| Groundwater is a main source of water supply for life of urban-rural residentsand industrial-agricultural production. Especially in most areas of north China,groundwater has become an important or the only source of water. But the pollutionof groundwater in China is very common at present. Shallow ground water in manycities cannot be drunk directly, so that it has threatened the security of drinking waterand health of people.The phenomenon of excessive iron and manganese is very common in NortheastChina. According to Standards for drinking water quality （GB54789-2006）, the ironcontent in drinking water cannot exceed0.3mg/L and the manganese content cannotexceed0.1mg/L. Drinking water with high levels of manganese content for long timecould cause inappetence, emesis, diarrhea, functional gastrointestinal disorders etc,and cause a lot of inconveniences and problems to our work and daily life. Therefore,treatment of groundwater with high concentration of manganese has aroused a lot ofattention from scholars.Nowadays the domestic and international technology of removing manganesemainly includes natural oxidation, contact oxidation, biological oxidation andmedicament oxidation. In view of the characteristics of northeast small towns, such asthe economic condition is relatively undeveloped, the temperature is low in winterand the manganese content in groundwater is high, it is suitable to use thehigh-efficiency contact oxidation method for the treatment of groundwater with highconcentration of manganese. According to the differences of the filter materials, thematurity periods of the filter for manganese removal are different. The start-up ofcontact oxidation filter is basically nature immobilized at home and abroad, e.g.activated filter membrane is naturally formed through the filtration ofmanganese-containing groundwater. But the maturity period of the filter formanganese removal in this method is very long, which is relatively faster to be1month and slower to be half a year or even longer. Therefore it appears especiallyimportant to develop a method for quick start-up of filter for removing manganese bycontact oxidation method.In this research a new method for quick start-up of filter for removingmanganese is developed. River sands are used as raw materials. Ozonenon-continuous aeration is applied to shorten the maturity period of the filter and theactivated filter membrane for manganese removal is quickly formed on the surface ofriver sand filters. Consequently, the quick start-up of filter for removing manganese isrealized. Some factors in the quick start-up process and in the follow-up operationprocess are studied to determine the optimal conditions for quick start-up process andthe follow-up operation process. The mechanisms of manganese removal areresearched in depth to confirm the principle of manganese removal using contact oxidation method. Enlarged experiment is carried out based on small experiment. Thefeasibility of quick start-up of filter for removing manganese by contact oxidationmethod is further confirmed.Results of the study are as follows:1. It is confirmed that the quick start-up of manganese removal filter can berealized by using ozone non-continuous aeration. The start-up conditions are studiedfrom aspects of medium sizes, amount of aeration, raw water’s concentration and flowrate. The optimal conditions for quick start-up phase is selected to be that, the mediumsize of the filters is2-3mm, the amount of aeration is50ml·min-1, the manganeseconcentration is3.0mg·L-1during aeration and1.5mg·L-1during operation, the flowrate of raw water is0.3m·h-1.2. The capacity of manganese removal of the mature filters are studied in theoperation precess after maturity of the manganese removal filter. In this experimentpH, DO and flow rate are researched as important factors to increase the manganeseremoval validity of the filters. And then the optimal conditions for the filter operationare determined to be pH≥7.0, DO＞6.5mg·L-1and flow rate＜0.6m·h-1. Thebackwash period of the filter is15days. The optimal backwash intensity andbackwash time are respectively7.81L·s-1·m-2and5min.3. The principle of quick start-up of filter for removing manganese by contactoxidation method is researched in depth. In this research fresh river sands and matureriver sands are studied by scanning electronic microscope and energy spectrumanalysis to observe the surface changes of the river sands before and after maturity.According to the energy spectrum analysis and calculation the black floccules on thefilter surface is initially determined to be filter membrane for manganese removal. Itsessential component is MnO2·xH2O.4. In the enlarged experiment of quick start-up of manganese removal filter, theresults from the small experiment are calculated and regulated simply based on acertain scale. The parameters in the enlarged experiment are finally determined to beas follows: the Mn2+concentration in raw water are controled at3.0mg·L-1duringhigh concentration aeration and at1.5mg·L-1during low concentration aeration,ozone concentration is70mg·L-1, amount of aeration is1.0L·min-1, aerationfrequency is5times a day and everytime lasts10min, filtration rate is0.5m·h-1.Under the above conditions, the maturity period of enlarged filter is9days.5. The changes of manganese concentration in the filter layer under differentfiltration rates in the operation process after the maturity of the manganese removalfilter are investigated. The results indicate that the manganese concentration decreaseswith the depth of the filter layer, and the slower the flow rate is, the faster themanganese concentration decreases. The faster the filtration rate is, the bigger filterdepth is needed. When the filtration rate reaches1.0m·h-1, the filter depth of80cmcannot meet the requirement of manganese removal anymore. According to theconditions in this enlarged experiment, for the raw water with manganese concentration of1.0-1.5mg·L-1, the highest flow rate that can be treated by this deviceis0.7m·h-16. The backwash intensity and backwash time of the filter in this enlargedexperiment are determined to be7.81L·s-1·m-2and5min respectively. According tothe monitoring results of washed effluent, the filter can fast regain the ability ofremoving manganese from raw water, which can ensure the filter’s cleanliness andavoid the damage to the activated filter membrane on the filters surface. Thebackwash period of the filter is about15days. |
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