A bottom-up approach to model the environmental impact of the last-mile in an urban food-system

Addressing urban consumption and the inherent environmental impacts is considered indispensable for climate change mitigation. However, city-specific insights in urban food-systems are often missing. This study uses a novel bottom-up approach to evaluate the environmental impact of the last-mile of consumers within the food-system. Primary data was gathered by means of a survey (N=663) to model the last-mile, which was combined with secondary data sets, largely from regional studies. Jointly, they informed our hybrid Urban Metabolism - Life Cycle Analysis (UM-LCA) model. This model allowed us to assess the likely environmental impacts of the food-system on global warming, freshwater quality and land use, in relation to urban food consumption behaviour. In our case study, we found that last-mile movements of consumers account for as much as 5.3-5.8 percent of the food-system's total global warming potential. This is a considerable share, especially in proportion to the impact share of all other transport for distribution in the system (11.5-15.6 percent). This is a result of the numerous shopping trips, and while the majority of visits is almost equally shared by motorized and active modes, the vast majority of kilometres for the last-mile is travelled by motorized modes (68.2 percent). Furthermore, interesting differences could be found between city districts in terms of transport modes used by households resulting in different last-mile impacts, which is relevant to explore further for potential policy interventions to stimulate active modes. Food will inevitably get on the urban agenda, and therefore it is important to gain city-specific insights in relation to urban food consumption and its impacts. This study confirms that the influence of consumer choices is considerable and therefore it is worth further mapping these to develop adequate sustainability strategies. We argue that the bottom-up approach provides for both a measuring and monitoring tool, as well as an evaluation tool of urban policy and design towards more sustainable food systems.</p

Hybrid solar-seaweed biorefinery for co-production of biochemicals, biofuels, electricity, and water : Thermodynamics, life cycle assessment, and cost-benefit analysis

Combing solar energy with biomass processing facilities are emerging systems for efficient use of solar energy for electricity generation, energy storage, and production of renewable materials. In this work, we propose a novel combination of solar thermal energy systems with marine macroalgae biorefinery, which requires energy inputs for biomass cultivation and processing. In this work, we analyze a 10-ton dry weight per hour capacity pilot-scale hybrid solar seaweed biorefinery, located at the Mishor Rotem near Dimona, the current location for solar-thermal projects in Israel, where seaweed biomass supply comes from a hypothetical offshore farm located 15 km offshore. Our energy and mass balance analysis show that the overall First Law efficiency of the hybrid solar seaweed biorefinery system for the co-production of protein, hydrochar, ethanol, distilled water, and electricity is 32% and can exceed 40% with additional waste stream recycling. Our cost-benefit analysis of the proposed solar-seaweed biorefinery shows that the prices of seaweed, electricity, and protein are the key drivers of the profitability of the production process. The environmental impacts of the hybrid solar-seaweed biorefinery with intensified offshore cultivated biomass were quantified under various seaweed cultivation, transportation, and processing strategies

Polyhydroxyalkanoates and biochar from green macroalgal Ulva sp. biomass subcritical hydrolysates : Process optimization and a priori economic and greenhouse emissions break-even analysis

Although macroalgae biomass is an emerging sustainable feedstock for biorefineries, the optimum process parameters for their hydrolysis and fermentation are still not known. In the present study, the simultaneous production of polyhydroxyalkanoates (PHA) and biochar from green macroalgae Ulva sp. is examined, applying subcritical water hydrolysis and Haloferax mediterranei fermentation. First, the effects of temperature, treatment time, salinity, and solid load on the biomass and PHA productivity were optimized following the Taguchi method. Hydrolysis at 170 °C, 20 min residence time, 38 g L−1 salinity with a seaweed solid load of 5% led to the maximum PHA yield of 0.104 g g−1 Ulva and a biochar yield of 0.194 ± 1.23 g g−1 Ulva. Second, the effect of different initial culture densities on the biomass and PHA productivity was studied. An initial culture density of 50 g L−1 led to the maximum volumetric PHA productivity of 0.024 ± 0.002 g L−1 h−1 with a maximum PHA content of 49.38 ± 0.3% w/w Sensitivity analysis shows that within 90% confidence, the annual PHA production from Ulva sp. is 148.14 g PHA m−2 year−1 with an annual biochar production of 42.6 g m−2 year−1. Priori economic and greenhouse gas break-even analyses of the process were done to estimate annual revenues and allowable greenhouse gas emissions. The study illustrates that PHA production from seaweed hydrolysate using extreme halophiles coupled to biochar production could become a benign and promising step in a marine biorefinery