Background- I make biochar for gardening, and small scale carbon capture and storage. Most of my feedstock is clean, unpainted, untreated, end of life timber, but there is a small proportion of engineered particle board- MDF, chipboard, plywood and composite blocks containing, I believe, melamine formaldehyde binding resin. No halogens from PVC, no metals from CCA treated timber or old lead paint. I want to establish what pollutants may be produced- I would in a worst case scenario be burning less than 50kg of the suspect material per hour.

All the charring happens in TLUDs- Top Lit Up Draft burners where all the pyrolysis gases are ducted through the hottest zone of the burn- round about 800-900C. I'm currently working to improve residence times and temperature gradients- carbon particulates are a known issue.

Does any of the above sound like it'll produce anything nasty from the carbon, hydrogen, oxygen and nitrogen going into the mix? PAHs? Anything else above and beyond nitrogen oxides and carbon particulates from clean wood?

To put it another way, do I err in favour of creating a pollution factory, or in favour of condemning a potential feedstock to be a disposal nuisance?

Thanks for any replies- I'd like to lay this to rest.


I am by no means an expert in the pyrolysis of different woods by any means. But after spending some time reading through some papers for you, I found one which burns MDF in a slightly different burner to you (around 450-600C) and the ash produced contained formaldehyde at 1681 mg/kg.

doi:10.1016/j.enconman.2014.12.032 - incase you want a read yourself.

This document goes through different methods in producing biochars and says that providing the temperature of pyrolysis is above 500C, it shouldn't contain any PAH's or Dioxins within the biochar and if it does, it'll be several times lower than required clean up set by the Model Toxic Control Act.

Everything else I have read seems to not have specific analysis on what exactly is left within the biochar. There are plenty of organics released as gases during the process specifically above 500C which you could argue should no longer be in the biochar. Have a look around at papers, I know it's not a definitive answer but it might be a start for you.


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