Study On The Outbreak Conditions And Control Strategies Of Algal Blooms In Landscape Water With Reclaimed Water As Water Source

Using reclaimed water as a water source to supplement the urban landscape water plays a dual role of recycling water resources and alleviating water shortage.However,due to the shallow water depth and po or water mobility,the concentration of nitrogen and phosphorus nutrients in reclaimed water is relatively high,which is more likely to cause algal bloom.At present,there is insufficient understanding of the conditions and key factors of algal blooms in this kind of water,resulting in the limited effect of water bloom control.This paper takes Xi'an Moat as an example,using field monitoring and indoor and outdoor tests to clarify the temporal and spatial variation law of the water quality of the moat affected by reclaimed water,identify the response relationship between algal bloom and the main influencing factors(temperature,light,nitrogen and phosphorus nutrients),and obtain the suitable growth conditions of dominant algae species The research can provide scientific basis for the early warning and control of algal blooms in urban lakes with reclaimed water as the water source.The main conclusions are as follows:(1)Compared with the southeast Chengjiao wenchangmen section,the south to west gate section of the moat using reclaimed water is more likely to cause algal bloom in spring and,summer.The water temperature is between 19-33?,light intensity is between 1 000-80000lx,TN concentration is about 3.5mg/L,TP concentration is between 0.2-0.3mg/L,chlorophyll a concentration is more than 100mg/m3,and water flow is poor(flow rate is less than 0.15m/s).(2)In the reclaimed water,the dominant algae species in spring and summer are Microcystis flos-aquae(Cyanobacteria),Chlorella vulgaris(green algae)and Scenedesmus quadricauda(green algae),accounting for about 55%of the total number of algae,in which Microcystis flos-aquae accounted for 34%,Chlorella vulgaris accounted for 14%,and Scenedesmus quadricauda accounted for 7%.(3)The single factor rotation experiment showed that the optimum growth conditions for Microcystis flos-aquae were:temperature T=30?,light intensity=90001x,TN=3.5mg/L,TP=0.2 mg/L;the optimum growth conditions for Chlorella vulgaris were:temperature T=25?,light intensity=5000lx,TN=9mg/L,TP=0.3mg/L;the optimum growth conditions for Scenedesmus quadricauda were:temperature T=25?,light intensity=70001x,TN=9mg/L,TP=0.3mg/L.(4)Phosphorus concentration has a great influence on the growth of dominant algae.When the concentration of TP in the water decreased from 0.3mg/L to 0.2mg/L,the biomass of Microcystis flos-aquae and Chlorella vulgaris and Scenedesmus quadricauda increased,while when the concentration of TP decreased to 0.1mg/L,the biomass of the three dominant species decreased and the growth was inhibited.(5)The change of velocity has a great influence on the growth of algae.The growth rate of the three dominant algae species was the fastest when the flow rate was 0.05m/s,and the growth rate of the algae density can reach more than 300%;when the flow rate increased to 0.1m/s,the growth slowed down,and the decrease rate of the algae density is the lowest to about 90%;when the flow rate increased to 0.2m/s,the growth was obviously inhibited,and the mortality of the algae species increases.(6)Aluminum sludge in water supply plant can effectively absorb inorganic phosphorus,reduce phosphorus concentration in water and inhibit the growth of algae.Aluminum sludge can inhibit the growth of three dominant algae species,and effectively control the phosphorus concentration below 0.1mg/L.Among them,aluminum sludge has the strongest inhibition on the growth of Chlorella vulgaris.When the dosage of aluminum sludge was 3g/L,5 days after reaction,the density of Chlorella vulgaris decreased by 77%,the concentration of chlorophyll a decreased to 45mg/m3,and the concentration of total phosphorus decreased to 0.079mg/L.