Effects of Operational Parameters on Biofilm Formation of Mixed Bacteria for Hydrogen Fermentation

Jie Mei,Xun Zhu,Xianqing Zhu,Qiang Liao,Ao Xia,Abdul-Sattar Nizami,Huize Chen,Yun Huang

doi:10.3390/su12218863

Abstract

Dark fermentation of organic wastes, such as food waste and algae, via mixed hydrogen-producing bacteria (HPB) is considered a sustainable approach for hydrogen production. The biofilm system protects microorganisms from the harmful environment and avoids the excessive loss of bacteria caused by washout, which ensures that the dark fermentation process remains stable. In this study, a downflow anaerobic packed-bed reactor was commissioned to investigate the biofilm formation process of mixed HPB under various operational parameters. Scanning electron microscopy indicated changes in surface morphology during the biofilm formation period. Proteins and polysaccharides in extracellular polymeric substances were identified by confocal laser scanning microscopy to reveal their distribution characteristics. A hydraulic retention time of 0.5 d, a substrate concentration of 15 g/L and an HPB inoculum ratio of 35% were identified as the optimal operational parameters for biofilm formation. The diversity of bacteria between suspension and biofilm showed significantly different distributions; Clostridiales and Lactobacillales were identified as the dominant orders in the biofilm formation process. The abundances of Clostridiales and Lactobacillales were 15.1% and 56.2% in the biofilm, respectively.

Highlights

Hydrogen has received widespread attention worldwide because of its clean combustion characteristics and high calorific value (142 MJ/kg) [1,2]
SustainTahbielitiyn2n0o20v,a1t2i,o8n86o3f this study is to comprehensively study the impacts of key parameters, su3chofa1s5 the hydraulic retention time, substrate concentration and inoculum ratio, on the biofilm formation pfippfibnonorrirrorooommfiHccHceeeliiPmxPssxssseBseBddrooobebffficaciooHuucmmffitlliPotitliluxmxumrB.ereredemdffooHHiHHrrxmmPPePPBdBaBaBtticbbibboouiiiinonoolotf,fi,ffiuititlllolrommmmeiissnsn.ffvavaooTennerrhsmsmddettiiaagttgmototaaiiaototuueeinnnnnt,t,hddhpwweeeeurhrhmmrssiipttcciaiacohchnnrsrodowedwssoottottrhrhfuuuueetllccdhdtiitinunusppttrrresereeootrruaaavavncndciidtdtddyiieoeottinhnshggseseutuobdibdiddeieoisastatbtwtnwnrrtciacieebbeieeeununnffttootiivhovroraneanoorrpoopioioopfefeuuratraiasacscmttttibbiiioavovaanlencecpttsoseoeauufrfrrbibiaaaaassmnnttiiananeHHnnttctecPPhhereBBesses biofilm reactor
When the hydraulic retention time (HRT) was set at 3.5 d, the DW of the biofilm on the carrier slowly increased to 4.1 g/m2 over time to 2 d

Summary

Introduction

Hydrogen has received widespread attention worldwide because of its clean combustion characteristics (only water is a product) and high calorific value (142 MJ/kg) [1,2]. Fossil fuel reforming and water electrolysis are the major hydrogen production methods, which can produce hydrogen at a large scale. Water electrolysis consumes much electricity, which increases the cost of hydrogen production [3]. Such deficiencies limit the sustainability of hydrogen production. The process of producing hydrogen through dark fermentation by hydrogen-producing bacteria (HPB) is advantageous for low energy consumption [4]. Hydrogen production by dark fermentation has been established over several decades, such a technology is still in its infancy stage and has not yet been commercialized

Objectives

Methods

Results

Conclusion