Thermochemical pretreatment of meat and bone meal and its effect on methane production

Since the solubilization of meat and bone meal(MBM)is a prerequisite in many MBM disposal approaches,enhancement of the solubilization by means of thermochemical pretreatment was investigated in this study at two temperatures(55℃and 131℃)and six sodium hydroxide(NaOH)concentrations(0,1.25,2.5,5,10 and 20 g/L).The MBM volatile solid(VS)reduction ratio was up to 66%and 70%at 55℃and 131℃,respectively.At the same temperature,the VS reduction ratio increased with the increase in the dosage of NaOH.The study on the methane(CH4)production potential of pretreated MBM shows that the addition of NaOH at 55℃did not cause the inhibition of the succeeding CH4 production process.However,CH4 production was inhibited by the addition of NaOH at 131℃.The CH4 production potential was in the range of 389 to 503 mL CH4/g VS MBM and 464 to 555 mL CH4/g VS MBM at 55℃and 131℃,respectively.

Elevated atmospheric CO_(2) reduces CH_(4)and N_(2)O emissions under two contrasting rice cultivars from a subtropical paddy field in China

Elevated CO_(2)(eCO_(2))and rice cultivars can strongly alter CH_(4)and N_(2)O emissions from paddy fields.However,detailed information on how their interaction affects greenhouse gas fluxes in the field is still lacking.In this study,we investigated CH_(4)and N_(2)O emissions and rice growth under two contrasting rice cultivars(the strongly and weakly responsive cultivars)in response to eCO_(2),200μmol mol^(-1)higher than the ambient CO_(2)(aCO_(2)),in Chinese subtropical rice systems relying on a multi-year in-situ free-air CO_(2)enrichment platform from 2016 to 2018.The results showed that compared to aCO_(2),eCO_(2)increased rice yield by 7%-31%,while it decreased seasonal cumulative CH_(4)and N_(2)O emissions by 10%-59%and 33%-70%,respectively,regardless of rice cultivar.The decrease in CH_(4) emissions under eCO_(2)was possibly ascribed to the lower CH_(4)production potential(MPP)and the higher CH_(4)oxidation potential(MOP)correlated with the higher soil redox potential(Eh)and O_(2)concentration([O_(2)])in the surface soil.The mitigating effect of eCO_(2)on N_(2)O emissions was likely associated with the reduction of soil soluble N content.The strongly responsive cultivars had lower CH_(4)and N_(2)O emissions than the weakly re sponsive cultivars,and the main reason might be that the former induced higher soil Eh and[O_(2)]in the surface soil and had larger plant biomass and greater N uptake.The findings indicated that breeding strongly responsive cultivars with the potential for greater rice production and lower greenhouse gas emissions is an effective agricultural practice to ensure food security and environmental sustainability under future climate change scenarios.