Simultaneous removal of arsenic and antimony from mining wastewater using granular TiO2: Batch and field column studies

Coexisting arsenic (As) and antimony (Sb) in mining wastewater is a common and great concern. On-site simultaneous removal of As and Sb from mining wastewater was achieved by using a reusable granular TiO₂ column in this study. To evaluate the accuracy of the scale-up procedure, As and Sb adsorption from wastewater was studied in both large (600 g TiO₂) and small columns (12 g TiO₂) based on the proportional diffusivity rapid small-scale column tests (PD-RSSCTs) design. The comparable As and Sb breakthrough curves obtained from small and large columns confirmed the accuracy of the PD-RSSCT theory in the design of large-scale columns. Meanwhile, the consistent As and Sb adsorption results from batch and column experiments suggested that TiO₂ adsorption for As and Sb can be predicted from bench-scale tests. Charge distribution multi-site complexation (CD-MUSIC) and one-dimensional transport modeling integrated in the PHREEQC program were performed to study the adsorption behaviors of As and Sb on the TiO₂ surface. Coexisting ions, such as Ca^2 +, Mg^2 +, and Si^4 +, play an important role in As and Sb adsorption, and the breakthrough curves were well simulated after considering the compound ion effects. The results from this study highlight the surface reactions of As and Sb on TiO₂ and provide a practical way for on-site remediation of industrial wastewater.     

Effectiveness of aerobic pretreatment of municipal solid waste for accelerating biogas generation during simulated landfilling

Effect of aerobic pretreatment of MSW on landfill gas generation was investigated. Volatile solid (VS) loss of MSW is an effective and comparable indicator. Chinese MSW requires at least a reduction of VS about 27% (w/w) prior to disposal. Aerobic pretreatment of MSW reduced lag phase more than 90% before methanogenesis. Aerobic pretreatment degree influences quantity of gas generation. This study evaluates the effectiveness of aerobic pretreatment of municipal solid waste (MSW) on reducing lag phase and accelerating biogas generation. Aerobic pretreatment degree (APD) was determined on the basis of reduction in volatile solids (VS) on a wet weight basis. In this study, intermittent aeration (IA) was applied to three reactors as a main aeration mode; since a single reactor was operated under continuous aeration mode. However, the purpose of the experiment was to reduce VS content of waste, irrespective of the comparison between aeration modes. Fresh MSW was first pretreated aerobically with different aeration rates (10, 40, 60 and 85 L/min/m³) for the period of 30–50 days, resulting in VS-loss equivalent to 20%, 27%, 38% and 53% on w/w basis for the wastes A1, A2, A3 and A4, respectively. The cumulative biogas production, calculated based on the modified Gompertz model were 384, 195, 353, 215, and 114 L/kg VS for the wastes A0, A1, A2, A3 and A4, respectively. Untreated waste (A0) showed a long lag phase; whereas the lag phases of pretreated MSW were reduced by more than 90%. Aerobically pretreated wastes reached stable methanogenic phase within 41 days compared to 418 days for untreated waste. The waste mass decreased by about 8% to 27% compared to untreated MSW, indicative that even more MSW could be placed in the same landfill. The study confirmed the effectiveness of aerobic pretreatment of MSW prior to landfilling on reducing lag phase and accelerating biogas generation.     

Pollution profiles and physicochemical parameters in old uncontrolled landfills

The long-term effectiveness of the geological barrier beneath municipal-waste landfills is a critical issue for soil and groundwater protection. This study examines natural clayey soils directly in contact with the waste deposited in three landfills over 12 years old in Spain. Several physicochemical and geological parameters were measured as a function of depth. Electrical conductivity (EC), water-soluble organic carbon (WSOC), Cl⁻, NH₄⁺, Na⁺ and exchangeable NH₄⁺ and Na⁺ were used as parameters to measure the penetration of landfill leachate pollution. Mineralogy, specific surface area and cationic-exchange capacities were analyzed to characterize the materials under the landfills. A principal component analysis, combined with a Varimax rotation, was applied to the data to determine patterns of association between samples and variables not evident upon initial inspection. The main factors explaining the variation in the data are related to waste composition and local geology. Although leachates have been in contact with clays for long time periods (13-24 years), WSOC and EC fronts are attenuated at depths of 0.2-1.5 m within the clay layer. Taking into account this depth of the clayey materials, these natural substrata (>45% illite-smectite-type sheet silicates) are suitable for confining leachate pollution and for complying with European legislation. This paper outlines the relevant differences in the clayey materials of the three landfills in which a diffusive flux attenuation capacity (A_c) is defined as a function (1) of the rate of decrease of the parameters per meter of material, (2) of the age and area of the landfill and (3) of the quantity and quality of the wastes.     

Chemical oxygen demand reduction in coffee wastewater through chemical flocculation and advanced oxidation processes

The removal of the natural organic matter present in coffee processing wastewater through chemical coagulation-flocculation and advanced oxidation processes （AOP） had been studied. The effectiveness of the removal of natural organic matter using commercial flocculants and UV/H202, UV/O3 and UV/H2O2/O3 processes was determined under acidic conditions. For each of these processes, different operational conditions were explored to optimize the treatment efficiency of the coffee wastewater. Coffee wastewater is characterized by a high chemical oxygen demand （COD） and low total suspended solids. The outcomes of coffee wastewater treatment using coagulation-flocculation and photodegradation processes were assessed in terms of reduction of COD, color, and turbidity. It was found that a reduction in COD of 67% could be realized when the coffee wastewater was treated by chemical coagulation-flocculation with lime and coagulant T-1. When coffee wastewater was treated by coagulation-flocculation in combination with UV/H2O2, a COD reduction of 86% was achieved, although only after prolonged UV irradiation. Of the three advanced oxidation processes considered, UV/H2O2, UV/O3 and UV/H2O2/O3, we found that the treatment with UV/H2O2/O3 was the most effective, with an efficiency of color, turbidity and further COD removal of 87%, when applied to the flocculated coffee wastewater.     

温度和污泥浓度对短程内源反硝化脱氮的影响

采用SBR反应器,以亚硝酸盐(NO2-)作电子受体,对温度和污泥浓度对短程内源反硝化脱氮的影响进行了研究。结果表明,在15～30℃范围内,随着温度的升高,短程内源反硝化速率逐渐增高,温度每升高10℃,反硝化速率增加3倍。温度一定时,污泥浓度增加,短程内源反硝化速率也相应增加,当MLSS从4000mg/L变化到12000mg/L时,反硝化速率从开始的0.0259gN/(gVSS·d)增加到了0.0378gN/(gVSS·d),即增大了近1.5倍,即采用较高污泥浓度可以大大节省反应时间。     

风浪扰动下的太湖悬浮物实验与模拟

采用太湖湖区底泥,根据波浪水槽实验总结了各种扰动强度下太湖底泥的起动切应力.波浪水槽可以系统地模拟太湖常见的波浪强度.通过实验确定了太湖底泥的临界切应力为0.050 Pa,采用国外先进的FVCOM模型计算模拟了太湖流场和悬浮物分布并和太湖实测资料进行了对比,结果较为合理,证明了模型的有效性.由于目前太湖的野外监测资料存在较明显的时空不一致性.模型参数率定的精度受到了较大影响,太湖悬浮物与太湖底泥的内源释放以及水体的透明度有较大关系,因此通过室内实验研究太湖的悬浮物规律对太湖的富营养化治理具有重要意义.     

一体式膜生物反应器污水资源化技术研究

膜生物反应器是高效的污水处理工艺,但其高气水比运行条件产生的动力消耗与国外膜组件昂贵的价格成为膜生物反应器在我国应用的主要限制因素。为此本研究采用分体曝气形式,选择国产高抗污性能PVDF中空纤维膜,设计了间歇式膜生物反应器,研究了污泥浓度、曝气量和水力停留时间对一体式膜生物反应器去除污染物效果的影响。在低气水比条件下,MBR处理生活污水的研究表明,出水COD<50mg/L,BOD<10mg/L,NH3—N<20mg/L,浊度<3NTU,悬浮固体浓度为零,优于生活杂用水水质标准(CJ25.1-89)。     

污泥和餐厨垃圾联合干法中温厌氧消化性能研究

采用完全混合式反应器R1～R5(进料脱水污泥与餐厨垃圾的湿重混合比分别为1:0、4:1、3:2、2:3和0:1),在半连续运行的状态下,考察了停留时间(solid retention time,SRT)为20 d时脱水污泥和餐厨垃圾混合干法厌氧消化的产气性能、有机质降解性能和系统稳定性.结果表明,随着进料中餐厨垃圾所占比例的增大,系统的产气率和甲烷产率呈上升趋势,产气中甲烷含量呈下降趋势,污泥中添加餐厨垃圾有助于在利用原有消化罐容积的前提下显著提高有机负荷和体积产气率.餐厨垃圾比例越大,混合物料的水解速率常数越大,有机质降解率越高,R1～R4中有机质水解速率常数分别为0.25、0.61、1.09和1.56 d-1,有机质降解率分别为37.4%、50.6%、60.7%和68.2%,水解速率差异是导致VS降解率不同的主要原因.随着餐厨垃圾比例的增大,系统内pH、总碱度(total alkalinity,TA)、总氨氮(total ammonia nitrogen,TAN)和游离氨氮(free ammonianitrogen,FAN)呈下降趋势,当污泥中添加的餐厨垃圾提高60%时,系统内pH、总碱度、总氨氮和游离氨氮分别下降6%、16%、22%和75%.游离氨和Na+分别是影响污泥和餐厨垃圾单独干法消化稳定性的重要因素,污泥和餐厨垃圾混合消化可降低潜在抑制性物质的浓度,显著提高系统稳定性.     

取样量与烘干时间对总悬浮物测定结果的影响

就取样量和烘干时间两个因素的变化对总悬浮物测定结果的影响程度进行了探讨。结果表明 ,取样量是造成悬浮物测定结果准确与否的主要因素 ,而不同的烘干时间对测定结果的精密度不会造成明显的影响。随着取样量的逐步减少 (从 2 0 0 0 ml减至 50 ml) ,平行样的相对偏差则从 2 7%上升到 4 5 5%。为了使相对偏差≤ 1 5% ,取水量必须满足其中的总不可滤残渣达到 6 2 mg以上。