Fuller’s earth is an adsorbent material used in the electric industry for dielectric oil regeneration. The high amount of polyaromatic hydrocarbons removed from oil and adsorbed in the Fuller’s earth makes this material a hazardous waste. It is necessary to implement a toxicity test and apply a suitable treatment to safely dispose of this waste in a landfill or repurpose it for reuse. In this paper, the toxicity of Fuller’s earth contaminated with dielectric oil is assessed before and after treatment. The toxic potential of the Fuller’s earth and the dielectric oil extracted through decontamination processes was evaluated in two types of soil with different carbon contents, analyzing the effects on the test organisms, Eisenia Foetida earthworms. These tests showed that decontaminated Fuller’s earth is non-toxic, and that the toxicity of the contaminated Fuller’s earth, or its extracts after treatment, represented by the median lethal concentration (LC50) depends significantly on the type of soil used.

Introduction. Dielectric oil is classified as a hazardous material by the EPA (Environmental Protection Agency of the United States of America). The oil is composed primarily of naphthenic, aromatic, and paraffinic hydrocarbons. With the continuous use of these oils in power equipment such as transformers and cables, reactions occur that create deposits on the equipment, making their renaturation costly. This article proposes a solvent extraction technique. A compact treatment plant was proposed to allow for the cost-effective and environmentally safe management of this type of hazardous waste.Objective. The objective of this research was to develop a treatment system for Fuller’s earth contaminated with dielectric oil using solvent extraction with ethanol and TRITON to reduce the carbon footprint for users in the electrical industry.Methodology. The properties of the solvent, such as chemical affinity and boiling point, were evaluated while the contaminant was being removed. After treatment with the proposed system, the contaminated Fuller’s earth met the cleanup standards required by current Colombian environmental regulations. To this end, a pilot treatment system was built to test the treatment process on 1 kg of contaminated Fuller’s earth and evaluate the best alternative found in the reactor, using ethanol extraction.Results. The results of the study show that extraction with industrial-grade ethanol (96% purity) removed the greatest amount of dielectric oil. The amount in the soil after treatment averaged 0.5 ppm, the maximum value permitted by law (Resolution 1170 of 1997 of the Department of Environmental Management).Conclusions. The ethanol extraction process offers a new solution for the final disposal of Fuller’s earth contaminated with dielectric oil, which until now has been carried out by incineration, and constitutes an environmentally friendly option for the management of hazardous waste.

The oxygen depletion in worldwide oceans and inland waters is becoming an increasingly prevalent problem. Here, two comparative study sites, Baltic Proper (BP) and Shuikou Reservoir (SR), were selected to identify the dynamics of dissolved oxygen (DO) and the related physicochemical response by conducting five field investigations over one year period. The DO concentrations were 0–9.9 mg L⁻¹ and 0.3–8.7 mg L⁻¹ in BP and SR, with average oxygen change rates of −0.016~0.014 mg L⁻¹ d⁻¹ and −0.022~0.018 mg L⁻¹ d⁻¹, respectively. Such oxygen dynamics were highly related to salinity, temperature, turbidity, and chlorophyll-a than nitrogen and phosphorus. The persistent hypoxia (i.e., DO < 2 mg L⁻¹) emerged below 63 m in BP during all sampling months where the reversal points of Brunt–Väisälä frequency N expressed in the form log₁₀[N² (s⁻²)] were −4. The seasonal hypoxia covered the downstream of SR at depths below 11.5 m in September with the highest log₁₀[N² (s⁻²)] between −3.95 and −3.64. The log₁₀[N² (s⁻²)] ≈ −4 may indicate the occurrence and development of hypoxia in both regions. In the case of the persistent and seasonal hypoxic conditions in BP and SR, the impact of temperature and turbidity on DO was opposite. Low oxygen levels in SR occurred under elevated temperature and turbidity. Additionally, under hypoxic conditions in both regions, NO₃⁻ and NH₄⁺ concentrations significantly depended on DO changes. This study contributes to the understanding of seasonal changes in oxygen dynamics in different water bodies, and highlights different oxygen conditions and physicochemical responses to the oxygen changes.