M B Beck* and J Chen**
*Warnell School of Forest Resources
University of Georgia, Athens, Georgia 30602-2152
(email:mbbeck@arches.uga.edu; phone: (706) 542 0947; fax: (706) 542 0857)**Department of Environmental Systems Engineering
Tsinghua University, Beijing, ChinaAbstract
The purpose of an urban wastewater infrastructure, or so we have long supposed, is to produce a sparkling liquid product, from which a bothersome solid by-product must be removed and disposed of elsewhere. Our objective is to explore the potential for turning this convention, in principle, on its head. The goal is to conceive of an infrastructure whose purpose is instead to produce an ideal solids product – the "perfect fertilizer" – from which (coincidentally) a nevertheless benign liquid by-product must be siphoned off and re-used elsewhere.
There are clearly plenty of other visions one might cherish, however. We could, for example, have suggested having more of the same, more of the now somewhat denigrated "end-of-pipe, centralized" system, albeit honed to engineering perfection through the implementation of High-Performance Integrated Control (H-PIC). Or we could have suggested something radically different, a return to the natural, decentralized way of doing things, wherein the horny hand of the engineer would be removed from the associated self-organizing, self-stabilizing ecological systems. Sanitary engineering and wastewater treatment are at present enjoying a healthy, strikingly near-philosophical, debate – unusual for such lowly subjects, well down in the intellectual pecking order. Pitted in one corner is a position oriented towards the radically different and caricatured as embracing low technology, decentralization, autonomy of operation, and the self-design of natural, ecological systems (for example, Niemczynowicz, 1993; Otterpohl et al, 1997); in the other is a position of high technology and centralization, associated with the widespread application of engineered process intensification, instrumentation, control, and automation (Schütze et al, 1999; Beck, 1999).These exaggerated distinctions are important – very important – for the purposes of debate, discussion, and the cultivation of a richness of options for the future. Yet our primary goal is to cut across the dichotomy in a slightly different direction, to arrive at a vision responding to this observation: that the task of a wastewater infrastructure, beyond the maintenance of hygiene, is to keep the soil fertile (Otterpohl et al, 1999). We shall assemble just one interpretation of a vision designed to meet this task, stated thus:
Given the plethora of candidate unit process technologies, compose from these parts the whole of an entire infrastructure whose impact will be to restore – to the maximum extent possible (to some quasi-pristine, pre-city status) – the global cycles of materials circulating around the city and the spectrum of disturbances to which its surrounding aquatic environment is subject. Furthermore, achieve this composition subject to the constraint of using to the full the sunk societal investment in today's paradigm of North American and European sewerage and wastewater treatment systems.
In other words, if we took out all of today's technologies, leaving the empty concrete, steel and brick hull of our existing urban wastewater infrastructure, what would we put back into this shell – to do better next time, some several decades hence?
Any response to such an immense challenge will for the time being be highly speculative and technically defective; but our purpose is to provide as specific a platform as possible for discussion, reflection, and further contemplation. In this paper, we provide an impression of the changing terms of the debate about the future forms of urban wastewater infrastructure and then set out our vision of one such scenario, for producing the perfect fertilizer. Our vision, however, will catapult us perhaps some 75 years into the future. What, then, should be done now to ensure we have the best possible chance of reaching it, while not foreclosing on adapting instead to the other (target) visions we shall surely generate in the next 10 years? For this we shall examine the extent to which H-PIC enhances the scope for flexibility in moving along a path of adaptation from the present sunk investment in urban wastewater infrastructures, specifically those of densely populated, core, inner-city areas (as opposed to the low-density, suburban fringes).