Dark fermentative biohydrogen production by mesophilic bacterial consortia isolated from riverbed sediments

https://doi.org/10.1016/j.ijhydene.2010.03.010Get rights and content

Abstract

Dark fermentative bacterial strains were isolated from riverbed sediments and investigated for hydrogen production. A series of batch experiments were conducted to study the effect of pH, substrate concentration and temperature on hydrogen production from a selected bacterial consortium, TERI BH05. Batch experiments for fermentative conversion of sucrose, starch, glucose, fructose, and xylose indicated that TERI BH05 effectively utilized all the five sugars to produce fermentative hydrogen. Glucose was the most preferred carbon source indicating highest hydrogen yields of 22.3 mmol/L. Acetic and butyric acid were the major soluble metabolites detected. Investigation on optimization of pH, temperature, and substrate concentration revealed that TERI BH05 produced maximum hydrogen at 37 °C, pH 6 with 8 g/L of glucose supplementation and maximum yield of hydrogen production observed was 2.0–2.3 mol H2/mol glucose. Characterization of TERI BH05 revealed the presence of two different bacterial strains showing maximum homology to Clostridium butyricum and Clostridium bifermentans.

Introduction

Hydrogen gas has been considered as a clean and efficient renewable energy carrier based on the fact that it is renewable and does not produce secondary pollutant. Since hydrogen reacts with oxygen to form water as the by-product, hydrogen from renewable sources is considered as the ultimate clean and climate neutral energy system. Traditionally hydrogen can be produced by thermo-chemical or electrolytic methods. However, biological hydrogen production is considered as an environmentally friendly and economically sustainable method and has got potential advantages over other processes because of its low energy requirements and reduced initial investment costs [1]. Hydrogen can be obtained from algae and cyanobacteria through biophotolysis of water, photosynthetic bacteria through decomposition of organic acid (Rhodobacter sp.), and fermentative bacteria (Enterobacter sp., Clostridium sp., Escherichia coli) [2], [3]. Dark fermentative hydrogen production seems to be an efficient process over other biological hydrogen production processes since this process can make use of organic wastes as the feeding substrate, which can be recycled at the same time [4].

Renewable sources like biomass could be used as substrate for production of hydrogen through dark fermentation. Wide range of raw materials like starch, cellobiose, sucrose, or xylose can also be used as substrate. Starch is found predominantly in many common waste products released from agricultural and food industry. Starch is a complex form of carbohydrate and can be hydrolyzed into glucose and maltose by acid or enzymatic hydrolysis. Further the simpler form of carbohydrates so released can be converted into organic acids and then into hydrogen gas [5]. The initial hydrolysis is the rate-limiting step in microbial conversion and determines the efficiency of dark fermentative hydrogen production by using starch as the substrate. Glucose and sucrose also serve as interesting model substrates due to their easy biodegradability nature [6].

Reports are also available on the use of pure cultures or mixed consortia for biohydrogen production using sugars or complex substrates such as organic wastes [7]. Various factors such as temperature, initial pH, feeding substrates, substrate concentration, and source of inoculation have also been studied relating to fermentative biological hydrogen production [8], [9], [10], [11]. Though isolation of hydrogen producing microbes is reported from various sources, only one report is available on the isolation of hydrogen producing microbes from river sediments [12]. Riverbed sediments particularly from urban rivers have high organic load and can be considered ideal for isolation of fermentative bacteria capable of producing hydrogen from organic wastes.

Hence in this study, investigations were made to evaluate the effect of different carbon sources, nutrient solution, substrate concentration, pH, and temperature on fermentative hydrogen production by using anaerobic bacterial consortia isolated from riverbed sediments. Five different carbon sources; sucrose, starch, glucose, xylose, and fructose, were employed as the substrate. Attempts were also made to explore the bacterial composition in a glucose fed bacterial community by employing non-culture-dependent 16S rDNA sequencing approach.

Section snippets

Seed inoculum

Seed inoculum was obtained from riverbed sediments from Yamuna River, flowing below the Delhi-Noida-Direct flyway, New Delhi, India (28°37′40″N 77°15′21″E). This river is highly contaminated with organic pollutants. The sediment samples were collected from seven different sites of Yamuna riverbed, under anaerobic conditions as per the standard sample collection protocols described in American Public Health Association (APHA) guidelines. The sediment samples were then transferred to the

Isolation of hydrogen producing microbial consortia

To isolate hydrogen producing bacterial strains, initially seven riverbed sediment samples of Yamuna River, New Delhi, were investigated for hydrogen production. Initially a set of fourteen enrichment cultures was established with DMI medium supplemented with either sucrose or glucose. The gas chromatography results demonstrated that among fourteen enrichments cultures derived from seven sediment samples, only eight enrichments showed bacterial activity and hydrogen production. It was observed

Conclusions

The present work demonstrated the production molecular hydrogen through dark fermentative hydrogen by anaerobic bacterial consortia isolated from riverbed sediments. The selected consortium TERI BH05 has the potential to produce hydrogen by utilizing five different carbon sources, starch, sucrose, glucose, fructose, and xylose. This indicates that this consortium may have the ability to utilize different carbohydrate rich waste biomass stream to produce biohydrogen. Presence of nitrogenous

Acknowledgement

The authors are thankful to Dr R. K. Pachauri, Director General, TERI, New Delhi, for providing infrastructure to carry out the present study. We gratefully acknowledge the financial support assisted by Hindustan Petroleum Company Limited (HPCL).

References (35)

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