| In recent years, Chinese key lake eutrophication is still very serious, several major municipal lake is in eutrophication status, such as the west lake, dianchi lake and so on. The current main measures to improve water quality of large lake are waste water collection, sediment dredging engineering, fishing regulation, the restoration of wetland and water diversion project, etc. Take water diversion project for example, it is a measure that large number of clean water is introduced into lake as additional water resoure to improve the lake water quality. Now, the water diversion project has become an important menthod to improve lake water quality. But the diversion water is usually polluted by non-point source of pollution and has high nitrate-N content. Actually it's a very common problem of diversion projects for many lakes treatment and needs a directing research.In this research, many performance tests have been done to treat the nitrate micro-polluted surface water by using combined process of biofilter-ecological wetland and adding ethanol as the external carbon source. Under the conditions of hydraulic loading 2 m3/(m2·h), water temperature 16℃and C/N(CODcr/NO3--N) ratio 6:1, the combined process of biofilter-ecological wetland set-up was completed 16 days later and nitrate removal percent was more than 80% by using inoculation start-up method. For combined process of biofilter-ecological wetland denitrifying operation, C/N was an important parameter. The results of the study showed that, under the conditions of hydraulic loading 4 m3/ (m2·h), water temperature 2025℃, C/N(CODcr/ nitrate) ratio 6:1, nitrate removal percent was under 60% and nitrite concentration of effluent was up to 0.29 mg/L in bio-filter-ecological wetland reactor, organic carbon source was seriously insufficient in the reactor. When C/N ratio is 10:1, nitrate removal rate was more than 90%, nitrite concentration of effluent was less than 0.05 mg/L in bio-filter-ecological wetland reactor. Otherwise, the CODcr value of effluent was close to that of influent, carbon pollution was not introduced. So, in order to get better nitrate removal efficiency and reduce nitrite accumulation in the denitrifying process, C/N ratio can not less than 10 when ethanol as a additional carbon source. Under low-temperature conditions, biofilter-ecolo gical wetland denitrification efficiency severely suppressed in the temperature range of 2 to 10 degree, and the removal percent of nitrate could approach 60% when the water tempreture was between 13 to 17 degree . When the water temperature was above 20 degree, nitrate removal percent is higher than 90% in the bio-filter-ecological wetland reator, and the effluent nitrite concentration was below 0.05 mg/L, temperature is no longer restraining factors of denitrification efficiency in the reator. In the water temperature range of 20 to 25 degree, nitrate removal percent of bio-filter-ecological wetland reactor was more than 90% when the hydraulic loading was below 8 m3 / (m2·h), but when hydraulic loading increased to 10 m3 / (m2·h), nitrate removal rate of bio-filter-ecological wetland declined to 60%, nitrite nitrogen accumulated to 0.12 mg/L, the data showed that 8 m3 / (m2·h) is the maximum hydraulic load. Head loss in Bio-filter in unit time increased with the growth of temperature, accordingly reverse wash frequency also increased. Under high temperature conditions, Bio-filter need reverse wash every other day. The gas-water joint three sections of backwashing method is used in this study. After the backwashing, it needs about 90min for bio-filter to recover to former level.The reactor restarted after lied idle for 30 days, and could achieved steady state in 14 days with excellent denitrifying performance. In addition, the denitrifying dynamics simulation was studied in the condition of plenitudinous carbon sources based on Monod equation. The result showed that the simulation data can joint very well with practical ones. |
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