Role of membrane pore size in tertiary flocculation/adsorption/ultrafiltration treatment of municipal wastewater

Flocculation, adsorption onto powered activated carbon (PAC), and ultrafiltration (UF), alone and in combination, were tested for tertiary treatment of the secondary effluent from municipal wastewater treatment at the Ashkelon plant (in southern Israel). Encouraging and reliable results of total organic carbon (TOC) of <3 mg/l were achieved with a combination of 130 mg/l FeCl₃, 0.6 g/l PAC and UF. The relative contribution of the UF membrane to the reduction of TOC changed with the molecular weight cut-off (MWCO) of the membrane, from a negligible 2.9% for a 100-kDa-MWCO membrane to 17% for 10- and 2-kDa membranes. The latter membranes, however, developed significant fouling, with a 35% drop in flux during first 30 min of the filtration cycle. The flux drop for the 50- and 100-kDa membranes was in the low range of 3%. The optimal MWCO interval of 20- to 50-kDa in combination with flocculation/PAC pretreatment gave a significant reduction in organic content with minimal membrane fouling. Detailed GC–MS analysis showed that the combined treatment gave very efficient retention of organic compounds with molecular weights below 800 Da, with the consequent absence of harmful compounds in the tertiary effluent. It was therefore concluded that the recommended flocculation/adsorption protocol constitutes an effective pretreatment for UF and that the obtained tertiary effluent can be used for unrestricted irrigation.     

The characteristics of metallocene/Ziegler-Natta hybrid catalysts supported on the recrystallized MgCl2

A metallocene catalyst or a metallocene/Ziegler-Natta hybrid catalyst supported on MgCl₂ was studied for application to the commercial slurry phase process and to the control of MWD of the polymer produced. The MgCl₂ support was prepared by the recrystallization method with different solvents: alcohols and H₂O. The recrystallized MgCl₂ support was pretreated with triisobutylaluminum (TiBAL) or trimethylaluminum (TMA), methylaluminoxane (MAO), to give different supporting environments. Metallocene/Ziegler-Natta hybrid catalysts on MgCl₂ were prepared by first supporting the metallocene catalyst, followed by the Ziegler-Natta catalyst after pretreatment with an alkylaluminum compound. The type of solvent plays a role in providing a suitable environment in the support for impregnating catalysts. The hybrid catalyst, whose support was recrystallized in n-propanol (n-PrOH) and pretreated with TiBAL, showed the highest molar ratio of Zr/Ti= 1/2.71. But the hybrid catalyst, whose support was recrystallized in H₂O and pretreated with MAO, showed the best hybrid effect showing a variety of bimodal peaks in proportion to the ratio of MAO/TEA in GPC analysis. This effect might be due to steric factor and polarity of solvent, as well as the pretreatment material. It is concluded that the MWD of polyethylene produced by metallocene/Ziegler-Natta hybrid catalyst that is supported on MgCl₂ can be controlled by regulating the amounts of MAO and TEA added as cocatalysts and by the use of different solvents and pretreatment materials.     

Electrocoagulation pretreatment of seawater prior to ultrafiltration: Pilot-scale applications for military water purification systems

The objectives were to investigate the performance of a pilot-scale electrocoagulation (EC) reactor and to determine the feasibility of using in-line EC as a pretreatment to ultrafiltration (UF) of seawater. Work was conducted at Port Hueneme, CA, using components of a U.S. military water purification system. Ferric chloride in-line coagulation was also tested. Both the EC and ferric chloride pretreatments improved UF membrane performance compared to UF without in-line coagulation. EC resulted in slightly greater increases in transmembrane pressure (TMP) than observed following ferric chloride pretreatment during sub-critical flux UF. Substantial accumulation of precipitates developed on the EC electrodes during the testing period. X-ray diffraction identified magnetite, maghemite, lepidocrocite, and akaganeite phases. Accumulation of these precipitates was due in part to conservative hydraulic design of the EC unit. It is recommended that EC units should be designed with short hydraulic retention times and higher electrode current density in order to increase upflow (scour) velocity and thus inhibit accumulation on the electrodes. Progressively longer cycling times for polarity reversal are also recommended. This research indicates that EC offers the potential for a feasible and effective pretreatment strategy for mobile water production facilities.     

Feed water pretreatment for desalination plants

Effective membrane pretreatment is a crucial requirement for trouble free and cost effective RO desalination. Pretreatment construction costs are significant and may reach as much as 10%-20% of the total desalination plant capital costs. This paper presents a general review of the central factors involved in assessing raw water quality. The main foulant categories are described and the various unit operations commonly applied are reviewed. Pretreatment aspects of desalination offer fertile grounds for advancing desalination technologies. Promising research directions are highlighted.     

苏州某自来水厂排泥水处理系统运行优化试验研究

为提升自来水厂排泥水处理系统运行效率,降低水厂耗水率,开展排泥水预处理试验和浓缩池动态模型试验.结果表明:与预处理前相比,投加0.3 mg/L阳离子型PAM,可以使排泥水中粒径小于5μm的颗粒占比减少22％,粒径大于10μm的颗粒占比提高110％,颗粒沉降速率提高20％,上清液浊度下降75％.根据浓缩池动态模型试验结果...     

A highly active catalyst, Ni/Ce–ZrO2/θ-Al2O3, for on-site H2 generation by steam methane reforming: pretreatment effect

The steam treatment effect has been investigated over the doubly impregnated catalyst, Ni/Ce–ZrO₂/θ-Al₂O₃, in steam methane reforming (SMR). The catalyst was remarkably deactivated by steam treatment but reversibly regenerated by H₂-reduction. XRD results showed that the steam treatment resulted in the formation of NiAl₂O₄ which is inactive for SMR but it was reversibly converted to Ni by the reduction. The reversible oxidation-reduction of Ni state was also evidenced by XPS and it was observed that the formation of NiAl₂O₄ is more favorable at higher temperature. It is most likely that the alumina support is only partially covered with Ce–ZrO₂ and most Ni directly interacts with θ-Al₂O₃ which would probably make easy formation of NiAl₂O₄ in the presence of steam alone. The results imply that, during the start-up procedure in SMR, too high concentration of steam could deactivate seriously Al₂O₃ supported Ni catalysts.     

采用Fenton试剂预处理糠醛废水的研究

采用Fenton试剂处理糠醛废水,主要考察了H_2O_2/Fe~(2+)的投配比、H_2O_2投加量、H_2O_2的投加方式和反应时间对废水COD和BOD去除率的影响.通过试验确定最佳反应条件为:H_2O_2/Fe~(2+)的投配比2∶1、H_2O_2投加量0.5 Q、H_2O_2分5批投加、反应时间80 min的条件下,糠醛废水的BOD/COD由原始的0.23提高到0.65左右,COD_(cr)去除率在52%左右.     

浅谈涤粘混纺织物退浆—苛化一步法前处理工艺

针对涤粘混纺织物采用分散／活性染料染色的中深鲜艳色效果不佳的问题,采用退浆－苛化一步法平幅前处理工艺。经过小试和大试,取得了理想的提深效果。     

冷轧堆前处理加工在民丰厂的实践

介绍了冷轧堆前处理加工大生产的经验,包括设备组成;助剂及工艺条件优选;技术关键及有待改进的方面等等。     

胡麻纱前处理工艺初探

本文着重对胡麻纱前处理采用煮练→优氯净处理→氧漂的工艺进行了探讨。