The Study On The Modified Denitrifying Filter In Advanced Wastewater Treatment

Finding a high efficiency and low investment technology used for advanced wastewater treatment has great importance not only to boost water reclaimation industry but also to help water environement recovery. In order to enhance the performance of tertiary denitrifying filter aimed to reuse final effluent from biological nutrient removal plants, two different methods were used in this experiment for comparision.The first method is a 2-stage configuration tertiary filter with different filter media. Filter 1 was designed for removing nitrate from the biological treatment effluent with EC (expanded clay) as its filter media. The sand filter column that connected with denitrifying filter was designed for further COD, nitrate and suspended solids removal.The second method is to use a sand filter + sulfur/limestone column reactor. The sand filter was designed to remove SS and part of DO. The sulfur/limestone column was filled with sulfur and limestone mixed at a ratio of 3:1 aimed to remove nitrate.The result of the first methodUp to 90% of NO3—-N removal efficiency was consistently achieved with moderate methanol supplied. The effluent pH was higher than influent pH, there was a minus relationship between effluent pH and effluent nitrite concentration. About 3.00mg alkality (CaCO3) was produced with 1mg nitrate reduced. It was found that when C/N was higher, the nitrate removal rate was higher, the ORP of effluent was lower. In addition, there was a very good linear relationship between the cosumed TOC/reduced nitrate and influent C/N. Futher study on ORP proved that there was an index relationship between the effluent ORP and effluent NOx—concentration. High SS removal efficiency was achieved in column 2, the effluent SS concentration was kept below 1mg/L.With excessive methonal, up to 80% of nitrate removal effieciencies was constantly achieved with a EBDT (it indicated the empty bed detention time of the EC column) of 15min,10min,5min or 2.5min. The result of the second methodWith the EBDT (it indicated the empty bed detention time of the sulfur column) of 2h and 0.5h, the sand filter got a high removal efficiency of turbidity, although the influent SS concentration fluculated greatly, the effluent turbidity was stably kept below 1NTU. The turbidity increased after the sulfur/limestone column, and was not stable. In this experiment, the ratio of produced sulfate and reduced nitrate was between 7.12 and 12.87. The average effluent pH was 0.47 below the average influent pH.