Search

Volatile fatty acids (VFA) play an important role in the biodegradation of organic wastes and production of bioenergy under anaerobic digestion, and are related to malodors. However, little is known about the dynamics of VFA during dairy manure storage. This study evaluated the characteristics of VFA in dairy manure before and after anaerobic co-digestion in a laboratory experiment using eight lab-scale reactors. The reactors were loaded with four different types of dairy manure: (1) liquid dairy manure from a freestall barn, (2) mixture of dairy manure and co-digestion food processing wastes at the inlet of an anaerobic digester, (3) effluent from the digester outlet, and (4) the liquid fraction of effluent from a solid separator. Four VFA (acetic, propionic, butyric, and 2-methylbutyric acids) were identified and quantified in weekly manure samples from all reactors. Results showed that the dominant VFA was acetic acid in all four manure sources. The off-farm co-digestion wastes significantly increased the total VFA concentrations and the proportions of individual VFA in the influent. The dairy manure under storage demonstrated high temporal and spatial variations in pH and VFA concentrations. Anaerobic digestion reduced the total VFA by 86%–96%; but solid–liquid separation did not demonstrate a significant reduction in total VFA in this study. Using VFA as an indicator, anaerobic digestion exhibited an effective reduction of dairy manure odor offensiveness. [ABSTRACT FROM AUTHOR]

Volatile fatty acids (VFA) are among the most abundant volatile organic compounds in dairy manure and are associated with odour nuisance. This paper presents research results of VFA production during a three-month storage of dairy manure from four different sources: a dairy barn (raw), the inlet of an anaerobic digester (influent), the digester outlet (effluent), and the effluent after solid separation (effluent SS). Manure from each source was studied in two lab-scale reactors that were continuously ventilated with fresh air in the manure headspace to simulate manure storage conditions. Two manure samples were taken weekly in the top and bottom manure layers from each reactor for VFA analysis. Five VFA (formic acid, acetic acid, propionic acid, butyric acid, and 2-methylbutyric acid) were identified in all reactors using high performance liquid chromatography (HPLC). The dominant VFA was formic acid for the influent and acetic acid for the other three manure sources. The overall average concentrations of the five VFA were 1963 ± 685 (mean ± standard deviation), 14,175 ± 4825, 286 ± 98, and 169 ± 80 mg l−1 for the raw, influent, effluent, and effluent SS, respectively. The “pre-consumer” organic wastes mixed with dairy manure in the influent significantly increased the total VFA concentrations and the proportion of individual VFA. Concentrations of VFA demonstrated highly temporal and spatial variations. Anaerobic digestion significantly reduced formation of VFA in the effluent and effluent SS. However, the complexity of VFA characteristics made it difficult to reliably model and predict the concentrations and compositions of VFA in dairy manure. [ABSTRACT FROM AUTHOR]