Part 4: #sewage #sludge & #PyCCS

In my last article on sewage sludge, I mentioned that the pyrolysis of sludge can be considered a pyrogenic carbon capture and storage technology. I will concentrate to these points:

Pyrolysis process

The pyrolysis of biomass is an old technology: Heating the material under conditions of reduced oxygen will result in a carbonized biomass, called biocoke. This was done for many centuries in smoky charcoal pits by the black men deep in the forests.

The required heat was produced by partial incineration of the feed stock, so pit output was about 10 to 20% of the input and depended mostly on the charcoal burner's experience. But in any case it was NOT a carbon capture process, because the charcoal was need for steel smelting and other processes. At the end of the day all stored carbon was released again.

Pyrolysis technology

https://mythaigarden.blogspot.com/2013/01/burning-charcoal.html

Nowadays most green (urban) gardening people who want to produce charcal for TerraPreta do the same as centuries before:

• The requisite heat is still produce by partial incineration in a more or less open system. This is generally done by burning the pyrolysis gas. But this process is also not a CCS-technology.
• The modern way can only be by a combination in production of different products and a minimum of emissions!

For the pyrolysis there are temperatures need of about 500°C. For activation to increase the inner surface you need 800°C or more. So main question is: How can we create heat without incineration, means CO2-production?

•  Using sun light collectors
•  Electrical heating with renewable electric power, ex.g. from wind power plants

Second question is, what we can do with the process gas and its condensates?

• In small "household-size" factories the output will pollute the environment. This cannot be the way!
• Or you either utilize a "processor" with a collecting system taking in the hot gas output for further processing mostly using electric power production by CHP.
• Or you use an industrial size carbonization plant, which converts also liquids and permanent gas to new raw materials. By the way: Higher process temperature increases the production of hydrogen ...

Third questions is, how we can reach limiting values, like heavy metals, PACs, dioxines?

• In a simple "handmade" process, there is a high risk to produce PAC and sometimes also dioxines in reason of undefinded/uncontrolled conditions.
• In a industrial process you have stable and controlable process conditions which are cracking dioxines & PACs. So the output of a contaminated input can be much cleaner than a handmade biochar!

Regulations

Fertilizer regulations are mostly put into place with a view of protecting the soil. This is still OK, but we actually need to keep the whole worldwide system in mind! So the question is: What is more important?

• Getting permission for using a sludge char, when all possible risks are excluded. This still means we have to incinerate sewage sludge and blow out a lot of CO2, or
• alternatively get permission for using a sludge char if the contamination levels are OK - then we can directly reduce CO2 emissions....

Of course, only sewage sludge with a minimal level of contaminants should be used as PyCCS-fertilizer in food production, but sewage coke with low level contamination could also be used for forest re-agriculturation.

By using sludge pyrolysis in Germany we can reduce the CO2-impact by more than 2,500,000 tons per year. This is almost the same footprint of more than 280,000 Germans.

Conclusio

But: In (German) regulations for fertilizer permission there is the wording more important than chemical values:

• all kind of char from clean biomass -> allowed
• non/low-contaminated char from contaminated biomass -> not allowed
• slugde ashes -> allowed
• (dry) sludge itself -> allowed
• non/low-contaminated char from sludge -> not allowed

Only in case of permission due to fertilizer regulations it is allowed to give a PyCCS-char into the ground, ex.g. forest!

But if there is an EU-permission for the fertilizer, this product has also a German permission...

If there is anyone interested to start into these business: there are waiting 300 tons of (actually non-permitted) sludge char... send me a mail!