Dynamic Modelling of Hydrogen Sulphide in Auckland’s Sewer System

M. Foglia, K. Chakravarthy, S. Shipton - DHI Water and Environment, New Zealand

B. Tomicic - DHI Water and Environment, Denmark

A. Wong - Watercare Services Limited, New Zealand

Introduction
The formation of Hydrogen Sulphide (H2S) is a serious problem in sewer systems worldwide. H2S in sewers leads to a hazardous work environment for the maintenance crew, and the corrosion of sewer infrastructure can necessitate premature repair or replacement. The problem is increasing due to a combination of climate change, water saving programmes, increased urbanisation with separate sewer systems, and centralised wastewater treatment with long rising mains, resulting in higher retention times and anaerobic conditions in pressurised sections of the network. As H2S is the primary source of corrosion and odour problems, it is essential to understand the dynamics of its formation and mitigation measures.

To understand and tackle H2S in a city-wide network, a biokinetic H2S modelling approach has been developed and integrated into a fully dynamic hydraulic and advection-dispersion model. The approach is based on the state-of-the-art Wastewater Aerobic/anaerobic Transformations in Sewers (WATS) conceptual model (Hvitved-Jacobsen 2013) and is integrated with a hydraulic and advection-dispersion model.

The application of the methodology was piloted on the Army Bay sewer network, which experiences severe problems with the formation of hydrogen sulphide. The project objective was to establish if a standard calibrated hydraulic model can be used to assess the current state of the H2S formation and develop and test mitigation measures.