More efficient method of ridding farms of waste suggested

BIOCHAR has potential to make anaerobic digestion of animal manure a more efficient method to rid farms of waste while producing methane for energy, Texas A&M University researchers say.

Biochar, a man-made charcoal material composed of agricultural wastes including manure, crop residues and forage grasses, can be used as sustainable fertilisers and to filter a broad range of contaminants, including antibiotics, pesticide and hormones in wastewater and water. It can also capture greenhouse and odorous gases such as carbon dioxide and ammonia.

Chemical and environmental engineer Eunsung Kan says present management of animal manure includes applying waste to croplands. This often generates odours and greenhouse gasses and can cause ecological problems downstream, such as algae blooms and contaminated groundwater.

“The value of the new research is that manure can be a problem source, and anaerobic digestion using biochar serves to dispose of manure while producing methane to power the farm and possibly be sold to local utilities,” Kan said.

Anaerobic digestion of manure results in low pH and other undesirable conditions in the bioreactor, which slow down or inhibit methanogenic bacterial growth and metabolism when operating conditions aren’t optimal, he said.

Environmental engineer Hyun Min Jang and Kan tested low biochar-to-manure ratios with promising results.

Dairy manure mixed with no biochar and 0.1-1 per cent biochar showed that adding biochar increased methane production by about 40 per cent and reduced the time to achieve target biogas production by 50- 70 per cent.

“It decreased the lag phase, which is the time that elapses before production starts, and cut the biogas production time in half each time we added more biochar,” Jang said. “Production time is a significant factor for a dairy with say 1,000 cows that produce 8,000 kilograms of dry manure each day, but reducing the digestion time also means the size of the anaerobic bioreactor reduces by half.”

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