Thermophilic Anaerobic Digestion of Second Cheese Whey: Microbial Community Response to H2 Addition in a Partially Immobilized Anaerobic Hybrid Reactor

Giuseppe Lembo,Valentina Mazzurco Miritana,Massimiliano Fenice,Giulia Massini,Antonella Signorini,Antonella Marone,Silvia Rosa

doi:10.3390/pr9010043

Abstract

In this study, we investigated thermophilic (55 °C) anaerobic digestion (AD) performance and microbial community structure, before and after hydrogen addition, in a novel hybrid gas-stirred tank reactor (GSTR) implemented with a partial immobilization of the microbial community and fed with second cheese whey (SCW). The results showed that H2 addition led to a 25% increase in the methane production rate and to a decrease of 13% in the CH4 concentration as compared with the control. The recovery of methane content (56%) was reached by decreasing the H2 flow rate. The microbial community investigations were performed on effluent (EF) and on interstitial matrix (IM) inside the immobilized area. Before H2 addition, the Anaerobaculaceae (42%) and Lachnospiraceae (27%) families dominated among bacteria in the effluent, and the Thermodesulfobiaceae (32%) and Lachnospiraceae (30%) families dominated in the interstitial matrix. After H2 addition, microbial abundance showed an increase in the bacteria and archaea communities in the interstitial matrix. The Thermodesulfobiaceae family (29%)remained dominant in the interstitial matrix, suggesting its crucial role in the immobilized community and the SHA-31 family was enriched in both the effluent (36%) and the interstitial matrix (15%). The predominance of archaea Methanothermobacter thermoautrophicus indicated that CH4 was produced almost exclusively by the hydrogenotrophic pathway.

Highlights

Introduction in published maps and institutionalThe dairy industry is one of the main sources of industrial wastewater in Europe with cheese whey (CW) and second cheese whey (SCW) making up a large part [1]
The acetic acid was the unique volatile fatty acids (VFAs) found during the anaerobic digestion (AD) process, moving from an average value of 210 ± 5.6 mg L−1 during the first 10 days to that of 37 ± 2.4 mg L−1 at the end of AD
Members of Methanobacteriaceae family dominated in both experimental phases, as well as in effluent and interstitial matrix, showing values of relative abundances higher than 74%

Summary

Introduction

Introduction in published maps and institutionalThe dairy industry is one of the main sources of industrial wastewater in Europe with cheese whey (CW) and second cheese whey (SCW) making up a large part [1]. Similar to CW, SCW is a highly pollutant dairy waste with a significant organic load (biochemical oxygen demand (BOD) ≈ 30 g/L, chemical oxygen demand (COD) 60–80 g/L, and lactose. The high organic loads of both SCW and CW represent severe disposal and pollution issues for the dairy industry and a huge opportunity for bioenergy and biochemicals production [2,3,4]. It is known that the high -fermentable organic content and low bicarbonate alkalinity of raw SCW, as well as of CW, unbalance the AD process towards an accumulation of volatile fatty acids (VFAs), and a decrease in the pH values far below the optimum value for the methanogens is often observed [6]

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