内聚营养源SRB污泥固定化连续处理含锌废水的研究

【作者】 李二平；

【导师】 闵小波；

【作者基本信息】 中南大学 ， 环境工程， 2010， 硕士

【摘要】 含锌废水来源广泛,具有持久性、毒性大等危害,对环境及人类容易造成严重危害。该类废水治理方法很多,生物法主要是通过生物有机体或其代谢产物与金属离子之间作用而达到净化的目的,具有低成本、环境友好等优点。硫酸盐还原菌(SRB)在处理高硫酸盐有机废水、矿山酸性废水、电镀废水等方面取得了较大进展,具有“以废治废”、处理重金属种类多、处理彻底、处理潜力大等特点。但也存在营养源不能被生物充分利用,导致出水COD偏高,重金属离子对SRB毒害作用影响处理效果等缺陷。本研究提出内聚营养源SRB污泥固定化技术。将SRB所需碳源固定在小球内部,并构造出SRB生长良好的内部环境,不仅克服了重金属离子对SRB的毒害,而且通过碳源内聚避免了有机物的污染,因此它在重金属废水低廉高效处理方面体现了较大的应用潜力。本论文在热力学理论计算的基础上,采用包埋法,以驯化15d后的活性污泥为包埋对象,系统地考察了进水SO42-浓度、pH、固定化小球与废水质量比及水力滞留时间等因素对含锌废水处理效果的影响,并测定了连续运行系统对各种污染物处理效果以考察其稳定性,同时对SO42-还原动力学、除锌机理以及传质过程进行了理论研究。(1)根据化学热力学平衡原理,绘制了Zn2+-S2-H2O系溶解平衡pC-pH关系图,Zn2+-S2-H2O系热力学平衡研究表明：Zn(OH)2固相在pH值在9.41时,最低溶解度10-5.61mol/L;ZnS固相在pH值为8.36时,最小溶解度为10-7.69mol/L;当S2->Zn2+(mol/L)时,pH在0-14范围内只生成ZnS沉淀,不会产生Zn(OH)2物质。(2)通过对包埋载体材料的筛选,确定以聚乙烯醇(PVA)为骨架添加少量活性炭、海藻酸钠、SiO2.Fe粉,并采用正交试验和单因素试验选择与优化包埋条件,确定的最佳条件为：PVA用量为12%,海藻酸钠用量为0.1%,SiO2用量为4%,污泥用量25%,交联剂pH值为6.5。在此条件下制得的固定化小球处理效果较为理想,在进水Zn2+浓度为200mg/L时,其去除率可达92.5%。(3)连续化处理废水试验表明：进水SO42-浓度4151mg/L,Zn2+浓度100mg/L,pH为5.9,固定化小球与废水质量比为1：2,水力滞留时间(HRT)为4h,Zn2+去除率达98%以上,出水Zn2+低于2mg／L,COD低于100mg/L,达到《污水综合排放标准》(GB8978-1996)。Zn2+稳定达标时间为13h；固定化小球经五次再生使用,出水Zn2+均稳定达标12-14h。通过对沉淀机理分析可知,锌离子去除主要通过生成ZnS沉淀,吸附机理去除次之,过程中不会产生Zn(OH)2沉淀。(4)利用稳态法得出：SO42-催化还原速率与SO42-浓度的函数关系曲线遵循米氏方程式规律,当CSO42-＜3259mg/L,SO42-还原遵循酶反应动力学一级反应,反应速率与进水SO42-浓度成正比；当CsO42->3259mg/L,遵循酶反应动力学零级反应,反应速率为与硫酸根浓度无关。(5)由固定化小球表面电位测定可知：废水pH在4-7范围时,小球表面电位为正值,小球表面带正电荷,废水中Zn2+离子被排斥,S042-通过小球表面进入内部被还原,还原产物S2-离子穿出小球表面与废水中Zn2+产生ZnS沉淀,Zn2+去除率达98%以上,经4次再生试验Zn2+去除率仍保持在98%左右,固定化小球可以重复使用。当废水pH在8-10范围时,固定化小球表面电位为负值,小球表面带负电荷,废水中Zn2+被吸引进入小球内部,SO42-离子与小球内部多肽结构形成化学键也被吸附,故锌离子也有较好的脱除效果,Zn2+去除率也可达97%左右,但由于锌离子对SRB的毒害,小球不能重复利用。更多还原

【Abstract】 Zinc-containing wastewater endangers environment and human health because it contains various poisonous and persistant pollutants. There are many methods developed for its treatment.Biological method has received much attention becauce of its low cost and environmental friendly. Sulfate reducing bacteria(SRB),one of the promosing biological method, has the characteristics of using waste sludge to treat wastewater, being suitable for various heavy metals and high removal rate, and has been widely used in the treatment of organic wastewater, acid mine drainage and electroplating wastewater. However, there are still some drawback in it, such as low-usage of nutrition, high effluent COD and toxicity of metal ion.A novel technology,immobilized SRB sludge beads with inner cohesive nutrient source, was proposed in this study for treatment of heavy metal wastewater. It can provide a reticular structure for SRB sludge to resist heavy metals poisoning and organic pollution from outer environment.The entrapping method was used with sludge acclimatized of 15 days as entrapped objectives in this study. The effects of some factors, such as influent SO42-, pH, mass ratio of beads to liquid and HRT, on the treatment of Zinc-containing wastewater were systematically investigated, and the eduction kinetics of SO42,mechanism of zinc removal,mass transfer process were also included. The main conclusions of this study are as follows:(1)The pC-pH diagrams of Zn-S2--H2O system are plotted according to thermodynamic equilibrium. Zn(OH)2 has the minimum solubility of 10-5.61 mol/L at pH 9.41,and the minimum solubility for ZnS (10-7.69mol/L) is obtained at pH 8.36.In the thermodynamic equilibrium system of Zn(OH)2 and ZnS,only ZnS precipitation is generated when the concentration of S2- is greater than that of Zn ion.(2) PVA is chosen as main entrapping carrier involves adding small amount of active carbon, alginate, SiO2, Fe.According to orthogonal tests and single-factor experiments, the optimal parameters are that:PVA concentration of 12%, active carbon of 5%,Alginate of 0.1%, SiO2 of 4%, activated sludge of 25% and pH 6.5 for crosslinking agent. Under the condition, the highest removal rate of Zn2+ reachs 92.5% with influent Zn2+ concentration of 200mg/L(3)The results of the continuous treatment show that the removal rate of Zn2+ is greater than 98%,and Zn2+ concentration in effluent meets integrated wastewater discharge regulation (GB8978-1996) under the condition:4150mg/L of SO42-, Zn2+ of 100mg/L, pH 5.9 in influent, mass ratio of beads to liquid 1:2 and HRT 4h. The stable operation time of reactor is 13h and it is in the range of 12-14h even after five cycles-regeneration. Based on the analysis of precipitation mechanism, Zn removal was mainly caused by the formation of ZnS precipitation, Zn adsorption on immobilized SRB beads is secondary to Zn removal,and no Zn(OH)2 precipitates were observed. (4) When SO42- concentration is below 3259mg/L, SO42- reduction follows first-order enzyme kinetics.The reaction rate is proportional to SO42- concentration, when SO42- is over 3259mg/L, it follows zero-order enzyme kinetics and the reaction rate is independent of SO42-concentration. (5)At pH 4-7,the surface e of immobilized SRB beads is positive charged which tend to repulse Zn2+ in wastewater, and attract SO42-, Moreover, SO42- adsorbed on the surface diffused into the inner and was reduced to S2-. S2- can pass through the bead surface and form ZnS precipitate with Zn2+ resulting high Zn2+ removal rate (about 98%).At pH 8-10 the surface of immobilized SRB beads is negative charged, exhibiting higher affinity for Zn2+. For SO42-, it can be adsorbed to immobilized SRB beads by chemical binding with inner polypeptide. Therefore, Zn2+ removal rate is also high (97%), however, the beads cannot be reused due to the toxicity of Zn2+ to SRB.更多还原