Optimizing sludge dewatering with a combined conditioner of Fenton's reagent and cationic surfactant

Enhancing sludge dewatering is of importance in reducing environmental burden and disposal costs. In this work, a cationic surfactant, cetyl trimethyl ammonium bromide (CTAB), was combined with Fenton's reagent for sludge dewatering. Results show that the Fenton-CTAB conditioning significantly promotes the sludge dewatering. Using combined techniques of response surface methodology and uniform design, dosages of Fe²⁺, H₂O₂, and CTAB for water content response were optimized to be 89, 276, and 233?mg/g dry solids (DS), respectively. The water content of sludge decreased from 79.0% to 66.8% under the optimal conditions. Compared with cationic polyacrylamide, the Fenton-CTAB system exhibited superior sludge dewatering performance. To gain insights into the mechanisms involved in sludge dewatering, the effects of Fenton-CTAB conditioning on the composition of extracellular polymeric substances (EPS) and the morphology of the sludge flocs were investigated. The decomposition of EPS into some dissolved organics and the release of proteins in tightly bound EPS facilitated the conversion of bound water to free water and further reduced the water content of sludge cake. After conditioning, morphology of sludge showed aggregation. Overall, the enhanced sludge dewatering by Fenton-CTAB treatment provides an efficient way for management of sewage sludge.     

Size distribution of particulate polycyclic aromatic hydrocarbons in fresh combustion smoke and ambient air: A review

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous in the atmosphere and they mostly stem from the imperfect combustion of fossil fuels and biofuels. PAHs are inherently associated with homogenous fine particles or distributed to different-sized particles during the aging of air masses. PAHs carried by fine particles undergo a long-range transport to remote areas while those adsorbed on coarse particles have a shorter lifetime in ambient air. More importantly, PAHs with higher molecular weights tend to be bound with finer particles and can deeply enter the lungs, posing severe health risks to humans. Thus, the environmental fate and health effects of particulate PAHs are strongly size-dependent. This review summarizes the size distributions of particulate PAHs freshly emitted from combustion sources as well as the distribution patterns of PAHs in ambient particles. It was found that PAHs from stationary sources are primarily bound to fine particles, which are slightly larger than particles to which PAHs from mobile sources are bound. In ambient air, particulate PAHs are distributed in larger size modes than those in the combustion fume, and the particle size decreases with PAH molecular weight increasing. The relevant mechanisms and influencing factors of particle size distribution changes are illustrated in this article, which are essentially attributed to combustion and ambient temperature as well as the physical and chemical properties of PAHs. Overall, the study on the particle size distribution of PAHs will contribute for a full understanding of the origin, atmospheric behaviors and health effects of particulate PAHs.     

洛川红黏土-黄土记录的风向变化及磁组构与磁化率对气候变化的敏感性对比

磁组构分析是研究季风风向的一种常用手段。对洛川黄土剖面黄土-红黏土界线附近地层进行磁组构研究表明:洛川剖面新近纪—第四纪过渡时期,风向整体呈南北向,且从红黏土沉积阶段到黄土沉积阶段,风向呈现顺时针方向的微小偏移,这可能与新近纪到第四纪的气候变化背景有关。另外,磁化率各向异性度P、磁线理L、磁面理F等参数曲线与磁化率曲线的对比显示:磁化率各向异性P、L、F参数的变化稍超前于磁化率曲线的变化,这与蓝田段家坡剖面的磁组构研究结果类似。导致以上结果的原因尚未确定,但可能与磁组构信息被记录于沉积物的速度快于沉积物磁化率值的改变有关。     

Pre-treatment of pyridine wastewater by new cathodic–anodic-electrolysis packing

A novel cathodic–anodic-electrolysis packing(CAEP) used in the treatment of pyridine wastewater was researched, which mainly consisted of 4,4′-diamino-2,2′-disulfonic acid(DSD acid) industrial iron sludge. The physical properties and morphology of the packing were studied. The CAEP was used in a column reactor during the pretreatment of pyridine wastewater. The influence of p H, hydraulic retention time(HRT), the air–liquid ratio(A/L)and the initial concentration of pyridine were investigated by measuring the removal of total organic carbon(TOC) and pyridine. The characterization results showed that the bulk density, grain density, water absorption percentage and specific surface area were 921 kg/m3,1086 kg/m3, 25% and 29.89 m~2/g, respectively; the removal of TOC and pyridine could reach50% and 58% at the optimal experimental conditions(p H = 3, HRT = 8 hr, A/L = 2). Notably,the surface of the packing was renewed constantly during the running of the filter, and the handling capacity was stable after running for three months.     

Photocatalytic properties of P25-doped TiO2 composite film synthesized via sol–gel method on cement substrate

TiO_2 films have received increasing attention for the removal of organic pollutants via photocatalysis. To develop a simple and effective method for improving the photodegradation efficiency of pollutants in surface water, we herein examined the preparation of a P25-TiO_2 composite film on a cement substrate via a sol–gel method. In this case, Rhodamine B(Rh B)was employed as the target organic pollutant. The self-generated TiO_2 film and the P25-TiO_2 composite film were characterized by X-ray diffraction(XRD), N_2 adsorption/desorption measurements, scanning electron microscopy(SEM), transmission electron microscopy(TEM), and diffuse reflectance spectroscopy(DRS). The photodegradation efficiencies of the two films were studied by Rh B removal in water under UV(ultraviolet) irradiation. Over 4 day exposure, the P25-TiO_2 composite film exhibited higher photocatalytic performance than the self-generated TiO_2 film. The photodegradation rate indicated that the efficiency of the P25-TiO_2 composite film was enhanced by the addition of the rutile phase Degussa P25 powder. As such, cooperation between the anatase TiO_2 and rutile P25 nanoparticles was beneficial for separation of the photo-induced electrons and holes. In addition, the influence of P25 doping on the P25-TiO_2 composite films was evaluated. We found that up to a certain saturation point, increased doping enhanced the photodegradation ability of the composite film. Thus, we herein demonstrated that the doping of P25 powders is a simple but effective strategy to prepare a P25-TiO_2 composite film on a cement substrate, and the resulting film exhibits excellent removal efficiency in the degradation of organic pollutants.     

2,4-二氯苯酚在黄土中的吸附-解吸行为研究

本以自制的模拟系统研究了溶液浓度、离子强度、pH值和常见金属离子对2，4-二氯苯酚在黄土中迁移行为的影响，并对实验数据用Freudlich和Langmuir经验公式进行了拟合。结果表明，2，4-二氯苯酚在黄土中的吸附／解吸过程包括两个阶段：渗滤液浓度在初始阶段降低迅速，在第二阶段变化缓慢逐渐达到平衡。用分布活性模型能很好地解释这一结果。在实验条件下，离子强度对迁移行为影响不显。在实验的pH范围内，随着pH的升高，吸附量降低，相应的解吸量加大；与碱金属离子Mg^2 、Ca^2 相比，过渡金属离子Zn^2 、Mn^2 和Cd^2 的存在能显促进黄土对2，4-二氯苯酚的滞留能力。但滞后因子尺始终较低，表明天然黄土对如2，4-二氯苯酚这样的水溶性有机物染物的滞留能力较差。在对被这类有机物污染的土壤进行修复过程中，有机物对地下水可能造成的影响是必须予以考虑的因素。     

青藏高原东缘黄土与环境变化研究进展

系统分析了青藏高原东缘黄土地层研究的主要内容和方法,指出了该区黄土与环境变化研究中存在的问题及未来研究方向.青藏高原东缘山原峡谷地带呈不连续分布的黄土地层,是1.15 MaB.P.以来冰缘物质风成沉积的结果.黄土沉积和成壤特征反映了沉积以来的古气候演变特征,也为青藏高原隆升和冰川研究提供了证据.黄土台地的形成与早期人类...     

深切悼念刘东生先生

中国"黄土之父"、著名地质学家、环境学家、中国科学院资深院士--刘东生先生因病医治无效,于2008年3月6日11时52分在北京逝世,享年91岁.     

西北黄土对五氯酚钠的吸附及影响因素研究

以西北地区天然黄土为供试土样,通过吸附热力学和动力学试验研究了五氯酚钠(PCP-Na)在黄土上的吸附行为,并对可能的影响因素如溶液pH值、初始质量浓度及土壤粒径对PCP-Na在供试土样上吸附的影响进行了探讨。结果表明:PCP-Na在西北黄土上的动力学吸附过程符合准二级吸附动力学模型,其平衡吸附时间为16 h;西北地区黄土对PCP-Na的等温吸附较好地符合Freundlich吸附模型;黄土对PCP-Na的吸附自由能变(ΔG)、吸附焓变(ΔH)及吸附熵变(ΔS)均为负值,表明吸附是一个自发的放热过程,并且吸附过程中体系混乱度减小。溶液pH值和初始质量浓度对PCP-Na在黄土上的吸附影响较大。溶液pH值在4~10之间升高,PCP Na平衡吸附容量呈先减小后增大的趋势,当溶液pH值为6时吸附容量最小;PCP-Na初始质量浓度从6 mg/L增至40 mg/L,其在黄土上的吸附容量从33.43 mg/kg增至100.93 mg/kg。黄土颗粒粒径越小,PCP-Na在土样上的吸附容量越大,黄土粒径由0.075 mm增至0.425 mm,吸附容量由134.26 mg/kg降至28.71 mg/kg。     

渗流作用下节理型黄土开挖边坡塌滑破坏分析

黄土节理在黄土地区普遍发育.通过野外现场地质调查。发现调查区域黄土开挖边坡垂直节理较多,不稳定的黄土边坡体被黄土垂直节理分割后,与其下部缓倾角黄土节理组合而成的裂隙滑动面在降雨作用下往往能形成塌滑破坏。建立了调查区域露天煤矿某黄土开挖边坡的概化三维数值分析模型,模拟分析了在3种降雨条件(20 mm/d,40 mm/d,100 mm/d)下降雨2 d后概化模型的孔隙水压力、位移、塑性区面积情况,提出此类黄土开挖边坡应注意黄土垂直节理与缓倾角黄土节理组合而成的裂隙滑动面的防治,为工程地质条件地区相同的黄土开挖边坡塌滑变形破坏分析以及防治提供了一种可行的分析方法。