title: Volatile fatty acids (VFAs) production from swine manure through short-term dry anaerobic digestion and its separation from nitrogen and phosphorus resources in the digestate.
abstract: The sustainability of an agricultural system depends highly upon the recycling of all useful substances from agricultural wastes. This study explored the feasibility of comprehensive utilization of C, N and P resources in swine manure (SM) through short-term dry anaerobic digestion (AD) followed by dry ammonia stripping, aiming at achieving (1) effective total volatile fatty acids (VFAs) production and separation; (2) ammonia recovery from the digestate; and (3) preservation of high P bioavailability in the solid residue for further applications. Specifically, two ammonia stripping strategies were applied and compared in this work: (I) ammonia stripping was directly performed with the digestate from dry AD of SM (i.e. dry ammonia stripping); and (II) wet ammonia stripping was conducted by using the resultant filtrate from solid-liquid separation of the mixture of digestate and added water. Results showed that dry AD of the tested SM at 55 °C, 20% TS and unadjusted initial pH (8.6) for 8 days produced relatively high concentrations of total VFAs (94.4 mg-COD/g-VS) and ammonia-N (20.0 mg/g-VS) with high potentially bioavailable P (10.6 mg/g-TS) remained in the digestate, which was considered optimal in this study. In addition, high ammonia removal efficiencies of 96.2% and 99.7% were achieved through 3 h' dry and wet stripping (at 55 °C and initial pH 11.0), respectively, while the total VFAs concentration in the digestate/filtrate remained favorably unchanged. All experimental data from the two stripping processes well fitted to the pseudo first-order kinetic model (R(2) = 0.9916-0.9997) with comparable theoretical maximum ammonia removal efficiencies (Aeq, >90%) being obtained under the tested dry and wet stripping conditions, implying that the former was more advantageous due to its much higher volumetric total ammonia-N removal rate thus much smaller reactor volume, less energy/chemicals consumption and no foaming problems. After 8 days' dry AD and 3 h' dry ammonia stripping, the separated liquid containing VFAs and the recovered ammonia were both marketable products, and the solid residues with averagely higher C/N ratios of 25.7 than those of raw SM (18.0) meanwhile maintaining a relatively high bioavailable P content of 8.1 mg/g-TS can serve as better feedstock for methane fermentation.
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Weiwei
authors.initials: W
authors.lastname: Huang
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Wenli
authors.initials: W
authors.lastname: Huang
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Tian
authors.initials: T
authors.lastname: Yuan
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Ziwen
authors.initials: Z
authors.lastname: Zhao
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan.
authors.forename: Wei
authors.initials: W
authors.lastname: Cai
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan. Electronic address: zhang.zhenya.fu@u.tsukuba.ac.jp.
authors.forename: Zhenya
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan. Electronic address: lei.zhongfang.gu@u.tsukuba.ac.jp.
authors.forename: Zhongfang
authors.initials: Z
authors.lastname: Lei
authors.affiliation: School of Water Resources and Environment, China University of Geosciences Beijing, Key Laboratory of Groundwater Circulation and Evolution (China University of Geosciences Beijing), Ministry of Education, Beijing 100083, China.
authors.forename: Chuanping
authors.initials: C
authors.lastname: Feng
mesh_terms: D000383:Agriculture; D000641:Ammonia / Q000737:chemistry; D000693:Anaerobiosis; D000818:Animals; D019149:Bioreactors; D005232:Fatty Acids, Volatile / Q000737:chemistry*; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008372:Manure; D008697:Methane / Q000737:chemistry; D009584:Nitrogen / Q000032:analysis*; D010758:Phosphorus / Q000032:analysis*; D013552:Swine; D013696:Temperature; D014865:Waste Disposal, Fluid / Q000379:methods*
chemical_list: D005232:Fatty Acids, Volatile; D008372:Manure; D010758:Phosphorus; D000641:Ammonia; D009584:Nitrogen; D008697:Methane
keywords: Dry ammonia stripping; Dry anaerobic digestion; Phosphorus fractionation; Swine manure; Volatile fatty acids