CAS OpenIR
复配絮凝剂协同去除焦化废水中难降解有机污染物和氰化物的研究
Alternative TitleStudy on Inorganic-organic Composite Coagulant for Synchronous Removal of Refractory Organic Pollutants and Cyanides in Coking Wastewater Treatment
沈健
Thesis Advisor张懿
2013-09
Degree Grantor中国科学院大学
Degree Name博士
Degree Discipline化学工艺
Keyword焦化废水,混凝,复合絮凝剂,难降解有机物,氰化物
Abstract

焦化废水成分复杂,属于典型难处理工业废水。生化处理后仍存在多种低浓度难降解有机污染物(Refractory Organic Pollutants,ROPs)和氰化物,直接排入水环境容易引发生物毒害作用。2012年国家新颁布的焦化行业标准(GB 16171-2012),进一步提高了化学需氧量(Chemical Oxygen Demand,COD)、氰化物等排放指标。因此,先进实用的废水处理技术是焦化废水处理领域的急迫需求。混凝沉淀工艺具有成本低、高效以及操作简单等特点而被广泛应用于焦化废水深度处理工艺中,但现有絮凝剂对ROPs以及氰化物去除能力有限,造成出水COD和氰化物难以满足新标准的要求。为此,本文针对影响焦化废水达标排放的生化出水中ROPs和氰化物两类污染物,研制一种聚合铁基-阳离子型有机聚合的复配絮凝剂(PFSC);通过运用物理化学方法研究有机聚合物种类及阳离子型有机聚合物(CP)的复配比(Wp)对混凝效率、絮凝剂结构以及絮体结构的影响,探讨了复配絮凝剂各组分间相互作用机制,揭示了阳离子型有机絮凝剂去除氰化物和ROPs的作用机理;基于复配絮凝剂的氰化物和ROPs去除优化模型,进一步将复配絮凝剂应用于焦化废水深度处理工艺中。 主要研究内容及结果如下: (1)将聚合硫酸铁(Polymeric Ferric Sulfate,PFS)和CP通过混聚法,制备不同Wp的絮凝剂,并利用Fe-Ferron逐时络合比色动力学方法研究复配絮凝剂中铁形态分布。结果表明,随着Wp提高,复配絮凝剂中铁各种形态的百分比相对于PFS发生变化。当Wp为0.5%时,活性组分Feb含量最高。采用X射线电子衍射(X-ray diffraction,XRD), 傅立叶红外光谱(Fourier transform infrared spectroscopy,FT-IR), 扫描电子显微镜(Scanning electron microscope,SEM)和X-射线光电子能谱(X-ray photoelectron spectroscopy,XPS)对新型絮凝剂进行结构和形貌表征,SEM和XRD结果表明由于阳离子聚合物的加入,复合絮凝剂形貌以链状/网状有机聚合物包裹无定型态Fe为主。FT-IR以及XPS结果显示复配过程中,复配絮凝剂中各组分结构没有显著变化也没有形成新的化学键,可认为复配过程等同于物理混合。 (2)采用不同有机絮凝剂(阳离子型絮凝剂PFS-C和非离子型絮凝剂PFS-N),研究焦化废水氰化物(Fe(CN)63-)去除效果以及去除机制。结果表明,PFS-C混凝去除氰化物的效果远优于PFS-N混凝,残留氰化物浓度可降低至0.2 mg/L以下。进一步通过透射电子显微镜(Transmission electron microscopy,TEM)、XRD、FT-IR和XPS对絮体表征,发现由于PFS-C中存在N+结构,Fe(CN)63-以及带有负电荷的絮体(Fe(CN)63-吸附于Fe(OH)3)能够直接通过阳离子型絮凝剂中N+电中和和静电簇作用被去除,而PFS-N中的非离子N很难和Fe(CN)63-反应,表明复配絮凝剂中阳离子型聚合物的存在显著提高了氰化物去除能力。该混凝效率体现出的差异性受制于有机絮凝剂的作用机制。 (3)采用不同Wp的絮凝剂PFS、PFSC05、PFSC1和PFSC5(Wp分别记为0、0.5、1)处理焦化废水生化出水,系统考察阳离子型有机絮凝剂对絮凝剂的混凝效率、絮体性质及其混凝机制的影响。混凝效率结果表明:相对于其他絮凝剂,PFSC5混凝效率最高,氰化物和COD去除率分别降低95-97%和50-55%。采用小角激光散射技术和原位絮体形貌检测手段研究有机絮凝剂对絮体结构的影响,发现PFSC5产生的絮体分型维数大且微小絮体(10-100 μm)少,具有生长速度快、粒径分布更均一、高强度以及絮体结构易复原等特点。在焦化废水特定水质条件下(高离子强度),在高Wp的复配絮凝剂(PFSC5)中,阳离子型有机絮凝剂以吸附作用为主;在低Wp的复配絮凝剂(PFSC05)中, 阳离子型有机絮凝剂的混凝机制主要是静电簇作用。 (4)采用响应面法(RSM)中心组合设计(CCD)模块优化PFSC5和PFS的混凝过程絮凝剂投加量和废水pH影响因素,建立氰化物和COD去除模型。结果表明: PFS和PFSC5的最佳混凝条件为絮凝剂投加量为2000mg/L和废水初始pH 7.5,并且实验数据与模型预测数据吻合度高;PFSC5的COD和氰化物去除率分别为53.41%和94.85%,远高于PFS的COD和氰化物去除率(COD去除率:33.49%;氰化物去除率:30.10%)。 (5)将新制备的絮凝剂用于某化工厂焦化废水深度处理系统,进行连续中试及工业化试验。混凝出水中氰化物和浊度浓度(氰化物:低于0.2 mg/L,浊度:1-2 NTU)全部达到2012年焦化企业废水排放新标准(GB 16171-2012);COD去除率也从25-30%提高至55-60%,残留COD浓度降低至80-90 mg/L,大大降低后续处理难度。;Coking wastewater with complex ingredients is a typical industrial effluent which is difficult to be disposed. Large numbers of refractory organic pollutants (ROPs) and cyanides with low concentrations, which still exist in the coking wastewater after biological treatment, have adverse effects to the environment and living beings. Currently, new emission standard of pollutants for coking chemical industry, which is issued by Ministry of Environmental Protection of China, proposes more strict requirements in the aspects of chemical oxygen demand (COD) and cyanides. Thus, advanced practical wastewater treatment technology is the urgent demand in the field of coking wastewater treatment. Coagulation/flocculation has been widely applied in the coking wastewater advanced treatment process because of low cost, high coagulation efficiencies and easy operation. However, existing coagulants show limited abilities for the ROPs and cyanide removal, which result in the fact that coagulation effluent cannot meet new emission standards. In this paper, aiming at the ROPs and cyanides in the biological effluent of coking wastewater, composite coagulants (PFSC) were prepared by premixing polyferric sulfate (PFS) and cationic polymer (CP). By investigating the effects of organic polymers types and the weight percentages (Wp) of cationic polymer (CP) in the composite coagulant on coagulation efficiencies and the structural characterizations of coagulant and flocs via physical and chemical methods, the interaction between inorganic coagulant and organic polymer was explored and the CP roles for removing ROPs and cyanides were also proposed. Additionally, based on the optimization of coagulation process and removal models of the ROPs and cyanide, the novel composite coagulants were applied in the coking wastewater advanced treatment system. The main contents and results are following: (1) Composite coagulants were prepared by premixing PFS and CP coagulants with different Wp. Fe-Ferron method was used to examine Fe(III) species of PFS and PFSC. The results show that the contents of Fe(III) speciation vary with Wp. When Wp is 0.5%, the content of Feb is higher than that of any other coagulant. Moreover, the structural and morphological analysis of the coagulants were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS). The results of SEM and XRD reveal that the morphology of composite coagulant is the amorphous Fe which coated by chain/reticular organic polymer after CP being added. Additionally, the results of FT-IR and XPS suggest that the structure of each component has no obvious change and new chemical compound cannot be detected, which indicate physical mixture during the preparation process. (2) The effects of organic polymers on the removal mechanism of cyanides (TCN) in a coking wastewater were investigated by different flocculants (such as, cationic organic polymer and non-ionic polymer). During coagulation, PFS was used as a coagulant with the aid of a cationic organic polymer (PFS-C) or a non-ionic polymer (PFS-N). After flocculation-precipitation, physical and structural characteristics of the flocs were further analyzed by FT-IR, XPS, XRD and Transmission electron microscopy (TEM). The results indicate that the residual TCN concentration (in the form of Fe(CN)63-) is much lower after PFS-C flocculation (residual cyanides concentration less than 0.2 mg/L) than after PFS-N precipitation. This can be attributed to the different cyanides removal mechanisms of the individual organic polymers. Owing to the presence of N+ in PFS-C, Fe(CN)63- and negative flocs (Fe(CN)63- adsorb on ferric hydroxides) are directly neutralized by the N+ in the cationic organic polymer. The cationic polymer plays a significant role in TCN precipitation via charge neutralization and electrostatic patching. However, non-ionic N in PFS-N barely react with Fe(CN)63-. Therefore, cyanide removal ability has a obvious improvement due to the existence of CP, which indicate that the difference in coagulation efficiencies depend on the role of organic polymers (3) Composite coagulants (PFS, PFSC05, PFSC1 and PFSC5) prepared by PFS and CP coagulants with different Wp (Wp=0, 0.5, 1 and 5% respectively), were adopted to investigate systematically the effects of CP on coagulation efficiencies, flocs properties and flocculation mechanism by treating biological effluent of coking wastewater. The results of coagulation efficiencies show that PFSC5 exhibit superior coagulation performance at optimal conditions: the removal rate of TCN and chemical oxygen demand (COD) is 95-97% and 50-55%, respectively. The effects of CP on the properties and structure of flocs were investigated by small-angle laser light scattering (SALLS) and on-line particle size and shape analyzer. The results show that the flocs of PFSC5 are much denser and more uniform owing to the higher fractal dimension (Df) and less microflocs (10-100 μm), and also have higher growth rate and higher strength factor. Furthermore, the dense structure of the PFSC5 flocs can be restored after shear and more resistant to hydraulic conditions. Due to strong ionic strength in wastewater, the CP with high Wp (PFSC5) plays a significant role in adsorption, while the main mechanism of CP with low Wp (PFSC05) is electrostatic patch aggregation. (4) To investigate the effects of CP on coagulation process and build removal models, response surface methodology (RSM) was used. PFSC5 and PFS were used as the coagulants. The removal efficiencies for COD and cyanides obtained by PFSC5 were compared with those obtained by PFS as a conventional coagulant. Central composite design (CCD) and response surface method (RSM) were applied to optimize the operating variables (coagulant dosage and pH). Quadratic models developed for the two responses (COD and cyanides removal) studied indicate that the optimum conditions for PFSC5 and PFS are with dosage of 2000 mg/L at pH 7.5. The experimental data and model predictions agree well. The maximal COD and cyanides removal efficiencies of PFSC5 is 53.41% and 94.85% respectively, which higher than those of PFSC5 (COD removal rate: 33.49%; cyanides removal rate: 30.10%). (5) The new inorganic-organic composite coagulants were successfully applied in the pilot and full scale plant for coking wastewater advanced treatment in some chemical plant. The residual cyanides and turbidity concentration in the coagulation effluent is less than 0.2 mg/L and 1-2 NTU, respectively, which meet the requirements of new emission standard of pollutants for coking chemical industry (GB 16171-2012). Moreover, the COD removal rate increases from 25-30% to 55-60% and the residual COD concentration can be steadily decreased to 80-90 mg/L, which reduce treatment load for the follow-up technology. 

Language中文
Document Type学位论文
Identifierhttp://ir.ipe.ac.cn/handle/122111/26949
Collection中国科学院过程工程研究所
Recommended Citation
GB/T 7714
沈健. 复配絮凝剂协同去除焦化废水中难降解有机污染物和氰化物的研究[D]. 中国科学院大学,2013.
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