Sulfate reducing bacteria (1 Viewer)

[steve_ell]

hey can some one explain the me how SRB work. i can make sense of n e of the notes i have. also would like to know how you can work SRB into how acidic environments accelerate corrosion. n e ideas

thanx

 

[Paroissien]

What the hell are you talking about?

 

[steve_ell]

well it was obviouse i was playing games when i wrote that lol. so ill start again.

can someone explain to me how SRB work. i also would like to know SRB increase the rate of corrosion in acidic environments.

 

[mojako]

http://www.corrosion-doctors.org/Microbial/srb.htm
(or use google for more info)

dont think this is in the syllabus though.
chuck it to the bin ^_^
(unless u want to know this for interest)

 

[Paroissien]

Yeah, I didn't think it was in the syllabus, because I have never heard of it

 

[tina_goes_doo]

Sulfate reducing bacteria is in the elective topic shipwrecks. Look around it there because i think there was a post about that somewhere.

As to how they accelerate corrosion:

1. They produce acidic wastes in their normal metabolisms. Around shipwrecks and things there is more organic material for food so they rapidly multiply thus altering the pH.

2. They also produce H2S which is a weak acid.
SO42-(aq) + 10H+ + 8e- ---> H2S(aq) + 4H2O(l)

3. They also help produce metal sulfides which release a H+ ion.
H2S(aq) + 4Fe2+ ---> FeS(s) + 2H+


Hope that helps.

 

[tina_goes_doo]

Here's a pretty good thread too:

http://www.boredofstudies.org/community/showthread.php?t=42586

 

[Paroissien]

Ahh that's alright then. Shipwrecks is none of my business

 

[iyamahobbit]

Lol, nice to give ppl heart attacks about stuff like that once in a while...

The main thing about sulfur reducing bacteria:
> The bacteria are anaerobic, so they thrive in areas where there's no or little oxygen, such as at great depths
> Because oxygen levels decrease in greater depths (since the source of it is from the air, and lots of organisms use it up), without these bacteria, corrosion would otherwise be very slow/not occur at great depths, as oxygen is normally needed for corrosion to occur.

Instead, you get this -

Reduction
SO42- + 5H2O + 8e- ---> HS- + 9OH-

Oxidation (due to presence of the bacteria)
4Fe ---> 4Fe2+ 8e-

Overall:
So42- + 5H20 + 4Fe -----> Hs- + 9OH + Fe2+

 

[sneeble]

^^ That's not the end of the picture;

7OH- + HS- + 4Fe^2+ -> FeS + 3Fe(OH)2 + H2O

Thus black Iron(II) sulfude and the more typical product of rusting, Fe(OH)2

 

[DAAVE]

OK I have:

Anaerobic bacteria reduce sulfate ions:

SO4(2-) + 5H2O + 8e ----> HS(-) + 9OH(-)

and the oxidation of iron (*4):

4Fe ---> 4Fe(2+) + 8e

Addition of the equations, taking note that one Fe(2+) reacts with the HS-:

4Fe + SO4(2-) + 5H2O + 8e ---> FeS + 3Fe(OH)2 + H2O + OH(-)

Which forms black FeS and and normal Fe(OH)2

Is that right? BTW this is the theory of what they think happened on the titanic too right?

 

[Tommy_Lamp]

What I have memorised:
4Fe(s) + SO42- + 5H2O(l) ----> FeS(s) + 3Fe(OH)2(s) + H2O(l) + 2OH-(aq)
Black iron (II) sulfide forms on the steel along with iron (II) hydroxide (which in absence of O2 does not form iron (III) as in normal corrosion).

 

[DAAVE]

What I have memorised:
4Fe(s) + SO42- + 5H2O(l) ----> FeS(s) + 3Fe(OH)2(s) + H2O(l) + 2OH-(aq)
Black iron (II) sulfide forms on the steel along with iron (II) hydroxide (which in absence of O2 does not form iron (III) as in normal corrosion).

Oi just remember that:

Bacteria reduce sulfate
(SO4(2-) + 5H2O + 8e -> HS(-) + 9OH(-)
And Iron oxidises
4Fe --> 4Fe(2+) + 8e

and then add them together that way u can work ur way thru the process in the exam rather than give them one equation and go yeah something happens.

 

[Tommy_Lamp]

I thought about that and asked my teacher and tutor and they both agree that its better to give an overall equation and then give an explanation of it, alot simpler for the student and still answers the question.

 

[sneeble]

A fellow TAFE student, how rare...

I've got all the equations memorised (yes, it was boring writing them out till they stuck) so I'll decide which to use based on the question... If there even is one on sulfate reducing bacteria.

 

[Tommy_Lamp]

What TAFE are you at?

I find that the elective topic questions in HSC exams are so much simpler then the trials, they seem to only ask the easier questions :x

 

[sneeble]

Ultimo, just next to central station.

I did 3u English with a chick from Brookvale TAFE this year... She hates my guts

Anyway, HSC questions are simple compared to trial questions but they're also simple to screw up. If you can't/forget to differentiate between "explain", "define", "describe" and "assess" and their synonyms you're up shit creek without a paddle...

 

[Tommy_Lamp]

Which girl, Belinda maybe? Odds are I know her

Yeah true about the Glossary, but most are self-explanatory and if you've done enough test papers you don't even think about the word because you know straight away

 

[sneeble]

Emily was her name... I think she was doing mostly humanities subjects; modern history, geography...

Anyway, this damned computer is wasting my prescious time so I'm going to turn it off and haul a good 8 hours of chem before I go to sleep tonight.

All the best everyone!