摘要
利用微生物方法去除污泥中重金属 (生物淋滤法 )具有成本低、去除效率高、脱毒后污泥脱水性能好等优点 ,近年来在国际上备受关注。生物淋滤法采用的主要细菌为氧化亚铁硫杆菌 ( Thiobacillus ferrooxidans)和氧化硫硫杆菌( Thiobacillusthiooxidans) ,在其作用下 ,污泥中以难溶性金属硫化物被氧化成金属硫酸盐而溶出 ,通过固液分离即可达到去除重金属的目的。污泥的生物淋滤效果受温度、O2 和 CO2 浓度、起始 p H、污泥种类与浓度、底物种类与浓度、抑制因子、Fe3 +浓度等的影响。较为详细地介绍了生物淋滤法的作用机理及高效去除污泥中重金属的操作程序 ,并对其在环境污染治理方面的应用前景作了分析。
Land application is becoming the more appropriate option for the final disposal of sewage sludge from wastewater treatment plants.However,the presence of heavy metals such as zinc,copper,chromium,cadmium and lead at levels higher than the recommended levels is always one of the major obstacles to its general use.Reduction of heavy metals in sewage sludge through source control is relatively expensive and impractical.Therefore,removal of heavy metals prior to land application has led to the development of chemical methods,such as EDTA extraction and acid solubilization,and bioleaching (also called biological solubilization).Chemical solubilization of heavy metals from sewage sludge has never been applied because of high cost,operational difficulties and large consumption of chemical agents.Bioleaching appears to be more practical and economically viable alternative for sludge decontamination and management.Under optimunm bioleaching conditions,Zn,Cd,Ni and Cu can be almost completely removed,whereas the removal efficiency of Pb and Cr is lower.The major microorganisms responsible for bioleaching are a variety of acidophilic and chemoautolithotrophic bacteria such as Thiobacillus ferrooxidans and Thiobacillus thiooxidans, which can be isolated from sewage sludge.Other bacteria such as Leptospirillum ferrooxidans or heterotrophic acidophiles can also be involved.Their biological characteristics are briefly described while the pattern of bio-oxidation of Fe 2+ by T.ferrooxidans is discussed in detail in this review. The solubilization mechanism of bioleaching can be direct and indierct.In the direct mechanism,metal sulfides can be oxidized into sulfates by these acidophiolic bacteria.In the indirect mechanism,Fe 3+ generated from the oxidation of Fe 2+ by T.ferrooxidans or other iron-oxidizer reacts in a purely chemical way with metal sulfides to produce Fe 2+ again.This Fe 2+ can be oxidized by T.ferrooxidans repeatedly in a cyclic process.Sulfur produced in this process will then be oxidized intlo sulfuric acid by these bacteria,which caused the decrease in pH.Bioleaching is a simple and inexpensive process consisting of preacidification of sludge to pH 4.0 or 4.5 (preacidification is not required according to some authors),addition of low-cost substrate such as metallurgical grade FeSO 4·7H 2O,or elemental sulfur,and recirculation of the partially leached sludge as inoculum.Nutrient amendmen including nitrogen,phosphate and other nutrients is inessential due to the presence of sufficient nutrients in sewage sludge.After aerobic incubation for a few days or weeks,the leached sludge can be dewatered using centrifuge of other solid-liquid separation methods.The leached sludge can be neutralized with lime,while precious metals can be recovered from the solution phase. The process efficiency is dependent on several factors including temperature,oxygen and carbon dioxide concentration,initial pH,the types and concentration of substrates,the types and solids concentration of sewage sludge,inhibitory factors,and ferric iron,etc.Among these factors,temperature,oxygen and carbon dioxide concentration,initial pH,and the types and concentration of substrates,are key parameters for optimizing the bacteria growth.Different sewage sludges (primary,activated sludge and anaerobically digested sludge),when subjected to different treatment conditions,show different metal removal efficiency.In operational design,inhibitory factors such as heavy metal ions,anions and dissolved organic matter must be elimuinated of diminished before recirculation of the partially leached sludge as inoculum.Besides,keeping a high ferric iron is in favor of the indirect attack on the metals sulfides. Bioleaching has several advantages as compared to chemical methods,which can be enumerated as follows:reducing acid consumption by more than 80%,increasing the specific resistance coefficient to filtration significantly,easier dewatering of the leached sludge without the addition of polymeric flocculation agents,and lower leaching
出处
《生态学报》
CAS
CSCD
北大核心
2002年第1期125-133,共9页
Acta Ecologica Sinica
基金
国家自然科学基金 ( 2 0 1 770 1 6 )
江苏省自然科学基金 ( BK2 0 0 1 0 72 )资助项目
关键词
生物淋滤法
污泥
重金属
去除
bioleaching
sewage sludge
heavy metals
removal
