Chemical Pretreatments to Enrich the Acidogenic Phase in a System Coupled Packed Bed Reactor with a UASB Reactor Using Peels and Rotten Onion Waste

Abstract

A large amount of onion wastes are produced by both domestically and industrially, making it necessary to search for a reuse process. These wastes causing odor and in some cases causes harm to the environment. At 2017, Mexico produced 1.6 million tons of which 10% are classified as organic waste. The aim of this study was to contribute to the reduction of onion peel residues, using chemical pretreatments (H2SO4, HCl, H3PO4 and NaOH) to enrich the acidogenic phase in the anaerobic digestion (AD) to improve the yield of methane in a system coupled packed bed reactor with an Up-flow Anaerobic Sludge Blanket reactor (UASB) using peels and rotten onion waste. In anaerobic digestion of white onion residues in a single stage (PBR1) presented inhibition due to the accumulation of VFA during the first days, which delay the onset of the methanogenic phase, which occurred 63 days after the start of the experiment. Pretreatment with H2SO4 (PBR2) decreased the start time of the methanogenic pathway, from 63 days to 35. In the same way, the coupling of the UASB reactor to the packed reactor (PBR3) allowed the decrease of the methanogenic step after 14 days, and the total time for this process was 35 days. The yield for PBR1 was 0.013 m3 CH4 kg VSrem−1, for PBR2 0.014 m3 CH4 kg VSrem−1 and PBR3 0.017 m3 CH4 kg VSrem−1. The total yield of PBR3 + UASB was 0.41 m3 CH4 kg VSrem−1.