Effect Of Iron And Nickel Salt On The Anaerobic Co-Digestion Of Cow Dung And Phragmites Australis

In this study, the mixture of phragmites australis-cow dung as raw material for fermentation, and the anaerobic fermentation experiments adding with metal salt were conducted under the medium temperature35℃conditions. The influence of metal salt on biogas properties, pH, organic matter degradation and enzyme activities of fermentation were researched, and the mechanism of metal salt on anaerobic fermentation was discussed preliminary. The results showed that:(1) Adding ferrous salt and nickle salt both could promote the arrival of the peak gas production and increase the cumulative biogas yield,10.0mg Fe/L treatment group gained the highest cumulative gas yield32.46mL/gTS, and0.8mg Ni/L treatment group received the highest cumulative gas yield32.70mL/gTS,1.0mg Fe/L and2.0mg Ni/L treatment groups obtained their highest methane content in the first eight days of fermentation67.91%and76.77%, respectively.(2) In the process of anaerobic fermentation, the pH value firstly increased then decreased, then increased again, and adding metal salt had no significant effect on pH value.(3) The forth day of fermentation, iron salt showed inhibition on COD, and promoted cellulase and dehydrogenase activity, and had adverse effect on protease activity; iron salt also showed inhibition on COD, and iron salt had no effect on cellulase, and played an inhibation role on protease activity and positive role on dehydrogenase activity.(4) The eighth day of fermentation, iron salt still showed inhibition on COD, and showed positve effect on cellulase and protease activity, and have inhibition effect on protease activity; the low concentration of nickel salt had positive effect on COD and protease activity, but high concentration had inhibiting effect, and nickel salt promoted the acitivity of cellulase and had no effect on dehydrogenase activity.(5)The thirteenth day of fermentation,1～5mg Fe/L significantly reduced the COD content, and ferrous salt had no effect on cellulase activity, the low concentration of ferrous salt had positive effect on protease and dehydrogenase activity while high concentration had adverse effect; the influence of nicke salt on COD is not significant, and nicke salt played a positive role in promoting cellulase and protease activity, and have adverse effect on dehydrogenase activity.(6) At the end of fermentation, the influence of ferrous salt and nicke salt on organic content and enzyme activity was same, namely, ferrous salt and nicke salt had inhibition on COD and cellulase activity, and had no effect on protease activity, and promoted dehydrogenase activity.Iron salt promoting the activity of cellulase and dehydrogenase was the main reason of enhancing biogas production during the start-up stage of fermentation, while nickel salt was mainly to promote the effect of dehydrogenase ctivity; Iron and nickel salt had positive effect on ellulase and protease activity that was the main reason of metal salt treatment group improving the efficiency of biogas production at gas production peak stage. Adding metal salt had important meaning in improving the efficiency of co-digestion of phragmites and cow dung anaerobic fermentation. This study had guiding significance in practical application of biomass fermentation technology.