Effect of Localized Temperature Difference on Hydrogen Fermentation

Seongwon Im,Alsayed Mostafa,Om Prakash,Kyeong-Ho Lim,Dong-Hoon Kim,Mo-Kwon Lee

doi:10.3390/en14216885

Abstract

In a lab-scale bioreactor system, (20 L of effective volume in our study) controlling a constant temperature inside bioreactor with a total volume 25 L is a simple process, whereas it is a complicated process in the actual full-scale system. There might exist a localized temperature difference inside the reactor, affecting bioenergy yield. In the present work, the temperature at the middle layer of bioreactor was controlled at 35 °C, while the temperature at top and bottom of bioreactor was controlled at 35 ± 0.1, ±1.5, ±3.0, and ±5.0 °C. The H2 yield of 1.50 mol H2/mol hexoseadded was achieved at ±0.1 and ±1.5 °C, while it dropped to 1.27 and 0.98 mol H2/mol hexoseadded at ±3.0 and ±5.0 °C, respectively, with an increased lactate production. Then, the reactor with automatic agitation speed control was operated. The agitation speed was 10 rpm (for 22 h) under small temperature difference (<±1.5 °C), while it increased to 100 rpm (for 2 h) when the temperature difference between top and bottom of reactor became larger than ±1.5 °C. Such an operation strategy helped to save 28% of energy requirement for agitation while producing a similar amount of H2. This work contributes to facilitating the upscaling of the dark fermentation process, where appropriate agitation speed can be controlled based on the temperature difference inside the reactor.

Highlights

Accepted: 19 October 2021The development of hydrogen (H2 ) production technology has gained significant attention due to its high energy content (142 kJ/g) and its cleaner nature on combustion [1,2,3].At present, the commercial production of H2 is achieved via coal gasification, gas reforming, etc., which are not sustainable and environmentally benign due to the depletion of the fossil fuels and the generation of greenhouse gaseous emissions [4,5]
Among various bio-H2 production routes, the production of green hydrogen by use of organic wastes as feedstock has a huge potential to become an important source of hydrogen in the future if operating under ambient temperature and pressure conditions
The variations at the different heights of the bioreactor are depicted in The temperature at the different of layer the bioreactor arearound depicted in

Summary

Introduction

The commercial production of H2 is achieved via coal gasification, gas reforming, etc., which are not sustainable and environmentally benign due to the depletion of the fossil fuels and the generation of greenhouse gaseous emissions [4,5]. Among various bio-H2 production routes, the production of green hydrogen by use of organic wastes as feedstock has a huge potential to become an important source of hydrogen in the future if operating under ambient temperature and pressure conditions. Dark fermentative H2 production (in short “dark fermentation”), in particular, is considered an environmentally friendly and practically suitable process for commercial bio-H2 production, due to its high production rate, simple operation, and handling of various organic wastes [8,9,10,11,12].

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