Study On Water Quality Characteristics And Regulation Technology Of Urban Landscape Water Body Under Reclaimed Water Recharge Condition

Reclaimed water has become an important supply source for landscape water bodies in water-deficient cities.However,because the main water quality indicators of the reclaimed water are quite different from the requirements of the environmental quality standards of surface water,how to effectively guarantee the water environment functions of the water bodies which are supplied by reclaimed water is an important topic with great concern.In order to solve these basic problems,the water quality of urban landscape water bodies supplied by reclaimed water and water quality control technology have been systematically studied.Moreover,the situation of representative urban landscape water bodies throughout the country were investigated,and several lab experiments were constructed to revealed the effects of typical pollutants such as nutrients in reclaimed water on the water quality of the water bodies.Finally,water quality benchmark and the impact of reclaimed water replenishment on the water quality of urban landscape water bodies,as well as the roles of in-situ and ectopic water purification technologies and comprehensive countermeasures were studied for improving functions of the landscape water bodies.The main results of this study are as follows:(1)Water transparency(SD)was used as a comprehensive indicator of landscape water quality,because the function of landscape water bodies is closely related to SD.Based on the investigation of 189 landscape water bodies in different cities across the country,and the long-term monitoring of 4 representative water bodies,SD?0.64m was proved as a necessary condition for ensuring the water quality of landscape water bodies supplied by reclaimed water.Moreover,SD was affected by the reproduction of algae significantly.If Chlorophyll a(Chl-a)is used as an algae control index,then the recommended value corresponding to SD is 10 mg/m³.Nutrients are the main cause of algae reproduction,thus,according to the correlation analysis between total nitrogen(TN)and total phosphorus(TP)and Chl-a,the recommended values of TN and TP for water bodies in different regions were proposed:half semi-arid area TN=12mg/L,TP=0.3mg/L;semi-humid area TN=11mg/L,TP=0.2mg/L;wet area TN=5mg/L,TP=0.1mg/L.(2)In order to solve the problem of eutrophication in landscape water bodies,the effects of nutrients and trace metals on the reproduction of microcystis aeruginosa were studied.The results show that,in addition to the TN and TP concentration and N/P,trace elements such as Fe,Mn,Zn and Cu that coexist in waters within a certain concentration range(Fe:500¹000?g/L,Mn:20⁸0?g/L,Zn:0.5⁵?g/L,Cu:1¹0?g/L)could promote the growth of algae.Moreover,the water quality matrix,which taking conventional nutrients and trace metal elements as evaluation factors,Chl-a as the evaluation objective was established,and then,the influence weight of each evaluation factor was analyzed.The results determine that in conventional nutrients,N/P was the main factor to control the water quality of landscape bodies,followed by orthophosphates,ammonia nitrogen,nitrate nitrogen and polyphosphates.With regard to trace metal elements,Mn was the main factor,followed by Fe,Zn and Cu.(3)The effect of reclaimed water replenishment ratio and the period of exchanging water on the functions of landscape water bodies were also studied.When the water bodies were replenished with reclaimed water that reached first grade A standard,it was easy to maintain the quality better than the recommended value when the reclaimed water did not exceed 50%of the supplementary water.However,when the proportion of reclaimed water was higher than 50%,the quality of the waters deteriorated significantly.Thus,it is necessary to shorten the period of exchanging water to maintain the water quality.If the landscape water bodies were supplied by the reclaimed water only,the appropriate period of exchanging water in spring and autumn should be within 5 days,and should be within 3 days in summer.(4)The performance of the in-situ and ectopic technologies for water bodies purification were also studied.The results show,the average reoxygenation coefficient(0.15 d^-1)of the waters replenished with reclaimed water was lower than that of the conventional water body(0.40 d^-1).Therefore,aeration was an important measure to improve the self-purification ability of the water bodies.The aeration rate should be determined based on the amount of reclaimed water and the demand for denitrification and organic matter removal.Ecological-biological combination in-situ purification technology was studied based on a case study.Combined with the in-situ purification by ecological floating bed,the bio-filming roles of three-dimensional elastic carrier in the bottom of the bed,the adsorption roles of light ceramsite filled in the floating cushion,and the uptake by the emerged plants could achieved effective in-situ nitrogen and phosphorus removal.However,compared with in-situ purification,the bypass circulation ectopic treatment represented by ecological filtration has better pollutant removal ability,and can simultaneously achieve hydraulic regulation of water bodies.Thus,it would be an effective measure to ensure the functions of landscape water bodies,especially when the period of water exchange was long.(5)The comprehensive technology of water quality and landscape functions improvement of urban landscape water bodies was studied according to the artificial landscape lake in Xi'an Siyuan College,which was replenished with reclaimed water.The results of long-term water quality monitoring and water quality simulation analysis show that even though the artificial landscape lake was supplied by reclaimed water completely,its landscape roles could be very well guaranteed through reasonable water regulation,natural aeration ad apted to local conditions,and improvement of water habitats based on aquatic plant.Therefore,it was not necessary to carry out the bypass circulation treatment...