Abstract
BackgroundWith the increasing global population and increasing demand for food, the generation of food waste and animal manure increases. Anaerobic digestion is one of the best available technologies for food waste and pig manure management by producing methane-rich biogas. Dry co-digestion of food waste and pig manure can significantly reduce the reactor volume, capital cost, heating energy consumption and the cost of digestate liquid management. It is advantageous over mono-digestion of food waste or pig manure due to the balanced carbon/nitrogen ratio, high pH buffering capacity, and provision of trace elements. However, few studies have been carried out to study the roles of and interactions among microbes in dry anaerobic co-digestion systems. Therefore, this study aimed to assess the effects of different inocula (finished digestate and anaerobic sludge taken from wastewater treatment plants) and substrate compositions (food waste to pig manure ratios of 50:50 and 75:25 in terms of volatile solids) on the microbial community structure in food waste and pig manure dry co-digestion systems, and to examine the possible roles of the previously poorly described bacteria and the interactions among dry co-digestion-associated microbes.ResultsThe dry co-digestion experiment lasted for 120 days. The microbial profile during different anaerobic digestion stages was explored using high-throughput 16S rRNA gene amplicon sequencing. It was found that the inoculum factor was more significant in determining the microbial community structure than the substrate composition factor. Significant correlation was observed between the relative abundance of specific microbial taxa and digesters’ physicochemical parameters. Hydrogenotrophic methanogens dominated in dry co-digestion systems.ConclusionsThe possible roles of specific microbial taxa were explored by correlation analysis, which were consistent with the literature. Based on this, the anaerobic digestion-associated roles of 11 bacteria, which were previously poorly understood, were estimated here for the first time. The inoculum played a more important role in determining the microbial community structure than substrate composition in dry co-digestion systems. Hydrogenotrophic methanogenesis was a significant methane production pathway in dry co-digestion systems.
Highlights
With the increasing global population and increasing demand for food, the generation of food waste and animal manure increases
The dry co-digestion experiment lasted for 120 days to determine the microbial profile during different anaerobic digestion stages
According to the daily specific methane yield (DSMY) data and C ODVFA concentration, the dry co-digestion process could be divided into three phases
Summary
With the increasing global population and increasing demand for food, the generation of food waste and animal manure increases. Dry co-digestion of food waste and pig manure can significantly reduce the reactor volume, capital cost, heating energy consumption and the cost of digestate liquid management. It is advantageous over mono-digestion of food waste or pig manure due to the balanced carbon/ nitrogen ratio, high pH buffering capacity, and provision of trace elements. The EU Landfill Directive (1999/31/EC) requires a diversion of BMW from landfill sites, and the Irish government increased the landfill levy from €30/ton of waste disposed in 2010 to €50/ton in 2011, €65/ton in 2012 and further to €75/ ton in 2013 [1] This provides a good opportunity for anaerobic digestion to be adopted for FW management by the industry. It is urgent to find alternative approaches to manage PM in a sustainable and economic way
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