Co-digestion of cow and sheep manure: Performance evaluation and relative microbial activity

Yu Li,Spyridon Achinas,Jing Zhao,Bert Geurkink,Janneke Krooneman,Gerrit Jan Willem Euverink

doi:10.1016/j.renene.2020.02.041

Abstract

This study evaluated the performance of anaerobic co-digestion of cow manure (CM) and sheep manure (SM) in both batch and continuous digesters at 37 °C. Synergistic effects of co-digesting CM and SM at varying volatile solids (VS) ratios (1:0, 0:1, 3:1, 1:1, 1:3) were observed in the batch experiment, with the most effective degradation of cellulose (56%) and hemicellulose (55%), and thus, the highest cumulative methane yield (210 mL/gVSadded) obtained at a CM:SM ratio of 1:3. Co-digesting CM and SM improved the hydrolysis, as evidenced by the cellulase brought by SM and the increases of cellulolytic bacteria Clostridium. Besides, co-digestion enhanced the acidogenesis and methanogenesis, reflected by the enrichment of syntrophic bacteria Candidatus Cloacimonas and hydrogenotrophic archaea Methanoculleus (Coenzyme-B sulfoethylthiotransferase). When testing continuous digestion, the methane yield increased from 146 mL/gVS/d (CM alone) to 179 mL/gVS/d (CM:SM at 1:1) at a constant organic loading rate (OLR) of 1g VS/L/d and a hydraulic retention time (HRT) of 25 days. Furthermore, the anaerobic digestion process was enhanced when the daily feed changed back to CM alone, reflected by the improved daily methane yield (159 mL/VS/d). These results provided insights into the improvement of methane production during the anaerobic digestion of animal manure.

Highlights

Intensive livestock farming has been increasingly developed over the last decades to satisfy our overwhelming demand for meat and dairy products [9]
The corresponding theoretical methane yield (TMY) for cow manure (CM) and sheep manure (SM) were 357 mL/gVSadded and 395 mL/gVSadded, respectively. These findings suggested that the co-digestion of CM and SM might have a better performance than the mono-digestion of CM (Table 1)
Lignocellulose content removal and methane yield in the batch test were improved when using a mixture of CM and SM (3:1, 1:1, 1:3 on volatile solids (VS) basis) as opposed to CM only

Summary

Introduction

Intensive livestock farming has been increasingly developed over the last decades to satisfy our overwhelming demand for meat and dairy products [9] These farms inevitably contribute to a considerable amount of manure annually [6]. The difficulty can be partly overcome by a pre-treatment which breaks up the complex structure (mainly between hemicellulose and lignin) and makes the lignocellulosic compounds more accessible for hydrolytic microbes. Another approach is through anaerobic co-digestion to increase the number of indigenous microorganisms with efficient degradation capabilities [35]. One contains active specialized hydrolytic microorganisms that work on the depolymerization of lignocellulose is preferred as a co-digestion partner

Methods

Results

Conclusion