【正文】 n is depreciation life （year）. Assume that the total investment amount is 3000 104y。 ??6 is other costs, which can be estimated as 5% of the previous five costs. 2. Analysis of Processing cost Take sewage treatment plant with the handling capacity of 30,000 t / d of North China as an example for analysis. a. Depreciation charges ???? Depreciation is a measure to recover the investment, which means extracting a certain amount of funds as a recovery of investment at the end of the year. According to the calculation method of the annuity, without extra consideration offinancial expense, the depreciation extracted every year is(Jin 2003) ??1 = ?? (1 ? ??)/(12 ??) (15) Where Z is total investment amount( 104 yuan)。 ??4 is maintenance cost。2 is personnel cost。 106 = 1. 1 (yuan) .Calculation on the Environmental external costs, the data are shown as the fllows: Table 3 pollutantcontentsand their pollution equivalent value(2011) pollutant Contents in the reverse osmosis brine/(mg/L) Contents after usage/(mg/L) pollution equivalent value/kg 1 280 4 3 250 1 NH4 ? N 30 Tp The total water amount Qingdao used in 2010 is 943 million m3，and its wastewater emissions amount is million tons， then(2011): 8156 Then it can be estimated that the environmental costs of used desalinated water： Environmental costs of concentrated brine emission can be calculated according to table 4 : Table 4：The chemical ponents’ nature of pollutants Measuring Items Original seawater（μmol/L） Concentrated brine（ μmol/） Pollution equivalent value(kg) Mn u NH4 ? N Taking the current technology level into account, the efficiency of the desalination processing is approximately among 40% to 50%. Daily seawater requirement of BaiFa project is 260000t. It produces 100000 t freshwater every day, with the emission concentrated brine160000t every day, so the quantity of emissions concentrated brine for producing unit desalinated water Q is the environmental costs of brine emissions are: ?? = ??1 + ??2 + ??3 + ??4 = 1. 1 + + = treatment model Another idea to increase the available freshwater is recycle. After treatment of the sewage treatment plant, reuse the wastewater that meets the national emission standards. Cost Analysis： 1. The cost of processing and its ponents For municipal wastewater treatment plant, domestic wastewater is the main sewage source. And nowadays, its processing has been relatively mature, of which the core technology is biological activated sludge process. ?? = ??1 + ??2 + ??3 + ??4 + ??5 + ??6 (14) Where is the month processing cost of the sewage treatment plant。P iis the prices of resource (yuan)。 =2. yuan/m3 Abide by the principle of cost minimization, the determination of the water transfer schemes need linear programming to solve. Linear programming As the figure shows, in order to simplify the transfer process, take one big city in each zone as a centralized point to study their water mobilization. Those centralized point turn to be respectively: A:Xining(+) B: Hohhot() C: Chengdu() D: Wuhan(+) E: Guangzhou(+108) F: Beijing() G: Harbin() Figure 7: Mobilization model ①Point A、D、E are water supply points, B、C、F、G are waterpoor points. A+D+E= B+C+F= So A、D、E don’t have enough water to meet the quantity B、C、F demand. While the distance between G and water supply points is the farthest， and the costs is the largest, so it can be ignored to transfer the freshwater to G zone. ②.It can be seen that D zone must supply water to B or F（DC），in order to avoid the costs caused by route repeat, when E provides water to B、 F, it can provide water to D firstly，then to B、F. ③.Because A zone had less water supply， and the distance between A and F is father than DF, and the distance between A and C is closer than CD and CE, so the routine AF can be excluded. So the feasible water supply line includes AC、AB、DB、DF、DC、EC、ED、（ED+DB）、（ED+DF） It can be sought by measuring tape through Baidu map that ED=838 km，EC=1233km，DF=1056km，DB=1061km，AC=703km，AB=984 km，CD=992km. It has been assumed that the water supply amount from A to B、C is respectively: ??1??13，the water supply amount from D to B、 C、F is respectively:??4??4??46，from E to B、C、F is respectively??5??5??56. Transportation costs of the unit volume of water are a， the transportation costs are W. So the Decision objective: minW=(703??12+984??13 +992??43+1061??42+1056??46+123353+189 9??52+1894) (7) Constraints (8) After solving it by LINGO， the optimal solution has been obtained： Namely the water supply A to B is 108m3 . D to C is 108m3. D to F is to C all is 108 108m3. Sensitivity analysis Obtaining the minimum value of the total cost of the diversion by the lingo software: the data obtained by the sensitivity analysis are as follows: It can be drawn from the above data that the reduction of the third and fourth rows of data would make the total cost reduce more. 100 million m3 water reduction of Zone D and Zone E would make the total cost reduce to 1056 a and 1297a respectively. In addition, 100 million m3 water reduction of zone C would make the increase of 64 a in the total cost. To sum up, just considering the economic cost of water diversion, water diversion can be changed as the follows: minimizing water diversion of D、 E zone or reducing its water transfer distance。 and it has a larger workload to survey, with higher costs and longer periods （Zhao 2002）. Considering that the underground reservoir just saves the local region39。 ③ Groundwater in reservoir regions has smaller evaporation loss, easy to conserve。??? is the maximum thickness the regulation and storage layer, that is, the water level difference value between the extreme