Effects of moisture and carbon/nitrogen ratio on gaseous emissions and maturity during direct composting of cornstalks used for filtration of anaerobically digested manure centrate

This study investigated the maturity and gaseous emission during direct composting of cornstalks used as organic media for filtration of anaerobically digested manure centrate. Effects of moisture and carbon/nitrogen (C/N) ratio on composting performance were evaluated. Results show that cornstalks could effectively retain suspended solids and organic matter in digested manure centrate to lower their C/N ratio and attain microbial inoculation. Filtered cornstalks became more compostable when their moisture decreased from 76% to 60% or C/N ratio increased from 12 to 24. Nevertheless, such adjustment aggravated the emission of greenhouse and odours gases during composting. Regardless of composting conditions, the phylum Firmicutes was the most dominant with reduced abundance during composting. Similar reduction also occurred to several abundant phyla, including Atribacteria, Synergistetes and Euryarchaeota. By contrast, the phylum Bacteroidetes, Chloroflexi, Proteobacteria and Actinobacteria enriched as composting progressed. In addition, compost maturity was insignificantly affected by matrix moisture and C/N ratio.