Studies On Combustion Characteristics And Pollutants Emission Of Sewage Sludge Conditioned With Fenton/CaO

With advancement of urbanization,amount of sewage sludge is produced in sewage treatment.If mishandled,the sewage sludge will become secondary pollution.The deeply dewatering of sewage sludge will create advantageous condition for the disposal,deeply dewatering sewage sludge will become the main object of sludge disposal.Sewage sludge incineration with the advantages of volume reduction,stabilization,harmlessness and energy recovery,is considered to be the important way among the methods of sludge disposal.Therefore,the study of the effects of conditioning agents on the incineration of deep dewatering sludge has become a hot topic.Firstly,in this paper,Sewage sludge were conditioned with Fenton's reagent/lime in three different dosages(Fe²⁺/H₂O₂/Ca²⁺=30/30/70 mg/g dry solids,Fe²⁺/H₂O₂/Ca²⁺=50/30/100 mg/g dry solids,Fe²⁺/H₂O₂/Ca²⁺=70/30/100 mg/g dry solids)and then dewatered through the ultrahigh pressure filtration system.And the four deep dewatering sludges were respectively named as S0,S1,S2 and S3.The results indicated that the water content of three conditioned sludge cakes were respectively 51.26%,46.25%and 44.73%,which meet the needs of sewage sludge's deeply dewatering.After conditioning,the volatile matter and fixed carbon in the sludge reduced significantly while the ash content is increased;the content of sulfur in sludge increased,while the content of carbon,hydrogen and nitrogen reduced,and the heat value dropped significantly.XPS analysis showed that sulfate,sulfone,sulphoxide,aromatic sulphur,aliphatic sulphur and mercaptan were the main sluphur functionalities in the sludge.After conditioning,the content of sulfate increased,while the organic sulfur was decomposed or converted into a more stable form.Inorganic ammonium nitrogen,protein nitrogen and heterocyclic nitrogen?pyrrole and pyridine?were the main nitrogen functionalities in the sludge.After conditioning,the content of the four forms of nitrogen reduced.Secondly,effects of Fenton/Ca O dosage and heating rate on the combustion characteristicsofdeeplydewateredsewagesludgewereinvestigatedby thermogravimetric analysis?TG-DTG?.Then calculated the parameters of combustion kinetics and established the kinetic equation of each sludges sample.The results indicated that three degradation stages,i.e.dehydration,combustion of volatile and combustion of the fixed carbon were identified in the combustion process of the conditioned sludge.Compared with raw sludge,burnout index C_b of S2 and S3 decreased slightly,while C_b of S4 was increased,which implied that sludge's conditioning at the largest dosage?S4?was helpful for the burnout of sludge.Volatile releasing index D of three conditioned sludges increased by 1.1,1.97,1.73 times respectively,which showed that sludge's conditioning with Fenton/Ca O was helpful for the initial combustion.However,flammability index C and the comprehensive combustion index S decreased respectively by 0.78-0.95 times and 0.52-0.75 times,which implied that sludge's conditioning with Fenton/Ca O reduced the overall combustion performance of sludges.Among three conditioned sludges,the combustion characteristics?D/C/S?of S3 were the largest,which implied that sludge's conditioning with an appropriate dosage was favorable for combustion.The mass average apparent activation energies of sewage sewage and three conditioned sludges were calculated with Ozawz-Flynn-Wall method and Kissinger-Akahira-Sunose method.It was found that,compared with raw sludge,the mass average apparent activation energies of conditioned sludges during stage?(E_m1)decreased,while the mass average apparent activation energies of these during stage?(E_m2)increased.Overall,the mass average apparent activation energies of these during the whole combustion process?E_m?decreased,and E_m of S3 was the lowest among conditioned sludges.Finally,using a laboratory tube furnace to study SO₂ and NO_X emission characteristics of the deeply dewatering sludge in incineration.The results indicated that as the temperature from 500?to 1000?,the SO₂ emission presented a gradually increasing trend.The NO_X emission increased from 500?to 600?and declined from600?to 1000?.For SO₂ emissions,at 600-800?,the SO₂ emission of conditioned sludges was lower than those of raw sludge.However,at 800-1000?,the SO₂ emission monotonically increased as the composite conditioner increased.For NO_X emission,the average NO_X concentration monotonically increased at 600-700?,while monotonically reduced at 800?as the composite conditioner increased.At 900-1000?,the NO_X emission order followed as:S3>S1>S2>S0.Compared to N₂/O₂ atmosphere,conditioning sludge combustion under an 80%CO₂/20%O₂ atmosphere might simultaneously reduce the SO₂ and NO_x emissions,and the effect of De-NO_X was obvious.Besides,as the oxygen concentration increased,the SO₂ and NO_X emission also increased.