Study On Purifying Urban River Waters By Biofilm Coupled With Aquatic Plant

The deterioration of urban river water brings a bad influence to urban environment gradually, which has attracted a widespread attention, thus making it an urgent problem to be solved. Biofilm and floating bed are two important technologies of purifying urban river waters for their good environmental benefits, low running costs and so on. In order to provide technical support for the practical engineering application of river water body restoration, the promotion of river water purifying by biofilm, plant floating bed, floating bed coupled with the biofilm and addition of benthic animal to floating bed&biofilm coupling system were studied in this paper.(1) Controlling the intermittent aeration of biofilm systems under different anoxic-aerobic intermittent aeration, which the highest removal efficiency29.1%of TN was realized under the condition of16:8anoxic-aerobic intermittent aeration and the highest removal efficiencies of NH4+-N and TP91.8%and31.2%respectively, were realized under the condition of4:4anoxic-aerobic intermittent aeration. Controlling the dissolved oxygen (DO) of biofilm systems in different concentrations, the system achieved the highest removal efficiency38.2%of TN and the highest NO2-N accumulation rate (the concentration of nitrite in effluent was an average2.98times than that of inflow in48days) when DO concentration was controlled at0.5～1mg·L-1, which indicated an obvious inhibition of nitrite-oxidizing bacteria when DO in within this range and it meant the effect of shortcut nitrification-denitrification in the system was achieved. Trials of different aeration rates in biofilm systems were set under low temperature conditions. The aeration systems achieved higher pollutions removal efficiencies than no aeration system. When the aeration rate was1L·min-1, the system did not get the highest NH4+-N removal rate, but the highest TN and TP removal rates (23.8%and22.2%respectively), the decontamination capability of biofilm system that could be enhanced by aeration under low-temperature, and an appropriate amount of aeration would be more effectively.(2) When the floating beds were planted with a single species of plant, the concentrations of nitrogen and phosphorus of Caldesia parnassifolias system were below "environmental surface water quality standards" class Ⅱ after7days. The rates of total nitrogen increment and TN removal was the highest (87%) by Caldesia parnassifolias system, meanwhile, Cyperus alternifolius system was in the second place in the rates of total nitrogen increment and TN removal (67.5%). The ratio of total nitrogen in stem leaf was the highest87.2%in the whole plant of Cyperus alternifolius, while the ratio of phosphorus in stem leaf was the highest88.9%in the whole plant of Sagittaria sagittifolia, which meant the nutriment can be removed from water by harvesting the plants aboveground. In addition, Cyperus alternifolius showed an adaption to the environments of low nitrogen and phosphorus concentrations and low temperature, which was conducive to long-term effects of waters purifying. When the floating beds were planted with mix plants, the positive enhancement effects of different combinations were in a proper order as follow, Caldesia parnassifolias+Ipomoea aquatica Forsk., Caldesia parnassifolias+Cyperus alternifolius, Sagittaria sagittifolia+Cyperus alternifolius.(3) In the simulative river reactor, the effects of waters purifying by the simulative two-stage technology of biological removal of nitrogen with different aeration conditions and simulated AO technology were compared. When the aeration was0.24L·min-1, the simulative river reactor with the simulative two-stage technology got the highest TN removal rate (35.1%). With Cyperus alternifolius alone in the reactor, the COD and TP removal effects is notable. On the operation of the coupling system, when the pollution concentration of inflow water is changed, NH4+-N and COD removal rates were less affected, but the removal rates of TN and TP were greatest affected while the waste water load was in the two-fold (decreased by25.7%and19.3%compared with one-fold, respectively). Changes in HRT brought small impact on the system effluent relatively, but the effects of removal rate of TN and TP got to the maximum at HRT of24h (decreased by44.2%and37.1%respectively).(4)In the simulative river reactor, the TP removal rate was increased by adding the amount of Misgurnus anguillicaudatus, but the removal rate of NH4+-N was decreased (at most21.3%promotion of the concentration of NH4+-N). With the amount increase of Cipangopaludina chinensis, the removal rates of NH4+-N, TN and TP were improved separately (the highest rise1.8,2.5,1times, respectively). When both of the benthonic animals were added to the simulative river reactor, it got a more effective pollution removal rate of the pollutants than either was added alone. By adding benthonic animal to floating bed&biofilm coupling system to build a complex ecosystem, it will facilitate the effect of each unit and produced a complex function, so that the average removal rates of NH4+-N, TN, TP, COD reached to75.4%,61.2%,50.0%,83.7%respectively.