Our use of pharmaceuticals, pesticides and personal care products leads to an increase of organic micropollutants (OMPs) into the aquatic environment. Conventional wastewater treatment plants are not designed for the removal of OMPs and need to be upgraded to reduce OMP contamination. The adsorption of OMPs to zeolites is proposed as an alternative treatment method. Zeolites are synthesized as powders, however they need to be shaped into pellets to be used in water treatment practice. This research focussed on engineering zeolite pellets and which properties of these pellets are important for the adsorption of OMPs.
First the influence of the calcination temperature and binder content on the mechanical stability and porosity of the pellets was analysed. Second, the influence of two different preparation techniques (extrusion and high-shear granulation) and the introduction of a polymer on the mechanical stability, porosity and adsorption kinetics of the pellets was assessed. Third, the effect of the porosity on the breakthrough for an empty bed contact time (EBCT) of 20, 5 and 1 minute(s) was determined according to the linear driving force (LDF) model. It was found that an increasing binder content and calcination temperature increased the wear resistance and porosity of the pellets. However, the effect on the porosity is minimal. The introduction of the polymer had opposite effect on extruded and granulated pellets. For extruded pellets, the introduction of the polymer increased the porosity. However, the granulated pellets showed a decrease in porosity. A relation was found between the porosity and the wear resistance and between the porosity and adsorption kinetics. A larger porosity decreased the wear resistance of the pellets and increased the kinetic rate constant. The porosity was of great importance in relation to the breakthrough. First, the porosity in the zeolite pellets determined to a great extent the bulk density of the filter bed. A higher bulk density resulted in a later breakthrough point. The bulk density was also influenced by the shape of the pellet. Spherically-shaped (granulated) pellets had a higher bulk density than rod-shaped (extruded) pellets. Second, the porosity was related to the kinetic rate constant. At lower EBCTs (5 and 1 minute), the kinetic rate constant had an influence on the breakthrough point. For these EBCTs, a higher kinetic rate constant led to a later breakthrough point. It was recommended to optimize the zeolite pellets by making the extruded pellets in a more spherically-shaped form and to start column experiments to validate the LDF-model.

The Dutch drinking water benchmark has been carried out every three years since 1997. In 2011, the benchmark was incorporated into the Drinking Water Act. As a result the benchmark switched from a voluntarily benchmark executed by the Association of Dutch water companies to a mandatory benchmark executed by the Human Environment and Transport Inspectorate. In addition, the drinking water companies have to hand in an improvement plan 6 months after the benchmark publication. Based on interviews with benchmark coordinators of drinking water companies the influence of the inclusion of the benchmark into the Drinking Water Act on the improvement driven part of the benchmark is studied. For this purpose, the following four issues are discussed: changes experienced as a consequence of the shifting from a voluntarily to a mandatory benchmark, influence of mandatory character of the benchmark on the drivers, identified by de Goede et al. (2016), the role of the improvement plans and a new instrument to stimulate improvement.

The differences between the voluntarily and mandatory benchmark are identified: the benchmark switched from being only an improvement driven instrument to an instrument for accountability as well and the drinking water organizations lost control over the development of the benchmark. The influence of the mandatory character on the drivers for performance improvement have been determined: only the driver 'enhanced transparency' is (positively) influenced. In order for the improvement plans to be able to have a positive effect on the stimulation of improvement, a feedback system should be implemented and the publications of the benchmark and improvement plans have to be faster. The benchmark is still thought to be useful, although an adaptive benchmark could stimulate improvement again.