Research On The Effect Of Magnetite Nanoparticles On Anaerobic Fermentative Hydrogen Production From Wastewater

Energy shortage and environmental pollution has become important factors limiting the rapid economic development, hydrogen because of its efficient, clean, renewable and other advantages has attracted much attention. Anaerobic fermentation bio-hydrogen production can be used for treatment of high concentration organic wastewater, livestock manure, excess sludge, municipal solid waste and crop straw, which can obtain clean energy at the same time in the efficient degradation of organic waste. However, system stability, and hydrogen production and other issues restricting this technology industrial applications. Fe is anaerobic fermentation process the most important elements of the bacteri a to produce hydrogen, by adding different valence and different forms of Fe and its compounds to the anaerobic fermentation system improving the hydrogenase activity of hydrogen-producing bacterial to promote hydrogen production performance of the system has become the hot spot in the field of research.This study proposes adding Magnetite Nanoparticles(MNPs) into the anaerobic digestion system, investigate its effects on the promotion of hydrogen production processes, preliminary elaborate mechanism of MNPs promote anaerobic fermentation hydrogen production by analysis of key enzyme activity、succession of microbial community and morphology and distribution of Fe and so on.To determine the optimal size and optimal concentration of MNPs playing promoting effect in the process of anaerobic fermentation hydrogen production, the anaerobic sludge from biohydrogen fermentation anaerobic was used as the inoculum, glucose was used as substrate, investigated the effect of different size(0-100 nm) and concentration(0-800 mg/L) of MNPs on anaerobic fermentation hydrogen production by static experiment. The results showed that MNPs had no effect on glucose degradation efficiency which more than 99%. Fermentation type had a change trend from butyrate type to ethanol type, the p H of system had been improved a small margin than the control group, final p H stable at 4.0 above. Cumulative hydrogen production present ed the trend that first increased and then decreased with size increased from 0- 20 nm to 80- 100 nm, concentration increased from 0 to 800 mg/L of MNPs. Comprehensive comparison the best hydrogen production performance of the system was obtained when MNPs in the 40-60 nm size range, adding a concentration of 50 mg/L(0.018 g/g VSS), the maximum cumulative hydrogen quantity and hydrogen production rate achieve to 236 m L and 31.6 m L/h, respectively, which selected as the optimal size and concentration.Study analyzed the effect of MNPs on occurrence state, the activities of hydrogenase and dehydrogenase, structure and abundance of microbial community in anaerobic fermentation process with continuous flow anaerobic reactor under the condition of optimal batching. The results showed that, MNPs can slowly release Fe2+/Fe3+ into the anaerobic system, then concentration were maintained about at 5.10 mg/L and 0.20 mg/L. Due to the presence of MNP, fermentation type transformed from butyrate type to ethanol type, the p H of the system increased about 4.5 to about 4.7, hydrogen content and hydrogen production rate increased by 15% and 54.7% compared with the control group. Five kinds of chemical speciation of Fe content had improved to varying degrees since MNPs added, but the anti-spinel structure of MNPs did not change. The presence of MNPs did not significantly affect the species of sludge organic functional groups, only affects the content of organic functional groups. The total amount of dissolved organic matter in the reactor increased and the content of protein-like improved significantly.MNPs resulted in the increase of microbial community abundance and diversity in the reactor while microbial community structure had undergone significant change, the relative abundance of Clostridium decreased from 40.55% to 11.45%, while the relative abundance of Unclassified Bacteroidales and Ethanoligenens increased from 13.53%, 6.09% to 22.79% and 12.56%, respectively. Dominant populations changed from Clostridium Unclassified to Bacteroidales, thus theoretically demonstrated fermentation type transformed from butyrate type to ethanol type.In addition, compared with the control group, the activities of hydrogenase and dehydrogenase were increased from 0.216 m L/(g VSS˙min) and 13.92 ug/(g VSS˙min) upto 0.301 m L/(g VSS˙min) and 20.36 ug/(g VSS˙min) after adding MNPs in the reactor, respectively. Hydrogen content and hydrogen production rate were higher than adding ferric ion into the system, the percentage improvement of reactor R1 was reactor R2 1.88 and 1.8 times,respectively.The mechanism of MNPs promote hydrogen production mainly displays in: intracellular and extracellular MNPs can promote hydrogenase and ferredoxin activity potentially, bacterial nanowires promoted glucose transportation through the cell walls, at the same time with MNPs can increase electron transfer rate between cells, and lead to hydrogen production performance was improved.