Multi-perspectives' comparisons and mitigating implications for the COD and NH3-N discharges into the wastewater from the industrial sector of China

Abstract

Taking China as a case study, we analyzed the underlying driving forces of two discharges-chemical oxygen demand (COD) and ammonia nitrogen (NH3-N)-from both periodic and structural perspectives by the Logarithmic Mean Divisia Index (LMDI) method. Changes in the two discharges were decomposed into three effects: the economic output effect, the industrial structure effect and the discharge intensity effect. The discharge intensity effect could be further decomposed into the cleaner production (technologies') effect and the pollution abatement (technologies') effect. Results showed that the economic output effect was mainly responsible for the growth of the two discharges; the average annual contribution rates were 10.77% and 10.39%, respectively. Inversely, the pollution abatement (technologies') effect presented the most obvious mitigating effects (-9.71% and -9.52%, respectively). Furthermore, the clean production (technologies') effect followed it (-4.36% and -5.22%). So, we found that the discharge intensity effect played a crucial role in the reduction of the two discharges. Then, the mitigation effect of industrial structure adjustment was the weakest (-0.19% and 0.47%). However, we could still not ignore the potential impact of industrial structure optimization for reducing the absolute amount of discharges in the long run. In addition, to simultaneously reduce the COD and NH3-N discharges, the sub-sectors of "Processing of Food from Agricultural Products (I7)", "Manufacture of Foods (I8)", "Manufacture of Raw Chemical Materials and Chemical Products (I20)", "Manufacture of Non-metallic Mineral Products (I24)" and "Smelting and Pressing of Non-ferrous Metals (I26)" were suggested to be given prior consideration for the design of related mitigation policies. Finally, some particular policy implications were also recommended for reducing the two discharges.