Evaluation of sewer infiltration/inflow using COD mass flux method: case study in Prague

Area of Science:

• Environmental Engineering
• Wastewater Management
• Hydrology

Background:

• Combined sewer systems are susceptible to infiltrating waters, affecting operation and maintenance.
• Accurate assessment of infiltrating water volume is crucial for effective sewer management.

Purpose of the Study:

• To develop and validate a methodology for quantifying parasitic water flow in combined sewer systems.
• To assess the impact of infiltrating waters on sewer system components and structural integrity.

Main Methods:

• Utilized diurnal variation of chemical oxygen demand (COD) load.
• Employed continuous water quality monitoring with in-line absorption spectrometry.
• Applied Monte Carlo simulations to a 7-year flow rate data series for statistical validation.

Main Results:

• Successfully identified components of the diurnal wastewater hydrograph, isolating parasitic water contributions.
• Provided specific data on infiltration and inflow (I/I) and structural conditions for sub-catchments.
• Demonstrated the importance of long-term data series for reliable results.

Conclusions:

• The developed methodology effectively quantifies infiltrating water in combined sewers.
• Results offer valuable insights for sewer system operation, maintenance, and reconstruction planning.
• Monitoring period length significantly influences the relevance and accuracy of obtained data.