| Sludge, as by-product of sewage treatment plant, is discharged increasingly with population growth and urbanization. The fate of sludge includes exhausting and agro-utilization. The former such as landfilling, incineration are applied and forbidden decreasingly because of environmental pressure and resources waste. Oppositely, the agro-utilization is used increasingly, because that it not only effectively makes use of nutrients but also has low expenditure and large treatment amounts. Agro-utilization includes two methods, one is directly applying sludge to farmland after being simply treated, and the other is manufacturing organic or organic-inorganic complex fertilizers. These treatments have become problematic because heavy metals in sludge may enter into environment and potentially posing a threat, consequently, it is essential to remove heavy metals from sludge by means of physical, chemical and biological methods.Chemical agents are being employed widely for its quickly effect and maneuverability. Many attentions have been paid to the leaching of chemical agents such as strong inorganic acids, organic acids and chelators in the past decades. However, there are little reports about combination agents, especially using surfactants to enhance remediation of chelators. The chelators-enhanced extraction of heavy metals from contaminated soils by surfactants has become increasingly interest. Considering the comparability of sludge to soil, it is feasible to extracting heavy metals from sludge by chelators and surfactants, too.Firstly, the security of heavy metals was evaluated within four sorts of sludge, while the efficiency of removal of heavy metals by agents was assessed, and then the standards and the evaluation system of chemical method were suggested. Secondly, the simulated leaching and surging experiments were conducted to determine the removal of Cd, Cr from sludge by several agents solely or jointly. Finally, the nitrogen lost and forms of Cd, Cr were investigated contrastively among treated sludge, aiming to provide scientific basis for proper agro-utilization of sludge.The raw sludge, activated sludge, I - anaerobically digested sludge and II - anaerobically digested sludge were sampled from the Tiangjiaqiao sewage plant in Chongqing. At the base of heavy metals' detection of several kinds of sludge, the security of sludge was assessed bymonomial index and Nemerow index according to GB4284-84. The result showed as follows: the heavy metals were enriched gradually in the order of II - anaerobically digested sludge > I -anaerobically digested sludge > activated sludge > raw sludge. Although the content of heavy metals was below the national standard, the cadmium in II- anaerobically digested sludge was nearly exceeding the standard. Therefore, it hampered agro-utilization of sludge, and it is essential to remove the heavy metals.The compare of the way of removing heavy metals from the sludge showed that it is feasible to use agents. The aims of screening agents were described to remove heavy metals efficiently, to save useful matter, to lower cost, to operate easily. So the targets could be suggested as removal ratio of heavy metals, the lost ratio of nutrient, contemporary, wastewater amount, economic efficiency, and maneuverability index.Citric acid (CTA), EDTA and sodium dodecyl sulfate (SDS) were used to extract cadmium(anionic) and chromium(anion) in II -anaerobically digested sludge. The experiments consisted of A, B, C, D groups. A group was leaching test by agents solely. Each sample was treated with three different extractors, namely, 0.05, 0.1,0.2 and 0.3mol L"1 CTA, 0.025, 0.05, 0.125 and 0.25mol L'1 EDTA, 0.005, 0.01 and 0.02 mol L'1 SDS. The leaching dose was arranged two levels (/ e, 500ml kg"1 and 1000ml kg"1); B group was was leaching test by agents jointly, in which 0.3 mol L"1 CTA and 0.25 mol I/'EDTA were mixed with 0.005, 0.1 and 0.2mol L"'SDS, respectively. The leaching way including mixing treatment (/ e, the volume rate of the two solution was 1:1) and the leachin...
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