| Biological conditioning is a new type of conditioning technology.It has the advantages of mild reaction conditions,greatly improved sludge dewaterability and can eliminate the bad smell of sludge cake.In recent years,it has gradually attracted people's attention.However,the current biological conditioning method using elemental sulfur as the main substrate and Thiobacillus as the functional bacteria also has problems such as residual elemental sulfur in the sludge cake and high sulfate concentration,which may bring pollution risks to the environment.In order to avoid the influence of sulfur residue in biological conditioning,this study tried a new method of sludge biological conditioning with calcium nitrate as the biological matrix and denitrifying bacteria as the functional bacteria.The main research conclusions are as follows:By comparing with calcium chloride and potassium nitrate,the improvement of sludge dewaterability by adding calcium nitrate is more significant.After the addition of calcium nitrate,the sludge dewaterability is significantly improved by the Ca2+ adsorption bridge effect and denitrification.The CST and SRF of the treated sludge were reduced to 66.2 s and 0.89×1014 m/kg,respectively.The water content of the sludge cake after suction filtration was 85.2%.The total EPS protein in the sludge is degraded by denitrifying bacteria,which was 83.0% lower than that of the control group.The electron microscope analysis of the sludge before and after conditioning show that the sludge particles were smoother after conditioning,holes and cracks appeared on the surface.It indicated that the denitrifying bacteria destroyed the EPS structure of the sludge during the conditioning process,more bound water was released,and the sludge dewaterability is improved.By investigating the effect on sludge dewaterability under different dosages and different dosage frequencies of calcium nitrate,it was found that when calcium nitrate with a nitrate concentration of 100 mg/g TS was added and added in once,sludge dewatering performance works best.The CST,SRF and water content of sludge decreased by 65%,73.2% and 12.8%,respectively,compared with the control group.The total EPS protein of the sludge after conditioning was reduced by 74.7% compared with the control group,and the sludge became more electrically neutral.Excessive addition of calcium nitrate causes nitrate accumulation,inhibits the efficiency of denitrification reaction,and the effect of improving sludge dewaterability is not obvious.However,the high frequencies and small amount of calcium nitrate added will affect the activity of denitrifying bacteria,thus affecting the conditioning effect of sludge dewaterability.The conditioning effect of electrochemical and ozone pretreatment combined with calcium nitrate on sludge dewaterability was investigated.The results show that electrochemical pretreatment can effectively increase the rate of denitrification,and the removal rate of NO3--N reaches 22.80 mg/?L·h?.The effect of ozone pretreatment to release carbon source is better.After pretreatment,the sludge CST is increased to 473.1 s.After conditioning,the sludge CST can be reduced by 57.1%,and then the sludge is mechanically filtered,the water content of sludge cake reaches 68.2%.It indicates that the pretreatment combined with calcium nitrate can enhance the denitrification reaction and improve the sludge dewaterability.However,due to the release of a large number of organic compounds,the dosage of calcium nitrate needs to be appropriately increased.Finally,the effect of calcium nitrate on sludge dewatering performance under semi-continuous conditions was initially investigated.After setting the hydraulic retention time?HRT?for 4 days,3 days and 2 days respectively,it was found that the denitrification reaction in the system was stable at 4 days and 3 days HRT,the sludge dewaterability was improved.When the HRT is 2 days,the loading of calcium nitrate is too large,and the concentration of NO3--N in the sludge begins to accumulate.Long-term operation will definitely destroy the stability of the system. |
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