Carbon costing for mixed-use greywater recycling systems

Abstract

Urbanisation in the twenty-first century is accompanied by higher water demands per unit area of available space.The ability of water providers to meet these demands long term will require sustainable innovations in terms of water supply. Previous research by the authors has shown that urban mixed-use systems that share greywater (GW) between high-rise domestic dwellings (where GW production exceeds non-potable demands) and high-rise offices (where non-potable demands exceed GW production) could overcome these difficulties. This paper explores the carbon costs (embodied and operational) of such an urban arrangement by investigating the influence of membrane bioreactors (MBRs), constructed wetlands (CWs), building heights, floor plate areas and cross-connection distances.Five water supply scenarios are considered: scenario 1 (conventional mains treated offsite); scenarios 2a and 2b (individual GW treatment via CW/MBR); scenarios 3a and 3b (shared GW treatment via CW/MBR). Over a 15-year period it is shown that shared CW treatment had the lowest carbon dioxide emissions, saving up to 11% compared with conventional mains, whereas a shared MBR increased carbon dioxide emissions by up to 27%. Furthermore, most carbon dioxide savings occur when the ratio (height or floor area) of office building to residential building is 2:3.

A Benchmarking System for Domestic Water Use

“…In addition the impact of the highly influential parameters highlighted herein should to be investigated. In all cases transport and treatment of water will have an additional cost that needs to be factored in [38]. As water efficiency measures are improved the requirement for non-potable supplies within buildings (be it domestic or other) decreases and hence the payback period will become longer, although if external demands, in particular gardening (but also vehicle washing) are included payback periods will improve significantly.…”

Advancing City Sustainability via Its Systems of Flows: The Urban Metabolism of Birmingham and Its Hinterland

“…Local sourcing could be achieved by extracting groundwater (assuming this was free from industrial contamination and did not require more pumping than at present) or by harvesting rainwater and, combined with local storage in rainwater harvesting tanks, this could be used to satisfy non-potable water demands (toilet flushing, garden irrigation, etc.). Given that there is also an energy cost in treating water, as well as material cost (the chemicals used for water treatment, for example), using non-potable water for these uses makes additional energy and resource savings [110][111][112]. Furthermore, from a sustainability viewpoint, a reduction in water leakage would be beneficial for the city.…”

Using Mass Flow Analysis (MFA) to estimate the performance of scenarios for a rainwater harvesting system in Tyseley, Birmingham, UK

“…The water demands (litres per person per day) shown in Table 1 were assumed for domestic properties in Tyseley based on the work of Zadeh et al [13]. A sensitivity analysis of socio-technological influences has been investigated previously by Zadeh et al [14] and is beyond the scope of this research. The household demand for every occupant is assumed identical and therefore the only influencing factor in household demand is occupancy rate (which is assumed to vary from 1 to 5 for Tyseley); these are shown in Table 2.…”