Life-cycle perspectives for urban water systems planning

Abstract

Urban water systems around the world are going through a period of substantial change: they are evolving towards more complex water supply alternatives; are being placed under increasing pressure to achieve higher quality effluent and biosolids discharges; and are being confronted with a growing number of broader environmental management challenges. This thesis explored the use of the Life Cycle Assessment (LCA) methodology for assisting in that process of change, because of LCA's strengths in combining practicality and flexibility with 'big picture' thinking. The overarching goals were to: (1) explore LCA principles that do or do not provide useful perspectives for urban water planners, and (2) identify situations where the benefits from life-cycle thinking will be impeded by gaps in data and modelling approaches.The analytical starting point was a comparison of two different configurations for a city-scale, integrated water supply and wastewater system: a 'traditional' approach dependent on lowenergy dam-sourced mains water supply; and one with a more complex mix of contemporary water supply infrastructure intended to reduce the intensity of freshwater extraction and nutrient discharge. This change incurs a substantial increase in energy use, meaning the reduced pressure on local aquatic ecosystems may come at the expense of large increases in other life-cycle impacts. Notably however, the results generated in this thesis indicate that an exclusive focus on energy use is unlikely to be a robust approach to factoring these bigger picture environmental impacts into water industry decision making. Furthermore, it is the wastewater components of the system, rather than the water supply components, that make the largest contribution to most of the life-cycle impacts. An excessive focus on the energy or greenhouse gas (GHG) implications of growing urban water demands is, therefore, unlikely to chart the industry on an optimal course to a more environmentally benign system configuration.The estimates for direct (scope 1) greenhouse gas emissions in this thesis utilise a comprehensive set of locally relevant empirical data and expert knowledge. Based on that, direct emissions could comprise 20% or more of the overall GHG footprint for urban water infrastructure systems. The substantial spatial variability associated with all the largest direct emission sources should be an important consideration in the urban water decision making process. For assessing the option to dispose of sewage treatment plant (STP) biosolids onto farmlands, the uncertainty associated with estimating field fluxes of carbon and nitrogen is likely to be more important than the more traditional focus on biosolids transport energy.The second major case study considered in this thesis is focussed on the issue of biosolids reuse for agricultural purposes. When that practice is assessed against a broader set of impact categories than just energy use or GHG emissions, it becomes apparent that conventional life-cycle impact assessment (LCIA) mod...

Connection of neighboring wastewater treatment plants: economic and environmental assessment

“…First, by using the maximum values allowed by the legislation we are probably overestimating these impacts. Second, the limitations of current toxicity models for assessment of metals are being discussed in literature (Hospido et al, 2005;Corominas et al, 2013b;Lane, 2015) and studies have confirmed wide variability of the toxicity impacts depending on the method used (e.g. (Gandhi et al, 2011) and have reported large uncertainties (Niero et al, 2014).…”

“…(Gandhi et al, 2011) and have reported large uncertainties (Niero et al, 2014). Lane (2015) argues that LCA Terrestrial Ecotoxicity models contradict the best available Australian risk assessment, and should be excluded from analysis of biosolids disposal options. In fact, application of biosolids to agriculture is a common practice in Spain which is also promoted by the government with the objective to achieve 70% of biosolids application to agriculture in 2015 (BOE núm.…”