Applicability of advanced oxidation processes for treatment and recovery of washing machine effluent: On-site application with new washing machine design

Abstract

Water scarcity has become one of the most important problems that society must overcome. The effect of climate change with the addition of increased freshwater consumption stands as one of the major problems related to water scarcity. There has been a great increase in domestic-based wastewater generation over a couple of decades. Among the sources of domestic type wastewater, washing machines play a significant role in freshwater consumption, which corresponds to 80-100 liters per working cycle. In this study, it is aimed to perform a feasibility study of various types of Advanced Oxidation Processes (AOPs) to treat laundry wastewater originating from washing machines by reducing organic pollutant load, along with the elimination of dye stuff and surfactant content that was released from textile fibers. Wastewater characterization from different stages of wastewater discharge was analyzed and AOPs including O3, H2O2, O3/H2O2, O3/UV, H2O2/UV, and O3/H2O2/UV were applied to determine the most efficient AOPs. Experimental tests were carried out in labaratory-scale photoreactor with 3liter capacity and lamp of 41 W power. Specific volumes of wastewater was fed to system along with determined ozone (O3) and hydrogen peroxide (H2O2) concentrations respectively. Treatment applications were carried out for 2 hours and samples are taken at regular time intervals to analyze treatment efficiency. Results showed that photolytic oxidation differed significantly from sole chemical oxidation. Among O3/UV, H2O2/UV and O3/H2O2/UV methods, H2O2/UV yielded the best chemical oxygen demand (COD) and methylene blue active substance (MBAS) reduction rates among other methods. An additional set of the design of experiments (DOEs) is performed to analyze the effect of parameters that effect treatment efficiency such as type of detergent used (liquid or powder), effect of microfiber filtration and H2O2 concentration used. Results of DOEs show that COD and MBAS content of wastewater discharge during the rinsing stage of the washing cycle could be reduced by up to 95% and 98%, respectively under optimum conditions of wastewater originated by liquid detergent, the case of microfiber filtration and higher H2O2 concentrations. Another aspect of treatment was analyzed as microorganism growth on stored wastewater since it is known that wastewaters having organic content is expected to be suitable for microorganism growth. Microorganism counts were done by taking water samples at first, fourth and seventh days to see the trend of microorganims growth. Microorganisms count results showed that the rate of microorganism growth is greatly reduced in AOP-applied wastewater when compared to raw wastewater. Based on the outcomes, it is concluded that AOPs with fiber filtration can be effective in reducing organic pollutant load, as well as discoloration and providing hygiene. UV absorbances were analyzed in water samples to see the degradation of dye stuff in laundry wastewater, since it is important to eliminate all of dying components due to the fact that they may cause additional staning on white garmets during next washing cycle. UV absorbance results showed that dye stuff released from textile textures can be effectively eliminated by the application of additional filtration. AOPs treated wastewater also was analyzed using whiteness index to see the potential stainnig cause by treated wastewater. Staining results were satisfactory, meaning to significant staining was observed on white garments, which means that treated laundry wastewater can be recycled inside the washing machine and can be used during the next washing cycle without compromising the cleaning performance of the washing machine. As a result, AOP treatment and recycleing of laundry rinsing wastewater may enable to lower the water consumption and provide more sustainable washing machine operation designs.