6ee93bfe-ce6f-47e9-b408-f731014f9bfc20211115045012720naun:naunmdt@crossref.orgMDT DepositInternational Journal of Geology1998-449910.46300/9105http://www.naun.org/cms.action?id=28304720214720211510.46300/9105.2021.15https://www.naun.org/cms.action?id=23318A.SilvaCESAM & Environmental and Planning Department University of Aveiro 3810-193-Aveiro, PortugalI.CapelaCESAM & Environmental and Planning Department University of Aveiro 3810-193-Aveiro, PortugalL.ArrojaCESAM & Environmental and Planning Department University of Aveiro 3810-193-Aveiro, PortugalH.NadaisCESAM & Environmental and Planning Department University of Aveiro 3810-193-Aveiro, PortugalThis work studied the influence of effluent recirculation upon the kinetics of anaerobic degradation of dairy wastewater in intermittent UASB (Upflow Anaerobic Sludge Bed) reactors. Several laboratory-scale tests were performed with different organic loads in a UASB reactor inoculated with flocculent sludge from an industrial wastewater treatment plant. The data obtained were used for determination of specific substrate removal rates and specific methane production rates and adjusted to kinetic models. A high initial substrate removal was observed in all tests due to adsorption of organic matter onto the anaerobic biomass which was not accompanied by biological substrate degradation as measured by methane production. Initial methane production was about 45% of initial soluble and colloidal substrate removal rate. This discrepancy was observed mainly in the first day of all experiments and was attenuated in the second day. Effluent recirculation raised significantly the rate of removal of soluble and colloidal substrate and methane productivity as compared to literature results for batch assays without recirculation.111520211115202135405https://www.naun.org/main/NAUN/geology/2021/a102004-005(2021).pdf10.46300/9105.2021.15.5https://www.naun.org/main/NAUN/geology/2021/a102004-005(2021).pdf10.1016/j.watres.2005.01.020H. Nadais, I. Capela, L. Arroja, A. Duarte, “Optimum cycle time for intermittent UASB reactors treating dairy wastewater”, Water Research, vol. 39, no. 8, pp. 1511-1518, 2005. 10.1002/bit.21095N. Coelho, A. Rodrigues, L. Arroja, I. Capela, “Effect of non-feeding period length on the intermittent operation of UASB reactors treating dairy effluents”. Biotechnology Bioengineering, vol. 96, no 2, pp. 244– 249, 2007. M. Viñas, C. Galain, M. Lois, “Treatment of proteic wastewater in continuous and intermittent UASB reactors”,. 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