The Design Of Continuous Flow Bioleaching Reactor And Engineering Application In The Treatment Of Tannery Sludge

The bioleaching technology,originated from biohydrometallurgy industry,has been applied in the field of the treatment of environmental pollution,such as removal of heavy metals from sewage sludge.We have done much work on the removal of heavy metals from municipal sludge and tannery sludge by bioleaching in rencent years.Up to date,we have succeeded in bioleaching of tannery sludge in terms of metals removal using the stirred tank reactor and air lift reactor at the piolot scale.In this study we try to develope a continuous flow bioleaching reactor for the continuous bioleaching of tannery sludge.There are three problems needed to be solved for tannery sludge,namely,odour,high content of heavy metals,and difficulty in dehydration.Among the three aspects mentioned above,the odour is venenous directly to environment;the harm of heavy metals pollution is potential and perennial.However it is difficult for sewage sludge to further reduce its volume through natural gravitity condensation.Recently many researchers have found that the bioleaching technology could resolve these problems entirely.In the paper,the trials consist two parts,one part was the trials in laboratory,including that the tannery sludge releasing H₂S was simulated in space,and some trails by bioleaching in flasks.The trials in the flasks were conducted with different amout of Fe²⁺ in combination with S powder as energy substrates and using the supernatant of bioleached sludge as circumfluence matter. The second part involved in the design of a continuous flow bioleaching reactor and the operation of the designed reactor.With a pulse tracing technique,the hydraulic property of the reactor was studied,through which the limitation of reactor could be found.The trial of HzS release showed the tannery sludge could release H2S when placed,stirred and acidified, and the rate of release enhanced in turn.In device designed by ourselves,the concentration of H₂S is up to 9 mg/L when placed after stirred,77mg/L when stirred and 100mg/L when acidified.There are much reduced S in tannery sludge,which could be turn to H₂S,and released to the surroundings when it cumulates to saturation.The trails in flasks showed that the addition of Fe²⁺ in sludge bioleaching system accelerated acid production found in the regime of pH＞2 with comparison to the control without addition of Fe²⁺.However,the increase of Fe²⁺ resulted in more ferric precipitates in bioleached sludge by which,in turn, soluble Cr³⁺ might be re-attenuated through co-precipitation.Thus,the solubilization efficiency of sludge-born Cr facilitated by the addition of Fe²⁺ hardly differed from that from the control.In addition,the addition of Fe²⁺ improved,to a lesser extend,sludge dehydration,as exhibiting a lower sludge specific resistance due to Fe²⁺ addition compared to the control.In the light of the cost of chemical agent（FeSO₄·7H₂O） and bioleaching efficiency after the addition of Fe²⁺,it was concluded that,for tannery sludge bioleaching, additional Fe²⁺ perhaps was unnecessary for improving obviously Cr solubilization and sludge dehydration.The acidified liquid of bioleaching as circumfluence matter is available for tannery sludge treatment by bioleaching,but the effect was inferior to that by acidic bioleached sludge.However,the liquid after enhanced is helpful greatly to the bioleaching. In the flasks,after bioleaching for 7days,the pH of sludge using acidified liquid and acidic bioleached sludge as inoculum decreased below 2.10 and 2.04,while two kinds enhanced liquid is 2.06 and 1.99,respectively only after 5 days.The continuous flow bioleaching reactor with work volume of 700L,including the main-body,aerating system,heating system,feeding and cicumfluence system was developed.The paper also discussed theoretically about energy which was exhausted when the tannery sludge disposed by bioleaching technology in the actual engineering.The energy exhausted by 1T tannery sludge on aeration is about 10 times than sewage treatment; In addition,the energy being equal to 2kg standard mode is on heating.The total price is about 4-6 yuan RMB.The piolot scale trails with continuous flow bioleaching reactor consisted three parts.First having batches disposal test,6 batches disposal were made constantly,the percentage of solide was 1.5-2%,the pH of the bioleached sludge decreased about 2 through 2-3 days,the solublization efficiency of Cr was up to 70%,the settlement and dehydration property of bioleached sludge were enhanced greatly,furthermore the bioleaching process has no odor.Second,having continuous flow test,the continuous flow disposal ran about 20 days,the result showed that 175L tannery sludge was disposaled and the pH of bioleached sludge could decrease about 2.1 at the case of mean residence time of 4 days,and the reactor can resist shock loading.Third with a pulse tracing technique, concentrated H₂SO₄ as tracer,the hydraulic return mixing of reator was studied,which showed the reactor resulted in hydraulic return mixing case,the amout exceeded 0.6L/min. The critical flux was about 91.8L/h,the optimum size of caliber joined the section was 2.38 cm².The resut of trail showed the design of reactotr existed limitation,we can improve the parameter of design to enhance the treatment effect of reactor in the future.