Integration of population forecasting in providing decision support system for municipal solid waste landfill siting (Case study: Qazvin province)

Rapid urban expansion along with population growth, has significantly amplified the production of municipal solid waste (MSW) in recent years. Despite the importance of burying solid waste as one of the most efficient ways in waste management cycle, its basic standards have been neglected in many parts of Iran. Recently, the Geographic Information System (GIS) has been recognized as a suitable tool in landfill site selection studies. In addition, Multi-Criteria Decision Making (MCDM) has been introduced as a well-known technique to investigate complex decision-making issues such as landfill selection, and the Analytical Hierarchy Process (AHP) is one of the well-known methods of MCDM.  In general, landfill siting based on GIS has two main screening steps including first, removing unsuitable land areas and then ranking remaining areas. Additionally, waste landfill siting mainly depends on information availability related to population characteristics. In this way, it is needed to forecast population in the future. Qazvin as a province in the central part of Iran, is facing a population growth in the recent decade. Comparing the population in 2011 and 2016, it showed an increase of about 1.17 percent of average annual growth in Qazvin's population. Therefore, with regard to the increasing population in this newly established province, it is considered critical to conduct a landfill site selection procedure. To achieve the aim, the present research intended to establish a landfill site regarding environmental factors and using integrated GIS-AHP approach which incorporated into the population forecasting in Qazvin province.

The present study was conducted in three main steps include; initial waste Landfill siting using Multi-Criteria Evaluation (MCE), determination of the required landfill area based on population forecasting up to 2046 and final locating of waste landfills using Single Objective Land Allocation (SOLA) in TerrSet software. In the first step, the initial Landfill siting was conducted by the integrated GIS-AHP approach during the process of identifying and selecting the criteria, weighting the criteria, standardizing the criteria and finally integrating the criteria with the Weighted Linear Combination (WLC) method. In the second step, the area required for waste disposal sites was estimated based on population growth rate, per capita waste generation (kg per day) and average groundwater depth. In order to forecast the population growth up to 2046, reports of Iran's Plan and Budget Organization was used.  In the third step, the final sitting of the municipal solid waste was determined with a SOLA in TerrSet software. The initial suitability map was entered into the model as the base input. Also, the estimated area from the second step. In this study, two scenarios were implemented.  In the first scenario, in order to select the appropriate locations, the condition of having the highest value of the map was applied, and in the second scenario, in addition to the mentioned condition, the need to have a 10 km buffer for each of the selected options was considered.

According to the expert's opinions and environmental standards, seven ecological and socio-economic criteria were suggested that each criterion consists of several sub-criteria. Then by implementing the AHP method on the experts’ judgment, the final weight of each criterion and sub-criterion was obtained. After preparing the GIS layers, each of the invoice layers was standardized according to the functions in the fuzzy membership tool and was classified with a range of numbers from 0 to 255. The results showed that in the study area the combination of AHP and GIS for landfill siting is significantly compatible with field observations. GIS is a very powerful tool that could provide a quick assessment of the study area to determine the appropriate location for landfill. The selection of criteria was one of the most important steps in this research. The environmental factors should be considered along with economic factors in choosing a landfill site. Therefore, the eight main criteria of distance from the road, elevation, slope, distance from residential areas, distance from surface waters, distance from protected areas, geology, hydrology and land use were used in their research. The criteria were divided into three parts; morphological, environmental and socio-economic. In this research, in addition to the mentioned criteria, various natural and human parameters such as distance from energy transmission lines, distance from industrial towns and railways, etc. were also used to double the comprehensiveness of the present study. By integrating standardized GIS layers with WLC method, the initial map indicating the distribution of suitability of different sites to waste disposal location in Qazvin province was prepared. By implementing the AHP method into each criterion and combining in GIS, the waste disposal areas in the study area were classified into four classes. According to this classification, the initial map was divided into very good, appropriate, inappropriate and very poor areas.  According to the initial suitability map, the cities of Takestan, Abik and Buin Zahra, with an area of 50.15, 14.55 and 54.48 km2, respectively, had a good condition for landfill location. The suitable places for landfill were the flat territories near the urban and had the advantage of the appropriate access path. Then, using land use allocation algorithm, the best landfill site was identified in two scenarios and three location options for each scenario. In the first scenario, the maximum map value was applied to select the location options. In the second scenario, in addition to the mentioned condition, a 10 km buffer was considered for each location option. Finally, site number one of the first and second scenarios and site number three of the second scenario were identified as priorities. Site number one was selected in the range of Buin Zahra city and near the village of Elahabad. While site number three was located 15 km away from the waste management department of Qazvin city and near the Zinabad village.

It should be noted that not only the final location of municipal solid waste landfills has not been determined in recent years, but also a comprehensive program in the field of reducing waste production and implementation of waste separation plans from the source in the studied cities has not been implemented.Formation of a future forecasting section on the organizational structure of landfill waste management systems can not only reduce environmental risks but also bring sustainability to economic and social resources.