High Organic Loading Treatment of Synthetic Soy-sauce Production Wastewater Using a Combined System Consisting of a Psychrophilic (20 ºC) UASB Reactor and a DHS Reactor at Ambient Temperature

Abstract

To establish an effective soy-sauce production wastewater treatment system, we designed a combined system consisting of a psychrophilic (20 ºC) up-flow anaerobic sludge blanket (UASB) reactor and a down-flow hanging sponge (DHS) reactor under ambient temperature. The COD removal rate of 87±7％ was achieved at a 26±3.6 kgCOD m^-3 d^-1 organic loading rate (6,500±900 mgCOD L^-1 as influent synthetic soy-sauce based wastewater) in the UASB reactor. 16S rRNA gene sequence analysis revealed that syntrophs belonging to class Deltaproteobacteria, phylum Firmicutes, and phylum Thermotogae, Bacteria belonging to phylum Synergistetes, and methanogens mainly degrade approximately 40％ of the COD of soy-sauce-based synthetic wastewater in the UASB reactor. Syntrophic associations require low hydrogen partial pressure because of the difficulty of this reaction. Therefore, this study revealed that the UASB-DHS system can be applied to real soy-sauce production wastewater containing high organics and sodium concentrations because syntrophic associations were well developed.