| Sewage sludge could be used as an agricultural organic fertilizer after vermicomposting,as it's riched in various nutrients,such as nitrogen,phosphorus,potassium,etc.It is crucial to study on the transformation of nitrogen in soil after adding dissolved organic matter(DOM),since a great quantity of DOM will be fertilized into soil with the application of treated sludge,which may bring about strong effect on nitrogen circulation system.In this paper,the changes of DOM in sewage sludge treated witheisenia faetida were studied using molecular weight grading,polarity separation and spectroscopy.After that,the effects on nitrogen indexes and properties of soil,caused by tyrosine and glucose,which were typical in DOM,were analyzed.Meanwhile,the potential nitrification rate(PNR)of soil was monitored during incubation,and the effects of exogenous organic matters on the abundance of amoA genes in soil was analyzed by real-time fluorescence quantitative PCR.The data of exogenous organic matter test is very meaningful,thus an effective basis can be provided for land application of sludge.The main conclusions of this study are as following:(1)The results of dissolved organic matter(DOM)in sewage sludge before and after vermicomposting showed that content of DOM in treated sludge below 300Da increased after vermicomposting,6.5%higher than that of control sludge,but components above 8000Da reduced 56.3%.Meanwhile,the proportion of hydrophilic component in treated sludge was 50.8%higher than that in control group.The spectrums analysis indicated that the experimental sludges contained carboxylic acid,aromatic substance,etc.After vermicomposting,the contents of polysaccharide and aromatic compounds in DOM increased,with protein and molecular weight decreased.Fluorescence spectras showed that the original sludge contained a large number of proteins and humus,produces tryptophan,tyrosine,glucose and other substances after 120 days' degradation,and humification of treated sludge is higher than that of control sludge.DOM concentration of treated sludge was smaller and the degradation rate was faster.Based on the above analysis,tyrosine and glucose were selected,which were typical components in treated sludge,as the exogenous organic matter for the following nitrogen transformation test in(2)It was found that the application of wormcast could improve fertility and electrical conductivity of soil significantly,compared with the soil without wormcast(BK).The addition of tyrosine inhibited the mineralization in soil,while glucose promoted the mineralization.Adding tyrosine and glucose inhibited the nitrification in soil,and the inhibitory effect of glucose was 62.2%higher than that of tyrosine.There were significant differences in soil mineralization and nitrification rates between different components and different dosages of earthworm manure.Adding organic matters can reduce the leaching loss of nitrate,preventing nitrogen loss from soil.(3)The results of PNR and AOA,AOB amoA gene copies numbers revealed that exogenous organic matter could significantly inhibit soil potential nitrification rate,meanwhile,there was a significant positive correlation between PNR and mineralization in soil(P<0.05),but not for nitrification rate.The amoA gene abundance of AOA was higher than that of AOB in soil,and addition of organic matters could significantly promote the transcription level of ammonia oxidation proces.AOA and AOB of the glucose group showed similar trends,while the tyrosine group did not.In tyrosine group,AOA and AOB were significantly correlated with the nitrification rate and the amount of tyrosine,but in glucose group,there was a significant positive correlation only among AOB and mineralization,PNR and so on.In addition,the significant differences of PNR inhibition rates and amoA gene copies numbers were found between soil samples with different doses of exogenous organic matters(P<0.01). |
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