A research agenda for the future of urban water management: exploring the potential of non-grid, small-grid, and hybrid solutions. Environmental Science and Technology.

Integrating microalgae systems (MAS) at municipal wastewater treatment plants (WWTPs) to produce of bioenergy offers many potential synergies. Improved energy balances provide a strong incentive for WWTPs to integrate MAS, but it is crucial that WWTPs maintain their barrier function to protect water resources. We perform a prospective analysis of energy and emission balances of a WWTP with integrated MAS, based on a substance flow analysis of the elements carbon (C), nitrogen (N), and phosphorus (P). These elements are the main ingredients of wastewater, and the key nutrients for algae growth. We propose a process design which relies solely on resources from wastewater with no external input of water, fertilizer or CO(2). The whole process chain, from cultivation to production of bioelectricity, takes place at the WWTP. Our results show that MAS can considerably improve energy balances of WWTPs without any external resource input. With optimistic assumptions, they can turn WWTPs into net energy producers. While intensive C recycling in MAS considerably improves the energy balance, we show that it also impacts on effluent quality. We discuss the importance of nonharvested biomass for effluent quality and highlight harvesting efficiency as key factor for energy and emission balances of MAS at WWTP.

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The conventional urban water infrastructure concept, as it is implemented in industrialised countries as well as in urban areas in developing countries face increasing problems not only caused by investments required, but also by major problems with respect to retrofitting, upgrading and inflexibility with respect to future developments. Identifying alternative approaches to provide urban water services and finding ways to make a transition from the technological trajectory of the conventional urban water infrastructure system to more sustainable ones is of interest for both the developing and the developed countries. The paper describes essential aspects associated with innovation processes in urban water infrastructure systems and presents an agent-based model to simulate these innovation processes. Additionally, first simulation results are presented.

The paper deals with the problem of finding an optimal, closed-loop control strategy for water distribution among crops grown in an irrigation system. The proposed approach yields a strategy that allows the utilization of prior "soft" information. The control strategy is then optimized using a mixed simulation-optimization method. The results which are illustrated by a Saudi Arabian case study show that it is possible to improve the crops' annual yields, both in terms of their expected value as well as in terms of their temporal distribution over the planning horizon.