| Sewage-sludge is the vice product of the wastewater treatment,which is a kind of organic garbage but as well as a reused resource.The study of reused treatment/disposal mode of sewage-sludge has therefore become a research focus for several decades.In this work presented in the paper,sewage-sludge was treated/disposed by the mixture method of aerobic compost and earthworm compost.Specifically,in the process of aerobic compost,things such as temperature,rate of water content,organic matter,PH,EC and nutritive salt were investigated.Moreover,in the second process,namely earthworm compost,each reactor was added earthworm with the density as 1.5 kg/m2,2.5 kg/m2 and 3.5 kg/m2 respectively.The rate of water content of the compost body was controlled as around 60%.With the purpose of providing technological support of earthworm treatment,those things including physicochemical property,organic matter and heavy metals were studied in our work.Similarly,performance of each reactor was analyzed contrastively.Results obtained in the process of aerobic compost could be summarized as following:(1)For each rector,when the rate of water content was changed from 74% to 49.1%-53.2%,there was a significant reduce in sludge volume.The organic matter fraction decreased from 43.9% to 35.6%,35.1%,35.4 and 35.2% respectively.At the same time,with the increase of temperature,a large number of pathogenic bacteria were killed.Microbe decreased significantly,creating a benign condition for earthworm compost.(2)Similarly,with the passage of reaction time,the value of PH decreased first and then increased,and finally still became a little higher than the initial.Besides,the content of soluble ion decreased,abating the EC of sewage-sludge in every reactor,with reducing amount as about 12.9%.Results obtained in the process of earthworm compost could be summarized as following:(1)After reacting,the PH value of every reactor was 6.8,6.7 and 6.6 respectively,with decrease rate as 9.9%,9.5% and 11.3%.But the PH of control group was 7.3.In general,the value of EC of every reactor rose.Specifically,every rector’s EC increase increasingly during the first forty days,and reached the maximum value on the fortieth day,at 1.09 ms/cm,1.08 ms/cm and 1.19 ms/cm respectively,with increase rate as 34.9%,43.7% and 44.3% respectively.In the late stage of treatment,the decrease of EC became slowly but still kept higher than the control group,whose value was 0.92 ms/cm.The earthworm treatment could advance the content of dissolve ion in sludge.(2)The degradation of organic matter was conducted by the interaction of earthworm and microbe.After earthworm treatment,the organic matter of each reactor decreased to 29.4%,27.1% and 28.6% respectively,with the decrease rate as 16.3%,23.5% and 18.8% respectively.All were higher than the control group,whose degradation rate was 7.8%.There was a significant difference of degradation between reactors with different earthworm density,and the degradation rate of the reactor V2 was the highest among all.(3)After earthworm treatment,the decrease rate of TN content of each reactor was 20.0%,25.2% and 27.1% respectively,while the decrease rate of TP was 10.6%,16.4% and 18.1% respectively.Thus,the earthworm treatment has a great effect on the TN removal but has a weak effect on the removal of TP.Different earthworm density has a significant effect on the TN removal.Considering cost,the earthworm density of the V2 rector,namely 2.5 kg/m2,may be the best density which could be applied.(4)On the removal of Cu,Zn and Pb in earthworm treatment,there was only absorption,not accumulation.The content of Cu in reactor V1,V2 and V3 decreased to 157.25 mg/kg,146.15 mg/kg and 138.75 mg/kg respectively,with decrease rate as 15.1%,21.1% and 25.0% respectively.The content of Zn in reactor V1,V2 and V3 decreased to 914.13 mg/kg,867.75 mg/kg and 809.91 mg/kg respectively,with decrease rate as 20.1%,25.0% and 30.1% respectively.The content of Pb in reactor V1,V2 and V3 decreased to 59.35 mg/kg,54.02 mg/kg and 51.31 mg/kg respectively,with decrease rate as 12.1%,20.0% and 24.0% respectively.Therefore,earthworm has the stronger absorption of Zn while has weak absorption of Pb.And the absorption of Cu is moderate.There was a close relationship between earthworm addition and heavy metals removal.Considering the heavy metals removal,the best earthworm density may be is 2.5kg/m2.(5)The killing rate of bacteria in each reactor was 97.0%,98.8% and 97.7% respectively while that of the reactor was only 78.1%.The killing rate of fecal coliform was 100% in every reactor except the control group,whose killing rate of fecal coliform was 90.8%.Consequently,earthworm compost could effectively reduce the amount of pathogenic microorganism in sludge,promoting stabilization and harmless effect of sludge. |
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