Extraction Of Heavy Metal In Municipal Sludge With Chemical And Physical Method And Modality Heavy Metal

With the acceleration of urbanization , urban sewage treatment rate hasincreased annually , and municipal sewage sludge also increased dramatically.Most municipal sewage sludge is rich in organic matter, nitrogen and phosphorusand other nutrients, which is valuable to be reused. But because there is more orless heavy metal in sludge, resource recycling of sludge is limited. Therefore,how to remove heavy metals in sludge effectively becomes key point to maketreatment and disposal and resource utilization of the sludge.This paper studied the chemical methods to remove six heavy metal in sludgeand affecting elements , with the filter-pressing sludge as the experimentalsample.Besides, based on experiment above, we got a kind of compound reagentto achieve better extracting rate. With the microwave and ultrasonic methods, weconducted its effect on the extracting result of compound reagent. Under thecondition of selected microwave and ultrasonic time and power, we do experimentto analysis how the microwave-intensified and ultrasonic-intensified compoundreagent to affect the heavy metal speciation fraction in sludge.By the range analysis of orthogonal experiment result , we studied theinfluence of selected elements. The type of extracting reagent affect mostobviously, secondly extracting time, thirdly solid/liquid ratio. For the process ofextracting heavy metal in sludge , pH is the most importang affecting element.Extracting effect decreased with pH rising. For the acidification of inorganic acid,the extracting result is remarkable in the range of pH 1~2.Extracting rate of low molecular weight organic acids was stable to themaximum in the concentration of 0.1mol/L. Oxalic acid is better than other lowmolecular weight organic acids in extracting capability. Extracting rate of highmolecular weight organic acids was stable to the maximum in the concentration of 0.1mol/L. And HEDTA was better than other high molecular weight organic acids inextracting capability. Solid-liquid ratio affecting on the extracting result of heavymetals lies in the impact of the mass transfer. In experimental range , the bestsolid-liquid ratio was 1:50 (g/mL).Under the extraction time of 8 hours , theextracting effect of each metal achieved better results.Orthogonal Experiment results of complex reagent showed that the 5thcompound reagent can achieve the highest average extracting rate of 67.35 %, inthe composition of pH 3.5, oxalic acid concentration of 10mmol/L, HEDTAconcentration of 75 mmol/L, ammonium nitrate concentration of 2 mmol/L.Microwave can strengthen compound reagents with energy in order to improvethe extracting rate, but the effect on various metals is different. In the experimentalrange,the best time of microwave was 13min,the best microwave power was 539W.Ultrasonic had synergistic effect on extracting process of the compound reagent.The best time was the 660s,when the power is 125W,achieving the best synergy.Heavy Metals speciation has significant influence for the extracting agent ,and the species distribution of heavy metals changed in sludge after the compoundreagents extracted. Seen from the experiment , the percentage of organic phasedeclined, the proportion of ion-exchange and carbonate increased. For each step ofT-SEP extraction, microwave and ultrasound enhancement was different, mainlyinfluenced the organic groups in sludge, and proteins and fulvic acid and humicacid.which composed of extracellular polymers.