Control Technology And Mechanism Of Diffuse Pollution At Wuhan City Zoo

With the rapid development of tourist industry, diffuse pollution in the urban tourist area has increased and has a profound effect on the water quality and ecosystem degradation of nearby streams and reservoirs. However, the control technology and mechanism of diffuse pollution in the urban tourist area has received little research attention. Therefore, a systemic research was conducted on the characteristics, control technology, control mechanism and control principle of diffuse pollution in the case study of Wuhan City Zoo, Wuhan, Hubei Province. The main results of this study are as follows:(1) In comparison with other urban areas, the primary characteristics of diffuse pollution at Wuhan City Zoo includes: 1) The diffuse pollution arose from both diffuse and small scattered point sources; 2) Although the first flush effect was weaker than that of other urban areas, it was also observed in the urban tourist area; 3) Nitrogen and phosphorus were the main pollutants in runoff and the particulate matter was the main form of pollutants; 4) Ecological engineering technology was an effective way to control the diffuse pollution.(2) Based on the above pollution characteristics, an online pond-wetlands system in the Orangutan House Catchment, and an offline filtering ditch-pond system in the Canine House Catchment, was designed to control the diffuse pollution at Wuhan City Zoo, respectively. The results showed that: 1) The online control system could store the runoff of 66.7mm rainfall completely, and the offline control system could store the runoff of 31.3mm rainfall; 2) The retention rates of TSS, COD, TN, TP for the online mode accounted for 98.2%, 97.8%, 97.9% and 98.0%, respectively and those for the offline mode accounted for 86.4%, 85.5%, 83.9% and 82.9% in 2005; 3) The online control system may be better adapted to urban zoos, suburbs and towns that have abundant available land area. On the other hand, the offline control system can save land resources and is more effective and economical for diffuse pollution control in urban areas, such as industrial and residential areas.(3) To study the control mechanism of the online system, the spatio-temporal variation and correlation of nutrients in water, soil, sediment and hydrophytes were investigated in the wetland and pond. The results indicated that: 1) ORP (oxidation and reductant potential) varied within the ranges of-120～220mv in the wetland and pond. During the range, sulfur, iron and manganese systems were the main redox process. The correlation coefficient between ORP and the other parameters were in the following order: DO＞pH＞SpCond＞Mn＞NH₄⁺-N＞Fe²⁺＞T＞TDN＞TDP; 2) Except for DO, ORP and Sulfate, the concentration of other parameters were higher on rainy days than those on dry days; 3) The adsorption of soil and substrate materials was the main approach to remove pollutants from wetland. The concentration of soil pollutants increased from 2004 to 2006 gradually; 4) Wetland sediment was not only the sink, but also the source of pollutants. The concentration of nutrients in the sediment, which were higher than those in the soil, was concentrated on the first 10cm layer; 5) During the decomposing process, the hydrophytes in the wetland not only released pollutants, but also adsorbed pollutants. The concentration of nutrients in the hydrophytes was higher in the winter than that in the summer; 6) In the winter, the removal efficiency for pollutants decreased with the increasing of hydraulic load in the wetland.(4) To study the control mechanism of the offline system, the adsorption and removal capacities of different substrate materials were also investigated. Our results were as follows: 1) According to correlation coefficient, the adsorption of soil, aluminite stone, ceramic granule, steel slag, limestone, gravel and vermiculite could be described by the equation of Freundlich suitably, and that of sand and zeolite could be described by the equation of Langmuir; 2) The equation time of different substrate materials was in the following order: zeolite, vermiculite＞sand, ceramic granule＞others. The removal efficiency of the substrate materials for NH₄⁺-N was higher than that for NO₃^--N; 3) The removal efficiency of the substrate materials for dissolved reactive phosphorus was higher than that for other phosphorus. The equation adsorption capacity of the substrate materials was in the following order: zeolite, soil, vermiculite＞steel slag, limestone, ceramic granule＞gravel, sand, aluminite stone. The order of dynamic adsorption capacity was as follows: zeolite, soil, limestone, aluminite stone＞steel slag, gravel, sand＞ceramic granule, vermiculite.(5) The control strategy of diffuse pollution in the urban tourist area should be an integrated project, which is given priority to management practice. All the control practices, which are economical, effective, ecological and landscaping, should be connected with the development target of the tourist area. The main control principles include source control, water quantity control, water quality control and total suspended solids control.