Greywater irrigation as a source of organic micro-pollutants to shallow groundwater and nearby surface water

Increased water demands due to population growth and increased urbanisation have driven adoption of various water reuse practices. The irrigation of greywater (water from all household uses, except toilets) has been proposed as one potential sustainable practice. Research has clearly identified environmental harm from the presence of micro-pollutants in soils, groundwater and surface water. Greywater contains a range of micro pollutants yet very little is known about their potential environmental fate when greywater is irrigated to soil. Therefore, this study assessed whether organic micro-pollutants in irrigated greywater were transferred to shallow groundwater and an adjacent surface waterway. A total of 22 organic micro-pollutants were detected in greywater. Six of these (acesulfame, caffeine, DEET, paracetamol, salicylic acid and triclosan) were selected as potential tracers of greywater contamination. Three of these chemicals (acesulfame, caffeine, DEET) were detected in the groundwater, while salicylic acid was also detected in adjacent surface water. Caffeine and DEET in surface water were directly attributable to greywater irrigation. Thus the practice of greywater irrigation can act as a source of organic micro-pollutants to shallow groundwater and nearby surface water. The full list of micro-pollutants that could be introduced via greywater and the risk they pose to aquatic ecosystems is not yet known

Study of hydrodynamics and mass transfer in the bench-scale membrane testing devices

Computational fluid dynamics (CFD) was used to study hydrodynamics and mass transfer in a conventional circular bench-scale membrane testing device, and improved geometry of the device was proposed. The conventional and modified geometries were fabricated for experimental validation of the simulation results. It was observed that the modified cell outperformed the conventional cell in terms of distribution of mass transfer coefficient and shear stress on the membrane surface. Further, the ranges of average shear stress and mass transfer coefficient in the modified membrane testing cell for crossflow rates between 25 and 60 L/h overlaped with the corresponding ranges observed in a spacer-filled membrane channel. Hence, the modified geometry is a better choice for membrane testing and can also be extended to study the performance of antifouling membranes