| It is necessary to study the effect of nitrogen and phosphorus on the algae bloom and how to control the eutrophication of landscape water replenished with reclaimed water,which is more likely to cause eutrophication because of higher concentrations of nitrogen and phosphorus.In this paper,the changes of nutrient concentrations and algae biomass during the process of production of reclaimed water and replenishment of landscape water were firstly described by monitoring.Then,simulated reclaimed water was prepared in the laboratory to study the effects of concentration,formand proportion of nitrogen and phosphorus on the growth,toxicity and enzyme activity of Microcystis aeruginosa(M.A.).Furthermore,the effects of different water quality and volume on the growth of three blue-green algae were compared with the reclaimed water and the surface water.Finally,coagulation was used to treat landscape waters with different eutrophication levels.The main conclusions were as follows:(1)The results showed that flocculation-precipitation played a major role in the removal of inorganic nitrogen and phosphorus,algal density and chlorophyll a during the process of reclaimed water production,where the removal rates of algae density and chlorophyll a(chla)were 72.29% and 77.68%,respectively,corresponding to the average values of 4.44×103 algae cells/m L and 5.97?g chla/L in the effluent respectively.On the other side,the algae density and chla could arrive at 8.08×105 cells/m L and 81.73?g/L,which were 27.76 and 5.10 times those of raw reclaimed water respectively,when the reclaimed water was used to replenish the landscape water for 4 days in summer.Moreover,Chlorella vulgaris was the dominant algae in summer although the algae species in the simulated water varied with time.Hence,in order to reduce the risk of algal outbreak effectively,the residence time of reclaimed water for landscape reuse should not exceed 3 days as the standard for reclaimed water as scenic water(GB/T 18921-2002)suggested.(2)The maximum density of M.A.increased with NO3-–N/NH4+–N ratios when the concentration of PO43--P and TIN in the reclaimed water was constant.The specific growth rate increased with concentration of PO43--P under a higher NO3-–N/NH4+–N ratio and it grew better under the higher NO3-–N concentration.Ammonium was the first nitrogen source utilized during M.A.growth,whereas nitrate was the alternative nitrogen source when the ammonium was lower than 0.18~0.40 mg/L.However,phosphorus uptake by M.A.was hardly affected by the initial nitrogen concentrations and ratios.(3)It revealed that the release of MC-LR was not affected by the limitation of PO43--P but was related to the growth phase.The maximum concentration of MC-LR was 7.51~8.51 ?g/L at the exponential phase.The correlation between dehydrogenase activity and specific growth rate was more significant under the most favorable water quality.The activity of superoxide dismutase was negatively correlated with the concentration of TIN when the composition and proportion of inorganic nitrogen were same.(4)The growth potential of M.A.,Chlorella sp.and Pseudomonas sp.in the reclaimed water was higher than that in the surface water.During the 14-day cultivation,M.A.appeared to grow positively while the maximum densities of Chlorella and Pseudomonas sp.were 4.93×106 cells/m L and 2.21×106 cells/m L in the reclaimed water.In addition,the adaptability of Chlorella was the strongest while Pseudomonas sp.was the worst whether in reclaimed water or surface water.The result of cultivation with different proportions of water sources revealed that reclaimed water should not exceed 25% when it was reused for landscape water to control harmful cyanobacteria blooms.(5)Algal cells decreased from 107 to 104 when the dosage of 70 mg PAC/L was adopted.Under this dosage,the maximum removal rate of chla,PO43--P and TP in moderate were 57.84%,83.33% and 79.22% while their responding values in severe eutrophic landscape water 68.02%,72.00%,79.22% and 68.78%,respectively.The removal rate of chla and PO43--P in the moderate eutrophic landscape water by combination of PAM and PAC was up to 86.67% and 64.48%,respectively,when the optimum dosage was 1 mg PAM/L + 30 mg PAC/L.However,that removal rate in the severe eutrophic landscape water was 80.10% and 59.19%,respectively,when the optimum compound dosage of PAM and PAC was 2 mg/L and 50 mg/L. |
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