Comparison of risks, costs and environmental impacts associated with wastewater collection systems

Local authorities are continually faced with the challenges of providing the most cost effective solution for reticulated sewerage infrastructure. The days of automatically providing a gravity sewer system and limiting the decision making process to the depth of sewers and the number of pump stations are long gone. Local authorities can now choose from gravity, vacuum and pr essure systems or a combination of these systems.

The challenge for Local authorities is to bring the options for sewerage reticulation into line with the reliability and longevity of gravity sewer systems, which we are all well familiar. It has long been acknowledged that inflow and infiltration is the most significant issue affecting gravity systems. Both vacuum and pressure systems eliminate most of these extraneous flows, benefiting both the wastewater treatment plant and ultimately the disposal system.

This paper will outline the installation costs and maintenance costs as well as the social implications (health, inconvenience) and importantly the environmental drivers (infiltration, exfiltration, overflows) that should be considered in any decision. The installation of any reticulated sewerage system will have a social impact of some sort, be it disruption during construction or the stimulation of growth in the community. Environmental impacts are usually separated into two groups being, impacts during construction and impacts during operation.

This paper shall discuss these issues in more detail and provide local authorities with a comprehensive overview of current issues associated with wastewater collection systems in the 21st Century.