Flow analysis of major and trace elements in residues from large-scale sewage sludge incineration

Increase of sewage sludge (SS) has led to the construction of more incineration plants, exacerbating to the production of SS incineration residues. However, few studies have considered the mass balance of elements in large-scale SS incineration plants, affecting the residues treatment and utilization. In this study, flow analysis was conducted for major and trace elements in the SS, the fly ash (sewage sludge ash, SSA) and bottom ash from two large-scale SS incineration plants. The elemental characteristics were compared with those of coal fly ash (CFA), and air pollution control residues from municipal solid waste incineration (MSWIA), as well as related criteria. The results showed that the most abundant major element in SSA was Si, ranging from 120 to 240 g/kg, followed by Al (76–348 g/kg), Ca (26–113 g/kg), Fe (35–80 g/kg), and P (26–104 g/kg), and the trace elements were mainly Zn, Ba, Cu, and Mn. Not all the major elements were derived from SS. Most trace elements in the SS incineration residues accounted for 82.4%–127% of those from SS, indicating that SS was the main source of trace elements. The partitioning of heavy metals in the SS incineration residues showed that electrostatic precipitator ash or cyclone ash with high production rates were the major pollutant sinks. The differences in some major and trace elements could be indicators to differentiate SSA from CFA and MSWIA. Compared with related land criteria, the pollutants in SSA should not be ignored during disposal and utilization.     

粉煤灰和活性污泥对好氧填埋渗滤液组分的影响

通过在好氧反应器中添加粉煤灰和活性污泥来加速固体废物的降解。实验结果表明,添加粉煤灰不但改善了氧气扩散,而且增强了反应器对各种污染物的去除能力,对渗滤液中COD、NH4+、NO3-的去除率分别达到75%、68%和65%以上;添加活性污泥引入了一定量的微生物,也有利于固体废物的降解,渗滤液中COD、NH4+、NO3-的去除率分别达到了90%、65%和77%。因此,通过添加粉煤灰和活性污泥来加速固体废物降解是可行的。     

粉煤灰合成NaA型沸石对重金属离子的吸附动力学

以粉煤灰为原料,采用两步法合成了单一沸石矿物种的NaA型沸石,对合成产物的结构和性能进行了表征.通过静态吸附实验,研究了NaA型沸石对水溶液中Cu(ΙΙ)、Cr(Ⅵ)和Zn(ΙΙ)离子的吸附特性,从动力学角度探讨了吸附机理.结果表明,在所研究的浓度和pH值条件下,NaA型沸石对3种重金属的吸附符合Langmuir等温吸附方程,静态饱和吸附量(Qm)分别为82.30,65.96,47.78mg/g;3种金属离子在水溶液中的存在方式和大小是影响它们吸附行为的主要因素,通过动边界模型推算表明:NaA型沸石对Cu(ΙΙ)和Zn(ΙΙ)离子的吸附过程的速度控制步骤为液膜扩散,对Cr(Ⅵ)离子的吸附过程的速度控制步骤为颗粒扩散,3种金属离子的吸附过程符合伪二级方程.     

Formation characteristics of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and coplanar PCBs in fly ash from a gasification–melting process of municipal solid waste

PCDDs/DF and Co-PCB (dioxin) formations were studied with ash from a newly developed gasification and melting process for municipal solid waste. Ash samples were heated in a laboratory-scale fixed-bed reactor. Emphasis was placed on the effects of the type and composition of ash, temperatures, gas residence time, and gaseous organic precursors. Investigations using macroscopic and homologue distribution analyses led to the following conclusion. The ash from the gasification–melting process had the ability to generate dioxins in flue gas. A possible carbon source is unburned carbon in the ash samples, although this was very low (less than 0.01%). An experimental result that the level of dioxins generated from preheated fly ash obtained from a conventional incinerator was much lower than that from nonheated fly ash supported this conclusion. Dioxin concentrations obviously showed temperature dependence and peaked at 350°C. Dioxins formed in a gasification–melting process ash were readily desorbed from the surface, probably because of the low carbon content of the ash. There was no experimental evidence that gaseous organic precursors fed to the reactor generated dioxins. Therefore, an organic precursor was not essential for the formation of dioxins. A good linear relationship obtained between PCDDs/DFs and gas residence time also supported the assumption. Received: February 14, 2000 / Accepted: June 30, 2000     

酸浸粉煤灰混凝法处理制革废水的研究

笔者研究了在热电厂粉煤灰中加入少量的鼓风炉铁泥和适量的助溶剂HS,在加热条件下用稀硫酸搅拌浸取2h后,制得集物理吸附和化学混凝为一体的混凝剂。这种混凝剂与聚硅酸铝铁(PSAF)絮凝剂配合处理COD为1500～2000mg/L制革废水,SS,COD,硫化物和铬的去除率分别为95%,93%,92%和88%。该法的显著特点是混凝沉降速度快,污泥体积小,处理废水费用低,此外还探讨了酸浸粉煤灰混凝剂对制革废水的混凝沉降机理。      

煤灰预处理-好氧生物技术处理有机废水的研究

介绍了煤灰预处理-好氧生物技术对有机废水的处理研究。结果表明,当有机废水中COD_Cr为1162mg/L,SS为382mg/L时,该技术对有机废水COD_Cr的去除率达96.9%,悬浮物的去除率达91.5%,处理废水的运行费用为0.22元/t。      

垃圾焚烧飞灰熔融渣特性分析

研究了熔融固化产物--熔融渣的特性.结果表明:熔融渣的主要成分为CaO,Al₂O₃和SiO₂,其含量占总质量的99%左右,而SO₃,K₂O,Na₂O和Cl在熔融渣中的含量明显降低,其质量分数分别从原始飞灰中的10.74%,8 58%,3.81%和20.59%降低到0.17%,0.04%,0.23%和0.11%;熔融渣中碱性氧化物和酸性氧化物的含量基本相同,碱度接近于1.0;重金属Cr和Zn的固定率较高,分别为94.2%和81 7%,而Cu,Pb和Cd的固定率较低,分别为31.4%,14.5%和24.6%;采用美国TCLP方法测试的熔融渣中重金属浸出量均低于国家危险废物浸出毒性鉴别标准限值.      

改性粉煤灰及其处理废水的机理

应用正交设计的基本理论,研究了PDMDAAC(聚二甲基二烯丙基氯化铵)改性粉煤灰的最佳条件,并将改性粉煤灰用于模拟印染废水的处理,探索了改性粉煤灰处理废水的机理。结果表明,在原PDMDAAC的pH下．控制PDMDAAC的浓度为40g／L,恒温30℃．反应1h为最佳改性工艺,改性粉煤灰处理废水的机理以吸附电中和为主。     

垃圾焚烧飞灰熔融过程重金属的迁移特性实验

对垃圾焚烧飞灰的熔融处理过程中重金属的迁移特性进行了实验研究.在自行设计的实验台上研究熔融温度、时间、气氛、冷却方式等条件对几种重金属固化特性的影响.结果表明,熔融可以固化大部分重金属,同时飞灰中重金属在熔融过程中的固化特性因种类不同呈现显著差异,Cd、Pb属于易挥发金属,而Ni、Cr和Zn不易挥发;飞灰成分、温度、气氛和冷却方式对各种重金属的影响程度各不相同.     

Optical and Chemical Methods of Metal Ash Analysis and Tin Recovery

‘Metal ash’ presents a waste disposal problem in most of the developing countries as the industries employ obsolete technologies. In this paper we describe analysis of tin ash, zinc ash and aluminium ash by means of optical methods, such as X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), electron probe micro analysis (EPMA), scanning electron microscopy (SEM) and chemical methods. The results of tin ash obtained by XRD method matched well with the cassiterite, a naturally occurring mineral of tin. ICP-MS studies reveal the presence of a large number of tracer metals, which may cause pollution by tertiary dispersion and this aspect is discussed. Conversely, the data generated by chemical methods are limited. However, the methods are simple and cost-effective. Then, they can easily be adopted by low-budget industries. Simple and cost-effective process to recover tin from tin ash is described. It is based on heating tin ash with sodium cyanide to about 900°C to separate tin component from the metal ash. The process recovers good quality tin and offers a very high yield. The process can be scaled up to small pilot plant.