气提式砂滤器在水产养殖系统中的水质净化效果

摘要

Traditional pressure sand filter after long time working intercepts large amounts of solid particles and leads to difficult backwash. In order to solve these problems, this study developed an airlift sand filter that can backwash itself while operating by optimizing a traditional filter. The airlift sand filter itself had filtration, separation, flotation, and self-cleaning functions, and could replace the traditional sand filters such as filter cell without valve, mechanical air flotation and other physical filtration device in aquaculture workshop. In the airlift sand filter, quartz sand (in diameter of 1-2 mm) was used as the filter medium, and the aquaculture sewage was flowed upward slowly from the bottom, thus quartz sand could intercept the suspended solids. Meanwhile, the fixed flow gas flowed from the bottom pushed dirt and quartz sand upwards simultaneously. During this process, sand and water were sufficiently contacted with each other. The interaction force between the sand and seawater resulted in production of a large number of bubbles. The suspended solids were then wrapped with the bubbles while quartz sand was cleaned by the sand washing device on the top of the system. The cleaned sand fallen back to the filter system by the gravity, and the suspended solids and waste water flowed out of the outfall. The airlift sand filter has the advantages of simple equipment, convenient operation, backwash without stopping the equipment, smooth and continuous system running, low energy consumption and easy to maintain and repair. The efficiency of the airlift sand filter used for marine recirculating aquaculture systems of the suspended solids (SS) and chemical oxygen demand (COD) was tested. Results showed that removal efficiency of SS and COD by this filter was 41.31%and 34.04%, respectively. Before the filtration, the number of large particles suspended solids (60 μm or higher) was 11.1%, its mass fraction was 71.77% and its mass concentration was 93.53 mg/L. The water processing decreased the number, mass fraction, and mass concentration of the large particles suspended solids to 0.68%, 38.07%, and 15.72 mg/L, respectively. At the beginning of the test, the number of micro particles (60μm or less) was 88.92%, its mass fraction was 28.23%, and its mass concentration was 36.79 mg/L. After the treatment, the micro particles below 30μm accounted for 87.45%, its number of mass fraction was 13.61%, and its mass concentration was 5.62 mg/L. These results suggested that the effect of particulate removal treatment was obvious. Meanwhile, the treatment also reduced the content of ammonia nitrogen and nitrite in the system. After filtration, the suspended solids in recirculating aquaculture systems were≤67.33 mg/L, meeting the requirements of the water treatment in marine recirculating aquaculture workshop by China.%为解决传统压力式砂滤罐长时间工作后截留大量固体颗粒物而导致的难以反冲洗的问题，该研究在原有设备基础上进行技术改进；研制出了1种可以边工作边反冲洗的气提式砂滤器；气提式砂滤器集过滤、分离、气浮、自动清洗等功能于一体，可以替代传统用于养殖车间的砂滤罐、无阀滤池、微滤机、机械式气浮等物理过滤装置；试验用1～2 mm石英砂作为过滤介质，过滤水以向上流方向从气提式砂滤器底部慢慢上升，污物被石英砂截留，同时，从底部流入定流量气体，使得污物和砂粒同时被提起，最终在顶端的洗砂装置中石英砂被清洗干净并由于重力作用而落回系统，污物和废水从排污口流出；试验表明，气提式砂滤器设备简单、操作简便，不需停机反冲洗，系统运行连续平稳，能耗小并且易于日常维护和检修；数据表明，这种气提式砂滤器对海水循环水养殖系统中的颗粒悬浮物（suspended solids，SS）和化学需氧量（chemical oxygen demand，COD）平均去除率分别为（41.31%±7.72%）、34.04%，同时也降低了氨氮、亚硝酸盐含量，过滤后养殖水颗粒悬浮物质量浓度≤67.33 mg/L。气提式砂滤器在海水循环水养殖系统中进行物理过滤，是1种行之有效的方法，满足了养殖车间的水处理要求。