Anaerobic sequential batch reactor for CO-DIGESTION of slaughterhouse residues: Wastewater and activated sludge

Abstract

This work aims to determine the potential to produce biomethane by means of an Anaerobic Sequential Batch Reactor used to process two types of slaughterhouse wastes: raw slaughterhouse wastewaters and a sludge obtained after a specific treatment. In this study different hydraulic retention times (15, 10, 8, 6, 4 days) were applied and the reactor's performance was evaluated. The behavior of the main parameters associated to biodegradation processes, such as total biomethane production or anaerobic population dynamics were studied. The highest methane production and biodegrading factors removals were achieved when using 10-8 days of hydraulic retention times, obtaining around 0.31 ± 0.03 LCH4/gCODt and 0.51 ± 0.06LCH4/gTVS with removal percentages between 16 and 22% for COD and between 47 and 34% for TVS thanks to the higher microbial population. Therefore, the proposed AnSBR system has the potential to generate 5.23·105 kW h/year when operating under optimal HRT conditions (HRT 8–10 d). At these conditions, long chain fatty acid hydrolysis limitation are not a problem for a stable AD process performance due to a proper balance of different microbial groups: Eubacteria:Archaea ratio of 2.0; low but stable hydrolytic acidogenic bacteria proportion (13%), high proportion of Acetogens (44%) and preferred acetoclastic methanogen (32%) than hydrogenotropic methanogens (3%). So, the conditioning of the substrate such as pre-treatment of the sludge and the mixture in a proper proportion to the slaughterhouse wastewater achieve optimal organic load and microbial population, that improve the biomethane production in ACoD of Slaughterhouse residues in AnSBR systems during stable operation (HRT 15-8d). Even, a positive linear correlation between organic loading rate and Archaea activity was observed. However, at HRT 6d and 4d hydraulic retention times, the reactors started to suffer destabilization.