Traditional wastewater management uses end-of-pipe approaches to remove pollutants in wastewater before discharge. Although effective in human health protection for decades, this approach of removal and disposal requires a high investment of energy and materials and overlooks the values of the key nutrients in wastewater such as phosphorus (P). Phosphorus in wastewater comes from the human metabolites of food, resulted from crop uptakes of fertilizer that ultimately derived from phosphate rock (PR). PR, however, could be depleted in this century, which would lead to a global food crisis. To address the question whether nutrient recovery is indeed a more efficient strategy from a system perspective and provides more benefits to society, this research compares fertilizer production from struvite to the traditional commercial fertilizers (e.g., diammonium phosphate, DAP). Emergy defined as the available energy required directly and indirectly through all transformations to make a product, process, or service is the tool used for system analysis in this study. Emergy accounting provides system analysis of total resource use and whole system efficiency. The results show that struvite production uses one order of magnitude less emergy than DAP production to produce one unit of fertilizer, indicating that struvite production is a more efficient process. This research sheds light on alternative nutrient management through nutrient recovery, which may achieve economic and environmental benefits and overall higher system efficiency.

Urban water systems are an example of complex, dynamic human–environment coupled systems which exhibit emergent behaviors that transcend individual scientific disciplines. While previous siloed approaches to water services (i.e., water resources, drinking water, wastewater, and stormwater) have led to great improvements in public health protection, sustainable solutions for a growing global population facing increased resource constraints demand a paradigm shift based on holistic management to maximize the use and recovery of water, energy, nutrients, and materials. The objective of this review paper is to highlight the issues in traditional water systems including water demand and use, centralized configuration, sewer collection systems, characteristics of mixed wastewater, and to explore alternative solutions such as decentralized water systems, fit for purpose and water reuse, natural/green infrastructure, vacuum sewer collection systems, and nutrient/energy recovery. This review also emphasizes a system thinking approach for evaluating alternatives that should include sustainability indicators and metrics such as emergy to assess global system efficiency. An example paradigm shift design for urban water system is presented, not as the recommended solution for all environments, but to emphasize the framework of system-level analysis and the need to visualize water services as an organic whole. When water systems are designed to maximize the resources and optimum efficiency, they are more prevailing and sustainable than siloed management because a system is more than the sum of its parts.

To limit effluent impacts on eutrophication in receiving waterbodies, a small community water resource recovery facility (WRRF) upgraded its conventional activated sludge treatment process for biological nutrient removal, and considered enhanced primary settling and anaerobic digestion (AD) with co-digestion of high strength organic waste (HSOW). The community initiated the resource recovery hub concept with the intention of converting an energy-consuming wastewater treatment plant into a facility that generates energy and nutrients and reuses water. We applied life cycle assessment and life cycle cost assessment to evaluate the net impact of the potential conversion. The upgraded WRRF reduced eutrophication impacts by 40% compared to the legacy system. Other environmental impacts such as global climate change potential (GCCP) and cumulative energy demand (CED) were strongly affected by AD and composting assumptions. The scenario analysis showed that HSOW co-digestion with energy recovery can lead to reductions in GCCP and CED of 7% and 108%, respectively, for the upgraded WRRF (high feedstock-base AD performance scenarios) relative to the legacy system. The cost analysis showed that using the full digester capacity and achieving high digester performance can reduce the life cycle cost of WRRF upgrades by 15% over a 30-year period.