Heavy Metals Bioleaching From Contaminated Sediments By Indigenous Sulfur-oxidizing Bcteria

The bioleaching process is based on the catalytic oxidation and bio-acidification by sulfur-oxidizing bacteria (SOB). The method has advantages of mild reaction conditions, less acid consumption as well as low operation cost. But the novel technology has just started that the bioleaching applied in removing metals from polluted sediment, more study should be explored.The research studied the effect of total solids concentration, sulfur concentration as well as temperature on heavy metals(Zn, Cu, Cr) bioleaching from contaminated sediment by sequencing batch test on the shaking table. And the results showed that the removal efficiency of Zn, Cu, Cr is 62%, 78%, 25% respectively under the conditions of 10% total solids concentration, 3g/L sulfur concentration and the temperature of 28℃.In addition, the research discovered that approximately some 50% or more powdered sulfur wasn't been oxidized (S0 content 16~24kg/t dried sediment), and the residual powdered sulfur can promote microbial reacidification of leached sediments due to its form of uneasy reuse. According to the physical properties of powdered sulfur, the forms of spheroidal and flaky sulfur (named sulfur prill and piece) were made to applied in the heavy metals bioleaching. The result is that the different sulfur forms of powder, prill and piece may provide the energy effectively for the sulfur-oxidizing bacteria. The sulfur-oxidizing rate in the process of sulfur powered adding is higher than others. However the unused sulfur prills and pieces can be recycled availably, and the sulfur pieces was more stablily. The analysis of chemical speciation of metals in sediment using the BCR sequential extraction method, indicated that during bioleaching, most of the oxidizable and reducible forms of metals were transformed to acid soluble, posing a favorable condition for subsequent metals removal, whereas the residual form remained steady. After bioleaching, a majority of those unbioleached heavy metals in sediments existed mainly in stable forms which made a higher security for final disposal of treated sediments.The Centrifugal impeller reactor designed by the investigator was used into practice for bioleaching process in order to promote the engineering-oriented of bioleaching technology. It was demonstrated forcefully that the heavy metals can be removed effectively through several continuous baths. Systematic Analysis on the properties of the original and leached sediments, we can find as follows: the vary amount of heterophic bacteria is slight and contrary to that of coliform and streptococcus bacteria which 90% dissappeared; the loss of organic matter and total nitrogen is relatively small, but the loss rate of total phosphorus is up to 78%, even if like that, each nutrient index was still higher than the soil background value; the dewatering performance of leached sediment is highly improved. After that, the the reseach utilized alkaline residue as additive to assist cement-based solidification/stabilization of leached sediment with the goal of innocuous management,. The unconfined compressive strength of solidified bodies made of leached sediment is more than 100kpa at the curing time of 14d and the cement admixing amount of 0.2~0.4kg/kg, which the strength is satisfied with the requirement of fill and landfill disposal; the heavy metals'leaching ratios of the solidified bodies decreased a great degree resulted form the toxicity extraction test. Based on the solidification effect, the cement admixing amount of 0.2kg/kg is more appropriate for practical application.Based on the results mentioned above, we can conclude that bioleaching is an effcetive technology in removing heaby metals from contaminated sediments.