How to minimize disinfection by-products during the production of high quality recycled water

Advanced Water Treatment Plants (AWTPs) produce high quality recycled water (HQRW) treating secondary treated wastewater by means of coagulation, microfiltration, reverse osmosis filtration, advanced oxidation and final disinfection with chlorine. Chloramines are used prior to the membrane filtration to keep biofouling on the surface of the reverse osmosis membranes manageable. When organic and inorganic substances in water react with disinfectants such as chloramines, disinfection by-products (DBPs), which can be of concern due to their potential adverse effects on human health, are formed. This paper investigates the formation of DBPs during HQRW production at two full scale AWTPs and at bench scale. Concentrations measured in the chloraminated reverse osmosis feed water during the sampling campaigns at full scale were generally low, with individual DBP concentrations not greater than 3 μg/L. However, haloacetonitriles (HANs) were measured at levels close to the Queensland (Australia) regulation for water recycling. During bench scale experiments, formation of all DBPs measured proved to increase with contact time except haloketones which showed a rapid initial formation in the first half an hour, followed by a much slower rate of formation. The rejection behaviour of different DBPs by reverse osmosis membranes at full scale varied depending on the DBP intrinsic properties. For example, bulky molecules were well rejected while polar compounds, such as the HANs, showed a poorer rejection. Besides size exclusion, solute-membrane interactions play an important role in determining the extent of DBP removal. 201