Experimental Study On Bioleaching Of Cr From Tannery Sludge In An Inner Loop Reactor

Bioleaching of Cr from tannery sludge has been studied. The affecting factors of bioleaching such as temperature, energy substrates and dissolved oxygen have been investigated, and the influences of reactor structure,aeration intensity and dosing rate of sludge on the startup and operation of the inner loop reactor have been researched.⑴The addition of more than 20% domesticated municipal sludge could complete the startup of bioleaching quickly. Single substance S as an energy substrate could not only start the bioleaching process, but also offer electron donator collaborating with the original ferrous in tannery sludge to accelerate the rate of reproduction Thiobacillus thiooxidans. But adding ferrous sulfate only was unable to complete the startup of bioleaching. The effect of three temperatures 24℃, 28℃and 32℃on the bioleaching have been studied, and it was found that temperature had little effect on bioleaching.⑵Under the condition of room temperature (19-25℃), aeration intensity(66.7L/h·L) and 25 days aeration operation of tannery sludge which had 97.8% water content of initial in the inner loop reactor, the startup of bioleaching was completed when pH decreased to 2.0. Indigenous bacteria in the sludge rather than the single species domesticated had a stronger ability to adapt to the environment, but had the relatively slow process of adaptation, the less obviously leaching effect and the longer leaching cycle.⑶With the volume of 15L, the ratio of high/diameter (3.4:1), the ratio of areas (Ad/Ar) 1.04:1, and aeration intensity of 66.7L/h·L in the inner loop reactor and after 30 days of operation when the pH value of this system decreased to 1.77, the removal rate of chromium reached 82%, the removal rate of Pb, Cu, Cd, Mn and Zn reached 95.9%, 72.1%, 93.1%, 93.2% and 88.7% respectively, and the loss of N and P of tannery sludge reached 36.86% and 63.74% respectively.⑷When aeration intensity was 33.4 L/h·L and dosing rate was 3-4% , the Cr concentration in solid and liquid was stable, the reactor achieved continuous operation, and in this state, with the increasing of dosing rate,bioleaching could result in the loss of nutrients such as N and P in tannery sludge.⑸In order to achieve a continuous-flow operation of the bioleaching reaction in shorter HRT, it was suggested that enlarging the volume of the reactor and the pilot-scale experiment should be carried out; particularly the application of commercialization of thiobacillus as the inoculums was adopted. The single substance S has been used as energy substrate, but the inherent Fe2+ in tannery sludge was not given special attention. Through the latter part of research, the changes of states of iron in sludge could be used to study which bacteria or both plays a leading role when bioleaching was realized with the indigenous bacteria.