Influence Of Upflow Velocity And Organic Loading Conditions On The Hydrogen-Producing Granular Sludge

Hydrogen has the characteristics of high calorific value,no pollution and renewable,As a kind of "green energy".Upflow anaerobic sludge blanket(UASB)hydrogen-producting reactor has the characteristics of high biomass and strong impact load capacity,which is the current research hotspot.The liquid upflow velocity and organic load are the basic process parameters for the operation of the UASB hydrogen-producting reactor.The influence mechanism of the hydraulic and organic loading conditions on the system is investigated.The interaction between the two particles and the characteristics of the granular sludge and the biodegradation law can be studied.The rational design,optimized operation of the existing process and the transformation of the reactor provide strong support for the existing system.In this study,in order to explore the effects of liquid upflow velocity and organic load on the UASB hydrogen production system,a self-designed UASB reactor was used to cultivate hydrogen-producing granular sludge.The hydrogen production rate,sludge mass,pH,oxidation reduction potential(ORP)and other fermentation characteristics and changes in the composition and content of extracellular polymeric substances(EPS)were investigated during startup process.Then,the liquid upflow velocity and organic load were changed respectively,and their effects on hydrogen production characteristics and granular sludge properties were analyzed.Research results are as follows:(1)The reactor was started successfully after 70 days,and stable anaerobic hydrogen-producing granular sludge was formed,which presents a well-defined porous network structure;and the hydrogen production rate was kept within the ranges 4.48?4.98 L/(L?d),the pH was kept within the ranges 5.0?5.61,the ORP was kept within the ranges-506?-565 mV,Showed better stability.The increase of EPS promotes the granulation of sludge.The content of loosely bound EPS(LB-EPS)is higher than the tightly bound EPS(TB-EPS)in the early stage,which is beneficial to the binding of fine particles and flocs.After the completion of granulation,the TB-EPS content was 29.50 mg/g VSS higher than the LB-EPS,which was beneficial to maintain the stability of granular sludge structure.(2)Under the feed concentration maintained at 9.3 g/L,the results showed when the upflow velocity increased from 0.15 m/h to 0.6 m/h,The EPS content increased from 99.48 mg/g VSS to 214.51 mg/g VSS,and the average particle size of granular sludge increased from 0.7 mm to 1.48 mm;the proportion of LB-EPS decreased while the proportion of TB-EPS increased;granular sludge Strength increased.When the upflow velocity increased to 1.2 m/h,the reactor operation was unstable,the biomass decreased,and the sludge settling performance deteriorated.Therefore,the granular sludge cultured under the upflow velocity of 0.6 m/h has better performance.(3)Under the liquid upflow velocity of 0.15 m/h,The organic load increased from 40 gCOD/(L?d)to 80 gCOD/(L?d),the hydrogen production rate gradually increased,and VSS increased from 42.99 g/L to 78.68 g/L,and the average granular size increased from 0.7 mm to 1.92 mm,and the EPS content of granular sludge increased from 103.49 mg/g VSS to 283.85 mg/g VSS.And when the organic load was 80 gCOD/(L?d),the rate of hydrogen production reached a maximum of 9.02 L/(L?d);the content of butyric acid plus acetic acid accounts for 68% of the total liquid phase product and the system showed butyric acid type fermentation;glucose utilization rate is higher than 97%;the granular sludge has higher EPS content,TB-EPS content is 194.64 mg/g VSS,its content is 2.18 times that of LB-EPS,granular sludge has compact structure and good settlement performance.The organic load increased to 90 gCOD/(L?d),the hydrogen production rate decreased,and the system operation was unstable.