consideration of the following detailed description and 
from the accompanying drawing.

DETAILED DESCRIPTION 
FIG. 1 depicts a preferred embodiment of the present invention. The 
digester 1 has a digester housing 2 comprising a cylindrical midsection 3 
with a conical top 4 and bottom 5. 
Within the digester housing 2 is a digester heater 6. Also within the 
digester housing 2 are magnetic field producing means 7. These magnetic 
field producing means are preferably a single electromagnet, but can be a 
series of electromagnets or a single naturally occurring magnet or a 
series thereof or any other means of producing a magnetic field. Although 
FIG. 1 shows the magnetic field producing means 7 within the digester 
housing 2, they may be located elsewhere, such as outside the digester 
housing 2, so long as they produce a magnetic field within the housing 2. 
Commnicating with the interior of the digester housing 2 are an organic 
wastes slurry line 8, an organic wastes sludge line 9 and a bio-gas 
collection line 10. 
In practice, a slurry of organic wastes is continuously fed to the digester 
1 via organic wastes slurry line 8. The organic wastes are fermented in 
the digester 1 to produce bio-gas which is removed as it is formed from 
the digester 1 via bio-gas collection line 10. Simultaneously, organic 
wastes sludge is formed and extracted from digester 1 via organic wastes 
sludge line 9. 
The digester is heated by digester heater 6 to facilitate fermentation of 
the organic wastes to produce the bio-gas product. To further facilitate 
such fermentation, bacteria are added to the organic wastes. This may 
either be done shortly before the organic wastes slurry is introduced into 
the digester 1 or thereafter. The bacteria are magnetotactic in nature and 
respond to a magnetic field created within the digester 1 by magnetic 
field producing means 7. Depending upon the polarity of the magnetic field 
produced and the polarity of the magnetotactic bacteria, the bacteria will 
migrate either toward or away from the magnetic field producing means 7. 
In this case, a magnetic field is chosen such that the bacteria will 
migrate toward the magnetic field producing means 7 and away from the 
point where organic wastes sludge collect to be withdrawn from the 
digester 1. This situates most, if not all, of the bacteria in the 
reactive zone and away from the sludge zone of the digester 1. The 
reactive and sludge zones are shown generally in FIG. 1, the reactive zone 
being simply the area of the digester 1 where most, if not all, of the 
fermentation reaction takes place and the sludge zone being simply the 
area of the digester 1 where organic wastes sludge collects and very 
little, if any, fermentation reaction occurs. 
By situating the magnetotactic bacteria in the manner just described, the 
loss of bacteria from the digester 1 is prevented and the bacteria are 
located where they can work productively from a fermentation standpoint, 
both of which allow for an increased flow of material through the digester 
1 and a more efficient process overall. 
It is to be understood that the present invention is not limited to that 
precisely as described hereinabove. Many modifications and variations of 
this invention will be apparent to those skilled in the art. It is, 
therefore, intended that the scope of the invention be solely limited by 
the claims appended hereto.