Study Of Solid-state Anaerobic Digestion Characteristics Of Pig Manure In Different Control Measures

With the continuous development of pig industry in China,pig manure?PM?has become one of the most serious sources of environmental pollution.PM contains a large amount of readily biodegradable organics,which can be converted into biogas with high methane content efficiently by anaerobic digestion.At present,there are two kinds of anaerobic digestion—solid-state anaerobic digestion?SS-AD?and wet anaerobic digestion.And compared with wet anaerobic digestion,SS-AD has advantages of water conservation,convenient management and low energy consumption in winter.After the digestion,substrate contains low water and can be easily treated,thereby achieving zero emission.Under the condition of increasingly scarce water resource in the global,this technology conforms to the demand of resource utilization and water conversation.However,the process of SS-AD is very complex and the SS-AD of PM can easily result in serious acid inhibition for the low water content,so the reaction of SS-AD can not proceed normally,or even be ceased.This study was mesophilic batch fermentation under same temperature?37°C?and water content?80%?condition.To investigate the most efficient treatment of starting the fermentation and the variations of methane production and volatile fatty acids?VFAs?,mono-PM SS-AD,adding vermiculite,co-digestion of PM with maize straw?MS?,leachate recycling and layered seeding were carried out.Ammonia nitrogen and soluble chemistry oxygen demand?SCOD?were analyzed.The results are as follows:1.In the first experiment,it can be concluded that layered seeding can start the fermentation quickly and shorten fermentation time.The highest cumulative specific methane yield?SMY?was 139.2 mL CH₄/g VS in 56 days.Leachate recycling can accelerate mass transfer rate and decrease volatile fatty acids?VFAs?concentration significantly.During the experiment,the concentration of total volatile fatty acid?TVFA?was around 0.66 mg/g in SS-AD of leachate recycling,and the cumulative SMY was 16.7%lower than the SS-AD of layered seeding.Adding vermiculite can decrease VFAs concentration in a certain degree and attain higher methane production.However,the efficiency of methane production was poor.The SS-AD of mono-PM was inhibited seriously at the first 22 days of the fermentation,and barely produced methane.In the treatment of co-digestion of PM and MS,in which substrate was mixed homogeneously with inoculum,the highest TVFA concentration was 19.08 mg/g,and SMY in the first20 days was around 0.1 mL CH₄/g VS/d.2.In the second experiment,water content of vermiculite was almost zero,and free-water content was high,which may lead to the increase in mass transfer rate and reproduction rate of microorganisms.In this way,the fermentation can proceed smoothly.In SS-AD of layered seeding,leachate recycling and the treatment of the combination of these two treatments,methane productions had no significant difference compared with the control group.In the SS-AD of leachate recycling,the cumulative SMY in38 days was 212.0 mL CH₄/g VS,which was the highest compared with the other treatments.The lowest cumulative SMY was 192.9 mL CH₄/g VS in 38 days in the SS-AD of the combination of leachate recycling and layered seeding.TVFA concentration was lower than 1.24 mg/g in this experiment.Because of high free-water content,layered structure can be easily destructed,so layered seeding is not suitable for the SS-AD of adding vermiculite.Compared with the first experiment,layered seeding is more suitable for the SS-AD of PM with MS.3.In the third experiment,it is concluded that the height of layers and the size of contact area of substrate and inoculum were two important factors in the expanded experiment.Without taking these two factors into account in this experiment,methane production was not meet expectation.In the SS-AD of layered seeding,the cumulative SMY in 36 days was 126.7 mL CH₄/g VS,which was 17.8%lower than the SS-AD of mono-PM and 12.6%lower than the SS-AD of PM and MS.