This study was performed to investigate the effect of different levels of dietary crude protein (CP) on composition of odorous compounds and bacterial communities in pig manure. A total of 48 male pigs (average initial body weight 45 kg) fed diets containing three levels of dietary CP (20%, 17.5%, and 15%) and their slurry samples were collected from the pits under the floor every week for one month. Changes in composition of odorous compounds and bacterial communities were analyzed by gas chromatography and 454 FLX titanium pyrosequencing systems, respectively. Levels of phenols, indoles, short chain fatty acid and branched chain fatty acid were lowest (p<0.05) in CP 15% group among three CP levels. Relative abundance of Bacteroidetes phylum and bacterial genera including Leuconostoc, Bacillus, Atopostipes, Peptonphilus, Ruminococcaceae_uc, Bacteroides, and Pseudomonas was lower (p<0.05) in CP 15% than in CP 20% group. There was a positive correlation (p<0.05) between odorous compounds and bacterial genera: phenol, indole, iso-butyric acid, and iso-valeric acid with Atopostipes, p-cresol and skatole with Bacteroides, acetic acid and butyric acid with AM982595_g of Porphyromonadaceae family, and propionic acid with Tissierella. Taken together, administration of 15% CP showed less production of odorous compounds than 20% CP group and this result might be associated with the changes in bacterial communities especially whose roles in protein metabolism.

The potential of various biochars to remove 15 odorous volatile organic compounds emitted from swine manure were investigated via laboratory sorption experiments. Nine biochars made from pyrolyzing poultry litter, swine manure, oak, and coconut shell at 350 °C and 500 °C and a commercial coconut-shell activated carbon were evaluated for their sorption capacities toward the odorous compounds. These 15 odorous volatile organic compounds (VOCs) consisted of reduced sulfur compounds, volatile fatty acids, phenolic, and indolic compounds. The sorption capacities of these biochars were investigated using a laboratory-scale sorption column system. Among the 15 targeted VOCs, acetic acid was the most predominant compound in the emitted gas from swine manure; however, its contribution to the complex swine manure odor mixture was minimal. Dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) were the two most odor-causing VOCs in the swine manure emissions based on single compound odor active values. Livestock-manure-based biochars were poor sorbents for DMDS and DMTS. In contrast, plant-biomass-based biochars had considerably larger sorption capacity for DMDS and DMTS. Oak biochar pyrolyzed at 500 °C (OK500) showed high sorption capacities for both DMDS and DMTS. Although the sorption capacity of OK500 for DMDS is less than that of commercial activated carbon, it may provide additional income for users if the spent OK500 biochar can be sold as a soil amendment.

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