温度和反冲洗对饮用水生物滤池影响的研究

研究了温度和反冲洗对生物滤池的影响.试验结果表明,生物活性和生物量随温度的降低而下降,有机物的去除率和去除量受温度影响不明显,温度对氨氮和亚硝酸盐氮的去除率和去除量有一定影响;反冲洗使生物量减少,同时提高了生物活性,有机物、氨氮的去除率在反冲洗2 h后基本恢复到反冲洗前的水平.     

V型滤池气水反冲洗过程滤料流失影响因素分析

根据V型滤池生产运行参数和设计规范的相关规定,确定了气水同时反冲洗阶段气冲强度、水冲强度及排水槽高度的取值范围.通过模型滤柱系列对比试验,分析气冲强度、水冲强度及排水槽高度对流失滤砂质量、粒径的影响.结果显示,水冲强度是影响滤料流失的主要因素,随排水槽高度增加,跑砂量显著减少、流失滤料粒径减小.     

Arsenic removal through adsorption, sand filtration and ultrafiltration: In situ precipitated ferric and manganese binary oxides as adsorbents

This study proposes a process consisting of in situ precipitated ferric and manganese binary oxides (FMBO) adsorption, sand filtration, and ultra-filtration (UF) for arsenic removal. Bench scale studies indicate that the FMBO shows higher capability of removing arsenic than hydrous ferric precipitate (HFO) and hydrous manganese oxide (HMO). This is ascribed to the combined effects of oxidizing As(III) and adsorbing As(V) for FMBO. The continuous experiments indicate that this process is effective for arsenic removal. In the presence of 0.624 mg/L As(III), when the Fe(II) dosage is 3 mg/L and the KMnO₄ dosage is equivalent to the sum of As(III) and Fe(II), the residual As concentration is as low as 29.2 μg/L. The adsorption of arsenic onto FMBO is fast, and the hydraulic retention time (HRT) of 45 s is enough for the adsorption unit. Sand filtration leads to more than 90% of arsenic removal, and UF further removes the particulate arsenic that passes through the sand filter. During the backwashing of the sand filter, the maximal aqueous arsenic concentration is 0.105 mg/L (at 150 s), and the dissolution of arsenic from FMBO is neglectable. The main operating cost of this process is as low as 0.355 RMB/m³, which is acceptable in rural areas for arsenic removal in engineering.     

Suspension concentration profiles during rapid gravity filter backwashing

Rapid gravity, granular media filters are widely used in the water and wastewater treatment industries. Regular backwashing to clean the filters is a vital part of their efficient operation. Experimental data on the development of suspension concentration profiles through laboratory scale filter beds during the backwash process were obtained. Previous attempts to obtain and record backwash profiles of this type have been unsuccessful due to the limited range of existing turbidimeters. The results have been used to validate a new model developed by the authors.     

SEC反冲洗泵换型改造

由于杭州湾海水泥沙含量较高,对泵水力部件具有较大的冲蚀作用,秦山第二核电厂SEC反冲洗泵在改造前往往连续运行6个月左右,就需要对其进行解体检修,更换叶轮、泵壳、泵盖部件,造成检修成本较高。通过换型改造,提高了泵的耐冲蚀能力,使得检修周期大大延长,节省了大量检修成本。本文通过对换型改造前后SEC反冲洗泵结构、使用情况的介绍,并从结构、涂层等方面分析了此次改造成功的原因,希望对其他类似泵改造工作提供一些借鉴。     

Effect of backwashing on activated carbon adsorption using plug flow pore surface diffusion model

A fixed bed is gradually exhausted from top to bottom without backwashing; however, backwashing can rearrange the concentration gradient in the bed. After backwashing, saturated particles which are located at the top of the bed are homogeneously distributed in the bed. The used model to predict adsorption and backwashing effect of organic component is the plug flow pore surface diffusion model (PFPSDM). A sensitivity analysis was performed to determine which parameters have the greatest impact on the model results for components which can represent various organics. In addition, the effects of backwashing were examined by rearranging concentration gradient. For single component sensitivity analysis, the molecular weight was an important parameter. The breakthrough of the smaller molecular weight component was impacted more by backwashing. The SPDFR showed a significant impact on the breakthrough pattern. When surface diffusion was the dominant mechanism, high SPDFR, the breakthrough profile was sharper than when pore diffusion was dominant, low SPDFR. The adsorbability was an important parameter in determining the breakthrough pattern. As expected, the strongly adsorbable component showed the later breakthrough. Backwashing yielded earlier breakthrough for all single components and multi-components examined.     

Perchlorate removal in sand and plastic media bioreactors

The treatment of perchlorate-contaminated groundwater was examined using two side-by-side pilot-scale fixed-bed bioreactors packed with sand or plastic media, and bioaugmented with the perchlorate-degrading bacterium Dechlorosoma sp. KJ. Groundwater containing perchlorate (77microg/L), nitrate (4mg-NO(3)/L), and dissolved oxygen (7.5mg/L) was amended with a carbon source (acetic acid) and nutrients (ammonium phosphate). Perchlorate was completely removed (<4microg/L) in the sand medium bioreactor at flow rates of 0.063-0.126L/s (1-2gpm or hydraulic loading rate of 0.34-0.68L/m(2)s) and in the plastic medium reactor at flow rates of <0.063L/s. Acetate in the sand reactor was removed from 43+/-8 to 13+/-8mg/L (after day 100), and nitrate was completely removed in the reactor (except day 159). A regular (weekly) backwashing cycle was necessary to achieve consistent reactor performance and avoid short-circuiting in the reactors. For example, the sand reactor detention time was 18min (hydraulic loading rate of 0.68L/m(2)s) immediately after backwashing, but it decreased to only 10min 1 week later. In the plastic medium bioreactor, the relative changes in detention time due to backwashing were smaller, typically changing from 60min before backwashing to 70min after backwashing. We found that detention times necessary for complete perchlorate removal were more typical of those expected for mixed cultures (10-18min) than those for the pure culture (<1min) reported in our previous laboratory studies. Analysis of intra-column perchlorate profiles revealed that there was simultaneous removal of dissolved oxygen, nitrate, and perchlorate, and that oxygen and nitrate removal was always complete prior to complete perchlorate removal. This study demonstrated for the first time in a pilot-scale system, that with regular backwashing cycles, fixed-bed bioreactors could be used to remove perchlorate in groundwater to a suitable level for drinking water.     

Toward an Optimization of the Backwashing Process in the Flexible Fiber Filter

Abstract

Backwashing process was used to recover the retention capacity of a deep bed filter. A field scale fiber filter was operated with an in‐line injection of a coagulant for the treatment of natural surface water (Nak‐dong River in Korea). A mass balance of SS could be made thus allowing a direct estimation of the effectiveness of the backwashing process. The purpose of this paper was to study the influence of two parameters of backwashing (air injection and number of backwashing stages) on its effectiveness. The backwashing efficiency was estimated through the initial pressure drop after the backwash, the effluent quality, the duration of the filtration time between two successive backwashes, and the detached mass of retained suspended solids. Conditions could be found for removing 99% of the retained SS. As a general conclusion, the effectiveness of backwashing mainly depended upon air injection. The duration of air injection and the number of sequences were the most important factors related to the efficiency of backwashing.     

颗粒滤料反冲洗技术现状与应用进展

过滤是水处理的常用手段之一,反冲洗是保证滤料过滤性能的重要手段。重点介绍了颗粒滤料反冲洗技术的工作原理及特点,反冲洗方式、工艺优化及工艺理论研究进展及应用现状,并分析了颗粒滤料反冲洗技术的发展趋势。     

An experimental study of UF membrane fouling by humic acid and sodium alginate solutions: the effect of backwashing on flux recovery

One of the critical issues for the successful application of ultrafitration in water treatment is membrane fouling due to dissolved organic matter, which negatively affects productivity, product quality and process cost. The aim of the present study is to contribute to the understanding of fouling phenomena by organic matter and the efficiency of the backwashing technique, which is applied in practice to restore membrane flux. In this experimental study commercial humic acid and sodium alginate have been used as model substances representative of natural organic matter and extracellular organic matter, respectively. All fouling experiments were carried out in a special single fiber apparatus. An important parameter considered in the study of both model substances is the concentration of calcium ions, which promote their aggregation and influence the rate of flux decline, the reversibility of fouling and rejection. Membrane fouling by humic acid appears to be the outcome of simultaneous action of several fouling mechanisms. Initially, a relatively rapid irreversible fouling takes place due to internal pore adsorption; however, progressively pore blocking becomes important and a fouling layer develops on the membrane. Sodium alginate fouling on the other hand is apparently due to two consecutive mechanisms; i.e. a rapid irreversible fouling due to internal pore constriction, followed by cake development on the membrane surface which becomes the dominant mechanism. Comparing fouling in both cases it can be inferred that even though sodium alginate fouling is more severe than the one caused by humic acids, it is to a large extent reversible by backwashing. On the contrary, fouling caused by humic acid is characterized by greater and increasing with calcium addition irreversibility, which is not remedied by the periodic backwashing. The different fouling propensity of the two types of macromolecules is apparently due to differences of their physical–chemical characteristics.