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Communications in Nonlinear Science and Numerical Simulation 14 (2009) 1746–1757 www.elsevier.com/locate/cnsns
GIS-based optimization for the locations of sewage treatment plants and sewage outfalls – A case study of Nansha District in Guangzhou City, China Y.W. Zhao a,*, Y. Qin a, B. Chen a, X. Zhao a, Y. Li a, X.A. Yin a, G.Q. Chen b a
State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing 100875, China b National Laboratory for Complex Systems and Turbulence, Department of Mechanics, Peking University, Beijing 100871, China Received 19 June 2007; received in revised form 20 November 2007; accepted 2 December 2007 Available online 29 February 2008
Abstract Based on GIS technology, eco-suitability evaluation method integrating economic, social and ecological factors is employed to optimize the locations of the sewage treatment plants and outfalls in this paper. The ecological indices considering eco-sensitivity areas as key elements of the integrated evaluation system are allotted to the water subsystem, riparian zone subsystem, and land subsystem. A novel integrated eco-suitability evaluation index system encompassing ten criteria and fifteen indices is established to generate the distributed eco-suitability map of the concerned areas and determine the possible locations of sewage treatment plants and sewage outfalls according to the eco-suitability levels. With the case study of Nansha District in Guangzhou City, China, 212 km2 areas of land are found to be suitable for locating the sewage treatment plants, 87 km2 areas of water suitable for sewage release, and 6 km2 area of riparian zone unsuitable for sewage outfalls. Ó 2008 Elsevier B.V. All rights reserved. PACS: 89.60.Fe Keywords: Sewage treatment plant; Outfall; Eco-suitability evaluation; GIS
1. Introduction Since the outflow from sewage treatment plants can easily pollute the water around the outfalls with its high volume and heavy pollution load [1,2], the locations of outfalls are considered to be one of the most essential elements that affect the surrounding water quality and aquatic wildlife [3,4]. Thus, it is necessary to address the issue of suitable locations for the sewage treatment plants and sewage outfalls.
*
Corresponding author. E-mail address:
[email protected] (Y.W. Zhao).
1007-5704/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cnsns.2007.12.016
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Many countries and regions have issued the design standards of sewage treatment plants. Several factors to ensure that the sewage treatment plants will not cause interference or detractions from the natural, scenic, aesthetic, scientific, or historical value of the area are covered in the US standard [5]. In Australia, water source and resident conditions are chosen as the essential elements of optimization for locations of sewage treatment plants [6]. In China, there is a recommended design standard for outdoor wastewater engineering [7], which takes resident, construction cost and water quality into account. Besides, land-use, utility service, noise control, air quality control, permit requirements are mentioned as the equally important factors [8,9]. Meanwhile, some methods, e.g., fuzzy optimization model and grey correlation model, have been put forward to solve the location of sewage treatment plant [10,11]. Numerical simulation methods, such as interior point algorithm, Nelder–Mead simplex method, duality method, and characteristicsmixed finite elements method, are also performed to find the optimal locations of the wastewater outfalls that yield the lowest cost of the system with guaranteed water quality denoted by BOD, DO and heavy metal [12–16]. Although various theories and methods for optimization of location have been proposed, some other critical factors are still ignored, such as the distribution of aquatic animals, water sources and mangroves in riparian zone and nature reserve that affect the locations of sewage treatment plants and sewage outfalls as well. A more integrative way is needed to deal with the location problem of sewage treatment plants and sewage outfalls. The land suitability evaluation is initially used in land-use planning of Staten Island New York City [16] and later generalized to the regional land classification and city planning [17–25], aiming at identifying the most appropriate spatial pattern for future land uses according to specify requirements, preferences, or predictors of some activities [26–28]. Developed from the land suitability evaluation, the eco-suitability evaluation concerns on whether the study area including water, riparian zone or land is suitable for the particular application considering environmental effects and development planning. Some indices focusing on water, riparian zone and land are chosen to work out the most suitable places for the sewage treatment plants and sewage outfalls. Taking Nansha District in Guangzhou City as a case, this study intends to optimize the possible locations of sewage treatment plants and sewage outfalls using the proposed eco-suitability method and provide theoretical support for the decision-makers. 2. Methods Generally, there are three steps for locating sewage treatment plants and sewage outfalls based on GIS technology according to the systemic and integrated principles in the following part. 2.1. Data collection The data are obtained from maps of land-use and landform obtained by the TM image in ERDAS IMAGINE 9.0, river map from the Ministry of Water Resources, distribution of wetlands, scenery spots, aquatic and terrestrial animals from the Planning of Agriculture and Forestry, water quality and flow monitoring data from local Environmental Protection Administration, public facilities from the Planning of Traffic and Public Construction, and the socio-economic situation from the statistic yearbooks compiled by the local government. 2.2. Spatial analysis of GIS All the information is translated into theme data of indices in ArcGIS 9.0, with each index corresponding to a vector theme and a table, in which each item corresponds to an element in the vector theme. The value of each item, which can be changed into standard score according to evaluation standards, represents the characteristic of the element of the specific index. Then, each single-index vector theme is converted into grid theme based on the Grid Model of ArcGIS 9.0. A matrix Vk showing the distribution of the kth index is expressed as below
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0
ak11
B ak B V k ¼ ðakij Þmn ¼ B 21 @ akm1
ak12
ak22
akm2
ak1n
1
ak2n C C C; A
ð1Þ
akmn
where akij is the standard value of eco-suitability of the kth index for the grid which is in line i in row j, m and n are the dimensions of Vk. The standard value of the index is converted from the original value according to the standard of index system. The grids outside the study area are set zero. Further, the grid themes and their weights are imported in the Weighted Overlay Model of ArcGIS 9.0 to obtain the data and map of integrated eco-suitability evaluation. The matrix V representing the integrated ecosuitability distribution of water, riparian zone and land can be formulated as below 00 k 1 1 0 1 b11 b12 b1n a11 ak12 ak1n n BB k C Bb C k k C X BB a21 a22 a2n C C B 21 b22 b2n C k ð2Þ V ¼ ðakij Þmn W ¼ BB C W k C ¼ ðbij Þmn ¼ B C; @@ A A @ A k¼1 bm1 bm2 bmn akm1 akm2 akmn where Wk is the weight of the kth index, bij is the value of integrated eco-suitability of the kth index for the grid which is in line i in row j. From the final matrix V, we can get the suitable, generally suitable, unsuitable grids according to evaluation standards. 2.3. Integrated eco-suitability evaluation Integrated eco-suitability evaluation is based on the results of the eco-suitability evaluation of single-index. The locations of sewage treatment plants and sewage outfalls are decided by indices for water, riparian zone and land subsystems. Hence, related indices that embody the evaluation objectives should be selected as shown in Table 1 [10,28]. The key point of eco-suitability evaluation is to determine the evaluation standard, which is suggested to be divided into three levels comprising suitable, generally suitable and unsuitable ones. Analytic hierarchy process (AHP), which is a decomposition of a complex problem into a hierarchy with objective at the top of the hierarchy, criterions and sub-criterions at levels and sub-levels of the hierarchy, and decision alternatives at the bottom of the hierarchy [29], is chosen to decide the weights of the eco-suitability indices.
Table 1 Eco-suitability evaluation index system Objective
Criteria
Index
Water
Eco-sensitivity area of water Self-purification capacity
Distance from habitat of rare aquatic animals Distance from habitat of economic fish Maximum permissible pollution load
Riparian zone
Water source Eco-sensitivity area of riparian zone
Distance from sources of drinking water and industrial water Distance from protected habitat
Land
Eco-sensitivity area of land
Distance from protected forests, grass and wetlands Distance from habitat of rare terrestrial animals Distance from scenery spots Distance from residents Coordination of land-use Convenience of sewage reuse Slope Landform Ground work carrying capacity Wind direction
Sanitary protection Coordinated development Sewage reuse Geography condition
Climate condition
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Data collection
Indices selection
Standard selection
Eco-suitability evaluation of single index
Water
Weight
Riparian zone
Land
Weight
Weight
AHP
GIS
Integrated eco-suitability evaluation Water
Riparian zone
Land
Locations of sewage treatment plants and sewage outfalls Fig. 1. Optimization for locations of sewage treatment plants and sewage outfalls.
The detailed optimization procedure for the locations of sewage treatment plants and sewage outfalls is shown in Fig. 1. 3. Case study 3.1. Study area The Nansha District is located in the south Guangzhou City (Fig. 2), with the annual average temperature in this district 21.9 °C and the annual average precipitation 1582 mm. There are six towns (Nansha Economic and Technological Development Town, Pearl River Town, Huangge Town, Hengli Town, Wanqingsha Town and southeast of Lingshan Town) and seven rivers (including Jiaomen River, Hongqili River, Shizi River, Humen River, Shanghengli River, Xiahengli River and Fuzhou River) within the district. Nansha District is at the central of water network of the Pearl River Estuary, where three of the biggest entrances (Humen, Jiaomen and Hongqimen) are located. There are 357 km2 land areas and 181 km2 water areas in the Nansha District, of which the key eco-sensitive habitats are forests, wetlands of mangroves and reed, spawn field and feeding field of fish. Nansha District is one of the key areas of Guangzhou City in its development planning. Logistics industry, port-centered industry, equipment industry and high-tech industry are developed in the first place while shipbuilding industry, steel industry, petrochemical industry and automobile industry in the second place. There are 69 million tons of sewage and 157 million tons of industrial wastewater generated from Nansha District in 2003. Thus, optimizing the locations of sewage treatment plants and sewage outfalls is urgent for the harmonious development of both Nansha District and Guangzhou City.
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Fig. 2. Location of Nansha District in Guangzhou City, China.
3.2. Data sources The data are collected from TM images of Nansha District and its vicinity, river map from the Ministry of Water Resources of Nansha District, distribution of wetlands, scenery spots, aquatic and terrestrial animals from the Planning of Agriculture and Forestry in 2005, water quality and flow monitoring data from the Report of Nansha Environmental Investigation in 2003, public facilities from the Planning of Traffic and Public Construction of Nansha District in 2004, development planning of Nansha District and the socio-economic situation from the statistic yearbook compiled by the government of Nansha District.
Table 2 Eco-suitability evaluation of water Criteria
Eco-sensitivity of water Capacity of self cleaning
Index
Weight
Distance from spawn field of economic fish Distance from food field of economic fish Maximum permissible pollution load of CODcr (t/a km1)
0.2 0.2 0.6
Level Suitable
Generally suitable
Unsuitable
3
2
1
>1000 m >1000 m >3000
500–1000 m 500–1000 m 3000–2000
