Sewer-mining: A water reuse option supporting circular economy, public service provision and entrepreneurship

Water scarcity, either due to increased urbanisation or climatic variability, has motivated societies to reduce pressure on water resources mainly by reducing water demand. However, this practice alone is not sufficient to both protect resources and guarantee the quality of life water services underpin especially within a context of increased urbanisation. As such, the idea of water reuse has been gaining momentum for some time in the water sector and has recently found a more general context within the emerging concept of the Circular Economy. As a result of this growing trend, water recycling schemes at various scales have been applied worldwide. The most common scale of water reuse is reusing the effluent of a wastewater treatment plant for irrigation or industrial uses (e.g. cooling towers, or rinsing). This is favoured by economies of scale, but to be economically viable it requires that the recycled-water user is close enough to the treatment plant (and at a more or less similar or lower elevation), otherwise capital and operational costs for transmission getratherhigh. Another downside with this scale of (centralised) reuse is that this scheme does not break the monopoly of water supply, since it is again the water company that runs the treatment unit and provides the effluent for reuse and as such offers reduced benefits in terms of job creation, innovation drive and entrepreneurship. On the other side of the scale spectrum, at the level of the household, reuse options include mostly the reuse of grey water for non-potable uses (such as toilet flushing and garden irrigation). Although promising and with significant potential for demand reduction, this scale of reuse is not necessarily cost effective, with all costs borne by the end user, and usually relies on additional motivation, such as drought conditions or environmental attitudes to be implemented. This study argues for an intermediate scale of water reuse, termed sewer-mining, which is a water recycling scheme at the neighbourhood scale. We suggest it provides a feasible alternative reuse option when the geography of the wastewater treatment plant is problematic, it relies on mature treatment technologies and presents an excellent opportunity for Small Medium Enterprises (SME) to be involved in the water supply market, thus securing both environmental, social and economic benefits (including but not restricted to water for ecosystem services). To support this argument, we report on a pilot sewer mining application. The pilot, integrates to important subsystems: a packaged treatment unit and an Information and Communications Technology (ICT) infrastructure that would allow an operator to manage remotely several sewer mining units thus rendering the provided service economically viable even for SMEs. The paper reports on the pilot’s overall performance and critically evaluates the potential of the sewer mining idea to become a significant piece of the circular economy puzzle for water.