| Ammonia and acid inhibition is a highlighted issue involved in the anaerobic digestion(AD)of high ammonia nitrogen and high organic load waste.This will cause a series of problems in AD,such as system instability,low operating efficiency,methane quality degradation,and prolonged AD periods.In this study,carbon-based ferromagnetic biochar was prepared under the pyrolysis temperatures of 300?,500?,and 700?by precipitation and soaking processes.Based on this,methanogenesis characteristics and metabolic mechanism of AD in high loads substrates mediated by carbon-based ferromagnetic biochar were carried out.And the experiments were conducted to:(1)Study the physical and chemical characteristics of ferromagnetic biochars,and select one which can significantly promote AD;(2)Reveals the mechanism of removing ammonia and acid inhibition by ferromagnetic biochar in AD system with high ammonia nitrogen load.(3)Explore the characteristics and mechanism of ferromagnetic biochar mediated methanogenesis in AD system with high organic load;(4)Investigate the effect of ferromagnetic biochar addition on the structure succession of microbial community in AD system with high organic load.The results showed that:(1)With the increase of pyrolysis temperature,the yield of biochar shows a downward trend,the BET specific surface area and total pore volume of BJH increase,and the average pore size decreases.The loading rate of iron deposits on PBC-Fe prepared by the dipping method is from 8.47%?22.89%,which is higher than the loading rate(3.69%?17.19%)on BC-Fe prepared by the precipitation method;The BET specific surface area of carbon-based ferromagnetic biochar(16.8906?133.6287m~2/g)is significantly larger than that of original biochar(4.8601?6.9150 m~2/g).500BC-Fe has a total pore volume of BJH(0.2167 cm3/g)which is 10 times higher than that of original biochar 500BC;The adsorbed ability of ammonia-nitrogen by biochar is between 2.01mg/g?9.23mg/g.Most of the biochar reaches the equilibrium of ammonia-nitrogen adsorption within 20min.In the 300PBC-Fe group,the adsorption of ammonia-nitrogen is mainly concentrated in the period of 20min-40min.The ammonia-nitrogen removal rate of 300PBC-Fe is 18.79%.(2)Under high ammonia nitrogen loading,the addition of ferromagnetic biochar can accelerate the conversion of organic matter into acetic acid in AD,increase the yield of acetic acid,and accelerate the decomposition rate of acetic acid.Also can improve propionic acid metabolism and alleviate the accumulation of propionic acid effectively.The addition of ferromagnetic biochar promotes the rapid decomposition of butyric acid into acetic acid,prevent butyric acid accumulation.Under a high ammonia nitrogen loading of 1400mg/L,500PBC-Fe added group has an average acetic acid metabolic rate of 162.9 mg/L·d.The average metabolic rate of propionic acid in 500PBC-Fe added group is 63.9 mg/L·d.The average metabolic rate of butyric acid in 500PBC-Fe added group is 60.9 mg/L·d.Under the high ammonia nitrogen loading,the time for methanogenesis stage is overall delayed.The addition of ferromagnetic biochar improved the stability of the AD system significantly,reduced the negative impact of high ammonia nitrogen loading on methane production,maintain a high methane yield,and accelerated the methanation process.The 500PBC-Fe group has up to a peak methane production of 235.5 Nm L/day,the cumulative methane production is 1159.9 Nm L,and the methane volume reaching 80%of the total methane production on the 9th day of AD.(3)The addition of ferromagnetic biochar can effectively alleviate the ammonia and acid inhibition caused by the intermediate metabolites in AD with high organic load,enhance the buffer capacity of digestion liquid,improve the degradation ability of organic substrates,and improve the utilization efficiency of fermentation raw materials;In the AD,the ammonia nitrogen removal rate of the ferromagnetic biochar added group was21.7%-23.7%,the COD removal rate was 64.88%-66.75%,the TS degradation rate was29.35%-35.14%,and the VS degradation rate was 53.78%-60.64%.The p H value is maintained steadily in the range of 6.5-7.2;In the AD of high organic load,the ferromagnetic biochar produced by the pyrolysis impregnation method at 500°C(500PBC-Fe)added group can significantly increase methane production,improve methane quality,increase methane production rate,and shorten AD time to accelerate the methanation process.The cumulative methane production was 3927.1Nm L,the average methane content was 157.1Nm L/day,the peak methane content was 390.2 Nm L/day,and the AD period(25d)was 28.6%shorter than that of the group without added biochar(35d).(4)In the 500PBC-Fe addition group,the methanogenesis efficiency(98.4%)and the biochemical methane potential(96.9m L/g·VS)had been improved significantly.Modified Gompertz and Logistic kinetic equations are used to predict the methane production of AD with high organic load.The results agreed that the addition of 500PBC-Fe could significantly promote the raw material utilization in high organic load AD,improve methane quality,increase methanogenesis rate,shorten methanogenesis retention time and AD time.Modified Gompertz equation curve fitting regression analysis shows R~2 value is 0.9970,the relative deviation between the predicted result and the measured result was 8.2%.The R~2value of the Logistic equation curve fitting result is 0.9964,and the relative deviation between the predicted result and the measured result was 2.3%.The accuracy of prediction results by Logistic equation is 6.0%higher than that of Modified Gompertz equation.(5)Based on 16S r RNA high-throughput sequencing technology,the microbial communities were analyzed in terms of abundance and diversity,composition,differences,and phylogeny.The evolution and phylogeny mechanism of bacteria/archaea on 500PBC-Fe from time and space dimensions were studied and discussed.The addition of 500PBC-Fe reduces the complexity of the bacterial community during the period of peak gas production in AD,and strengthens the enrichment of dominant bacteria;The diversity of archaea increases,and the structural stability of microorganisms was strengthen;500PBC-Fe mediated promote the enrichment of iron reducing bacteria(IRB)like Clostridium?sensu?stricto?1,and strengthen the nutrition metabolism between IRB and methanogens;Methanosarcina and Methanobacterium are more prefer to enrich in500PBC-Fe surface,and Methanosaeta and Methanobrevibacter are apt to enrich in areas with loose surface structures such as anaerobic sludge added with carbon-based ferromagnetic biochar.At the same time,addition of 500PBC-Fe can enrich the type of metabolism of the AD system,which change from single acetic acid utilization AD to the conversion of two types of methane conversion coexisting with acetic acid utilization and hydrogen nutrition. |
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