AD plant foam and H2S solutions?
- Thread starter Chippy
- Start date
- Location
- Cumbria
Whao there Mugger, you make a statement, you then ask a question which directly relates to your statement.
What is your agenda ?
Just out of interest, what is a 'retention rate ' ?
- Location
- Cumbria
If you have a waste plant, to spread digestate without a permit you need to be PAS110 accredited.
This ensures the material is fully recovered and fully digested (almost - 0.5g/l VS). this also ensures the taxpayer is getting value for money from anaerobic digestion, as it is the taxpayer who subsidises through the tariffs.
This is very difficult to achieve at less than 20 days HRT. However, as no permit is required to spread (agricultural exemption) with own on-farm wastes, this should not be interpreted as an excuse not to do the job properly.
There is a tight rope between equipment and cost v return on investment on small plants, this should be recovered by ensuring all off-takes are utilised and exploited (gas/electricity/heat/digestate/nutrient). You are not breaking any rules by not following the code of practice, however if this becomes wide-spread, there is a risk it may come home to roost.
This ensures the material is fully recovered and fully digested (almost - 0.5g/l VS). this also ensures the taxpayer is getting value for money from anaerobic digestion, as it is the taxpayer who subsidises through the tariffs.
This is very difficult to achieve at less than 20 days HRT. However, as no permit is required to spread (agricultural exemption) with own on-farm wastes, this should not be interpreted as an excuse not to do the job properly.
There is a tight rope between equipment and cost v return on investment on small plants, this should be recovered by ensuring all off-takes are utilised and exploited (gas/electricity/heat/digestate/nutrient). You are not breaking any rules by not following the code of practice, however if this becomes wide-spread, there is a risk it may come home to roost.
Are you in start up phase?
In my experience of slurry only AD, foaming is normally caused when you are inputting more slurry than the reactor can cope with. In startup for instance once you get up to temp the temptation to put in as much slurry as the temp allows.
Retention time is also a big factor. This is because of ratios of fresh slurry against fully active bacteria (gas producing slurry) To much fresh slurry and the bugs can't cope and effectively go into overdrive.
If your not in startup try and increase your retention time and make sure your air pumps are working correctly.
You wouldn't over feed your cows and not expect them to get the sh1!s!
In my experience of slurry only AD, foaming is normally caused when you are inputting more slurry than the reactor can cope with. In startup for instance once you get up to temp the temptation to put in as much slurry as the temp allows.
Retention time is also a big factor. This is because of ratios of fresh slurry against fully active bacteria (gas producing slurry) To much fresh slurry and the bugs can't cope and effectively go into overdrive.
If your not in startup try and increase your retention time and make sure your air pumps are working correctly.
You wouldn't over feed your cows and not expect them to get the sh1!s!
Yes I’m kind of in startup because currently putting 16000 litre in a day but will soon be 20000. Running one engine 24/7 with 16000 litre of slurry. Temperature at 32 but target is around 38. Temp slowly increasing.
The new biolectric tanks are bigger therefore increasing retention time but unfortunately I’ve got one of the first
The new biolectric tanks are bigger therefore increasing retention time but unfortunately I’ve got one of the first
H2S issue sounds like its down to PH in startup phase and should settle in time. Try to get the tank as settled as possible for a week or two inputting the same amount and not letting the temp increase more than a degree a day.
Its all about consistency with slurry only AD so when you do start to increase the input do it slowly
Its all about consistency with slurry only AD so when you do start to increase the input do it slowly
The Son
Member
- Location
- Herefordshire
I only use slurry in the summer to help with dymatter and my H2S production always increases.
Get my carbon from environ £1370 for m3
Get my carbon from environ £1370 for m3
Digester Man
Member
You need to forget about carbon and get yourself a fresh air injection pump which will dramatically drop your h2s and costs virtually nothing to run
Edit: You could also add iron to the digester if the above does not completely solve your h2s problems, but it will be an on going cost as well..
Edit: You could also add iron to the digester if the above does not completely solve your h2s problems, but it will be an on going cost as well..
mawleymoos
Member
- Location
- Shropshire
We had a foaming issue recently, after a crusting issue (due to a mixing problem) but as mugger says, it settled down and went away! However we are adding some trace elements (hopefully only short time)! Sulphur is goin up and down as the bugs are settling again, but have been down to less than 100 before carbon and down to 7 at the engine!! Currently averaging about 48kw/hr on about 30m3 if slurry! Not sure if there is any more poke left! Would have liked 60kw/hr! But that might just be too greedy!!
mawleymoos
Member
- Location
- Shropshire
Anybody adding silage strippings? Not sure if that added to our crusting issue? Too scared to do it again! Thinking that they would give our cows belly ache! So probably do the same to the digester!
I’m adding a bag of iron sulphate a day but it’s not helped so wondering if it’s some cheap sh!t. Today we started putting liquid iron sulphate in so hopefully it’s better. Still putting cooking oil in but hasn’t seemed to completely get rid of it.
It’s hard to not let it go back to a crust! It works so well with a crust!!!
It’s hard to not let it go back to a crust! It works so well with a crust!!!
Digester Man
Member
Here's my air injection pump, time to get yourself one. It is so simple, should be standard on any AD plant. Turned off I am at >2000ppm, turned on I am around 100ppm at 0.4% o2
Air filter, blower, and teed off into two flow meters for my two fementers
Air filter, blower, and teed off into two flow meters for my two fementers
Digester Man
Member
It pumps fresh air into the head space in the tank so that it mixes with the gas. Bacteria in the air react with the H2S and turn it into H and S, the S then drops into the slurry and passes out at the end of the process.
Can't really say what your pumps are doing without seeing them and what they are hooked up to.. but I am sure your plant provider can confirm this. I really cannot see you being at >2000ppm if you are injecting air and adding iron
Can't really say what your pumps are doing without seeing them and what they are hooked up to.. but I am sure your plant provider can confirm this. I really cannot see you being at >2000ppm if you are injecting air and adding iron
- Location
- North Norfolk
If adding air it is important that you monitor the oxygen content of the gas. It should be about 0.5%. If it goes near 1% then the anaerobic bugs will be unhappy.