Current and prospective situation of municipal solid waste final disposal in Mexico: A spatio-temporal evaluation

Mexico, similarly to other developing countries, has planned landfilling as the central technology to manage municipal solid waste (MSW). In this research, the current and future situation of final disposal of MSW in Mexico was studied, focusing on the spatial and temporal evaluation of final disposal sites (FDS), landfill gas (LFG) emissions, and potential power generation in an 80-year horizon. Geographic information systems were applied for spatial evaluation. The Mexico LFG 2.0 model was used to estimate the LFG emissions in 1782 FDS in operation, considering statal MSW characteristics and local FDS features. The transition towards a MSW management system that is less dependent on final disposal was carried out via a sensitivity analysis of the reduction of FDS in LFG emissions, power generation, and greenhouse gases (GHG) emissions. The study estimated that Mexico had an LFG generation of 2298 Mm3 in 2020, where only 4.6% of FDS were suited for power generation, up to 2534 GWh y-1. This electricity can avoid the emission of 1.45 Mt CO2 , since fossil fuels are predominant in the Mexican power grid. The sensitivity analysis showed that suppressing MSW landfilling could reduce 1636 Mt CO2 eq over the period studied compared to the business-as-usual scenario. The power generation potential of LFG has been used scarcely (165 GWh y-1). Public policies may focus on proposing economic incentives and establishing conditions for a biogas market, increasing the number of SL that use LFG for energy purposes

Towards a cleaner Mexican tortilla industry: a prospective life cycle assessment approach

International audienceOne of the most prevailing foods in the Mexican diet is the tortilla. Annually, 56.7 and 79.5 kg of tortillas are consumed in urban and rural areas. The objective of this study is to evaluate the environmental impacts of tortillas from white (WM) and yellow maize (YM) consumed in the Monterrey Metropolitan Area (MMA) in northeastern Mexico, using a prospective life cycle assessment approach (LCA). Four different sources of maize were chosen according to their production importance. The life cycle inventory included the national and foreign agricultural production, transportation, and tortilla-processing plant modules. The premise python package and the Superstructure were used to transform the ecoinvent database v3.8 to the prospective approach using the Shared Socioeconomic Pathway 2 (SSP2). It was found that the production of 1 kg of tortillas from national YM and WT has a climate change indicator of 0.731 and 0.575 kg CO2 eq, respectively. Tortillas from foreign YM have up to 31% less climate change impact than the national WM. Maize agricultural production is the activity with the highest environmental impact, representing 65% of the environmental impact of the process. The contribution of electricity in the tortillas production system could be reduced from 22% to 4% if the energetic transition in Mexico follows the SSP2. This work provides the first approach to use the prospective LCA towards a cleaner production of the tortilla industry. The next step should be to develop fertilization reduction strategies with a prospective LCA approach

Biorefinery concept comprising acid hydrolysis, dark fermentation, and anaerobic digestion for co-processing of fruit and vegetable wastes and corn stover

International audienceA new biorefinery conceptual process is proposed for biohydrogen and biomethane production from a combination of fruits and vegetables wastes (FVW) and corn stover (CS). The objective of this work was to perform the acid hydrolysis (HCl 0.5 % v/v, 120 °C, 2 h) of the FVW and CS at 3:1 dry basis ratio, and to process its main physical phases, liquid hydrolyzates (LH) and hydrolyzed solids (HS), by mesophilic dark fermentation (DF) and anaerobic digestion (AD), respectively. In DF of LH as carbon source, hydrogen was produced at maximum rate of 2.6 mL H2/(gglucose h) and maximum accumulation of 223.8 mL H2/gglucose, equivalent to 2 mol H2/molglucose, in a butyric-pathway driven fermentation. HS were digested to methane production assessing inoculum to substrate ratios in the range 2-4 ginoculum/gVS. The main results in AD were, 14 mmol CH4/gvs. The biorefinery demonstrated the feasibility to integrate the acid hydrolysis as pretreatment and subsequently use the LH for hydrogen production, and the HS for methane production, with an energy yield recovery of 9.7 kJ/gvs, being the energy contribution from anaerobic digestion 8-fold higher than of dark fermentation

PHOTO-FERMENTATIVE HYDROGEN PRODUCTION FROM ORGANIC ACIDS MIXTURES EVALUATED THROUGH PREDICTIVE MODELS FOR Rhodobacter capsulatus STRAINS

International audienceThis research aimed to evaluate growth and hydrogen production from Rhodobacter capsulatus DSM155 and B10 strains in function of volatile fatty acids (VFA) media composition, as well as to assess the light intensity effect on hydrogen production. The growth of DSM155 and B10 was verified in media containing either acetic acid, butyric acid, or sodium lactate, or a mixture of them (ABL medium), being the ABL medium that produced the maximum cell dry weight, 2.15 and 1.67 g/L for DSM155 and B10, respectively. Biohydrogen production was evaluated in media containing acetic and butyric acids (AB medium), and ABL medium. Both strains presented the highest hydrogen production using ABL medium, being the highest 239.2 mL H2 for DSM155. Finally, light intensity (10, 20, and 30 klux) effect on biohydrogen production was studied using the best strain and medium, i.e., DSM155 and ABL medium. DSM155 produced hydrogen increasingly in the order 10, 20, and 30 klx (2753.5, 2850.5, and 2946.3 mL H2/Lop, respectively); however, the light conversion efficiency into hydrogen showed an inverse trend, 7.47, 4.16, and 2.67 %. In conclusion, R. capsulatus DSM155 is advisable for biohydrogen production using ABL medium in the range 10-30 klux. Moreover, further work is recommended on DSM 155 using organic acid-rich real effluents from dark fermentation

Evaluation of feeding strategies in upflow anaerobic sludge bed reactor for hydrogenogenesis at psychrophilic temperature

International audienceThe present work evaluated the biohydrogen production from a 0.4 L upflow anaerobic sludge blanket reactor type (UASB) operating at psychrophilic temperature (21 ± 2 °C) at different feeding strategies varying hydraulic retention times (HRT) and sucrose concentration in the feeding. First strategy (24 h/31c) fed semi-continuously 31 gsucrose L−1 at 24 h HRT; second strategy (12 h/19c) fed semi-continuously 19 gsucrose L−1 at 12 h HRT; third strategy (4 h/8c) fed continuously 8.3 gsucrose L−1 at 4 h HRT.After 70 days of operation, the UASB accumulated 65.44 L H2. The average HY for the whole operation during the three strategies was 62.6 NmL H2 gsucrose−1, and average hydrogen content was 69.04%. In general terms, the best operation strategy was 12 h/19c since it presented good set of results, the best HY (70.6 NmL H2 gsucrose−1) and a comparable hydrogen production rate (2.6 L (L d)−1) to that obtained in 4 h/8c strategy (3.17 L (L d)−1). The average gross energy potential rate from the 12 h/19c strategy was 46.21 kJ (L d)−1, whereas energy heating losses were circumvented due to operation at psychrophilic regime. Indeed, psychrophilic or room temperatures should be broadly regarded as an effective alternative towards net energy gains in biohydrogen production

Batch biohydrogen production from dilute acid hydrolyzates of fruits-and-vegetables wastes and corn stover as co-substrates

International audienceFruits-and-vegetables wastes (FVW) and corn stover (CS) are two of the most recurred lignocellulosic biomasses used for biofuel production. In this work, the co-processing of FVW and CS for biohydrogen production was proposed and evaluated through a set of experimental designs. First, a 52 general factorial was applied on the dilute acid pretreatment at five levels of FVW:CS ratios (0:1, 1:3, 1:1, 3:1 and 1:0 dry mass basis) and two levels of the type of catalyst (HCl or H2SO4 at 0.5% in volumetric basis). Then, biohydrogen production using the dilute acid hydrolyzates was carried out in batch mode at 35 ºC in a 3 2 factorial design, the factors being the inoculum to substrate ratio (0.8, 1.0, and 1.2 g g-1) and the initial concentration of reducing sugars (10, 13 and 16 g L-1). The effects of the type of acid catalyst and the FVW:CS ratio were significant in terms of sugars production and yield. The best catalyst was HCl for the 3:1 FVW:CS ratio, which produced monomeric sugars concentrations of 10.0, 3.7 and 2.9 g L-1 for glucose, xylose and arabinose, respectively. The acid hydrolyzates proved to be suitable for biohydrogen production, reaching yields of 2.31 mol H2 mol-1glucose and hydrogen production rates of 8.83 mL H2 h-1. An economic prospection at lab scale demonstrated that production of hydrogen presented net revenues of 0.009 USD per kg of co-substrates (wet basis), resulting in 24 % profitability of hydrogen production over its production costs. Therefore, this co-processing is an interesting proposal with further applications on biorefinery models

The role of livestock feed fertilization as an improvement of sustainability in the dairy sector

International audienceFertilization of crops used as feed in the dairy industry represents up to 50% of greenhouse gases and 30% of its milk production costs. The environmental impacts of this activity are associated with the industrial production of fertilizers, their application to crops, and tillage practices. Proper fertilizer selection for feed production is an alternative to increase the sustainability of the dairy industry. This research evaluated the environmental and economic impact of optimizing crop fertilizer doses with a parametric linear programming model. The environmental impact and prices of fertilizers were evaluated following the life cycle assessment methodology and governmental information in a representative supply chain of the Mexican Bajio region. Optimization results show that if an N–P–K dose prioritizes using the most economical fertilizers in the region, the potential savings in fertilizer costs will reach 29.6 MUSD y-1 compared to conventional fertilization. Comparing the results with conventional fertilization strategies, reductions in greenhouse gas emissions of 22 g CO2 eq per kg of milk can be achieved, achieving up to 2.2% of Mexico's commitments in the COP21 agreement for the livestock sector. Optimal use of fertilizers from an economic and environmental perspective contributes to sustainable dairy production

Conversion of banana peel into diverse valuable metabolites using an autochthonous Rhodotorula mucilaginosa strain

Low-cost substrates are an exciting alternative for bioprocesses; however, their complexity can affect microorganism metabolism with non-desirable outcomes. This work evaluated banana peel extract (BPE) as a growth medium compared to commercial Yeast-Malt (YM) broth in the native and non-conventional yeast Rhodotorula mucilaginosa UANL-001L. The production of carotenoids, fatty acids, and exopolysaccharides (EPS) was also analyzed. Biomass concentration (3.9 g/L) and growth rate (0.069 g/h) of Rhodotorula mucilaginosa UANL-001L were obtained at 200 g/L of BPE. Yields per gram of dry biomass for carotenoids (317 µg/g) and fatty acids (0.55 g/g) showed the best results in 150 g/L of BPE, while 298 µg/g and 0.46 mg/g, respectively, were obtained in the YM broth. The highest yield of EPS was observed in 50 g/L of BPE, a two-fold increase (160.1 mg/g) compared to the YM broth (76.3 mg/g). The fatty acid characterization showed that 100 g/L of BPE produced 400% more unsaturated compounds (e.g., oleic and ricinoleic acid) than the YM broth. Altogether, these results indicate that BPE is a suitable medium for producing high-value products with potential industrial applications

Application of a sustainable location index approach to landfill site selection in Monterrey, Mexico

Landfilling is the main method to manage municipal solid waste (MSW) in Latin America due to the economic, technological and political characteristics of the region. The disposal of MSW in landfill sites may affect the quality of the environment and compromise a considerable share of the municipal budgets. The selection of suitable sites reduces the environmental and economic impact of landfills. In the present study the sustainable location index (SLI) is proposed as a methodology to assess environmentally, and economically, sanitary landfill site selection in the Metropolitan Area of Monterrey, a representative large-size city of Latin America. EVIAVE methodology was modified to include administrative and economic dimensions, which are assessed as a sustainable approach using together the SLI integrated with geospatial and multicriteria analysis tools. The assessment showed that the zones with the lowest SLI changes drastically when the importance of the economic or environmental factor varies. This result suggest that the inclusion of sustainability in landfill site selection decision-making is complex and it may requires the inclusion of local particularities such as municipal budgets, policies of MSW management and public perception about environmental deterioration

The use of broccoli agro-industrial waste in dairy cattle diet for environmental mitigation

Livestock feed production for the intensive dairy industry has a significant environmental impact. This study evaluated the potential to reduce the environmental impacts of milk production in Guanajuato, Mexico, by incorporating broccoli stems (BS), an abundant agro-industrial waste product with high nutritional value, into dairy cattle feed. The potential reduction of environmental impacts from adding BS to cattle diet formulation was estimated using a life cycle assessment and a linear programming model which considered nutritional requirements as constraints. Two scenarios for milk production were considered: an optimized conventional diet and an optimized diet including BS. The results indicated that incorporating BS in cattle feed could reduce greenhouse gas emissions by 118 g CO2 eq kg−1 fat-and-protein corrected milk (FPCM and agricultural land occupation by 0.002 m2a kg−1 FPCM but increased fossil depletion by 4 g oil eq kg−1 FPCM. BS can replace 11.1% of conventional feeds and maximize the incorporation feeds with low environmental impacts in the diet, such as alfalfa hay and maize silage. A sensitivity analysis of the economic allocation showed that the maximum price of BS to remain environmentally viable was 19.28 USD t−1 on a fresh matter basis