Research On The Removal Of Nitrate In Water By Biological Zeolite Reactor

Recently, COD and ammonia nitrogen could be removed thoroughly in sewage plants. However, researches on nitrate removal are still difficult and hot topics. The COD concentration of the effluent quality was low in this study. A sulfur-zeolite fixed bed reactor was used to remove the nitrite, while autotrophic denitrify bacteria, sulfate reducing bacteria and colorless sulfur bacteria were used to remove nitrate in influent.The results showed that the nitrate can be removed effectively by the autotrophic denitrify process in the sulfur-zeolite fixed bed reactor. More than 95% of nitrate can be removed while the volume ratio between sulfur and zeolite was 1:2, hydraulic retention time was 2h, and the inlet COD was 50mg/L. The removal ratio of total nitrite could still reach 80% without carbon source, and the outlet pH could keep at 7.0 without the addition of calcium carbonate. Besides, the temperature had little influence on the removal ratio of nitrate, and the removal ratio of total nitrite could still reach 91.1% at 12℃. The quality of outlet water from the stuff of sulfur/zeolite was obviously better than that of sulfur/ calcium carbonate and that of sulfur/ activated carbon.On the basis of above study, the sulfate from the process of autotrophic denitrify was removed by adding sulfate reducing bacteria to the sulfur-zeolite fixed bed reactor. The sulfur cycle was going on with the oxygen technology which transformed the sulfate to sulfur, and the secondary pollution was avoided. The results showed that the sulfate in outlet water was kept within state water quality standards I (sulfate<250mg/L) when the nitrate in inlet water was under 84mg/L and the temperature kept at 26℃. The sulfate reducing bacteria were much more likely to be affected by temperature than that of autotrophic denitrify, and the sulfate reducing bacteria lost much activity when the temperature was below 20℃.