Research On Pretreatment And Methane Production For Cotton Stalk During Anaerobic Digestion Process

China is the largest cotton producer with the cotton output accounting for 25%of the total world's cotton production.After the harvest of cotton,there are a lot of remaining cotton waste,such as stalk,leaves,and cotton shell.The cultivation of cotton results in the wastes of cotton stalk(CS)amounting 40 million tons annually.At present,the treatment method of a large quantity of CS waste is mainly straw recycling and burning.CS contains amount of carbohydrates,such as cellulose and hemicelluloses,which can be converted by microorganism into biogas,and bioethanol.Biogas is paid increasing attention because its production process and conditions are simpler than the production of other biofuels,which make biogas production more practical.Moreover,the anaerobic digestion(AD)process can not only treat the abundant organic waste,but also produce clean energy and organic fertilizer.In this study,cotton stalk,as material,was used for researching pretreatment and anaerobic digestion process.The anaerobic digestion experiment designed by central composite design(CCD)of response surface methodology(RSM)and used experimental methane yield and volatile solid(VS)removal as the response values.The purpose of this study was to investigate the effects of organic loading and feedstock to inoculum(F/I)ratio on the AD process.The results showed that the interactions of organic loading and F/I ratio influenced experimental methane yield and VS removal significantly.According to the analysis of the results fitted by RSM,0.79 and 25.61 gVS/L were regarded as the optimal F/I ratio and organic loading for AD experiment of CS.The effects of various pretreatments including H2SO4,H3PO4,NaOH,KOH,Ca(OH)2,alkali hydrogen peroxide(AHP),and steam explosion(SE)on AD process were researched systematacially.The results showed that the cumulative methane yield(CMY)of 1%H2S04-treated CS and 4%H3P04-treated CS were greatly inferior to KOH,NaOH,Ca(OH)2,AHP,and SE pretreated CS.The CMY of 1%Ca(OH)2-treated CS was 47.3%and 48.5%lower than 3%KOH-treated CS and 1.5%NaOH-treated CS.The CMY were 177.1,178.6,171.8 mL·gVS-1 from 3%KOH-treated CS,1.5%NaOH-treated CS,and SE pretreated CS at 1.5 MPa for 5 min,which had no significant difference(?>0.05).The highest CMY of 192.4 mL·gVS-1 was obtained after 3%AHP pretreatment of CS,and the methane yield improved by 254.28%than the untreated CS.According to characteristic analysis of pretreatment solution,the results showed that the COD and soluble saccharides of AHP pretreatment were less than that of KOH and NaOH pretreatment,which implied that AHP pretreatment could not only effectively increase the methane yield,but also decrease the loss of degradable organic matters.In this research,the effects of time and temperature in AHP pretreatment on AD of CS were also investigated.In all the AHP pretreatment temperature(room temperature,40 ?,and 60 ?),the CMY of 6h-treated CS had no significant difference(a>0.05)with 12h-treated CS and 24h-treated CS.The results showed that AHP pretreatment worked effectively in the first 6h.In addition,with the increase of temperature and time of AHP pretreatment,the loss of degradable organic matters increased,which was not good for the subsequent AD experiment.In summary,this study systematacially researched on anaerobic digestion process of cotton stalk.The research can provide useful data information for practical application in AD process.It lays a foundation for process development of straw waste into renewable resources.