Besides nutrientes, mass balance and appropriated microorganisms, the control of temperature, humidity and aeration are the most important parameters to get a good and fast composting process. However, industrial application for composting organic solid residues needs to control these parameters, otherwise there is a decline in its quality.
Hi Paulo,
there are a range of approaches to composting organic residues. pH control is not really an option the humic / organic content of composts tends to buffer strongly to around pH8 by the end of the process and the degradation of organic residues usually determines the pH at the start.
So as far as design methods go there are 3 major options and variations on each.
1) open piles, turned regularly and watered can be quite effect - are cheap, do not allow odour control and are the slowest and messiest process.
2) aerated static piles. An aeration system draws air through a pre-mixed pile of material. Air can then be biofiltered to control odour. Aeration can be used both humidity and temperature of the system. Mixing of the pile is not necessary. This is a much more rapid process but requires more technical input to operate properly. A variation of this is a 'tunnel' type process where material passes slowly through a 'corkscrew' style tunnel which mixes and aerates. Works well for large volumes with continuous through-put - expensive and needs technical support.
3) 'In vessel" composting. A closed system that can be aerated in response to temperature and oxygen availability. Humidity can also be controlled via probes. Can be very rapid and efficient. Commonly used for preparing mushroom composts as the temperature control can be specific enough to 'pasteurise' the contents of the vessel.
Hope this helps,
cheers,
Richard
Thanks a lot Dr. Richard. However, I'd like to know if there is any
method to control humidity...in the residues that we are working
they lost a lot of water, probable because of the high porosity.
Do you have any idea to solve this problem?
Thank you again for your valuable time.
Hi Paulo,
keeping moisture content in compost is always a challenge. Close systems make it much easier, so long as the initial water content is OK. In open systems we have used drippers on the top of aerated static piles with covers. It takes a bit of trial and error but drippers on a timer and aeration on another timer can be balanced to get a good aeration /humidity regime. It does not need either continuous aeration (which tends to dehydrate) or watering. Good absorbent material in the starting mixes is also useful. Ground pine bark chips help with both water holding capacity and in providing air spaces to maintain aerobic conditions.
hope this helps,
cheers,
Richard
Hello R ichard,
Thank you very much. This is a good idea! I'll try.
Cheers
Paulo
Richard,
We used 30% of Itree pruning from the steets and got a good aeration/humidity control. However, I still have troubles with high pH and ammonia emmissions.
Cheers,
Paulo
High pH and ammonia means a significant amount of anaerobic activity. This could be due to a high nitrogen content, but principally to low oxygen concentrations. You can aerate either by regular turning or by forced aeration. If the pile gets too wet it will block air pores and then anaeorbiosis kicks in and it gets smelly and sloppy - aeration is the answer to this problem too!
hope this helps
cheers,
Richard
Thanks again Richard! I'm gonna check all and will send you a feed back.
Cheers,
Paulo
Hi Fabiana, I think the high nitrogen content is what is causing the problem in this case . What is your feedstock?
The elevated temperature probably volatilises the ammonia. Oxygen above around 8% should be sufficient to keep the process aerobic. Adding woodchips or cellulosic wastes to increase the C:N ratio should help.
Ammonia is definitely a result of anaerobic activity and even though an O2 probe can be detecting high levels of oxygen in the air spaces there can be considerable anaerobic activity in clumps and less well aerated areas. No compost system is fully aerobic the goal is to keep the majority of it aerobic.
cheers,
Richard
Hi Fabiana,
ah, that explains it. Your temperature profile is 'runnning ahead' of microbial activity, lower temperatures might help. I did the same early on - my problem was hydrolysis and then lots of VFA's - acidic and very smelly!! In lab systems I found using building insulation (foil coated glasswool) around 20 L vessels worked very well, and with the right mix did not need any additional heat.
BTW Galway is a beautiful place to live!
cheers,
Richard
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