Evaluation of odor emissions from amended dairy manure: Preliminary screening

Manure amendments have shown variable effectiveness in reducing odor. Twenty-two amendments were applied to dairy manure then evaluated for odor reduction efficacy after storage at 20°C for 3 d and 30 d. Amendments represented differing primary modes of action including: microbial digestive, oxidizing, disinfecting, masking, and adsorbent. Each amendment was added to 2 kg dairy manure (1:1.7 urine:feces; 12% total solids) following recommended rates. In this preliminary screening, one sample (n=1) of each amendment was evaluated along with untreated manure (Control). Odor emission from each treated manure and Control was estimated twice by five or six qualified odor assessors (n=10 or 12) after each storage duration, using an international standard for triangular forced-choice olfactometry. Odor quality was defined using hedonic tone, Labeled Magnitude Scale and ASTM methods for supra-threshold odor intensity, and an odor character wheel for descriptors. For selected treatments, odor emissions were significantly reduced relative to Control at 30 d versus 3 d incubation (P<0.0001). However, no amendment was significantly effective for both incubation times. Likewise, for all amendments tested, aging the manure slurry for 30 d significantly reduced odor emission and odor intensity (P<0.0001). A proprietary microbial amendment (Alken Enz-Odor + Clear Flo: aerobic/ facultative microbes with growth factors), disinfectant (hydrogen peroxide), and masking agent (Hyssopus officinalis essential oil) provided significant short-term control of odor (P <0.06). However, after 30 d seven amendments significantly increased odor emission (P<0.02) while only two amendments offered a significant efficacy (P<0.0001): a proprietary microbial aerobic/facultative product (Bio-Regen) and a proprietary mix of chemicals (Greaseater), both with weekly re-application. Hedonic tone observations suggested an improvement to "slightly to moderately unpleasant" smell versus untreated manure for all amendments except clinoptilolite zeolite adsorbent. Hedonic tone improvement was correlated with reduced manure odor supra-threshold intensity.