Study On Treatment Of Low C/N Ratio Wastewater Using Modified Vermiculite

With the improvement of living standards and the changes of lifestyle, the composition and proportion of urban sewage have been correspondingly changing, with the increase of nitrogen in wastewater, but the concentration of COD is low. Therefore, the phenomenon of high-nitrogen contamination with low COD is evident. Based on the traditional theory of denitrification, enough organic substance must be prepared to realize the process of denitrification. Thus the treatment of such a low C/N wastewater needs a high content of organic carbon resource, which will correspondingly increase the costs. So how to realize the high efficiency of nitrogen removal is the key of the experiment.Vermiculite, as a kind of clay minerals, has great characteristic of adsorption and ion exchange capacity for its unique layered structure, so there will be wider application prospects in wastewater treatment. The great performance of adsorption of ammonia nitrogen make vermiculite becomes an excellent bio-film carrier. If vermiculite is applied to suspended carrier biological fluidized bed reactor, the high nitrogen removal rate could be achieved.First of all, the experiment studied the adsorption equilibrium time of natural vermiculite and the adsorption effects of ammonia nitrogen and COD under the condition of different size. The ammonia nitrogen adsorption equilibrium time of natural vermiculite was 3.0 hours. Different sizes of the natural vermiculite influence the removal efficiency slightly, and the ammonia nitrogen and COD removal rates were 25%~26% and 16%~22% respectively. Among them, the natural vermiculite with size over 100 mesh had the best effect of ammonia nitrogen and COD adsorption and the highest removal efficiency. That indicated the smaller the size, the more adsorption of ammonia and COD. In addition, the influence of different pH and temperature on the adsorption of ammonia and COD were studied. The results showed that pH influence ammonia nitrogen adsorption strongly, the natural vermiculite for removal rate of ammonia nitrogen increased with the pH. The adsorption effect of ammonia nitrogen was the best when pH was 7. The ammonia nitrogen adsorption capacity of natural vermiculite was decreased gradualy with the increasing temperature. Some modification experiments of natural vermiculite were conducted, which involved heat-modified, salt-modified and acid-modified mainly, and identified the best modified condition. Through the static adsorption experiments, the adsorption capacity of ammonia nitrogen for heat-modified, acid-modified and salt-modified vermiculite was measured. The heat-modified vermiculite under the same temperature had different adsorption effect of different size on ammonia nitrogen and COD. The removal rates of ammonia nitrogen and COD were the highest when the size of the modified vermiculite was over 100 mesh. When the size of heat-modified vermiculite was the same, the variation of temperature influenced the adsorption of ammonia nitrogen and COD significantly. Vermiculite was burned at 200℃, the removal rate of ammonia nitrogen and COD were the highest, The removal rates of ammonia nitrogen and COD were up to 57.84% and 59.08%.d as the temperature increased, the removal rates drop. The adsorption of ammonia and COD increased with the size of salt-modified vermiculite decreasing. The removal rates of ammonia nitrogen and COD were up to 59.82% and 61.23%, respectively when the size of salt-modified vermiculite was over 100 mesh. Vermiculite modified with different acid concentrations had slight different effect on adsorption of ammonia nitrogen and COD, and the removal rates of them were 40%~60% and 35%~50% respectively. In the three modified experiments, the results showed that salt-modified had the best effect on adsorption of ammonia nitrogen and COD and the highest removal rate, followed by heat-modified and acid-modified. The adsorption effects of heat-modified vermiculite and salt-modified vermiculite were not so different,Considering the potential toxic action to the microbes by salt-modified vermiculite.200℃heat-modified vermiculite was applied as packing in this experiment.The experiment adopted the method of synchronized culture to domesticate and cultivate sluge. After more than 30 days acclimated, activated sludge showed a good flocculation and precipitation. Microscopic examination found that the sludge contained a large number of zoogloea, epistylis and rotifer, while ammonia nitrogen removal rate reached to 73%. SV% remained in 20~30%, and MLSS maintained about 3000mg/L. Acclimated activated sludge was inoculated into the reactor with biofilm culturing, and the modified vermiculite under the condition of 200℃has been used as carrier in this reactor. After 35 days, the system has worked stably. A thin light brown layer of biofilm was present to the surface of filler with dense and sticky. The results showed that the biofilm had already matured and had a good effect on nitrogen removal.Selecting modified vermiculite under the temperature at 200℃as filler, well domesticated activated sludge was applied to biological fluidized bed reactor. Inspecting the effect on nitrogen and COD removal at the different conditions of temperature, pH, DO and aeration in the reactor, and determine the best operating conditions. The best removal efficiency of ammonia-nitrogen can reach to 96.64% with continuous aeration at 30℃, pH=8, DO=3mg/L, the lowest concentration of ammonia nitrogen in effluent water was 1.25mg/ L. A small amount of nitrate nitrogen was accumulated.