Effects of Lipase Addition, Hydrothermal Processing, Their Combination, and Co-Digestion with Crude Glycerol on Food Waste Anaerobic Digestion

Xiaojue Li,Naoto Shimizu

doi:10.3390/fermentation7040284

Abstract

To enhance anaerobic fermentation during food waste (FW) digestion, pretreatments can be applied or the FW can be co-digested with other waste. In this study, lipase addition (LA), hydrothermal pretreatment (HTP), and a combination of both methods (HL) were applied to hydrolyze organic matter in FW. Furthermore, the effects of crude glycerol (CG), which provided 5%, 10%, and 15% of the volatile solids (VS) as co-substrate (denoted as CG5, CG10, and CG15, respectively), on the anaerobic digestion of FW were assessed. With an increasing proportion of CG in the co-digestion experiment, CG10 showed higher methane production, while CG15 negatively affected the anaerobic digestion (AD) performance owing to propionic acid accumulation acidifying the reactors and inhibiting methanogen growth. As the pretreatments partially decomposed hard-to-degrade substances in advance, pretreated FW showed a stronger methane production ability compared with raw FW, especially using the HL method, which was significantly better than co-digestion. HL pretreatment was shown to be a promising option for enhancing the methane potential value (1.773 NL CH4/g VS) according to the modified Gompertz model.

Highlights

Carmen VeigaAccording to FAO estimates, approximately 1.3 billion tons of food waste (FW) are generated annually across the entire food supply chain [1]
After lipase addition (LA), hydrothermal pretreatment (HTP), and HL pretreatments, the volatile solids (VS) ratio dropped to 7.23%, 6.75%, and 5.80%, respectively (Table 2), indicating that pretreatments promoted the solubilization of solids in FW
The main hydrolysates of lipids from FW were VFAs and long-chain fatty acids (LCFAs), which should be converted to acetate through β-oxidation and to biomethane [12]

Summary

Introduction

Carmen VeigaAccording to FAO estimates, approximately 1.3 billion tons of food waste (FW) are generated annually across the entire food supply chain [1]. Between 2010 and 2016, global food waste accounted for 8–10% of all man-made greenhouse gas emissions, leading to an annual loss of approximately USD 1 trillion [2]. Current traditional practices, such as incineration and landfill, help release some stress from garbage siege; a series of problems require urgent attention, including the further cost of waste disposal, the lack of land space, groundwater pollution by leachate, and the emission of greenhouse gases that need further treatment [3]. Anaerobic digestion (AD) is widely accepted as the most effective technology for energy production and adds value to agronomic organic waste [7], while simultaneously reducing secondary environmental pollution during the digestion process [8,9]

Objectives

Methods

Results

Conclusion