外文资料Removal of natural organic matter (NOM) in drinking water treatment by coagulationmicrofiltration using metal membranesTorove Leiknes, Hallvard degaard, Hvard MyklebustDepartment of Hydraulic and Environmental Engineering, NTNU, Norwegian University of Science and Technology, S.P. Andersensvei 5, N-7491 Trondheim, NorwayAbstractDrinking water sources in Norway are characterized by high concentrations of natural organic matter (NOM), low pH, low alkalinity and low turbidity. The removal of NOM is therefore in many cases a general requirement in producing potable water. Drinking water treatment plants are commonly designed with coagulation direct filtration or with NF spiral wound membrane processes. This study has investigated the feasibility and potential of using inorganic metal microfiltration membranes in a submerged membrane configuration with coagulation pre-treatment for drinking water production. Variations in operating modes and conditions were tested, from dead-end operation to semi sequencing batch operation using air scouring and backwashing cycles for membrane cleaning and fouling control. Fluxes around 180 LMH at trans membrane pressures below 0.3 bar where achieved over production cycles in excess of 50 h. Treatment efficiencies in general showed 95% colour removal, 85% UV removal, 6575% TOC removal and 0.2 NTU turbidity and non-detectable suspended solids in the permeate. The initial results show that MF metal membranes is an interesting alternative to sand filtration in coagulation/direct filtration for treating drinking water.Keywords: Natural organic matter、Coagulationmicrofiltration、 Metal membranes1. IntroductionAbout 90% of Norwegian drinking water supplies are from surface water sources, generally from lakes which typically have very low turbidity, alkalinity and hardness but high colour resulting from natural organic matter (NOM). One of the major problems of using surface water sources in northern climates is high content of NOM and total organic carbon (TOC). Removal of NOM is required since coloured water is unattractive to consumers, results in colouring of clothes during washing, can cause odor and taste, increases corrosion and biofilm growth in the distribution network, and is a precursor to the formation of disinfection by-products (DBP) when water is disinfected. Halogenated compounds resulting from chlorination of drinking water containing concentrations of NOM has been a major concern since their discovery in the early 1970s as some of the chlorination by-products are carcinogenic. Drinking water sources in Norway are commonly described as having high colour, low pH and low alkalinity where typical values are given in Table 1. The removal of NOM is therefore a major treatment requirement in the production of potable water where concentrations typically in the 3080 mg/L Pt true colour range are reduced to less than 10 mg/L Pt.The most common drinking water treatment plant designs in Norway are based on coagulation and direct filtration or nanofiltration (NF) membrane filtration processes 13. Coagulation direct filtration plants (enhanced coagulation) are still the dominant treatment plant design option.In the last 1015 years membrane processes based on nanofiltration (NF) using spiral would module configurations have been success- fully used in Norway for removing NOM, and approximately 100 membrane plants are in operation today. The NF membrane plants are commonly designed to operate with a constant flux of 17L m2 h1 (LMH) at a trans membrane pressure (TMP) of 36 bar with a water recovery of 70%. Some of the disadvantages of the NF spiral wound membrane systems used are a relatively low recovery, high energy consumptions due to the operating pressures, and fouling by the NOM and sub-micron particulates resulting in the need for a daily cleaning procedure in addition to the periodic maintenance cleaning procedures 13,14. In a recent survey about experiences with different treatment plant types, both the operators and owners of treatment plants using membranes were generally very satisfied with using membrane technology. However, the survey also indicated an interest in alternative membrane treatment plant designs that were more energy efficient and which could reduce the necessary cleaning frequency by efficient fouling control. Two approaches can be followed to achieve this; using various pre-treatment options of the raw water prior to the NF filtration units or by using different types of membranes , membrane modules and operating options. Studies using microfiltration (MF) and ultrafiltration (UF) membranes as well as alternative membrane module designs (hollow fiber cross-flow modules and submerged modules) combined with pre-treatment by coagulation to reduce and control fouling have been reported 1,47,911. They all demonstrate the advantages and ben- efits of combining coagulation pre-treatment with membran