A Novel Up-Flow Anaerobic Sludge Blanket Solid-State Reactor for the Treatment of Fruit and Vegetable Waste

Abstract

In this work, a novel up-flow anaerobic sludge blanket solid-state reactor was proposed for the degradation of fruit and vegetable wastes, RAFAELL for its acronym in Spanish (Reactor Anaerobio de Flujo Ascendente Empacado con Lecho de Lodos). The design considers a solid-state section: This is a pre-treatment stage (disintegration) in which organic solid wastes are subjected to shear to increase both the number of particles smaller than 105 μm and the concentration of dissolved solids (particles smaller than 2.5 μm). Hydrolysis and acidogenesis reactions are also presented in the solid-state section. The design also considers a section of sludge blanket to increase the residence time of the cells. The recirculation stream transports the faster biodegradable fraction from the solid-state section to the sludge blanket section, favoring methane productivity. The design includes a buffer section, where the alkalinity leaving the sludge bed consumes the acidity produced in the solid-state section, allowing greater stability of the pH in the reactor. In assessing the behavior of the proposed digester, good volatile solid removal efficiencies (67%) were obtained in 4 days of solids retention time, with an acceptable methane productivity between 0.5 and 3.6 L_CH4/(L · day) for loads between 1 and 10 g VS/(L · day). The productivity expressed in L_CH4/(g SV_consumed · day) was between 0.027 and 0.116 L_CH4/(g SV_consumed · day).