Browsing by Autor "Mercedes Iriarte"

Now showing 1 - 10 of 10

Effect of solar water disinfection (SODIS) on model microorganisms under improved and field SODIS conditions
(UWA Publishing, 2007) Simon Dejung; Iván Alexei Pérez Fuentes; Gabriela Almanza; Ruth Jarro; Lizeth Navarro; Gina Arias; Evelin Urquieta; Abraham Torrico; Wilma Fenandez; Mercedes Iriarte
SODIS is a solar water disinfection process which works by exposing untreated water to the sun in plastic bottles. Field experiments were carried out in Cochabamba, Bolivia, to obtain standard UV-A (320–405 nm) dose values required to inactivate non-spore forming bacteria, spores of Bacillus subtilis, and wild type coliphages. inactivation kinetics for non-spore forming bacteria are similar under SODIS conditions, exhibiting dose values ranging between 15 and 30 Wh m–2 for 1 log10 (90%) inactivation, 45 to 90 Wh m–2 for 3 log10 (99.9%), and 90 to 180 Wh m–2 for 6 log10 (99.9999%) inactivation. Pseudomonas aeruginosa was found to be the most resistant and Salmonella typhi, the most sensitive of the non-sporulating organisms studied here. Phages and spores serve as model organisms for viruses and parasite cysts. A UV-A dose of 85 to 210 wh m–2 accumulated during one to two days was enough to inactivate 1 log10 (90%) of these strong biological structures. The process of SODIS depended mainly on the radiation dose [Wh m–2] an organism was exposed to. An irradiation intensity exceeding some 12 Wm–2 did not increase the inactivation constant. A synergistic effect of water temperatures below 50 °C was not observed. Data plotting from various experiments on a single graph proved to be a reliable alternative method for analysis. inactivation rates determined by this method were revealed to be within the same range as individual analysis.
First insight into microbial diversity and ion concentration in the Uyuni salt flat, Bolivia
(University of Puerto Rico at Mayaguez, 2016) Cesar A. Pérez-Fernández; Mercedes Iriarte; Wilber Hinojosa-Delgadillo; Andrea Veizaga-Salinas; Raúl J. Cano; Jessica C. Rivera; Gary A. Toranzos
The most important hypersaline environment in Bolivia is the Uyuni salt flat. It is the largest salt flat in the world and, it presents certain unique chemical characteristics and composition on its surface such as a gradient of ion concentrations from south to north. The autochthonous microbial communities in these salt flats have yet to be studied in detail, and it is not clear if these communities are somehow homogeneous across in the ca. 10,000 km2 flat. The present study was done in order to describe the structure of the microbial communities and determine any possible correlations with abiotic factors. Total DNA was extracted from rock salt samples obtained at different locations, and 16S rDNA followed by Terminal Restriction Fragment Length Polymorphism (T-RFLP) analyses. Statistical analyses of the communities indicated that the highest diversity indices were found in the southern area, and the microbial communities were clustered in three groups for bacteria and in two groups for archaea. This variation could be explained by different concentrations of lithium and calcium, in addition to other abiotic variables on the surface crust. Our results indicate that even under extreme hypersaline conditions abiotic factors such as wind or geological activity may determine the composition of the resident microbiota.
Managing Microbial Risks from Indirect Wastewater Reuse for Irrigation in Urbanizing Watersheds
(American Chemical Society, 2016) Matthew E. Verbyla; Erin M. Symonds; Ram C. Kafle; Maryann R. Cairns; Mercedes Iriarte; Alvaro Mercado; Olver Coronado; Mya Breitbart; Carmen Ledo; James R. Mihelcic
Limited supply of clean water in urbanizing watersheds creates challenges for safely sustaining irrigated agriculture and global food security. On-farm interventions, such as riverbank filtration (RBF), are used in developing countries to treat irrigation water from rivers with extensive fecal contamination. Using a Bayesian approach incorporating ethnographic data and pathogen measurements, quantitative microbial risk assessment (QMRA) methods were employed to assess the impact of RBF on consumer health burdens for Giardia, Cryptosporidium, rotavirus, norovirus, and adenovirus infections resulting from indirect wastewater reuse, with lettuce irrigation in Bolivia as a model system. Concentrations of the microbial source tracking markers pepper mild mottle virus and HF183 Bacteroides were respectively 2.9 and 5.5 log10 units lower in RBF-treated water than in the river water. Consumption of lettuce irrigated with river water caused an estimated median health burden that represents 37% of Bolivia's overall diarrheal disease burden, but RBF resulted in an estimated health burden that is only 1.1% of this overall diarrheal disease burden. Variability and uncertainty associated with environmental and cultural factors affecting exposure correlated more with QMRA-predicted health outcomes than factors related to disease vulnerability. Policies governing simple on-farm interventions like RBF can be intermediary solutions for communities in urbanizing watersheds that currently lack wastewater treatment.
Managing microbial risks in informal wastewater-irrigated agriculture through irrigation water substitution
(Elsevier BV, 2022) Luis Fernando Perez-Mercado; Cecilia Lalander; Abraham Joel; Jakob Ottoson; Mercedes Iriarte; Björn Vinnerås
On-farm measures can be used in multi-barrier schemes to manage microbial risks from consumption of wastewater-irrigated vegetables, especially where informality of the practice determines minimal external support for farmers. Evidence indicates that cessation of irrigation greatly reduces microbial contamination on leafy vegetables, but at the expense of produce quality. Replacing wastewater with higher-quality irrigation water during the last days of cultivation is an alternative to cessation of irrigation that does not compromise produce quality. This study evaluated the effect of wastewater substitution under on-farm conditions on different indicators of microbial contamination of lettuce. Lettuce was cultivated in experimental plots and irrigated with three water sources: spring water, water from a wastewater-polluted river and effluent from a primary wastewater treatment plant, but with the river water replaced by spring water in half the plots about two weeks before harvest. The experiment was repeated four times in different seasons. Irrigation water samples collected during cultivation and lettuce samples collected at harvest were analysed for helminth eggs, Escherichia coli and coliphages. Variables characterizing the irrigation practices and environmental conditions were recorded. There were no significant differences in helminth egg or E. coli concentrations on lettuce (medians ranged from −0.7 to −0.1 log10 eggs g−1 and 0.6–1.4 log10 cfu g−1, respectively) between any of the treatments involving wastewater irrigation; no statistical analysis was possible for coliphages because concentrations on lettuce were mostly at or below the detection limit (94% of samples). Variables associated with temperature and soil explained helminth egg and E. coli concentrations on lettuce, while number of days of irrigation with spring water (representing wastewater substitution) was significant only for E. coli. It was concluded that the experimental conditions were suboptimal for successful implementation of wastewater substitution for on-farm microbial risk management, but key variables for successful implementation were identified.
Microbiota dispersion in the Uyuni salt flat (Bolivia) as determined by community structure analyses
(Springer Science+Business Media, 2019) Cesar A. Pérez-Fernández; Mercedes Iriarte; Jessica C. Rivera; Raymond L. Tremblay; Gary A. Toranzos
Pathogens and fecal indicators in waste stabilization pond systems with direct reuse for irrigation: Fate and transport in water, soil and crops
(Elsevier BV, 2016) Matthew E. Verbyla; Mercedes Iriarte; Alvaro Mercado; Olver Coronado; Mariela De La Cruz Almanza; James R. Mihelcic
Pathogens in crop production systems irrigated with low-quality water in Bolivia
(UWA Publishing, 2018) Luis Fernando Perez-Mercado; Cecilia Lalander; Abraham Joel; Jakob Ottoson; Mercedes Iriarte; Carla Oporto; Björn Vinnerås
In dry areas, the need for irrigation to ensure agricultural production determines the use of all available water sources. However, the water sources used for irrigation are often contaminated by untreated or minimally treated wastewater. Microbial risks from reusing wastewater for vegetable irrigation can be addressed by installing environmental barriers that pathogens must cross to reach humans in the reuse system. Knowledge of pathogen flows inside the system and pathogen removal potential is the first step towards devising a risk management strategy. This study assessed microbe prevalence in farming systems in the Bolivian highlands that use wastewater-polluted sources for irrigation of lettuce. Samples of soil, lettuce and different water sources used in the farming systems were taken during one crop season and concentrations of coliphages, Escherichia coli and helminth eggs were measured. The results showed high spread of these microorganisms throughout the whole system. There was a significant correlation between microbial quality of water and of the harvested produce for several microorganisms. The microbial prevalence in protected shallow wells was found to be significantly lower than in other water sources. These findings can help formulate feasible risk management strategies in contexts where conventional technologies for microbial removal are not possible.
Solar Drinking Water Disinfection (SODIS) to Reduce Childhood Diarrhoea in Rural Bolivia: A Cluster-Randomized, Controlled Trial
(Public Library of Science, 2009) Daniel Mäusezahl; Andri Christen; Gonzalo Durán Pacheco; Fidel Alvarez Tellez; Mercedes Iriarte; María Eugenia Hincapié Zapata; Myriam Cevallos; Jan Hattendorf; Monica Daigl Cattaneo; Benjamin F. Arnold
www.ClinicalTrials.govNCT00731497 Please see later in the article for Editors' Summary.
Solar water disinfection (SODIS) of Escherichia coli, Enterococcus spp., and MS2 coliphage: Effects of additives and alternative container materials
(Elsevier BV, 2011) Michael B. Fisher; Mercedes Iriarte; Kara L. Nelson
Taenia eggs in a stabilization pond system with poor hydraulics: concern for human cysticercosis?
(Pergamon Press, 2013) Matthew E. Verbyla; Stewart M. Oakley; Louis A. Lizima; Jie Zhang; Mercedes Iriarte; Andrés Tejada‐Martínez; James R. Mihelcic
The objective of this study is to compare the removal of Taenia eggs to the removal of Ascaris eggs in a wastewater stabilization pond system consisting of three ponds in series, where the hydraulic residence time distribution has been characterized via a tracer study supported by computational fluid dynamics modeling. Despite a theoretical hydraulic retention time of 30 days, the peak dye concentration was measured in the effluent of the first pond after only 26 hours. The smaller-sized Taenia eggs were detected in higher concentrations than Ascaris eggs in the raw wastewater. Ascaris eggs were not detected in the pond system effluent, but 45 Taenia eggs/L were detected in the system effluent. If some of these eggs were of the species Taenia solium, and if the treated wastewater were used for the irrigation of crops for human consumption, farmers and consumers could potentially be at risk for neurocysticercosis. Thus, limits for Taenia eggs in irrigation water should be established, and precautions should be taken in regions where pig taeniasis is endemic. The results of this study indicate that the theoretical hydraulic retention time (volume/flow) of a pond is not always a good surrogate for helminth egg removal.