Stabilization of Anaerobic Co-Digestion Process via Constant the Digestate Solids Content

Risu Na,Naoto Shimizu,Keisuke Uchitani,Kazuto Yoshida

doi:10.3390/pr9020197

Abstract

The process instability of anaerobic digestion (AD) is a common issue and may result in underperformance or short-term process failure. Extensive research has shown that total solids (TS) content in AD has a significant impact on system stability and performance. However, no study has examined the feasibility of stabilizing the AD process by maintaining constant TS content in the digestate. In this study, an innovative control approach based on constant TS content in the digestate during AD was developed using a mass balance equation. Two levels of TS content (desired values of 4% wet basis (w.b.) and 6% w.b.) were compared with conventional control. The process stability was examined by monitoring digestate components and pH. Substrate-specific methane yield (m3 CH4/kg VS) was used to assess the effectiveness of the controlled conditions. The results showed that the digestate TS content during AD can be controlled and that the digestion process can be stabilized by controlled conditions. In addition, constant TS in the digestate (within 1% w.b. of the desired level) gave increased levels of biogas production (10.2%), methane (13.5%), and substrate-specific methane yield (43.3%) at 4% TS, and respective increases of 16.6%, 21.2%, and 20.8% at 6% TS when compared with standard operation.

Highlights

With the development of global industrialization and urbanization, the output of municipal solid waste (MSW) is increasing at an alarming rate
The amount of biogas generated in week 7 when no raw material was added was about 1.5 n-m3, which was much less than the other phases in which measurement was possible
Except for the period when the raw materials were not added in week 7, when comparing the phase that adopted constant conditions (Phases 1 and 4) and the phase that was performed under conventional conditions (Phase 2), the biogas production and methane concentration were increased by 10.2% and 13.5%, respectively, in Phase 1, and by 16.6% and 21.2%, respectively, in Phase 4

Summary

Introduction

With the development of global industrialization and urbanization, the output of municipal solid waste (MSW) is increasing at an alarming rate. According to World Bank statistics, the world generates 2.01 billion tons of MSW in 2016, which is expected to grow to 3.40 billion tons by the year 2050 [1]. The two major components of MSW are food waste (FW, 44%) and paper waste (PW, 17%) [2]. Considering the negative environmental impacts of landfilling and incineration of MSW [3], sustainable management of MSW is becoming an imminent global issue. AD has received increased attention in recent years because it is widely used on a global scale and can simultaneously achieve waste treatment and energy recovery [5]

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