The discharge of large amounts of oily sludge heat treatment residues constitutes a severe threat to the environment. However, little is known about the toxicity of these heat-treated residues. Current research has mainly focused on the toxic effects of single heavy metals or single hydrocarbons on plants, whereas the phytotoxic effects of hydrocarbon–metal mixtures have remained largely unexplored. In this study, pot experiments were conducted to evaluate the effects of different proportions of heat treatment residues (pyrolysis, heat-washing, and high-temperature oxidation residues) from three kinds of oily sludge on the physiological and biochemical parameters of mung bean plants. Higher proportions of residues decreased the germination rates and enzyme activity of mung beans compared to uncontaminated soil. When pyrolysis residue, hot-washing residue, and high-temperature thermal oxidation residue are used in green planting soil, their content must be lower than 30%, 90%, and 70%, respectively. Additionally, our findings indicated that the accumulation level of pollutants in oily sludge heat treatment residues was not high. However, the three kinds of residues exhibited different degrees of plant toxicity. The pyrolysis residue still exhibited strong ecotoxicity, even at low concentrations. In contrast, the toxicity of the hot-washing residue was much lower than that of the pyrolysis residue and the high-temperature thermal oxidation residue. Our findings indicated that mung bean is highly tolerant of contaminated soil and is therefore well suited for phytoremediation applications.
Supercritical water oxidation (SCWO) technology is efficient and offers significant development potential for hazardous waste treatment. The use of water in a supercritical state with special physical and chemical properties for refractory organic matter processing offers significant advantages. This article summarizes (i) the mechanism of SCWO technology and its research progress for oily sludge treatment; (ii) the effects of reaction temperature, pressure, residence time, oxygen ratio, catalyst, antioxidant, and other factors on oily sludge treatment; and (iii) problems in the current process. Finally, SCWO technology for the future development of oily sludge treatment is discussed.
Oily sludge is the production and collection of a mixture of oil and sludge produced during crude oil processing. It contains crude oil, heavy metals, organic toxins, and harmful substances. It is characterized by high water content, poor fluidity, and large volume. Recycling and disposal have always been important aspects of environmental protection in the petroleum industry. Therefore, the safe treatment of oily sludge is particularly important. Hydrothermal oxidation technology is an emerging technology in which the treatment of oily sludge is comprehensive and without secondary pollution. This article describes the basic principles and research progress of wet oxidation and supercritical water oxidation and focuses on the latest experimental research, advantages and disadvantages, and development prospects in the treatment of oily wastewater.
The biofilms generated in a fire extinguishing water supply system can cause corrosion and a reduction in the water supply capacity; thus, degrading the system performance. To mitigate microbial corrosion, appropriate disinfection measures are necessary. In this study, the secondary addition of chlorine is employed to investigate the kinetics of chlorine decay, and shock disinfection is applied to investigate the removal efficiency of corrosion bacteria, and the microbial composition of a biofilm on the pipe wall was also clarified. The results show that the residual chlorine content in the secondary chlorination process was directly correlated with the decay rate of residual chlorine and the corrosion rate of the pipe wall. Additionally, the chlorine impact disinfection method could reduce the electrochemical corrosion phenomenon of the pipe wall. When the concentration of chlorine was 3 mg/L, the removal rate of corrosion bacteria was higher in 60 min than in 30 min. Specifically, most of the bacteria were inactivated in 60 min and the biofilm was severely damaged. Shock disinfection could significantly inactivate all microflora in the biofilm; the relative abundances of microflora varied significantly, while the change of microflora at the phylum level was insignificant. This study can provide theoretical support for the secondary addition of chlorine and shock disinfection in a fire extinguishing water supply system.
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