I never heard of gasification (instead of combustion) which is actually carbon negative. It puts biochar back into the soil which increases plant growth while decreasing the water needed to grow the crops--beneficial in places like California.
I also learned about several companies in Africa that convert human waste into safe fuel briquettes that burn longer and cleaner than charcoal and are much less expensive to purchase. 1 ton of briquettes saves 88 trees! The "yuck factor" is overcome by the cost savings and efficiency even though they are used mainly in cook stoves. I like the efficiency and beauty of recycling waste!