| Massive emission of nutrients such as nitrogen, phosphorus is easy to cause water eutrophication, especially for lakes and reservoirs. The composition of nitrogen in water is complex. DON, as one of the important parts of nitrogen, has big impact on water environment which can not be ignored. But up to date, research on nitrogen forms in lakes and reservoirs is not comprehensive, and the relationship between DON and water environmental factors is not clear. Moreover, the effective methods for removing DON remain to be explored. Therefore, it is necessary to explore the characteristics of nitrogen forms in lakes and reservoirs, and to analyze the relationship between DON concentration and environmental factors, and also to seek effective method for removing DON. Those reserchs are of great significant for protecting water bodies of lakes and reservoirs and for ensuring the safety of drinking water.This thesis selected Reservoir Songshanhu, Reservoir Yantian and Reservoir Shuilianshan, which are source water for drinking, as investigation objects. Through field investigation and sample analyses, the characteristics of nitrogen forms in water have been analyzed, and the relationships of the DON concentration and DON occupied ratio with water quality factors have been established. Then, the removal effect and mechanism of DON have been also discussed experimentally by enhanced coagulation and activated carbon adsorption.Through investigation and experimental analyses, the following knowledges have been obtained:(1) Nitrogen in the lakes and reservoirs water is mainly composed of ammonia, nitrate, nitrite and DON, and the average proportion of different forms of nitrogen in the monitoring period were 6.83%~38.20%, 1.82%~57.45%, 0.87%~4.23% and 19.78%~37.75% respectively. Eutrophication level of Yantian Reservoir changed between medium and rich. Both levels of Songshan Reservoir and Shuilianshan Reservoir were rich. Nitrogen was an important factor that leading to cause water eutrophication.(2) DON concentration of the investigated reservoir ranged from 0.37 mg/L to 1.10 mg/L, and accounted for 12%~59% proportion of TN. Comparing the different lakes and reservoirs, concentration of DIN exhibited the same variation with concentration of TN, but concentration of DON didn’t change correspondingly. Meanwhile, DON had positive correlation with TP, Water temperature and CODMn, but negative correlation with pH and DO. And the correlations of TP、pH and CODMn were significant.(3) Aluminium sulphate(AS) and polyaluminium chloride(PACl) were selected as coagulants to remove DON in raw water. The results show that the removal effect of single coagulation was poor. The removal rate of AS and PACl were 6.93% and 7.20%, respectively. For enhancing removal effect, cationic polyacrylamide was selected as coagulant aid, and the removal rate of AS and PACl increased by 16.28% and 25.42%, respectively. While adsorption pretreatment by activated carbon could improve DON removal rate significantly. The removal rate of AS and PACl could reach 50.87% and 52.90%, respectively.(4) Cocoanut shell activated carbon was used as adsorbent to carry out adsorption test of simulated DON water. The results show that the time of reaching adsorption equilibrium were about 180 min and the change of pH would lead the significant decrease of adsorption capacity. The performance of the activated carbon in adsorbing asparagic acid followed the the pseudo-second order adsorption kinetics and Langmuir equations of adsorption isotherm(R2>0.99). And the phases of film diffusion and internal diffusion were the control phases of adsorption. The analysis of thermodynamic indicate that the adsorption reaction was exothermic and it couldn’t react spontaneously under normal temperature and pressure. Meanwhile, 1% NaOH solution was suitable for regeneration of coconut shell activated carbon. |
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