Contribution of wastewater treatment engineering measures in cities to reducing NH3–N export to sea from subarea and river network perspectives using ecological network analysis: A case study of Fuzhou, China

Evaluating the weight or contribution of effective wastewater treatment measures to the generation, discharge and degradation of water pollutants is hindered by a lack of systematic methods. Ecological network analysis is applied in this study to evaluate the contribution of sponge cities (SCs), wastewater treatment plants (WWTPs) and river pollution control facilities (RPCFs) to controlling NH3–N water pollution. Modeling the characteristics of river networks at the subarea scale and river network scale is proposed. Taking Fuzhou city, which is located in the coastal river network area in southern China, as the case city, the contribution of engineering measures to pollution control of NH3–N in the period of 2010–2020 and 2025 at subarea and river network scales is calculated, predicted and analyzed. The main results show that from a system perspective, (1) WWTPs have made the largest contribution among the three engineering measures, with maximum weights of 28.9% and 2.3% in the subarea and river network scales, respectively; (2) after 11 years of construction, the contribution of WWTPs has been significantly improved, with maximum increases of 13.4% and 1.6% in the subarea and river network scales, respectively; (3) the positive impact of SCs is mainly reflected in 2017 at two scales; and (4) by 2025, the roles of SCs and WWTPs will be further enhanced in all subareas at two scales. Focusing initially on the contribution of wastewater treatment engineering measures, this study provides a method from a system perspective rather than a terminal water quality perspective. This study also supports decision-makers in scientifically formulating the construction plan of water pollution control engineering measures to ensure a better future for all in China as well as in other regions of the world. [Display omitted] •Cities located in China's coastal river network are threatened by water pollution.•Chinese government has carried out a series of wastewater treatment measures.•Engineering measures have played positive roles in the generation, discharge and degradation process of NH3–N.•The wastewater treatment plants contribute more than sponge cities and river pollution control facilities.•By 2025, the roles of sponge cities and wastewater treatment plants will be further enhanced.