Use of chemometrics methods and multicriteria decision-making for site selection for sustainable on-site sewage effluent disposal

Abstract

This paper presents a study undertaken to evaluate site suitability for sewage effluent renovation based on physico-chemical characteristics of the soil. The results obtained showed that as the soil becomes acidic, the phosphorus concentration in the soil reduces accordingly. The chloride ion concentration was found to be a reliable indicator for evaluating the soil capacity to remove nitrogen. A high cation exchange capacity (CEC) can enhance the renovation of sewage effluent. Soils with high quartz content had a low CEC with high organic matter content (OM) being able to compensate. Therefore, an understanding of the micro-nutrients in the soil, organic matter content and chloride ion concentration are important.

To facilitate a multi-variate approach for site selection, multicriteria decision-making methods (MCDM) methods, PROMETHEE and GAIA, were applied for analysis of a sequence of three matrices consisting of 8, 16, and 48 soil site objects respectively, and seven soil property parameters. Matrix models and the interpretation of results are discussed in detail. From these analyses, PROMETHEE II net outranking flows,￪, found that two sites were always among the top three ranks of the three matrix models, which suggested that they were the most suitable for sewage effluent renovation. The criteria CEC and OM, were particularly important for the selection of these better sites, but pH and Cl- attributes discriminated the weaker performing sites from the better ones; as well the PO43- and the NH3-N criteria were in general opposition to CEC, OM, pH and Cl- but were much less effective as discriminators. Consideration of net outranking flows suggested an approach method for the selection of other possibly suitable sites for sewage effluent renovation.