Evaluation of Groundwater Infiltration in Sewer Networks Using Fluorescence Spectroscopy

Abstract

Diagnosing water infiltration is imperative to assess the integrity and operation performance of sewer networks, which is challenging and costly due to the complex nature of these networks. This study proposes a simple approach to evaluate the extent of groundwater infiltration via a fluorescence spectroscopy method, i.e., the identification and quantification of the fluorescent signature components of the dissolved organic matter sewage. A newly built sewer network in Shantou, Southern China, was selected for the case study, and a mass balance method based on water quality characteristic factors (total phosphorus and NH4+-N) was applied in parallel for comparison. The results showed that the mass balance method was substantially influenced by fluctuations in sewage and external water concentrations, rendering it unreliable due to the extensive data and calculations required. Conversely, three-dimensional excitation–emission matrix–parallel factor analysis enabled the identification of terrestrial humus compounds as the signatures of underground water sources. The estimation indicates that the groundwater proportion across the four surveyed inspection wells along the pipeline network ranged from 10.8 ± 2.5% to 9.6 ± 3.5%, conforming to the allowable groundwater infiltration limits set for municipal sewage pipelines (10–15%). This study presents a simple method for the in-depth analysis of groundwater infiltration in urban sewage networks, providing valuable insights into maintaining water quality and network integrity.

Characterization of sewage quality and its spatiotemporal variations in a small town in Eastern Guangdong, China

“…Due to the high groundwater table in the study area, as evidenced from the high water level in the manholes, groundwater infiltration could be a more important factor resulting in the low COD/TN ratio of the sewage. Our recent study shows that groundwater accounted for approximately 10% of the sewage flow in the study area, even in the dry season (Li L. et al, 2023). To further quantify the relative contribution of biological degradation and groundwater infiltration to the sewage strength, a further study in a relatively long sewer without branch interconnections seems necessary.…”

“…Moreover, groundwater infiltration to the sewers has not been considered in most of the reports, which might have biased the result. Our recent study has shown that groundwater accounted for approximately 10% of the sewage flow in a sewer in South China, even in the dry season (Li L. et al, 2023). As the decrease in COD and total nitrogen (TN) along the sewers could be the combined effect of biological degradation and dilution of unfiltered groundwater, reduce in the COD/TN ratio along the sewer is expected if biological degradation is the dominant process.…”