Estimation of heavy metal transformations in municipal solid waste

The behaviour of heavy metals bound to municipal solid waste (MSW) and exposed to 2 decades of anaerobic waste stabilization processes have been estimated. Heavy metal solid forms in a waste degradation residue have been compared with a reconstructed waste similar to that initially disposed of in 1973. The initial waste was composed of a mixture of shredded MSW (95% dry wt.) and anaerobic sewage sludge (5% dry wt.). A sequential chemical extraction method has been used to fractionate the heavy metals into five categories of available and reactive solid forms. The results imply that these forms can be ascribed to approximately 30% of the total content of the heavy metals in the degraded waste and the portion of heavy metals bound to oxidizable solid forms seems to be higher in the degraded than the fresh MSW. The bulk of the remaining heavy metals are assumed to be less available and bound into resistant lattice structures, such as metal and polymer items. A comparison between fractionation patterns of the waste in this study and of a few sediments collected from different environments imply similarities between the fresh MSW and an oxic sediment from one site and the sewage sludge and anoxic sediments from another site. Fractionation patterns of the degraded waste are found to be quite similar to those of the anoxic sediments, except for Pb, Ni and Cd which are more similar to fresh MSW.     

嘉兴垃圾填埋场渗滤液的土柱淋滤实验研究

通过室内淋滤实验分析垃圾渗滤液-水-岩相互作用过程。实验发现Cl-的保守性是相对的,其中在粉砂土中Cl-存在吸附解吸现象,平衡浓度为4446mg/L时,分配系数Kd=0.18L/kg,而在壤土(亚粘土)中Cl-保持保守。SO42-和F-积极参与水岩相互作用,粉砂土和壤土对SO42-和F-均有较强的吸附作用。阴离子交换作用的结果使大量的NO 3-从粉砂土中解吸出来。     

Anaerobic digestion of the organic fraction of municipal solid waste: influence of co-digestion with manure

Anaerobic digestion of the organic fraction of municipal solid waste (OFMSW) was investigated in two thermophilic (55 degrees C) wet digestion treatment systems R1 and R2. Initially OFMSW was co-digested with manure with a successively higher concentration of OFMSW, at a hydraulic retention time (HRT) of 14-18 d and an organic loading rate (OLR) of 3.3-4.0 g-VS/l/d. Adaptation of the co-digestion process to a OFMSW:manure ratio of 50% (VS/VS) was established over a period of 6 weeks. This co-digestion ratio was maintained in reactor R2 while the ratio of OFMSW to manure was slowly increased to 100% in reactor R1 over a period of 8 weeks. Use of recirculated process liquid to adjust the organic loading to R1 was found to have a beneficial stabilization effect. The pH rose to a value of 8 and the reactor showed stable performance with high biogas yield and low VFA levels. The biogas yield from source-sorted OFMSW was 0.63-0.71 l/g-VS both in the co-digestion configuration and in the treatment of 100% OFMSW with process liquid recirculation. This yield is corresponding to 180-220 m3 biogas per ton OFMSW. VS reduction of 69-74% was achieved when treating 100% OFMSW. None of the processes showed signs of inhibition at the free ammonia concentration of 0.45-0.62 g-N/l.     

Electrolysis of soluble organic matter in leachate from landfills

Laboratory experiments were conducted to investigate the effectiveness of electro-chemical methods for treating leachates from municipal garbage landfills. Chemical oxygen demand (COD) removal range from 30 to 50% were obtained with a batch electro-chemical reactor using two different electrode pairs, Fe---Cu or Al---Cu. Both electrolysis and electro-coagulation were observed for the removal of the organic matter in the leachates, with the former mechanism being the dominant in this investigation. The organic matters were found to be electrolyzed at an applied voltage as low as 2.0 V. IR spectra analyses of treated leachates confirmed that intense oxidation took place throughout the electro-chemical experiments.     

The influence of weathering and organic matter on heavy metals lability in silicatic, Alpine soils

We investigated the effect of organic matter and weathering on the lability and solid phase speciation of heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in two contrasting subalpine regions in the Italian Alps. Cr, Ni and Cu could be linked to weathering. This was not the case for Pb. Since organic matter (OM) influences the solid phase speciation of heavy metals, the total organic C and N content, the C and N content of different density fractions of OM and also of the labile (oxidised by H₂O₂) and stable (H₂O₂-resistant) fractions were determined. Soil OM stocks were high and soils on north-facing slopes had more OM than the south-facing sites to which they were paired. Density measurements and the H₂O₂ fractionation indicated that the higher OM content on north-facing sites was due to an accumulation of weakly degraded organic material. Due to higher weathering intensity on north-facing sites, the abundance of the EDTA-extractable heavy metals was higher than on south-facing sites. All EDTA-extractable heavy metals showed a good correlation to the water-soluble phenolic concentrations which indicates that the metals were probably translocated as metal-organic complexes. Pb and Cu correlate not only to the light (density < 1 g/cm³) and labile, organic fraction but also to the heavy (density > 2 g/cm³) and stable fraction. High-mountain ecosystems like the Alps are sensitive to changing environmental conditions such as global warming. A warmer climate and the more favourable conditions it brings for biological activity, especially at cooler sites, will probably lead in the short- to mid-term to an increased loss of accumulated, weakly degraded OM. As the Pb and Cu content is significantly related to the labile organic matter pools, the risk exists that an increase in OM mineralisation could affect the storage capacity and mobility of these metals in soils.     

掺烧城市垃圾残渣硅酸盐水泥性能及重金属浸出行为研究

通过生料易烧性试验、熟料矿物岩相分析、XRD、SEM、水泥胶砂强度试验、重金属离子浸出试验等,对利用城市垃圾分拣残渣配料煅烧硅酸盐水泥熟料及其水化反应的特征进行了研究。结果表明:城市垃圾分拣残渣配料制成的水泥熟料,其矿物结构与常规的硅酸盐水泥熟料相同;其烧成温度有降低的趋势;其水化产物和凝结硬化过程与常规硅酸盐水泥相同;熟料煅烧和凝结硬化过程对城市垃圾中重金属离子的固化有一定的辅助作用。     

城市生活垃圾中优先流规律的穿透试验研究

城市生活垃圾具有大孔隙特性,优先流是垃圾中水分运动的重要形式,目前垃圾中优先流基本规律尚不明确,优先流数值分析时相关参数的选取尚缺乏依据。通过垃圾柱穿透试验研究城市生活垃圾中的优先流,以Cl-为示踪剂,进行了不同埋深和龄期试样、不同高度试样和不同入渗强度的穿透试验,得到溶质穿透曲线,运用对数正态分布模型和双峰概率密度模型拟合试验结果,定量分析了垃圾中优先流规律。结果表明,通过大孔隙运移的溶液占比在55%~70%之间,垃圾中优先流现象明显。随着垃圾的埋深和龄期增加,参与溶质运移的孔隙比例增加,但通过大孔隙运移的比例减少,优先流程度降低;试样高度增加,参与溶质运移的孔隙比例增加,但其内部大孔隙贯通性变差,通过大孔隙运移占比减小,优先流程度降低;入渗强度增大,参与溶质运移的大孔隙占比增加,优先流程度增大。双峰概率密度模型比对数正态分布模型能更好地描述垃圾中溶质运移的优先流规律,同时为使用两域模型进行垃圾水分运移分析时的参数取值提供了依据。     

Aging of air pollution control residues from municipal solid waste incinerator: role of water content on metal carbonation

This work studies the effect of water content on the aging of APC residues, with a liquid to solid ratio (L/S) of 0.25 or 10, aged with or without exposure to ambient air. After the residue was mixed with water, CaSO4 and (Na,K)Al3(SO4)2(OH)6 in the raw sample yielded ettringite. When CO2 were available, this ettringite was further transformed to gypsum, calcite and possibly gibbsite. Experimental data revealed that the concentrations of Pb, Zn, Cd, Hg, and Cu fell with age, whereas that of Cr increased. Given L/S=10, excess Ca2+ ions were present in the suspension, so a precipitate of primarily calcite crystals of sizes under 5 microm formed on the air-water surface. This layer significantly reduced the rates of decline of Pb, Zn, Cd and Hg contents, and also reduced the increasing rate of Cr content in the suspension. This result follows from the mass transfer barrier of CO2 added at the air-water surface and the occurrence of subsequent chemical reactions in the suspension. An estimate of the mass transfer rate revealed that the rate-controlling step with L/S=10 was the dissolution and diffusion of CO2 in the bulk solution. However, at L/S=0.25, the rate-limiting step was the dissolution of metals from ash particles. Water content is a very important process factor, whose distribution in the sample, and the resulting competition between carbonate ion flux and heavy metal flux, govern the reaction time required during the natural aging process.     

废弃混凝土中重金属浸出性研究

以我国现有废弃混凝土为原料,研究废弃混凝土中重金属含量,采用模拟德国水槽试验法,以不同粒径、不同pH值、不同重金属元素(Cd、Cr、Cu、Ni、Pb、Z)为影响因素,研究废弃混凝土中重金属离子的浸出性,结果表明,废弃混凝土中不同重金属含量不同,以Zn含量最高,Cr含量最低;粒径在1mm以上时随着粒径增加重金属浸出性减小...     

生活垃圾焚烧炉渣制备免烧墙体砖对环境负荷的影响

运用生命周期评价法,以试验和生产数据为基础,参考有关统计数据及资料,对利用生活垃圾焚烧炉渣制备免烧墙体砖、灰砂砖及烧结砖进行比较分析,探讨功能单位墙体砖制备过程及与其相关的原料开采、原油生产、电力生产和煤炭生产过程对环境负荷的影响.结果表明,功能单位焚烧炉渣免烧墙体砖、灰砂砖和烧结砖的环境负荷分别为3.51x10-12/a.3.58x10-12/a和6.60x10-12/a;生活垃圾焚烧炉渣免烧墙体砖与烧结砖相比,可减少不可再生资源消耗54%,与灰砂砖和烧结砖相比,可分别减少不可再生能源消耗43%和62%.     

垃圾土电阻率特性试验研究

以重庆市长生桥垃圾填埋场作为研究对象,基于垃圾土颗粒导电性分类,通过室内试验测试了不同因素(添加不同溶液、孔隙率、含水率、温度等)影响下垃圾土电阻率变化特征。试验结果表明:当垃圾土中添加渗滤液、Na Cl、Zn Cl2和柴油4种溶液时,垃圾土电阻率随垃圾土中孔隙率的增加均呈递减趋势;孔隙率一定时,随含水率的增加垃圾土中固液并联导电在垃圾土导电通路中的比例增大;渗滤液对垃圾土电阻率的影响在一定程度上受稀释作用控制,且随含水率的增加而减小;随着温度的升高,垃圾土的电阻率呈指数函数衰减趋势;含水率一定时,孔隙率的变化将引起垃圾土中3种导电模式的互相转化,且电阻率随孔隙率的增加呈幂函数减小趋势;利用高密度电阻率层析技术,对现场垃圾填埋体进行了电阻率实测,同时结合室内试验测试结果对电阻率剖面进行了分析;研究结果可为分析因降解引起的垃圾填埋体中渗滤液的富集状态和运移途径的变化,以及评价垃圾土内部结构的演化提供理论支持。     

城市生活垃圾降解-压缩特性试验研究

为了研究垃圾土在好氧和厌氧阶段因外部温度场的变化对降解特性的影响,选取重庆市某垃圾场作为研究对象,进行了两种不同温度控制的降解试验,同时对渗滤液中可溶解有机碳含量进行了追踪测试,试验结果表明：①不同有机物含量垃圾土试样,当外部温度场小于22℃或者大于45℃时,温度对有机质降解的影响较小;②当温度在22℃~45℃时,根据垃圾土产气量、渗滤液溢出量以及质量损失率得出此温度区间对垃圾中有机质的降解起明显加速作用,降解反应程度在41℃时最大;③根据温度-质量损失率关系,推导了考虑温度效应的分阶段垃圾土降解率计算模型,并且得出垃圾土的降解率在0~180 d符合自然降解规律,为时间的函数;在180~360 d,降解率为时间和温度的双重函数;模型验证结果表明,计算结果与试验结果能够比较好的吻合。     

城市固体废弃物动力特性试验研究

参照杭州天子岭填埋场城市固体废弃物(MSW)主要成分,人工配制固体废弃物试样,利用中型动三轴试验仪研究其在较大应变范围内MSW的动力特性。MSW的动剪切模量Gd和阻尼比D随着动剪应变γd的变化曲线与泥炭土的相关曲线形状基本一致,并且在相同应变时数值相差不大。在相同的动剪应变水平下,随着围压的增大,Gd增加而D减小;当动剪应变增大时,Gd减小而D增大。由于MSW的高压缩性,初始孔隙比不同对试样的动力特性影响不大。同时进行了现场剪切波速试验,确定了最大动剪切模量Gdmax的估算式。为便于应用,建议了归一化Gd和D与动剪应变依赖关系的取值范围和平均值曲线,并将其与OII填埋场MSW动力特性的研究结果进行对比,可以看出MSW的成分对其动力特性的影响还是比较大。     

Arsenic speciation and mobilization in CCA-contaminated soils: influence of organic matter content

A laboratory incubation experiment was conducted to investigate the influence of organic matter content on arsenic speciation and mobilization in chromated copper arsenate (CCA)-contaminated soils. The study was performed with four synthetic CCA-contaminated soils, with a range of organic matter content (mixture of peat moss and poultry manure) varying between 0.5% and 15% (w/w), under unsaturated and aerobic conditions for 40 days. Changes in water-soluble arsenic speciation (As(V), As(III), MMAA, DMAA) were monitored over time in soil extracts by HPLC-ICP-MS and in the soil solid phase (As(III), As(V)) by a solvent extraction method. Irrespective of organic matter content, As(V) was the predominant soil bound and aqueous phase arsenic species. However, over 40 days, a high soil organic matter content (7.5% and 15%) was able to entail formation of soil bound As(III). Moreover, total water-soluble arsenic was positively correlated with dissolved organic carbon (r(2)=0.88). However, the organic matter content did not influence arsenic speciation in the soluble fraction; neither As(V) reduction nor arsenic biomethylation occurred within 40 days. An increase in dissolved organic carbon content promoted both As(V) and As(III) solubilization in soils. Also, over time, organic matter contents of 7.5% and 15% entailed the persistence of soluble As(V), likely due to the high content of dissolved organic compounds which prevented its sorption onto soil. Based on this data, the environmental risk of aerobic CCA-contaminated soils rich in organic matter may be due to an enhanced availability of soluble As(V) over time, rather than to the formation of the more toxic and more mobile As(III).     

Characterization of soluble organic matter of waste activated sludge before and after thermal pretreatment

Microwave (MW) irradiation and conventional heating (CH) at 96 °C was successful in disrupting the complex waste activated sludge (WAS) floc structure and releasing extra- and intra-cellular biopolymers, such as protein and sugars from activated sludge flocs into soluble phase along with solubilization of particulate chemical oxygen demand (COD). Soluble CODs of CH and MW-irradiated WAS were 361±45% and 143±34% higher and resulted in 475±3% and 211±2% higher cumulative biogas productions (CBP) relative to the control at the end of 23 days of mesophilic anaerobic digestion, respectively. Ultrafiltration (UF) was used to characterize the soluble molecular weight (Mw) distributions of control (unpretreated), CH and MW-irradiated WAS. Depending on the Mw fraction, the range of substrate volumetric utilization rate increases from anaerobic digesters was between 94% and 84% for CH and 26–113% for MW compared to the control for the first nine days of the digestion. Digesters treating high Mw (>300 kDa) materials resulted in smaller biodegradation rate constants, k, indicating that microorganisms require a longer time to utilize high Mw fractions which are most likely cell wall fragments and exopolymers.     

The influence of spent household batteries to the organic fraction of municipal solid wastes during composting

The objective of this work was to investigate the potential transfer of 9 heavy metals from spent household batteries (zinc-carbon and alkaline-manganese batteries) to the organic fraction of municipal solid wastes during active composting. Six runs were performed including one control and 2 replications. Eleven types of alkaline and non-alkaline batteries were added at 3 different levels to the organic fraction of municipal solid wastes, namely at percentages equal to 0.98% w/w (low), 5.2% w/w (medium) and 10.6% w/w (high). Experiments were performed in 230 l insulated plastic aerobic bioreactors under a dynamic air flow regime for up to 60 days. Iron, copper and nickel masses contained in the organic fraction of the wastes were found significantly higher in the high level runs compared to the corresponding masses in the control. No metal transfer was obtained in the low and medium level runs. Metal mass balance closures ranged from 51% to 176%. Metals' concentrations in the leachates were below 10 mg l⁻¹ for most metals, except iron, while an increasing concentration trend versus time was measured in the leachates of the high level runs. In all cases, the contents of 5 regulated heavy metals in all end products were below the Hellenic limits.     

Changes in organic matter and residual effect of amendment with two-phase olive-mill waste on degraded agricultural soils

Agricultural soils from many parts of the Mediterranean region are very poor in organic matter and are exposed to progressive degradation processes. Therefore, additions of the olive-mill waste from a continuous two-phase system as an organic amendment can improve soil quality and hence mitigate the negative environmental and agronomic limitations of these soils. A field study under semiarid Mediterranean conditions was conducted to evaluate the changes in organic matter after four consecutive annual additions of olive-mill watery husk (OMWH) waste and the de-oiled two-phase olive pomace (TPOP) waste on an olive grove soil: a cutanic Luvisol (CL). Treatments included a control, OMWH (30 and 60 Mg ha(-1), DW equivalent), and TPOP (27 and 54 Mg ha(-1), DW equivalent). Also, a two-year greenhouse study using wheat (Triticum aestivum L.) was conducted to evaluate the residual effects of adding OMWH to CL soil and to a degraded Leptic Cambisol (LC). Treatments included five OMWH rates ranging from 0 to 40 Mg ha(-1). Significant increases in total organic carbon (TOC), water soluble organic carbon (WSOC), humic and fulvic acids, and aggregate stability were observed in the treated plots, and the highest humification index was obtained when OMWH was applied at the lowest rate. The increase in aggregate stability correlated positively and highly significantly (P<0.01) with the humic and fulvic acid and WSOC contents. In the greenhouse, significant increases in TOC, carbohydrates, aggregate stability, total N, available K, and cation exchange capacity were observed in both soils. However, available P decreased significantly. There was an increased residual fertilization effect of OMWH for both soils. The best fits to grain yield and OMWH rates were with a linear regression for the CL soil (R(2)=0.957 and P<0.01), and a quadratic regression for the LC soil (R(2)=0.960 and P<0.01).     

重庆市城市生活垃圾的蠕变特性研究

首先以分别加载的方式对以重庆市城市生活垃圾典型组分为依据配制的垃圾试样进行不同应力水平的室内压缩蠕变试验,进而根据蠕变元件的基本性质和试验过程中试样反映出的变形特征,利用HK和PTH蠕变模型对生活垃圾的蠕变曲线进行拟合,并总结得出蠕变模型的基本参数。研究表明,HK和PTH模型对试验数据的拟合程度都比较好,此两种模型对于垃圾填埋场的容量计算和沉降规律研究具有一定的参考价值。     

城市固体废弃物残余变形特性试验研究

利用中型动三轴仪,对城市固体废弃物（MSW）进行了残余变形试验研究,采用改进的沈珠江模型对MSW的残余变形模型参数进行拟合,在此基础上,讨论了不同破坏标准下的应力水平对模型参数的影响,建议了适合MSW的残余变形模型应力水平指数。MSW属于应变硬化型材料,应力和应变曲线没有明显的峰值,不同破坏标准条件下,相同固结比的MSW具有不同的应力水平,因此建议用固结应力比来代替应力水平,提出了适用于MSW的残余变形修改模型,修改后的模型不必考虑破坏标准对残余变形参数的影响,应用更加方便。     

Bioreactivity of leachate from municipal solid waste landfills - assessment of toxicity

With the UK producing 400 million tonnes of waste each year, the problem of waste disposal is recognised as one of the most serious environmental problems facing the nation. Of this, over 35 million tonnes is municipal waste, largely derived from households, but also includes some commercial and industrial waste. There are strong national and international concerns about the possible adverse health effects of living in the vicinity of municipal waste landfills. An understanding of the ranges of toxicity of landfill emissions is crucial to determine the degree of concern we should have about the potential effects they could have upon nearby populations and the surrounding environment. Leachates from three different types of landfills have been collected and screened for their potential to induce toxicity. Bioreactivity was measured by a plasmid DNA scission assay (PSA), and 2',7'-dichlorodihydrofluorescin fluorescence (DCFH). The results indicate that leachates cause damage to plasmid DNA in a dose-dependent manner and that toxicity varies between different types of landfills as well as within individual waste sites. Overall, the data implies that the complex chemistry involved in leachate formation has yet to be delineated in terms of the toxicological response.