Material requirements were estimated using the prototype bill of materials for each system and vendor websites. Materials and processes for each component were identified, and in many cases, when reported masses could not be found, the mass of a component was estimated using the item's geometry, density, and characteristics of similar components. Impacts associated with electricity were calculated from each system's energy requirements and the unit environmental impacts associated with the energy source. In the case of the photovoltaic energy scenarios for the NEWgenerator and Reclaimer, electricity generation impacts during operation were assumed to be 0; however, impacts associated with solar panels, batteries, etc. are included in the construction impacts. Direct GHG emissions from excreta included CH4 and N2O released from the degradation of bodily waste, whereas biogenic CO2 emissions were considered to not contribute to climate change. By mass, methane from biogenic sources is estimated to contribute 34 times the climate change impact of non-biogenic carbon dioxide (34 kg CO2eq per kg CH4), while N2O has an impact 298 times that of carbon dioxide (298 kg CO2eq per kg N2O) . Total methane and N2O emissions were multiplied by these factors to represent all direct emissions as an equivalent mass of carbon dioxide. Overall, total environmental impacts were estimated from each of these three sources (materials, energy, and direct impacts from excreta) over each system's lifetime. To combine and normalize these impacts, it was assumed material impacts could be evenly distributed across each year of the lifetime (i.e., total impacts were divided by the lifetime to calculate an impact per year). Total impacts of each system were normalized to a per capita basis over the course of a year (i.e., kg CO2eq•capita -1 •year -1 ).