两套过滤器反冲洗程序并行解决方案

该反冲洗系统是以艾默生DeltaV为控制系统,采用SFC（Sequential FunctionChart）顺序控制功能进行组态设计。介绍了＇过滤器反冲洗顺控流程,包含反冲洗联锁、反冲洗间隔时间、反冲洗时间、反冲洗跳过等,能提供两套过滤器反冲洗程序并行解决方案。     

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.     

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.     

Effects of backwashing on the prosobranch snail Potamopyrgus jenkinsi Smith in granular activated carbon (GAC) adsorbers

Granular activated carbon (GAC) adsorbers are often the penultimate stage of surface water treatment and provide ideal habitats for invertebrates. Proliferation of chlorine-resistant invertebrates in GAC adsorbers may lead to their efflux into distribution systems, possibly resulting in contamination of customers' tap water. GAC adsorber sampling and laboratory experiments were undertaken to determine the effects of routine backwashing on GAC adsorber populations of the chlorine-resistant snail Potamopyrgus jenkinsi at a water treatment works. GAC adsorber sampling results suggested that routine backwashing altered the spatial distribution of snails, but not their overall abundance. In small-scale glass columns 40-50% of the smallest (0.3-0.6 mm shell height) juvenile snails were removed by a GAC backwash bed expansion of 30-40%; however, bed expansions of greater than 20% were not possible in the GAC adsorbers.     

Modeling of backwash cleaning methods for RO membranes

A new comprehensive and time-dependent 2D model using finite element method (FEM) was developed to account for different versions of the backwash (BW) cleaning method for RO membranes. Two distinct cases of backwash were identified: Case 1, which has no applied pressures and velocities; and Case 2, where inlet velocity and pressure are applied in the feed channel, and in some cases pressure is also applied in the permeate channel. The model was verified by comparing it to existing BW data from both cases. The current 2D model is accurate enough to describe the actual 3D time-dependent BW process. Case 1 reduces to a 1D model agrees with the existing 1D analytical model and was found to be fully predictive. Case 2 deals with reported studies in a 2D format, and is suited to an industrial interest of keeping desalination setup unchanged while activating BW membrane cleaning. Water and salt diffusion coefficients were determined and found to be dependent on feed concentration and applied pressures. Dynamic change of concentration profiles of feed and permeate channels were illustrated. The resulting profiles reveal that in Case 2, changes in feed concentration profiles are negligible, while all other profiles of both cases change substantially with time.     

A comparison of hydrodynamic methods for mitigating particle fouling in submerged membrane filtration

Hydrodynamic methods are used for mitigating particle fouling and for enhancing the filtrate flux in submerged membrane filtration. In the comparison membrane blocking-cake formation filtration system, the effects of filtration pressure, aeration intensity, backwash duration and stepwise increasing pressure on the filtration resistances and filtration flux are measured and discussed. Aeration is helpful for reducing particle deposition on the membrane surface, while stepwise increasing pressure can mainly mitigate internal fouling of the membrane. Periodic backwash can significantly reduce both the resistance caused by the membrane internal fouling and by cake formation; consequently, it can effectively recover the filtrate flux. In contrast, increasing the pressure in constant pressure filtration leads the flux to be decreased due to more severe membrane blockage. According to the comparison of the long-term flux and the received filtrate volume, among these hydrodynamic methods, the periodic backwash with longer duration is the optimal strategy for the filtration.     

Neural network modeling and optimization of scheduling backwash for membrane bioreactor

Backwash scheduling for a membrane bioreactor was experimentally examined and theoretically modeled via neural networks. Flux was determined for different backwash and service time runs. Vacuum and backwashing streams pressure for different timing regimes were used to observe and monitor the fouling and a cake layer accumulated on the membrane surface causing a decline in the flux for the submerged membrane bioreactor. Experimental results were employed to develop an artificial neural network model (ANN) to predict the membrane flux as a function of the backwash and service times. Such modeling entails using a fairly large number of experimental data to reconcile model predictions with actual flux measurements in order to validate the ANN model. The ANN model was shown to be accurate in predicting the flux of the membrane and can be utilized to find optimum backwash scheduling strategy for such reactors.     

微滤膜法饮用水处理工艺中膜污染控制的研究

采用150 m3/d的微滤膜法饮用水处理中试研究了膜污染的控制方法,包括反冲洗、混凝预处理以及在线的通量维护措施--EFM(Enhance Flux Maintenance).结果表明,单独采用水反冲洗时,膜比通量的恢复效果较差,采用气水联合反冲洗时效果明显好转,膜污染速率降低为原来的44%.混凝预处理能够很好地控制膜污染,其主要作用在于降低滤饼层阻力和减轻不可逆膜污染.在研究的范围内,混凝剂投加量越高,对膜污染的控制作用越好.EFM能够阶段性地去除膜污染,有效地恢复膜比通量,因而能够显著地延长化学清洗周期,减少化学清洗频率.     

Application of hybrid coagulation–microfiltration process for treatment of membrane backwash water from waterworks

A coagulation–microfiltration (MF) system was studied to treat the discharged membrane backwash water (MBW) to meet the drinking water quality requirements. The values of dissolved organic carbon (DOC) and trihalomethanes formation potential (THMFP) in MBW were higher than those in Luan River water (LRW, the raw water for a pilot-scale membrane plant, which produced MBW used in this study), and organic matter enriched in MBW distributed mainly in molecular weight (MW) > 10k Da. When 15 mg FeCl₃/L and 15 mg/L powdered activated carbon (PAC) were added into the system, the average concentration of DOC was reduced from 5.731 mg/L in MBW to 3.377 mg/L in the treated water, and the average UV₂₅₄ was reduced from 0.047 to 0.030 cm⁻¹. The removal of organic matter was main in the range of MW > 30k Da. Efficient organic removal by the hybrid coagulation–MF system resulted in significant reduction of THMFP in the treated water. Concentrations of trihalomethanes, turbidity, bacteria and coliforms in the treated water were below the limit value of the drinking water standards. The results show that the treated water from MBW is with satisfactory organic and microbiological quality.     

超滤膜污染及其预防方案比较

超滤系统的主要功能是去除水中的生物污染物、颗粒物、胶体、浊度、细菌,超滤对水中的浊度几乎可以完全去除,对细菌和大肠杆菌的去除率〉99％,对水中的有机物、氨氮、总铁、总锰也均有一定的去除。超滤膜作为东区污水回用装置超滤系统的核心,其生产稳定性对整个回用水系统至关重要。但是超滤膜的污染自膜投入使用的那一刻起就存在．超滤膜的污染主要体现在超滤膜的结垢、微生物污染、超滤膜过滤截留在膜面外固体物质的污染以及膜的损坏。而在生产实践中预防超滤膜污染的方法主要有：严格控制超滤原水浊度和SS值;投加一定量的次氯酸钠做好杀菌;通过气擦洗和反冲洗减少对超滤膜的污堵;定期对超滤膜进行清洗,减少垢类物质的生成;严格控制超滤单元的产水率。