Lifecycle sustainability assessment for the comparison of traditional and sustainable drainage systems.

Urban drainage is a topic of increasing interest due to its key role for managing water-related disasters, which are being exacerbated by the effects of Climate Change and urbanization. Since traditional drainage systems struggle to deal with the combined action of these phenomena, Sustainable Drainage Systems (SuDS) are gaining attention as an alternative to help manage these high-water management demands. In this context, this research aimed at conducting a lifecycle sustainability assessment for comparing the economic, environmental and social performance of both drainage systems. The three dimensions of sustainable development were addressed with the support of the concepts of Net Present Value (NPV), Life Cycle Assessment (LCA) and a combination of the Leopold matrix and a semi structured interview, respectively. The results of applying this approach to the case study of the Rancho Bellavista housing development (Querétaro, Mexico) showed that SuDS outperformed traditional drainage systems in environmental and social terms; however, their high maintenance costs and shorter life expectancy hindered its economic feasibility. As such, future urban plans should focus on complementary designs whereby the strengths of both drainage alternatives are combined to boost their contributions to achieving sustainable development.

Photorespiration in an outdoor alkaline open-photobioreactor used for biogas upgrading.

The rates of oxygenic and carbon fixation photosynthetic processes of a microalgae consortium were simultaneously evaluated under steady-state performance in an bench scale alkaline open-system exposed to outdoor conditions in Mexico City. A synthetic methane-free gaseous stream (SMGS) similar to biogas was used as inorganic carbon source and model of biogas upgrading. The microalgae CO2 fixation rates were calculated through a novel methodology based on an inorganic carbon mass balance under continuous scrubbing of a SMGS similar to biogas, where the influence of pH and temperature time-depended oscillations were successfully incorporated into the mass balances. The oxygenic activity and carbon fixation occurred at different non-stoichiometric rates during the diurnal phase, in average carbon fixation predominated over oxygen production (photosynthesis quotient PQ≈ 0.5 mol O2 mol-1 CO2) indicating photorespiration occurrence mainly under dissolved oxygen concentrations higher than 10 mg L-1. The oxygen and inorganic carbon mass balances demonstrated that photorespiration and endogenous respiration were responsible for losing up to 66% and 7% respectively of the biomass grew at diurnal periods under optimal conditions. In favoring photorespiration conditions, the microalgae biomass productivity (CO2 effectively captured) can be severely decreased. A kinetic mathematical model as a function of temperature and irradiance of the oxygenic photosynthetic activity indicated the optimal operation zone for this outdoor alkaline open-photobioreactor, where irradiance was found being the most influential parameter.