Improving biomethane yield by strengthening acidification of maize stover in two-phase anaerobic digestion

In this study,the acidification and two-phase anaerobic digestion(AD)were conducted in batch and continuous stirred tank reactors,respectively,to determine the effect of acidification on methane production in AD.The results showed that two-phase AD achieved an observable enhancement in the methane production under optimal acidification conditions(organic loading rate of 60 g TS/L,the ratio of raw material to inoculum(based on dry weight)of 2:1,the temperature of 45℃,urea concentration of 4%,and time of 6 d).Under these conditions,the daily biogas and biomethane productions were 0.48 L/g TS and 0.30 L/g TS,respectively,which were 26.32%and 57.89%higher than those of the untreated group,respectively.The ammonia nitrogen(AN),alkalinity,and pH value of the methanogenic phase of C4 continued to increase up to 956 mg/L,5680 mg/L,and 7.41,respectively,after 60 d,which might have destroyed the stability of the system.Therefore,for the purpose of reusing the nitrogen source,reducing AN,and maintaining the stability of the reaction system,another set of acidification and two-phase AD with water pretreatment using the discharge of the methanogenic phase of C4 as the inoculum was subsequently conducted.The results showed that the daily biogas productions of single-phase and two-phase AD were 5.26%and 15.79%higher than that of the untreated group,respectively;similarly,their daily methane yields were 10.42%and 21.05%higher than that of the untreated group.

Experimental study on specific grinding energy and particle size distribution of maize grain,stover and cob

Reducing the particle size of biomass is of great significance for rational and efficient utilization of biomass.In this study,maize grain,stover,and cob were comminuted at different speeds(2000-2800 r/min)by hammer mill with a mesh size of 2.8 mm.The mechanical energy for smashing three selected samples was obtained directly through the sensor and data testing system.Experimental results demonstrated that the maize cob had the highest total specific energy while the maize grain had the lowest(135.83-181.10 kW·h/t and 27.08-36.23 kW·h/t,respectively).In addition,for the same material,higher hammer mill speed generated more specific energy consumption.And the effective specific energy of maize stover had a similar trend to the total specific one.However,the effective specific grinding energy of maize cob and grain increased initially and then decreased with the increase of rotating speed.The fitting curves of the specific energy to mill speeds were determined,and the range of determination coefficients of the regression equation was 0.933-0.996.Particle size distribution curves were drawn by sieving the pulverized particles of the three samples based on a series of standard sieves.Fourteen relevant parameters characterizing the particle size distribution were calculated according to the screening data.Calculation results demonstrated that larger rotational speed leads to smaller particle sizes.Combining the size parameters,distribution parameters,and shape parameters,it was found that the distributions of the three samples all exhibit a distribution of“well-graded fine-skewed mesokurtic”.The Rosin-Rammler function was considered to be suitable for characterizing the particle size distribution of maize grain,stover,and cob particles with a coefficient of determination between 0.930 and 0.992.