生物硫氧化与硫还原促进污泥重金属脱除与分离的作用机制及调控原理

High levels of heavy metals present in sewage sludge often limits its land application as a valuable fertilizer. The heavy metal content in sludge is about 0.5-2% on a dry weight basis, and in some cases, extremely high levels up to 4% of the total metal have been reported. Developing cost-effective methods to remove metal pollutants from sludge, especially those highly loaded industrial sludge, is very essential for a sustainable sludge management. An integrated process comprising bioleaching with sulfur-oxidizing bacteria (SOB) and bioprecipitation with sulfur-reducing bacteria (S0RB) provides a potential route for deep removal/recovery of sludge-borne heavy metals. In the elemental sulfur (S0) based bioconversion process, heavy metals can be leached from sludge through acidification of sludge driven by SOB, and then leached metal ions can be seperated (as the form of metal sulfides) from acidic leachate through sulfidogenic step driven by S0RB. The unoxidized elemental sulfur particles in the biooxidation step can be reused for the subsequent bioreduction step, and the sulfur bioreduction process require only a small amount of carbon source. The purposes of the present study are to (1) determine the influence of the SOB-mediated sludge bioleaching on the sulfur surface properties and species (e.g., the contributions of sludge EPS, hydraulic shearing and acidic erosion to the changing sulfur surface interactions, wettability and morphology); (2) identify the involvement of intermediate sulfur species during the bioreduction of elemental sulfur under acidic conditions (e.g., the key terminal electron acceptor); (3) examine the important process parameters affecting the rapid formation of S0RB-promoted metal sulfide minerals in the acidic leachate (e.g., the role of S0RB cell and sulfur particle as a potential crystal nucleus); (4) evaluate the long-term performance of the sulfur bioconversion process in treatment of heavy metal-polluted sludge using a pilot-scale bioreactor system. The expected outcome from this work will contribute to better understanding about the importance of biological sulfur cycle for the metal contamination control and provide useful information for the development of highly efficient bioremediation strategies for heavy metal-loaded sludge.

污水处理厂（特别是混流入大量工业废水的污水厂）污泥中高浓度重金属很大程度上制约了污泥的安全处置和资源化。硫氧化和硫还原分属两个相反的转化过程，各自有产酸促进不溶态金属溶解脱除和产硫化物促进溶解态金属沉淀分离的作用。本项目尝试将上述两个相反的反应过程耦合衔接，构建以单质硫（S0）微生物氧化-还原为中心的生物硫循环工艺，经济、高效脱除与分离污泥重金属的新原理、新方法。主要研究内容包括：生物硫（S0）氧化浸出污泥重金属过程中硫表面特性和形态的演化特征及影响机制；酸性pH环境下生物硫（S0）还原过程中硫化学形态转化；生物硫（S0）还原促进污泥浸出液中重金属硫化物矿物快速形成的影响因素及晶核诱导效应；以及重金属污泥生物硫循环工艺处理系统的有效性和稳定性。项目研究成果将有助于丰富和深化人们对极端酸性环境下生物硫循环过程及其重要性的认知，同时也为重金属污泥生物硫循环脱毒处理技术的工程实践提供科学依据。

污水厂污泥中高浓度的重金属制约了污泥处理处置及资源化的空间。本项目采用生物硫氧化与硫还原对污泥重金属进行分离去除。通过恒温摇瓶培养和生物反应器，研究了硫在生物氧化还原过程中的分子形态转化和代谢产物生成；解析了生物硫氧化与硫还原体系中微生物区系结构的演替规律；探讨和初步评估了类芬顿氧化强化生物硫氧化促进污泥深度脱水的效果以及小型连续流生物硫循环工艺处理重金属污泥的效果及稳定性。研究表明：（1）生物硫氧化处理改性后的硫的化学成分虽仍为S0，但却呈现出极好的亲水性，同步辐射XANES检测发现其中存在较大比例的聚合硫Sn（>50%）和一定量的有机硫（约10%），环状硫的含量极少；生物硫还原反应的关键活性中间产物为新生态的纳米硫；（2）Illumina MiSeq 高通量测序发现，维持酸性条件下生物硫还原高效进行的微生物主要为Romboutsia和Desulfurella；Pseudomonas可能是促进生物硫氧化最主要的微生物；（3）类芬顿氧化可强化生物硫氧化显著的提高污泥深度脱水，污泥比阻（SRF）和毛细吸水时间（CST）可快速降至1011m kg-1和8.2s。这可能与类芬顿氧化加速污泥细胞破解和亲水性EPS释放，进而有利于污泥结合水向自由水转化有关；（4）以虾壳粉（5g/L）为能源底物的生物硫氧化与硫还原可将污泥中不同种类重金属以硫化物沉渣的形式被去除，Cu、Zn和Ni的去除率可达90%，Pb去除率约70%。该项目研究成果对于完善硫生物地球化学循环过程以及推动含重金属污泥生物脱毒技术的工程应用具有重要意义。