Quality Variations Of The Landscape Water With Different Ratio Of Reclaimed Water Supply

Along with social progress, people strongly require landscape water body day by day. However, most cities in northern China are short of water resources. And water shortage has become the primary factor in limiting the development of water landscape. Reclaimed water has the advantages of stable water quantity and water quality. If reclaimed water is used to landscape water body, it not only can save the operating cost of water landscape, but also can effectively improve the waste of water resources and environmental pollution. However, reclaimed water contains nutritive salt such as nitrogen and phosphorus, which is with high concentration and belongs to the eutrophic water. If landscape water body is supplied with reclaimed water for a long time, it will produce water bloom and lose its landscape function. In order to reasonably and effectively control the operation of landscape water body, the research on the influence of different HRTs and the proportion of reclaimed water on the eutrophication of landscape water body has significant application value.This experiment adopted five artificial landscape pools with the same size to simulate the eutrophication characteristics of landscape water body. During the period, it strictly monitored the changes in external environment, gave full consideration to the factors such as season and climate, respectively replenished water based on different HRTs and the proportion of reclaimed water, and observed the changes in water over time. The results were as follows:(1) in spring, HRT of landscape water body was closely related to the growth of algae. When HRT was less than 10 d, water dilution effect was more obvious due to the shorter HRT and chlorophyll a also maintained at a lower concentration due to its dilution effect; when HRT was 20 d and 30 d, hydraulic retention time was longer. So that algae could gradually use nutrients in water; in the meantime, compared with the dilution effect of water, the growth effect of algae in water became the dominant factor. Therefore, algae would mass propagate and accumulate; however, when HRT was infinitely long, water body was prone to eutrophication, for flow speed was too slow. Therefore, in spring condition, HRT less than 10 d could avoid the eutrophication of landscape water body. At the same time, algae grew rapidly and the phenomenon of water bloom easily appeared in spring, so the empirical date in summer was conducive to the maintenance of better water quality in water distribution and the proportion of the adopted reclaimed water was 25%.(2) in summer, water body was more prone to eutrophication, so the way of controlling HRT to alleviate the eutrophication of water body became very important. When HRT was 2d, the faster HRT enabled water chlorophyll a to maintain at a relatively low concentration; when HRT was 3d and 4d, algae grew relatively fast and the dilution of water failed to reduce the concentration of chlorophyll a; when HRT was 5d, water body was prone to eutrophication, for hydraulic retention time was longer; water distribution experiment showed that when reclaimed water accounted for 75% and 50%, nutritive salt was sufficient and conducive to the growth of algae. The concentration of chlorophyll a in water grew at the top speed and water body was deteriorated to the greatest extent; when the reclaimed water accounted for 100% and 25%, the nutritive proportion of algae was out of balance and chlorophyll a grew slower than 75% and 50%. Therefore, when the reclaimed water was used to replenish landscape water body in summer, HRT of water body should be kept within 2d and the proportion of reclaimed water should be less than 25%.(3) in autumn, the air temperature was not high and the illumination time was not long. The environment was not conducive to the propagation of algae. Therefore, the HRT could be properly extended to 10 d. And at this time, the proportion of reclaimed water would not determine the degree of the eutrophication of algae, which should be controlled within 50% to reduce the indicators of water body such as turbidity and chromaticity.(4) in winter, HRT had a small impact on the growth of algae in landscape water body. When HRT was less than 20 d, the faster HRT could better maintain chlorophyll a at a relatively low concentration and keep water body with a better surface. According to experimental data, it could be concluded that when the HRT was controlled to 20 d and the proportion of reclaimed water was controlled to 50%, the goal of saving cost and avoiding the waste of water resources could be achieved and landscape water body could be maintained at a better ornamental level.