Enrichment of Secondary Wastewater Sludge for Production of Hydrogen from Crude Glycerol and Comparative Evaluation of Mono-, Co- and Mixed-Culture Systems

Abstract

Anaerobic digestion using mixed-culture with broader choice of pretreatments for hydrogen (H2) production was investigated. Pretreatment of wastewater sludge by five methods, such as heat, acid, base, microwave and chloroform was conducted using crude glycerol (CG) as substrate. Results for heat treatment (100 °C for 15 min) showed the highest H2 production across the pretreatment methods with 15.18 ± 0.26 mmol/L of medium at 30 °C in absence of complex media and nutrient solution. The heat-pretreated inoculum eliminated H2 consuming bacteria and produced twice as much as H2 as compared to other pretreatment methods. The fermentation conditions, such as CG concentration (1.23 to 24 g/L), percentage of inoculum size (InS) (1.23% to 24% v/v) along with initial pH (2.98 to 8.02) was tested using central composite design (CCD) with H2 production as response parameter. The maximum H2 production of 29.43 ± 0.71 mmol/L obtained at optimum conditions of 20 g/L CG, 20% InS and pH 7. Symbiotic correlation of pH over CG and InS had a significant (p-value: 0.0011) contribution to H2 production. The mixed-culture possessed better natural acclimatization activity for degrading CG, at substrate inhibition concentration and provided efficient inoculum conditions in comparison to mono- and co-culture systems. The heat pretreatment step used across mixed-culture system is simple, cheap and industrially applicable in comparison to mono-/co-culture systems for H2 production.

Alternate green approach of spent media utilization for hydrogen and for lipid production

“…23.6% glycerol, 35.9% carbon, 5.7% moisture, 3.2% nitrogen, 3.1% ash, <1.0-0.5% methanol and 67.56% matter organic non-glycerol (MONG) [16]. The pH of the crude glycerol was around 3.4 ± 0.1 [4].…”

“…Across the world, a new initiative of bioconversion of crude glycerol (CG) (by-product of biodiesel industry) to hydrogen (H 2 ) production has been carried out to expand biodiesel industry [2,3]. The characteristics of CG, such as low market value, feedstock availability [3], with increased reduction state in comparison to other organic wastes; make it suitable for microbial conversion to H 2 over other value-added products [4].…”

Effect of hydraulic retention time on the modelling and optimization of joint 1,3 PDO and BuA production from 2G glycerol in a chemostat process

“…(high amount of sulfur and LCFA, very low pH, etc) in crude glycerol (CG) derived from meat processing waste cause increased inhibition in comparison to impurities in CG derived from pure substrates [59,60]. In a previous study, for instance, a hexane-extraction step was applied in order to reduce the concentration of lipids and (long chain) fatty acids present in the 2G crude glycerol and evaluate its potential inhibitory effect on the microbial growth [6].…”

“…Besides their ability to metabolize a wider range of carbon sources, MMC further offer the advantage of cheaper inocula generation and maintenance, higher robustness against contaminations, as well as a more cost effective alternative to genetically engineered strains [23,24]. This is of particular importance in the case of 2G crude glycerol derived from meat processing waste, which is known to have increased inhibiting effect in comparison to crude glycerol types derived from plant and/or cooking oils [25].…”

Biorefinery for Glycerol Rich Biodiesel Industry Waste

“…Comparisons of mono-, co-and mixed cultures revealed that maximum H 2 production of 29.8 mmol/L at 2 % w/v CG with mixed cultures. Another factor which helped to enhance H 2 production process efficiency was heat treating the feed-100°C for 15 min, primarily to get rid of H 2 consumers [59].…”