Esteban Manuel Villena-Martínez

This study presents a sustainable and eco-friendly methodology to enhance the physico-mechanical properties of fine-grained soils through the incorporation of biosolid ashes (BA) derived from the San Blas Wastewater Treatment Plant in Tarija. Currently, this approach provides an alternative for the reuse of more than 3,500 tons of sludge per year, a figure expected to increase significantly with the planned operation of the plant on the left bank of the Río Guadalquivir. The methodology not only improves the mechanical performance of local silt-clay soils but also promotes the valorization of residual sludge, aligning with circular economic principles and reducing the environmental impacts associated with conventional waste disposal. The biosolids were subjected to controlled incineration at 900–1000 ° C, generating ashes with a specific gravity of up to 2.52, which were then incorporated into soils at dosages ranging from 5% to 30%. Comprehensive laboratory testing included Atterberg limits, moisture content, specific gravity, modified Proctor tests for maximum and optimum dry density, consolidation, direct shear, and CBR tests on both natural soils and treated mixtures. Results demonstrated reductions in plasticity index of up to 9.5%, substantial increases in shear strength and bearing capacity, and compressibility reductions of up to 45%. CBR strength improved by more than 100% for mixtures containing 30% BA, with optimal performance observed at 10–15% BA content (average specific gravity 2.40). These findings confirm that biosolid ashes are an effective and environmentally responsible additive for geotechnical soil stabilization, offering a sustainable solution that simultaneously addresses construction requirements and promotes ecological waste management in Tarija.

The accelerated deterioration of water quality in the city of Tarija, Bolivia, has caused several water sources in the Municipality of Tarija to be discontinued due to the presence of toxic contaminants. The current water purification systems that are used in Tarija do not guarantee the elimination of heavy metals; in addition, political and social interest conflicts are a serious problem in the execution of projects and new public investment alternatives, with these being the main problems found in the sector. Reverse osmosis (RO) water purification technologies are one of the most effective contemporary alternatives for the elimination of contaminants in water, such as heavy metals; however, their application and implementation in countries with little or no experience in this type of technology require acceptance and knowledge on behalf of the interested parties. Political and social conflicts between interested parties generate scenarios that affect hydrological planning. Analysis of the actors in the urban and municipal sphere of the city of Tarija, Bolivia, provides a case study for adequate water governance and enabled us to come to a consensus for the implementation of RO. The results show 23 fundamental actors in water management in the Municipality of Tarija, with local actors being those with the greatest influence and power in decision-making. Our analysis of social networks showed an important polarization in the power of decision makers, with municipalities and legislative entities being those that decide on public investments. The interested parties showed considerable interest in the application of RO as a technology that can provide definitive, short-term solutions to the problems of water stress and the water crisis in the Municipality of Tarija and its application in small towns with a high level of social and environmental vulnerability.

Manganese is the Earth’s crust’s third most abundant transition metal. Decades of increased mining activities worldwide have inevitably led to the release of large amounts of this metal into the environment, specifically in water resources. Up to a certain level, manganese acts as an essential micronutrient to maintain health and support the growth and development of microorganisms, plants, and animals, while above a specific limit, manganese can cause toxicity in aquatic and terrestrial ecosystems. There are conventional ways to remove manganese from water, such as chemical precipitation, sorption, and biological methods. However, other treatments have yet to be studied much, such as reverse osmosis (RO), which has demonstrated its effectiveness in the removal of heavy metals and could be a suitable alternative for manganese removal if its energy consumption is reduced. This research presents mathematical and statistical modeling of the behavior of a system in laboratory-scale RO. The principal finding was that it is possible to remove Mn using the RO operated with low pressures without decreasing the sustainable removal efficiency. Reducing the operating costs of RO opens the possibility of implementing RO in different contexts where there are problems with water contamination and economic limitations.

Like other Latin American countries, Bolivia is in the race towards development, which has caused many economic activities to be carried out without due consideration for the care of the environment. At this point, it is essential to carry out environmental inventories to preserve the quality of ecosystems and natural resources, such as water. As water is vital, it needs to be adequately monitored and managed to prevent its degradation. This research presents the results of monitoring the main sources of water supply in two continuously growing departments of Bolivia, La Paz, and Tarija. The main objective of this study was to evaluate the suitability of the water to which the population has access, with particular attention to heavy metals with concentrations that exceed the permitted limits. The metals found were arsenic, chromium, mercury, manganese, iron, zinc, and tin in the Milluni area, and lead, iron, and manganese in the Guadalquivir area. Exposing the presence of metals in water sources implies immediate attention by decision-makers to take action to reduce the risk to public health. In addition, this study exposes a Bolivian reality that could encourage other countries in similar contexts to conduct similar studies on their water sources.

An investigation of primary water sources in two Bolivian basins identified the presence of heavy metals toxic to health that exceeded the permissible limits for drinking water. Lead deposited in the San Jacinto and Huacata–Tarija reservoirs within the Guadalquivir basin and arsenic in the Milluni–La Paz basin were identified. The work studies reverse osmosis (RO) to remove Pb and As. The main contribution of this research is the development and construction of a mathematical model based on the Spiegler–Kedem concentration polarization model using different concentrations of Pb and As. The model makes it possible to design high conversion facilities (>80%) and optimize the process from the point of view of energy efficiency in future works. The model was developed to also include an Arrhenius temperature adjustment factor that allows for an accurate prediction of the process performance. The experimentation was carried out in two RO pilot plants using polyamide membranes. The model fits correctly with a maximum relative error between the experimental and theoretical flows of 5.4% and 4.4%. Among the benefits of the study, it guarantees the rejection of metals greater than 99%, even at low pressures.

An effective alternative for water purification is reverse osmosis (RO). Laboratory-scale RO modeling is widely applied worldwide, and allows the evaluation of the behavior of the system to find the most convenient operating variables to be applied in future industrial scale-ups. Statistical models provide a wide range of information that allows a statistical prediction of the operation of the plant, and allows us to obtain efficiency indices in its development; these are useful in the planning, operation and monitoring process in RO plants. The mathematical models describe the physical behavior of the membrane and allow the identification of optimal operating conditions, taking into account economic aspects, guaranteeing a greater implementation of RO technology in developing countries which have problems with water contaminated with toxic heavy metals. The present work shows a review of different statistical and mathematical models, and the suitability of these in the analysis of RO in the separation of heavy metals in drinking water that can be applied in countries with serious environmental problems. Bolivia and several river basins, such as the Guadalquivir and Milluni, present this type of problem. A comparative method is proposed to establish the advantages and selection criteria to apply the different models in RO.

Bolivia is among the countries with the highest availability of freshwater globally. However, many of its natural sources are impacted by anthropogenic activities, such as mining. Water is intimately linked to public health and is essential to achieving sustainable development. It is necessary to preserve water resources by designing and validating monitoring programs that help control the quality of the sources that supply important population centers. The study area in this research is the upper part of the Milluni micro-basin, whose lagoon system supplies water for two large cities. Milluni is close to illegal and abandoned mining areas, making the region highly vulnerable to heavy metal contamination. This study aimed to optimize the resources available for monitoring Milluni. The frequency of monitoring was statistically determined, and the correlation between parameters measured in situ (pH and conductivity) and metal ion concentrations to determine low-cost indicators to monitor the presence of heavy metals. A multivariate analysis of friction of the results of the pilot year of the monitoring program designed for Milluni, considering the characteristics and economic limitations, is presented. An approximation of the quality of the surface water resources of Milluni is presented as a result of the monitoring operations.