| Heavy metals in sewage sludge used for land application can be accumulated and be released in the soil environment, which caused serious environmental risks. So chemical extraction procedure was applied for removal of heavy metals from sewage sludge and ultrasound / microwave radiation was used to improve the chemical extraction rate of heavy metals for the safe land application of sewage sludge.A four-step sequential extraction procedure was used to investigate the heavy metal speciation in sludges from different stages of wastewater treatment process and from dewatered room of different wastewater treatment plants. The relationship between Water soluble, acid soluble, reducible, oxidisable, and residue fraction and sludge physiochemical properties was studied. The potential environmental risks heavy metals in sludges were evaluated.Total heavy metal in sludge is much higher than background value in the black soil, which is a potential risk to the environment. Cu, Zn, Cd, Mn in sludge has a serious pollution risk. Cu, Pb, Cr in sludge poorly migrate in soil environment, however Zn and Mn have strong mobility. Pb distribution in sludge has no changes during the wastewater treatment procedure, Ni has opposite change, Cd mainly exists in the organic form. Water soluble, acid soluble, reducible fraction of Pb and Al have positively related to physiochemical properties, water soluble, acid soluble, reducible fraction of Cu, Cr, Mn, Cd, Ni positively related with organic content in sludge.Chemical removal procedure indicated that the type of chemical agents used in extraction procedure is a key factor for removal of heavy metals from sludge, extraction time and solid-liquid ratio are also important factor for achieving high heavy metal extraction rate. 1:50 is an optimal solid-liquid ratio and 8h is an optimal extraction time for chemical extraction procedure. Extraction rate of heavy metals with organic acids are higher than extraction rate with organic acids, chelating agents, inorganic salts, increasing with decreasing pH. Oxalic acid is better than citric acid, succinic acid, aspartic acid on removal of heavy metals from sludge. HEDTA is better than EDTA and DTPA for extraction of heavy metals. Inorganic salts have low removal rate of heavy metals. The mixed agents of HEDTA and oxalic acid are better than a single reagent to remove heavy metals from sludge.Microwave / Ultrasound assisted chemical removal procedure presented that Heavy metal removal rates of them increase by increasing of radiation time and power density. Microwave / Ultrasound radiation on chemical extraction at high power density is more effective than it is at low-power-density. In the same energy density, long time and low power density radiation rate is better than a short time and high power density radiation rate on heavy metal extraction. The maximum removal rate of heavy metals at 7.7 W/mL can be achieved after 180s microwave radiation, the order of individual heavy metal removal rate is Zn > Ni > Cu > Mn > Cd > Cr > Pb. Microwave radiation have no further effects heavy metal removal when the energy density reached 1260 J/mL. The maximum removal rate of heavy metals at 2.5 W/mL ultrasound energy density can be achieved after 660sultrasound radiation, the order of individual heavy metal removal rate is Zn > Cu > Ni > Mn > Cd > Cr > Pb. ultrasound radiation have no further effects heavy metal removal when the energy density reached 1350 J/mL. Magnetic stirring on heavy metal removal procedure can enhance the rate of extraction with ultrasound radiation.Organic matter infrared and fluorescence characteristics and heavy metal speciation distribution in untreated sludge, microwave treated sludge and ultrasound treated sludge before and after four steps sequential extraction procedure showed that water soluble, acid soluble and reducible fraction of Cu, Zn, Cd, Mn, Cr, Ni were extracted from sludge, and Cd and Pb was resorbed by dissolved organic matter. Microwave / ultrasound treatment can change the group of original sludge; water soluble heavy metals are complexed with -OH groups of water-soluble alcohol and phenol; acid soluble heavy metals mainly exists in form bound with inorganic carbonate, partly existed in form bound with unsaturated olefins in ultrasound treated sludge; reducible heavy metals mainly were bound with C-O and C-N groups of organic matters; oxidisable heavy metals were complexed with direct paraffin and–OH groups between phenolic molecules. Dissolved protein, humic acid, fulvic acid substances were extracted by microwave / ultrasound assisted chemical extraction procedure. Water soluble heavy metals are bound with–OH groups of fulvic acid and humic acid matter in sludge; acid soluble heavy metals were wrapped in denatured protein matters; reducible heavy metals were bound with C-O and C-N groups of in fulvic acid / protein substances; oxidisable heavy metals were bound with -CH2- and OH groups of humic acids / protein substances.Ultrasound radiation for improving the HEDTA-Oxalic extraction rate of heavy metals from sludge is more effective in 0-900 and 1350-1800 J/mL, microwave radiation is better than ultrasound radiation in 975-1275 J/mL, Ultrasound treatment has similar effects on heavy metal extraction with microwave treatment in 900-975 and 1275-1350 J/mL. Ultrasound and microwave treated sludge have high nutrient content and showed potential agricultural application value. Mobile fraction of Cu, Zn, Mn, Cr and Ni in sludge was extracted, which shows the low mobility in soil environment. The risk degree of potential accumulated environment from heavy metals in sludge is lowed to moderate level. Heavy metals can inhibit vegetables grown, inhibition of heavy metals in microwave treated sludge is strong at low sludge fertilization, and inhibition of heavy metals in ultrasound treated sludge is strong at high sludge fertilization. Sludges after microwave and ultrasound assisted HEDTA-Oxalic extraction of heavy metals can be safely utilized in sludge land application.
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