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. 2020 Jul 7;12(13):5459.
doi: 10.3390/su12135459.

Human Health, Economic and Environmental Assessment of Onsite Non-Potable Water Reuse Systems for a Large, Mixed-Use Urban Building

Sam Arden  1 , Ben Morelli  1 , Mary Schoen  2 , Sarah Cashman  1 , Michael Jahne  3 , Xin Cissy Ma  3 , Jay Garland  3
Affiliations

Human Health, Economic and Environmental Assessment of Onsite Non-Potable Water Reuse Systems for a Large, Mixed-Use Urban Building

Sam Arden et al. Sustainability. .

Abstract

Onsite non-potable reuse (NPR) is being increasingly considered as a viable option to address water scarcity and infrastructure challenges, particularly at the building scale. However, there are a range of possible treatment technologies, source water options, and treatment system sizes, each with its unique costs and benefits. While demonstration projects are proving that these systems can be technologically feasible and protective of public health, little guidance exists for identifying systems that balance public health protection with environmental and economic performance. This study uses quantitative microbial risk assessment, life cycle assessment and life cycle cost analysis to characterize the human health, environmental and economic aspects of onsite NPR systems. Treatment trains for both mixed wastewater and source-separated graywater were modeled using a core biological process-an aerobic membrane bioreactor (AeMBR), an anaerobic membrane bioreactor (AnMBR) or recirculating vertical flow wetland (RVFW)-and additional treatment and disinfection unit processes sufficient to meet current health-based NPR guidelines. Results show that the graywater AeMBR system designed to provide 100% of onsite non-potable demand results in the lowest impacts across most environmental and human health metrics considered but costs more than the mixed-wastewater version due to the need for a separate collection system. The use of multiple metrics also allows for identification of weaknesses in systems that lead to burden shifting. For example, although the RVFW process requires less energy than the AeMBR process, the RVFW system is more environmentally impactful and costly when considering the additional unit processes required to protect human health. Similarly, we show that incorporation of thermal recovery units to reduce hot water energy consumption can offset some environmental impacts but result in increases to others, including cumulative energy demand. Results demonstrate the need for additional data on the pathogen treatment performance of NPR systems to inform NPR health guidance.

Keywords: decentralized treatment; life cycle assessment; life cycle cost assessment; membrane bioreactor; non-potable reuse; quantitative microbial risk assessment.

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Conflict of interest statement

Conflicts of Interest: There is no conflict of interest.

Figures

Figure 1.
Figure 1.
Onsite NPR treatment system unit processes. Reported LRVs apply to both mixed-wastewater and graywater treatment systems; for UV, different doses were used among the systems. AeMBR—aerobic membrane bioreactor, AnMBR—anaerobic membrane bioreactor, B—bacteria, LRV—log reduction value, P—protozoa, RVFW—recirculating vertical flow wetland, UV—ultraviolet, V—virus, and NPR—non-potable reuse.
Figure 2.
Figure 2.
System diagram for the threeNPRwastewater treatment systems. AeMBR—aerobic membrane bioreactor, AnMBR—anaerobic membrane bioreactor, LCI—life cycle inventory, NPR—non-potable reuse, RVFW—recirculating vertical flow wetland, and WAS—waste activated sludge.
Figure 3.
Figure 3.
Comparison of the 95th percentile annual infection risk from NPR combined across pathogens for each treatment system. Bars represent risks calculated using the same dose-response functions used for the LRTs, i.e., the upper-bound dose response for Cryptosporidium and lower-bound dose response for Norovirus. The tails represent the risks calculated using the lower- and upper-bound dose responses. The AeMBR/AnMBR assumed the same treatment performance variability and thus have the same predicted risk. AeMBRs and AnMBRs share LRVs based on common use of ultrafiltration membranes.
Figure 4.
Figure 4.
Life cycle cost assessment results of NPR systems: (a) shows results across systems for Scenario 2, where treatment capacity is equal to non-potable demand. Results include operation and infrastructure costs (positive), centralized wastewater treatment costs (positive), potable cost offsets (negative) and avoided energy cost (negative). Red squares indicate net costs; (b) shows NPV across Scenarios 1 through 3, where Scenario 2 costs (Full Treatment) correspond to net costs illustrated in Figure 4a. GW = graywater, WW= wastewater.
Figure 5.
Figure 5.
Global warming potential of NPR systems: (a) shows results across systems for Scenario 2, where treatment volume is equal to non-potable demand. Results include operation and infrastructure impacts (positive) and applicable avoided product credits (negative). Red squares indicate net impacts; (b) shows net impacts across Scenarios 1 through 3, where Scenario 2 (Full Treatment) corresponds to the net impacts illustrated in Figure 5a. GW = graywater and WW= wastewater.
Figure 6.
Figure 6.
Summary of relative indicator results for seven environmental impact categories as well as cost and human health risk for (a) graywater treatment systems within the Full Treatment Scenario and (b) for the AeMBR treating either mixed wastewater or graywater. All results except risk are presented relative to the minimum result for that indicator in each figure, such that minimum impact equals zero. Risk results are presented relative to the health benchmark (10E-4 ppy), such that a risk equal to the health benchmark would be 100%. LCA metric translations: acidification—acidification potential, energy—cumulative energy demand, eutrophication—eutrophication potential, fossil fuel—fossil fuel depletion potential, global warming—global warming potential, particulates—particulate matter formation potential, and water—water use.
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References

    1. U.S. EPA Water Reuse Action Plan; EPA-820-R-20–001; Environmental Protection Agency: Washington, DC, USA, 2019.
    1. Morelli B; Cashman S; Ma X; Garland J; Bless D; Jahne M Life Cycle Assessment and Cost Analysis of Distributed Mixed Wastewater and Graywater Treatment for Water Recycling in the Context of an Urban Case Study (No. EPA/600/R-18/280); U.S. Environmental Protection Agency: Cincinnati, OH, USA, 2019.
    1. U.S. EPA Onsite Non-Potable Water Reuse Research. Available online: https://www.epa.gov/water-research/onsite-non-potable-water-reuse-resear... (accessed on 21 May 2020).
    1. NBRC. Making the Utility Case for Onsite Non-potable Water Systems; National Blue Ribbon Commission for Onsite Non-potable Water Systems, 2018; Available online: http://uswateralliance.org/sites/uswateralliance.org/files/publications/... (accessed on 3 July 2020).
    1. Kehoe P; Chang T Public Health and Utility Leaders Collaborate to Advance Onsite Reuse 2019 In Proceedings of the 34th Annual WateReuse Symposium, San Diego, CA, USA, 10 September 2019.

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