Operation And Regulation Of Photo-fermentative Biofilm Reactor For Enhanced Hydrogen Production And Its Mechanism

Human society faces two main problems: environmental pollution and energy crisis.Future energy develops with increase of energy density,reduction of cost and environmental impact.Photo-fermentative hydrogen production draws wide focus owing to its special metabolic characteristics,which degrades organic matter from wastes,and fixes solar energy to green renewable hydrogen.Photo-fermentative biofilm reactor is the key technology to treat environmental pollution and accomplish hydrogen energy.However,main researches just focused on nutritional and environmental factors by now.At the meantime,the mechanism of the biofilm enhancing photo-fermentative hydrogen production was limited in molecular level.Thus,this paper operated photo-fermentative biofilm reactor with Rhodopseudomonas sp.nov.strain A7 as hydrogen producer and silicon carrier as biofilm basement.The study explored the regulation of bacteria in different stages,chiral change of key factors and biofilm on operation of reactors.In addition,the biofilm enhancing hydrogen production mechanism was researched based on proteome and extracellular polymeric substances(EPS).Start-up of photo-fermentative biofilm reactor biofilm decides economic competitiveness and reactor performance thus was first explored.It concluded that a novel means by adding decline-period bacteria(Rhodopseudomonas sp.nov.strain A7)in biofilm reactor on day 0 could successfully accelerated start up reactor and improve hydrogen production.Hydrogen production in biofilm reactor added with decline-period bacteria on day 0 bounced up to about 273 m L/(L·d)and cumulative hydrogen production reached 2925 m L/L.In contrast,little hydrogen was obtained do day 1 in control reactor without decline-period bacteria and its cumulative hydrogen production reached only1167 m L/L.Adding decline-period bacteria in biofilm reactor at initial could quickly start up the reactor and improve hydrogen production.However,adding decline-period bacteria on day 2,when hydrogen producer was in logarithmic period,influenced little on start-up and hydrogen production of photo-fermentative reactor.The accelerated startup and improved hydrogen production were achieved by the increase of bacterial ability.Data analysis concluded biofilm formation and addition decline-period bacteria expressed the combined effects on accelerated start-up.Along with the photo-fermentative hydrogen production,the necessary component L-cysteine could be transferred to D-cysteine.Besides,bacteria could accumulate Dcysteine in stable period and decline period.Effects of L-cysteine and D-cysteine on photo-fermentative biofilm reactor need to be explored.The conclusion showed different cysteines expressed distinguished effects.D-cysteine added on day 0 when hydrogen producer was in lag period inhibited cells proliferation and hydrogen production.The inhibitory effects increased with the D-cysteine concentration.When D-cysteine > 0.3g/L,hydrogen production was totally stopped.D-cysteine played as the quorum sensing factor for lag-period bacteria.D-cysteine added in logarithmic period of hydrogen producer influenced little on hydrogen production and bacterial growth of reactor.Although biofilm showed little influence on D-cysteine limit concentration(0.3 g/L)under which the bacteria magnify and produce hydrogen,biofilm could still enhance hydrogen production.Compared to D-cysteine,L-cysteine could improve photofermentation.Biofilm and control reactor without L-cysteine obtained cumulative hydrogen production of 1267 m L/L and 915 m L/L,respectively while biofilm and control reactor with L-cysteine obtained 1647 m L/L and 1080 m L/L,respectively.Because of the obvious improved effects of L-cysteine and inhibitory effects of D-cysteine,transformation from L-cysteine to D-cysteine needed to be monitored and restricted in photo-fermentation.Then mechanism of biofilm enhancing photo-fermentative hydrogen production was explored after accomplishing operation strategy of reactors.Cumulative hydrogen production of control reactor reached 1811 m L/L while the value of biofilm reactor reached 3050 m L/L.Biofilm could improve the hydrogen production efficiency about68.4%.Under biofilm regulation,proteins inside cells significantly changed.Proteins related to nitrogenase,ATP,TCA,flagellin,transmembrane transport,flagellar and chemotaxis were up-regulated while those concerned photosystems were down-regulated.Proteins related to nitrogenase and TCA were up-regulated about 1.8 to 2.6 folds and 2.0to 2.6 folds respectively.As nitrogenase could reduce [H] to hydrogen using electron and energy,improved nitrogenase and TCA activity directly magnified photo-fermentative hydrogen production.Proteins related with photosynthetic pigments were down-regulated which relieved the excessive oxidative state and enhanced the light distribution.Thus,light utilization efficiency was improved in photo-fermentative bacteria leading to enhanced hydrogen production.Sulfur metabolism changes under biofilm regulation also created the better low-oxidative/high redox state for hydrogen production.In addition,Rhodopseudomonas A7 could form a complex mature three-dimensional biofilm on carrier.Composition and structure of EPS were efficiently influenced by the formation of biofilm,such as benzene and O-H structure.These changes illustrated the aggregation and functions in different bacteria changed too.Secondary proteins structure in EPS were also influenced.Secondary proteins structure in EPS from biofilm cells mainly possessed occupied ? type which was 49.8% thus these proteins tended to construct globular proteins,which was highly specific and sensitive to regulating bacterial metabolism.At the meantime,Secondary proteins structure in EPS from free cells mainly possessed ?+?or ?/? which occupied about 51.3% thus guaranteed proteins in EPS of free cells functional and structural integrity.Photo-fermentative bacteria were functional separated and ecological partitioned with carrier introduction which was beneficial to improvement of photo-fermentative hydrogen production.This study optimized the photo-fermentative biofilm reactor operation parameters and obtained an effective strategy.Thus,this study supported the theoretical basis and technical support for enlargement and scale application of photo-fermentative hydrogen production.