Use of multidimensional testing to evaluate the impacts of treated wastewater discharge on river water quality - Hotelling test case

Abstract

Abstract Water bodies often suffer from the discharge of nutrient loading from agricultural and urban areas that compromises the quality of water. This study presents the application of the Hotelling test to evaluate the impacts of treated wastewater, discharged from a municipal wastewater treatment plant (WWTP), on the quality of river water. The quality of water was described by different pollution indicators, including COD, BOD5, TSS, NH4-N, NO2-N, NO3-N, TKN, TN and TP. The water samples were collected at three different locations: 500 m above the discharge point, at the wastewater discharge point and 1000 m below the wastewater discharge point. The tests of single pollution indicator showed differences between the two locations. Specifically, the results show that each single comparison controlled type I error at 0.05, while the family-wise error rate for the tests of all marginal hypotheses was controlled at 0.37. Testing for single indicators separately may not reveal true multivariate differences. In order to overcome this limitation, a modified version of T2 Hotelling test was used with robust James-Stein type estimators of covariance matrix. Major differences in the overall water quality were observed mainly for the concentration of nitrogenous compounds and found to significantly influence the water quality of the receiving river.