Biogas production in a tropical landfill: Long-term monitoring results and analysis of variables of influence.

The use of landfill gas for power production is a very attractive option in tropical sanitary landfills mainly in developing countries, where the waste composition, water content, and the climate conditions are favorable to a fast depletion of waste organic matter and a robust short term biogas production response. In this paper, the results of long-term monitoring and methane extraction activities in a tropical landfill are presented, and the obtained results are analyzed taking into account the structure of the prokaryotic communities and the fugitive emissions through the temporary covers. It is shown that waste depletion by aerobic processes and fugitive emissions are probable related to the drop in the efficiency of the extraction system verified in the field and that the performance of the temporary covers is of paramount importance when implementing good practices of waste management in sanitary landfills. The fugitive emissions through temporary covers was estimated at about 12% of the methane production in the field, and the distance from drains and sampling depth were confirmed as having an influence on the environmental conditions for waste depletion and on the relative abundance of the bacterial communities.

Analysis of column reactor results with organic decay by native organic microbiota and varying permeability.

Field bio-remediation techniques (FBRT) can be a low cost method to avoid the removal of top layers of soil which are rich in organic matter and bio diversity. The use of native microorganisms in FBRT is preferable because non-indigenous species can transfer their genetic material to the environment with negative impacts on the local ecological equilibrium. Petroleum Produced Water (PPW) is an important pollutant source in onshore production areas. However, due to high sodium concentrations in PPW and the occurrence of organic matter in dissolved and dispersed forms, obtaining pollutant transport parameters may be a difficult task. Results of column tests performed using a natural soil permeated by PPW are presented. All the samples presented a permeability decrease over time and the total hydrocarbon petroleum (TPH) breakthrough curves presented evidence of biological decay. Soil samples underwent biological characterization after tests (Metagenomic analyses and cultural media tests). Curves were modelled in an incremental way using a non-constant decay rate to better simulate the growing process of the microorganisms and consider the occurrence of varying velocity/permeability. Biological characterization results indicate the native organisms that are potentially more able to degrade PPW, including four bacteria (Bacillus and Lysinibacillus genus) and two fungi species (Malassezia and Talaromyces genus) that have not previously been mentioned in the consulted literature. The obtained results contribute to the development of more sustainable FBRTs focusing on native microorganisms, already adapted to the local environmental conditions.

Lead concentrations in whole blood, serum, saliva and house dust in samples collected at two time points (12 months apart) in Santo Amaro, BA, Brazil.

UNLABELLED: Whole Blood Lead Level (BLL) is the main marker used to verify lead contamination. The present study explores how BLL is associated with lead concentrations in serum, saliva and house dust. Samples were collected twice from Santo Amaro, BA, Brazil, a region that was contaminated by a lead smelter in the past; a time interval of 12 months was allowed between the two collections. It is noteworthy that the following measures have recently been taken to diminish exposure of the population to lead: streets have been paved with asphalt, and educational campaigns have been launched to reduce exposure to contaminated dust. RESULTS: Compared with the first time point, all the samples collected at the second time point contained lower lead concentration (p<0.05), which suggested that the adopted measures effectively reduced exposure of the population to lead present in contaminated soil and dust. Statistically significant correlations only existed between lead in blood collected in the first year and lead in blood collected in the second year (Spearman's r=0.55; p<0.0001; n=62), and lead in house dust collected in the first year and lead in house dust collected in the second year (Spearman's r=0.5; p<0.0001; n=59). CONCLUSIONS: Results support the validity of lead determination in blood and in house dust to assess lead exposure over time. However, lead in blood and lead in dust did not correlate with lead in serum or lead in saliva.

Avaliação da exposição ao Pb e Cd em crianças de 0 a 17 anos por consumo de alimentos vegetais cultivados em solos contaminados no município de Santo Amaro (BA) / Evaluation of Pb and Cd exposure in children 0 to 17 years of age by consumption of vegetable food cultivated in soils contaminated in Santo Amaro (BA)

O objetivo do presente trabalho foi estimar as doses de exposição aos contaminantes chumbo (Pb) e cádmio (Cd) em crianças de 0 a 17 anos de idade via consumo de alimentos vegetais cultivados em quintais contaminados, localizados no entorno de uma metalúrgica desativada, no município de Santo Amaro, Estado da Bahia. Para a estimativa das doses foi utilizada a metodologia de avaliação de riscos sobre a saúde humana, especificamente a etapa de análise da exposição, determinando as concentrações dos metais e variáveis sociodemográficas das crianças. As doses de exposição estimadas para ambos os contaminantes superaram os valores recomendados pela Organização Mundial da Saúde (OMS), atingindo valores máximos de exposição de 166,9 μg.kg−1 dia−1 e 2,95 μg.kg−1 dia−1 para o Pb e o Cd, respectivamente, por consumo de frutas. Os resultados comprovam que o consumo de alimentos vegetais cultivados em quintais pela população residente próxima à antiga fábrica é uma importante rota de exposição atual aos metais, representando um risco para a saúde da população.

This paper aims to estimate the exposure of children between 0 to 17 years old to lead (Pb) and cadmium (Cd) via ingestion of vegetables cultivated in contaminated backyards located in the surroundings of a deactivated lead metallurgy in Santo Amaro, Bahia, Brazil. For the estimation of the exposure doses, the risk assessment on human health methodology, exposure analysis, was used, determining the concentrations of metals and socio-demographic variables of children. The estimated doses for both contaminants exceeded the values recommended by the World Health Organization (WHO). Maximum obtained values were 166.9 μg.kg−1 day−1 and 2.95 μg.kg−1 day−1 for Cd and Pb, respectively, due to fruits consumption. The results show that the consumption of vegetables cultivated in the backyards by the population living near the deactivated metallurgical plant plays an important role in the exposition of the population to metals.

An attempt to perform water balance in a Brazilian municipal solid waste landfill.

This paper presents an attempt to model the water balance in the metropolitan center landfill (MCL) in Salvador, Brazil. Aspects such as the municipal solid waste (MSW) initial water content, mass loss due to decomposition, MSW liquid expelling due to compression and those related to weather conditions, such as the amount of rainfall and evaporation are considered. Superficial flow and infiltration were modeled considering the waste and the hydraulic characteristics (permeability and soil-water retention curves) of the cover layer and simplified uni-dimensional empirical models. In order to validate the modeling procedure, data from one cell at the landfill were used. Monthly waste entry, volume of collected leachate and leachate level inside the cell were monitored. Water balance equations and the compressibility of the MSW were used to calculate the amount of leachate stored in the cell and the corresponding leachate level. Measured and calculated values of the leachate level inside the cell were similar and the model was able to capture the main trends of the water balance behavior during the cell operational period.

A laboratory study on the MSW mechanical behavior in triaxial apparatus.

Shear strength characterization of MSW materials is a mandatory task when performing analyses related to landfill design and landfill geometry improvements. Despite the considerable amount of research focusing on MSW mechanical behavior there remain certain aspects which are not completely understood and deserve attention in particular the case of the undrained behavior of MSW. This paper presents the results of a comprehensive laboratory testing program using a large-scale triaxial apparatus at the Federal University of Bahia, Salvador, Brazil. The effect of factors such as confining pressure, unit weight, fiber content, rate of loading and over-consolidation on the MSW mechanical response were investigated. Tested samples presented typical MSW shear/strain curves (concave upward) in all the tests, despite the pore water pressure reaching levels almost equal to the confining pressure. The obtained results show that increasing confining stress, unit weight, loading rate, fiber content and over-consolidation lead to an increase in the MSW shear strength. The importance of the fibrous components in the waste behavior is highlighted and graphs showing the variation of the MSW shear strength with fiber content in different drainage conditions are shown. The authors believe these results could be of interest to many companies, especially considering the new trend of plastic material recycling (prior landfilling) for energy recovery purposes.

Evaluation of the geotechnical properties of MSW in two Brazilian landfills.

The characteristics of municipal solid waste (MSW) play a key role in many aspects of waste disposal facilities and landfills. Because most of a landfill is made up of MSW, the overall stability of the landfill slopes are governed by the strength parameters and physical properties of the MSW. These parameters are also important in interactions involving the waste body and the landfill structures: cover liner, leachate and gas collection systems. On the other hand, the composition of the waste, which affects the geotechnical behavior of the MSW, is dependent on a variety of factors such as climate, disposal technology, the culture and habits of the local community. It is therefore essential that the design and stability evaluations of landfills in each region be performed based on the local conditions and the geotechnical characteristic of the MSW. The Bandeirantes Landfill, BL, in São Paulo and the Metropolitan Center Landfill, MCL, in Salvador, are among the biggest landfills in Brazil. These two disposal facilities have been used for the development of research involving waste mechanics in recent years. Considerable work has been made in the laboratory and in the field to evaluate parameters such as water and organic contents, composition, permeability, and shear strength. This paper shows and analyzes the results of tests performed on these two landfills. The authors believe that these results could be a good reference for certain aspects and geotechnical properties of MSW materials in countries with similar conditions.

Municipal solid waste effective stress analysis.

The mechanical behavior of municipal solid waste (MSW) has attracted the attention of many researchers in the field of geo-environmental engineering in recent years and several aspects of waste mechanical response under loading have been elucidated. However, the mechanical response of MSW materials under undrained conditions has not been described in detail to date. The knowledge of this aspect of the MSW mechanical response is very important in cases involving MSW with high water contents, seismic ground motion and in regions where landfills are built with poor operation conditions. This paper presents the results obtained from 26 large triaxial tests performed both in drained and undrained conditions. The results were analyzed taking into account the waste particles compressibility and the deformation anisotropy of the waste samples. The waste particles compressibility was used to modify the Terzaghi effective stress equation, using the Skempton (1961) proposition. It is shown that the use of the modified effective stress equation led to much more compatible shear strength values when comparing Consolidated-Drained (CD) and Consolidated-Undrained (CU), results, explaining the high shear strength values obtained in CU triaxial tests, even when the pore pressure is almost equal to the confining stress.