Cost-effectiveness of nitrogen mitigation by alternative household wastewater management technologies

Abstract

Household wastewater, especially from conventional septic systems, is a major contributor to nitrogen pollution. Alternative household wastewater management technologies provide similar sewerage management services but their life cycle costs and nitrogen flow implications remain uncertain. This paper addresses two key questions: (1) what are the total costs, nitrogen mitigation potential, and cost-effectiveness of a range of conventional and alternative municipal wastewater treatment technologies, and (2) what uncertainties influence these outcomes and how can we improve our understanding of these technologies? We estimate a household nitrogen mass balance for various household wastewater treatment systems and combine this mass balance with life cycle cost assessment to calculate the cost-effectiveness of nitrogen mitigation, which we define as nitrogen removed from the local watershed. We apply our methods to Falmouth, MA, where failing septic systems have caused heightened eutrophication in local receiving water bodies. We find that flushing and dry (composting) urine-diversion toilets paired with conventional septic systems for greywater management demonstrate the lowest life cycle cost and highest cost-effectiveness (dollars per kilogram of nitrogen removed from the watershed). Composting toilets are also attractive options in some cases, particularly best-case nitrogen mitigation. Innovative/advanced septic systems designed for high-level nitrogen removal are cost-competitive options for newly constructed homes, except at their most expensive. A centralized wastewater treatment plant is the most expensive and least cost-effective option in all cases. Using a greywater recycling system with any treatment technology increases the cost without adding any nitrogen removal benefits. Sensitivity analysis shows that these results are robust considering a range of cases and uncertainties.

Comparing the Life Cycle Energy Consumption, Global Warming and Eutrophication Potentials of Several Water and Waste Service Options

“…The human health impacts of the evaluated decentralized systems are not higher than the centralized service option [37]. Moreover, the recent cost analysis [39] suggests that the life cycle costs of the proposed alternative systems (such as composting and urine-diverting toilet options) are cheaper than a conventional centralized sewer. This is especially true in Cape Cod and the surrounding region where the cost estimates for conventional sewers are particularly high [36].…”

“…The Cape Cod community is evaluating a range of potential water system configurations in order to mitigate the coastal eutrophication, reduce energy consumption, protect public health, and sustain economic development. In order to assist in the evaluation of the technology candidates, we assessed the water system options in a series of work from the environmental, human health [37], resilience [38], and economic [39] and overall metric perspectives [27]. As an integral part of holistic assessment, this analysis followed the LCA standard principle described by the International Organization for Standardization's (ISO) 14040 series to quantify the energy consumption, GHG emissions and nutrient releases of five design options.…”

“…The nitrogen and phosphorus outputs for the septic elements came from the pilot testing datasets from the Barnstable County Department of Health and the Environment in Cape Cod. The assumptions about volatilization of nitrogen species for storage and transport stages of compost and urine were provided in our prior work [39]. The nutrient releases from digestate applied as an alternative fertilizer for local farmlands were computed based on the literature values [55,68,69].…”

Sustainable Water Systems for the City of Tomorrow—A Conceptual Framework

“…Some examples of these tools are metrics that evaluate particular dimensions such as: human health with risk assessment [31], and economic and environmental dimensions with footprints (e.g., ecological, water, and carbon), life cycle impact assessments, triple bottom line reporting, and benefit-cost analysis [142,143]. There is a plethora of publications about footprints (89,976 approximately) and life cycle assessment of water systems (21,316 approximately), but less about studies about integrated water systems such as: sustainability indicators (1434 approximately), benefit-cost analysis (531 approximately) and triple bottom (166 approximately), which indicates a gap of knowledge needed for holistic analysis of water systems (number of citations obtained from [144]).…”

Struvite Recovery From Source-Separated Urine Utilizing Fluidized Bed Technology

“…Investigation into nitrogen mitigation in domestic residences has revealed the least cost-effective method to be traditional centralized wastewater treatment with combination of urine separation and solid waste treatment being the most cost efficient (Wood et al 2015). Full-scale or even partial application of urine-separation and treatment is limited by the current infrastructure and cost associated with construction.…”