| Agricultural non-point source pollution as one of the main causes of eutrophication of Dianchi lake, while lakeside as transition zone of agricultural point source pollution through runoff into Dianchi transition zone, and it have both upstream runoff’s purification problems and the problems of purification of range farmland return water. After appropriate transformation,We made use of lakeshore region ditch conditions for improve its water purification, and it is important for controlling agricultural non-point source pollution. On the basis of a static test, we tested in the songhua dyke’s abandoned district dynamic field. The main results were showed as follows:(1)We artificially planted submerged plant and breed aquatic animals by using tail water of sewage treatment station as raw water and the water tank as container. The results showed that the different combinations of submerged plants and aquatic animals had different effect of water purification. It has, better purification effect of the combinations of snail+mussels+myriophyllum verticillatum+potamogeton crispus. The highest removal rate to total nitrogen reached61.19%, the total phosphorus reached79.20%, the COD was15.96%, whose removal efficiency was not obvious.(2) We purified upstream water and runoff water around the experiment area by using the original ditch as sedimentation tank→filler pool→reoxygenation pool→Biological recovery pool after properly reconstruction and regionalization. The results showed that the system could adapt to the field situation of dealling with a substantial change of the hydraulic retention time (drying up to21.97h),and it can achieve better purification effect. Through one year’s observation,we found that this technology had a good purification effect on total nitrogen(average purification rate of63.40%),ammonia(average purification rate of43.90%), nitrate(average purification rate of71.00%) and total phosphorus(average purification rate of50.9%%).But it had no effect on COD. After transformation, the overall removal efficiency of ditch-pond system is superior to natural ditch. (3).The purification effect for total nitrogen, ammonia,nitrate was unobvious under the condition of sedimentation tank’s HRT is3.19-227h and average HRT is55.95h. While it was better for total phosphorus and COD. The average removal rate of sedimentation tank for each pollutantwas that total phosphorus30.32%, ammonia21.35%, COD16.49%, nitrate5.88%and total nitrogen5.5%.(4)The volume loading of filler pool to total nitrogen and nitrate were obvious than phosphorus, ammonia and COD. The highest HRT was200h, and the lowest was2.8lh. Especially when HRT was3.48h, the total nitrogen,nitrate,ammonia and total phosphorus’ load volume reached to the highest values compared to other HRT.,they are14.78g/m3·h,1.50g/m3·h,18.39g/m3·h,1.40g/m3·h. Accordingly, the average removal rate for each pollutant reached33.69%of total nitrogen,nitrate54.35%, ammonia35.80%,total phosphorus48.21%.The efficiency of filler pool for removing total nitrogen and nitrate was better than total phosphorus,ammonia and COD.(5)The highest HRT of reoxygenation pool’s was497h, and the lowest was7.00h. The average value was55.95h. The purification effects of reoxygenation pool for total nitrogen,total phosphorus,nitrate,ammonia and COD were good. Which the average volume to nitrate was3.21g/m3·h, and it was the highest.’s highest The average removal rate of reoxygenation pool to nitrate was60.37%. Average removal of other contaminants reached31.19%of total phosphorus, ammonia41.17%, COD15.62%,total nitrogen36.53%. It played a key role of submerged plants in reoxygenation pool for removing nitrogen and phosphorus.(6)Highest HRT of biodiversity restoration pool’s was466.7h, and the lowest was6.56h, the average value was101.69h. It had a better effect of biodiversity restoration pool’s purification effect on on total nitrogen than other contaminants, and the average volume load was1.53g/m3h. The average removal of each contaminants reached24.31%of total phosphorus,ammonia29.18%, COD14.29%, nitrate40.89%, total nitrogen35.88%. It was the best that the Biological recovery pool’s removal to nitrate.(7)On the whole, the removal of COD was mainly in Biological recovery pool; and the removal of ammonia was mainly in reoxygenation pool; the removal of nitrate is mainly in the filler pool and reoxygenation pool; and the removal of total nitrogen is mainly in filler pool and reoxygenation pool. The removal of total phosphorus is mainly in sedimentation tank and reoxygenation pool. The sedimentation tank’s purification efficiency for COD was highest, reaching16.5%. The filler pool’s purification efficiency was the best for total phosphorus, reaching33.26%, and the reoxygenation pool’s purification efficiency was the best for ammonia(41.17%), nitrate (60.37%)and total nitrogen(36.53%).The system’s efficiency was limited for purifying COD. |
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