Comparing the Bio-Hydrogen Production Potential of Pretreated Rice Straw Co-Digested with Seeded Sludge Using an Anaerobic Bioreactor under Mesophilic Thermophilic Conditions

Abstract

Three common pretreatments (mechanical, steam explosion and chemical) used to enhance the biodegradability of rice straw were compared on the basis of bio-hydrogen production potential while co-digesting rice straw with sludge under mesophilic (37˝C) and thermophilic (55˝C) temperatures. The results showed that the solid state NaOH pretreatment returned the highest experimental reduction of LCH (lignin, cellulose and hemi-cellulose) content and bio-hydrogen production from rice straw. The increase in incubation temperature from 37˝C to 55˝C increased the bio-hydrogen yield, and the highest experimental yield of 60.6 mL/g VS removed was obtained under chemical pretreatment at 55˝C. The time required for maximum bio-hydrogen production was found on the basis of kinetic parameters as 36 h-47 h of incubation, which can be used as a hydraulic retention time for continuous bio-hydrogen production from rice straw. The optimum pH range of bio-hydrogen production was observed to be 6.7˘0.1-5.8˘0.1 and 7.1˘0.1-5.8˘0.1 under mesophilic and thermophilic conditions, respectively. The increase in temperature was found useful for controlling the volatile fatty acids (VFA) under mechanical and steam explosion pretreatments. The comparison of pretreatment methods under the same set of experimental conditions in the present study provided a baseline for future research in order to select an appropriate pretreatment method.

Seed Pretreatment for Increased Hydrogen Production Using Mixed-Culture Systems with Advantages over Pure-Culture Systems

“…Mixed-cultures are more suited for industrial purposes due to their lower operating costs, the convenience of microbial diversity and the fact fermentation helps to reduce the organic loads of effluent treatments [10]. During fermentation, steps of acidogens with acetogens are necessary for hydrogen production, however, hydrogenotrophic methanogens and acetoclastic methanogens should be minimized, as they consume hydrogen along with the produced CO 2 to release methane [16,19]. To overcome this hurdle, steps such as aeration of sludge, high dilution rates in the case of continuous fermentation and different pretreatment methods have been utilized.…”

“…The acid-treatment at pH 3 resulted in a 333-fold increase (from 0.24 mL to 80 mL H 2 /g of VS) in the hydrogen yield in comparison to alkali-treatment at pH 10 with a 200-fold increase (from 0.24 mL to 46.3 mL H 2 /g of VS) [62]. During pH adjustment, generally HCl or orthophosphoric acid for acid treatment and NaOH for alkali treatment are employed [16]. The acid-treatment at pH 3 results in an enrichment of hydrogen-producing organisms, eliminating the growth of methanogens and improving hydrogen production in comparison to alkali-treatment at pH 10 [62].…”

“…However, by blocking the methanogenesis step hydrogen production using mixed-culture systems is more feasible [14,15]. The mixed-culture system depends on the pretreatment step used for the seed inoculum, such as heat-, chemical-(acid, base), aeration-, electrical-and combined-pretreatments to block the methanogens and to increase hydrogen production [16].…”

Enhancing Anaerobic Digestion: The Effect of Carbon Conductive Materials

“…In spite of these advantages, the energy balance is not as favourable as in the traditional thermal pre-treatment due to the impossibility of recovering energy by recycling of heat, and also the fact that conventional thermal process is capable of accumulating heat for adjusting the high peak demand with the production stage; the latter is, however, not available for any other technology in which the energy demand is associated with the direct use of electricity [33]. The addition of bases or acids, to improve thermal degradation, has demonstrated to be a feasible option, particularly in the case of thermo-alkaline pre-treatments, which can improve biogas production up to a 54% when evaluating the digestion of waste activated sludge [34] and has proven to be the preferred choice when the pre-treatment is intended for attaining the delignification of biomass [35].…”

Thermal Effects

“…Furthermore, the cumulative methane production was remarkable improved after thermal-alkaline pretreatment of sludge. Co-digestion of sludge with rice straw pretreated by steam explosion, mechanical and chemical methods at 37 °C and 55 °C was studied to evaluate the relationship of digestion temperature and pretreatment (Sattar et al, 2016). The highest bio-hydrogen production of 60.6 ml/g VSremoved was achieved at 55 °C with alkaline pretreatment, because the temperature played a key role on the volatile fatty acids production.…”