Closing the water cycle

To close the water cycle, steps need to be taken to treat effluent for organic micropollutants. Today’s WWTPs have not been specifically designed to remove such substances – which can encompass a wide range – from the wastewater. In cases where this is actually done, the quality of the wastewater improves considerably. This offers the possibility of using the effluent for other, higher-value applications, rather than discharging it into surface water. Previous research investigated the degree to which the effluent from WWTP Wervershoof would need to be treated in order to satisfy the same quality requirements met by WRK water (pre-treated water from the IJsselmeer lake). The questions raised by this research need to be answered before there can be a closed water cycle.


The plan is to combine ozonation with ceramic membrane filtration for the effluent treatment in Wervershoof. The international literature, as well as our earlier experiments, indicate that this approach can produce a synergetic effect, but how this actually arises is still not adequately understood. It is thought that hydroxyl radicals are formed, whereby the interaction not only results in less membrane fouling (as has already been established), but also in the extra degradation for instance of organic micropollutants. In order to optimise this effect, and the associated treatment, a better understanding of the underlying processes is required.

Another problem related to the use of ozone is the formation of bromate. The use of innovative dosing techniques could possibly reduce local ozone concentrations, and thus control bromate formation. There are also indications that the combination of ozone with ceramic membranes helps in this regard.


Better water quality, less membrane fouling, and controlled bromate formation: with a greater understanding of underlying mechanisms, the ozonation of effluent could possibly produce these results through the degradation of organic micropollution. Presumably the optimisation of ozonation is related to an interaction between the TiO2 top layer of the membrane and ozone, whereby radicals can be formed which degrade organic micropollutants. Moreover, a study will be conducted on how bromate formation can be reduced by adjusting the ozone dosage rates. Together, these elements would not only make the process more effective, but also more efficient, and therefore less costly and environmentally harmful. This project will also investigate the extent to which the WWTP effluent, as a result of the proposed treatment, satisfies the high quality requirements for WRK water, as well as which other application opportunities would be opened for this water.


The research is investigating the processes that take place when ozone interacts with the ceramic membrane surface. If radical formation does in fact occur, this would not only counter membrane fouling, but might also contribute significantly to the degradation of organic micropollutants and the limitation of bromate formation. This means that a better understanding of the underlying processes helps to optimise the total effect. In addition, with the help of techniques developed by PWNT, we aim to adjust the ozone dosage with a view to preventing or limiting bromate formation as much as possible.