Wastewater infrastructure : Challenges for the Sustainable City in the New Millennium

Aspects of the technologies that might be employed in the wastewater infrastructures of cities in the longer-term future are discussed. For this purpose a wastewater infrastructure is defined as the string of unit process technologies used to recycle and return the waterborne residuals of a city to its surrounding environment. In the cities of Europe and North America, for example, this infrastructure conventionally comprises the urban sewer network, wastewater treatment plant, and receiving water body. To provide context and direction for the discussion, the impact of the city and its wastewater infrastructure on the surrounding environment is reviewed over a time-scale of centuries. Two analogies are employed in order to illustrate this impact: the concept of a cityʹs ‘metabolism’ within the global cycling of materials; and the notion of gauging the ‘health’ of the system through something akin to measuring the ‘pulse-rate’ of an organism. Three scenarios are drawn for the possible pattern of adaptation and more radical change in the technological composition of the cityʹs future wastewater infrastructure. These may culminate in a structure altogether different from that with which we are familiar today, i.e. a decentralised, highly segregated system in which control and manipulation of the composition of any residual at its source is maximised. Further, it is argued that the issue of reliability of performance may be a critical (technological) factor in choosing a preferred form of wastewater infrastructure. We do not discuss the economic, social or cultural dimensions of our subject; we acknowledge that these are likely to be decisive considerations, the seeming technological attraction of any option notwithstanding.