Study On The Effect Of Tween-20 And Na₂S₂O₃ Enhanced Sludge Bioleaching

Sludge dewaterability and removal of sludge-borne metals by bioleaching reaction, need to add sulfur powder as the energy substance of Thiobacillus. However, for the insolubility of S0, it hard to disperse in the reactor and contacted the bacteria sufficiently. S0 using rate is low, limit the reaction. The rate of microbial sulfur oxidation was low, which limited the reaction. This topic firstly optimized the bioleaching reaction conditions in shake flask. And then, the optimum technological conditions of Tween-20 and Na₂S₂O₃ enhanced sludge bioleaching were optimized in the 100 L reactor. This study would provide theoretical reference and parametric basis for the engineering application of the sludge bioleaching technology and the resource utilization of the cake.An orthogonal experiment（5 factors and 4 levels） was designed, to study the effect of Tween-20 on the bioleaching of sewage sludge. The orthogonal experiment showed that: factors of Fe SO4, sludge moisture rate, sludge return ratio on bioleaching sludge SRF values influence is extremely significant（p < 0.001）; effect of amount of Tween-20 on test results also significantly（p < 0.05）, effect of S0 on test results less significant（p > 0.05）. The optimal test combination was: the sludge reflux ratio was 30%, the amount of Fe SO4 was 8 g/L, the moisture content of sludge was 97%, the amount of Tween-20 was 1 g/L and the amount of S0 was 2 g/L. Then, the Na₂S₂O₃ instead of S0 and Tween-20 were used to study the effect of on the bioleaching efficiency of sewage sludge（orthogonal test of 4 factors and 4 levels）. The results showed that the factor Fe SO4, Na₂S₂O₃, sludge reflux ratio and the moisture content of sludge had a significant effect on the SRF value of the sludge（p < 0.001）. The optimal conditions were as follows: the amount of Fe SO4 was 8 g/L, the moisture content of sludge was 97%, the reflux ratio of sludge was 30% and the amount of Na₂S₂O₃ was 1.5 g/L.On this basis, a 100 L reaction system was designed, and the 4 factors 3 levels of orthogonal experiment were investigated. The experimental results indicate that: the sludge reflux ratio on the cake moisture rate had significant effect（0.01 < p < 0.05）, the effect of aeration rate on the results was also significant（0.01 < p < 0.05）, HRT also had a certain effect on the test results（0.5 > p > 0.1）, and the effect of the nutrient type on the test results was small. These factors showed an affecting order of: sludge reflux ratio > aeration rate > HRT > nutrient type. Then, the optimum operating conditions were: reflux ratio was 64%, the aeration rate was 1.6 m3/h, HRT was 2 d and the nutrient was X+Y（1 g/L S0, 0.5 g/L Tween-20, 0.75 g/L Na₂S₂O₃ and 8 g/L Fe SO4）. Based on the achieved optimum condition, the treatment effects of 3 batches sludge were validated. The results showed that the filter cake moisture content could be less than 60%, and the amount of heavy metals（Cu, Zn, Pb and Cr） were far less than limited value, while the amount of organic matters decreased less than 5%. Therefore, the treated filter cake was very suitable for landscaping, composting, and incineration power generation and other resource utilization.