Research On Pretreatment And Anaerobic Digestion Of Hybrid Broussonetia Papyrifera Waste

Due to the world energy crisis,the overuse of fossil energy not only accelerates the exhaustion of energy but also causes severe pollution for our environment.Therefore,in current years,human investment in renewable energy is gradually increasing.In this way,the application of biomass energy has become one of the feasible ways to solve the energy problem.The hybrid Broussonetia Papyrifera(BP)is one kind of economical and high-quality trees planted in China widely.Its leaves can be used to produce animal feed,however,in addition to the available parts,there will be a large number of wastes,such as branches and trunks.At present,the disposal methods for these wastes are burning or discard,which not only result in severe environmental pollution but also waste energy.Handling BP wastes by the technology of anaerobic digestion(AD)has many advantages.On the one hand,it converts organic wastes into clean energy,on the other hand,the high production of the BP wastes provides a stable raw material supply for anaerobic digestion.Therefore,this research explored the methane yield potential of BP wastes as well as the co-digestion and pretreatments to improve the methane-production performance of BP wastes.The main research findings are as follows:Firstly,the potential of methane yield under different organic loadings of BP wastes were researched.The results showed that the highest experimental methane yield(EMY)of BP wastes was 248.5 mL/gvs which obtained at the organic loading of 15 gvs/L.When the organic loading was low(5 gvs/L),there were the problems of long lag period and low methane yield,while the EMY gradually decreased with the increase of organic loadings when the organic loading was higher than 15 gvs/L.Secondly,three kinds of livestock manures,including pig manure,chicken manure,and cow manure,were applied for co-digestion with BP wastes at different mixing ratios.The synergistic effect index(SEI)was used to evaluate the synergistic effect in co-digestion,which was the relevant improvement ratio of the EMY and the weighted experiment methane yield(WEMY).The results showed that when the mixing ratio between each of three kinds of manures(pig manure(PM),chicken manure(CHM),and cow manure(COM))and BP wastes was 1:2,it reached the highest SEI,which were 12.6%,16.0%,and 4.0%respectively.The EMY were 365.8,347.5,and 273.4 mL/gvs,respectively.Moreover,the addition of PM in co-digestion could significantly increase the methane production rate in the early stage of anaerobic digestion.Excessive lag period in the anaerobic co-digestion of CHM and BP wastes could be shortened by the addition of BP wastes.In addition,NaOH,KOH,H2SO4,HC1,and alkaline hydrogen peroxide(AHP)were used to pretreat BP wastes at the concentration of 2%,3%,4%,and 5%.The results showed that the 4%AHP-treated BP wastes obtained the highest EMY(327.4 mL/gvs),which was 42.4%higher than that of the unpretreated control group.Besides,the biodegradation rate of 4%AHP-treated BP wastes reached 90.9%.Finally,the response surface methodology(RSM)was used to explore the effects of three factors(pH,concentration,and duration of AHP pretreatment)of AHP pretreatment of BP wastes.The results showed that pH value had no significant effect on EMY of BP wastes.The most significant factor was the pretreatment time,and the optimal pretreatment time increased with the increase of H2O2 concentrations.The optimal conditions for AHP pretreatment of BP wastes were the pH value of 7.6,the H2O2 concentration of 7%,and the pretreatment time of 36.2 hours.Under these conditions,the EMY of BP wastes was 335.3 mL/gvs,which was close to the predicted value of 351.6 mL/g,,s.The biodegradation rate was 91.4%,which was 42.6%higher than that of the unpretreated control group.The results indicated that it was a feasible way to use BP wastes to produce methane by AD,and this study also provided useful data and theoretical basis for the future research and application of BP wastes in AD process.