Abstract
The rich content of nutrients in human waste provides an outlook for turning it from pollutants to potential resources. The pilot-scale resource-oriented toilet with forward osmosis technology was demonstrated to have advantages to recover clean water, nitrogen, phosphorus, potassium, biogas, and heat from urine and feces. For the possibility of further full-scale implementation in different scenarios, six resource-oriented toilet systems and one conventional toilet system were designed in this study. The methodology of cost-benefit analysis and life cycle assessment were applied to analyze the life cycle economic feasibility and environmental sustainability of these systems. As results indicated, resource-oriented toilets with forward osmosis technology concentrating urine proved to have both economic and environmental benefit. The economic net present value results of new resource-oriented toilets were much better than conventional toilet. The energy consumption in resource-oriented toilets contributes a lot to the environmental impacts while resource recovery such as the fertilizer production and fresh water harvest in resource-oriented toilet systems offsets a lot. Taking both life cycle economic feasibility and environmental sustainability into consideration, the partial resource-oriented toilet (only recovering nutrients from urine) is the best choice, and the totally independent resource-oriented toilet could be applied to replace conventional toilets in areas without any external facilities such as sewer and water supply system etc.
Highlights
The main objective of this study is to design toilet systems for different scenarios based on the pilotscale resource-oriented toilet using forward osmosis (FO) technology, and evaluate economic feasibility and environmental sustainability of each system using the methodology of cost-benefit analysis and life cycle assessment
The results indicate that resource-oriented toilets (2 urinals and 8 closet pans for 20 years use) with forward osmosis technology concentrating urine have 20e43 Â 104 CNY improvement in economic net present value (ENPV) results
The liquid fertilizer production in resource-oriented toilet systems offset a lot of environmental impacts as it provides an alternative choice for agriculture besides commercial fertilizer production
Summary
The discharge of wastewater from the toilet containing human waste and flush water will cause the waste of nutrients and Abbreviation list: SA, Scenario A; SB1, Scenario B1; SB2, Scenario B2; SC1, Scenario C1; SC2, Scenario C2; SC3, Scenario C3; SC4, Scenario C4; FO, forward osmosis; RO, reverse osmosis; ED, electrodialysis; LCA, life cycle assessment; ENPV, net economic present value; CNY, China Yuan; USD, United States dollar; TOrCs, trace organic compounds; STPs, sewage treatment plants; N, nitrogen; NH3-N, ammonia nitrogen; TN, total nitrogen; P, phosphorus; TP, total phosphorus; CODCr, dichromate oxidizability; K, potassium; TDS, total dissolved solids; GWP, Global Warming Potential; AP, Acidification Potential; EP, Eutrophication Potential; ODP, Ozone Layer Depletion Potential; ADP elements, Abiotic Depletion Elements; ADP fossil, Abiotic Depletion Fossil; FAETP, Freshwater Aquatic Ecotoxicity; HTP, Human Toxicity Potential; MAETP, Marine Aquatic Ecotoxity; POCP, Photochem. A typical secondary sewage treatment plant consumes 0.3e0.6 kWh electricity in treating 1 m3 wastewater per day (McCarty et al, 2011). The energy consumption in conveyance is several times more than that in treatment (Englehardt et al, 2013). The massive energy consumption in collection and treatment will result in negative impacts of environment, waste of resource and cost in construction and operation (Yan et al, 2017). There is a paradox in existing sewage treatment processes, that is, the use of a large number of energy and chemicals to treat sewage, but eventually results in a huge waste of resource and a heavy burden to both environment and economy
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