Biomethane Production from Anaerobic Co-Digestion of Selected Organic Fraction of Municipal Solid Waste (OFMSW) with Sewage Sludge: Effect of the Inoculum to Substrate Ratio (ISR) and Mixture Composition on Process Performances.

Gaspare Viviani,Santo Fabio Corsino,Michele Torregrossa

doi:10.3390/ijerph182413048

Abstract

The aim of this study was to evaluate the effect of the inoculum to substrate ratio (ISR) and the mixture ratio between organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) on the methane production potential achievable from anaerobic co-digestion (AcoD). Biochemical Methane Potential (BMP) assays at mesophilic temperature were used to determine the best AcoD configuration for maximizing methane yield and production rate, as well as to address possible synergistic effects. The maximum methane yield was observed at ISR of 1 and 60% OFMSW: 40% SS as co-digestion mixture, whereas the highest methane production rate was achieved at ISR of 2 with the same mixture ratio (207 mL/gVS/d). Synergistic effects were highlighted in the mixtures having OFMSW below 60%, determining an increase of approximately 40% in methane production than the OFMSW and SS digestion as a sole substrate. The experimental data demonstrated that co-digestion of OFMSW and SS resulted in an increase in the productivity of methane than anaerobic digestion using the sole substrates, producing higher yields or production rates while depending on the ISR and the mixture ratio.

Highlights

In the last decade, the population growth, the increase of urbanization and the economic development contributed to an overproduction of the municipal solid waste (MSW), which generation is approximately 1.2 kg per capita per day and is expected to increase in the coming decade by more than 50% [1]
The highest volatile solids (VS) reduction was obtained in the Mix6 (71%), thereby indicating that the VS reduction performances increased with the initial content of VS in the mixture
The low values of VS reduction obtained at inoculum to substrate ratio (ISR) of 0.05 could be attributed to the scarce biodegradability of the activated sludge and to the large volume of solid waste compared to the inoculum that could result in accumulation of ammonia or volatile fatty acids that could inhibit methanogens

Summary

Introduction

The population growth, the increase of urbanization and the economic development contributed to an overproduction of the municipal solid waste (MSW), which generation is approximately 1.2 kg per capita per day and is expected to increase in the coming decade by more than 50% [1]. The organic fraction of municipal solid waste (OFMSW). The OFMSW is characterized by a massive amount of putrescible materials because of the presence of residual food waste, kitchen, and restaurant that involve the generation of methane and leachate [5]. To mitigate the environmental pressure caused by the disposal of OFMSW in landfill, alternative management practices have been implemented in recent years, consisting of anaerobic digestion (AD) and/or composting [6]. Anaerobic digestion is a biological process that involves the conversion of organic matter in a mixture of methane (45–55%), carbon dioxide (35–40%)

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Conclusion