Backwashing and conditioning of a deep bed filter

The traditional conceptual model explaining the initial effluent degradation as a result of the backwashing, is proved to be insufficient.Mathematically and experimentally it is demonstrated that the initial effluent degradation is 95% due to an inadequate pore structure of the filter bed. An increased coagulant dose at the start of the filtration or a preconditioning of the filter bed during the last minutes of the backwashing operation, can reduce the initial turbidity peak. Such a treatment has also consequences for the complete filter run.     

Optimization of the extended terminal subfluidization wash (ETSW) filter backwashing procedure

The increased passage of particles and microorganisms through granular media filters immediately following backwashing is a common problem known to the water treatment community as filter "ripening" or maturation. While several strategies have been developed over the years to reduce the impact of this vulnerable period of the filtration cycle on finished water quality, this research involves a recently developed filter backwashing strategy called the extended terminal subfluidization wash (ETSW). ETSW is a method of terminating the backwash cycle with a subfluidization wash for a period of time sufficient to pass one theoretical filter-volume of water upward through the filter. ETSW was shown to remove significantly greater quantities of backwash remnant particles thereby reducing the magnitude of filter ripening turbidity and particle count spikes. Optimum ETSW flow rates were determined for deep-bed anthracite and granular activated carbon filters herein by monitoring filter effluent turbidities and particle counts during the filter ripening period. Optimality of the coagulation process was also shown to influence the magnitude of filter ripening particle passage. ETSW was found to be equally effective for biological and conventional deep-bed anthracite filters.     

Attrition of granular filter media during backwashing with combined air and water

Attrition resistance of granular filter media is becoming increasingly important as materials such as GAC and anthracite are being more frequently used as filter media. The purpose of this study was to evaluate the attrition experienced by various media during backwashing by performing accelerated backwash tests in a pilot column, using a combined water and air backwash at combinations that gave the condition known as collapse-pulsing. Since the dominant mode of attrition was assumed to be abrasion, the effluent was sampled at a number of intervals to determine the amount of fine material in the effluent. Coal based GAC exhibited the highest weight loss (∼ 7%) and sand the least (∼ 2%).     

新型BIOSMEDI滤池的开发研究

开发了一种适用于微污染原水预处理及污水深度处理的新工艺———BIOSMEDI滤池 ,它以轻质滤料为过滤介质 ,采用与填料相适应的独特滤池构造 ,同时采用脉冲反冲洗、气水同向流。该滤池具有滤料比表面积大 ,不易堵塞 ,滤层阻力小 ,滤速高 ,反冲洗耗水、耗气小等优点。试验表明 ,该生物滤池在 10℃以上时氨氮的去除负荷≥ 0 .5kgNH3-N/(m3·d)。     

A biofiltration model for tertiary nitrification of municipal wastewaters

The main objective of this work concerns the evaluation of the biological aerated filtration model found in GPS-X^®, which had never been evaluated with adequate data. This model is interesting since it integrates the physical and biological phenomena involved during filtration with a low complexity of use. The validation of the model parameters combines experimental and theoretical approaches. Experimental data were recorded at a semi-industrial pilot scale submerged biofilter operated at a tertiary nitrification stage, receiving the effluent of a medium loaded activated sludge process for municipal wastewater. Also, several protocols were regularly applied to characterize the biofilm and the nitrogen removal performances: dry density and thickness of biofilm, nitrification rates and corresponding quantity of autotrophic biomass accumulated inside the filtering media, quantity of extracted autotrophic bacteria in the backwash water, nitrification capacity along the biofilter, as well as nitrogen compounds in the effluent. For short-term dynamic conditions, a set of reliable parameter values has been used to predict nitrogen removal for different data sets. For long-term dynamic periods, the need to adapt some of the parameters from one set of data to another is demonstrated. It is shown that the hydraulic loading rate and the backwashing frequency are the main parameters responsible for these modifications.     

Management and design implications of a mathematical model of a rapid gravity sand filter backwash

A model has been proposed and tested describing the removal of water from the bed surface of a rapid gravity sand filter during a backwash. The model can be used in design to predict the minimum height of the weir above the expanded bed required to prevent media loss and also the minimum length of time for a backwash to obtain a clean bed.     

江北水厂水质稳定性处理介绍

重庆市万州江北水厂水源为甘宁水库,净水工艺采用机械混合-超脉冲澄清池-气水反冲洗均质滤料滤池。针对该水厂供水区出现的黄水问题,进行了水质稳定性分析,并提出了相应的解决措施。     

Impact of backwashing procedures on deep bed filtration productivity in drinking water treatment

Backwash procedures for deep bed filters were evaluated and compared by means of a new integrated approach based on productivity. For this, different backwash procedures were experimentally evaluated by using a pilot plant for direct filtration. A standard backwash mode as applied in practice served as a reference and effluent turbidity was used as the criterion for filter run termination. The backwash water volumes needed, duration of the filter-to-waste period, time out of operation, total volume discharged and filter run-time were determined and used to calculate average filtration velocity and average productivity.     

Filter backwash and start-up strategies for enhanced particulate removal

A significant consideration in forward planning for water treatment works design and operation concerns the effectiveness of a filtration plant in providing a barrier to particulates in the low micrometre size range, including Cryptosporidium oocysts. The performance of rapid gravity filtration plants is believed to be dependent on backwash and start-up regimes. It was the aim of this study to optimize direct sand filtration by identifying optimum filter backwash and start-up conditions which minimized the passage of particulates into the filtrate. The filter ripening period has long been identified as a cause for concern with respect to particulate passage into the filtrate; this work has shown that up to 40% of all particles that pass into supply during a 48 h run, do so in the first hour of operation. Optimum combined air water “collapse-pulsing” backwash durations were identified that reduced the number of 2–5 μm particles entering the filtrate, especially during the ripening period. Slow start-up was also found to reduce the number of 2–5 μm particles in the filtrate during the ripening period. The reductions in particulate passage resulting from a slow start was found to be media dependent, with smaller media requiring a longer slow start duration than coarser media.     

Effect of backwashing on perchlorate removal in fixed bed biofilm reactors

The influence of backwashing on biological perchlorate reduction was evaluated in two laboratory scale fixed bed biofilm reactors using 1- or 3-mm glass beads as support media. Influent perchlorate concentrations were 50 microg/L and acetate was added as the electron donor at a concentration of 2 mg C/L. Perchlorate removal was evaluated at various influent dissolved oxygen (DO) concentrations. Complete perchlorate removal was achieved with an influent DO concentration of 1mg/L resulting in bulk phase DO concentrations below the detection limit of 0.01 mg/L. The influence of increasing influent DO concentrations for 12 h periods was evaluated before and after individual backwash events. Partial perchlorate removal was achieved with an influent DO concentration of 3.5 mg/L before a strong backwash (bulk phase DO concentrations of approximately 0.2mg/L), while no perchlorate removal was observed after the strong backwash at the same influent DO level (bulk phase DO concentrations of approximately 0.8 mg/L). The immediate effect of backwashing depended on influent DO concentrations. With influent DO concentrations of 1 mg/L, strong backwashing resulted in a brief (<12 h) increase of effluent perchlorate concentrations up to 20 microg/L; more pronounced effects were observed with influent DO concentrations of 3mg/L. Daily weak backwashing had a small and, over time, decreasing negative influence on perchlorate reduction, while daily strong backwashing ultimately resulted in the breakdown of perchlorate removal with influent DO concentrations of 3 mg/L.     

深床过滤中的生物硝化动力学研究

研究了深床过滤条件下的生物硝化技术，建立了硝化反应动力学模型和生物膜传质模型。试验结果表明，深床过滤条件下的生物硝化反应动力学级数为零级，出水氨氮、硝酸盐氮浓度与床层深度或HRT具有良好的线性关系；合适的HRT=1．1～1．25h，DO〉2．0mg／L（即气水比〉4．0），此时对氨氮的去除率可达90％以上；采用正向加压水冲洗与反向加压气洗相结合的反冲洗方式，可有效恢复深床过滤的效率和生物硝化反应效率。     

Non-steady state simulation of BOM removal in drinking water biofilters: applications and full-scale validation

A biofilter model called "BIOFILT" was used to simulate the removal of biodegradable organic matter (BOM) in full-scale biofilters subjected to a wide range of operating conditions. Parameters that were varied included BOM composition, water temperature (3.0-22.5 degrees C), and biomass removal during backwashing (0-100%). Results from biofilter simulations suggest a strong dependence of BOM removal on BOM composition. BOM with a greater diffusivity or with faster degradation kinetics was removed to a greater extent and also contributed to shorter biofilter start-up times. In addition, in simulations involving mixtures of BOM (i.e. readily degradable and slowly degradable components), the presence of readily degradable substrate significantly enhanced the removal of slowly degradable material primarily due to the ability to maintain greater biomass levels in the biofilters. Declines in pseudo-steady state BOM removal were observed as temperature was decreased from 22.5 to 3 degrees C and the magnitude of the change was significantly affected by BOM composition. However, significant removals of BOM are possible at low temperatures (3-6 degrees C). Concerning the impact of backwashing on biofilter performance, BOM removal was not affected by backwash resulting in biomass removals of 60% or less. This suggests that periodic backwashing should not significantly impact biofilter performance as observed biomass removals from full-scale biofilters were negligible. In general, the simulation results were in good qualitative and quantitative agreement with experimental results obtained from full-scale biofilters.     

Non-steady state simulation of BOM removal in drinking water biofilters: model development

A numerical model was developed to simulate the non-steady-state behavior of biologically-active filters used for drinking water treatment. The biofilter simulation model called "BIOFILT" simulates the substrate (biodegradable organic matter or BOM) and biomass (both attached and suspended) profiles in a biofilter as a function of time. One of the innovative features of BIOFILT compared to previous biofilm models is the ability to simulate the effects of a sudden loss in attached biomass or biofilm due to filter backwash on substrate removal performance. A sensitivity analysis of the model input parameters indicated that the model simulations were most sensitive to the values of parameters that controlled substrate degradation and biofilm growth and accumulation including the substrate diffusion coefficient, the maximum rate of substrate degradation, the microbial yield coefficient, and a dimensionless shear loss coefficient. Variation of the hydraulic loading rate or other parameters that controlled the deposition of biomass via filtration did not significantly impact the simulation results.     

福州西区水厂双阀滤池的改造

福州西区水厂将原有的双阀滤池改造为V型滤池,重点介绍了进水系统、滤板系统、反冲洗排水系统、滤后水系统、反冲洗系统的改造。实践表明,改造后滤后水平均浊度<0.3NTU,反冲洗耗水量<2%,滤池实现了全自动化运行。     

滤池气水反冲洗应用技术研究

对气水反冲洗工艺应用过程中存在的一些主要问题，如气水反冲参数选择、反冲洗时布气均匀性，进气进水压力计算方法及气水反冲跑砂等问题进行研究，提出切实可行的解决方法。     

BIOFILM FORMATION IN GRANULAR-BED FILTERS

A high microbiological quality of drinking water must be ensured to protect public health. The filtration techniques that are used in treating drinking water play an important role; however, a biofilm can form on granular-media filters and the accumulated bacteria can slough off and enter the filtered water.
The aim of this research was to examine (a) the potential for biofilm formation and detachment from filter sand, and (b) the effect of different backwash regimes on biofilm removal. During the operation of the filter, bacteria became attached to the sand media, particularly in the top 30 mm of the filter bed. A water-only backwash at 20% and 40% bed expansion demonstrated poor removal of biofilm throughout the depth of the bed. Collapse-pulsing is a more efficient method and results in a reduction in the number of bacteria in the filtered water.     

滤池反冲洗水的超滤处理回收中试

采用内压式中空纤维超滤膜处理水厂砂滤池的反冲洗水，处理水量为2．4m^3／h，结果表明：滤池反冲洗水经超滤处理后，“两虫”被完全去除；超滤出水经消毒后可进入清水池，回收率〉95％，既减少了水资源浪费，又不影响水厂主流程；可将超滤处理成本控制在0．13元／m^3以内。     

Using a geotextile with flocculated filter backwash water and its impact on aluminium concentrations

The use of geotextiles (i.e. geotextile tubes) in wastewater treatment applications is ever increasing. This paper examines the potential of using a geotextile to improve upon the treatment of aluminium present in a filter backwash water that is generated from a water treatment plant in Halifax, Canada. A field investigation to ascertain the distribution of aluminium in the filter backwash water treatment process is provided and compared to regulatory guidelines at the environmental compliance point. It is shown that aluminium is undergoing incomplete treatment at various times throughout the year. To examine a potential corrective action, the results of bench scale studies are presented in which cationic additives (i.e. CaO, MgO, and Fe₃O₄) are combined with a polymer to remove aluminium from solution and flocculate particulate matter from the filter backwash water. A geotextile is utilized to retain particulate matter generated from this process. It is shown that the combined use of the cationic additive with polymer can successfully reduce aluminium concentrations in the filter backwash water and that filtration via a geotextile can retain the aluminium particulate in the filter backwash water to levels close to regulatory requirements. Further optimization with the flocculation process is recommended prior to pilot testing.     

Development of a biological filtration model applied for advanced treatment of sewage

A mathematical model of biological filtration process is developed in this paper. A biological filtration process has advantages that filtration action and biological activities are combined in a single reactor with aid of filter media. Both physical and biological functions are incorporated in this developed model to simulate both mechanisms. Backwashing is expressed by the assumption that a mean captured solids concentration is input as data, and a captured solids concentration is kept at that value during each filtration run. The developed model is applied to explain the experimental performance with biological filtration reactors, in which batch cultivation of autotrophic bacteria and continuous treatment of actual sewage are carried out. Its applicability is discussed by comparing the simulated results with the experimental data. This model can favourably estimate maximum accumulation of autotrophic bacteria on the medium in batch cultivation, long-term treatment performance in continuous treatment, details of water quality profiles through the filter bed, and biomass. Required hydraulic retention time for nitrification and an appropriate recirculation ratio in a winter season are discussed with this model. This model predicts that a HRT of 1.1 h or above is required to achieve nitrification with remaining NH4(+)-N of less than 1 mgN/L and that an appropriate recirculation ratio is 2-3.     

微絮凝-深床直接过滤及工艺参数研究

针对北京市水源九厂的低浊水质进行了将聚合氯化铝应用于微絮凝－深床直接过滤工艺的中试,讨论了滤档深度与质超大粒径的滤料优选、直接过滤过程最佳化学与水力学参数以及反冲洗技术参数的优化及其影响因素,最后与现有水厂运行处理的综合效能有经济效益进行了对比,为微絮凝－深床过滤工艺的实际应用提供了基础研究依据。