Hydrolysis and Methanogenesis in UASB-AnMBR Treating Municipal Wastewater Under Psychrophilic Conditions: Importance of Reactor Configuration and Inoculum.

Judit Ribera-Pi,Ewan Mcadam,Antonio Campitelli,Irene Jubany,Ana Soares,Xavier Martínez-Lladó,Bruce Jefferson,Marina Badia-Fabregat

doi:10.3389/fbioe.2020.567695

Abstract

Three upflow anaerobic sludge blanket (UASB) pilot scale reactors with different configurations and inocula: flocculent biomass (F-UASB), flocculent biomass and membrane solids separation (F-AnMBR) and granular biomass and membrane solids separation (G-AnMBR) were operated to compare start-up, solids hydrolysis and effluent quality. The parallel operation of UASBs with these different configurations at low temperatures (9.7 ± 2.4°C) and the low COD content (sCOD 54.1 ± 10.3 mg/L and pCOD 84.1 ± 48.5 mg/L), was novel and not previously reported. A quick start-up was observed for the three reactors and could be attributed to the previous acclimation of the seed sludge to the settled wastewater and to low temperatures. The results obtained for the first 45 days of operation showed that solids management was critical to reach a high effluent quality. Overall, the F-AnMBR showed higher rates of hydrolysis per solid removed (38%) among the three different UASB configurations tested. Flocculent biomass promoted slightly higher hydrolysis than granular biomass. The effluent quality obtained in the F-AnMBR was 38.0 ± 5.9 mg pCOD/L, 0.4 ± 0.9 mg sCOD/L, 9.9 ± 1.3 mg BOD5/L and <1 mg TSS/L. The microbial diversity of the biomass was also assessed. Bacteroidales and Clostridiales were the major bacterial fermenter orders detected and a relative high abundance of syntrophic bacteria was also detected. Additionally, an elevated abundance of sulfate reducing bacteria (SRB) was also identified and was attributed to the low COD/SO42– ratio of the wastewater (0.5). Also, the coexistence of acetoclastic and hydrogenotrophic methanogenesis was suggested. Overall this study demonstrates the suitability of UASB reactors coupled with membrane can achieve a high effluent quality when treating municipal wastewater under psychrophilic temperatures with F-AnMBR promoting slightly higher hydrolysis rates.

Highlights

Low strength municipal wastewater is characterized by its low organic content (COD < 500 mg/L) and high solids content (TSS < 250 mg/L) (Henze et al, 2008)
The most widely used technology for wastewater treatment is based on the activated sludge process, but this implies a high cost for aeration as well as the generation of high amounts of biomass that needs to be further managed (Metcalf et al, 2003)
Since upflow anaerobic sludge blanket (UASB) reactors are fed in upflow mode they act as settling devices in which non-settable biomass is released and settable biomass is kept in the reactor

Summary

Introduction

Low strength municipal wastewater is characterized by its low organic content (COD < 500 mg/L) and high solids content (TSS < 250 mg/L) (Henze et al, 2008). The most widely used technology for wastewater treatment is based on the activated sludge process, but this implies a high cost for aeration as well as the generation of high amounts of biomass (sludge) that needs to be further managed (Metcalf et al, 2003). Since UASB reactors are fed in upflow mode they act as settling devices in which non-settable biomass is released and settable biomass is kept in the reactor. This characteristic allows the better exploitation of the reactor working volume (Metcalf et al, 2003). The characteristics of municipal wastewater still constitute a challenge for anaerobic systems in temperate climates (Stazi and Tomei, 2018)

Objectives

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Results