| Ammonia nitrogen is one of the main factors that cause the watereutrophication. To satisfy the improving public requirements of environmentquality, more and more stringent standards of ammonia nitrogen emission wereworked out, which made the development of economical and efficient ammonianitrogen treatment technology a research focus for environmentalists.As an agriculture production country, there are a lot of agricultural wastessuch as straw, corncobs, walnut shells produced every year, the vast majority ofwhich can only be discarded or only as a fuel for peasants. It does not only wasteresources and increase the environmental burden. As a kind of importantbiomass resources, agriculture waste has many advantages, such as renewable,shorter regeneration cycle, biodegradability and environment friendly. The usingof agricultural waste in water treatment can not only reduce processing costs, butalso can use the existing green resource, which provides a new way for thecomprehensive utilization of agricultural waste. In this experiment, the walnutshells were used as the media of biological aerated filters to study the surfacecharacteristics of the media and the removal effect of ammonia nitrogen inwastewater, and finally the operation parameters of biological aerated filterswere optimized. The work got the following conclusions:1) The tests results of physical properties of walnut shell showed that thewalnut shell was mainly composed of acid-insoluble lignin and cellulose, whichwere hard to biodegraded, and this meant that the walnut shell was biologicallyand chemically stabilized for the biological aerated filters media. Compared withthe other media of biological aerated filters, the walnut shell had more specificsurface area and higher void ratio, which was beneficial to the biological aeratedfilters media.2) The experiment of biofilm formation of biological aerated filters showedthat microbes could adhere to the surface of walnut. The removal rates of COD and ammonia nitrogen in both walnut shell media biological aerated filters andthe ceramic grain media biological aerated filters were basically the same, whichwere80%and90%, respectively. The biofilm formation of walnut shell mediaproceed a bit more slowly, which took27days, compared with the ceramic grain,which took21days. The variation tendency of nitrate and nitrite in effluent ofthe reactor showed that the nitrification in walnut shell media biological aeratedfilters was slightly weaker than that in ceramic grain media biological aeratedfilters, which took more time to get steady.3) Hydraulic load play an important part on the COD and ammonia nitrogenremoval rate of the reactor. The results showed that the removal rate of COD hada small change whereas the removal rate of ammonia nitrogen had a sharpdecrease with the increase of the hydraulic load. When the hydraulic loadvarying from0.5m/h to0.8m/h, the ammonia nitrogen removal rate had not yetdecreased much. When hydraulic load reached1.2m/h, the ammonia nitrogenremoval rate fell rapidly from70%to46%, and decreased to38%whenhydraulic load reached1.8m/h. In order to guarantee the COD and ammonianitrogen removal efficiency at the same time,0.8m/h should be the appropriatehydraulic load.4) A high ratio of gas and water is beneficial to the degradation of organicpollutants, but it is disadvantage for denitrification. When the ratio of gas andwater was higher than6:1, COD and ammonia nitrogen removal rate were90%and70%respectively. A high ratio of gas and water would make biofilm washedoff and the COD removal rate slightly decreased; hence,6:1should be suitablefor the reactor.5) The specific surface area of biologically walnut shell was higher thanthat of walnut shell, and the SEM image of biologically walnut shell showed thatthere were many micropores on the surface of it. This meant that something inthe surface of walnut shell was metabolized by microbes. Meanwhile, this newmicropores could provide new attachment points for microbes, which was goodfor the efficiency of the reactor. |
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