Two-phase partitioning bioreactors: towards a new generation of high-performance biological processes for VOC and CH4 abatement.

The intense research and development conducted over the past 30 years in the field of air pollution control have increased the acceptance of biotechnologies as cost-efficient technological solutions to mitigate atmospheric pollution. Despite the low operating cost of biofilters and biotrickling filters, the limited mass transfer rates of certain key air contaminants from the gas phase to the microbial community and the perceived limited robustness of biotechnologies still make physical-chemical technologies the preferred methods for air pollution control. In this context, the addition of a non-aqueous phase to conventional bioreactors, in the so called two-phase partitioning bioreactors (TPPBs), can overcome the above mentioned limitations and trigger the consolidation of biotechnologies for the removal of odors, volatile organic contaminants (VOCs) or greenhouse gases. TPPBs have been successfully implemented in stirred tank, airlift, biofilter and biotrickling filter reactors for the removal of hydrophobic VOCs and CH4 at unprecedentedly high removal rates. The high affinity of the non-aqueous phase for the target gas pollutant creates a new and efficient mass transfer pathway and increases process robustness compared to conventional biotechnologies. Finally, recent studies have shown that the use of hydrophobic biomass can boost the abatement performance of TPPBs by one order of magnitude

Migration and Poverty in Mexico’s Southern States

While Mexico's southern states differ substantially in terms of their migration profile, many of the issues confronted by the three states are the same. In this paper, we focus on five questions: (a) How large are migration flows, and what can be expected in the future?; (b) To what extent does migration increase per capita income and thereby reduce poverty?; (c) What are the determinants of migration?; (d) What is the impact of remittances on poverty, inequality, and development?; and (e) What programs are implemented by the government to increase the benefits from remittances, and what can be done to reduce the cost for migrants of remitting?Mexico; Migration; Remittances; Poverty; Policies

Modeling of fungal biofilter for the abatement of hydropic VOCs

[Abstract] This work describes the growth of filamentous fungi in biofilters for the degradation of hydrophobic VOCs. The study system was n-hexane and the fungus Fusarium solani B1. The system is mathematically described and the main physical, kinetic data and morphological parameters of aerial hyphae were obtained by independent experiments for model validation. The model proposed in this study describes the increase in the transport area by the growth of the filamentous cylindrical mycelia and its relation with n-hexane elimination in quasi -stationary state in a biofilter. The model describing fungal growth includes Monod-Haldane kinetic and hyphal elongation and ramification. The reduction in the permeability caused by mycelial growth was further related to pressure drop by Darcy’s equation. The model was verified with biofiltration experiments using perlite as support and gaseous n-hexane as substrate

Phenomenological model of fungal biofilters for the abatement of hydrophobic VOCs

This work describes the growth of filamentous fungi in biofilters for the degradation of hydrophobic VOCs. The study system was n-hexane and Fusarium solani B1. The system is mathematically described and the main physical, kinetic data and morphological parameters were obtained by independent experiments and validated with data from laboratory experiments. The model describes the increase in the transport area by the growth of the filamentous cylindrical mycelia and its relation with n-hexane elimination in quasi-stationary state in a biofilter. The model describing fungal growth includes Monod-Haldane kinetic and hyphal elongation and ramification. A specific surface area of transport (SSAT) of 1.91 × 105 m2 m-3 and a maximum elimination capacity (EC) of 248 g m-3 h-1 were obtained by the mathematical model simulation, with a 10% of error with respect to the experimental EC

Influence of growth and high mould concentration on the pressure drop in solid state fermentations

#Aspergillus niger$ was grown on Amberlite IRA-900 imbibed with a solution containing high concentrations of sucrose (Si = 100, 200, 300 and 400 g/litre) in static aerated fermentors. Growth was followed in dry biomass, biomass protein, CO2 production and pressure drop (DP). The DP allowed the monitoring of germination, vegetative growth, militation and the onset of sporulation for the four concentrations of sucrose studied. Concentrations up to 103 mg dry biomass/g dry support were obtained with Si = 400 g/litre and these reduced the relative intrinsic permeability to 0.0125. Under this condition the mould occupies 34 % of the free space. DP increase was related to CO2 production. (Résumé d'auteur

Do indigenous peoples benefit from poverty programs? Evidence from Mexico´s 2000 census

Indigenous peoples are among the poorest in Latin America, and it is often argued that social policies do not reach them. At the same time, several countries have implemented in recent years new programs for poverty reduction that should have benefited the indigenous. In this paper, we use data from Mexico's 2000 census to test whether indigenous peoples living in the southern states of Chiapas, Guerrero and Oaxaca benefit from three large government programs: PROGRESA, FISM, and PROCAMPO.

Phase partition of gaseous hexane and surface hydrophobicity of Fusarium solani when grown in liquid and solid media with hexanol and hexane

The filamentous fungus, Fusarium solani, was grown in liquid and solid culture with glucose, glycerol, 1-hexanol and n-hexane. The partition coefficient with gaseous hexane (HPC) in the biomass was lower when grown in liquid medium with 1-hexanol (0.4) than with glycerol (0.8) or glucose (1) The HPC for surface growth were 0.2 for 1-hexanol, 0.5 for glycerol, 0.6 for glucose, and 0.2 for F. solani biomass obtained from a biofilter fed with gaseous n-hexane. These values show a 200-fold increase in n-hexane solubility when compared to water (HPC = 42). Lower HPC values can be partially explained by increased lipid accumulation with 1-hexanol, 10.5% (w/w) than with glycerol (8.5% w/w) or glucose (7.1% w/w). The diameter of the hyphae diminished from 3 μm to 2 μm when F. solani was grown on solid media with gaseous n-hexane thereby doubling the surface area for gaseous substrate exchange. The surface hydrophobicity of the mycelia increased consistently with more hydrophobic substrates and the contact angle of a drop of water on the mycelial mat was 113° when grown on n-hexane as compared to 75° with glucose. The fungus thus adapts to hydrophobic conditions and these changes may explain the higher uptake of gaseous hydrophobic substances by fungi in biofilters