Investigation Of Landscape Water In Xi’an And Water Quality Control To Prevent Eutrophication

The water quality and eutrophication of six landscape waters in Xi’an were surveyed and assessed firstly; and then two representative landscape waters were selected to study their water quality, phytoplankton algae and sediment sludge through one yaer’s continuous monitoring. Principle component analysis(PCA) was conducted to analyze the relationship among environmental factors. Meanwhile, canonical correspondence analysis(CCA) was performed to investigate the relationship between environmental factors and dominant species. Water quality and eutrophication assessment were eatabilished by improved fuzzy comprehensive evaluation method and comprehensive trophic level index(TLI), respectively. Finally, the bench scale of biological aerated filter(BAF) was set up to purify the landscape water in serious eutrophication rapadly. The main results are as follows:(1) In the six landscape waters surveyed, Moat River was in serious eutrophication status, both Xing-qing Lake and Feng-qing Lake were in middle eutrophication status, Nan Lake and Han-cheng Lake were in light eutrophication status, and Wei-yang Lake was in mesotrophication status. In addition, Chlorophyta was the dominant algae in Nan Lake, and Cyanophyta was the dominant algeae in other landscape waters.(2) The water quality of Feng-qing Lake and Moat River both varied with the seasons: the water quality of Feng-qing Lake was best in winter and worst in summer, and the main contaminant was chemical oxygen demand(COD); a total of 39 genera of phytoplankton belong to 6 phyla were dentified, with an average algae cells density of 863.9±732.6×105 cells/L in Feng-qing Lake, and the dominant species contained Pseudanabaena sp, Chlorella sp, Closterium sp and Raphidiopsis sp. While the water quality of Moat River was worst in spring and summer, and the main contaminant were total nigrogen(TN), total phosphorus(TP) and ammonia nitrogen(NH3-N); a total of 53 genera of phytoplankton belong to 7 phyla were dentified, with an average algae cells density of 758.4±830.7×105 cells/L in Moat River, and the dominant species contained Oscillatoria sp, Closterium sp, Trachelomonas sp, Euglena sp, Cyllotella sp, and Synedra sp. Therefore, the main features of water quality in urban landscape waters were seasonal and genera differences. Furthermore, the concentration of nitrogen and phosphorus in sediment sludge of two landscape waters varied with seasons: TN in sediment sludge of Feng-qing Lake was highest in spring(11.04 mg/g) and lowest in summer(9.98 mg/g) while the value of Moat River was highest in summer(13.52 mg/L) and lowest in winter(8.76 mg/L); the concentration of TP in sediment sludge in Feng-qing Lake and Moat River were all lowest in winter and highest in summer, however, the concentration of TP in summer and winter of Moat River were 3.95 and 2.36 times higher than that in Feng-qing Lake, respectively.(3) The PCA and CCA results indicated that T, TP, TN, SD and DO were the most important environmental factors in Feng-qing Lake; TN, PO43--P, COD, T and Chla were the most important environmental factors that influence the dominant algae in Feng-qing Lake, in which TN and salinity had considerable influence on P. limnetica, T and COD were the mian environmental that influenced R. curvata, Cosmarium sp and C. vulgaris were mostly influenced by T, TP, PO43--P, SD, NH3-N, and pH value. T, TP, TN, Chla, COD and DO were the most important environmental factors in Moat River; T, TN, NH3-N, pH and salinity were the most important environmental factors that influenced the dominant algae in Moat River. Among them, T had considerable influence on Closterium sp and Cyllotella sp, T, SD and PO43--P had strong influence on Oscillatoria sp and Euglena sp, Closterium spand Synedra sp were mostly influenced by TP, COD, pH, TN, NH3-N and salinity. Therefore, the algae in different landscape waters were influenced by different environmental factors.(4) A BAF was set up to purify the effluent of Moat River under the condition of HRT of 3 hours and gas-water ratio of 2:1. The average removal rate of Chla, aglae removal rate of turbidity was 83.3%.