Treatment of hospital wastewater by supercritical water oxidation process.

Hospital wastewater contains several micro and macro pollutants that cannot be removed efficiently by conventional treatment processes. Thus, generally hybrid and multistage treatment methods are suggested for the treatment of hospital wastewater. Supercritical water oxidation (SCWO) is a promising method for the removal of emerging organic pollutants from hospital wastewater in one step and a very short reaction time. In this study, supercritical water oxidation (SCWO) process was used for the removal of pharmaceuticals in addition to conventional pollutants from real hospital wastewater. As a result of a series of preliminary studies, the optimum conditions were selected as 450 °C, 60 s, and 1:1 for temperature, reaction time, and oxidant ratio (H2O2/COD), respectively, for the treatment of hospital wastewater at 25 ± 1 MPa. The removal rates were determined above 90% for COD, BOD, TOC, TN, and SS from hospital wastewater. Phosphorus removal was greater than 90%, while the removal rates were around 80% for phenol, AOX, and surfactants in hospital wastewater. A total of 9 pharmaceuticals were observed in the real hospital wastewater samples. The highest removal rate was obtained for Paracetamol as 99.9%, while the lowest removal rate was obtained for Warfarin as 72% after SCWO treatment of hospital wastewater. As a result, it can be concluded that SCWO process is sufficient for the treatment of hospital wastewater without the need of additional treatment steps, with high removal rates in a short reaction time.

In situ gas fuel production during the treatment of textile wastewater at supercritical conditions.

Supercritical water gasification has recently received much attention as a potential alternative to energy conversion methods applied to aqueous/non-aqueous biomass sources, industrial wastes or fossil fuels such as coal because of the unique physical properties of water above its critical conditions (i.e. 374.8 °C and 22.1 MPa). This paper presents the results obtained for the hydrothermal gasification of textile wastewater at supercritical conditions. The experiments were carried out at five reaction temperatures (between 450 and 650 °C) and five reaction times (between 30 and 150 s), under a constant pressure of 25 MPa. It was found that the gaseous products contained considerable amounts of hydrogen, carbon monoxide, carbon dioxide, and C(1)-C(4) hydrocarbons, such as methane, ethane, propane and propylene. The maximum amount of the obtained gaseous product was 1.23 mL per mL textile wastewater, at a reaction temperature of 600 °C, with a reaction time of 150 s. At this state, the product comprised 13.02% hydrogen, 38.93% methane, 4.33% ethane, 0.10% propane, 0.01% propylene, 7.97% carbon monoxide, 27.22% carbon dioxide and 8.00% nitrogen. In addition, a 62.88% decrease in the total organic carbon (TOC) content was observed and the color of the wastewater was removed. Moreover, for the hydrothermal decomposition of the textile wastewater, a first-order reaction rate was designated with an activation energy of 50.42 (±2.33) kJ/mol and a pre-exponential factor of 13.29 (±0.41) s(-1).

Treatment of whey wastewater by supercritical water oxidation.

Whey wastewater is a by-product of cheese industry, which causes environmental pollution problems due to its containment of heavy organic pollutants. Conventional methods such as biological treatment and physico-chemical treatment are insufficient or ineffective. In this paper, the treatment of cheese whey wastewater has been carried out by supercritical water oxidation, using hydrogen peroxide as oxidant. The reaction conditions ranged between temperatures of 400-650°C and residence times of 6-21 s under a pressure of 25 MPa. Treatment efficiencies based on TOC removal were obtained between 75.0% and 99.81%. An overall reaction rate model, which consists of the hydrothermal and the oxidation reactions, was determined for the hydrothermal decomposition of the wastewater with an activation energy of 50.022 (±1.7) kJmol(-1) and a pre-exponential factor of 107.72 (±4.1) s(-1). The oxidation reaction rate orders for the TOC and the oxidant were 1.2 (±0.4) and 0.4 (±0.1) respectively, with an activation energy of 20.337 (±0.9) kJmol(-1), and a pre-exponential factor of 1.86 (±0.5) mmol(-0.6)L(0.6)s(-1) in a 95% confidence level.