| The leather industry is superiority conventional industry of our country,which made important contribution for national economic development,providing all kinds of leather products for our daily life.However,a large amount of tannery sludge with a high chromium content(1 to 4%)is also produced during the leather production process.Lack of effective treatment measures,piling up chromium sludge illegally on the farmland has become a common phenomenon.Safe disposal of high concentrations of tannery sludge is a challenging task facing the environmental area.Tannery sludge with a large amount of organic matter,nitrogen,phosphorus and other nutrients that plants need to grow.Tannery sludge can be reused has been attracted more attention.In this paper,with the aid of acidophilic sulfur-oxidizing bacteria which was enriched and acclimated in the sludge of the local tannery sewage treatment plant as bioleaching bacteria,adopting the long-term open-air tannery sludge as research object,the effect of pre-aeration on the bioleaching of tannery sludge and the removal of heavy metals in the tannery sludge by the bioleaching and the effect of system p H on dewatering performance of sludge during bioleaching processes were discussed under various conditions.Then,analyzing the nature of sludge before and after bioleaching and evaluating its resource potential;Finally,some suggestions were put forward for the improvement of resource utilization of tannery sludge by bioleaching method.The main achievements are as follows:(1)Although the tannery sludge with high nutritional value(such as organic matter,total nitrogen and other nutrients)can be converted into high-valued agro-products,the contents were 30.21%,37 g/kg.However,the content of Cr,Cd,Zn in the sludge was 22400,35.8,3010 mg/kg,all of which exceeded the GB 4284-2018 "Agricultural Sludge Control Standard." Particularly,Cr content is about 22.4 times higher than the heavy metal control standard,limiting the utilization of tannery sludge in agriculture.(2)The addition of natural mineral activator(Microbial activator)based on sulfur powder could enrich the acidophilic sulfur-oxidizing bacteria in the sludge of the tannery sewage treatment plant successfully,and reducing the initial p H of the sludge could accomplish the enrichment process in advance.The indigenous acidophilic sulfur-oxidizing bacteria acclimatized by the tannery sludge could speed up the bioleaching process and improve the removal rate of Cr in the sludge.(3)The test shows that when the initial p H value of the tannery sludge was 5,the solid content was 5%,and the dosage of energy substances natural mineral activator based on sulfur powder was 9 g/L,the better bioleaching will be achieved.The use of natural mineral activators for tannery sludge microorganisms provides an important guarantee for the biological release of toxic and harmful substances from special high-heavy metal tannery sludge.(4)The study found that pre-aeration treatment at one day of tannery sludge can significantly improve the sludge environment,significantly accelerate(at least 8 d)the bioleaching process of tannery sludge,and significantly increase the removal rate of typical heavy metal Cr(above 95%)and other heavy metals in tannery sludge.It provides innovative theoretical support and technical guarantee for the harmless and resource utilization of tannery sludge.In addition,pre-aeration treatment can slash the capillary suction time(CST)of sludge,improving the dewatering performance of sludge.Nonetheless,when the p H value of bioleaching system is less than 2.1,the CST of the sludge will increase and the dewatering performance will be deteriorated.Therefore,ensuring the removal rate of heavy metals,the p H value of sludge in the bioeaching process should not be lower than 1.67 as much as possible.(5)To make the tannery sludge harmless,the bioleaching process of tannery sludge with the innovative use of natural mineral activator has greatly reduced the content of Cr,Cu,Cd,Pb,Zn in tannery sludge.After the process of detoxification(removal of heavy metals)by this process,the removal rates of Cr,Cu,Cd,Pb,and Zn all reached more than 88%,the removal rates were 96.36%,88.49%,99.24%,93.73%,and 99.71%,the contents were 814,4.43,0.27,16.8,8.85 mg/kg,all meeting the requirements of class B sludge of GB 4284-2018 "Agricultural Sludge Control Standards." The sludge after bioleaching can be used in agricultural land such as gardens,pastures and other non-value edible crops.Especially after the bioleaching through this process,The tannery sludge with abundant nutriment(The total amount of residual nitrogen is 27.9 g/kg,which is far higher than the requirements of fertile fertilizers).Therefore,the use of a mixed natural mineral activator for bioleaching to removal heavy metal from the tannery sludge for reuse is worthy of in-depth research and promotion. |
PDF Full Text Request