Waste-Free Animal Agriculture that Co-Produces Biogas Energy and Organic
Fertilizer: A Holistic Approach
Abstract
A novel anaerobic digester system called Holistic DigesterTM System
(HDS) was developed. The pilot prototype was constructed and tested
twice (4 months each) at the NCSU Field Laboratory for raising 60 feeder
pigs to market age for each test. The structure and operation of HDS,
the performance of live animal growth, chemical analyses of biogas and
the resulting digestate, and the production of a potential organic
fertilizer, are presented in this communication. It was concluded that:
1) this operation demonstrated the feasibility of HDS with live animals
on farm; 2) daily biogas (approximately 50% methane) was produced
consistently during each of the two studies; 3) animals grew well in the
modified house with a pit for manure slurry collection. The weight gain
of the pigs and feed conversion rate met the top 25% of the industrial
average; and 4) the liquid digestate of the primary digester flowed into
the secondary digester preloaded with dry switchgrass, which absorbed
the liquid and incubated into a final product. Chemical analysis
indicated that NPK values were retained and enriched in the final
product, potentially, an organic fertilizer. The new prototype HDS that
co-produces biogas and organic fertilizer was successfully tested and,
furthermore, HDS left no waste nor wastewater on farm. It is believed
that HDS will not only improve the cyclic bioeconomy, but also enforce
the environmental and economic sustainability of animal agriculture.