| In this study, according to the water quality characteristics of low temperature and low turbidity, seasonal algae outbreak, high organic matter and ammonia nitrogen content in plain reservoirs and existent problems in the actual operation process of filters in water purification plants,a research on dual-media filters was studied based on the mechanism and operating characteristics of filters, combined with the preliminary investigation. The filtration performances of different types of anthracite -sand filters were studied by experiment with response surface method used to analyze the relationship between the factors and the response parameters,and the design of filter backwash system was carried out with the investigation. The feasibility of zeolite as the upper media was discussed and decontamination capability of zeolite-sand filters was studied. Combined with ozone process,the removal efficiency of organic matter and ammonia nitrogen was analyzed.Research content mainly includes four aspects:(1) parameter construction and optimization of anthracite-sand filters in condition of raw water with low temperature and low turbidity.(2) feasibility of zeolite as the upper filter media and the effect of treatment analysis.(3) treatment effect analysis of ozone/dual-media filters in condition of raw water with high organic matter and high ammonia content.(4) response surface method analysis on relationship between parameters and influence factors.In the study of anthracite-sand filters treating water with low temperature and low turbidity, the parameters which affect the filtration performance were selected and analyzed.By comparing relevant indexes such as filtration cycle.turbidity and particle counts of filtered water, head loss et al in different filtration rate,gradation of media and layer depth,the influence of factors on filtration performance was analyzed,the optimal construction parameters and were selected and the turbidity removal mechanism was studied.The study showed that, sand effective grain size was the main factor affecting filtration performance,filters with sand effective grain size 0.5mm (USA gradation) performed best,filters with sand effective grain size 0.55mm(Domestic gradation) took the second place,and filters with sand effective grain size 0.6mm performed worst.The optimal operating conditions were 9m/h (40cm/50cm), 10m/h (20cm/70cm),12m/h (20cm/70cm) and 14m/h (20cm/70cm) with sand effective grain size 0.5mm.By investigation and experiment,the influence of backwash method on backwash effect was analyzed,calculation method of corresponding parameters was proposed.Combined with the idea of automatic control,automatic control system of filters was designed,especially backwash process.On the basis of the research of traditional anthracite-sand filters, the type of upper filter material was changed, and the feasibility of zeolite as upper filter media was discussed. By using the same test method, the relevant indexes of effluent were analyzed. The results showed that,compared with conventional anthracite-sand filters, zeolite didn’t show good filtering performance.It has lower mechanical strength and larger specific gravity,so it’s not suitable as upper layer media.Filters were characterized by quickly increasing head loss and shorter filtration cycle.According to the the water quality characteristics of high organic matter and ammonia nitrogen content,a removal of organic matter and ammonia nitrogen in water was carried out by aerating ozone in pre-filtered water based on ozonation of ozone to degrade organic compounds and biological effect of microorganism in filters. In the experiment, the removal efficiency of anthracite-sand filter, activated anthracite-sand filter and carbon-sand filter was compared after bio-membrane hanging. The adsorption and biological effects of filter media were discussed.The results show that, the removal of organic matter and ammonia nitrogen in water of activated anthracite-sand filter and carbon-sand filter were best with ozone dosage 5mg/L and ozone exposure time 10 minute,while conventional anthracite-sand filter performed worse.The removal rate of CODMn was 58.9%,79.2% and 81.4% respectively for Column A,Column B and Column C,the removal rate of UV254 was 87.8%,93.4% and 95.6%,the removal rate of NH3-N was 73.2%,88.3% and 92.2%.The removal rate of CODMn, was 25%, 46.5% and 42.5%, respectively, and the removal rate of NH3-N was 36%,42% and 43.3%, respectively. Adopting biological active filter material in the period of high organic matter and ammonia nitrogen content in water can make full use of the degradation of pollutants in the filter, effectively reducing the organic matter and ammonia nitrogen content in filters’effluent.Expert Design software was used to analyze the test results of anthracite-sand filters. Response surface method was used to establish the function model between the response parameters and factors.With the analysis of the relationship between the parameters and the factors, the experimental results in Chart.3 were compared with the results produced by response surface.The research showed that the Expert Design software can be used to improve the test analysis to the rational level, which can be in line with the theoretical analysis. |
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