How to start a Bio- digester 4

[myango]

hi,
what is the best way of starting a biodigester whose inlet is distillery slops from distillation of fermented molasses to alcohol.the biodister is to produce methane gas to fire dual fired boilers. we started it using human waste but it seems it has not picked up yet since we are using alot of lime to stabilise the pH SO AS NOT TO KILL THE microbes. has anyone any help.

thanks
D. Kipkosgei
chemical engineer.

 

[StoneCold]

Seroney
I am disapointed that you have not gotten any response yet. I don't have any answers for you but I am interested in what the others have to say.
Wouldn't there be microbes in the fermented material coming from the plant that you could use to make the methane? I am not sure why you would put human waste into the tank get it going. Could air be the problem? I would guess that if you want to produce methane then you need to keep air out of the system as much as possible and have an anaerobic process.

Goodluck

StoneCold

 

[AsgIv]

Seroney,

given that ythe conditions are anaerobic and pH and temperature are right is it possible you are having any contaminants in the system? If not, maybe you will get better results using cow manure.

 

[myango]

we used sewarage from human waste (am sorry stonecold ) because we believed that it has enough microbes to act on the slops in the digester to produce methane and reduce its COD and BOD . we hAVE never used cow manure though we would wish to try. our major problem actually is to reduce the cost of lime consumption coz it takes most of our money. we are currently forced to buy the lime since our effluent into the rivers have to meet minimum statutory regulations. we dont have a stabilization pond before the bio- digester and we dont know whether it will it help reduce the COD levels that would affect the pH of the digester. otherwise and grateful for your contributions .
D. Kipkosgei
chemical engineer

Dickens K. Seroney (B. Tech in Chem and process eng.)Moi,Kenya
Planning and development engineer.

 

[LAsludge]

Two main bacteria groups are involved. The first turn waste into acids. The second group turns the acids into methane. The first group work much faster than the second group (10x) and lower the ph. The second group is very sensitive to ph change and will die off if the ph get too low.

The most common problem in starting a biodigester is overfeeding and killing off the methane bacteria.

The following link should give you help.

http://www.ees.adelaide.edu.au/pharris/biogas/beginners.html#Pages

Also google "anaerobic digestion" for more help.

 

[LAsludge]

Seroney

Here's something else that you might find useful. It's an excerpt from another foreum.

...........................

(Posted on AD listserver in response to a question about measuring digester
performance - CH4, CO2, H2S, pH and what is useful in day to day operation.)


If you want to keep it simple, forget pH - this will only tell you
what you did wrong last week and has no place in the operation of a
digester on a day to day basis.
The biogas composition and quality is the pulse of the digesters
condition.
golden rule No.1 If the boiler does not light - stop feeding the
digester until it does light. The understanding of this is that
overloading generates VFA (Volatile Fatty Acids) in the digester in
excess of the consumption by methanogenic bacteria. Since production
of VFA is accompanied by CO2 gas production, if there is a biological
overload caused by excess feed, this will cause an immediate increase
in CO2. High CO2 and relatively low methane gives a gas that will not
ignite in a boiler set up for burning normal gas. If you are using
Drager tubes for CO2 analysis, then if the CO2 increases to above 50%
slow down the feed and stop the feed at 55%CO2.
golden rule No. 2 Feed daily and never feed more than 30% VS today than
you did yesterday. (this is to do with the rate of growth of the
methanogenic populuation under ideal conditions.)
This assumes temperature control to better than 1 deg C per day (we
work to 0.1 in the control loop) in digesters with a minimum of 35 deg.
(we run in excess of 38 deg. C)
Thats it! - how to run a digester without a lab.
However,
If you really want to monitor the digester especially at start up then
the TVA [Total volatile acid] level in the digester is the best
indicator of inhibition in the methanogenic stage. Good for digesters
in the 1-4 volumes of biogas per day range. Use 1000mg/l VFA as the
peak level during start up and aim for 280mg/l in normal production,
350 mg/l max peak after shock loading. If the VFA level goes higher
than this level, shut off the digester feed pump for a couple of hours.
On very high rate digesters, you could also use chromatography to
measure the concentration of individual species of the VFA - these form
a series with heavyweights at one end (proprionate and butyrates) and
light VFA (acetate) at the other. By tracking these every other day,
you will be able to see the development of heavyweight VFA at times of
chemical inhibition or overloading and hence you can throttle the
digester feedpump or feed composition to maximise gas production
without overloading the biology. Useful if you are working at 5-7
volumes of biogas per volume of digester per day and have a white coat
management structure.
In case you are wondering what happens to pH - well during high VFA
concentrations of say 1000 or even 3000mg/l VFA, the pH stick at around
7.2 due to two buffering systems, the carbonate-bicarbonate system and
ammonia system from decomposition of proteins. When finally it
unsticks and the pH is seen to jump to 6.8 and falling it is all too
late, the buffers are used up and the low pH inhibits the consumption
of VFA by poisoned methanogens. The VFA build up accelerates making
the inhibition of methanogenesis worse and bingo you now have a tank
of vinegar! This is what the pH meter will tell you - but then you
will know this from the smell! :-/
Best Regards
Les. Gornall

.............................

It's not me. Hope this helps.
LAsludge

 

[myango]

Hi,
am happy it worked,i even got a promotion . i wish i would invite you all.i dont know how i will reciprocate.


Dickens K. Seroney (B. Tech in Chem and process eng.)Moi,Kenya
Planning and development engineer.