Intensification of supercritical water oxidation (ScWO) by ion exchange with zeolite for the reuse of landfill leachates.

The disposal of solid residues in sanitary landfills results in the formation of a complex, variable, and recalcitrant wastewater, known as leachates. Supercritical water oxidation (ScWO) can be applied to treat leachates although most studies are based on removing the most relevant contaminants, such as organic matter and ammonia. Therefore, comprehensive analysis of this process is essential for large-scale applications. In this study, we investigated a system composed of ScWO and ion exchange using zeolite (ScWO/zeolite) for the reuse possibilities of treated leachates based on different regulations for municipal wastewater reuse. This system was applied to both raw leachate (RL) and leachate treated via conventional processes at the studied landfill (PL). The continuous ScWO reactor operated under a pressure of 23 MPa at 600 °C without the addition of oxidants. A commercial zeolite (clinoptilolite) in a fixed-bed glass column was used for ion exchange. The intensified system significantly improved the characteristics of RL by removing 89% of COD and 99% of NH3-N. Moreover, the contaminant concentrations of PL were within the limits for discharge and reuse, except arsenic and molybdenum contents. The unexpected high concentrations of arsenic in RL and PL necessitated the requirement of further investigation of the complex and toxic characteristics of leachates. Nevertheless, the intensified process was conducted without the addition of oxidants or auxiliary substances and resulted in a less expensive and more environmentally -friendly process that can be applied for the treatment of leachates with similar characteristics.

Evaluation of hospital laundry effluents treated by advanced oxidation processes and their cytotoxic effects on Allium cepa L.

Hospital laundries are responsible for a significant part of the amount of wastewater that is generated in hospitals. Hospital laundry wastewater represents a complex mixture of chemicals that arouse concerns about possible environmental risks. The objective of the present study was to evaluate the cytotoxicity of different laundry effluents from the Regional University Hospital of Maringá, Paraná, Brazil, on Allium cepa L. meristematic root cells. The effluents were characterised as rinsing, wetting, prewashing, washing, softening, wastewater (the effluent generated at the end of the washing process), the wastewater that was treated by physicochemical (PC) processes and the wastewater that was treated by advanced oxidation processes (PC + UV, PC + H2O2 and PC + UV/H2O2). The mitotic indexes were calculated by scoring 5000 cells per group and the statistical analyses were performed by one-way ANOVA, followed by Tukey's post-test (α = 0.05). Results showed that the rinsing, wetting, prewashing and wastewater laundry effluents were cytotoxic at 24 h of exposure, significantly reducing the mitotic index. Despite the slight cytotoxicity of the PC + UV/H2O2 treatment, physicochemical and advanced oxidation processes efficiently reduced the critical parameters of wastewater, such as the biochemical and chemical oxygen demands, to tolerable levels of effluent discharge. It is essential to perform constant monitoring of these effluents in order to reduce the possible occurrence of environmental impacts.

Intensification of supercritical water oxidation (ScWO) process for landfill leachate treatment through ion exchange with zeolite.

Over the past few years, supercritical water oxidation (ScWO) has shown great potential for application to landfill leachate treatment, providing substantial organic matter degradation in terms of biochemical oxygen demand (BOD), chemical oxygen demand (COD), and total organic carbon (TOC). However, the conversion of ammonia, which is present at high concentrations in leachates, is the rate-limiting step during ScWO and usually requires large amounts of oxidants, the addition of catalysts, or severe operating conditions. Aiming at proposing a treatment system that effectively removes both organic matter and ammonia from leachate, this paper evaluates the intensification of the ScWO process through ion exchange with zeolite. Thus, ScWO was operated under a pressure of 23 MPa at 600 and 700 °C, without the addition of oxidants. The zeolite (clinoptilolite) was used without any modification inside a glass column. The ScWO (600 °C)/zeolite system removed 90% ammoniacal nitrogen (NH3-N), 100% nitrite (NO2-N), 98% nitrate (NO3-N), color, and turbidity, 81% TOC, and 74% COD, suggesting that this system is a promising alternative for leachate treatment. However, the final NH3-N and COD values were slightly above the limits (20 and 200 mg L-1, respectively) stipulated by the Brazilian environmental legislation. These results suggest that further improvements are still required for the application of the intensified ScWO to be feasible. Notably, ammonium-saturated clinoptilolite is amenable for regeneration or can be applied to soil as a slow-release fertilizer.

Treatment of hospital laundry wastewater by UV/H2O2 process.

Hospitals consume a large volume of water to carry out their activities and, hence, generate a large volume of effluent that is commonly discharged into the local sewage system without any treatment. Among the various sectors of healthcare facilities, the laundry is responsible for the majority of water consumption and generates a highly complex effluent. Although several advanced oxidation processes (AOPs) are currently under investigation on the degradation of a variety of contaminants, few of them are based on real wastewater samples. In this paper, the UV/H2O2 AOP was evaluated on the treatment of a hospital laundry wastewater, after the application of a physicochemical pretreatment composed of coagulation-flocculation and anthracite filtration. For the UV/H2O2 process, a photoreactor equipped with a low-pressure UV-C lamp was used and the effects of initial pH and [H2O2]/chemical oxygen demand (COD) ratio on COD removal were investigated through a randomized factorial block design that considered the batches of effluent as blocks. The results indicated that the initial pH had no significant effect on the COD removal, and the process was favored by the increase in [H2O2]/COD ratio. Color and turbidity were satisfactorily reduced after the application of the physicochemical pretreatment, and COD was completely removed by the UV/H2O2 process under suitable conditions. The results of this study show that the UV/H2O2 AOP is a promising candidate for hospital laundry wastewater treatment and should be explored to enable wastewater reuse in the washing process.