Characteristics of Biogas Production from Organic Wastes Mixed at Optimal Ratios in an Anaerobic Co-Digestion Reactor

Young-Ju Song,Jun-Gyu Park,Ji-Hwan Cha,Beom Lee,Kyung-Su Oh,Dae-Won Pak

doi:10.3390/en14206812

Abstract

This study determined the optimal mixing ratio of food waste and livestock manure for efficient co-digestion of sewage sludge by applying the biochemical methane potential (BMP) test, Design Expert software, and continuous reactor operation. The BMP test of sewage sludge revealed a maximum methane yield of 334 mL CH4/g volatile solids (VS) at an organic loading rate (OLR) of 4 kg VS/(m3·d). For food waste, the maximum methane yield was 573 mL CH4/g VS at an OLR of 6 kg VS/(m3·d). Livestock manure showed the lowest methane yield. The BMP tests with various mixing ratios confirmed that a higher mixing ratio of food waste resulted in a higher methane yield, which showed improved biodegradability and an improved VS removal rate. The optimal mixing ratio of 2:1:1 for sewage sludge, food waste, and livestock manure was determined using Design Expert 10. Using continuous co-digestion reactor operation under an optimal mixing ratio, greater organic matter removal and methane yield was possible. The process stability of co-digestion of optimally mixed substrate was improved compared with that of operations with each substrate alone. Therefore, co-digestion could properly maintain the balance of each stage of anaerobic digestion reactions by complementing the characteristics of each substrate under a higher OLR.

Highlights

The amount of sewage sludge is increasing owing to economic and population growth, sewage sludge treatment, and disposal are limited by existing methods because of the prohibition of sea dumping by the 1972 London Convention and 1996 London Protocol [1,2]
The biodegradability of particulate organic matter can be determined by measuring the ratio of biodegradable volatile solids (BVS) to total volatile solids (TVS) in the substrates [18]
The BVS portion of the TVS of the target substrate was decomposed into biogas; the degree of BVS can be predicted by measuring the methane yield

Summary

Introduction

The amount of sewage sludge is increasing owing to economic and population growth, sewage sludge treatment, and disposal are limited by existing methods because of the prohibition of sea dumping by the 1972 London Convention and 1996 London Protocol [1,2]. Landfilling, incineration, and recycling are alternative methods to marine dumping. These methods are difficult to develop and secure owing to limitations such as landfill capacity and air pollution [3]. Most engineered AD reactors are operated at a lower efficiency (20–40%) than the actual designed efficiency [5]. Most AD reactors cannot meet the design standard of 1.6–4.8 kg volatile solids (VS)/(m3·d) owing to the low biodegradable organic fraction. In addition to these problems, AD is sensitively affected by operational factors such as pH, temperature, nutrients, and toxic substances. Obtaining a high process stability is not easy because of problems such as a long hydraulic residence time and a low growth rate of methanogenic bacteria [6]

Methods

Results

Conclusion