Potable water reuse applications can provide a safe and sustainable water supply where conventional freshwater resources are limited. The objectives of this study were fourfold: (i) to analyse existing potable water reuse applications regarding operational characteristics and energy demands, (ii) to determine the theoretical energy potential of wastewater and identify opportunities for energy recovery, (iii) to define design requirements for potable water reuse schemes that integrate energy recovery and (iv) to propose strategies for more energy efficient potable water reuse schemes. Existing potable water reuse schemes commonly utilize conventional wastewater treatment processes including biological nutrient removal followed by advanced water treatment processes. While meeting high product water quality, these treatment schemes are characterized by relatively high specific energy demands (1.18 kWh/m3). Given that the theoretical energy potential of municipal wastewater is approximately two times higher (2.52 kWh/m3), opportunities exist to integrate energy recovery strategies. We propose three alternative potable water reuse schemes that integrate energy recovery from carbon via methane and nitrogen via either the coupled aerobic–anoxic nitrous decomposition operation process or partial nitritation/anammox. Compared to conventional potable water reuse schemes, the energy requirements of these schemes can be reduced by 7–29% and the overall energy balance by 38–80%.
Potable water reuse through the use of treated wastewater effluents has been practiced for more than 50 years. The majority of projects worldwide are characterized as indirect potable water reuse, where an environmental buffer (groundwater aquifer or surface water reservoir) provided retention, additional attenuation, and blending prior to use as drinking water. In order to protect public health, these projects have utilized different treatment processes and combinations to establish multiple barriers against microbial and chemical contaminants. Due to the advancements in environmental analytical chemistry and the recognition of contaminants of emerging concern occurring in reclaimed water that might exhibit adverse health effects, additional advanced treatment processes (including ozone, advanced oxidation, activated carbon) were implemented. With increasing reliability of advanced water treatment processes and operational experience over several decades, the role of the environmental buffer to provide treatment and retention time has been revisited in projects that came online during the last 10 years. Recent trends are favoring direct potable water reuse applications in particular in the USA and Southern Africa that might evolve as the new paradigm for drinking water augmentation using impaired source water. However, questions remain regarding proper protection of public health, reliability and degree of treatment, appropriateness and design of monitoring strategies, maintenance requirements, and cost.
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