Environ Sci Pollut Res DOI 10.1007/s11356-017-8560-1
RESEARCH ARTICLE
Biohydrogen production from sugarcane bagasse hydrolysate: effects of pH, S/X, Fe2+, and magnetite nanoparticles Karen Reddy 1 & Mahmoud Nasr 2 & Sheena Kumari 1 & Santhosh Kumar 3 & Sanjay Kumar Gupta 1 & Abimbola Motunrayo Enitan 1 & Faizal Bux 1
Received: 30 August 2016 / Accepted: 2 February 2017 # Springer-Verlag Berlin Heidelberg 2017
Abstract Batch dark fermentation experiments were conducted to investigate the effects of initial pH, substrate-tobiomass (S/X) ratio, and concentrations of Fe2+ and magnetite nanoparticles on biohydrogen production from sugarcane bagasse (SCB) hydrolysate. By applying the response surface methodology, the optimum condition of steam-acid hydrolysis was 0.64% (v/v) H2SO4 for 55.7 min, which obtained a sugar yield of 274 mg g−1. The maximum hydrogen yield (HY) of 0.874 mol (mol glucose−1) was detected at the optimum pH of 5.0 and S/X ratio of 0.5 g chemical oxygen demand (COD, g VSS−1). The addition of Fe2+ 200 mg L−1 and magnetite nanoparticles 200 mg L−1 to the inoculum enhanced the HY by 62.1% and 69.6%, respectively. The kinetics of hydrogen production was estimated by fitting the experimental data to the modified Gompertz model. The inhibitory effects of adding Fe2+ and magnetite nanoparticles to the fermentative hydrogen production were examined by applying Andrew’s inhibition model. COD mass balance and full stoichiometric reactions, including soluble metabolic products, cell synthesis, and H2 production, indicated the reliability of the experimental results. A qPCRResponsible editor: Angeles Blanco Electronic supplementary material The online version of this article (doi:10.1007/s11356-017-8560-1) contains supplementary material, which is available to authorized users. * Faizal Bux
[email protected] 1
Institute for Water and Wastewater Technology, Durban University of Technology, Durban 4000, South Africa
2
Sanitary Engineering Department, Faculty of Engineering, Alexandria University, Alexandria 21544, Egypt
3
Department of Biotechnology and Food Technology, Durban University of Technology, Durban 4000, South Africa
based analysis was conducted to assess the microbial community structure using Enterobacteriaceae, Clostridium spp., and hydrogenase-specific gene activity. Results from the microbial analysis revealed the dominance of hydrogen producers in the inoculum immobilized on magnetite nanoparticles, followed by the inoculum supplemented with Fe2+ concentration. Keywords Biohydrogen . Dark fermentation . Full stoichiometry . Hydrogen-producing microbes . Magnetite nanoparticles . Sugarcane bagasse hydrolysate
Introduction Hydrogen is a promising energy carrier that has been recognized as a rescuer fuel of the future (Singh et al. 2013). Hydrogen has high energy content per unit mass (∼122 kJ g−1), which 2.75 times greater than that of other hydrocarbon-based fuels (Nasr et al. 2013a). Additionally, hydrogen is a clean and environmentally friendly fuel, since it does not produce toxic emissions during combustion (Akutsu et al. 2009). Moreover, hydrogen can be used in fuel cells, internal combustion engines, and gas turbines (Lay, 2000). In this context, huge efforts should be exerted to maximize the hydrogen gas productivity. Biological hydrogen production can be carried out via various processes, such as direct photolysis of water by green algae, indirect photolysis of water by cyanobacteria, photofermentation of organic acids by anaerobic photosynthetic bacteria, and dark fermentation of organic substrates by anaerobic fermentative bacteria (Akutsu et al. 2009; Nasr et al. 2015). Recently, bioH2 production through dark fermentation has gained increasing attention, mostly due to the economic advantages of coupling waste reduction with recovery of renewable energy without an external energy input (Li and Ren, 1998; Singh et al. 2013). Under anaerobic conditions,
Environ Sci Pollut Res
fermenting bacteria can convert substrates (e.g., carbohydrates or sugars) to hydrogen gas and organic acids (Pattra et al. 2008). Additionally, fermentating bacteria need to conserve energy and balance electron equivalents (e− eq) between end products (Lee and Rittmann, 2009). However, accumulation of the metabolic products during hydrogen fermentation can result in an inhibition to the microbes’ activities (Singh et al. 2013). Additionally, soluble microbial products can become a major e− eq sink during fermentation, and thus, further experimental works need to be conducted to maximize e− eq flowing to H2. Renewable bioenergy sources, such as biomass-derived sugars and organic wastes, have been reported as promising substrates for fermentative hydrogen production. Some of these wastes are by-products/residues of food-processing plants and agricultural processes (Lay, 2000). Sugarcane bagasse (SCB) hydrolysate contains high amounts of sugar that can be converted into hydrogen gas by fermentating bacteria (Pattra et al. 2008). Different groups of bacteria, such as Enterobacter, Clostridium, and Bacillus, have been reported to produce hydrogen through dark fermentation from SCB hydrolysate (Wang et al. 2007). Substrate-to-biomass (S/X) ratio and pH are two key parameters that have been investigated to obtain enriched culture of hydrogen-producing bacteria (Nasr et al. 2013b). Moreover, recent studies have investigated the effects of iron concentration and hematite/magnetite nanoparticles on hydrogen fermentation (Das et al. 2006; Zhang et al. 2005; Zhang and Shen, 2007). Hydrogenase enzymes are classified according to the metal content at their respective active sites into nickel–iron [Ni–Fe] hydrogenases and iron–iron [Fe–Fe] hydrogenases (Das et al. 2006). The existence of Fe2+ in the core structure of hydrogenase suggests its crucial effect on the activity of enzyme-catalyzed reactions for H2 production (Mohanraj et al. 2014). Previous articles have reported the enhancement effect of Fe2+ on biohydrogen production through influencing the activity of hydrogenases (Wang and Wan, 2008; Mohanraj et al. 2014). Recent studies have also reported the application of nanoparticles to improve the bioactivity of hydrogen-producing bacteria (Han et al. 2011; Nasr et al. 2015). The addition of nanoparticles to the fermentation system can improve chemical reaction rates, leading to increased hydrogen production (Gadhe and Gupta, 2007). This can be due to their capability to support high surface area, as well as due to their uniquely physical and chemical properties (Nasr et al. 2015). This work was conducted to (1) develop an anaerobic dark fermentation process that generates hydrogen gas from SCB hydrolysate, (2) determine the optimal operating conditions (pH, S/X ratio, Fe2+, and magnetite nanoparticles), (3) establish COD mass balance and full stoichiometry, (4) study the kinetics of hydrogen production using the modified Gompertz model, (5) investigate the inhibitory effects of Fe2+ and
magnetite nanoparticles on the fermentative hydrogen production, and (6) identify and quantify the dominant hydrogenproducing microbes in the fermenters.
Materials and methods Seed microorganisms (thermal pre-treatment) The inoculum was obtained from an anaerobic holding tank of a domestic wastewater treatment plant situated in KwazuluNatal Province, South Africa. The collected sludge was thermal pre-treated at 70 °C for 30 min using an oven (IncoTherm, Labotech, South Africa) to eliminate methanogenic and other hydrogen-consuming bacteria (Nasr et al. 2015).
Acid pre-treatment of sugarcane bagasse Samples of raw SCB were obtained from Kashmeers Sugarcane Juice Ltd., Durban, South Africa. The gathered samples were sun-dried, then blended and dry-milled using a blender (Waring Laboratory Science, South Africa). The milled samples were then sieved to a size
