Journal of Environmental Engineering

Groundwater vulnerability to geogenic groundwater contamination underlies the complex interplay between various intrinsic geological, hydrogeological, and geochemical characteristics in an aquifer system. Identifying the risks to groundwater quality in this regard is a very engaging process that needs to consider the source and nature of groundwater contamination from the perspective of ongoing external and internal processes within the area/region under study. Arsenic contamination in groundwater has stood out due to its worldwide spread and lethality. It is an established fact that most arsenic sources are predominantly geogenic in nature. Yet, the mechanisms of its mobilization in groundwater appear to be triggered by anthropogenic factors many times. However, the propositions are still being debated and are in an ever-evolving stage. Assessment of groundwater vulnerability to arsenic contamination may thus be considered a potentially valuable management tool for enabling major decisions on preventative groundwater protection, and there is apparently an urgent need to develop robust approaches for the same. One can easily find reviews on groundwater vulnerability per se, but the current review reflects relevant and recent core data compilation/consolidation specifically on arsenic vulnerability assessment. The current work attempts to provide a comprehensive review of the occurrence of arsenic in the subsurface environment, along with the earlier and recent approaches involved in groundwater vulnerability assessment, including mathematical, geostatistical, process-based simulation, and machine learning methods. This paper considers and compares available case studies in this regard and highlights the potential of integrated/hybrid modeling to achieve the best possible outcomes.

Abstract

In this study, we evaluated the utilization rate of organic substrates contained in sanitary landfill leachates (SLLs) by fixed and suspended biomass reactors. Five bioreactors were designed, constructed, and tested for chemical oxygen demand (COD) removal. We applied three levels of organic loading in the influent for each bioreactor, including (1) a rotating biological contactor (RBC) (12, 20, and $25\mathrm{g}\mathrm{COD}/{\mathrm{m}}^2/\mathrm{day}$); (2) a trickling filter (TF) (2.67, 5.33, and $8\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3/\mathrm{day}$); (3) an upflow anaerobic sludge blanket (UASB) (13.31, 15.98, and $18.65\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3/\mathrm{day}$); (4) an upflow anaerobic filter in two separated stages (UAF-2SS) (3.71, 2.76, and $1.8\mathrm{kg}\mathrm{COD}/{\mathrm{m}}^3/\mathrm{day}$); and (5) an upflow anaerobic filter in three separated stages (UAF-3SS) (2.25, 3.45, and ${4.44\mathrm{kg}\mathrm{COD}/\mathrm{m}}^3/\mathrm{day}$). Two equations for predicting the substrate utilization rate (SUR) of organic compounds by microorganisms were calibrated and validated, modeled under a nonsteady state condition. We modified Monod’s equation to obtain the significant organic SUR and COD removal efficiency by the biomasses. These kinetic parameters were performed by the microorganisms fixing controlled experimental conditions for pH (8–9) and temperature for the UAFs (20°C, 27°C, and 34°C) and the remaining reactors (18°C– 20°C). The SUR and COD removal efficiency results were as follows: for UASB, $-400$ to $-800\mathrm{mg}/\mathrm{L}/\mathrm{h}$, 70% to 85%; for UAF-3SS, $-100$ to $-300\mathrm{mg}/\mathrm{L}/\mathrm{h}$, 85% to 95%; for UAF-2SS, $-100$ to $-200\mathrm{mg}/\mathrm{L}/\mathrm{h}$, 70% to 85%; and for RBC and TF, $-50$ to $-250\mathrm{mg}/\mathrm{L}/\mathrm{h}$, 70% to 80%. The results were mainly influenced by the structural arrangement of the organic compounds being biodegraded and the geometric configurations of the bioreactors in multiple separated stages, allowing the influence of the solubility of the recalcitrant substances, which varied from 7 to 14:1 COD dilition, to obtain subinhibitory levels for the microbial metabolism and achieve a high COD removal efficiency.

Practical Applications

Two of the five bioreactors evaluated in this study, the upflow anaerobic filter in two separated stages and the upflow anaerobic filter in three separated stages, are proposed and designed as innovative reactors for treating groundwater from tropical aquifers contaminated with hydrocarbons. Additionally, UAFs were configured in a coupled bioreactor arrangement (i.e., a sequencing batch reactor followed by UAFs) to restore water quality by removing organic compounds in tropical rivers. By comparing the five bioreactors, the capacity for the chemical oxygen demand removal was significant related to the organic substrate utilization rate (SUR) for treating sanitary landfill leachates with low recalcitrance levels (i.e., rapidly biodegradable). Rapidly biodegradable SLLs can be associated with La Cortada-SLL percolated from the cells/trenches excavated for the disposal of municipal solid waste (MSW) (i.e., Pamplona Municipality, Colombia) due to the contents of a high fraction of putrescible wastes (67%) and a high biochemical oxygen demand/chemical oxygen demand ratio (62%). This level ratio produced a suitable SUR obtained from the microbial metabolism starting with the upflow anaerobic sludge blanket reactor ($-400\mathrm{t}\mathrm{o}-1,200\mathrm{mg}/\mathrm{L}/\mathrm{h}$) followed by the remaining bioreactors ($-150\mathrm{t}\mathrm{o}-350\mathrm{mg}/\mathrm{L}/\mathrm{h}$). Upflow anaerobic filters in multiple separated stages reactors constitute a feasible technical option for overcoming medium to high recalcitrance levels in SLLs obtained from cells/trenches excavated storing around 25% components fraction (e.g., metals, plastics, rubber, leather, textiles).

In the industrial mining environment, coal dust pollution has been a persistent issue, causing harm to both human health and the ecosystem. Starch–based polymers have emerged as promising solutions for dust suppression in mines. These polymers not only effectively control dust dispersion but also offer environmental benefits. Derived from natural sources and biodegradable, starch–based polymers align with sustainability concerns in resource extraction industries. Their ability to bond with coal dust particles improves air quality and safety for workers and communities. Sustainable practices are essential to mitigate the environmental and health impacts of coal mining despite its importance in global energy production. The thesis research focused on creating an environmentally friendly dust suppressant gel, CSS-g-AA-AEO 0.04%, to tackle the ongoing problem of coal dust pollution in mining environments. The researchers combined cassava starch with acrylic acid using graft copolymerization techniques to yield the innovative CSS-g-AA gel. Structure tests using x-ray diffraction and infrared spectroscopy (IR) clearly showed that the grafting process was successful, indicating that the gel was flexible and could be used for various applications. Extensive research efforts, including simulations, precise surface tension measurements, and comprehensive contact angle analyses, led to the identification of a surfactant with exceptional wetting properties, a 0.04% AEO surfactant. scanning electron microscope (SEM) and EDS analyses showed that the dust suppressant had good adhesion and adsorption effects on coal. The water retention capability exhibited an evaporation percentage of 90.94%, whereas wind erosion control achieved a lower dust suppression of 16.2%. This difference is of particular significance, especially under challenging high wind conditions. Incorporating starch solidification within the gel further bolstered its efficacy as a sustainable solution for coal dust suppression, emphasizing its potential as a game-changing approach to combating coal dust pollution while advocating for sustainable mining practices. These groundbreaking findings underscore the immense promise and viability of CSS-g-AA-AEO 0.04% as a cutting-edge, environmentally conscious strategy to mitigate coal dust pollution and promote sustainable mining practices for a cleaner and healthier environment.

Abstract

The treatment of sludge is one of the main sources of carbon emissions throughout the entire life cycle of sewage treatment. This study conducted carbon emission analysis on the sludge treatment process of a sewage treatment plant in Guangzhou, China, and offered a carbon accounting boundary calculation process for the sludge called the deep dehydration–drying–incineration process. An international standard method was improved to offer a carbon emissions accounting method for direct carbon emissions, indirect carbon emissions, and carbon sink for the sludge treatment of the effluent treatment plant. Research has found that the amount of sludge treatment is directly proportional to carbon emissions and carbon sinks. When the sludge treatment capacity reaches 600 t or more, almost zero carbon emissions are achieved, and the carbon emissions generated during the incineration stage of sludge treatment are the highest in all process steps. In addition, there is a significant positive correlation between dry sludge treatment capacity and carbon emissions from drying/integration. There is a significant positive correlation between dry sludge treatment capacity and direct emissions caused by incineration, but there is no correlation with carbon emissions generated by the use of electricity/chemicals. This study offered important data support and technical reference for the resource development and low-carbon disposal regulation of sludge, and a basis for the calculation of carbon emissions throughout the entire process of sludge treatment.

Practical Applications

The paper explored the carbon emission accounting method for sludge treatment. An international standard method has been improved to offer an accounting method for direct carbon emissions, indirect carbon emissions, and carbon sequestration of sludge treatment in sewage treatment plants, providing possibilities for carbon accounting throughout the entire life cycle of sewage and sludge in sewage treatment plants. The results show that the sludge treatment capacity is directly proportional to carbon emissions and carbon sinks. When the sludge treatment capacity reaches 600 t or more, almost zero carbon emissions are achieved, and the carbon emissions generated during the sludge treatment incineration stage are the highest in all process steps. In addition, there is a significant positive correlation between dry sludge treatment capacity and carbon emissions from drying/integration. There is a significant positive correlation between dry sludge treatment capacity and direct emissions caused by incineration, but there is no correlation with carbon emissions generated by the use of electricity/chemicals. The research results contribute to the resource utilization and low-carbon disposal of sludge.