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Abstract
Over recent decades, the environmental regulations on wastewater treatment plants
(WWTP) have trended towards increasingly stringent nutrient removal requirements for
the protection of local waterways. However, such regulations typically ignore other
environmental impacts that might accompany apparent improvements to the WWTP. This
paper quantitatively defines the life cycle inventory of resources consumed and emissions
produced in ten different wastewater treatment scenarios (covering six process configurations
and nine treatment standards). The inventory results indicate that infrastructure
resources, operational energy, direct greenhouse gas (GHG) emissions and chemical
consumption generally increase with increasing nitrogen removal, especially at discharge
standards of total nitrogen <5 mgN L(-1). Similarly, infrastructure resources and
chemical consumption increase sharply with increasing phosphorus removal, but operational
energy and direct GHG emissions are largely unaffected. These trends represent a trade-off
of negative environmental impacts against improved local receiving water quality.
However, increased phosphorus removal in WWTPs also represents an opportunity for
increased resource recovery and reuse via biosolids applied to agricultural land.
This study highlights that where biosolids displace synthetic fertilisers, a negative
environmental trade-off may also occur by increasing the heavy metals discharged to
soil. Proper analysis of these positive and negative environmental trade-offs requires
further life cycle impact assessment and an inherently subjective weighting of competing
environmental costs and benefits.