A numerical model to optimize LNAPL remediation by multi-phase extraction

Enhanced treatment of multiphase extraction wastewater from contaminated sites with Cu-Ce modified GAC three-dimensional electrodes

A three-dimensional (3D) electrode system is widely recognized as an effective technology for enhancing electrocatalytic effect. In this study, Cu-Ce modified granular activated carbon (GAC) particle electrodes were prepared using the impregnation method and applied to handle multiphase extraction wastewater. Structural and electrochemical characterization revealed that while the specific surface area of Cu-Ce/GAC decreased by 13.94%, the active area was 2.6 times greater than that of GAC. In addition, the influences of distinct impregnation concentrations, calcination temperatures, and calcination times on the performance of Cu-Ce/GAC electrodes were investigated. The results suggested the optimal preparation conditions of 15 mmol/L, 500 °C and 2 h. Under these conditions, the Cu-Ce/GAC electrode achieved a 92.39% removal of chemical oxygen demand (COD) from a multi-extract of groundwater, with an energy consumption of 13.44 kWh/(kg∙COD). The degradation efficiency improved by 62% compared to the conventional 2D system, while energy consumption decreased by 60%. The main organic pollutants in the multiple extracts, including benzene, toluene, dichloromethane, trichloromethane, were removed at rates exceeding 90% after 60 min treatment. This study yields a methodological and engineering approach for treating multiple extracts wastewater from contaminated groundwater.

Biochar enhanced the stability of toluene removal in extracted groundwater amended with nitrate under microaerobic conditions

Groundwater pollution caused by the leakage of petroleum and various fuel oils is becoming a serious environmental problem. In this study, carbon-based materials including biochar and hydrochar were applied to investigate the effects of additives on the toluene removal in the extracted groundwater under microaerobic condition with the addition of nitrate. Biochar and hydrochar could adsorb toluene, and thus enhance the toluene removal in the system. The toluene removal efficiency was 8.2-8.9 mg/(g·h) at the beginning, and then decreased with time in the control and the hydrochar treatment, while it remained the stable values in the biochar treatment, owing to the fact that biochar could reduce the NO3--N loss by partial denitrification. Moreover, biochar could prompt the growth of toluene-degrading bacteria including Thauera, Rhodococcus, Ideonella and Denitratisoma, which had the capability of denitrification. However, hydrochar could stimulated the growth of denitrifiers without toluene-degrading capacity including Candidatus Competibacter and Ferrovibrio, which might play a key role in the partial denitrification of the system. The findings are helpful for developing remediation techniques of contaminated groundwater.

Efficient remediation of soils contaminated with petroleum hydrocarbons using sustainable plant-derived surfactants

Surfactant-enhanced multiphase extraction is recognized as an effective method to remove petroleum related contaminants from soil. Owing to the high biodegradability and low biotoxicity, plant-derived surfactants are considered as promising alternatives to synthetic surfactants. In this study, two plant surfactants were respectively extracted from Sapindus mukorossi (PS-1) and Fructus Gleditsiae sinensis (PS-2). Component analysis and chemical structure characterization indicated that triterpenoid saponins were the main components of both plant surfactants. The removal efficiency of tetradecane by PS-1 and PS-2 was 75.6% and 62.2%, respectively, which was comparable with that by Tween-80. The results were validated by column leaching experiments. The abundant hydroxyl, aldehyde and epoxy groups in the plant surfactants made them readily self-assemble to form micelles via hydrogen bonding and van der Waals interactions, which promoted the solubilization of tetradecane in the liquid phase, particularly at appropriate ionic strength and temperature. Due to the reduced electrostatic attraction by the acidic and ionizable functional groups in the plant surfactants, their sorption capacities (0.15 and 0.24 g1-n Ln·kg-1 for PS-1 and PS-2, respectively) onto the soil were much lower than that of Tween-80, making them much easier to be extracted from contaminated soil. This study would deepen our understanding to improve the performances of plant surfactants in petroleum hydrocarbons-contaminated soil remediation.

Groundwater and soil contamination by LNAPL: State of the art and future challenges

Contamination by Light Non-Aqueous Phase Liquids (LNAPL) represents a challenge due to the difficulties encountered in its underground assessment and recovery. The major risks arising from subsoil LNAPL accumulation face human health and environment, gaining a social relevance also in the frame of a continuously changing climate. This paper reports on a literature review about the underground contamination by LNAPL, with the aims of providing a categorization of the aspects involved in this topic, analyzing the current state of the art, underlying potential lacks and future perspectives. The review was focused on papers published in the 2012-2022 time-interval, in journals indexed in Scopus and WoS databases, by querying "LNAPL" within article title, abstract and/or key words. 245 papers were collected and classified according to three "key approaches" -namely laboratory activity, field based-data studies and mathematical simulations- and subordinate "key themes", so to allow summarizing and commenting the main aspects based on the application setting, content and scope. Results show that there is a wide experience on plume dynamics and evolution, detection and monitoring through direct and indirect surveys, oil recovery and natural attenuation processes. Few cues of innovations were found regarding both the use of new materials and/or specific field configuration for remediation, and the application of new techniques for plume detection. Some limitations were found in the common oversimplification of the polluted media in laboratory or mathematical models, where the contamination is set within homogeneous porous environments, and in the low number of studies focused on rock masses, where the discontinuous hydraulic behavior complicates the address and modeling of the issue. This paper represents a reference for a quick update on the addressed topic, along with a starting point to develop new ideas and cues for the advance in one of the greatest environmental banes of the current century.

Soil heterogeneity influence on the distribution of heavy metals in soil during acid rain infiltration: Experimental and numerical modeling

Acid rain is a global environmental problem that mobilizes heavy metals in soils, while the distribution and geochemical fraction of heavy metals during acid rain infiltration in heterogeneous soils are still unclear. In this study, we performed column experiments to investigate the distribution and geochemical fraction of Cu, Pb, Ni and Cd in heterogeneously layered soils during continuous acid rain infiltration. Chloride ion used as a conservative tracer was found to be uniformly distributed during acid rain infiltration, showing insignificant preferential flow effects in the column. In contrast, however, the distribution of heavy metals was highly non-uniform, especially in the silty soil at the lower part of the column, indicating a heterogeneous distribution of adsorption capacity. In addition, in the control experiments with neutral rain infiltration, uniform distribution of heavy metals was observed, indicating that the heterogeneous distribution of adsorption coefficient during acid rain infiltration was mainly caused by different pH buffering capacities. A numerical model considering water flow and solute transport was developed, where the average water-solid distribution coefficient (K_d) in Layer 2 was only 1.5-12.5% of that in Layer 1 during acid rain infiltration. The model could predict the variation of heavy metal concentrations in soil with the majority of error less than 35%, confirming that different K_d induced the heterogeneous distribution of heavy metals. In addition, the geochemical fraction of heavy metals in the upper coarse sand layer remained stable, while the acid-extractable fractions in the lower loam and silt loam layer gradually increased. Our findings suggest that soil heterogeneity, especially chemical heterogeneity affected by rainfall acidity, has an important influence on the infiltration, migration and geochemical fraction of heavy metals in soils. This study could help guide the risk assessment of heavy metal-contaminated sites that were polluted by acid rain or landfill leachate.

Groundwater quality

Groundwater is a vital component of water supply for residential, industrial, and agricultural purposes. However, many groundwater basins are being used unsustainably and groundwater contamination is a growing water quality problem. Although anthropogenic activities and natural processes have been increasing the contamination in this valuable water resource, several remediation techniques have been developed in the last few decades to reduce these contamination levels. This review paper focuses on the recent studies developed on groundwater pollutions, remediation practices, and groundwater quality management. PRACTITIONER POINTS: Groundwater pollution is mainly due to anthropogenic activities and it is considered as a growing water quality problem. Groundwater bioremediation is one of the sustainable long-term solutions that uses the microorganisms to degrade the complex environmental pollutants. Groundwater quality management techniques play a significant role to restore or maintain water quality, which is critical for the sustainable development.

Sustainable soil use and management: An interdisciplinary and systematic approach

Soil is a key component of Earth's critical zone. It provides essential services for agricultural production, plant growth, animal habitation, biodiversity, carbon sequestration and environmental quality, which are crucial for achieving the United Nations' Sustainable Development Goals (SDGs). However, soil degradation has occurred in many places throughout the world due to factors such as soil pollution, erosion, salinization, and acidification. In order to achieve the SDGs by the target date of 2030, soils may need to be used and managed in a manner that is more sustainable than is currently practiced. Here we show that research in the field of sustainable soil use and management should prioritize the multifunctional value of soil health and address interdisciplinary linkages with major issues such as biodiversity and climate change. As soil is the largest terrestrial carbon pool, as well as a significant contributor of greenhouse gases, much progress can be made toward curtailing the climate crisis by sustainable soil management practices. One identified option is to increase soil organic carbon levels, especially with recalcitrant forms of carbon (e.g., biochar application). In general, soil health is primarily determined by the actions of the farming community. Therefore, information management and knowledge sharing are necessary to improve the sustainable behavior of practitioners and end-users. Scientists and policy makers are important actors in this social learning process, not only to disseminate evidence-based scientific knowledge, but also in generating new knowledge in close collaboration with farmers. While governmental funding for soil data collection has been generally decreasing, newly available 5G telecommunications, big data and machine learning based data collection and analytical tools are maturing. Interdisciplinary studies that incorporate such advances may lead to the formation of innovative sustainable soil use and management strategies that are aimed toward optimizing soil health and achieving the SDGs.