Wasp_Model,_an_Effective_Method_to_Improve_Water_Quality_in_Water_Treatment_Process

WASP Model, an Effective Method to Process Introduction WASP EUTRO predicts dissolved oxygen (DO), carbonaceous biochemical oxygen demand (CBOD), phytoplankton, carbon, chlorophyll-a, ammonia, nitrate, organic nitrogen, and orthophosphate in bed and overlying waters by combining a kinetic structure adapted from the Potomac Eutrophication Model with the WASP transport structure. DYNHYD simulates variable tidal cycles, wind, and unsteady flows. It also produces an output file that supplies flows, volumes, velocities, and depths (time averaged) for the WASP modeling system. TOXI, EUTRO, and DYNHYD can be achieved because of the basic principle of the WASP model that is based on the fundamental form of conservation equations. Model Principle proper loading, transport, and transformation parameters, and via expanding infinitesimally small control volumes into larger adjoining”segments” (Zuxin Xu et al., 2006). The volume and dimensions of the control volume are given by the differential lengths (dx, dy, and dz) along each of the axes(x, y, and z) where the volume is the product of these lengths (V= dxdydz). The conservation equation can be simply illustrated as: Eq (1) means the time rate of change or accumulation per unit volume within the control volume is equal to the sum of the fluxes ( rate of transport an intrinsic property), through all control surfaces(open boundaries or faces of the control volume). The flux change per unit length along the axis is equal to the flux in minus flux out. And the change in the flux is also the rate of the change per unit length along the axis multiplied by the differential length of the control volume. Thus, a six fluxes conservation equation becomes: Eq (3) can be defined as the basic principle of WASP. When the water quality model is three dimensional, the equation can be defined as: When the water quality model is two dimensional, the equation might be where A is the cross-sectional area, m2; C is the concentration of the water quality constituent, mg/L or g/m3; Ux is the longitudinal advective velocities, m/day. These equations above-mentioned(1, 2, 3, and 4) are all limited to an ideal condition to the real world, WASP becomes another thing, just like Suzhou Creek Rehabilitation Project. This paper aims to illustrate an effective water model, WASP, by address the following objectives: (1) WASP is an effective method to help improve water conditions (2)WASP can be used to analyze a variety of water quality problems in diverse water bodies(Wu and Catherine, 1995). Suzhou Creek Rehabilitation Project Suzhou Creek Suzhou Creek is a tributary of Huangpu River in Shanghai, China(Figure 2). Beginning from Guajingkou at Taihu Lake, it passes Suzhou City of the Jiangsu Province, crossing Shanghai, and finally pouring into the Huangpu River in Waibaidu. The average width of Suzhou Creek is 70-80 m at high tide time, and its flow is controlled by tide with 6.0 m3/s in average. Suzhou Creek has more than 10 small tributaries, most of them being controlled by gates. The reasons why WASP was chosen in Suzhou Creek Rehabilitation Project are as follows(Zuxin Xu et al.,2006): The overflow of the combined waste water pumping stations was discharged into the Suzhou Creek during storm events. A large amount of waste water from city was discharged into Suzhou Creek and its tributaries directly. The sewage plume was stagnated in the city reaches owing to the tide effect of the Huangpu River A wide range of constituents(e.g. BOD, DO, NH3-N) can be simulated in WASP. The model principle in Suzhou Creek Rehabilitation Project is different from Eq.(3), because the diffusion and boundary loading problem are taken into account. Model Principle Considering vertical and lateral homogeneity, the mass balance equation can be written as In this equation, A is the cross-sectional area, m2; C is the concentration of the water kinetic transformation rate, positive is source, negative is sink, g/m3-day; and t is the The Variables and Corresponding_ Modules_ BOD, DO,and NH3-N are conventional variables. Considering the complexity of pollutants in Suzhou Creek, CODCr should be considered in this model(Xu et al., 2002). TOXI module was used to simulate the concentrations of CODCr. And the modified S-P equation was used to simulate DO, NH3-N, and BOD(BOD was divided into CBOD -carbonaceous biological oxygen demand and NBOD-nitrogenous biochemical oxygen demand). Nine monitoring stations on the main channel and 14 monitorings on the tributaries are shown in Figure 3. Results and Analysis Effects of Suzhou Creek Rehabilitation Project After years of efforts, the purpose of Suzhou Creek Rehabilitation Project were almost achieved: Water quality of Suzhou Creek met the water standard of recreation use on the annual average basis after the blackness and stink of the main channel was almost eliminated. The monitoring data of Wuning Road Bridge (Table 2) indicated that the water quality of the main channel of Suzhou Creek had become better and better for these years. The ecosystem of Suzhou Creek was gradually restored and improved(Table 3). Table 3 indicates that species number and diversity of aquatic organisms between 1999 and 2002 had increased remarkably. Feasibility of WASP Scheldt Estuary The Scheldt Estuary is located in the northwest of Belgium and the southwest of the Netherlands. The Schedldt Estuary drainage covers a very densely populated and highly industrialized region(Figure 8). The industrial compounds known as polychlorinated biphenyls (PCB) were present in the Scheldt Estuary, and its concentration levels in the Scheldt river were much higher than in any other river draining to the North Sea(Vuksanovic et al., 1996). The model principle equation can be written as:∂H∂t +D∂U∂x= 0 (6) where H is the water surface elevation, m; D is the water depth, m; U is the longitudinal velocity, m/s; t is the time, s; and x is the longitudinal distance, m. The results of this study showed that the agreement between the calculated and measured water level is quiet good. The results mean that WASP can be applied into the Scheldt Estuary successfully. Tenmile Creek contributed significant metals loadings to Tenmil Creek(Brian et al.,2005). The results of Tenmile Creek shows that some uncertainty exists in the metal partition coefficients associated with significance of precipitation reactions ,and in locations of unidentified sources and losses of metal(Brian et al.,2005). These results mean that WASP model can also be used in Tenmile Creek. Conclusion These findings suggest that the WASP model might be operationally efficient in helping to improve polluted water, and then improving living conditions in urban area. References: U.S.EPA(2008) Ecosystem Research Division. Water Quality Analysis Simulation Program (WASP). http://www.epa.gov/ATHENS/research/modeling/wasp.html. Last access date: Nov 23rd, 2008 V.Vuksanovic, F. De Smedt*, S. Van Meerbeeck. Transport of polychlorinated biphenyls (PBC) in the Scheldt Estuary simulated with the water quality model WASP (1996). 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