Solidification Efficiency and Mechanism of Conventional Curing Agents for Sewage Sludge Stabilization and Dewatering

One of the challenges faced by sewage sludge treatment and disposal is its higher water content,and how to efficient dewater those hazardous materials properly is welcome in practice. This study stabilized the sewage sludge via the using of conventional curing agents and calcined aluminum salts,and the corresponding dewatering mechanisms and structural changes of the stabilized sludge were further comparable analyzed.Experimental results showed that wollastonite and kaolin exhibit a relative higher dewatering efficiency as compared to other conventional curing agents; however the releasing rate of heavy metals of Cu,Cr,Ni for kaolin solidification and Zn,Pb for wollastonite solidification is higher than the sludge samples solidified by other curing agents. For comparison,the sludge samples solidified by calcined aluminum salts (AS),calcium ash,Mg-based curing agent,tricalcium aluminate( C_3A) show a lower heavy metals leaching potential and unconfined compressive strength. In addition,the economic characteristics and local availability of AS,calcium ash,C_3A and CaO makes it have a broad prospect in extension and application. These findings are of great significance for stabilization and dewatering of sewage sludge.

Simulated Leaching Research on the Effects of Sewage Sludge on Nutrients and Heavy Metals in Aeolian Sandy Soil

[ Objective] The study aims at discussing the feasibility of urban sewage sludge applied to desertification forestland. [ Method] Through the simulated leaching test, the effects of sewage sludge application on the content of nutrients and heavy metals in aeolian sandy soil were ana- lyzed. [ Result] After the simulated leaching with sewage sludge, the contents of total nitrogen （TN）, total phosphorus （TP）, available nitrogen （AN） and available phosphorus （AP） in each layer of aeolian sandy soil increased significantly, and the increase in 0 -20 cm soil was more signifi- cant than that in 20 -40 and 40 -60 cm soil. Meanwhile, the content of each heavy metal in 0 -20 cm soil rose significantly, while the increase was small in 40 -60 cm soil. In addition, after the application of sewage sludge, the Nemrew Index of aeolian sandy soil was 0.67, lower than the na- tional soil quality standard of forestland （0.70）, and the short-time application of sewage sludge to sandy soil did not cause serious pollution. How- ever, if sewage sludge has been applied to aeolian sandy soil for a long term, the potential hazard of heavy metals （especially Cd） caused by loneterm accumulation should be paid more attention to.

Effects of Heavy Metals on Activated Sludge Microorganism

The efforts of heavy metals on activated sludge microorganisms are reviewed. Although some heavy metals play an important role in the life of microorganism, heavy metals concentrations above toxic levels inhibit biological processes. Copper, zinc, nickel,cadmium and chromium were mostly studied because of their toxicity and widely used, regardless of single or combination. The microorganism response to these heavy metals varied with species and concentrations of metals,factors such as pH, sludge age, MLSS etc. also affect toxicity on the microorganism. The acclimation could extend the microorganism tolerance of heavy metals. The effects of heavy metals on sludge microorganisms could be described with different models, such as Sigmoidal and Monod equation. The kinetic constants are the useful indexes to estimate the heavy metals inhibition on activated sludge system. Methods to measure the toxicity and effects on microorganism community were also reviewed.

Engineering and microstructure properties of contaminated marine sediments solidified by high content of incinerated sewage sludge ash

Management of incinerated sewage sludge ash(ISSA)and dredged contaminated marine sediments(CMSs)is a great challenge for Hong Kong and other coastal cities due to limited landfilling capacity.The present study investigates the use of high content(20%of sediment by mass)of ISSA in combination with cement/lime for solidification/stabilization(S/S)treatment of CMSs to provide a way to reuse the wastes as construction materials.The results showed that ISSA being a porous material was able to absorb a large amount of water rendering a more efficient solidification process of the marine sediment which normally had a very high water content(w80%).The S/S treatment improved the engineering properties of the sediment,but reduced the workability,especially for the lime-treated samples.Lime can be used to replace ordinary Portland cement(OPC)for better heavy metal immobilization and carbon emission reduction.The hardened sediment samples prepared with 10%of lime and 20%of ISSA could attain a strength of 1.6 MPa after 28 d of curing.In addition,leaching tests confirmed that there was no environmental risk induced by these stabilized materials.The formation of hydrated cementitious compounds including calcium silicate hydrate(CeSeH)/calcium aluminate silicate hydrate(C-A-S-H)/hydrocalumite/calcite was mainly responsible for the strength development in the ISSA/lime-treated sediments.

Physicochemical and environmental properties of arsenic sulfide sludge from copper and lead-zinc smelter

Physicochemical properties of arsenic sulfide sludge(ASS) from copper smelter(ASS-I) and lead-zinc smelter(ASS-II) were examined by XRD, Raman spectroscopy, SEM-EDS, TG-DTA, XPS and chemical phase analysis method. The toxicity characteristic leaching procedure(TCLP), Chinese standard leaching tests(CSLT), three-stage sequential extraction procedure(BCR) and batch leaching experiments(BLE) were used to investigate the environmental stability. The ASSs from different smelters had obviously different physicochemical and environmental properties. The phase composition and micrograph analysis indicate that ASS-I mainly consists of super refined flocculent particles including amorphous arsenic sulfide adhered with amorphous sulfur and that ASS-II mainly consists of amorphous arsenic sulfide. The valence state of arsenic in both sludges is trivalent, but the valence composition of sulfur is quite different. The ASSs have thermal instability properties. The results of TCLP and CSLT indicate that the concentrations of As and Pd in the leaching solution exceed the standard limits. More than 5% and 90% of arsenic are in the form of acid soluble and oxidizable fractions, respectively, which explains the high arsenic leaching toxicity and environmental activity of ASS. This research provides comprehensive information for the disposal of ASS from copper and lead-zinc smelter.

The Effects of Environmental Materials on Pb and Cd Solidification

The leaching experiments of soils contaminated by heavy metal Pb or Cd were conducted with four kinds of environmental materials, polymer absorbent material （PAM）, coal-based nutrient （CBN）, mineral adsorption material （MAM） and mineral chemical material （MCM） to explore Pb and Cd solidification effects. Then the Fourier Transform Infrared Spectrometer （FTIR） analysis was used to explain the solidification mechanism of the effective environmental materials, and the Scanning Electron Microscope （SEM） test was applied to demonstrate their solidifi- cation morphology. The results showed that MCM was the best material for Pb solidification, and Pb concentration in the leachate accounted for 68.6% of that in CK; MAM was the best material for Cd solidification, and the Cd concentration accounted for 74.6% of that in CK. The FTIR analysis showed the functional groups, such as C-OH in MCM and COOH in MAM, could explain the adsorption mechanism by ion exchange and chemical bond force. The SEM images indicated there were obvious adsorption morphological changes in MCM and MAM after adsorbing Pb and Cd respectively.

Environmental availability and ecological risk assessment of heavy metals in zinc leaching residue

Four different methods,namely mineralogical analysis,three-stage BCR sequential extraction procedure,dynamic leaching test and Hakanson Potential Ecological Risk Index Method were used to access the environmental activity and potential ecological risks of heavy metals in zinc leaching residue.The results demonstrate that the environmental activity of heavy metals declines in the following order：CdZnCuAsPb.Potential ecological risk indices for single heavy metal are CdZnCuAsPb.Cd has serious potential ecological risk to the ecological environment and contributes most to the potential toxicity response indices for various heavy metals in the residue.

The Cement Solidification of Municipal Solid Waste Incineration Fly Ash

The chemical composition, the content and the leachability of heavy metals in municipal solid waste incineration （ MSWI） fly ash were tested and analyzed. It is shown that the leachability of Pb and Cr exceeds the leaching toxicity standard, and so the MSWI fly ash is considered as hazardous waste and must be solidifled. The effect of solidifying the MSWI fly ash by cement was studied, and it is indicated that the heavy metals can be well immobilized if the mass fraction of the fly ash is appropriate. The heavy metals were immobilized within cement hydration products through either physical fixation, substhtaion, deposition or adsorption mechanisms.

Recovery and stabilization of heavy metal sludge (Cu and Ni) from etching and electroplating plants by electrolysis and sintering

This work dealt with the recovery and stabilization of the sludge with heavy metals (Cu and Ni) produced from etching and electroplating plants. The heavy metals in the sludge were deprived of by acid leaching, followed by precipitation with 28% NH4OH, and finally by electrolysis. In the electrolysis, the recovery percentage and purity were investigated at different electronic currency and temperature. The metal-deprived sludge was stabilized by mixing with glass powder and clay, followed by sintering at high temperature. How the ratio of glass powder to metal-deprived sludge affected final products (sludge bricks) was explored, in terms of specific gravity, absorption capacity, unconfined compressive strength, morphology, the volume shrinkage ratio and burn-up ratio. The volume shrinkage ratio and burn-up ratio of sludge bricks increased with metal-deprived sludge contents. The heavy metal remaining in sludge bricks was assessed through TCLP (toxicity characteristic leaching procedure) and by the analysis of SEM and EDX. The results from TCLP showed that the contents of leached metals were all below the regulatory criteria. This fact approved the feasibility of our method.

Leachability of heavy metals from solidified sludge

Solidified sludge undergoes progressive depletion of the alkalinity materials under natural weathering condition and releases out of heavy metals. The leaching of heavy metals from solidified sewage sludge was studied by acid neutralization capacity (ANC) test and flow-through leaching test. The results of ANC test showed that heavy metals release at high concentration when the pH of extract lowers than 6. The disintegration of solidified sludge and the transformation of heavy metals are the main reasons for the resolubilisation of contaminants. Flow-through leaching test indicated that leaching of heavy metals from solidified sludge occurs in a slow way. A mathematical model has been developed to predict the stabilization time of heavy metals in solidified sludge. The research results showed that decreasing hydraulic conductivity is more important than cement addition for controlling the release of heavy metals from solidified sludge.

Value-added recycling of sludge and sludge ash into low-carbon construction materials:current status and perspectives

Sludge as the by-product of wastewater treatment usually accumulates toxic substances that require specific treatment before disposal.With the increase of sludge production,the safe and economic treatment of sludge has become a global issue.Construction filed provides a solution for consuming huge volumes of sludge and sludge ash owing to the similar chemical composition with cementitious materials.This paper critically reviewed the current status of recycling sludge and sludge ash into low-carbon construction materials and highlighted the future perspectives of sludge-derived construction materials.Furthermore,the immobilization mechanisms of heavy metals in sludge-derived construction materials were elaborated to promote the actualization of sustainable management of sludge and sludge ash.

水泥协同垃圾焚烧飞灰固化渗滤液污泥试验研究

采用硫铝酸盐水泥协同生活垃圾焚烧飞灰作为胶凝材料对渗滤液污泥进行固化,通过无侧限抗压强度试验、浸出毒性分析和微观测试,探索水泥与飞灰的复合固化效果和固化机理.结果表明:当水泥掺量不小于20%时,固化试样的28 d无侧限抗压强度满足填埋强度要求;飞灰是水泥固化渗滤液污泥的优良辅助固化剂,其对水泥固化试样无侧限抗压强度的增强效应存在最优掺量;10%的飞灰可替代10%的水泥而使固化试样达到更好的固化效果;复掺30%或40%水泥+15%飞灰的试样可同时满足填埋强度和浸出毒性的要求.

堆存陈化中电解锰渣重金属形态及环境风险演化

为了探究电解锰渣堆存陈化过程对其重金属赋存形态及环境风险演化的影响规律,采用XRF、XRD和SEM等微观试验对比分析了新鲜与陈化电解锰渣的易溶盐含量、化学成分、微观形貌和相变组成等微观特性差异.此外,基于批次浸出试验和改进BCR顺序提取法评估了新陈电解锰渣中重金属和氨氮的环境风险.结果表明,在堆存陈化过程中,电解锰渣的微观结构呈松散演化,易溶盐含量由12.25%降低至4.38%,酸溶态和可还原态重金属占比逐渐减少,重金属Mn由超高风险降低至中风险,但重金属总量仍高达3.28×10^(4)mg/kg,环境风险严峻,氨氮浸出量虽有所降低,但仍然超出15.00mg/L阈值的2.54~3.84倍,部分氨氮和重金属在堆存过程中释放到周围生态中,需采取必要措施对电解锰渣进行处理.

复合稳定剂对污泥中重金属的稳定化效能研究

重金属赋存是制约污泥资源化利用的重要因素。选取碳酸钙(CaCO3)、羟基磷灰石(HAP)和海泡石(Sepiolite)3种稳定剂,以污泥干重的2%、5%、10%投加到供试污泥中,21 d后,采用四分法取样分析浸出毒性及重金属形态,结果表明:3种稳定剂对Cd的稳定作用较弱;另外,HAP的投入量与As的稳定效果成反比。将3种稳定剂按比例复配后,以同样方法研究各组配比对污泥重金属稳定效果,结果表明:HAP∶sepiolite∶CaCO3(质量比)为1∶1∶1时效果最好;此时,污泥中Cd的稳定率达到了80%以上,As、Cr、Pb及Cu的浸出稳定率接近100%,只有Zn和Ni的稳定率与单一稳定剂时相比无明显变化;Cd、Cr、Pb及Cu的稳定态较之前单一稳定剂作用无明显变化甚至减少,但复合稳定剂可提高残渣态的比例;As、Zn和Ni的形态则未有明显变化;复合稳定剂间的协同作用,促使Cd、Cr、Pb及Cu的形态向更稳定态转化。

污泥共热解制备污泥基生物炭及其在土壤回用中的改良效益

随着全球污泥产量的快速增长,对其的资源化处置是亟待解决的现实问题.相较于传统的填埋以及新型的焚烧工艺,污泥热解可实现污泥的无害化、减量化并生成具有土壤改良潜力的污泥基生物炭,是污泥处理的一种较优选择.本文以市政污泥为研究对象,全面综述了污泥不同热解方法对生成污泥基生物炭的物化性质和其对土壤改良效应的影响,重点介绍了污泥中磷和重金属在不同热解工艺中的迁移转化机制,污泥基生物炭对土壤物化性质的影响机理、对污染土壤的修复机制、对土壤中微生物和微生物酶等的作用机制.通过以上分析,能够以此为理论支撑指导制备具有定向改良土壤功能的污泥基生物炭.本综述将有助于污泥定向热解制备污泥基生物炭的进一步发展,为污泥基生物炭土壤改良提供理论参考和支持.

CGF固化/稳定化重金属污染土强度及浸出特性

通过CGF(由电石渣、粒化高炉矿渣、粉煤灰组成的固废基固化剂)固化/稳定化不同土质种类(由不同黏粒、粉粒、砂粒配比调配)、不同复合重金属(Cu、Ni、Pb、Zn)含量的污染土,借助宏微观试验研究固化/稳定化污染土的强度特性、重金属浸出特性以及固化/稳定化机理.研究结果表明:CGF固化/稳定化重金属污染土强度和重金属浸出浓度主要由养护龄期、重金属含量和土质种类共同决定;随着养护龄期的增加,固化/稳定化污染土强度逐渐增加,但不同重金属含量的强度变化规律不同,存在重金属“临界含量”;随着养护龄期的增加,重金属浸出浓度逐渐减小,其浸出浓度变化规律亦存在重金属“临界含量”,该“临界含量”由养护龄期和土质种类控制,固化/稳定化Clay污染土在7,28,90d的“临界含量”分别为200,300,600mg/kg,28d时固化/稳定化Clay、CSSM511、CSSM111污染土“临界含量”分别为300,200,200mg/kg,固化/稳定化CSSM011污染土不存在“临界含量”.CGF固化/稳定化重金属污染土作用机理包括固化剂对重金属离子的化学沉淀、包裹、吸附、离子交换等稳定化作用和土中黏土矿物对重金属离子的稳定化作用.

无机材料固化镉铅镍污染土的环境效应及失稳机制

固化污染土的环境效应是废土二次应用过程中需研究的工程问题。以镉、铅、镍污染土为研究对象,通过固化率指标初筛适宜固化材料配比,模拟干湿循环、长期浸水、高温、冻融循环环境,以浸出毒性指标评价水泥、水泥+粉煤灰、石灰固化后土体的环境效应,并结合微观形态及重金属形态分析,评价失稳机制。结果表明:无机材料可将土中重金属的固化率提高至90%以上,8%的石灰适用于镉污染土的固化,32%+8%的水泥+粉煤灰适用于铅及镍污染土的固化。水环境(干湿、浸水)条件下固化污染土均不存在环境风险,其浸出毒性均低于《危险废物鉴别标准浸出毒性鉴别》(GB 5085.3-2007)中的限值;但无机材料固化污染土对温度(高温、冻融)敏感,特别是水泥、水泥+粉煤灰固化污染土,在温度超过70℃时的浸出毒性超过标准中限值,在冻融循环5~7次时接近标准限值。高温会促使重金属赋存形态从稳定态向非稳定态转化,冻融循环会破坏重金属-固化产物体系的结构。无机材料固化重金属污染土的应用需要考虑环境温度的影响。

表面处理污泥渣料磨细粉水泥基材料活性激发及其机理

为了更好地提高掺加表面处理污泥与建筑渣土高温烧结渣料磨细粉(简称磨细粉)的火山灰活性,研究了Ca(OH)_(2)对掺加磨细粉硅酸盐水泥基材料的力学性能和重金属浸出规律的影响及机理,并通过XRD、SEM、BET、TG等微观测试技术分析材料的微细观结构特征。结果表明:Ca(OH)_(2)掺量为磨细粉水泥基材料中胶凝材料总质量的0.6%~0.8%时,磨细粉水泥基材料力学性能较优,在60 d时抗折强度和抗压强度较基准组分别提高了11.0%和7.8%;微细观测试结果表明,少量的Ca(OH)_(2)能增大磨细粉水泥基材料硬化浆体的比表面积,增加水化产物数量,提高硬化浆体结构密实性,但Ca(OH)_(2)掺量超过胶凝材料总质量的0.8%之后,对磨细粉水泥基材料结构和性能则会产生负面效应。研究还发现,掺加占胶凝材料总质量0.8%的Ca(OH)_(2)能有效降低磨细粉水泥基材料中有害重金属的浸出浓度,其中Cu、Ni、Zn浸出率比基准组分别降低了17.5%、13.0%、40.8%,可以确保磨细粉水泥基材料中有害重金属Cu、Ni、Zn和Cr的浸出值均低于《水泥窑协同处置固体废物技术规范》(GB/T 30760—2014)中规定的浸出浓度限值。

光伏电池生产和退役回收过程中重金属污染物的释放及环境风险

近年来,在“双碳”战略的指导下,以光伏为首的新能源因其绿色清洁、环境友好和可持续性而发展迅速。但就其生命周期来看,新能源并非完全无污染。本文以光伏为例,聚焦重金属问题,综述了光伏电池在生产制造至退役报废阶段的环境风险,分析了光伏电池尤其是其中的重金属可能产生的环境问题并提出了相应的建议,为我国的新能源绿色高质量发展提供参考。